NiMH & NiCad batteries - Electronic Circuits Projects Diagrams Free

mabauti · 16th November 2007, 01:20 AM

What precautions must I take when connecting (2 1.2VNiMH 1600mAH batteries in series) and (2 1.2VNiCad 600mAH batteries in series) in parallel in order to have 2.4V?

Sceadwian · 16th November 2007, 01:33 AM

Your question is too vague. Under most circumstances 2 3 or 4 cells in series will require no additional precautions as long as the cells are from the same production line at the same time.

With multiple cells in series it's common to be a little understated in it's charging requirements compared to a full cell and to do a low current equalizing charge periodically.

12 volt car batteries are after all in fact 6 2 volt (nominal) Lead acid cells in series.

audioguru · 16th November 2007, 01:50 AM

I think he wants to charge the old small-capacity Nicads from the newer higher capacity Ni-MH battery. That wastes power.

Instead of using 1600mAh plus 600mah= 2200mAh but it will never be reached, buy new 2500mAh AA Ni-MH calls. They just keep on going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and ....

Oznog · 16th November 2007, 02:25 AM

Even if you had 2x IDENTICAL 2.4V 1.6AH NiMH packs, you can't put them in parallel. Neither NiCd nor NiMH can be put in parallel, even though basic electronic theory predicts they'd be fine.

At odds with this practice is the charging voltage profile on these batts. When charging, typically one will take more current than the other leading to one fully charged batt and one partially charged batt. Continuing to charge may only result in further overcharging the already full batt.

So can we chare them separately and put them together to get one big storage batt? Unfortunately, no. When put in parallel, one batt will typically discharge into the other one- leading to one mostly dead batt and one which has been overcharged (which permanently decreases the batt's capacity).

Technically, you could charge separately and put each series string in series with a diode so it cannot take charging current from the other batt. Problem there is that's a 0.7v diode drop (Schottky may not be a great choice because of its own reverse leakage current). In a 2.4V batt losing 0.7v is probably not going to be acceptable.

Gayan Soyza · 16th November 2007, 02:26 AM

@ mabauti
Its useless isn't it? yes the above ideas are right better buy a higher capacity ones.
I always use same type & same capacity batteries.

audioguru · 16th November 2007, 03:25 AM

I built a little stereo amp for the beach. It used two series strings of 6 AA Nicads with the strings connected in parallel. It worked fine and lasted for many years.

After about 10 years it didn't work and I discovered that all 12 cells were shorted.

Gayan Soyza · 16th November 2007, 07:53 AM

My vote is giving to your stereo amp which worked with you for ten years and not for your batteries .

I have notice that some DIY circuits last longer than ready made ones.

mvs sarma · 16th November 2007, 01:39 PM

I feel , Mabauti wants to parallel two sets of 2.4V batteries. one is a set wirh ni-mh and another with ni-cd with different capacities.

TheVictim · 16th November 2007, 04:25 PM

I discovered the hard way that ni-cads' propensity for self discharge is magnified 198728912738912738912 times (OK, that's an exaggeration, but not by much) if they are in parallel. I built an external power pack for a very old laptop that ran for a dissappointing 20 minutes from some small ni-cad cells. I figured I'd get 40 minutes if I used another pack wired in parallel. I did, but if I let the thing sit for long after charging it would be stone dead. Eventually all the cells crapped out after a really short time.

Don't do it.

mabauti · 16th November 2007, 05:35 PM

Was the server down yesterday? I could not connect it >_>

anyway, I forgot to poste a figure ,sorry :

**Nigel Goodwin** · 16th November 2007, 05:49 PM

Quote:

Originally Posted by mabauti

Was the server down yesterday? I could connect it >_>

anyway, I forgot to poste a figure ,sorry :

No, don't do that! - BAD idea!.

speakerguy79 · 21st November 2007, 05:17 PM

But straight series connections are fine, yes?

I also doubt ballast resistors to balance current output from each would be of any use here?

**Nigel Goodwin** · 21st November 2007, 05:21 PM

Quote:

Originally Posted by speakerguy79

But straight series connections are fine, yes?

