What's the best way to charge batteries (Nicad or Nimh)?
Series or parallel?
I'm guessing parallel, but as I have a rechargeable light which
charges the battery in series is it worth taking them out of the light
to charge them with an external charger in parallel?
Do you mean batteries, or cells?
If you want to e.g. charge a pack of identical cells in more or less
identical state of charge, in a hurry, you need a delta peak charger.
And they need to be charged in series really.
No, not really. Its fine to charge more or less identical cells in
series at the same current. It sonds like its a trickle charge anyway.
Eventually the cells that charge first just get warm and dump the excess
charge as heat, the others stay on charging till they are full too.
have their problems.
If you charge in parallel there's no way to guarantee that they share
the charging current properly, thus the more discharged one will (at
least initially) get most of the current and that may be too much.
Also it may well be that one cell is old/faulty and won't charge to
the full correct voltage so the other (good) cell doesn't get fully
If you charge in series then cells with less capacity (older, more
misused) will get overcharged and/or better cells will be
When charging battery packs you usually can't avoid charging in series
and sets of cells in packs are going to be pretty similar so series
charging is acceptable if not ideal.
Well, of course, any pack will be charged in series, so I doubt it makes
The ideal way would be to charge each cell individually so it can be
measured individually as well. But provided the cells aren't run
completely flat this shouldn't matter in practice.
*Why is "abbreviated" such a long word?
Dave Plowman firstname.lastname@example.org London SW 12
On 2 Dec 2003 23:57:15 -0800, email@example.com
Individually; failing that - in series so long as the size, age and
discharge state is similar. Parallel charging won't work with a
constant current charger (which all NiMH and NiCd chargers are) and
will damage cells.
Unless you limited your charger to an intrinsically safe charge rate
of about C/20 this wouldn't work. Alkaline batteries require
constant current not constant voltage charging. You could certainly
put constant current sources in each battery feed, but this is
independent not parallel charging.
Simply putting a resistor from a voltage source would lead to a
variable charge rate. If the resistor was sized for the initial
charge rate it would be too large for the later charge rate, if sized
for the later it would be too small for the initial. The former
would have to be the solution chosen but the results would be
I am replying to this message as TNP seems to know a lot about charging
I have a good quality nicad charger (a Robbe Lader 6+2 if it makes any
difference) that I am loath to replace. I was wondering if it was
possible to add a delta V switch to the output that could disconnect the
cells when they are charged. Does anyone know of a circuit diagram on
the web that I could use to add this functionality?
You sure it isn't a delta peak already?
Ther are chips available that do all teh stuff you need.
HOWEVER a trip to the local model shop will net you a charger that will
generally do from 4-7 cells at usually about 3A, with built in delta
peak, for next to bugger all - about 25 quid from memory.
e.g. http://www.ripmax.com/FS_Access_Chargers.html and have a look see.
Ideal for sub C nicads,
There's the MAX712 IC used here:
and the esteemed Mr Parry has this:
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