Solar questions for another new guy.

jwdukes

Before I start, I want to thank you for the community you’ve already created with very valuable information made available. The only help I have comes from online so this is MUCH appreciated.
I have a ’95 Winnebago Rialta that I’m rigging out to live in full-time, and will be boon-docking the majority of the time; I also don’t want to rely on a generator. I just bought two NEW 325 watt Yingli panels that I plan to install flat; here are the specs:
Peak Power: 325 Wp
Peak Voltage: 37.3 Volts
Peak Current: 8.71 Amps
Open Circuit Voltage: 46.9 Volts
Short Circuit Current: 9.06 Amps
Max series Fuse: 20A
Diode rating: 15A

My major loads per day might roughly be:
-- In summer, Two fans (maybe 20-40 watts?) for 24hours in summer, or, a very small possibly, a swamp cooler (5amps) for 8(?) Hours.
-- In winter, my furnace (8amps?) for 3 hours to supplement a catalytic heater.
-- 3 amp (12 V) refrigerator (Norcold DE0751) for 24hours
-- 5 amp (12 V) laptop for 24 hours.
-- Eventually a stereo & subwoofer, unsure of wattage, would like to be able to run a couple hours at night.
-- LED lights, water pump, internet router, and propane alarm are other smaller loads
I’m pretty sure I can only fit a group 31 and group 27 battery into my coach’s bank, for a total of maybe 210 amp hours (?).
I’m completely new to RV’s & solar, so here are my questions:

1. Do you see this combination being sufficient? I’ve tried different online solar estimators. One may tell me this is plenty while others say I need over 800watts, but none account for battery type & bank size, which I would guess is essential for getting through the night.

2. I have room to add a third 325 watt panel, do you think it’s needed? Can one have too much PV? How reasonable is a third panel using only the two batteries?

3. I may be able to store another battery under the bed about 6 feet away from my coach bank; if I do need to add another battery, would I simply need one giant 6foot long cable and a shorter thick one to ground to the metal truck frame?

4. I have a small Coleman RV air conditioner (model 6727-736), but cannot find it’s amperage yet. Everywhere on the web tells me it can’t be done, but what would it take to run it for a few hours in the heat of the day with solar? I could easily add a third 325 watt panel, but if I were crafty enough and a little crazy, I might be able to design a rack for four 325 watt panels and 3 batteries. Do you know of any smaller A.C. units (my house window unit is 535 watt) or other options other than evaporative units that would work better?

5. The truck’s engine alternator charges coach batteries while driving, as do the generator & shoreline power via a converter/charger (Magnetek 7240); would any of these interfere with the charging solar system in any way?

6. From what I’ve found, it looks like my choices of MPPT charge controllers are from Morningstar, OutBack, Xantrex, Rogue, Blue Sky, and MidNite (available in a couple weeks). I read bad reviews about BZ controllers and don’t trust generic Chinese ones. I won’t need a remote display added because I can access the controller easily.

How do I size, compare, and choose one for my two 325 watt panels!? And how about if you think I need three panels?
I wish we had a chart with all of their specs & options listed side by side. What are your opinions? Keep in mind that I also need to know which will handle these high-volt panels.
I read in a thread that the BlueSky has a neat load control function: “When the battery goes to float, you can divert the PV directly to a load so that you can use that load directly from the PV and not mess up the float voltage of the battery”. Do others not have this and how useful is it?

6a. Will all of these controllers come with a thermometer to install in the battery bank to account for temperature?

7. I read that batteries need to be of the same manufacturer, installed new at the same time, and not discharged past 50% DOD. If you think I need to add a third battery to get me through the night using the extension-under-the-bed method mentioned above,
Two questions:
7a. Can a charge controller charge two different isolated banks at different rates if I wanted to use a different type & age (& cheaper) battery in the secondary bank? This might be used for non-vital loads like the subwoofer or TV. Is this where the load control function mentioned above will be used? Will the controller display state of charge for two different battery banks?
7b. If I decide to add a third battery tied into one bank a year later, how significant would the damage be by adding a new battery to the older two?

8. Will all of these charge controller’s display tell the batteries’ state of charge? I’m guessing it probably won’t be in the form of a percentage that I can easily understand, so then what value will it show to determine state of charge with? Amp hours? Volts?
Or if I absolutely must have a separate monitor (using a shunt?), what are some cheap options?

9. It seems like AGM batteries are worth the extra cost for their faster charging speed. What are your recommendations on where to find the best prices?

10. Do I wire my panels in parallel? If so, based on a voltage drop calculator found here: http://nooutage.com/vdrop.htm , running 17 feet from panels to controller with sum of 18.12 short circuit amps, I would use #8 guage wire to run from the panels to the controller for a 1-2% voltage drop, does that sound right? How then do I determine the wire size from the MPPT controller to the batteries? Contoller to batteries is ~ 4 feet.

11. Since I’ll probably go with AGM’s, will I need to change default charging points on the MPPT charger since they are able to charge faster? Is that an easy process?

