Re: Battery load testers

["Rob" <westco@jps.net>]

Roger,

It does help a lot.  Thanks for taking the time 
to make such a detailed response.

Rob


----- Original Message ----- 
From: "Roger Stockton" <rstockton@delta-q.com>
To: <ev@listproc.sjsu.edu>
Sent: Friday, May 31, 2002 12:31 PM
Subject: RE: Battery load testers


> 
> > -----Original Message-----
> > From: Rob [mailto:westco@jps.net] 
> > Sent: May 31, 2002 11:49 AM
> > To: ev@listproc.sjsu.edu
> > Subject: Battery load testers
> 
> > Now I am looking for a battery load tester to monitor the six 
> > 12-volt batteries in my Bombardier. I would like to be able 
> > to evaluate the batteries, diagnose battery problems and 
> > identify weak batteries in the string.  After doing some 
> > reading, it appears that the conductance meters made by 
> > Midtronics were easier to use and more accurate than a 
> > standard load tester (I think).  So I began to check out a 
> > PBT-100 ($109) and a Micro 400
> > ($349) testers, rather than buy a simple Electronic 
> > Specialities Digital 120 AMP Battery Load tester ($45).
> > 
> > Someone out there must know a lot more about battery load 
> > testers.  I would appreciate any advice.
> 
> I think it depends what sort of information you hope to get about the
> pack.  A traditional carbon pile load tester tells you about the ability
> of the battery to sustain a peak load (i.e. measure how many amps the
> battery can source when loaded such that its terminal voltage sags to
> ~9V).
> 
> The Midtronics tester (which I believe is what I had the opportunity to
> use when pit crewing for Rod Wilde on the Maniac Mazda a few Woodburns
> ago) essentially gives you the same information, but does so by
> measuring the battery impedance.  When you connect it to the battery it
> will advise you if the battery needs to be charged before testing.  If
> it decides the battery is sufficiently charged to test, it will proceed
> to provide you with an estimate of the battery's cranking amp capability
> (don't recall if it is CCA or CA).  I believe you can tell the unit what
> your minimum acceptable value is so it will deliver a PASS/FAIL verdict
> as well; if not, you must decide if the value represents a healthy,
> weak, or defective battery yourself.
> 
> I don't believe either of these tells you much about the capacity of the
> battery, which may well be the most important thing for an on-road EV.
> 
> If your load tester is sufficiently beefy, you could use it to perform a
> capacity test by dialing it up to a suitable load current and monitor
> how long it takes for the battery voltage to fall to some level.  If you
> want to be able to compare the result directly to the manufacturer's
> specifications, then you are pushed into performing a relatively deep
> discharge, however, if you want to monitor the relative health of the
> pack, you could standardise on a shallower discharge at a convenient
> rate (e.g. time to 1.90Vpc @ 50A) and keep a journal so that trends over
> time would become obvious and you could immediately identify a battery
> on its way out based on its differing behaviour in the periodic (e.g.
> monthly) test.
> 
> Hope this helps,
> 
> Roger.
>