NiMH cell charging
Engineer
battery expert!
We have two digital cameras, both Canons - an A75 and an SX100IS.
They gobble up AA MiMH cells, particularly the SX100IS which uses only
two. I have one NiMH charger and one old NiCAD charger.
I also have a variety of NiMH cells, from green "no name" ones to
state-of-the-art Sanyo "eneloop" types, with some other brands in
between.
Some questions:
Can I charge the NiMH cells in the NiCAD charger? I think this
charges them more slowly as they don't get as hot as in the NiMH
charger.
Could I even leave them in the NiCAD charger to stay fresh? Not so
sure about this as it does not shut off (old analog design) - but I
could regulate the input AC voltage to turn it into a trickle charger
(but NiMH's might not like that, either.)
So, all comments or suggestions elcomed... also any other other
proven, established NiMH lore or sources!
Thanks for all replies
Cheers,
Roger
William Sommerwerck
news:fdc6835c-65f9-4484...@34g2000hsh.googlegroups.com...
> Can I charge the NiMH cells in the nicad charger? I think this
> charges them more slowly as they don't get as hot as in the NiMH
> charger.
Yes.
> Could I even leave them in the nicad charger to stay fresh?
No. I wouldn't do this unless the charger were specifically designed for it.
NiMH cells show a voltage drop at full charge -- and require a heavy charge
to reach that point. It's unlikely a nicad charger would shut off at the
right point.
I don't think NiMH cells are bothered by a trickle charge.
You should get NiMH cells with at least 2500mAh capacity. They're not
expensive. I also recommend the Maha/Powerex MH-C9000 charger.
isw
"William Sommerwerck" <grizzle...@comcast.net> wrote:
> "Engineer" <junk...@rogers.com> wrote in message
> news:fdc6835c-65f9-4484...@34g2000hsh.googlegroups.com...
>
> > Can I charge the NiMH cells in the nicad charger? I think this
> > charges them more slowly as they don't get as hot as in the NiMH
> > charger.
>
> Yes.
>
>
> > Could I even leave them in the nicad charger to stay fresh?
>
> No. I wouldn't do this unless the charger were specifically designed for it.
>
> NiMH cells show a voltage drop at full charge -- and require a heavy charge
> to reach that point. It's unlikely a nicad charger would shut off at the
> right point.
>
> I don't think NiMH cells are bothered by a trickle charge.
Some of the data sheets I've looked at say that they don't like it. My
(limited) understanding is that if you treat a NiMH like a NiCd, it'll
work but it's life will be shortened.
Isaac
Dave Platt
>
>No. I wouldn't do this unless the charger were specifically designed for it.
>
>NiMH cells show a voltage drop at full charge -- and require a heavy charge
>to reach that point. It's unlikely a nicad charger would shut off at the
>right point.
You're right. Although NiCd cells do have a voltage dropoff at full
charge, it's more pronounced than in a NiMH. A charger originally
designed for NiCd cells may wait until the voltage drops off
significantly (negative-delta-V) before terminating the charge. By
this point, a NiMH will have been significantly over-charged, which
isn't good for it.
NiMH battery manufacturers tend to use a dual cutoff approach - shut
off when the cell temperature starts rising, or at zero-delta-V.
>I don't think NiMH cells are bothered by a trickle charge.
Depends on the charge level. A slow-charge rate (say, C/10 or C/20)
in an "overnight" charger may overcharge the NiMH cell if left
connected indefinitely.
A very low (e.g. C/100 or so) charge rate seems to be safe, I gather,
but it's also rather ineffective for NiMH cells - they have a poor
"charge acceptance" at low charge rates, and most of the power just
turns into heat.
The battery manuals I've read say that if you do decide to use a
maintenance charge (to keep the cells charged up indefinitely), what
works best is a pulse-charging technique. Hit 'em with a brief pulse
of current at a high rate (C or C/2 or so) every once in a while, and
let them rest between pulses. Time the pulses so that the total
charge delivered averages out to around 1-2% of their rated capacity
per day. This should keep them topped up (countering their tendency
to self-discharge) without overcharging them.
>You should get NiMH cells with at least 2500mAh capacity. They're not
>expensive. I also recommend the Maha/Powerex MH-C9000 charger.
For batteries which will be charged up, and then discharged heavily
within a few days to a week, that's good advice. Ditto if you're
planning to keep them hooked to a properly-designed maintenance charger.
