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Two batteries in series, can I connect a load to only one?

I have two 12 volt batteries connected in series in order to supply a motor that requires 24 volts. But I also have a strip of 12 volt LEDS that I would like to power. What I want to know is if it is possible to connect the strip to the terminals of one battery even though the two batteries are connected in series? I realize the easier way to do this is to step down the voltage, but please answer my question.

All comments are genuinely appreciated

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Yes you can do what is called center tap and have one or two 12 volt outputs and a 24 volt output like in this diagram.

12_24V.bmp

Yes. You can do this. If you've got all that junk (the two 12-volt batteries, the 24-volt motor, the 12-volt LED strip), then you can confirm for yourself that this works.

In fact you didn't really need to ask the Instructables Answers forum for permission first, to confirm whether or not some physical thing is physically possible, but maybe you are here looking for deeper answers. Like maybe you already know it works for a few seconds, but you are wondering what is the longer time impact on the batteries?

The two batteries, in series, can supply 24 volts to the motor, and simultaneously one of the batteries (you choose which one) can supply 12 volts to a single LED strip.

The only reason such a setup is distasteful, is because one of the batteries is supplying more current than the other, and thus one of the batteries is supplying more power than the other, and thus the batteries do not discharge at the same rate.

If you understand Kirchhoff's circuit laws, you can draw a diagram of your circuit, and discover which battery draws more current, and also how much. Upon request, I'll draw you a picture of this circuit, as I imagine it, and label the current through each branch, the voltage of each node, blah, blah, blah. Well, I mean it's easy if you know how to do it. But if you don't, then maybe seeing someone else draw a picture of it would actually be helpful to you.

Anyway, the uneven loading, the fact that one battery draws more current than the other, this only is a really problem when it comes time to recharge the batteries. Essentially, when it comes time to recharge the batteries, each battery should be treated as a single 12-volt battery, and each has a different level of discharge; i.e requires a different amount of energy to be replaced.

In contrast, if the two 12-volt batteries always shared the same current, then all the cells, from both batteries, could be assumed to be in the same state of discharge, and you basically can treat it (i.e. two 12-volt batteries in series) as a single 24-volt battery when it came time to recharge it, you know, charge it with your 24-volt battery charger, if you've got one of those.

If I could , I would flag your answer as exemplary but they don't provide that option.

You must be content to file this comment with all your other impeccable verbage :-)

seandogue1 year ago

You **can** but I wouldn't advise it, becuase it will imbalance the batteries. If you need the lower voltage, it's better to use a regulator on the output of the combined battery pack.

Wired_Mist1 year ago

+1 to Iceng and Downunder,

Yes you can, it's far from Ideal though

I'd buy some 24V Led strips ! Nice and cheep off Ebay

The 12V drain (Especially with a high Amp requirement) will mess with your batteries, and drain one faster. This will also make Charging/Balancing your battery system a Royal Nightmare !

If you insist on using 12V, Then go with Iceng's Answer.

iceng1 year ago

But if you have two 12v strips put one on each of the batteries to even out the loading.

It is possible but not ideal.
One battery will be drained at a different rate than the other, which in return also decreases performance for the motor.
If you don't use these "dimmers" for the strip you can simply add a suitable resistor in series for the 24V or even better use a voltage regulator and still use the dimmer.