Repacking drill battery

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I've got an 18v battery drill whose pack is just about completely dead. I've
been thinking about repacking it, but I'd really like to use
high-performance NiMH batteries in place of the current NiCads. The question
is, will the existing temperature sensor still work for terminating the
charge, or is the temp change for NiMHs too different?




Re: Repacking drill battery



"Russ"
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** Probably will be OK -  but check the rating on that temp sensor.

NiMH cells can be damaged by overcharging and overheating.

This link ,with seems pretty comprehensive, suggests 45 degrees C is the max
temp before charging at  1C ( ie 1.5 hours to full charge)  must terminate.

http://www.powerstream.com/NiMH.htm



.......   Phil



Re: Repacking drill battery


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Cheers Phil - I'll open up the pack and have a look at the sensor.




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Silicon Chip recently had an article about this sort of thing.
Worth a read, if only to discourage you.
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I think I might have seen that one - is that where they came up with a
ridiculously complicated charger to add temp sensing to cheapo drill packs?
The whole article seemed to be motivated by Jaycar stocking (overpriced)
Sub-C NiCads and needing something to help shift the buggers.



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I can't answer you question, but I've opened several brands of
recharger for 14.4 and 18 volt drill batteries, and none of them
had anything connected to the temperature sensor.

Just a possibly-relevant data point :-)

Clifford Heath.

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Some of the one's I've opened had encapsulated bi-metal strip cut-outs.

It would be better for the OP to stick with NiCd if that's what's used
originally, NiMh are not as good for high discharge current and easier to
damage by overcharging.



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That was true maybe 10 years ago, but these days you can get NiMHs that
out-perform NiCads in both capacity and current delivery. I am concerned
about overcharging though.



Re: Repacking drill battery



"Russ"
 ian field wrote:

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** The shortest safe discharge time for NiCds is about two minutes  -   as
used by model boat and model plane hobbyists.

Good quality sub-C cells will deliver 50 amps at about 1.1 volts this way.

Modern NiMH  sub-C cells can also be discharged in two minutes,  while
delivering up to 100 amps, since they have about twice the Ah capacity.

An electric drill normally draws far less current and so is no problem.



.......   Phil





Re: Repacking drill battery


At the risk of being a pain... if you are going to replace the batteries
completely, Lithium Polymers are the way to go. Varta (as one supplier)
will help out with charger application circuits too

Re: Repacking drill battery



"TonyR"

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**  No risk involved, mate  -   YOU  are a 100%  pain.


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** Straight down the pathway to hell................

http://en.wikipedia.org/wiki/Lithium-polymer


There are enormous problems with overcharging and over discharging.

Plus a 2 to 3 year limit on life, whether used or not.

Bad news for the OP's drill.



......  Phil



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I've actually had a lot of experience with Lithium Polymer  cells in
electric R/C planes, but there are a number of catches - I have a charger
that will do Lipos, but not 18V worth, but that aside, the big issue is that
lipos need careful management when in use - if you exceed their maxiumum
discharge rate, they'll die very quickly, and in the worst case, swell up
and explode - without some clever electronics, this would be a hard thing to
take care of in a drill where it's not uncommon to stall the motor.
Similarly, if they are allowed to discharge to too low a voltage, they'll
also fail prematurely.

With R/C electric planes, you can carefully choose the combination of motor,
gearbox and propellor such that you know the maxiumum current draw and match
it to the lipos you are using (or vice versa), and the speed controllers are
quite smart - particularly the brushless ones (brushless motors are pretty
much standard now) and can be programmed to sense the appropriate low
voltage point and either wind back the power, shut off, or pulse the power
to indicate to the pilot that it's time to land.

Given the huge advances in brushless motor, controller and battery
technology in the R/C field, I kind of wonder why you don't see more of it
flowing over into power tools, although it is kind of happening slowly with
the introduction of Lithium Ion-powered drills (still with brushed motors),
but they cost a bloody fortune.



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