I'm looking for a charge controller for my RV, high voltage.

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  • jackbombayjackbombay Solar Expert Posts: 46
    Re: I'm looking for a charge controller for my RV, high voltage.

    The charge controller is working fine I think, I have a voltage gauge mounted in the van where it is easy to see at all times. Last winter in 0* F weather the float voltage was at 15.2 and in the middle of summer in 90* weather the float voltage was 13.9 so I don't think there is an overcharging issue. I just never checked the water in the last 16 months, pure operator error. Eventually I'd love to get the batteries installed under the van so I really won't want to have to deal with checking water levels then. My last van with a solar system never seemed to use any water, it was one AGM and one lead acid battery so the charge controller was set for the lower float voltage of the AGM, maybe that was why. I know that system was not "ideal" but I never did have to mess with it at all either.

    Filling the batteries back up has brought them back a bit, hopefully enough to get through our upcoming road trip as I don't want to rush into an AGM purchase.

    As far as the different AGM batteries go what are some brands to look for? And what brands should I avoid? I'd like to go with 2 batteries, 100 AH each. I know I'm looking at close to $500 there. I assume I should get 2 at the same time, yea? Or can I get one and then add another 6months or a year later?

    TIA
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: I'm looking for a charge controller for my RV, high voltage.
    jackbombay wrote: »
    As far as the different AGM batteries go what are some brands to look for? And what brands should I avoid? I'd like to go with 2 batteries, 100 AH each. I know I'm looking at close to $500 there. I assume I should get 2 at the same time, yea? Or can I get one and then add another 6months or a year later?

    TIA

    Since you would be running them in parallel, I advise you to get them at the same time if you can. That way you will avoid potential problems when you parallel a (gently) used battery with a brand new one. Six months maybe, a year probably not.
    If you get a CC and panel set which is sized for two batteries, you will still be OK charging just one as long as the CC output limit is C/4 (or whatever the particular battery manufacturer specifies as max current.) That same CC might be undersized for two batteries. Another reason to get both at the same time.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,712 admin
    Re: I'm looking for a charge controller for my RV, high voltage.

    Your voltage is a tad on the high side--But not checking water for 16 months is the killer.

    AGM usually want slightly lower voltages than flooded cell (especially for floating). From the Concorde website:
    Charging Instructions:
    • Initial charge or recharge - 2.37 to 2.40 volts per cell at 25° C (77° F).
    • Float charge - 2.20 to 2.23 volts per cell at 25° C (77° F).
    • Conditioning charge - 2.58 volts per cell at 25° C (77° F).
    • Temperature compensation - 4.00 mV. per cell per degree C [Reference to 25° C (77° F)].

    This is for battery temperature (not ambient temperature) and is useful for battery temperatures from 0° C to 40° C. Contact Concorde Battery Corporation for temperatures that exceed this range.

    So, at ~77F, 6x2.20 volt float = 13.2 volts and 6x2.40 volts charging = 14.40 volts

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jackbombayjackbombay Solar Expert Posts: 46
    Re: I'm looking for a charge controller for my RV, high voltage.

    Hmmm, I'll check voltage vs temp more closely today.

    As far as AGM batteries go price does seem to vary a fair bit, which I'm sure has some bearing on quality.

    The "universal battery" has an appealing price ($182 each), http://www.solar-electric.com/unba100amagm.html But if the sunextender batteries are know to be significantly better I could save up money for a couple of them ($307 each) , http://www.solar-electric.com/pvx-1295.html.

    What is the reputation of the universal batteries?
  • BB.BB. Super Moderators, Administrators Posts: 29,712 admin
    Re: I'm looking for a charge controller for my RV, high voltage.

    I don't know... NAWS (our host, and none of us moderators are connected to NAWS other than through spam patrol here on the forums) would be a good place to have the discussion.

    From what I have seen here over the years, NAWS tries to provide quality product and has dropped suppliers that have had problems.

    Also, batteries are heavy and costly to ship (AGM's are sealed--so, I don't think, there are any restrictions unlike filled flooded cell batteries)... You might also check with a local battery warehouse and see if they can help you too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jackbombayjackbombay Solar Expert Posts: 46
    Re: I'm looking for a charge controller for my RV, high voltage.

