[time-nuts] OT Gel Cell question

Ed Palmer ed_palmer at sasktel.net
Mon Jul 28 23:31:41 EDT 2014

I talked about this earlier today, but my message disappeared along with 
a second message.  Neither made it to the list at all.  So out of three 
messages sent, so far only one made it to the list.  Let's see if this 
one makes it.

All UPSs have a problem when trying to figure out what float voltage to 
use since the correct voltage varies with temperature, amongst other 
factors.  Some UPSs use a low-tech way to avoid the problem. They use a 
standard current-limited constant-voltage charger, but after float 
charging the battery for a couple of days they disconnect the charger.  
Too simple!  They then monitor the battery and recharge as necessary.  
This simple trick can double the life of the battery because it 
eliminates the continuous overcharging that uses up the very limited 
amount of water in the cell.


On 7/28/2014 7:03 PM, Brian, WA1ZMS wrote:
> At the risk of adding fuel to the fire, I'd like to chime in and then will
> go quiet.
> Based on my first-hand day-job experience:
> The consumer UPS units I have seen seem to run the float-voltage on Gel Cells
> at the very high-end of the cell's spec.  The goal appears to be to get the
> battery back to full terminal voltage and do it fast. That way the next AC mains drop out can utilize the full capacity of the Gel Cells.  The long term downside is that the cell would rather float at about a volt less or so and thus the life of the cells are reduced rather sharply.  Great for the UPS vendors; they get to sell replacement cells!
> If one enters the 10kW and up category the game changes and the UPS vendors
> take much care to use a multi-stage charger system to get bulk charge into the
> cells, but not to float or "top off charge" the cells too much.
> Enter the modern AGM-I and AGM-II cells and it becomes a grey area that I am
> not well educated about.  I asked for hard data from the battery vendors, but
> the answers were mixed at best.
> Blunt answer I see is:
> Do not treat flooded lead acid the same as Gel nor as AGM-I nor AGM-II.
> And ALWAYS use temp sensors for best performance!
> My 2 cents in the RF/Telecom World.
> -Brian, WA1ZMS
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of paul swed
> Sent: Monday, July 28, 2014 8:17 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] OT Gel Cell question
> Elio
> Oh man I have seen the amp hour magic also.
> Thought maybe I was just getting older batteries. We have major home chains
> in the US that batteries sit around for quite some time as measured by the
> dust on them. So I was thinking that was the case.
> Regards
> Paul.
> On Mon, Jul 28, 2014 at 6:50 PM, Elio Corbolante <eliocor at gmail.com> wrote:
>> In my previous work I was developing UPSs: I can confirm that in the
>> last years the quality of the typical gel batteries has declined.
>> What once was 7Ah batteries now are sold as 9Ah ones!
>> And 5-6Ah ones are sold as 7Ah... :(
>> One of the best way to identify the "quality" of sealed batteries is
>> to weigh them: the heaviest have the highest capacity (and in general
>> are also the best because the producer didn't spare on materials).
>> _       Elio Corbolante.

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