Electronics > Power/Renewable Energy/EV's

Precharging new 12V lead acid gel cells for use in series

(1/2) > >>

5065AGuru:
Hi,

I just bought two new lead acid gel cells 12V 26AH to install into an HP 5089A backup power source.
The manual states " each battery should be pre-charged for 24 hours from a DC source set at 15.30 +- .01V and current limited to 2.0A +-.1A. "
Not that I don't trust HP but isn't that a bit high??

Any comments welcome.

Cheers,

Corby

thm_w:
It is high. It seems they are just worried about balancing the cells.
If you have a decent 12V battery charger I would hook them up to that in parallel and charge as normal.

If you want the thing to last forever you could replace with lifepo4.

mtwieg:
I'm guessing this is meant to be an equalization charge. But 24 hours is a very long time for an equalization charge (6-8 hours is more typical). I would not leave them unsupervised for so long, especially with sealed batteries.

edpalmer42:

--- Quote from: 5065AGuru on July 31, 2024, 11:18:40 pm ---I just bought two new lead acid gel cells 12V 26AH to install into an HP 5089A backup power source.
The manual states " each battery should be pre-charged for 24 hours from a DC source set at 15.30 +- .01V and current limited to 2.0A +-.1A. "
Not that I don't trust HP but isn't that a bit high??

--- End quote ---

I wouldn't say that's a bit high, I'd say it's ridiculously high!  A voltage that high will damage and/or reduce the life of any modern battery.

I had to check the manual to be sure and they do specify sealed lead-acid batteries.  I was expecting to see flooded wet cells since 15V3 could be considered an equalize charge.  It's almost like they converted the unit to sealed batteries and forgot to update the voltage.

Anyway, you should completely ignore that voltage.  Most sealed batteries these days are AGM batteries that specify a cycle-charge voltage in the range of 14V5 and a float voltage range of 13V6 to 13V8.  Most batteries actually print their desired voltages on the side.  I'm not sure it's necessary, but if you want, put the batteries in parallel and give them an overnight charge at 14V5.

You should also check all the other adjustments.  If I read the manual correctly, it specified an output voltage of 28V2 or 14V1 per battery.  That will age the batteries unnecessarily.  This is a float voltage application so the voltage should be reduced to an appropriate voltage, typically around 27V6.  Higher temperatures require a lower voltage setting so you should tend toward the low end of the acceptable voltage range.  You might want to adjust any alarm or cutout voltages to match the new float voltage.

The lower voltage may reduce the backup time.  If that's important, you can adjust the voltages higher, but at the expense of battery life.  You may also find that the batteries outgas more which might cause corrosion in the circuitry and could require more ventilation to clear out the hydrogen gas.  I've seen discussion on Time-Nuts about traces being eaten off the board by battery outgassing, but that was from batteries internal to the unit.

Ed

ConKbot:
If it's actually a gel cell and not AGM, then yeah, a "gassing" charge to balance the cells is generally a bad idea. AGM at least has a chance to get the gas out of the electrolyte. A proper gel cell doesn't and you can end up with gas bubbles holding the gelled electrolyte anyway from the plates.

Navigation

[0] Message Index

[#] Next page