    I'm in a small town, so no local battery warehouses, but I will be in Flagstaff this november so I could pick up batteries in person then.
  • jackbombayjackbombay Solar Expert Posts: 46
    Re: I'm looking for a charge controller for my RV, high voltage.
    BB. wrote: »
    Your voltage is a tad on the high side--But not checking water for 16 months is the killer.

    AGM usually want slightly lower voltages than flooded cell (especially for floating). From the Concorde website:



    So, at ~77F, 6x2.20 volt float = 13.2 volts and 6x2.40 volts charging = 14.40 volts

    -Bill

    Temps and voltage, 72* this afternoon, voltage is steady at 14.25, is my CC supposed to kick down to ~13.2 at some point? Because I have never seen it do that.

    This is the CC that I have.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: I'm looking for a charge controller for my RV, high voltage.
    jackbombay wrote: »
    Temps and voltage, 72* this afternoon, voltage is steady at 14.25, is my CC supposed to kick down to ~13.2 at some point? Because I have never seen it do that.

    This is the CC that I have.

    Depending on the CC you have, the transition from Absorb (fixed 14.25 volts, tapering current) may be made by the charging current hitting a low set point, which may not happen if there are loads connected, or may be based on time, which may not expire before the panels stop producing.

    Looking at the MorningStar documentation at the link you provided, however, I do not see any mention of three-stage charging or of Float voltage operation. In fact, the spec sheet shows:
    • Charge algorithm .......... constant-voltage
    series configuration

    If that really represents the CC design, then you should not expect the voltage to drop, and you may end up overcharging your batteries somewhat. Since the temperature compensation just senses the temperature at the controller itself, you run the risk of severely overcharging the batteries if they heat up locally as result of the charging or are mounted in a different temp area from the CC.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,712 admin
    Re: I'm looking for a charge controller for my RV, high voltage.

    "High float" voltages probably are not as bad for Solar (which is only 6-10 hours a day charging) if the bank is being cycled.

    If the bank was not being cycled, or being held at 14.25volts 24x7 -- Then you are probably reducing the long term life of any battery bank (and needing to add more water for flooded cell batteries).

    AGM batteries can sit for several months at a time (full charge, no load) before needing recharging. You have the choice of a better controller (i.e., more expen$ive) or simply turning of the controller for a month at a time when the RV is not being used (again, no draw on the battery bank).

    Otherwise, you can look at a new charge controller--The Rogue 30 amp 12/24 volt MPPT has lots of features at pretty good pricing. Or the MorningStar 15 amp MPPT 12/24 volt charge controller for smaller array would also be nice (and the controller is physically small too).

    The MorningStar supports a remote battery temperature sensor (and is highly recommended for this model).The Rogue--I am not sure about.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jackbombayjackbombay Solar Expert Posts: 46
    Re: I'm looking for a charge controller for my RV, high voltage.
    BB. wrote: »
    "High float" voltages probably are not as bad for Solar (which is only 6-10 hours a day charging) if the bank is being cycled.

    If the bank was not being cycled, or being held at 14.25volts 24x7 -- Then you are probably reducing the long term life of any battery bank (and needing to add more water for flooded cell batteries).

    This explains a lot, the bank was not being cycled (although the panel was covered with snow off and on through the winter) so it was off gassing quite a bit with the high charge rate, that also explains why my last system with one AGM and one wet cell battery never needed the water topped up because of the lower charge voltage I set the CC to on account of the AGM battery.
    BB. wrote: »
    AGM batteries can sit for several months at a time (full charge, no load) before needing recharging. You have the choice of a better controller (i.e., more expen$ive) or simply turning of the controller for a month at a time when the RV is not being used (again, no draw on the battery bank).

    Otherwise, you can look at a new charge controller...


    I think this is the best option for my needs, AGM batteries *and* a new controller, this MS 30 amp controller seems to do it all, remote temp sensor (sold separately) float charge, automated equalization charge, convenient load/solar off button... http://www.solar-electric.com/ps-30m.html that controller with 2 of the "universal battery" AGM that I linked earlier should give me a nearly maintenance free system with enough capacity for our needs.
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