question

hynter avatar image
hynter asked

load before batteries?

I don't have enough batteries.

I have 8 X 24v/8AH batteries connected parallel.

I have 2 x 24v/270W solar panels.

I have a 500-600w load

Without the load, the batteries charge to full within an hour or two.

Presently, AC load is plugged into inverter which is connected to battery bank. Victron charge controller is connected directly to battery bank.

To my mind, it seems like the charge controller charges the batteries and the inverter has to pull current out of the batteries....

When I connect the AC load, even during daytime sunlight, the batteries slowly drain. I'm thinking that the loss of power converting it to storage and immediately back out to power is big enough to be a concern, in addition to additional wear & tear on the batteries.


Would it help to wire the charge controller directly to inverter, thus sending current to inverter, letting "leftover" current go to the battery, and THEN allowing the load to pull from battery?

battery charging
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klim8skeptic avatar image klim8skeptic ♦ commented ·

"To my mind, it seems like the charge controller charges the batteries and the inverter has to pull current out of the batteries...."

That is the way it works, You can only pull out what you have put in.

Also batteries/inverters/panels/chargers are not 100% efficient, you have to add the losses up.


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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

You have 540Wp(watt peak) PV power under perfect conditions) PV power so under real conditions you maybe have 450W and than you have 500-600W of loads.

So you have more load than charge -> batteries get discharged.

Even under perfect conditions your PV-power barely cover your loads.

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hynter avatar image
hynter answered ·

@M.Lange

Thank you for replying.

>You have 540Wp(watt peak) PV power under perfect conditions) PV power


This is what has me most confused. I thought that (roughly) 1 watt at 24 volts was 2 watts at 12 volts. I expected to have far less than peak, but I expected to have an equivalent of (2 x 270 x 2) = 1080 watts peak. Is this not "how it works"?

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wkirby avatar image wkirby ♦♦ commented ·

Power is the constant. Power (W) = Vols (V) x Amps (A)
So, 240W of solar power connected via an MPPT controller will provide a battery charge current of 20A @ 12V or 10A @ 24V - assuming no losses.

If yo have two 270W panels then you have 540W no matter what your battery Voltage is.

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