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

[<daveb seanet com>]

thanks for the chart.  I have a hydrometer but have no idea if it is 
temperature compensated.  How does one tell? by how much you paid for it? 
;^)
> 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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