new to solar power

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Pete
Pete Registered Users Posts: 8 ✭
in Solar Beginners Corner #1
Hi all--- I am trying to charge a 35ah battery, the type that goes on the the electric carts you see in grocery stores and such. I tried using a 5 watt solar panel I purchased from Harbor Frieght, but does not seem to charge the battery. What size solar panel should I use to charge this battery.

Thanks,
Pete.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: new to solar power

    Welcome to the forum.

    It would help if you knew the battery manufacturer's recommended charging procedure. This is probably a sealed AGM or gel type battery.

    A 5 Watt panel produces less than 0.5 Amps of current. As a rule, a 35 Amp hour 12 Volt battery would 'like' about 3.5 Amps maximum current. That's going to require more like 55 Watts of panel: http://www.solar-electric.com/so55wamusomo.html

    It will also require a charge controller like this: http://www.solar-electric.com/sg-4.html
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
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    Re: new to solar power

    Cariboocoot is right. That 5 watt panel would do little more than offset the normal self-discharge of the battery.

    By the way, if the battery is left uncharged for too long, it will ruin the battery. It should be fully recharged as soon as possible.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #4
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    Re: new to solar power

    If it is indeed from a cart, often they are 24 volt, so let us know the voltage as well.
    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.
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #5
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    Re: new to solar power

    Sorry about that----Its a 12v-35ah battery, sealed AGM -- I bought it from Interstate battery, asked them if if a 5 watt panel would charge it and of course they said yes....

    Im only trying to run some lights at my camp in Maine, 8 -15 watt flourescent bulbs, with a 400 watt ac inverter.... This battery should be plenty for that-correct??
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
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    Re: new to solar power
    Pete wrote: »
    Sorry about that----Its a 12v-35ah battery, sealed AGM -- I bought it from Interstate battery, asked them if if a 5 watt panel would charge it and of course they said yes....

    Im only trying to run some lights at my camp in Maine, 8 -15 watt flourescent bulbs, with a 400 watt ac inverter.... This battery should be plenty for that-correct??

    Eight 15 watt bulbs is 120 watts which is 1 amp at 120 volts. That 1 amp at 120 volts will draw 10 amps at 12 volts (assuming the inverter is 100% efficient, which it isn't). Your battery has a total capacity of 35 amphours. If you draw more that half of that you will quickly kill the battery... so you have about 17 ah of useable capacity. Drawing 10 amps (at 12 volts) for 1.7 hours is about the limit.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #7
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    Re: new to solar power

    Thanks--- So I should probably switch over to the LED type bulbs, which draw half of the wattage
    Can I ask you what the formulas were for those calculations?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: new to solar power
    Pete wrote: »
    Thanks--- So I should probably switch over to the LED type bulbs, which draw half of the wattage
    Can I ask you what the formulas were for those calculations?

    Pretty much straight-forward math:
    8 * 15 Watts = 120 Watts. 120 Watts / 120 Volts = 1 Amp. 120 Watts / 12 Volts = 10 Amps.
    35 Amp hour battery @ 50% depth of discharge is: 35 / 2 = 17.5 Amp hours. 17.5 Amp hours / 10 Amps = 1.7 hours running time.
    (This is not 100% precise, but close enough to demonstrate the problem.)

    As vtMaps said, that does not include DC to AC conversion efficiency (usually around 90%) nor the consumption of the inverter itself. If you were using a good inverter like the Morningstar 300 that would add 10% on to the Watts consumed for the conversion and an addition 6 Watts to power the inverter. So the 120 Watts becomes 138, and the battery life gets even shorter.
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #9
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    Re: new to solar power

    Thank you all for your help....
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #10
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    Re: new to solar power

    One more question---If I purcahse a 100 watt panel and connect it to the proper charge controller will this speed up the charging, and I assume the charge controller protects the battery from the higher amperage output--you mentioned this battery likes about 3.5A maximum current.

