NIMH batteries - slightly OT

In the middle of last year I bought a digital SLR that runs on 4 x AA
cells. The instructions say that alkalines are OK for checking the
camera, etc, but 2400 mAh NiMH are the preferred option for normal use.

However, I've yet to find a 2400 mAh cell that, according to my chargers,
can hold more than 50% of the rated charge and I've tried some that can
barely manage 500 mAh. I've tried Maplins hybrids, cheapo budget
batteries, and Ansman, but none seem as good as a vanilla set of
alkalines. This has never been a problem with NiCDs of all sizes (except
those made by GP), but all the NiMH cells I've tried have been
disappointing to say the least.

I have decent peak chargers: a PC-controlled Vencon UBA III+ and a Pro-
peak Prodigy II set up for 500 mA charge and 250 mA discharge. Both
chargers measure input charge and capacity on discharge.

I'm asking here because I've never had a good experience with NiMH - not
with this camera or in the past.

I know there are people on r.a.s who know a lot about batteries. So, what
brands of NiMH battery have you had good results from, i.e. that actually
do what it says on the tin?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Martin,

Interesting that you've had so many problems with the NIMH batteries.
I've used them for years in RC and they are consistantly far better
than Ni-CD in every instance. I've used various chargers succesfully
and the only thing I would have you double check is your settings on
the fancy charger. Most have both settings for both NiCD and NIMH.

NIMH battereis will charge on a NiCD charger but will take much longer
(due to the charge rate on the common charger being set to the 1/10
rate for the NiCD not the NIMH). If the charger has a timeout, often
it will take 2 or more cycles to get the NIMH batteries topped.

One reason not to use the alkeline is that they cannot deliver the
current as rapidly as the NiCD or NIMH. They have lots of capacity ,
just a slower delivery.

Sorry I can't take a good look at your set up and provide more help.

Mike

Digital SLRs are notoriously more picky about battery voltage than
many other consumer electronics and are often unhappy with lower
voltage cells like NiMH.. I gave up trying with them in mine and
switched to single-use lithiums.

Others have reported better luck with newer technology NiMH batteries
such as Sanyo's Eneloops.

Mike

Martin,

Try charging at one amp to see what happens.

When I was flying electric RC Sailplanes, I would charge at one amp and
discharge at 60 amps or so, and could always charge to full capacity or
slightly beyond. They were Sanyo, but I doubt that the particular cells
are still made. They were 1700's and 1900's.

At 12:20 12 April 2009, Martin Gregorie wrote:
In the middle of last year I bought a digital SLR that runs on 4 x AA
cells. The instructions say that alkalines are OK for checking the
camera, etc, but 2400 mAh NiMH are the preferred option for normal use.

However, I've yet to find a 2400 mAh cell that, according to my
chargers,
can hold more than 50% of the rated charge and I've tried some that can

barely manage 500 mAh. I've tried Maplins hybrids, cheapo budget
batteries, and Ansman, but none seem as good as a vanilla set of
alkalines. This has never been a problem with NiCDs of all sizes (except

those made by GP), but all the NiMH cells I've tried have been
disappointing to say the least.

I have decent peak chargers: a PC-controlled Vencon UBA III+ and a Pro-
peak Prodigy II set up for 500 mA charge and 250 mA discharge. Both
chargers measure input charge and capacity on discharge.

I'm asking here because I've never had a good experience with NiMH -
not
with this camera or in the past.

I know there are people on r.a.s who know a lot about batteries. So, what

brands of NiMH battery have you had good results from, i.e. that actually

do what it says on the tin?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Sun, 12 Apr 2009 09:00:36 -0700, Mike Bamberg wrote:

Hi Mike,

Interesting that you've had so many problems with the NIMH batteries.
I've used them for years in RC and they are consistantly far better than
Ni-CD in every instance. I've used various chargers succesfully and the
only thing I would have you double check is your settings on the fancy
charger. Most have both settings for both NiCD and NIMH.

I can confirm I'm using NiMH chemistry settings. I can't tell you much
more about the Prodigy II - its a fairly typical $70 single stage peak RC
battery charger, so I can set charge/discharge rates and chemistry but
can't touch the peak settings.