Thank everyone SSSO much. I wish I had something to offer to compensate for your time. I can’t wait to get on the road full-time.

cptdondo

Re: Solar questions for another new guy.

jwdukes wrote: »

My major loads per day might roughly be:
-- In summer, Two fans (maybe 20-40 watts?) for 24hours in summer, or, a very small possibly, a swamp cooler (5amps) for 8(?) Hours.
-- In winter, my furnace (8amps?) for 3 hours to supplement a catalytic heater.
-- 3 amp (12 V) refrigerator (Norcold DE0751) for 24hours
-- 5 amp (12 V) laptop for 24 hours.
-- Eventually a stereo & subwoofer, unsure of wattage, would like to be able to run a couple hours at night.
-- LED lights, water pump, internet router, and propane alarm are other smaller loads
I’m pretty sure I can only fit a group 31 and group 27 battery into my coach’s bank, for a total of maybe 210 amp hours (?).
I’m completely new to RV’s & solar, so here are my questions:

Offhand, you have too much consumption and not enough battery bank.

My usage is similar to yours; assuming that the fridge consumes 40 AH / day, and you actually use your laptop 8 hours a day for a total of 80 AH. That's enough to draw your batteries down close to the 50% mark, so that's what you really want to replace.

Depending where you are, you may get that with your panels.... But I'd be really concerned about the limited batteries and the excessive consumption. When we boondock, we go into "power saving mode", where things like computer use are severely restricted, or we run the generator. I don't like running it, and in places I can't run it - I can't see firing up the genset in the middle of a wilderness at 5AM just because I was sloppy with my energy budget.

Read up on energy budgets, Peukert curves, and such. Don't be too concerned about the battery usage; too many people are opinionated fanatics on battery issues. I personally don't care if I cut my battery life by 20% because I don't spend every minute of every day babying them. I have 2 T-145s and one 12V deep-cycle cheapie from a discount store, in 2 banks that can be combined.

Forget running an AC from batteries; ain't gonna happen. The starting load is way too big; you need a reliable source of about 2500W @ 120VAC to do that, and inverters that size aren't cheap, and your batteries + solar panels won't provide the current you need.

Photowhit

Re: Solar questions for another new guy.

Lots of impressions here; for get the furnace suppliment your heater with a quilt. or a "sleep on top" bed warmer, 8 amps at 120volts will eat up more than you'll produce in a day.

Might try the the A/C with a 3rd panel and minimum of 440 amps at 12 volt storage (thats 4 golf cart batteries). I mention 12 volt as you have 12 volt apliances. Still this is only 3 hours of run time, perhaps 5-6 hours on thermostat for an @ 500 watt unit.

Your laptop is running 24hours a day? if so invest in a fitpc2 and a monitor so you can turn the monitor off and run at <10watts for what ever your doing while sleeping, driving, eating,... playing music?

How are you receiving internet? If your not internet intense, and plan on using hotspots to up and down load, you might try a Kindle for Email. I don't have internet at home and find the kindles G3/G4 coverage works well(and is gratis vs $60 month, for home phone and service for me) for keeping up with Email, not a full browser, but most Email mobile works fine (Hotmail and Gmail at least...)

A good honda generator might be the ticket for A/C, they are quiet and reasonably fuel effiecent.

BTW for 12 volt even with just 2 panels your alread out of the range for Rogue and Blue Sky CC I think, as I recall my Rogue will handle about 800 watts at 24 volts so 400 watts at 12 volts...

techntrek

Re: Solar questions for another new guy.

Get a catalytic heater like the Olympian Wave. More than enough output for that size camper and no electric required at all. Boondockers use them all the time for that reason.

A 1995 A/C will need about 1500 watts to run (the one on my new camper uses 1000 on low), and 2-3 times that for startup. 2-3 batteries is probably big enough to handle the startup surge but you'll need a 3 kw inverter w/6 kw surge and about 3.5 kw of PV panels to run the A/C directly, plus recharge the amount used during each startup, plus recharge what you'll need at night. And don't even think of trying to run it from the batts after late afternoon. For a few hours a day maybe 2 or 3 dozen times a year you might do better with a small genset like a Honda EU2000i

dwh

Re: Solar questions for another new guy.

jwdukes wrote: »

Before I start, I want to thank you for the community you’ve already created with very valuable information made available. The only help I have comes from online so this is MUCH appreciated.
I have a ’95 Winnebago Rialta that I’m rigging out to live in full-time, and will be boon-docking the majority of the time; I also don’t want to rely on a generator. I just bought two NEW 325 watt Yingli panels that I plan to install flat; here are the specs:
Peak Power: 325 Wp
Peak Voltage: 37.3 Volts
Peak Current: 8.71 Amps
Open Circuit Voltage: 46.9 Volts
Short Circuit Current: 9.06 Amps
Max series Fuse: 20A
Diode rating: 15A

My major loads per day might roughly be:
-- In summer, Two fans (maybe 20-40 watts?) for 24hours in summer, or, a very small possibly, a swamp cooler (5amps) for 8(?) Hours.
-- In winter, my furnace (8amps?) for 3 hours to supplement a catalytic heater.
-- 3 amp (12 V) refrigerator (Norcold DE0751) for 24hours
-- 5 amp (12 V) laptop for 24 hours.
-- Eventually a stereo & subwoofer, unsure of wattage, would like to be able to run a couple hours at night.
-- LED lights, water pump, internet router, and propane alarm are other smaller loads
I’m pretty sure I can only fit a group 31 and group 27 battery into my coach’s bank, for a total of maybe 210 amp hours (?).
I’m completely new to RV’s & solar, so here are my questions:

1. Do you see this combination being sufficient? I’ve tried different online solar estimators. One may tell me this is plenty while others say I need over 800watts, but none account for battery type & bank size, which I would guess is essential for getting through the night.

Not sufficient. Not even close. Figure you'll get 4 hours of decent sun on those panels per day. That might even be optimistic for a flat mount and if you park in the shade you get nothing.

