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### Topic: Series charging batteries? (Read 507 times)previous topic - next topic

#### WaitSome

##### Jun 23, 2019, 05:59 pm
Hi, I a making a data capture device with a Nano. The data capture sensor is 5vdc at tiny tiny mA, my meter does not even show current drain. I would like to battery power this but space is limited but I can fit 6 x AA batteries in nooks and crannies then wire them all in series.

I would then use a small buck converter to provide the 5vdc from the batteries. I'd like to use Li-Ion, but then I think I need a balance-charger and there's no room for that. So, Ni-Mh is the next choice.

Finally the question: If I solder the Ni-Mh batteries in series, can I just charge them at 9v x 100mA or whatever is needed?

Thanks

#### Grumpy_Mike

#1
##### Jun 23, 2019, 07:28 pm
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I can fit 6 x AA batteries in nooks and crannies then wire them all in series.
I would recommend using just 3 in series and running the system at just under 5V.

Quote
If I solder the Ni-Mh batteries in series, can I just charge them at 9v x 100mA or whatever is needed?
If these batteries are identical in condition, age, manufacture and charge you can.

#### PerryBebbington

#2
##### Jun 23, 2019, 07:32 pmLast Edit: Jun 23, 2019, 07:33 pm by PerryBebbington
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Finally the question: If I solder the Ni-Mh batteries in series, can I just charge them at 9v x 100mA or whatever is needed?
Yes, but give the current drain you say you need to supply you can charge at a lot less that 100mA.

You don't need 6 of them, Ni-Mh give about 1.2V, 4 in series give 4.8V, that will probably be OK connected directly to the 5V input pin. You say your circuit draws so little current you can't measure it, that being the case maybe charge at 5mA, which means from 9V you need 9 - 4.8 - 4.2V. 4.2V / 0.005 = 840ohms. I would think 1k ohms from about 9V would be fine. You could use a lower voltage and lower value resistor.

EDIT
Mike, you beat me to it. Question, I think Ni-Mh are 1.2V each, your reply suggests they are 1.5V each. Are you sure?

#### slipstick

#3
##### Jun 23, 2019, 08:19 pm
NiMH cells are 1.2V nominal. Fully charged 4 in series will typically show around 5.4V which should be o.k. for an Arduino.

Steve

#### Grumpy_Mike

#4
##### Jun 23, 2019, 08:54 pm
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No the question was two part. The first comment was about using 3 AA batteries not 6 of them and a regulator as indicated by the quote before the reply.

#### DrAzzy

#5
##### Jun 24, 2019, 04:25 amLast Edit: Jun 24, 2019, 04:27 am by DrAzzy
Yeah, you do NOT want the regulator in there - the quiescent current of most buck regulators will be more than the circuit you're powering. Generally for very low power devices running on battery, switch mode converters are no good, run with no regulator if you possibly can (as even a normal regulator has non-zero quiescent current used to power the regulator itself, which may still dominate power consumption, and the dropout dictates using more batteries in series). That's one of the advantages to running with "3.3v" board powered directly from a 1S LiPo...

Remember to remove the regulator and power LED from the nano. They will dominate power consumption otherwise.

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#### PerryBebbington

#6
##### Jun 24, 2019, 11:19 am

Quote
No the question was two part. The first comment was about using 3 AA batteries not 6 of them and a regulator as indicated by the quote before the reply.

#### WaitSome

#7
##### Jun 24, 2019, 04:12 pm
Thanks everyone, I was opting for the 6-AA and higher voltage for longer use life if I don't have time to get to the thing every few days to recharge it. In fact this morning I was looking at it and think I can squeeze in two more AA.

@grumpyMike: Should I stay with 6-AA and instead wire parallel and series for the 4.8v? As to charging, all the batteries are new Amazon Basics Ni-Mh.

Is there a LiPo battery solution that would be better? I am only discounting the Li-Po as I have not found a small enough balance charger to include in the enclosure. I'd like to keep it to single pair of wires connection for the charging. I have already included one of these into the case.

https://www.amazon.com/ThreeBulls-Pieces-5-5mmx2-1mm-Female-Connector/dp/B01N8VV78D

#### Grumpy_Mike

#8
##### Jun 24, 2019, 04:28 pmLast Edit: Jun 24, 2019, 04:29 pm by Grumpy_Mike
Six batteries in series will not last any longer than three batteries in series it is the current drain that matters.

Wiring batteries in parallel will in theory double the time you can draw a specific current but it is also a problem with cross charging. If the batteries are identical some people claim you can do this but I would not. If you must do it then connect them together with diodes.

Anyway you can't charge them when wired in parallel if you go down the rechargeable route.

#### WaitSome

#9
##### Jun 24, 2019, 10:54 pm
OK, thanks Mike. Clearly I am a little out of my depth with all this. I will look at using a 5v Li-Ion power bank. I can pull it apart to move the batteries to where I can squeeze them in, instead of the 6 x AA.

I am guessing they have some form of self contained batteries inside that I can move and extend the wires.

#### Grumpy_Mike

#10
##### Jun 25, 2019, 01:40 am
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I am guessing they have some form of self contained batteries inside that I can move and extend the wires.
Yes but often these are metal strips spot welded to the battery. If you try and solder wires directly on the battery one of two things will happen.
1) you can't supply enough heat with your iron to melt the solder as it all gets sucked into the battery.

2) you can supply enough heat and the battery explodes.

Try a non soldering way of extending the wires, like drilling a hole in the strips and attaching a solder tag with a nut and bolt. Solder the tag and wire before attaching the nut and bolt.

#### WaitSome

#11
##### Jun 25, 2019, 05:32 pm
Try a non soldering way of extending the wires
OK, thanks, great thinking there. That will save me from some unneeded excitement.

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