However, the Vencon UBA III+ is a different story, since its charging
cycle is completely user defined by graphically assembling a set of
modules to define a charging cycle for a specified chemistry. Programs
are generic: define charge rates and cutoff points in terms of cell
capacity and per-cell voltages. To do a charging run you tell it the
number of cells and capacity pull the details out of a battery database.
In this case I'm using its cutoff and rate for NiMH defaults and telling
it to charge 4 NiMH cells with 2400 mAh capacity. I'm using this
discharge + charge cycle:

1) Discharge at 0.5C to 0.9v/cell (it actually limits to 0.41C on
a cell this big)
2) Max rate (10 watts) until 1.3C or 2v/cell cutoff
3) Standard charge at 0.1C until 0.3C

Then it either rests a bit and before running another cycle or goes to
trickle charge at a 2% rate until you turn it off.

I've run two cycles on this set of new Ansaman batteries (all numbers are
mAh) after a couple of even less successful cycles on the Prodigy II:

Cycle 1 2 Cutoff condition
===== === === ================
Discharge 237 447 0.9v
Peak charge 388 611 2v peak
Std charge 720 720 0.3C supplied to batteries

My impression is that both chargers are cutting off too early.

I also see that the first UBA III+ cycle stuck 1100 mAh into the
batteries but only got 447 mAh out, which seems pretty dire for the third
charge of a new set of batteries.

I can configure the UBA III+ for cutoff voltage or inflection (2 mv/cell)
cutoff on peak charge rather than voltage - would this help?

NIMH battereis will charge on a NiCD charger but will take much longer
(due to the charge rate on the common charger being set to the 1/10 rate
for the NiCD not the NIMH). If the charger has a timeout, often it will
take 2 or more cycles to get the NIMH batteries topped.

Noted - I'm running another two cycles overnight tonight.

One reason not to use the alkeline is that they cannot deliver the
current as rapidly as the NiCD or NIMH. They have lots of capacity ,
just a slower delivery.

Fair comment.

How do NiMH stand up to continuous charging at a 1% or 2% rate? Thats my
usual maintenance regime for NiCDs and they have always performed well on
it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Sun, 12 Apr 2009 09:14:08 -0700, Mike the Strike wrote:

Digital SLRs are notoriously more picky about battery voltage than many
other consumer electronics and are often unhappy with lower voltage
cells like NiMH..

This one (a Pentax K100D) seems pretty happy with the batteries. I'm not
happy about the capacity I'm seeing. If I buy 2400 mAh cells I expect to
see 90% of that when cycle testing the new cells. If NiCDs can do that
and still give 80% if abused for a year or two I'm not even slightly
impressed with cells that can't even manage 50% of their rated capacity.

Others have reported better luck with newer technology NiMH batteries
such as Sanyo's Eneloops.

I'll look into those: thanks.

I've also heard that uniRoss are good - any comments or experience with
them?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Sun, 12 Apr 2009 19:30:04 +0000, M C wrote:

Martin,

Try charging at one amp to see what happens.

I'll try that tomorrow when the I've seen the results of tonight's
overnight cycling run.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Martin:

I have a Pentax *istDS and had a k200d, both of which are designed to
use 4xAA batteries. Many Pentax owners have reported similar
frustrations about NiMH battery life and operation. You might try one
of the digital camera forums (DPReview and Pentaxforums come to mind)
where these problems have been beaten to death.

Mike

Martin,
Tom Moore who is a test engineer for medical and military battery
packs wrote recently on a RC web site that the chief reason NiMh false
peak is the wrong charge rate. They should be charged at close to 1C
or the peak may not be detected. He also mentions that they should
never be left on trickle charge for an extended time and that trickle
charge as a regular charging method will eventually destroy them.

I have had good luck with Sanyo Eneloops 2000 mAh.

John

Martin,

I gave you some faulty info before. I said that I use to charge my seven
cell, 1900 packs, at 1 amp. That was wrong. It was 5 amps.

Today, after reading your post, I got an old seven cell, 1900 mAh, NiMH
pack out that had not been used for over 5 years, and began charging it
with my Great Planes Triton charger. At first I put it on auto
charge/discharge and got it up about 500 mAh, and then began charging and
discharging manually at an increasingly higher charge and discharge rate.
The last discharge was done at 3 amps and the last charge was 5 amps. The
result is that even after 5 years of no activity, the final charge
capacity is over 2000mAH and over 10 volts total which is pretty good for
an old unused battery pack. These are "Zapped" packs that supposedly
allow for higher voltage.

Anyway, just thought I would test and let you know, what good NiMH cells
can do.

Mike






At 21:58 12 April 2009, Martin Gregorie wrote:
On Sun, 12 Apr 2009 19:30:04 +0000, M C wrote:

Martin,

Try charging at one amp to see what happens.

I'll try that tomorrow when the I've seen the results of tonight's
overnight cycling run.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |