use 36V charger for 2 (or3?) 12V batteries?

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visfor
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Joined: 07/18/2007
Points: 15

Hello,
i have a 36 V 12 Ah battery and charger for a pedelec which is made of 3 12V lead batteries.
i want to use it for drive a pedelec which use a 24v 10Ah battery NiMH.
so my idea is to disconnect one of the 12 V battery and so :
1. if 3 similar batteries made a 36V 12Ah battery then 2 of them connected in serial make a 24V 12Ah? or am i wrong with the 12Ah?
2. if it is so, then i could drive the pedelec using 24V 10Ah NiMH with my new lead battery 24V 12Ah without problem?
3.can i then use the 36V charger to load the 24 V battery? how should i do that? or shall i buy a new charger? can you give me an example of a charger for me? actually i evn have 2 lead batteries of 36 V 12 Ah, so in total i have 6 time a 12V battery. if i drive with 2 batteries, then again the next 2 batteries and again the last 2 batteries: at the end i have 6 batteries that i want reload: if i take 3 of them (2 will have the same loading status having been used together and the third could have a non similar load status because having been used with another 12V battery): so what happens if i put the 3 together through the 36V charger?
thank you
visfor

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echuckj5
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Joined: 11/29/2006
Points: 394
Re: use 36V charger for 2 (or3?) 12V batteries?

Hello visfor,

Question 1. You are correct, you would have a 24 volt 12 amp battery pack.

Question 2. You are going to have some problems, but, they can be solved, not by me. The voltage of the 2 packs would have to be measured accurately and would have to be very close to each other in voltage. The 24 volt nimh pack would need to be paralleled with the 24 volt lead acid pack. The 2 packs, if the voltage is not the same, will spark when you connect them in parallel. There is a way to use diodes, to help separate the packs, some one else will have to answer that. The packs will have to be charged disconnected from each other, but again, there is a way to use diodes to prevent this, I think.

Question 3. NO! The 36 volt charger can only be used to charge a 36 volt series string of lead batteries. Again, all three lead batteries need to be very close in voltage to charge in series, this would be very hard to accomplish. The nimh pack should only use a charger made for nimh batteries of 24 volts.

Hope this helps, I don't know a good source of nimh chargers, others here can fill you in on running the packs in parallel and where to get chargers. Electronics is my weak subject.

chuck

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reikiman
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Joined: 11/19/2006
Points: 8456
Re: use 36V charger for 2 (or3?) 12V batteries?

batteryspace.com and all-battery.com both sell NiMH chargers (and packs)

Another consideration is the voltage changes differ in the chemistries as the pack discharges. I believe NiMH batteries stay at a more constant voltage until fully discharged while lead-acid has a gradually declining voltage. This will then make the NiMH side of the pack work harder to charge the lead-acid side of the pack, and the consequences might not be good.

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echuckj5
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Points: 394
Re: use 36V charger for 2 (or3?) 12V batteries?

Yea,

A lot of problems running two different type of batteries in parallel.

Solution, use a switch, or plugs, run one pack at a time. This would be a lot easier.

chuck

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visfor
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Joined: 07/18/2007
Points: 15
Re: use 36V charger for 2 (or3?) 12V batteries?

thank you very much for your inputs, it helps.

so now i know:

- i have 2 36v 12 Ah lead batteries and their charger.(from old pedelec)
- if i buy a new pedelec running 24v 10Ah NimH battery and if this 24V 10 Ah NiMH battery doesnt work well, then i could do following:
- open the 36V lead battery, take 2 of the 3 12V Batteries that are inside, put trhem in serial and so i will have a 24V 12Ah lead batterie that i could use on the new pedelec. I will not put this battery in parallel with the NiMH battery,it is not my intention, i will just replace it.so the new pedelec should work well with this. and to recharge the 24V 12Ah lead battery i will have to buy a charger for it. for about 25 dollars i should find a charger for this 24V 12Ah lead battery. the 36 v charger cannnot help here.
thanx again
visfor

Alphi
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Joined: 10/21/2007
Points: 37
Re: use 36V charger for 2 (or3?) 12V batteries?

universal smart chargers for remote controlled (RC) packs are cheap and reliable.. they are also small enough so that you can integrate them into your pack design..

if you bought 2 of them and split your pack into 12 volt blocks you could recharge it in 5 hours.

they cost about $17-25 USD each so cheap.

as for mixing your batteries.. don't do it..

a 10AH nimh pack will run out quicker than a 12AH sla pack..

once your nimh pack is exhausted the SLA batteries will force current through the depleted cells.. if you do this too much they will reverse in polarity and basically die.. no way to recover from that unless you have some really expensive gear to recondition them.. and even then reconditioning only works a small percentage of the time.

what I would do as has already been suggested is just unplug one pack and plug in the other when it goes flat.

once the SLA pack wears out go get another 10AH nimh pack and then you can hook them in parallel without too many dramas. and with far less weight on your ev.

I would even go further to suggest to make your Nimh Pack portable. embed the chargers in the pack and then you cant unplug it and charge it anywhere (like in the office, or at friends houses for example) this will give you added range..

most people design their evs with enough range for a round trip.. when in most cases they could get away with half as much capacity if they battery pack was detachable and could be plugged in anywhere.

my 2c

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