Need help with my camper van conversion solar/ battery issues

Newworldorder
Newworldorder Registered Users Posts: 2 ✭
in Off Grid Solar & Battery Systems #1
hi everyone thanks for your help, I’ll get right to it. 

I have a 2014 cargovan high roof that I converted and I went with a 400 watt solar system, 2x 6volt AGM batteries each having 190 amp hours. 

I have a 3000 watt inverter.

One thing I need help with is I was running a 900watt oil heater and I could see on my inverter that it was drawing 960 watts. 

So if I have a 190 amp hour battery bank I could run that for hours. 900 watts/ 120 = 7.5amps. So 190 /7.5 = a hella long time. I only had my heater working for 15 min and then a low battery voltage shut it down. 

I had 2 fully charged 6volt batteries in series so 12v and I am so confused why it wouldn’t run much longer. So it went from 12.9 down fast to 11.5 volts. Then when there was no load it went back to 12.1 volts 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    edited September 2019 #2
    960w@12v = ~80a, a significant load.  On a 190ah bank, that's almost C/2, so dead batteries in a couple of hours or less.  1amp at 120v = 10a at 12v (plus inverter and wire losses).

    You shouldn't regularly take the bank below ~50%.  190ah x 12v = 2280 watt-hours, so discharging to 50% would mean running the heater for an hour or so.  Deep cycle battery ah ratings are normally a 20hr rate of discharge.  At a 2hr rate, the effective capacity will be less than at 20hr.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    Also, a 3000w inverter is pretty big for a 12v system.  Many take a significant amount of power just staying "lit" or with small loads, so you may want to consider keeping it turned off unless needed for a (brief) large load.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #4
    And batteries are very easily damaged by over discharging, setting discharged for days/weeks/months at time (say less than 75% state of charge), and under charging...

    So, make sure you follow the battery mfg's charging instructions and get them back full so they don't  get damaged.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Newworldorder
    Newworldorder Registered Users Posts: 2 ✭
    #5
    Ok awesome, so it would not be 960/120. Since I have a 12v battery bank it would be 960/12? Ok 

    so I am planning on getting a tv so if that watts used to power it is 29 watts then 29/12=2.41 amp hours. 

    Thank u guys for your help eh. I very much appreciate it 
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  • 706jim
    706jim Solar Expert Posts: 520 ✭✭✭✭
    #6
    Run the TV. Forget the oil heater.
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,109 ✭✭✭✭✭
    #7
    And get an appropriately sized inverter for your new load profile.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #8
    Realistically, an inverter of a few hundred Watts is "appropriate" for the size battery bank you have... Just to give you an idea of the math:
    • 190 AH * 12 volts = 2,280 Watt*Hours of storage
    • Say 5 hours a night, for 2 nights (assuming bad weather and no solar charging), and 50% battery discharge (for longer life):
    • 2,280 WH * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 484.5 Watt average load
    Here is a nice 300 Watt TSW AC inverter @ 12 volts with search mode and remote on/off:

    https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html

    And don't forget your solar harvest. Note the following assumes the solar panels are mounted flat to your roof and your are up towards Edmonton Alberta... If you tilt the array (especially in the winter), you will get a better harvest--Likewise if your camping/traveling is more to the south:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Edmonton
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:

    JanFebMarAprMayJun
    0.79
         		1.70
         		3.15
         		4.56
         		5.32
         		5.66
     
    JulAugSepOctNovDec
    5.56
         		4.76
         		3.14
         		1.85
         		0.99
         		0.48
     

    More or less, less than 3 hours of sun per day (long term monthly averages), you probably need a generator to keep up (winter camping). For example, say March through September for dry camping:
    • 400 Watt array * 0.52 off grid system eff * 3.14 hours of sun per day ( Sept) = 653 Watt*Hours of average AC power today.
    And there is calculating the size of solar array for your battery bank... More or less, 5% rate of charge for weekend/summer usage. 10% - 13% to 20% for full time off grid usage of your battery bank. Many times, folks with RVs are limited by roof space (make sure there is nothing casting shadows across the panels from ~9 am to 3pm at least--Any shading dramatically reduces your solar harvest). A typical 10% nominal array would be:
    • 190 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 355 Watt array mominal
    So your 400 Watt solar array is a nice fit for your present battery bank.

    Of course, your personal power needs, when and where, any AC shore/genset charging, etc. will need to be taken into account. The above is just a stake in the ground for discussion.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #9
    Newworldorder said:
    Ok awesome, so it would not be 960/120. Since I have a 12v battery bank it would be 960/12? Ok 

    so I am planning on getting a tv so if that watts used to power it is 29 watts then 29/12=2.41 amp hours. 

    Thank u guys for your help eh. I very much appreciate it 
    Just to clarify the terms, amps is a rate of current flow, like miles per hour.  Amp-hours is a quantity of current, like miles travelled.  For the TV,  29w would be a rate of 2.41a@12v.  The quantity would be 2.41 x hours used, eg watching for 3hrs would be ~7.5 amp-hours.

    Note that this isn't including the power used to run the inverter.  They may have peak efficiency of ~85%, but can be much lower, especially running small loads on big inverters.  The big inverter might take more than the TV just being on.  If left on 24x7, it might use (eg) 30w x 24 = 720 watt-hours ÷ 12v = 60 amp hours.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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