Hello,

I have a solar panel that came with a 12v charge controller. It says I cannot charge a 6v battery with it. My project requires 6v. If I buy two 6v batteries and put them in series, but take power off of only one (see the schematic below) will this work?

 

No, it will not.

If the batteries are in series, then whatever charging current flows in one will flow in the other. The result is that as you replace charge in the battery being loaded, you will be overcharging the other battery.

Get a DC-DC converter to step the 12 V down to your 6 V.

 

No, it will not.

If the batteries are in series, then whatever charging current flows in one will flow in the other. The result is that as you replace charge in the battery being loaded, you will be overcharging the other battery.

Get a DC-DC converter to step the 12 V down to your 6 V.

I should then put a buck converter after the controller?

 

I should then put a buck converter after the controller?

Yes, which is the same thing as putting it across your 12V battery pack.

 

I should then put a buck converter after the controller?

That might work, but I would actually recommend using a 12 V battery that is compatible with the charge controller and then use a buck converter to power your 6 V load from the 12 V battery. That way you are using the charge controller the way that it was designed for. The exception that comes to mind would be if your load involves short-duration, high-current draws that you need a battery to source the surge currents so that you don't have to have an oversized converter.

 

A 7807 regulator should work fine.

+12-----------------------7807-----------------6VBAT-----------------(-)

 

A 7807 regulator should work fine.

+12-----------------------7807-----------------6VBAT-----------------(-)

But be sure that the battery chemistry you use can tolerate being held at 7 V. My understanding is that the gassing voltage for SLA batteries is 7.1 V. That means that your regulator can't be over by more than 1.4%. I'm not aware of any of the 78xx line of regulators that are that tight (the best I know of is 1.5%, which might be good enough, but you would need to look at the datasheet carefully to see if that tolerance is over the entire temperature range).

 

A 7807 regulator should work fine.

+12-----------------------7807-----------------6VBAT-----------------(-)

No. Use a switching power supply in solar and battery projects. A linear regulator will burn half the power.

 

No. Use a switching power supply in solar and battery projects. A linear regulator will burn half the power.

Very good point. It might not matter in a given application in which the available power (energy) is well over twice what is needed, so other considerations such as size and cost might dictate. But, all else being equal, use a switcher.

 

If your solar panel is plenty big enough for the project, connect it straight to the 6V battery. It won't work very efficiently, but it will work, and if you have an excess of solar power it won't matter.
You then need some sort of regulator to prevent the battery from overcharge.