# Solar Battery Tenders?

Registered Users Posts: 11
edited October 2015 #1
Hello, im new to Solar
I have an RV deep cycle battery that the gas leak detector is constantly drawing power, my one little solar tender cant keep up. I have another so can i just hook both solar tenders to it without battery damage?

• Registered Users Posts: 11
Can nobody answer this? Is this a solar forum or what?
Sorry--Sometimes we miss a question.

Anyway, do you know how much current @ 12 volts your leak detector takes? This one here take 75 mAmp (0.075 amps).

http://www.campingworld.com/shopping/item/classic-lp-gas-alarm-flush-mount-tan/56358

Your solar battery tender--We need more information. In general, 1% or less rate of charge (100 AH battery bank, 1 amp rate of charge or less), you do not have to have a battery charge controller.

When you get over that, you should have a battery charge controller to prevent overcharging the battery bank.

A typical solar tender may be ~6 Watts. If you mount it behind the windshield of a car/RV, you probably get 1/2 that...

For a 75 mAmp load and a solar charge controller, assuming ~2 hours of sun minimum (more towards winter, behind window--Guessing):
• 0.075 amps * 24 hours per day * 1/0.52 typical system eff * 1/2 hours of sun = ~1.7 Watt solar panel "break even" in winter/poor sun/behind window (guessing)
So--How much current does your LP leak detector take (do you want to turn it off when in storage?)?. How big is your battery bank (XYZ Amp*Hours @ 12 volts)? How many Watts is your solar tender? Does it have a charge controller?

As Lead Acid batteries age, they self discharge faster. If you have older batteries, they can discharge upwards of 1% (new batteries may be 0.1% or less).

A typical battery tenders solar panel tends to be small, and may not always work at at rated output (hot panel, behind window, etc.).

Do you have solar panels+solar charge controller for dry camping?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 11
Thanx for answering. I would imagine our leak detector is comparable to the one you showed. It cannot be shut off. We just have the one solar tender (it has overcharge protection) and not sure what its pushing (i think about 3 watts). My battery is about 96 AH @ 12v. No charge controller. Can i hook additional solar tenders to get more watts to that leak detector? I cant imagine adding more hurting the battery. Solars will be placed on roof of RV.
• Solar Expert Posts: 3,123 ✭✭✭✭
edited October 2015 #5
You can add more battery tenders without out too much worry as long as the one you start with has overcharge protection and  the total wattage is less than 15 watts.
SMA SB 3000, old BP panels.
• Registered Users Posts: 11

Sweet!!  May I ask how you come up with 15 watt cutoff?

Thanks guys

My guess... Typical RV battery is 80-100 AH, 1% max rate of charge if you do not have a charge controller--100 AH * 1% = 1 amp maximum.

Typical Tender panels have Vmp~15 volts... 15 Volts Vmp * 1 amp = 15 Watts

That be my thinking.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,123 ✭✭✭✭
edited October 2015 #8
BB. said:
My guess... Typical RV battery is 80-100 AH, 1% max rate of charge if you do not have a charge controller--100 AH * 1% = 1 amp maximum.

Typical Tender panels have Vmp~15 volts... 15 Volts Vmp * 1 amp = 15 Watts

That be my thinking.

-Bill
That was mine too. Except I went more conservative and thought that 12W would be OK and the existing 3W has a high voltage cutoff (presumably around Float voltage)
SMA SB 3000, old BP panels.
• Registered Users Posts: 11
Man, there is a high learning curve with this stuff.
Now you see why it takes some time to formulate a response--That first response usually includes a 1/2 dozen questions about your installation and intended usage.

Sorry for your first time frustration.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 11
yup, sorry for being impatient.
• Registered Users Posts: 11
what is Vmp?
• Solar Expert Posts: 3,741 ✭✭✭✭
serius said:
what is Vmp?
The voltage at which a solar panel is capable of producing the most power.  It is usually about 20% lower than the Voc (open circuit voltage) of the panel.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Registered Users Posts: 11
thanx