8.7a x 2 = 17.4a per hour x 4 = 69.6ah per day.

That's about how much you can generate per day (on average).

A 5a load running for 24 hours would draw out 120ah per day.


That''s the basics. You have to do the math. There are some fudge factors - for instance the laptop won't really draw 5a continuously, and you might get a bit more or less sun.

That's also not accounting for watts consumed by the system, so if your PV panels generate 70ah/day, you might end up with only 60ah actually into the battery and your inverter itself will use some of that just to run itself.

For you, I would say figure out the absolute max PV panels you can install, and the absolute max batteries, then use that to figure out the absolute max that you can generate and store.

Once you know that, then you can figure out what you can actually run from it - and for how long. Fridge you gotta have. Laptop 24/7 you don't. Router you don't need. Catalytic heater yes, furnace no. Fans yes, RV A/C...not a chance without generator or shore power.

2. I have room to add a third 325 watt panel, do you think it’s needed? Can one have too much PV? How reasonable is a third panel using only the two batteries?

If you have room for it and can afford it, then yes, as many panels as you can fit will be best - but still won't be enough.

3. I may be able to store another battery under the bed about 6 feet away from my coach bank; if I do need to add another battery, would I simply need one giant 6foot long cable and a shorter thick one to ground to the metal truck frame?

You could, but be aware that imbalance in the system will cause some batteries to charge/discharge a bit more than others and so you might wear out one much faster than another.

4. I have a small Coleman RV air conditioner (model 6727-736), but cannot find it’s amperage yet. Everywhere on the web tells me it can’t be done, but what would it take to run it for a few hours in the heat of the day with solar? I could easily add a third 325 watt panel, but if I were crafty enough and a little crazy, I might be able to design a rack for four 325 watt panels and 3 batteries. Do you know of any smaller A.C. units (my house window unit is 535 watt) or other options other than evaporative units that would work better?

There is absolutely no way you will run an RV air conditioner from a small PV system. RV A/C units run on 120v, so you'd need a big inverter to power it, and you would drain the batteries completely in minutes - and then it would take days or even weeks to fully recharge the battery.

There are many different swampers that can be used in an RV, but if you are dry camping then water is a BIG issue.

5. The truck’s engine alternator charges coach batteries while driving, as do the generator & shoreline power via a converter/charger (Magnetek 7240); would any of these interfere with the charging solar system in any way?

No. They are all just battery charging systems and they each have their own way of determining that the battery is charged and then they back off. Since they are all battery charging systems, they also all have their own methods to protect themselves from backfeed from some other system (the same way they protect themselves from backfeed from the battery).

6. From what I’ve found, it looks like my choices of MPPT charge controllers are from Morningstar, OutBack, Xantrex, Rogue, Blue Sky, and MidNite (available in a couple weeks). I read bad reviews about BZ controllers and don’t trust generic Chinese ones. I won’t need a remote display added because I can access the controller easily.

How do I size, compare, and choose one for my two 325 watt panels!? And how about if you think I need three panels?

Those panels have a decently high voltage. I would wire them in parallel because of possible shading issues. At less than 9a each, three panels would be 27a or less, so you need a charge controller capable of handling at least 30a on the input side. MPPT will down convert the voltage to charge a 12v battery, so you might be putting as much as 40a on the output side.

So for 3 panels, I would probably go with maybe a TriStar 45, but if you go more than 3 panels you would probably need to go up to a 60.

I wish we had a chart with all of their specs & options listed side by side. What are your opinions? Keep in mind that I also need to know which will handle these high-volt panels.
I read in a thread that the BlueSky has a neat load control function: “When the battery goes to float, you can divert the PV directly to a load so that you can use that load directly from the PV and not mess up the float voltage of the battery”. Do others not have this and how useful is it?

It could be very useful - for instance if you had a water heater with with both gas burner and electric element you could run the electric element as a dump load to make hot water.

But you don't need to worry about that because you won't be keeping up with all those loads, much less making extra.

6a. Will all of these controllers come with a thermometer to install in the battery bank to account for temperature?

Some come with a battery temp sensor, some it's an extra you have to buy separately. Most decent charge controllers have a place to connect a temp sensor, but you usually have to get the temp sensor that goes with that particular controller.

7. I read that batteries need to be of the same manufacturer, installed new at the same time, and not discharged past 50% DOD. If you think I need to add a third battery to get me through the night using the extension-under-the-bed method mentioned above,


Two questions:
7a. Can a charge controller charge two different isolated banks at different rates if I wanted to use a different type & age (& cheaper) battery in the secondary bank? This might be used for non-vital loads like the subwoofer or TV. Is this where the load control function mentioned above will be used? Will the controller display state of charge for two different battery banks?

Some can - it depends on the charger. Morningstar SunSaver Duo is designed for exactly that - but it's PWM and not MPPT.

For load control, you just connect different loads to different batteries.

Any controller designed for multiple banks should be able to display info for each bank.

7b. If I decide to add a third battery tied into one bank a year later, how significant would the damage be by adding a new battery to the older two?

No way to know really. But not much. A year's difference in age won't make nearly as much difference as wiring up the bank in an imbalanced fashion and working one battery harder than the others.

8. Will all of these charge controller’s display tell the batteries’ state of charge? I’m guessing it probably won’t be in the form of a percentage that I can easily understand, so then what value will it show to determine state of charge with? Amp hours? Volts?
Or if I absolutely must have a separate monitor (using a shunt?), what are some cheap options?