For batteries that you're planning to charge, and then leave on the
shelf (or in equipment) for weeks at a time, I think it's better to go
with the new style of "ultra-low self discharge" NiMH cells - Sanyo
Eneloops, or Powerex Immedions, or Hybrios, or types of that sort.
Their rated capacity is lower (2000-2100 mAh), but unlike the older
style of NiMH they'll hold most of their charge for months.
I second the recommendation for the MH-C9000. A very neat piece of kit.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Blarp
Charger: if it is an old < C/10 charger - no problem.
(I am doing it for years now, occasionally forgetting to take the
cells out etc. Very bad procedure, but does not seem to hurt cells
much)
If it is a fast charger - don't! delta V is different.
Most batteries fail in cameras due to Ri being too high, not due to
lack of capacity. Failing batteries may work well in e.g. a radio, but
not in the camera.
I seem to observe that *lower* capacity batteries perform *better*
with respect to Ri and lifecycle.
--
- René
William Sommerwerck
news:n5imi5-...@radagast.org...
> A very low (e.g. C/100 or so) charge rate seems to be safe,
> I gather, but it's also rather ineffective for NiMH cells -- they
> have a poor "charge acceptance" at low charge rates, and
> most of the power just turns into heat.
Maha says roughly the same thing. The recommend charging at at least 0.3C,
though it's not clear whether the reason is to push the cell towards a
significant delta-V at full charge, or to charge more "efficiently". I'm
bothered by the temperature rise, and tend to charge at 0.2C, which (based
on many years using nicads), seems downright excessive!
I don't expect any rechargeably battery to hold its charge indefintely. I
have a big pile of them, and charge them as I need them.
I might add that 2500mAh NiMH cells pretty much mark the end of the alkaline
cell, except for "intermittent", low-drain applications, especially where
frequently swapping the cells would be incovenient (eg, remote controls).
Such cells can provide at least the same run-time as a throw-away alkaline.
And, yes, I've checked and confirmed this.
> I second the recommendation for the MH-C9000. A very neat piece of kit.
I wish I'd one 20 years ago.
William Sommerwerck
> with respect to Ri and lifecycle.
Of course, lifecycle has to be weighed against how often you have to swap
out the cells. If a single high-capacity battery gives you no more than the
same total runtime over its life as multiple lower-capacity batteries,
you're still ahead of the game.
Dave Platt
William Sommerwerck <grizzle...@comcast.net> wrote:
>
>> A very low (e.g. C/100 or so) charge rate seems to be safe,
>> I gather, but it's also rather ineffective for NiMH cells -- they
>> have a poor "charge acceptance" at low charge rates, and
>> most of the power just turns into heat.
>
>Maha says roughly the same thing. The recommend charging at at least 0.3C,
>though it's not clear whether the reason is to push the cell towards a
>significant delta-V at full charge, or to charge more "efficiently".
I think it's the former. The higher charging current leads to a more
rapid flattening-out of the voltage-vs.-time curve, and also leads to
a more rapid rise in temperature at the full-charge point. Both of
these make it easier for a good charger's circuitry to detect the
full-charge point and shut down the current flow at the right time.
> I'm
>bothered by the temperature rise, and tend to charge at 0.2C, which (based
>on many years using nicads), seems downright excessive!
I believe that Powerex actually *increased* their minimum-charge-rate
recommendation for the MH-C9000 - it was originally .2C and now they
recommend .3C or above. This change, plus some firmware changes in
the more recent versions, seems to have eliminated the problem of "the
charger never shuts off, and the batteries get really hot" problem
that early revs of this charger were prone to.
I've been charging my various low-discharge AA cells in a C9000 at .5C
or so (the charger's 1000 mAh default rate) and they don't seem to
much, if any, warmer at charge-shutdown time than if I stick them in
an old-style .1C slow-charger and let 'em fill up. The C9000 appears
to detect the full-charge state quite reliably... I have yet to run
into a single hot-battery problem.
At this point, I prefer to stick with one of two charge regimes - a
fairly fast charge (.5C) using voltage-and-temperature cutoff, or a
slow one (.1C or below) using a timed cutoff.
>I might add that 2500mAh NiMH cells pretty much mark the end of the alkaline
>cell, except for "intermittent", low-drain applications, especially where
>frequently swapping the cells would be incovenient (eg, remote controls).
>Such cells can provide at least the same run-time as a throw-away alkaline.
>And, yes, I've checked and confirmed this.
I can well believe it.
The major niches I see for alkaline AAs are the ones you suggest (e.g.
remote controls) and long-storage-time emergency backup applications
(e.g. I keep a partial "brick" of AA alkalines with my amateur-radio
"go-kit", so I'd have a couple of days of on-the-air time prior to
having to drag out a recharger).
For my wife's digital cameras (and my own) I've settled on a
combination of low-discharge-rate NiMH for day-to-day use, and lithium
AA disposables for travelling (they're light, really long lasting, and
it saves the trouble of taking an overseas-voltage-qualified charger
along).
>I wish I'd one 20 years ago.
Yah. I've been rather dissatisfied for years with commercial NiCd/NiMH
chargers, and toyed with the idea of designing my own with a boatload
of flexibility and control, good full-charge detection, reconditioning
circuitry, etc. - an ideal application for a small microcontroller.
Never got around to doing it... and now there's no need to go to the
effort!
Engineer
> In article <n4CdnZHdx5Tsa8XVnZ2dnUVZ_snin...@comcast.com>,
Hi, everyone.
My sincere thanks for all replies and the aggregated expertise! It
seems that I should get a Maha/Powerex MH-C9000 charger. I'm presently
using a Sanyo "Super Quick Charger", model NC-MQH01U - bought with a
pack of NiMH's at COSTCO a couple of years ago for around $30. I've
no idea what the so-called "C-rate" is but the cells get quite hot
before it cuts off (my guess is that it does not have a temperature
sensors.) Does anyone know a good source, preferably in Canada, for
the Maha/Powerex MH-C9000 charger?
Cheers,
Roger
Thornhill, near Toronto, Ontario.
Rich Webb
wrote:
>Hi, everyone.
>My sincere thanks for all replies and the aggregated expertise! It
>seems that I should get a Maha/Powerex MH-C9000 charger. I'm presently
>using a Sanyo "Super Quick Charger", model NC-MQH01U - bought with a
>pack of NiMH's at COSTCO a couple of years ago for around $30. I've
>no idea what the so-called "C-rate" is but the cells get quite hot
>before it cuts off (my guess is that it does not have a temperature
>sensors.) Does anyone know a good source, preferably in Canada, for
>the Maha/Powerex MH-C9000 charger?
Apologies for jumping in late but before you buy, hop over to Amazon.com
and read the reviews on the MH-C9000.
--
Rich Webb Norfolk, VA
William Sommerwerck
> to Amazon.com and read the reviews on the MH-C9000.
I was particularly "impressed" with the reviewer who felt that its wealth of
features made it too difficult to use.
The point about watching what you're doing when recharging with such a
powerful unit is well-taken, though. I've had no problems with mine.
1PW
snip...snip
>
> Hi, everyone.
> My sincere thanks for all replies and the aggregated expertise! It
> seems that I should get a Maha/Powerex MH-C9000 charger. I'm presently
> using a Sanyo "Super Quick Charger", model NC-MQH01U - bought with a
> pack of NiMH's at COSTCO a couple of years ago for around $30. I've
> no idea what the so-called "C-rate" is but the cells get quite hot
> before it cuts off (my guess is that it does not have a temperature
> sensors.) Does anyone know a good source, preferably in Canada, for
> the Maha/Powerex MH-C9000 charger?
> Cheers,
> Roger
> Thornhill, near Toronto, Ontario.
Amazon will not ship this to Canada so says another poster.
Try: <http://www.paulsfinest.com/Maha-PowerEX-Charger-Info-sp-10.html>
--
1PW
Dave Platt
> seems that I should get a Maha/Powerex MH-C9000 charger. I'm presently
> using a Sanyo "Super Quick Charger", model NC-MQH01U - bought with a
> pack of NiMH's at COSTCO a couple of years ago for around $30. I've
> no idea what the so-called "C-rate" is but the cells get quite hot
> before it cuts off (my guess is that it does not have a temperature
> sensors.) Does anyone know a good source, preferably in Canada, for
> the Maha/Powerex MH-C9000 charger?
I'd suggest seeing if Thomas Distributing will ship to Canada.
William Sommerwerck
You need to know this!
C is the cell's capacity in mAh. This is usually right there on the cell.
For example, I have some decade-old Panasonic nicads marked 500mAh. (That's
not very high capacity, compared to recent cells.)
If you charged the cell at 50mA, that would be a 0.1C charge rate.
Engineer
wrote:
Indeed, yes... a bit arcane!
Typical NiMH's today (2008) are 2100 mAH so "0.1C" would be 210 mA.
