Subject:
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ni-cads in parallel
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 7 May 1996 12:22:45 GMT
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Original-From:
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Mark Noyes <[noyes@]NoSpam[odi.com]>
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Viewed:
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1363 times
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> Date: Mon, 6 May 1996 21:55:05 -0700 (PDT)
> From: "Jeff Keyzer" <jkeyzer@calweb.com>
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> >
> >
> > Don't do this. First off, you won't get more current, nicads already
> > can deliver gobs of current, enough to be dangerous. You want more
> > amp-hours, not more instantaneous amperage.
We've had a debate on this issue a couple of times on the rec.models.rc.air
newsgroup a couple times recently (check out www.dejanews.com) and the
consensus seemed to be that parallel packs should not be a problem.
> Yes. My problem is that my motors draw somewhere around 2 amps
> average, and the AA pack I have is rated at 600mAh. This isn't much fun, I'm
> tempted to leave the thing plugged in instead of charging it every few
> minutes! It's really not tooo bad, but irritating nonetheless. However,
> I'm going to be adding the Polaroid sonar module, which will probably chop a
> good slice off of that battery life, and I'm sticking on a servo as well.
>
> >
> > Use separate power supplies to run your servo and your HB. The HB
> > will run on as little as 6.2v (got to overcome the 1.2v characteristic
> > drop of the 7805 regulator). You could probably get away with 6v.
>
> Right now, I'm letting the HB use its internal 9.6V pack, and I
> intend on leaving it that way. It seems to be perfectly comfortable with
> it, and I'd really rather not risk shorting it out like last time. <cough
> cough>
>
> There's another issue, though. If I were to, say, use a sub C
> ni-cad pack for more mAh, that'd be great. However, I'd need to take a 4.8V
> tap off of it for the servo.
You should definitely go to a sub C pack before bothering with the parallel
packs if for no other reason than pure simplicity. The 1400 mAh variety
will give you more than a doubling of capacity. For a couple bucks more
you could go with 1700 mAh cells and get nearly triple the capacity.
If you really mean that you are running the motors off a 6V pack and not
a 6 cell pack, there's no good reason to add a separate 4.8 V tap. In
R/C applications, 6V packs are used quite regularly to get faster servo
response and in fact if you read the fine print you'll find that servo
manufacturers often quote their speeds at 6V. You will of course get a
slightly higher current drain but unless you are running more than a couple
of servos, the difference in current shouldn't be significant.
> Does this create the same sort of problem as
> putting cells in parallel? Obviously, certain groups of cells could end up
> less charged than others. Is this another potential problem? I suppose I
> could use _another_ battery pack for _just_ the servo, and then charge that
> one separately from the motor pack. Wow, this is getting complicated...
Draining 4 of the 5 cells at a higher rate does have the potential to
create problems but my bet is that the risk in this application is minimal.
At a minimum it would cause a peak charger (if you were using one) to
undercharge the pack as it would sense a peak in one of the cells before
the remaining 4 were fully charged.
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Message is in Reply To:
 | | Re: ni-cads in parallel
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| (...) Yes. My problem is that my motors draw somewhere around 2 amps average, and the AA pack I have is rated at 600mAh. This isn't much fun, I'm tempted to leave the thing plugged in instead of charging it every few minutes! It's really not tooo (...) (28 years ago, 7-May-96, to lugnet.robotics.handyboard)
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