Is 2.6V too low to discharge a 6 cell pack?

[Dan]

I just got a Duratrax Intellipeak charger (the Mini). It has a
discharge feature that discharges the packs to a fixed 2.6 volts. I
have read in several places that you shouldn't discharge packs below
~5 volts. So, it seems to me that the Duratrax unit will discharge
the packs to a lower voltage than they should ever reach. Does this
sound right? Any comments?

Thanks,
--Dan

[Jonathan Hodgson]

On 31 Jul 2003 12:59:18 -0700, Dan wrote:

> I just got a Duratrax Intellipeak charger (the Mini). It has a
> discharge feature that discharges the packs to a fixed 2.6 volts. I
> have read in several places that you shouldn't discharge packs below
> ~5 volts. So, it seems to me that the Duratrax unit will discharge
> the packs to a lower voltage than they should ever reach. Does this
> sound right? Any comments?

It depends how well-matched your cells are. If they're all spot-on, then
2.6 V will be exactly 0.433 V per cell. If they're not quite that good,
some will be lower and some higher; if any of the lower ones drop below
zero - IOW, get reversed - that's a Bad Thing.

Taking individual cells to zero volts - as on a discharge tray - is fine
(certainly for nicads; not sure about NiMH). Taking /packs/ to zero is
not, hence the usual 1.0/0.9 VPC recommendation.

HTH,
Jonny

[Dan]

I bought 5 "Duratrax Piranha 1900mah scx" packs, dirt cheap at 2/$30
they are the only packs I have. Do you think I should just go ahead
and use the discharge feature, or do you think continual discharging
to 2.6V will damage the packs? Discharging to 2.6V takes time, and if
it is a bad thing, hell I'll just recharge the packs saving both time
and money.

By the way, things have gotten CHEAP since the last time I was into
RC. 1900mah packs for $15? That was absolutely UNHEARD of 10 or 12
years ago when I drove RC cars. Computer controlled charger for $59,
that would have been $200+ back in the day (I drooled over the Tekin
charger back then).

Thanks,
--Dan

Jonathan Hodgson <jp_hodgson@eng1neer.com> wrote in message > It depends how well-matched your cells are. If they're all spot-on, then
> 2.6 V will be exactly 0.433 V per cell. If they're not quite that good,
> some will be lower and some higher; if any of the lower ones drop below
> zero - IOW, get reversed - that's a Bad Thing.
>
> Taking individual cells to zero volts - as on a discharge tray - is fine
> (certainly for nicads; not sure about NiMH). Taking /packs/ to zero is
> not, hence the usual 1.0/0.9 VPC recommendation.
>
> HTH,
> Jonny

[Jonathan Hodgson]

I probably *wouldn't* discharge cheap packs to 2.6 V.

Just recharge them most of the time; once a month, say, put a digital
voltmeter on each pack and watch it carefully to discharge to down about 5
or 6 volts, then unplug it.

I've reversed a few cells using a car headlamp bulb - if you let it go dim,
it's too low... BTW if one cell gets much hotter than the rest during
charging or running then it's cooked, probably due to reversal.

Jonny

On 1 Aug 2003 11:39:29 -0700, Dan wrote:

> I bought 5 "Duratrax Piranha 1900mah scx" packs, dirt cheap at 2/$30
> they are the only packs I have. Do you think I should just go ahead
> and use the discharge feature, or do you think continual discharging
> to 2.6V will damage the packs? Discharging to 2.6V takes time, and if
> it is a bad thing, hell I'll just recharge the packs saving both time
> and money.
>
> By the way, things have gotten CHEAP since the last time I was into
> RC. 1900mah packs for $15? That was absolutely UNHEARD of 10 or 12
> years ago when I drove RC cars. Computer controlled charger for $59,
> that would have been $200+ back in the day (I drooled over the Tekin
> charger back then).
>
> Thanks,
> --Dan
>
> Jonathan Hodgson <jp_hodgson@eng1neer.com> wrote in message
>> It depends how well-matched your cells are. If they're all spot-on, then
>> 2.6 V will be exactly 0.433 V per cell. If they're not quite that good,
>> some will be lower and some higher; if any of the lower ones drop below
>> zero - IOW, get reversed - that's a Bad Thing.
>>
>> Taking individual cells to zero volts - as on a discharge tray - is fine
>> (certainly for nicads; not sure about NiMH). Taking /packs/ to zero is
>> not, hence the usual 1.0/0.9 VPC recommendation.
>>
>> HTH,
>> Jonny