new to solar power

System · August 2008

OK, where do I start. Bought a small, week long (at most) cabin/RV to use for a few weeks a year.

It came with:
42w Uni-Solar panel (yeah, I know...)
1 - 12v marine battery, 105 Ah
1 - ETS brand 16 amp charge controller w/o LVD
1 Fuse (20amp?) between panel and controller
1 - 2300w generator

runs at most if all were on:
6 - 12v auto bulbs, 2 - 12v fluorescent lights

plus RV stuff incl:

12 - 12v lights, 1 - 12v fan, 1 - 12v Shurflow pump, 1 - propane Refer (only electronic monitor), 1 - RV furnace blower, 1 - 120v sump pump for well off of generator (23'deep)

So, just a few questions:

I just bought 2 - 6 volt GC batteries (210ah ea.) and will run in series for 12v. That means 210AH / 2 = 105 usable AH @ 50% discharge

1) At 50% discharge how long will it take, theoretically, to charge the batteries to full volts (13.7?) with the 42 watt panel (say 4 peak hours/day)?

2) Second, if I didn't destroy the battery when last up there, it has 105ah at full charge (52.5Ah at 50%), then if I connect it in parallel to the 2 new batteries, will I be decreasing the 100% Ah to 105 from 210 for all 3 batteries due to the lower Ah of the marine battery? And thus lose 105 Ah?

3) Third, can (should) I even PUT a 12 volt, marine battery in line with the other 2 - 6v batteries (even though they are in series = 12 volts) to "increase" battery capacity?

4) I want to get an 85-100 watt panel (Kyrocera, etc.)? Can I use the charge controller I have to hook up both panels (or even just the 85-100 watt panel?

5) I would like to get a new C-35 or SunSaver 20 amp CC. Would that be a wise choice?

6) If I get multiple panels and the voltage = say 36 volts, will the CC take that voltage and process it down to 12 volts, so as to not mess up my battery bank?

7) If I run a battery bank at 24 or 48 volts, how do I run 12 volt loads off of that? Do I need to step it down to 12v and if so how do I do that?

Cool Finally, (sorry), If I get a C-35 or SunSaver 20, if I have the panels go to the CC, then to the battery and then go from the battery to the load, how does the LVD cut the power off when the battery bank gets too low? Or do I have to put an external LVD between the battery and the load?

Whew......Sorry about the long post but I have been reading tons of stuff (on-line and in books) and as it usually goes, the more you learn, the more you realize you don't know. I'm simply trying to not have the lights, etc. go dim after 2 days of no sun ( and that happened!).

Thanks,

Tim

mike95490 · August 2008

Re: new to solar power

This is going to be a long reply Inbetween ?'s, best as I can do, waiting for homegrown & home made apple pie to cook...

Tim F. wrote: »

OK, where do I start. Bought a small, week long (at most) cabin/RV to use for a few weeks a year.

It came with:
42w Uni-Solar panel (yeah, I know...)
1 - 12v marine battery, 105 Ah
1 - ETS brand 16 amp charge controller w/o LVD
1 Fuse (20amp?) between panel and controller
1 - 2300w generator

runs at most if all were on:
6 - 12v auto bulbs, 2 - 12v fluorescent lights

plus RV stuff incl:

12 - 12v lights, 1 - 12v fan, 1 - 12v Shurflow pump, 1 - propane Refer (only electronic monitor), 1 - RV furnace blower, 1 - 120v sump pump for well off of generator (23'deep)

So, just a few questions:

I just bought 2 - 6 volt GC batteries (210ah ea.) and will run in series for 12v. That means 210AH / 2 = 105 usable AH @ 50% discharge

1) At 50% discharge how long will it take, theoretically, to charge the batteries to full volts (13.7?) with the 42 watt panel (say 4 peak hours/day)?

Call it 40W for rounding ease
1365 watts were burned (105ah @ 13V)
about 34 hours of perfect sun, not counting 20% charging losses, or 9 days at 4 hrs a day. By day 2, your batteries have started to sulphate, and die. By day 8 the sulphation has stopped, but your batteries are very sick now.

2) Second, if I didn't destroy the battery when last up there, it has 105ah at full charge (52.5Ah at 50%), then if I connect it in parallel to the 2 new batteries, will I be decreasing the 100% Ah to 105 from 210 for all 3 batteries due to the lower Ah of the marine battery? And thus lose 105 Ah?

Connecting batteries in parallel, that are not from the same batch from the factory, is risky.
The better quality batteries will try to service the whole load, till they are as bad as the worst battery.

3) Third, can (should) I even PUT a 12 volt, marine battery in line with the other 2 - 6v batteries (even though they are in series = 12 volts) to "increase" battery capacity?

Huh? As I read it, you are asking to make a 24V battery out of 2 6's and 12?
in line = series

4) I want to get an 85-100 watt panel (Kyrocera, etc.)? Can I use the charge controller I have to hook up both panels (or even just the 85-100 watt panel?

I know nothing about the ETS (never heard of them) charge controllers. I suspect they are worthless if you are trying to get max efficency out of them

5) I would like to get a new C-35 or SunSaver 20 amp CC. Would that be a wise choice?

6) If I get multiple panels and the voltage = say 36 volts, will the CC take that voltage and process it down to 12 volts, so as to not mess up my battery bank?

Only a MPPT style of controller can efficiently downconvert to battery voltage. There is a Sunsaver MPPT, about $220 ballpark, but at 12V, it's limted to 200W, or 24V / 400W.

7) If I run a battery bank at 24 or 48 volts, how do I run 12 volt loads off of that? Do I need to step it down to 12v and if so how do I do that?

