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# Two batteries, one panel

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I asked a few weeks ago about charging two batteries from one solar panel. I’ve now got a solar controller which can do this, see below, but I’m confused by the instruction manual, especially how I should set the “charging priority”. I assumed the unit would charge battery 1 until full, then move on and charge battery 2 until full, then go back to 1. I’m not sure what this charging priority is - image of the relevant page from the manual below. I’d be grateful to hear what you think it means.

Thanks.

James.

Edited by jambouk
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As I see it 2 battery must be the same  to set this like 2 gel as you can only put 1 number in ,   it look for the low battery and send more to the low one I set as 50/50  it spit the solar by 2

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It looks like the default priority of 9 will be like you assumed. If your solar panel delivers 1A for example, then battery 1 will get 900mA and battery 2  will get 100mA. When battery 1 is fully charged battery 2 will then get all the current. If battery 1 starts discharging then it will go back to the priority setting currents again.

It doesn't say what happens to battery 2 when both are fully charged. Hopefully it stops charging like battery 1 does when it is fully charged.

If the normal load on battery 2 is higher than battery 1 then you can lower the priority number so that battery 2 gets a bigger share of the solar panel current.

If you set it to priority 5 they will each get half the solar panel current.

All four of your batteries need to be of the same type. I assume they are from your previous post. Just different capacities. Battery 1 can be your 2 60Ah in parallel and Battery 2 can be your 2 50Ah in parallel. Or vice-versa.

Alan

Edited by symmetal

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Thanks.

I've ditched the two batteries in series idea for the time being, and just going to stick two big batteries in isolation,one connected to each of the outputs of the dual solar charger.

If the two batteries are the same, and the load placed on each is the same, would you set the charging priority to 50:50? I'm still not really sure why the maximum I can send to battery one is 90%, and why I can't send 100% to battery one until its fully charged, then send 100% of power to battery two etc.  Or is it sending 10% to battery two by default to at least put a bit of power into battery two to prevent it from degrading whilst battery one charges up?

James

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In the situation where you had a significant load on both batteries you may end up with battery 1 not reaching full charge and if you had that set to 100% priority then battery 2 would never get charged. 90/10 priority ensures battery 2 would at least get some charge. Once one battery is fully charged the other one gets the 100% charge anyway from the solar panel.

If the load on both batteries is similar then a 50/50 priority may be best to avoid battery 2 not receiving enough charge on dull/short days. If the solar panel puts out enough to comfortably charge both batteries then the priority is not really important.

Alan

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