Re: (ET) time for a new pack...

["David Roden (Akron OH USA)" <roden ald net>]

On 8 Aug 2001, at 8:29, daveb seanet com wrote:

>  1.  what do you measure to determine 50% of capacity?  pack voltage?
>  Can
>   you 
> determine this point by the fuel gauge reliably?  

The cheapest and simplest way to measure state of charge, assuming you 
run golf car batteries and not some kind of VRR ("sealed") batteries, is 
to use a temperature-compensated hydrometer.  Open-circuit voltage (when 
the batteries have been resting uncharged and unused for several hours,
preferably overnight) will give you a very rough approximation.  The
following figures are for a 12 volt battery, so halve the voltages for 6 
volters:

SG*                    voltage               status
1.265 - 1.280       12.85 - 12.95     fully charged
1.225                  12.45 - 12.65     25% discharged
1.190                  12.25 - 12.35     50% discharged
1.150                  12.00 - 12.10     75% discharged
1.120                  11.80 - 11.90     100% discharged

*A new battery will read 1.280 fully charged; a battery near the end of 
its service life will read 1.250 when fully charged.  The reduction in 
electrolyte concentration is caused by sulfation; the SO4 ions are bound  
up in crystalline lead sulfate and can't reform H2SO4.  Actually the 
other SGs should probably be ranges too -- but when you hit 1.120 the 
battery is essentially discharged regardless of age.

> Also I have heard an 80%
> soc figure tossed around as in never go below 80% ???

Battery depreciation accelerates rapidly below 80%.  Cycle life will 
suffer from regular discharges below that point.  

You are in danger of reversing a cell below 80%.  Cell reversal is  
invariably damaging, so if it's a genuine emergency (rare with ETs, I 
suspect) use as little current as possible.  Go slowly in low gear, with 
the speed control in the middle position, and turn everything but the 
drive motor off.


> 
>   2.  Are de-sulfating chargers totally bogus?   Has anyone proven to
>   their 
> satisfaction that they do work in certain situations?

I admit, I haven't tried them.  But I'm pretty skeptical.  

Some people, including a couple of pretty smart EV builders and a few 
Home Power writers, say that desulfators have worked for them.  However, 
I don't know of any truly independent scientific proof (that is, not 
sponsored by a desulfator manufacturer) that shows they have any effect 
that's better than a good, long, slow equalizing charge. 

I've heard that the instructions with desulfators usually call for  
installing the gadget(s) and then leaving the charger on for several days 
or weeks.  I believe that any results from this regimen would be produced 
equally well by just running the charger alone, without the gadget(s), 
for the same amount of time.  

But, I'm willing to look at evidence to the contrary.  If anyone can show 
me significantly increased capacity produced by a desulfator when 
compared with an ordinary equalizing charge, and do so with enough 
samples to make it statistically valid, I'll be very interested!



David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1979 General Engines ElectroPed 24vdc
1970 GE Elec-trak E15 36vdc
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