Charge controller will know the voltage of the battery, and how much it put in - but it can't tell how much was taken out so it can't figure out a percentage.

A battery monitor needs a shunt in the negative line so it can measure how much went out and how much went in - then if it knows the size of the bank (you have to tell it), it can calculate the percentage remaining.

Usually, you use a separate battery monitor and shunt, though I suppose there might be a charge controller out there that has a battery monitor built-in and can hook up to a shunt to get the measurements.

9. It seems like AGM batteries are worth the extra cost for their faster charging speed. What are your recommendations on where to find the best prices?

10. Do I wire my panels in parallel? If so, based on a voltage drop calculator found here: http://nooutage.com/vdrop.htm , running 17 feet from panels to controller with sum of 18.12 short circuit amps, I would use #8 guage wire to run from the panels to the controller for a 1-2% voltage drop, does that sound right? How then do I determine the wire size from the MPPT controller to the batteries? Contoller to batteries is ~ 4 feet.

I'll leave this for someone else...

11. Since I’ll probably go with AGM’s, will I need to change default charging points on the MPPT charger since they are able to charge faster? Is that an easy process?

Depends on the controller. Some just have dip switches for set it and forget it. Others you have to walk through the menu on the digital control. Most will have an easy way to tell it what type of battery it is connected to.

jwdukes

Re: Solar questions for another new guy.

Thanks everyone! You've all been very helpful, I suspected that my storage was low. After many more hours of reading and brainstorming how I could add more batteries, I removed my barrel seat in order to build a battery box with a bench on top that will allow me to hold 6 golf cart batteries. And after finding out that my refrigerator will cycle for a total run time of about 10 hours/day and my laptop doesn't draw that full 65Watts, I think I'll be okay. I have room for a third 325W panel and two more batteries (8 total), but I'd be pushing my weight capacity and would need to upgrade tire$. Here's the new numbers:
6 batteries = 600Ah x 12V = 7200 Wh storage (conservative)
A generous consumption for all loads = 2500 Wh consumed (generous)
Amount charge left in batteries = 4700 Wh remaining = 65% charged = 35% DOD (hey, not too bad!)
2 Solar Panels 640W 4hours 2560 Wh produced (conservative)

Ok, new questions:
1. Since the box I designed will be in the cabin, I will need to seal it and vent it outside somehow. Some of the bilge pumps I looked at consume 4-6amps! Do you think a simple 3W computer case cooling fan will work? If not, any other ideas?

2. Again, my panels are rated at:
Peak Voltage: 37.3 Volts
Open Circuit Voltage: 46.9 Volts
So which of these is used to determine their nominal voltage? 24V? 36V? 48V?? If it's 36V, can any MPPT CC be set up for that odd nominal number?

3. Charge controllers, I'm still confused on how to size one. When a charge controller states it's rated at a certain amperage, is that an input or output amperage at whatever nominal voltage? If this is output, how do I determine how much amperage I can put into a controller and at which voltage!? Here's two examples that confuse me:
a. The Outback FM60 states that it's "Maximum Solar Array STC Nameplate" is: 12 VDC systems 900 Watts / 24 VDC systems 1800 Watts / 48 VDC systems 3600 Watts / 60 VDC Systems 4500 Watts
Are these system voltages input or output!? If output, does this mean I need a huge 80 amp controller if I want to use three 325W panels!? OR if it's input, three of my panels are between 24 and 48 Volts each, meaning I'd be ok???

b. The Blue Sky SB3024i, for example, states that it's rated at 40 amp 12V or 30 amp 24V, is that nominal voltage regarding input from panels or output of a battery bank!?

4. To run a vent fan for my batteries as I mentioned above, I need an MPPT CC with an auxiliary output. I can't find any information saying that the Morningstar MPPT has one, can you confirm?
If true, that leaves me with Xantrex, BlueSky, and Outback...

5. I read bad reviews about the Outback controllers saying that they freeze up or lag and that their fan eventually needs replaced, have those been addressed with new firmware or something? BlueSky & Xantrex seem to use fins without fans. If all of this is true, I'm now down to Xantrex and BlueSky...

6. Can't all MPPT controllers do voltage conversion from high-volt panels like mine to a 12V nominal bank? Someone mentioned in a thread that BlueSky does not. If so, which do and which don't?, because they aren't very forthcoming about this when I'm looking at different ones. If it is true that BS does not convert my high-voltage panels, then my only choice left seems to be Xantrex 60amp MPPT CC, do you agree?

7. Say I used a high powered device during the sunny mid-day... if the batteries are already on float by the time I want to use that device for a short while, will the MPPT charge controller recognize the drain in batteries and go back into a bulkier charging profile given there is still enough sun & PV at that time to do so?

8. With MPPT auxiliary outputs, if it's agreed that I can run a smaller 3W fan, can that run direct from the controller or will I need a relay?

dwh

Re: Solar questions for another new guy.

jwdukes wrote: »

Thanks everyone! You've all been very helpful, I suspected that my storage was low. After many more hours of reading and brainstorming how I could add more batteries, I removed my barrel seat in order to build a battery box with a bench on top that will allow me to hold 6 golf cart batteries. And after finding out that my refrigerator will cycle for a total run time of about 10 hours/day and my laptop doesn't draw that full 65Watts, I think I'll be okay. I have room for a third 325W panel and two more batteries (8 total), but I'd be pushing my weight capacity and would need to upgrade tire$. Here's the new numbers:
6 batteries = 600Ah x 12V = 7200 Wh storage (conservative)
A generous consumption for all loads = 2500 Wh consumed (generous)
Amount charge left in batteries = 4700 Wh remaining = 65% charged = 35% DOD (hey, not too bad!)
2 Solar Panels 640W 4hours 2560 Wh produced (conservative)

You haven't accounted for system losses. Out of that 2500 wh produced by the PV, you won't get 100% into the battery and you will lose more to the inverter when you convert to 120v.

