Stupid questions from a beginner

Oldrep · June 2011

Sorry for the stupid questions, but after looking at this site I've discovered just how little I know. I have a place in the NW where we stay 6-8 months out of the year, currently in a trailer. I have about 240W from 3 Seimens solar panels putting out 12V to 4 12volt deep cycle batteries, with a Morningstar TS60 controller. It does a pretty good job so far.
I want to expand so got 4 Suntech 280watt panels (mod#STP280-24/Vb1). They are 48v so got a Morningstar TS60 MPPT which is supposed to handle dropping the 48v down to 12v to charge my battery bank, although of this I'm not certain. I currently just clip on a 800 watt inverter when 120volts is needed as most of the trailer runs on 12v.
Can I hook up the 4 new panels in parallel with a 48v output, run it to the new MPPT controller and charge my 12v battery bank okay? Is it over kill? Impossible to do and I should look at something different? Any advise is appreciated.

solarix · June 2011

Re: Stupid questions from a beginner

You don't sound stupid to me. I'd say your doing just right.

Cariboocoot · June 2011

Re: Stupid questions from a beginner

Yep. 48 Volt array to MPPT controller to 12 Volt charging output.

One caveat: those four (or any number over two) panels in parallel should each be fused according to their Isc rating to prevent accidents like fires - just in case something goes wrong with one of them.

Since we don't know the Amp hour rating of the batteries it's impossible to say if this is enough or too much panel. Four batteries in parallel, btw, also can present problems keeping the current flow even between them.

BB. · June 2011

Re: Stupid questions from a beginner

Ditto--Sounds like you are on the right track.

I would also like to ask about your current solar/battery setup...

What is AH rating of your battery bank? Are they flooded cell or AGM?

Ideally, the solar charge controller should be close to the batteries and have a fairly heafty cable for low voltage drop (ideally, less than 0.05 volt drop from charge controller to the battery bank).

Although, the MorningStar TS family of charge controllers are one of the few that have a remote battery voltage sense lead setup (yea for them!). If you don't have this setup and your leads from the battery bank to the charge controller are on the "long side"--You might want to connect the battery voltage sense leads. This may help you ensure the batteries are recharged as quickly as possible (no wasted sunlight).

Also, for both TS family charge controllers--you should look at getting the Remote Battery Temperature sensors too (I think you will need 1 for each controller). I assume your batteries see a fairly wide swing in temperatures and a battery temp sensor will help keep the batteries properly charged.

-Bill

PS: You can place the new panels in series (2 in series and then 2 strings in parallel = 4 panels). That will allow you to use smaller wire from the array to the MPPT charge controller--and if you want to mount the array further away from your RV--it will be easier with the "higher voltage" Vmp array.

Oldrep · June 2011

Re: Stupid questions from a beginner

Thanks for the support. I'm planning on wiring the panels up in parallel (they have mc4 connectors). I'm having problems finding the wiring/cables that I need. Any suggestions on where to find them? Seems no one close sells parts, just systems. Will I need fuses between panels? Between the panels and the controller? Whats your opinion on a battery bank of 4 12v batteries?

Oldrep · June 2011

Re: Stupid questions from a beginner

Sorry, I'm no where near the NW at the moment and don't remember the AH of the batteries. They are marine deep cycle batteries for what good that info will do. I'm in Calif currently and just trying to get what I need here before I go back up into the woods where stores are few and far between.

ggunn · June 2011

Re: Stupid questions from a beginner

Oldrep wrote: »

Thanks for the support. I'm planning on wiring the panels up in parallel (they have mc4 connectors). I'm having problems finding the wiring/cables that I need. Any suggestions on where to find them? Seems no one close sells parts, just systems. Will I need fuses between panels? Between the panels and the controller? Whats your opinion on a battery bank of 4 12v batteries?

You'll want a combiner box to hold your fuses and collect the output of your parallel source circuits. Midnite Solar makes good small scale combiners, and most solar sales outfits carry their stuff. Google "combiner box" and you'll get lots of options. You'll probably have to buy on line; as you say, most storefront outfits are installer/integrators and are selling systems.

BB. · June 2011

Re: Stupid questions from a beginner

Cutting of the mc4 connectors from the panels may void your warranty.

A simple option is to buy a male/female mc4 cable and cut it in half. Splice the cut ends into your power wiring.

-Bill

bobdog · June 2011

Re: Stupid questions from a beginner

Just a quick question...if he were to use in line fuses instead of a combiner box, wouldn't the fuses go on positive side?