Never EVER, EVER mix different types of batteries - it's just asking for disaster!.

mabauti · 21st November 2007, 07:35 PM

so, what extra connections/elements I must use?

speakerguy79 · 21st November 2007, 08:20 PM

I meant series connections of the same type of battery technology

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16th November 2007, 01:20 AM
mabauti Experienced Member	NiMH & NiCad batteries What precautions must I take when connecting (2 1.2VNiMH 1600mAH batteries in series) and (2 1.2VNiCad 600mAH batteries in series) in parallel in order to have 2.4V?

16th November 2007, 01:33 AM
Sceadwian Experienced Member	Your question is too vague. Under most circumstances 2 3 or 4 cells in series will require no additional precautions as long as the cells are from the same production line at the same time. With multiple cells in series it's common to be a little understated in it's charging requirements compared to a full cell and to do a low current equalizing charge periodically. 12 volt car batteries are after all in fact 6 2 volt (nominal) Lead acid cells in series. __________________ Curiosity killed the cat; That's why they have nine lives.

16th November 2007, 01:50 AM
audioguru Experienced Member	I think he wants to charge the old small-capacity Nicads from the newer higher capacity Ni-MH battery. That wastes power. Instead of using 1600mAh plus 600mah= 2200mAh but it will never be reached, buy new 2500mAh AA Ni-MH calls. They just keep on going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and going and .... __________________ Uncle $crooge

16th November 2007, 02:25 AM
Oznog Experienced Member	Even if you had 2x IDENTICAL 2.4V 1.6AH NiMH packs, you can't put them in parallel. Neither NiCd nor NiMH can be put in parallel, even though basic electronic theory predicts they'd be fine. At odds with this practice is the charging voltage profile on these batts. When charging, typically one will take more current than the other leading to one fully charged batt and one partially charged batt. Continuing to charge may only result in further overcharging the already full batt. So can we chare them separately and put them together to get one big storage batt? Unfortunately, no. When put in parallel, one batt will typically discharge into the other one- leading to one mostly dead batt and one which has been overcharged (which permanently decreases the batt's capacity). Technically, you could charge separately and put each series string in series with a diode so it cannot take charging current from the other batt. Problem there is that's a 0.7v diode drop (Schottky may not be a great choice because of its own reverse leakage current). In a 2.4V batt losing 0.7v is probably not going to be acceptable. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

16th November 2007, 02:26 AM
Gayan Soyza Experienced Member	@ mabauti Its useless isn't it? yes the above ideas are right better buy a higher capacity ones. I always use same type & same capacity batteries. __________________ Gayan Forum Supporter Last edited by Gayan Soyza : 16th November 2007 at 02:31 AM.

16th November 2007, 03:25 AM
audioguru Experienced Member	I built a little stereo amp for the beach. It used two series strings of 6 AA Nicads with the strings connected in parallel. It worked fine and lasted for many years. After about 10 years it didn't work and I discovered that all 12 cells were shorted. __________________ Uncle $crooge

16th November 2007, 07:53 AM
Gayan Soyza Experienced Member	My vote is giving to your stereo amp which worked with you for ten years and not for your batteries . I have notice that some DIY circuits last longer than ready made ones. __________________ Gayan Forum Supporter

16th November 2007, 01:39 PM
mvs sarma Experienced Member	I feel , Mabauti wants to parallel two sets of 2.4V batteries. one is a set wirh ni-mh and another with ni-cd with different capacities. __________________ Regards, Sarma.

16th November 2007, 04:25 PM
TheVictim Experienced Member	I discovered the hard way that ni-cads' propensity for self discharge is magnified 198728912738912738912 times (OK, that's an exaggeration, but not by much) if they are in parallel. I built an external power pack for a very old laptop that ran for a dissappointing 20 minutes from some small ni-cad cells. I figured I'd get 40 minutes if I used another pack wired in parallel. I did, but if I let the thing sit for long after charging it would be stone dead. Eventually all the cells crapped out after a really short time. Don't do it.

16th November 2007, 05:35 PM
mabauti Experienced Member	Was the server down yesterday? I could not connect it >_> anyway, I forgot to poste a figure ,sorry : Last edited by mabauti : 16th November 2007 at 06:47 PM.

21st November 2007, 05:17 PM
speakerguy79 Experienced Member	But straight series connections are fine, yes? I also doubt ballast resistors to balance current output from each would be of any use here?

21st November 2007, 07:35 PM
mabauti Experienced Member	so, what extra connections/elements I must use?

21st November 2007, 08:20 PM
speakerguy79 Experienced Member	I meant series connections of the same type of battery technology