Solar + Trojans = higher voltages

jfinet
jfinet Registered Users Posts: 5
Recently had solar system installed on our Arctic Fox and getting used to how it works ... with the recommended charging voltages for the Trojans and using a Tristar T-45 with temperature compensation ... some pretty high voltages are showing up on cold days ... 15 v and higher ... all good I guess for the Trojan batteries ... but what has been the experience here with trailer electronics not liking those higher voltages ... I have checked manuals for most items and some are rated high enough ... but water heater SW6DE does not list max voltage ... Suburban furnace shows 14.5 max volts ... anyway ... I see a lot of Tristar uses here ... and would really like to hear if this has been an issue for others ... oh ... when equalizing ... I have a isolation switch to separate the batteries from the trailer ... so not worried about the even higher equalization voltages ... thank you ... John

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar + Trojans = higher voltages

    High (and low) voltages on DC battery banks are a real issue... Most 12 volt "stuff" is designed for ~12-14.2 volt operating range--That of a car/boat/truck when the motor/alternator is running.

    A 12 volt off grid deep cycle battery bank can range from 10.5 to 15.5 volts (or even higher) over loads/state of charge/battery bank temperature/etc.

    For folks that live in a cold climate, an insulated battery box to keep the batteries closer to 77F/25C plus a remote battery temperature sensor for the charge controller is a big help.

    Using a disconnect switch for when you need to equalize the battery bank (hopefully, you do not need to do that too often--perhaps once every month or so) is another workable solution.

    And this leads to one of my preferences (for larger off grid power systems) to switch most of your loads to 120 VAC and get an AC Inverter with a wide input voltage range. The typical AC inverter will top out at 15 volts--A bit low for your needs. But some are available that go >16 VDC battery bus voltage. (for example, Samlex offers different model lines with 15 and 16.5 volt max input ratings).

    Many AC versions of appliances/lights can be much less expensive than the 12/24 VDC versions. And with Energy Star program, many of the 120 VAC devices are very power efficient now--So much so, that the 15% or so losses of the AC inverter are not worth worrying about (or just add an extra solar panel or two to the array to make up for inverter losses--solar panels are much less expensive than 10 years ago). 120 VAC also makes it much easier to send the power any distance away from the battery bank (120 Watt load, 10 amps with 1 volt wiring drop at 12 VDC, or 1 amp and 4 volt wiring drop at 120 VAC--difference between 10' easy at 12 volts vs 100'+ easy at 120 volts with a cheap extension cord).

    For small off grid systems--You are frequently between the rock and a hard place. The definite limitations of native 12 VDC appliances running on a deep cycle battery bus vs the costs to add an AC inverter and sizing the system up to support the fractional increase in loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar + Trojans = higher voltages

    I will 2nd the comments by "BB" re switching to 120 VAC and using an inverter capable of working with 16 VDC input. I still have a couple of automotive radios working on "12 VDC", but tend not to use them when the controllers have the battery voltage high, as the radios tend to get quite hot. So far they haven't burned out, but I know they're being badly stressed at times. Everything else is on 120VAC, and still the inverters I was using would shut down on cold Winter days when battery voltage reached 15.5, so I eventually went to 16VDC capable inverters and no more problems. Would have saved a bunch of money if I had done that from the start.
    I will also 2nd "BB's" comments re going with Energy Star AC appliances such as fridges and freezers. Their efficiency is now easily within reach of the best "high efficiency" DC models, and when replacement is needed, that cost far outweighs the cost of possibly needing an extra panel or two that may or may not be needed to supply the AC versions. In fact, even the difference in initial purchase cost will often more than take care of that. Sales info on the DC appliances would have you believe they are the only way to go, however real life experience has most definitely shown otherwise.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar + Trojans = higher voltages

    wayne,
    put a couple of diodes in series with one of the leads of proper current rating to drop the voltage a bit. it may put the voltage to the radio under 11v on the low end, but should still work fine. if it turns out to be too much for it to work on the low end you can get a cheap dc switch in parallel with the diodes to bypass them.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Solar + Trojans = higher voltages

    A quick reminder, Trojan does NOT recommend a regular equalizing, only equalizing when cells are significantly different.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • jfinet
    jfinet Registered Users Posts: 5
    Re: Solar + Trojans = higher voltages

    Follow-up … our TT is 22 ft … small … we live in it 3 months out of the year while fly fishing beautiful places … we don’t use tv or microwave and turn things off when not in use … have lots of LEDs … so the solar system is to allow us to dry camp for 10 days or so at a time … since we have already spent our budget on the solar we have … we would like to figure out how to deal with this system … without buying new appliances … not charging the Trojans at the maximum voltage recommended and/or not using temp compensation would be one option (replacing batteries a little earlier than otherwise and not getting 10 days) … not using certain items during the day when it is cold … etc … the items of specific concern are:
    SW6DE water heater … manual says 10.5 to 13.5 v range for ignitor … warns of damage to ignitor board with excessive voltage but does not specify max voltage … this is one I expect almost everyone has and can’t imagine using the high wattage electrical coil with inverter
    Norcold Ref N621L … control voltage 10.5 to 15.4 v max … assuming this applied to control board … heater … and ignitor board … we really would like the fridge to work on propane … the heart of the trailer according to my wife
    Furnace … Suburban … manual says 14.5 v DC max voltage … control board … if furnace only used when it is dark … this can be worked around … we mostly use Mr Heater when dry camping
    Shurflo 2088-422-144 water pump … tech support says pump can handle 15.5v ok with some increased noise and wear
    I have considered running a 14.6 v absorption profile and clamping the low temp compensation at 50 deg F to keep voltages below 15 v since all our camping is April – Oct … and in the winter in storage I have the trailer isolated from the batteries … I don’t expect to need to equalize often … it is in manual … and I can isolate the trailer during those infrequent events … I appreciate all comments on this issue … thanks … John
  • jfinet
    jfinet Registered Users Posts: 5
    Re: Solar + Trojans = higher voltages

    I just got an e-mail reply from Suburban re the max voltage for SW6DE ... it is 13.5 v ... they said the board could fail at 14 v and that is why they list the 13.5 v as max ... interesting ... since my Arctic Fox came with converter that bulked and auto equalized at 14.4 v ... guess the safe thing to do is shower at night ... or temporarily disconnect solar while water heater is running ... John