# Double battery chargers

#### Windseaker

Joined May 4, 2016
3
I am help grandson do a project and have attched a layout of what we want to do. I have a question about useing diodes
6V 330mA Outdoor Solar Panel 2w

I am trying to charge two separate batter packs to operate two small motors that is represented by light bulbs. One motor,1st slower and not often.

See this link for my materials,I have double supply.
http://www.reuk.co.uk/Basic-4-AA-Solar-Battery-Charger-Plans.htm

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#### Dodgydave

Joined Jun 22, 2012
10,964
It wont work with capacitors in series.

#### Tonyr1084

Joined Sep 24, 2015
7,454
It appears you have the Photo Voltaic (PV) panels in parallel configuration. When you place power sources in parallel their voltage (assuming both power sources are the same) will remain the same. When you put them in series (the positive of one connected to the negative of the other) then (the two remaining wires - one positive - one negative) will ADD their voltages together. In other words two SIX VOLT PV's in parallel will produce SIX volts, whereas two SIX VOLT PV's in series will produce 12 volts.

The way you have the target batteries (the AA Rechargeables in series) you will need more than 6 volts to charge them. I believe NiCad AA
Rechargeable batteries are 1.2 volts per cell. Each AA battery is a single cell. In series their voltages add together. You show two banks of batteries, one labeled 4 volts and one labeled 6 volts. You show a total of 9 batteries for a total of 10.8 volts. You can't charge 10.8 volts from 6 volts, your panels will need to be in series.

The capacitors? They block DC voltage. Like Dodgydave said, your circuit won't work. I also see a diode in between the two battery packs. The way its shown it will block current from flowing from one pack to the other. I understand the lights represent motors and the dotted lines indicate test leads. That's OK.

In your circuit you show capacitors and a diode - neither of which are needed in what you hope to do. I'll spend some time and bang out a drawing and post it to this thread, so watch for an edit.

Hope I can help.

#### Tonyr1084

Joined Sep 24, 2015
7,454
OK, I've drawn up something you might find useful. And I'm not certain of exactly how it will function but here it is:

PV1 & PV 2 are your PhotoVoltaic's (solar panels). BP1 & BP2 are your battery packs, consisting of 4 and 5 AA Rechargeable's (that's how you drew it). There are four test points from which you can test voltages (using a DVM (digital volt meter) or a light bulb rated at 12 volts)(or motors like you said).

Between test points 1 and 2 (TP1 & TP2) you should see 4.8 volts. Between TP2 & TP4 you should see 7.2 volts. WHAT? WAIT! 7.2 VOLTS? Yes. Because the PV set is producing 12 volts and BP1 is bucking that, 12 volts minus 4.8 volts will give you 7.2 volts. Even though BP2 is 6 volts it's going to be floating higher than that because of BP1 only bucking 4.8 volts.

Speaking of BP1, you should be seeing 6 volts across that because the PV's are producing 12 volts. Keep in mind this is all "Theory" and I'm not the best at theory. Trust me; any and all my mistakes or mis-statements WILL be corrected by others.

If you isolate (switch off) the PV's then you will have 4.8 volts and 6 volts respectively. Current flow numbers have always given me trouble. Your battery packs have a total of 10.8 volts across them when isolated from the PV's. I don't have LTSpice (circuit simulator) so I can't test out my theories on how this will work. Both you and I are learning. But I hope this helps.

The use of capacitors will do nothing for your circuitry. The use of a diode, when in the proper orientation will do nothing except drop the voltage slightly - depending on it's PN junction. Typical is about 0.7 volts dropped. So the use of a diode shouldn't have much of an effect on the circuit.

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#### Windseaker

Joined May 4, 2016
3
There was talk about exceed batter change draining back and out of the Photo Voltaic panels, is this true?
and what about over charging if circuit sit there?

Thank you

#### Dodgydave

Joined Jun 22, 2012
10,964
Put a shottkey diode in series with the photo cells to stop discharge.

#### Tonyr1084

Joined Sep 24, 2015
7,454
There was talk about exceed batter change draining back and out of the Photo Voltaic panels, is this true?
Honestly, I know next to nothing about PV's. I suppose it could be true. As for any "Overcharging" issues - I don't think that's going to be any concern (but again, I'm not the expert). It will also depend on your battery type. And I know even less about the differences between batteries.

As for using a diode in series - not a bad idea. Certainly won't hurt anything, and it will drop your voltage by about 0.7 volts. So depending on your batteries, the PV's and the sunlight your charge will vary. Just place the diode (arrow pointing from PV1 to TP1) in series with the rest of the circuit (like DodgyDave suggests).