camper van, need advice on a charge controller

05kas05
05kas05 Registered Users Posts: 3 ✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
ok i have a 1995 gmc vandura 2500 with 2 deka 8a31dt 105ah agm batteries connected in parallel for my house electrical needs.these are connected to the factory alternator with a dual sensing automatic charge relay and i also have a renogy 200 watt solar kit installed that i picked up off amazon, so far it is working fine and i have had no problems.
i am however looking to upgrade the charge controller on my setup because the renogy ones have been known to go out so I'm just planning ahead just incase.

i don't plan on adding any panels in the forseeable future. i don't run a lot of electrical but the main things that i do run are a fantastic vent, a 02 cool 12 volt fan, and a tf-51 truck fridge. the fridge is the only thing that will be running pretty constantly. now i am not a full-time van dweller and I'm usually only camping for a couple of days at a time not sure if this will make a difference. i was originally looking at a morningstar ps-30 but it does not have an agm setting and also everyone i asked said to get a mppt charge controller. so any thoughts or opinions are much appreciated
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: camper van, need advice on a charge controller

    Welcome to the forum.

    Basically the only thing that matters here is the amount of current you can get from the panels. From 200 Watts it's likely no more than 11 Amps (100 Watt panel with Vmp around 17.5 would be Imp of about 5.7 * 2 panels). If the Vmp is higher the current will be less.

    There is not much advantage to be had from MPPT on a system this small. Normal increase in current is about 10%, or 1 Amp here. That would not justify the roughly $300 price in my opinion.

    You don't even need a 30 Amp controller like the PS-30 (which in fact does have an AGM setting of 14.15 Volts Absorb or 14.4 Flooded). Frankly a SunSaver 20 would do (and also has an AGM setting of 14.1 Volts Absorb). About $85.

    Your two batteries @ 210 Amp hours total would get a charge rate of just about 5% maximum, which is pretty low. It would extend usage time but is not really sufficient for full solar charging while loads are running. Any chance you may add a third panel? That would bring you up to about 15 Amps and improve the charging markedly.
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  • 05kas05
    05kas05 Registered Users Posts: 3 ✭
    #3
    Re: camper van, need advice on a charge controller

    ok i did not realize it had an agm setting i saw flooded, sealed, and gel and was not sure if agm fell in there somewhere, so I'm guessing that sealed is the one to use for agm? i must have confused my self as i have seen others with an actual agm setting so i figured it did not have one. i could add some more panels at a later date if needed but i had not planned on it i figured i could get by with what i had. so with that said lets size the controller with the idea that i might add two more 100 watt renogy panels in the future i won't be able to fit more than this i know for certain. if i added 2 more would i or should i move to a mppt controller at this time or am i still good with the pwm type controllers? also for the controllers that don't have displays is there a battery monitor i should be looking at adding? sorry for all the noob questions i just want to get it done right .
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: camper van, need advice on a charge controller

    Difference between flooded and AGM in charging is that the latter has a lower Absorb Voltage. Some of them will even take the 14.4 setting for flooded these controllers offer, and some flooded cells are not satisfied with that low of an Absorb. So much depends on the battery in question!

    If you go up to three panels the 20 Amp controller will handle it because the Imp is <6 Amps thus the total is <20 Amps.

    If you go to four 100 Watt panels you might still 'get away' with the 20 Amp controller, depending on what exactly the Imp is but you would be in the danger zone for losing small amounts of power. At that level it may be feasible to go with MPPT. The output then becomes (400 Watts * 0.77 efficiency / 12 Volts) 25-26 Amps as opposed to (5.7 Imp * 4) 22.8 Amps. Again only about a 10% gain and you don't really need it with 210 Amp hours of battery, but you could use it. Otherwise you would need a 30 Amp controller (either PWM or MPPT) for four panels.
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  • 05kas05
    05kas05 Registered Users Posts: 3 ✭
    #5
    Re: camper van, need advice on a charge controller

    i really appreciate you taking the time to answer my questions, i think i have narrowed it down to either the prostar30 and adding a panel for now and maybe another later
    or would adding the sunsaver mppt to the two panels i have now to get the most out of them be a better option.
    i am thinking i would get more from the first choice but want to be sure before i pull the trigger.
    also as far as my little system goes do you think i would be better putting all the solar into the one battery with the fridge and fan.and then charging the other battery off the alternator for my lights and such or should i just keep them wired parallel and charging off the solar and the alternator.
    thanks again for the help it is appreciated.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: camper van, need advice on a charge controller

    I don't recall what the actual Vmp is on those panels. As a rule the MPPT will only give you about 10% more current on average over PWM. It usually isn't worth the extra money.

    Examples:

    100 Watt panel with Vmp 17.5 and Imp 5.7 will give 5.7 Amps on a PWM controller. On an MPPT controller it will give possibly (100 * 0.77 / 12) 6.4 Amps maximum. A difference of 0.7 Amps all else being equal, and that's not guaranteed.

    100 Watt panel with Vmp 18.9 and Imp 5.3 will give 5.3 Amps on a PWM controller. On an MPPT controller it will give possibly the same 6.4 Amps as per above. A difference of 1.1 Amps all else being equal.

    So if the panels have a particularly high Vmp for their size the MPPT advantage goes up. But weighed against the cost difference (ProStar 30 for $122 SunSaver 15 MPPT for $225) of $103 that's a pretty expensive 1 Amp increase. It's worse if the PWM controller is comparable in capacity (i.e. a 15 Amp ProStar is $90).

    Usually you want to keep your 'house' battery and 'vehicle' battery separate on an RV, with the ability to connect them so you can "borrow' power from the other system in an emergency. I would not split up the house bank into separate units though. Sometimes seeing the lights dim is a good indication something needs tending to, such as start the engine closing the switch and giving the bank a boost while you figure out what's gone wrong.
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