McGraw Edison Ni-Cads (KOH electrolyte) [RE-wrenches]

John Berdner jberdner at sma-america.com
Tue Jul 1 15:06:42 PDT 2003


John:
 
Edison cells are normally NiFe not NiCd. 
The railroads here in the US used NiFe for years because they were so
tough.
The downside is they are expensive, not very space efficient, and they
have high self discharge.
Great for severe cycling service but not so good for remote site OV
with low loads.
I allways thought Edison cells would be the ideal battery technology
for load shifting here in CA where we have time of day metering and an
almost 3:1 cost ratio :-)
 
The electrolyte is KOH and as you noted it is nasty - just alkaline
instead of acidic.
NiFe batteries have a virtually unlimited cycle life but you do need to
change the electrolyte from time to time.
Normally this is due to contamination due to atmospheric Carbon from
C02.
Some of the RR guys float a layer of oil (mineral oil I think) on top
of the electrolyte to slow the carbon absorbtion rate. 
>From what you describe it sounds like a electrolyte swap is in order. 
 
I have never done that myself but I know the guys at Home Power played
with Edison cells a few years back.
Perhaps one of them will chime in.
 
Best Regards,
 
John Berdner


>>> john at gosolar.co.nz 6/30/2003 10:59:37 PM >>>
Greetings all,

I've a customer with some Edison Ni-Cads that are about 12 years old
(or
thereabouts) and they had very light use. The stamp on the side is
ED-120, which I believe to be 120a/h per bank of 5 cells to make up
6v.
Generally the batteries look to be in good condition, hardly any
corrosion or spills, etc.

These were sold to another customer and when he tried to use them they
would only give about an hours use. We have been told various things
about checking the S.G. on them which was said to be about 1.20 but at
68degrees and evidentally temperature is pretty important. Also the
only
thing to top them up with is distilled water.

Owner A has left the country and No-one seems to know much about these
batteries locally and I have been told various things, probably more
heresay than reliable info. We have also heard that the KOH is nasty
stuff and treat it just like the cautions for H2S04.

I've been told that the electrolyte should be changed every 10 years
and
if thats the case these are overdue. And, after having changed the
electrolyte, it will take about 20 cycles to bring them back to
productivity (so the electrolyte can sink in, we are told)

The new owner is really keen to use them as he is a great person to
recycle and re-use and we both have heard some great things about
Ni-Cads except how to get them to a usable state.

If anyone has some first-hand experience and can help, please contact
me
off-list, your experiences would be greatly appreciated.

thanks a lot, John V, Christchurch,
N.Z.

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