I should check my Sanyo charger - my guess is that it exceeds "0.5C",
i.e. an amp, or so.
Still looking for a Maha/Powerex MH-C9000 charger.
Cheers,
Roger
William Sommerwerck
Just Google it.
The price has gone up in the past year, so look around a bit before buying.
UCLAN
> Still looking for a Maha/Powerex MH-C9000 charger.
William Sommerwerck
elsewhere.
UCLAN
> Thomas Distributing is a good company, but you can find it cheaper
> elsewhere.
I've been a Thomas Distributing customer ever since I had an intermittent
problem with a Maha battery charger and they sent me a new one (next day),
and didn't request I send the faulty one back. You can't beat their customer
service. Plus, they usually include batteries, battery cases, and charger
travel cases and cigarette lighter plugs with their chargers. Lowest price
isn't always the best deal.
William Sommerwerck
news:TRj9k.6178$to3....@newsfe15.phx...
> William Sommerwerck wrote:
Agreed, but the price difference is big enough to consider buying elsewhere.
I buy most of my rechargeables from Thomas. They have good prices and good
deals.
If you need lead-acid batteries, try www.batteryplex.com.
GMAN
I guess to me the only advantage with the C801D is the 8 cell capacity? The
drawback is not car charging.
UCLAN
>>I've been a Thomas Distributing customer ever since I had an intermittent
>>problem with a Maha battery charger and they sent me a new one (next day),
>>and didn't request I send the faulty one back. You can't beat their
>> customer service. Plus, they usually include batteries, battery cases, and charger
>>travel cases and cigarette lighter plugs with their chargers. Lowest price
>>isn't always the best deal.
>
> Agreed, but the price difference is big enough to consider buying elsewhere.
Really? A C9000 and deluxe case is $65 including shipping at Thomas. Newegg
wants $66 with shipping but no case. The cheapest Amazon vendor wants $65
including shipping, but again no storage case. 17StreetPhoto wants $67.40
including shipping, but no case. Thomas is looking good to me.
> I buy most of my rechargeables from Thomas. They have good prices and good
> deals.
I bought a dozen of the new type low-discharge NiMH AA cells from Thomas.
Love them. I'll never buy regular NiMH cells again.
> If you need lead-acid batteries, try www.batteryplex.com.
Don't use 'em, but thanks.
UCLAN
>>>Still looking for a Maha/Powerex MH-C9000 charger.
>>
>>http://tinyurl.com/5en3on
>
> Hey UCLAN, would you suggest the MH-C9000 or the MAHA MH-C801D ????
>
> I guess to me the only advantage with the C801D is the 8 cell capacity? The
> drawback is not car charging.
And the extra cost. Main question is do you *need* an 8-cell charger? If so,
get the C801D, and get a cheaper charger for the car. The heavy duty power
supply for the C801 is nice. I used to have a MH-C808M charger that had the
same type of supply. The C801 is the Cadillac of chargers, no doubt, but
unless you need the 8-cell capacity, I'd go with the C9000.
--
Raindrops on roses and whiskers on kittens.
GMAN
a second one.
UCLAN
>>>I guess to me the only advantage with the C801D is the 8 cell capacity? The
>>>drawback is not car charging.
>>
>>And the extra cost. Main question is do you *need* an 8-cell charger? If so,
>>get the C801D, and get a cheaper charger for the car. The heavy duty power
>>supply for the C801 is nice. I used to have a MH-C808M charger that had the
>>same type of supply. The C801 is the Cadillac of chargers, no doubt, but
>>unless you need the 8-cell capacity, I'd go with the C9000.
>
> Good suggestion, then if i needed more capacity i could just in the future buy
> a second one.
One more consideration: The C801 and its power supply require about FOUR
times more bench space than does the C9000.
GMAN
very similar to the C9000?
UCLAN
>>One more consideration: The C801 and its power supply require about FOUR
>>times more bench space than does the C9000.
>
> But technically does it do a better job or is the firmware and its capabilities
> very similar to the C9000?
Dunno. Have neither. I get by just fine with my ol' C401FS. I didn't like
the cell contacts in the 808. Don't know if the 801 uses the same contacts.
As I said, if you need 8 cell capability or want to spend 50% more money,
get the C801. Otherwise, go for the C9000. JMO.
Visit http://www.mahaenergy.com/store/viewItem.asp?idProduct=423 and
http://www.mahaenergy.com/store/viewItem.asp?idProduct=422 and compare
the two. Why not compromise and get the C800S?