BILL BAUER wrote in a message to Roy J. Tellason:
> BB> I've also been working with some gel cells and getting fair
> BB> results recharging those at pretty high voltages of 60 volts or
> BB> so. It's a lot harder to get much current through those than it
> BB> is car batteries.
> What amp-hour rating are the gels you're talking about?  I didn't think
> that those were really designed to do all that much with high currents...
 BB> Most of them are in the 2 to 7 ah range and most are 12 volts. 
 BB> They don't pass much current at all (milliamps usually) and 
 BB> when "dead" probably won't pass anywhere near their normal 
 BB> amount. I find that I can take a single 12 volt 6-7 ah gelcell 
 BB> and using the same charging setup I do on car batteries that I 
 BB> can hook up just 1 gelcel across the charger and get little or 
 BB> no results at all. If I did that with a car battery I would 
 BB> have fire flying all over the place and likely a blown circuit 
 BB> breaker or diode. 
One thing to bear in mind with gels is that they're spec'd at the _20-hour_ 
rate,  which means that a 7AH unit is typically looking at an optimum load of 
not more than 350 mA!
 BB> I normally put 8-10 gels in series when starting  with a fresh 
 BB> bunch of gelcell cores. Then after a few minutes I start using 
 BB> the voltmeter across each individual cell and pulling those 
 BB> with very low voltage readings. I replace those until all the 
 BB> cells are showing me a reading in the 11 to 13 volt range. 
I wonder if some of those which show you low voltage would come up if you 
left them on long enough.  Had these been sitting in a real discharged state 
for a long time?
 BB> Then I let those all charge for about 18 hours or so. I end up 
 BB> with most of those charging and hopefully ready to return to 
 BB> service. After that, I put another 8 to 10 in series and using 
 BB> the voltmeter weed out the ones with very low voltage readings. 
 BB> Once I get to that second stage I find that I am not likely to 
 BB> get any good ones no matter how long I leave them charging. I 
 BB> have only gotten my mitts on one bunch of about 40 or so 
 BB> gelcells so I don't have a lot of history to go on, but so far 
 BB> it looks like it's the way to go on rebuilding gelcells.
> I used to sell those for various applications, and there was a guy who
> wanted to use a 7 AH unit to intermittently supply short bursts of 3-4
> amps for as much as a minute at a time.  I recommended that he get
> something a little heavier,  and sure enough,  he was back after a few
> weeks and that unit he insisted on getting was fairly well cooked.
 BB> I would think so. Seems to me that you would just about need a 
 BB> car battery to supply that kind of current for even a short 
 BB> time although I have some 1000 watt UPS systems that *normally* 
 BB> use 4 gel cells of the 7 ah variety at 12 volts. In the 
 BB> *normal* configuration, they will supply a max of 5 amps for 
 BB> about 20 minutes to a computer or whatever. Since I often do 
 BB> things outside of *normal*, I am using one of them on my bbs 
 BB> system. It has 4 12 volt car batteries hooked up in parallel 
 BB> with the 4 gelcells and that will run the computer alone for 
 BB> about 3 or 4 days before it gets down to about 95 volts at 
 BB> which point the computer gives up the ghost and shuts down. 
I'd like to get a setup going here which would do that.  I thought about 
adding more capacity to this UPS I have here,  but asking them at the factory 
about it they nixed the idea,  told me it'd burn up the inverter.  They said 
"some" of their models would deal with more battery,  but it'd cost me maybe 
$1000 to find out.  I don't think I'm gonna do that,  though...   
 BB> Then I just recently paralled another bank of 8 big computer 
 BB> batteries on top of that. These are wet cells too and are 6 
 BB> volts each. They are rated at 100AH @ 8 hours each. They are 
 BB> Gould batteries and I can't get ahold of the Gould Co. to ask 
 BB> them how long those batteries would hold up under a 5 amp load 
 BB> so I don't really have the foggiest idea how long they would 
 BB> last. I got ahold of one idiot from Exide who told me that they 
 BB> would last about 20 minutes at 5 amps draw. When I told him 
 BB> that 4 7ah gelcells would do that then he admitted he didn't 
 BB> have the foggiest idea how long the big wet cells would last. 
 BB> It looks to me like that they would stand a draw of 100 amps 
 BB> for 8 hours so dividing that out for about an actual 3 amp draw 
 BB> they would last for at least 33.33333333 times 8 hours or 
 BB> something like 250 hours at which point they would be dead. 
 BB> That means about 10 days of running except that the computer 
 BB> would go dead at the point where they were drained down to 95 
 BB> volts.
Sounds good to me!
 BB> So ratio-ing that says that 95/122 (volts) would say that they 
 BB> would only be drawn down to about the 75% level during any 
 BB> given power outage. So 75% of 250 hours would be more like 
 BB> about 62.5 hours useful running time. That's about what I have 
 BB> been getting out of the 4 standard car batteries so with all 3 
 BB> banks hooked up to the unit it looks like I might be able to 
 BB> run for about 125 hours or about 5 or 6 days. 
 BB>  
 BB> Do you think my assumptions are pretty close or not?
Seems reasonable,  but as I'm pretty tired right now I'm not all that 
inclined to be critical,  so if there's something in there to be picked at 
I'll leave it for someone else...  
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