Camper Van System - charge controller options?

darren · August 2014

Hi All

I want to add solar to my Campervan. I use it extensively and would like to spend many days off grid without having to start the engine to replenish my house batteries. Initially I want to start out small but expand as I determine what more I want to run and for how long I end up off-grid before I relocate and recharge as I drive. Here is what I already own:

Tripp-lite PV2000 12v (2000watt 120v) inverter
Tripp-lite PV 400 12v ( 400watt 120v) inverter
2 12v 110 amp/hr lead acid batteries
HD solenoid connection to dual starter batteries / alternator for charging house batteries while driving

The fixed loads I have are:
12v freezer - 360 watts/day
Entertainment - 300 watts/day
Tools - 200 watts/day

So, with inverter losses I guess I use around 1000 watts/day

I only use the PV400 currently but have an A/C unit I would like to run off the PV2000 for 10 - 30 minutes before bedtime as needed if I can once I expand the system later. The A/C draws 8 amps @ 120v or 960 watts. When I have shore power it cools the camper down in 20 minutes or less.

I would also like to run a 12v water heating element to utilize any excess power the panels produce during and after the battery charging.

If I start with one or two 100 watt panels and have room for a maximum of six of these panels, what suggestions do you have for a charge controller for now and should I plan on it being the only one i use or should I upgrade it or add another one later? What are the better brands of controller out there in my size range?

Here are the specs of the panels I want to use:

Pmax = 100 watt
Vmp = 17.7v
Imp = 5.7a
Voc = 21.7v
Isc = 6.1a

Thanks,
Darren

Cariboocoot · August 2014

Re: Camper Van System - charge controller options?

Welcome to the forum Darren.

So basically you want to add some solar to extend your battery time. Often the limit with an RV application is what will fit on the roof. To overcome that some people go for detachable, portable panels that can be set in the sun while they park in the shade. This has advantages and disadvantages of course.

Okay, you've got 220 Amp hours @ 12 Volts and use about 1000 Watt hours per day. As it is that would be close to 50% DOD on those batteries: 1000 Watt hours / 12 Volts = 83 Amp hours not including losses/conversion.

Your panel choice at 5.7 Imp would require about four such panels to fully charge your 220 Amp hour battery bank. That's 400 Watts, and that's the 'tipping point' for going up to higher Watt panels (if they can be fitted) and an MPPT controller.

Space and budget limitations will probably interfere with using a couple of 200+ Watt panels and an MPPT controller. You save money over-all ($400-ish in panel, $300-ish in controller as opposed to buying several small panels at around twice the cost per Watt), but it hurts the capital outlay because you have to do it all at once.

Let's say you stick with the add-as-you-can plan. Get a PWM controller of around 30 Amp capacity now, so it will take four of those panels when you can afford them. Wire for the full current capacity now, so you don't have to re-wire later. With four panels in parallel you should have a fuse or breaker on each one, btw.

I don't know about adding the 12 Volt water heater: you probably won't have much surplus power and they aren't very efficient.

darren · August 2014

Re: Camper Van System - charge controller options?

Thanks for the welcome. The panel I plan to use is of a flexible variety and will work perfect with the curve of my roof and the size I have to work with. So I am stuck with that choice. I was thinking of running them series (2 to start then 6 at the most) to an MPPT controller. The only downfall I think I have is the 12v 2000 watt inverter which prevents me from going to a 24v battery bank. Would something like the Midnite Kid work in my situation? Or do I need to look to something in the 45 amp range even with series wiring the panels due to the 12v battery bank? The Kid would work well for 4 panels in series to my battery bank, but if I have to use two of them in tandem to proceed to six panels then maybe I should just look towards a 45 amp controller to start with. Too bad there is not a way to charge my batteries at 24v and run the inverter at 12v. Will the Midnite Kid controller run six of these panels into a 12v battery bank? Is there another controller I should be considering?

Thanks
Darren

BB. · August 2014

Re: Camper Van System - charge controller options?

Think twice about flexible panels... Many are thin film are about 1/2 as efficient as crystalline solar panels (under glass)... So, you can fit ~2x the square footage with flexible panels and still get about the same amount of power.