Rule of thumb is PV will give you 50% usable out of its rating. So with the math above, you'll really only see probably between 1200 and 1500 wh of actual usable power.

Which means that if you use 2500 Wh/day, then you're going to need some more PV.

Ok, new questions:
1. Since the box I designed will be in the cabin, I will need to seal it and vent it outside somehow. Some of the bilge pumps I looked at consume 4-6amps! Do you think a simple 3W computer case cooling fan will work? If not, any other ideas?

http://zephyrvent.com/specs.html

3 watts.

2. Again, my panels are rated at:
Peak Voltage: 37.3 Volts
Open Circuit Voltage: 46.9 Volts
So which of these is used to determine their nominal voltage? 24V? 36V? 48V?? If it's 36V, can any MPPT CC be set up for that odd nominal number?

Doesn't matter. You are using a 12v configuration battery bank. That's the only nominal you have to consider. If you used a PWM controller, then you would have to worry about matching the PV's nominal to the battery's.

But with MPPT it doesn't matter since the MPPT will down-convert to the battery nominal regardless of what the voltage is on the PV side.

You just have to make sure that your PV is setup according to whatever the input ratings are on the MPPT charge controller. Could be 39v on the input and 14.4 on the output, or it could be 72v on the input and still be 14.4 on the output - just depends on what range your MPPT controller can handle on the input.

3. Charge controllers, I'm still confused on how to size one. When a charge controller states it's rated at a certain amperage, is that an input or output amperage at whatever nominal voltage?

That's the output rating.

Even if you hooked up 40 amps worth of PV to a 30a controller, the controller will still only draw whatever it needs to produce 30a on the output side.

The PV makes power whenever there is sun on it - IF there is something attached to consume the current.

Electricity doesn't exist until something uses it. Until there is a load, there is no electricity - only the *potential* for electricity to exist.

If your PV can *potentially* produce 8a, but your load is only 5a - then only 5a will flow from the PV to the load since that's all that can be consumed. People wonder, "What happens to the other 3a?" - the answer is "Nothing, it never existed. That other 3a was simply a potential that never became realized."

If this is output, how do I determine how much amperage I can put into a controller and at which voltage!?

It's not a question of how much you can put in. It's a question of how much the controller can consume.

Controllers of course have ratings - limits as to how much potential can be connected to their input side. But as long as you stay within the controller's rated input, IT will determine how much it draws. It might be drawing the full PV output if the battery is low, and hardly drawing anything at all when the battery is in float.

Here's two examples that confuse me:
a. The Outback FM60 states that it's "Maximum Solar Array STC Nameplate" is: 12 VDC systems 900 Watts / 24 VDC systems 1800 Watts / 48 VDC systems 3600 Watts / 60 VDC Systems 4500 Watts
Are these system voltages input or output!?

Those are input numbers.

If output, does this mean I need a huge 80 amp controller if I want to use three 325W panels!? OR if it's input, three of my panels are between 24 and 48 Volts each, meaning I'd be ok???

The maximum input voltage for the FM60 is 150v.

The STC thing means that if you want to charge a 12v battery, the most PV the FM60 will ever use is 900w - so if you hooked up 3x 325w for 975w connected, it will never draw more than 900w if you are charging a 12v battery and so you have some excess potential that is going to waste.

But not really, since few panels will put out 100% of what they are rated at. They do get hot, and the hotter they get, the less they put out.

You could connect 3 x 48v panels in series and still be under the 150v max input rating of the FM60. There are some advantages to going with a higher voltage on the input side, though for an RV I would wire the panels in parallel instead of series due to shading issues.

b. The Blue Sky SB3024i, for example, states that it's rated at 40 amp 12V or 30 amp 24V, is that nominal voltage regarding input from panels or output of a battery bank!?

Output to the battery bank.

I can't find a manual for that model handy, but one site I saw said that the maximum input voltage for that model is 57 volts. So you can rig up your PV to a maximum of 57v on the input side, and it will put out either 24v or 12v nominal on the battery side.

Look at the Model Number - 3024. For a charge controller that often means that it will put out 30a @24v.

Take a guess what a Xantrex 6048 can do...

I don't think you need a diversion controller for an RV. As I said before, you'll be lucky to make back what you take out and you'll almost certainly not be making extra that needs to be diverted.

4. To run a vent fan for my batteries as I mentioned above, I need an MPPT CC with an auxiliary output. I can't find any information saying that the Morningstar MPPT has one, can you confirm?

If true, that leaves me with Xantrex, BlueSky, and Outback...

For a 3w fan I wouldn't bother - just let it run all the time.

5. I read bad reviews about the Outback controllers saying that they freeze up or lag and that their fan eventually needs replaced, have those been addressed with new firmware or something? BlueSky & Xantrex seem to use fins without fans. If all of this is true, I'm now down to Xantrex and BlueSky...

I dunno - I'll leave it for someone else to answer.