    Thanks again....
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #11
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    Re: new to solar power
    Pete wrote: »
    One more question---If I purcahse a 100 watt panel and connect it to the proper charge controller will this speed up the charging, and I assume the charge controller protects the battery from the higher amperage output--you mentioned this battery likes about 3.5A maximum current.

    Yes, the purpose of the controller is to protect the battery from overcharge. But very few of the inexpensive controllers allow you to restrict the current (3.5 amps) during bulk stage charging. You could use an AGM battery... they can handle higher charge rates.

    Perhaps you should just consider a larger battery for that 100 watt panel... it sounds like you need more battery capacity anyway (in terms of your load).

    One more thing... perhaps you should consider 12 volt lighting. That would eliminate the need for the inverter and its losses.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #12
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    Re: new to solar power

    The battery I have is I believe an AGM type, it's this one-- http://www.activeforever.com/p-27197-upg-ub12350-sla-12v-35ah-group-u1-battery.aspx?utm_source=froogle&utm_medium=csc&utm_content=A22617&utm_campaign=mobility-aids&gclid=CJufjLTtsrICFaUWMgodUwgAZA

    If I use 3-12 volt 50 watt dc bulbs wouldnt I still be drawing about 12.5 amps and my running time would be around 1.4 hrs with this battery, whereas if I use 3 LED lights which are only 8 watts each even with the losses of the inverter I would still have around 6 hrs of running time... A'm I correct
    Thanks...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
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    Re: new to solar power

    Well a 50 Watt 12 Volt bulb draws roughly 4 Amps so three of them would be 12 Amp draw +/-.
    8 Watts on 120 Volts is only 0.06 Amps so three of them would add up to less than 0.2 Amps on 120, or 2 Amps @ 12 Volts; 1/6th the current. In this case the inverter draw will be the greater amount of power used rather than the actual lighting.

    If I've done the math wrong someone please fix it.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #14
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    Re: new to solar power
    Cariboocoot wrote: »
    Well a 50 Watt 12 Volt bulb draws roughly 4 Amps so three of them would be 12 Amp draw +/-.
    8 Watts on 120 Volts is only 0.06 Amps so three of them would add up to less than 0.2 Amps, or 1/60th of the load. In this case the inverter draw will be the greater amount of power used rather than the actual lighting.

    If I've done the math wrong someone please fix it.

    Aren't you comparing amps at 120V with amps at 12V to get that 1/60? I think you should be comparing Watts to Watts, which is 24 vs 150, or 0.16 the load for 120V LEDs compared to 12V incandescents, ignoring inverter efficiency.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: new to solar power
    ggunn wrote: »
    Aren't you comparing amps at 120V with amps at 12V to get that 1/60? I think you should be comparing Watts to Watts, which is 24 vs 150, or 0.16 the load for 120V LEDs compared to 12V incandescents, ignoring inverter efficiency.

    That's exactly what I meant by "please fix it". I could sense there was something wrong.
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #16
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    Re: new to solar power

    Ok so bottom line is I'm better off with the LED lights---correct?----and the AGM battery can handle the possible higher charge rate with the 100 watt panel.

    Thanks
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #17
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    Re: new to solar power
    Pete wrote: »
    Ok so bottom line is I'm better off with the LED lights---correct?

    Generally fluorescent lights give you a bit more lumens per watt. (Best florescent - 100 L/W, best LED's - 94 L/W.) LED lights are better if you need small task lights, something that florescent are not good at.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #18
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    Re: new to solar power
    bill von novak wrote: »
    Generally fluorescent lights give you a bit more lumens per watt. (Best florescent - 100 L/W, best LED's - 94 L/W.) LED lights are better if you need small task lights, something that florescent are not good at.

    On the other hand, many LED lights can be dimmed to reduce the power draw when you do not need full light. That is harder with fluorescents unless you have multiple tubes individually switched.
    SMA SB 3000, old BP panels.
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  • Pete
    Pete Registered Users Posts: 8 ✭
    #19
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    Re: new to solar power

    What do you all think of this 100 watt panel..
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