Second, flexible panels may not last much more than 1-5 years (in my humble opinion). I would only use them as a last resort (or if they are a lot cheaper/better to mount vs glass panels).

Lastly--Always look at the panel Vmp and Imp ratings.... Vmp for a PWM controller on a 12 volt battery bank should be around 17.5 to 20 volts for optimum power transfer.

If the voltage is too low--It will not charge well/quickly on hot days. And if the Vmp voltage is too high--It will only use a fraction of the available panel wattage (i.e., a Vmp 30 volt panel on a PWM controller connected to a 12 volt battery bank will be about 58% efficient of panel's rated/usable output).

-Bill

Cariboocoot · August 2014

Re: Camper Van System - charge controller options?

Usually one does not use an MPPT type controller in an application like this. However, if it's in the budget the Kid would work well as you need <30 Amps to charge 220 Amp hours of batteries.

You would not want to put more than two panels in series, though. For one thing it increases the problems with incidental shadows knocking out the whole array and for another there is a reduction in controller efficiency the higher array Vmp is in respect to system Voltage. With four panels configured for two parallel strings of two in series you'd be at about the best (and no fuses required on only two parallel connections).

If you do need to exceed the 30 Amp rating the Kid can be paralleled with another, and for the most part there is no difficulty in running more than one controller on a battery bank.

darren · August 2014

Re: Camper Van System - charge controller options?

Thanks for the info.

Darren

soylentgreen · August 2014

Re: Camper Van System - charge controller options?

I have a similar setup. I use the Morningstar sunsaver duo charge controller which will charge both house and starting batteries and can handle up to 30 amps (if memory serves).

I suspect you may be under-estimating your loads and over-estimating your solar and battery. Running a 1kw air conditioner will absolutely hammer your 200AH batteries. Google the Peukert effect.

Are your batteries in good shape? If not, consider getting two costco 6v got cart batteries: about $90 each and are an excellent value and probably better than what you have.

Cariboocoot · August 2014

Re: Camper Van System - charge controller options?

If the numbers are right:

960 Watts for half an hour = 480 Watt hours / 12 Volts = 40 Amp hours, or about 20% of the total capacity of the battery bank. Your other loads, if we take the first post as Watt hours, add up to nearly twice as much: 860 Watt hours. That would be another 72 Amp hours. At that point you've just exceeded 50% DOD. You would be relying heavily on daytime use offset by PV production, which isn't going to happen with a single 100 Watt panel.

Now, how about a nice small inverter-generator as power supplement?

jimindenver · August 2014

Re: Camper Van System - charge controller options?

100w mounted is only going to good for a very low power user in a RV. I'm talking basic rig functions, LED lights and little if any furnace.

230w flat in good weather allowed us to run our 25 ft trailer with ease even though we needed the furnace every night and some days. It also covered some TV/DVD usage and even a short run of the microwave or hair dryer.

This last trip I took the two 245w panels that eventually will be mounted. Portable and tracking they gave us all the power we could use starting with the coffee maker in the morning, some hair dryer after showers, vacuum up the mess the dogs drag in and finally nuke a few taters at dinner. Also a TV/satellite system may run all day and into the night. We never had a issue with power even though it wasn't the best weather.

So I suggest you put what panels you can up top and fill the battery bay. If you still run out of power, it's time to conserve. Start out small if you must but get the controller that will handle the extra panels now.

soylentgreen · August 2014

Re: Camper Van System - charge controller options?

My hope (and my hope for others like us) is that Lithium batteries will solve many of our problems.

For example, LifePO4 batteries currently have something like 99% charge efficiency (vs. say 70% for Lead Acids), can discharge to 80%, have almost zero voltage drop, and don't suffer from the Peukert effect. From what I read, a 100Amp LiFePO4 battery is equivalent to more than double the equivalent amp-hour rated PBA battery.

Current issues: Cost, availability, home-brew quality, fly-by-night chinese companies, etc.

My current plan is to muddle through for another year or two on lead acids, then go to Lithium_whatever.

Camper Van System - charge controller options?

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