You need a device that can convert voltage from 1 value to another. They are called DC-DC converters, they consist of a high efficiency switching power supply and rectifier.
If you are handy with a headset magnifier and micro soldering iron, I have a way to take a bare bones factory converter, and mount it to a suitable circuit board. 120W capacity with proper cooling. 48V - 12.0V (.1% regulation)
http://www.naturalstudies.org/Photo_galleries/LED_driver/
the part that is the "guts" http://www.powerconversion.com/products/websheet/365/AEO is about $80, but then you need a board, and a handfull of other parts

Cool Finally, (sorry), If I get a C-35 or SunSaver 20, if I have the panels go to the CC, then to the battery and then go from the battery to the load, how does the LVD cut the power off when the battery bank gets too low? Or do I have to put an external LVD between the battery and the load?

I don't know if the sunsaver MPPT http://store.solar-electric.com/mosumpsochco.html
has built-in LVD, but the above page has a link to the specs where you could look it up

Whew......Sorry about the long post but I have been reading tons of stuff (on-line and in books) and as it usually goes, the more you learn, the more you realize you don't know. I'm simply trying to not have the lights, etc. go dim after 2 days of no sun ( and that happened!).

Thanks,

Tim

your welcome

niel · August 2008

Re: new to solar power

in addition to what mike has replied to you with you may find that the percent charge rate is of the order of about 3a/210ah=1.4%. this may be far too low to charge the battery as it should have about 3% minimumly in such a circumstance. this low is good for float and maintenance charges and the addition of another pv 50 watts or higher would do a world of good. most pvs will have a higher vmp than the unisolar so this is a bit of a mismatch, but if the battery needs it it will draw from both pvs.
as to the controller, i am not familiar with it either. assuming it to be an average pwm type it should be fine to use up to the max current rating on it. if it is a shunt type controller you may find it having to dissipate alot of heat when nearing the upper end of the charge cycle when it must regulate the charge to the batteries. this creating of more heat is the enemy of most things electronic and so i dislike the shunt types for this reason.
with an lvd this is a dedicated line that is fed to dedicated load(s) from either the controller or seperate lvd device. the loads are not directly connected to the battery(s) for lvd protection. when an lvd circuit activates it will switchout only those loads that are going through the lvd circuit. know that the loads that are connected directly to the battery(s) are not switched by an lvd so the battery(s) may still continue to be drained even when the loads through the lvd have switched out of line.

System2 · August 2008

Re: new to solar power

Thanks for the responses. Sorry my message was so long.

Niel, you hit the nail on the head. And just to re-affirm what you said:

If I buy a CC with an LVD then I have to connect my "load" wires to the output "screws" on the CC that says "load". Then when the CC senses that my battery bank is below the established voltage, then it will cut my "load" off. But, ONLY if I have my load connected to the CC in this way. So, whatever I have connected directly to the battery it won't be able to cut it off and thus won't. This leads me to 1 more question about this (I promise, only 1).

Does this mean then that when I connect my load to those "screws", that the load is still pulling from the battery(s)? And thus the battery is being charged through the CC and then the power from them is coming back through the CC to the load output and then to the load? It seems so simple and yet I can't find anywhere that that is the way it works. Not in the lit. or the manufacturers websites.

Thank you, thank you, thank you....

OK, just 1 more: If the above is true, then does the load actually take power from the PV at anytime in the process?

Tim

mike95490 · August 2008

Re: new to solar power

The CC does feed the Load from the battery. The CC takes the PV, does whatever conditioning it does, and delivers it to the battery. Internally, the Load, passes thru a voltage sensing circuit, to determine when to shut the Load down.
And someone else may explain it a different way. You mileage may vary.

niel · August 2008

Re: new to solar power

mike,
he asked if it was like being directly to the battery and it is not as it does go through the cc's lvd circuit. semantics issues i guess. he got my meaning though.
tim,
essentially yes. most controllers have to be connected to the battery to work so one can't normally go from pv to controller with lvd to loads and no battery, to my knowledge anyway. the pvs do not have to be connected for the lvd loads to function while being connected to the battery. i'm not sure of the pwm sunsavers with lvd as i never tried to go without a battery with the one i used to have. i didn't have that cc very long as i used to feed it with an automotive battery charger that went bad on me and destroyed the cc with utility ac. it did regulate the auto charger for me before the charger blew it out though.
2nd question's answer is only through the battery. if it didn't go through the battery the voltage would be much higher. the battery will get power from the pvs through the cc. think of the lvd as an addon circuit built into a cc for loads dependant on the voltage level of the batteries.

System2 · August 2008

Re: new to solar power

niel wrote: »

...you may find that the percent charge rate is of the order of about 3a/210ah=1.4%. this may be far too low to charge the battery as it should have about 3% minimumly in such a circumstance. this low is good for float and maintenance charges and the addition of another pv 50 watts or higher would do a world of good.

Well, I'm changing direction and thinking about an upgrade to a 130 watt Kyocera. It is rated at 7.39 (max amps). If this is true, then I would still only get a charge rate of around 3%. (Correct?) 7.39/210 = 0.035...In essence what does that buy me? It alsmost sounds like you can't get away with 2 simple GC batteries with a 130 watt PV. Or is my math off?

Tim

niel · August 2008

Re: new to solar power

i was saying to parallel another pv of 50w or higher to go with the one you already have. if you wish to replace it with the kyocera that is fine and what that gets you is a charged set of batteries and please understand that even at the 3.5% rate it will take quite some time to reach a full charge. you still need to watch you don't deplete the batteries beyond 50% if you want them to last so you still must limit yourself to around 105ah. of course if it's an emergency and you need more power then by all means use more, but understand that this will lower the lifespan of the batteries or kill them in short order when taking them down all of the way. lighter discharges will be even better, but not always practical for everybody.

new to solar power

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