Cariboocoot · June 2011

Re: Stupid questions from a beginner

bobdog wrote: »

Just a quick question...if he were to use in line fuses instead of a combiner box, wouldn't the fuses go on positive side?

That's pretty much standard DC practice, yes; fuses on the positive wire.

Not a good idea to have in-line fuses out in the weather, though. Since the panels all have to join up anyway, bringing the wires into a weather-tight box and having the fuses inside it is the usual solution.

Oldrep · June 2011

Re: Stupid questions from a beginner

I currently have 4-12v marine deep cycle flooded batteries. Spec's on the battery is; 105AH @ 20hr,,, 79 AH @ 5hr,,, 160Min @ 25 amps. At the moment the batteries are subject to temperature swings.

I have approx 25ft of 10 gauge wire from the solar array to the controller,,, #2 gauge wire 6-8ft from the controller to the battery bank. Both the battery bank and the solar array each have a 12vdc auto style cutoff switch. (This I know needs to be changed to a combiner box w/cutoff switch). This is used near Lewiston, Id.

What we'd like to work towards besides powering our trailer, is to have our system eventually power a "energy efficient" fridge 24/7 that shows 7.74amps on it's tag and a washing machine. I'm not sure of the spec's of the washer yet, but can always just use a gas generator for the little time that will run. I plan on running a 120v wire and putting an outlet in a building that is already there for the fridge and the washer since they will be housed there.

Now, I was thinking, and I'm sure that's a bad thing to do at times,, As suggested, If I put two of my 4 new panels in series with 2 in parallel, that will bring the voltage of the circuit way above 48v. Can I safely run that to the input of my controller (Morningstar TS60 mppt)?

On another note, It sounds like in reading through the forum that all the solar panels should be of the same type. No mixing of 45w panels with say a 95w panel of another manufacturer?

Thanks, Jim

Cariboocoot · June 2011

Re: Stupid questions from a beginner

Mixing panels: for parallel connections it's important that the Vmp be close (within 10% say). For serial connections it's important that the Imp be close (again about 10%). So yes you can connect a 40 Watt panel to a 140 Watt panel (+) to (+) and (-) to (-) if they both have a Vmp around 17.5 or so. Likewise (and a less likely scenario) you can connect them in series if they both have a Imp around say 7 no matter what the Vmp. The closer the panel specs, the better the mix will be. Identical panels is best, of course.

Morningstar's MPPT controller has a Vmax in of 150. That is based on the Voc of the panels. But it is also one of the controllers which is most efficient if the array Voltage isn't much more than 2X the system Voltage (nominal). You also may have to consider the problem of cold weather sending the Voc of a string of panels over the controller's limits, if such conditions may prevail.

Basically you've got 420 Amp hours total at 12 Volts. Ideally for full charge ability you'd want about 750 Watts of array for that. It's also about the point where you might consider going up to a 24 Volt system. especially with the desire for future expansion and running a refrigerator.

As for running a washing machine ... keep the generator handy. Much more practical for large, occasional loads than the amount of expansion necessary to do the same thing (which would be wasted the rest of the time).

Oldrep · June 2011

Re: Stupid questions from a beginner

My battery bank consists of 4-12volt marine deep cycle, flooded batteries wired in parallel for a 12v output, The spec's on a battery is ;
105 AH @ 20hr
79 AH @ 5hr
160Min @25amps

I have approx 25' of 10 gauge wire from my solar array ( total of 245W) to the controller. #2 gauge wire 6-8ft from the controller to the battery bank and #2 wire between the batteries. Both have a 12vdc cutoff switch like what's used for a car. I know now that I need to change that and use a combiner box with a cutoff sw and CB's..

The system is located in Northern Idaho near Lewiston, so probably not as much sun as in Az.

Our goal is to power our trailer along with a fridge 24/7 and washing machine. The fridge is "energy efficient" and has 7.74 amps on the tag. The washer I'm not sure of yet but can always just use my gas generator for what little that will run. My plan is to have the system close to the trailer for now and run a 120v line and outlet into a current building that the fridge and washer will be housed in.

As suggested, if I put 2 of my 4 panels in series with the other 2 in parallel, that's like 96v in the circuit. Can I hook that to my controller (Morningstar TS60 mppt) ?

In reading some of the posts here it seems that all of the solar panels should be of the same amperage and type. Is there problems mixing 45w and 95w panels, etc. of different manufactures?

Thanks, Jim

Oldrep · June 2011

Re: Stupid questions from a beginner

Sorry for the re-post. I thought maybe I goofed up the first time.

Thanks a bunch for the valuable info.

Stupid questions from a beginner

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