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Author Topic: Wiring similar batteries in series.  (Read 2284 times)

justboatonic

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Wiring similar batteries in series.
« on: August 29, 2011, 02:07:40 PM »

I have two 12v SLA's each rated at 4amp. From these, I want to a motor at 12v and a foggy mk2on a 24v supply.

I've read that wiring batteries in series could result in a situation which could cause problems between the two batteries. In reality, how likely is this though?

I mean people run batteries in series in lots of situations dont they without problems? Transmitters are an obvious example where you have 8 batteries in series and yet there's no problem. OK, the amps may be small in comparison but I've never seen an issue in over 25 years modeling. I could buy a convertor but seeing as I've got the 2 batteries, would rather use them first (tight wad I know!).

So, would I be ok to wire the two SLA's in series for a 24v supply and a single 12v supply off one of the batteries? Or am I going to blow my latest build to bits!?  <:(
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Shipmate60

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Re: Wiring similar batteries in series.
« Reply #1 on: August 29, 2011, 02:12:17 PM »

The simple answer is yes you can wire the batteries in series.
The safest way is to wire them in parallel first to equalise the charge then wire in series.

Bob
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justboatonic

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Re: Wiring similar batteries in series.
« Reply #2 on: August 29, 2011, 02:31:00 PM »

The simple answer is yes you can wire the batteries in series.
The safest way is to wire them in parallel first to equalise the charge then wire in series.

Bob

Thanks Bob.

So in reality how would you wire them in parallel and then in series to a separate 12v supply and a 24v supply? I can only envisage a separate parallel circuit and a separate series circuit. Sounds complicated  {:-{
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HS93 (RIP)

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Re: Wiring similar batteries in series.
« Reply #3 on: August 29, 2011, 02:34:46 PM »


this is what is needed

http://www.action-electronics.co.uk/pat.php


P103 PARALLEL POWER BOARD

pETER
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Shipmate60

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Re: Wiring similar batteries in series.
« Reply #4 on: August 29, 2011, 02:54:26 PM »

After leaving a while to cool down after charging just connect the positive to positive, negative to negative for about 10 mins then put in model and connect in series.

Bob
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justboatonic

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Re: Wiring similar batteries in series.
« Reply #5 on: August 29, 2011, 02:57:41 PM »

this is what is needed

http://www.action-electronics.co.uk/pat.php


P103 PARALLEL POWER BOARD

pETER

Nah, Peter. I need to get 24v out of the two 12v SLA's not increase amps. But thanks.
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justboatonic

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Re: Wiring similar batteries in series.
« Reply #6 on: August 29, 2011, 03:00:30 PM »

After leaving a while to cool down after charging just connect the positive to positive, negative to negative for about 10 mins then put in model and connect in series.

Bob

OK. Sounds simple enough. Why the cool down period though? I normally charge overnight (out of the boat) and dont connect up straight away so this wouldnt be a problem.)
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malcolmfrary

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Re: Wiring similar batteries in series.
« Reply #7 on: August 29, 2011, 03:09:53 PM »

There are two bits of trickyness.
Wiring two in parallel will equalize them provided no diodes are involved.  An easily measurable difference will result in a large current circulating until they have equalised, which SLAs do not like.  They are two sets of plates very close together.  With too much current heat is generated, but is not evenly distributed and so warps the plates.  in itself this is not good, if the warping gets too far, the plates contact thus shorting the cell.  The result of that can be very messy, what with spraying the surroundings with sulphuric acid.
Wiring two in series is not a problem.  Using a centre tap to provide an intermediate voltage can lead to problems.  The 0-12 volt battery carries both loads, the 12-24 volt one just the one load, so the 0-12 volt one discharges deeper in a given length of time.  If they are both charged together, you get to where one, having a deeper discharge, requires a larger charge and doesn't get it, the other gets overcharged.
Best to disconnect them and charge separately.  The charger is probably designed for a single battery anyway.  The inverter option does make life a lot simpler.
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john s 2

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Re: Wiring similar batteries in series.
« Reply #8 on: August 29, 2011, 07:54:45 PM »

If you need 24v. then i would buy a step up inverter about 12 from MMB  Please see other post on smoke makers. John.
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justboatonic

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Re: Wiring similar batteries in series.
« Reply #9 on: August 29, 2011, 11:24:18 PM »

Hmmmm. Thanks all for the comments.

Sounds like a convertor may be the simplest option.

Can I use the convertor to output 24v from a 12v SLA while still using the same SLA to also provide 12v for the motor? The SLA is 4 amps.

(The simplest solution would be to retain the two 12v SLA's, hook the convertor up to one SLA to output 24v and just hook the other SLA up to the esc but then Im adding more weight to the boat!)
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ACTion

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Re: Wiring similar batteries in series.
« Reply #10 on: August 30, 2011, 09:19:14 AM »

David
You really need to even the load between the two batteries, so connect them in parallel (via a P103, ideally). This will give you a nominal 8AH capacity @12v to power both the ESC and the DC/DC converter.
Dave M
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justboatonic

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Re: Wiring similar batteries in series.
« Reply #11 on: August 30, 2011, 12:02:33 PM »

David
You really need to even the load between the two batteries, so connect them in parallel (via a P103, ideally). This will give you a nominal 8AH capacity @12v to power both the ESC and the DC/DC converter.
Dave M

Thanks Dave.

This lectricery does me head in!  >>:-(
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