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 |