6. Can't all MPPT controllers do voltage conversion from high-volt panels like mine to a 12V nominal bank?

Yes - that's pretty much what MPPT does. It converts a higher voltage to a lower voltage, which if you do the math lower voltage equates to higher amperage for the same wattage of PV. So MPPT can take a PV that puts out say 8a at whatever voltage, and lower the voltage and get maybe 10a into the battery.

Someone mentioned in a thread that BlueSky does not.

That's gotta be bull, since it can take up to 57v on the input (according to that one mention that I saw) and charge a 12v or 24v battery.

EDIT: Hrmm...maybe not complete bull. I just found a site that says this:

"MPPT power converter can charge 12 volt batteries from 24 volt PV modules"

http://www.theresourcestore.ca/proddetail.php?prod=SB3024DiL

There is a link to the manual on Blue Sky's web site, but when I click it it says page not found.

Still...a 24v nominal PV should put out somewhere around 30v and a 12v battery would need about half that - so it MUST be down converting.

If so, which do and which don't?, because they aren't very forthcoming about this when I'm looking at different ones. If it is true that BS does not convert my high-voltage panels, then my only choice left seems to be Xantrex 60amp MPPT CC, do you agree?

As far as I know, *all* MPPT charge controllers down-convert voltage to increase amperage - that's one of the main tricks of MPPT.

7. Say I used a high powered device during the sunny mid-day... if the batteries are already on float by the time I want to use that device for a short while, will the MPPT charge controller recognize the drain in batteries and go back into a bulkier charging profile given there is still enough sun & PV at that time to do so?

Yup.

8. With MPPT auxiliary outputs, if it's agreed that I can run a smaller 3W fan, can that run direct from the controller or will I need a relay?

The auxillary output itself is a relay. It will be rated to a certain maximum current - usually 10a or 20a. If you need to control more than it is rated for, then you let that relay control a bigger relay, like a 50a or a 100a or whatever.

3w is nothing. As I said, I wouldn't even spend the money for a controller with an auxillary control - I'd just hook it up and let it run.

Well...actually I wouldn't. I would use AGMs and not have to worry about venting in the first place.

dwh

Re: Solar questions for another new guy.

Okay, I'm an idiot and it's late and I'm tired. I should have gone straight to NAWS' site instead of doing a Google search. Here is the spec sheet for the BlueSky 3024:

http://lib.store.yahoo.net/lib/wind-sun/SB3024iL.pdf

It says:

"PV Input Voltage 57VDC maximum"

So, to charge 12v or 24v it HAS to be down-converting. So whoever said it doesn't must have been incorrect.

dwh

Re: Solar questions for another new guy.

Yawn. Mmmm....coffee...

To clarify the PV nominal question and BlueSky thing a bit more:

Your panels are rated at 37.3v Vmp (volts max power - peak voltage under load).

Now, a 12v "nominal" battery actually takes up around 14.4v to push it up to full charge. For a 24v nominal battery, it would take 28.8v (14.4 x 2) to fully charge it. For a 36v nominal, it would take 43.2v (14.4 x 3). For a 48v battery, you need 57.6 (14.4 x 4).

That's just charging voltage. To equalize, you have to push the battery voltage up a little higher, so to EQ a 12v battery you need about 15v, to EQ a 24v you need 30v, etc.


So, your PV at 37.3 puts out a high enough voltage to charge and/or EQ a 12v or 24v battery, but not high enough to charge (or EQ) a 36v or 48v battery. Thus, your panels would be considered to be "24v nominal" panels.

Two of them in series would be a high enough voltage to charge/EQ a 36v or 48v battery.


All charge controllers require that the PV Vmp voltage be higher than the voltage at the battery. But if there is too great a difference in voltage between the PV and the battery, the flow of current will be inefficient.

I.e., if the battery is at 13v and the PV is putting out 37.3v, the battery will absorb less current than if the PV was putting out say 17v (higher voltage = lower amperage for the same wattage). So, a 17v PV would be considered to be a "12v nominal" panel, and would be a better match to a 12v nominal battery. The nominal rating of the PV would be important if you used a PWM charge controller.

It's not important though for an MPPT controller, because the MPPT will down-convert the voltage, thus reducing the voltage mis-match inefficiency. The nominal rating of the battery still matters with MPPT, but not the nominal rating of the PV.


The BlueSky 3024 MPPT can handle up to 57v on the input side - which is enough to charge 12v or 24v nominal*. Usually, the input rating on an MPPT controller is the "open circuit" voltage (Voc), which is higher than the voltage under load (Vmp).

The PV array voltage under load (Vmp) has to be higher than the voltage needed to charge the battery. The PV array voltage open circuit (Voc) has to lower than the max input Voc of the controller.

The BlueSky could handle your panels' 46.9v Voc if the panels were wired in parallel, but it couldn't handle the 93.8 Voc if you wired your panels in series.

The FM60-150 though can handle up to 150v on the input, so it could handle two, or even three of your panels in series. But that 150v is the "max". It could just as easily handle a lower voltage, such as the 46.9 if you wired your panels in parallel.


With a PWM controller, you want the PV array voltage to be higher than the battery voltage, but not a lot higher. With MPPT you don't have to worry about that - you just have to stay below the MPPT's rated max input Voc.



* Actually, I think it's high enough to also charge 36v nominal, but since that isn't a battery configuration that is used much (mostly only used for golf carts), I guess they decided not to support it.

BB.

Re: Solar questions for another new guy.

To add some other variables to DWH's observations--Solar panel Vmp/Voc is temperature dependent. So, if you run the panels on your roof in hot weather, no wind, and under strong sunlight (where else would you?), the Vmp may fall as much as 20%:

• 37.3v * 0.80 = 29.84 volts

Now, the above is a worst case temperature rise--But does demonstrate why the Vmp needs to be a fair bit higher than your battery charging voltage+controller drop+wiring drop.

Also, battery voltage goes up as temperature falls at –5 mV/°C /cell (–30mV/°C for a 12V battery)...

So hot panels and cold batteries are more "difficult" to charge than cold panels with hot batteries...

An MPPT type charge controller can make things "easier" when designing for a wide temperature range... You an set Vmp-array >> Vbatt-charging and have it work very nicely almost in any weather / temperature conditions.

And there are other issues too... Electrical "noise" on the battery bank (from AC inverters, desulfators, etc.) have been known to confuse MPPT charge controllers and prevent them from working correctly (producing less charging current than they should).

An inverter has been tested to confuse an older Bluesky controller, and a desulfator was (apparently) enough to confuse the Outback FM/FX charge controllers.

-Bill

dwh

Re: Solar questions for another new guy.

BB. wrote: »

To add some other variables to DWH's observations--Solar panel Vmp/Voc is temperature dependent. So, if you run the panels on your roof in hot weather, no wind, and under strong sunlight (where else would you?), the Vmp may fall as much as 20%:

• 37.3v * 0.80 = 29.84 volts

Now, the above is a worst case temperature rise--But does demonstrate why the Vmp needs to be a fair bit higher than your battery charging voltage+controller drop+wiring drop.

Ah - and there is why the BlueSky can take up to 57 Voc and still only be rated to charge a 24v nominal battery...the PV gets hot enough and the Vmp could drop below the 43v needed to charge a 36v battery.

jwdukes

Re: Solar questions for another new guy.

Keeping in mind that I want room for a third 325W panel, I got an email from a sales rep who made sizing the controller seem much easier, and according to him, with three 325 watt panels (975 watt array), I'd need an 80 amp controller. His math is
975 watt array / 12 volt battery bank = 80.91 amps controller.

1. Is this correct?

2. If so, aren't the only 80amp MPPT controllers the Outback FM80 and the new Midnite? Apollo has one, but I read a bad review comparative to a BZ review.

3. Since all of my loads are 12V, ... If I wanted to reconfigure my bank to charge at 36V, is there a gadget or other means to down convert that 36V bank back down to 12V for my loads? I'm guessing that'd be too much trouble if so and not worth the money I'd save from buying a 60amp controller over an 80amp, but I'm still curious.

Thanks guys. Btw, I don't need an inverter, I'll get a car charger for my laptop, but I have a small one should I ever need to temporarily use a power tool etc. And again, my consumption was generous, and generation & storage was conservative. I can cut back on stereo/TV on rainy days and I already know I'll have to park out of the shade.

dwh

Re: Solar questions for another new guy.

jwdukes wrote: »

Keeping in mind that I want room for a third 325W panel, I got an email from a sales rep who made sizing the controller seem much easier, and according to him, with three 325 watt panels (975 watt array), I'd need an 80 amp controller. His math is
975 watt array / 12 volt battery bank = 80.91 amps controller.

1. Is this correct?

The math is correct for the numbers he plugged in to the formula. The question is, are the assumptions correct.

He's assuming 12v. Well, okay that is the nominal voltage. However, for charging a 12v nominal battery, you would actually be putting out more like 14.4v, which alters the outcome of the formula some:

975w / 14.4v = 67.7a

Then, there is also temperature to consider. The hotter the panels get, the less they put out, and by their very nature they are dark in color and pointed at the sun so they do get hot. So, on average, they would probably be producing more like 80% of their rated output, which would then put you down into the realm where a 60a charge controller would be proper.

If you are parked in the snow, and it keeps the panels nice and cold, then they would be putting out their full rated amperage - or possibly even MORE than their full rated output.

How often is that going to happen? For me, maybe fairly often - when I was younger I was one of the kooks who would backpack in Yosemite in the winter - I like camping in the snow. For you...dunno.

Still, it makes sense to plan for what your average is going to be rather than the theoretical maximum.

Nevertheless, if you were going to plan for max, then it might be better to plan on using multiple charge controllers instead of one monolithic unit. You can hook up multiple charge controllers to the same battery bank, so if you needed to handle 80a (or a bit more maybe), then perhaps two of the TriStar 45s would be the way to go.

EDIT: Duh. Actually, with only 3 panels maybe a TriStar 45 for two panels and something smaller for the 3rd panel.


Another thing to consider is how much will the charge controller draw from the PV and for how long. Sure, you have the *potential* to make 80a of charge current, but even if the charge controller was putting that much into the battery - how long would it do so before the battery voltage rises and the charger starts throttling back?

Then, there is also one more thing to consider - the charge *rate* that the battery can handle. Normal batteries like a (maximum) charge rate of C/8. That means, that a battery bank rated at say 320ah @ 20hr rate would normally like a charge current of 320ah / 8 = 40ah.

Some batteries can handle higher charge rates. AGMs and GELs can usually handle somewhat higher than C/8, and there are some batteries that can even handle C/4.

So, depending on your battery bank capacity, and the rating of your batteries you need to take care to *limit* the charging current.

If you've a 320ah bank of batteries that can take a C/4 charge current, then they could handle 80a charging current. But that same bank made with batteries rated for C/8 would require you to stick to 40a or less of charging current.

(Engineers - double-check me on this. For some reason I feel like I'm overlooking something here...)


Okay...so say your battery bank could handle a max of 40a of charge current. The only real reason to have more PV than that would be so you could run loads while charging. If your batteries can take 40a of charge current, and you ALSO had 40a of loads running at the same time, then you might need an 80a charge controller (or a couple of 40s).

3. Since all of my loads are 12V, ... If I wanted to reconfigure my bank to charge at 36V, is there a gadget or other means to down convert that 36V bank back down to 12V for my loads? I'm guessing that'd be too much trouble if so and not worth the money I'd save from buying a 60amp controller over an 80amp, but I'm still curious.

Yes, there are various different DC-DC voltage converters available.

http://www.powerstream.com/dcdc.htm

Mangas

Re: Solar questions for another new guy.

Bill's point, "An inverter has been tested to confuse an older Bluesky controller, and a desulfator was (apparently) enough to confuse the Outback FM/FX charge controllers".

If I could slip in a quick question. As a side note what exactly happened with the desulfator? As mentioned to Dave, I consider my four desulfators "decorative" at this point.

I'm Still struggling whether to take our four desulfators off line or not. Do you think think they are impeding the performance of the two Outback FlexMax 80s? If there is any quantitative chance they may be, I'm pulling the fuses.

With that, I'll stand on the sidelines.

BB.

Re: Solar questions for another new guy.

These are probably the two posts with the most information... You can click on the "quoted link" for the full thread:

PhilS wrote: »

I pulled the fuses on both Desulfators to 'turn them off', weekend before last.

As I mentioned above, when I put a new FM60 onto a 1020 watt bank (48V? three pairs of Mitsubishi MF170) that did have an MX60, I got consistently less output than the MX had given on that bank . I had moved the MX to a new set of panels with 780 watts (54V, I think, 3 Sun HS130 panels in a string, two strings). I did this to put the better cooling fan on the bigger solar bank since I'm pushing the limits for a 12V battery bank. (OK, Bill, "exceeding" the limits" :roll: )

I posted at the Outback forum, and Outback contacted me after reading my post. She asked if I had a Xantrex inverter (yes, SW2512MC) and she mentioned there were conflicts with the earlier Revs and some Xantrex inverters. Because I had an earlier Rev than the 2.0, Outback shipped me a new one with the Rev 2.0.

The problem was better but not perfect. Randomly, the MX would outperform the FM. Also randomly, at the end of the day, the total KWH from the MX would be more than the FM. All panels together in a line, ground mount, no shading or other things that should cause that. Some days the FM did better and some the MX did better. I just accepted it because... I felt I had to.

Since deactivating the Desulfators, the FM always has more KWH at the end of the day.

Watching them occasionally this last weekend, the FM always outperformed the MX. And it seemed that both did much better (no measurements, just years of experience looking at the readings... it was like both the FM and MX had slurped down a Red Bull!). At the peak of the day, the FM was cutting off at 60 - 61 amps, as it's s'posed to but I haven't seen that since the FM was installed. The MX was hitting 58 amps, which it never did on this new set of panels. (It didn't seem to make any difference on my 3rd MX60 tied to 780 watts of panels but at 12V.)

So my unscientific conclusion is that the two DeSulfators DID interfere with the Outback controllers. They will remain "off" and THANK YOU WisJim for asking the question!!

Phil

And:

PhilS wrote: »

Good idea Dave, but absolutely not necessary now. Outback volunteered that there are "feedback" problems with "some Xantrex inverters". So Outback controllers are sensitive to "feedback" and by design that is what the desulfators do.

I am getting the performance out of the FM that I had originally anticipated. I look at total KWH on all three Outbacks when I get home from work every day.

Since installation, the FM would be about the same as the MX (more details in the other thread... the third MX has a 12V input and works the same before and after removing the desulfators).

I don't record the readings but generally the two used to be very close. Maybe 2.1KWH on the MX and 2.4 on the FM. Then the next day 2.3 on the MX and 2.1 on the FM.

Yesterday it was 2.8 on the MX and 3.9 on the FM. (the other MX was 2.1). It is absolutely a night & day difference in performance. That's about the ratio of the panels between the FM and MX, and tho the other MX was lower despite both MXs having 780 watts of solar input, the one MX is putting out more because of the higher input voltage. It's actually doing what it is supposed to, where the 12V input MX doesn't have a higher voltage to work with.

I mentioned in the other thread that for the first time since I installed the FM, it is clamping down at 60 - 61 amps at the best sunlight part of the day and the MX is hitting 58 amps at that time. I'd NEVER seen the FM get over 58 amps since I installed it... NEVER. When the MX was on that set of 1020 watt panels it never hit 60 amps either... which is why I bought the FM60 instead of the FM80.

If the time comes to add another bank of panels, I'll buy an MX80 for the 1020w bank and move the FM to whatever new panels I'd get. I actually don't anticipate getting any more panels though. I used to have a 1KW solar system, then it went to 2KW and I added an electric fridge which put it borderline. Adding the Sanyo dictated going to 3KW. I don't plan on adding any more loads... as Icarus is my witness

As I mentioned, I no longer keep a written log, but I check the readings EVERY day as soon as I get home, before entering the house and turning on loads. Disabling those desulfators made a "slap-in-the-face" difference.

-Bill

Mangas

Re: Solar questions for another new guy.

Thanks very much Bill. Enough for me.

I'm pulling the fuses.