Re: Batteries in Power Supply

Kevin,

What do the UPS people do? The ones I have taken apart all used
sealed Lead-Acid. I'm presuming that the batteries would only be
charged when the CNC is on so it should be a reasonable
charge/discharge cycle. With this type of supply I would be using
forced cooling which should dissipate any gases.

Bernard

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Kevin P. Martin"
<kpmartin@t...> wrote:

> Whether this works depends on part on what type of batteries they

are (you

> didn't mention).
> NiCd and NiMH batteries turn overcharging into heat, possibly

causing the

> batteries to explode.
> Lead-Acid batteries turn overcharging into hydrogen and oxygen

possibly causing

> the air in and around the batteries to explode.
>
> The "slow" NiCd and NiMH chargers prevent battery explosions by

limiting the

> charge current, which is why they take so long to charge.
> The "fast" chargers do one of two things: The use custom battery

packs which

> contain a thermal sensor (e.g. Makita cordless power tool

batteries) or they

> look for a specific blip in the cell voltage as the cell reaches

full charge.

> For NiMH batteries, once the blip is reached, the batteries

continue to generate

> some heat internally *even when you remove the charging current*
>
> You could adjust your input voltage to use voltage-limiting to avoid
> overcharging the cells, but it is not clear whether the cells

will "learn" their

> new customary charge level and still be subject to occasional

overcharging (say,

> when your house line voltage goes 2% higher for some reason).
> -Kevin Martin