Modified UPS with Golf Cart Batteries

 

I've got an APC Back-Ups ES500 UPS that I had modified to use a pair
of 220AH 6V golf cart batteries instead of the 7AH battery that's
inside the UPS.

It works, but there are a few things that concern me.  It's using a
240V AC 50 amp circuit breaker between the batteries and the UPS, and
it makes a buzzing noise when it's under load.  Is this safe?  I'm not
using it right now because I don't think it's right.

I'm looking for an appropriate DC fuse and cut-off switch, but the DC
fuse is not easy to find.  Is there generally any sort of
short-protection for the batteries built into the small APC UPS? Would
it be ok to not use any fuse?

The UPS has a 300 watt inverter, but I'm thinking it may place a
larger load on the batteries.  Would a 30 or 40 amp blade-type
automotive fuse be ok for this?

I also have a larger 12 amp battery charger that I'll use to recharge
the batteries after a long power outage.  Right now I'm cutting off
the batteries and unplugging/turning off the UPS during charging.  If
I left the batteries connected and the small internal UPS charger
going while using the external charger, would it cause problems?

 



  If there is, it will be short circuit protection that is appropriate for the
7AH battery that was supplied with your unit.  Your new batteries are capable of
hundreds of short-circuit amps.  A small circuit breaker might not be capable of
interupting that much current.


Only if you like fire.


     The largest blade-type fuse that you can find would might be a good start
until you find the correct part.  (Someone here will probably have a good
suggestion)  I would consider a special high-current fuse on the jumper between
the batteries, and then a smaller (perhaps 40 amp) fuse to feed the UPS.


     Those cheap UPSs come with a pretty primitive charging circuit.  If you
want your expensive batteries to last, you will buy the proper float charger.
http://www.batterytender.com/   I would find a way to kill the battery charger in
the UPS and use the small float charger to maintain your battery.  As you
suggest, you can use a larger "dumb" charger for a bulk charge following a power
failure.

Vaughn

 

On Sat, 21 Apr 2007 17:07:21 GMT, "Vaughn Simon"


of

of

It will interrupt the 25-30 amps the inverter will draw. No problem .
Fuse the systen AT THE BATTERY with a 40 amp MaxiFuse. Code is NOT an
issue with 12 volts DC.
 

No need for ANYTHING over 40 amps, unless the charger puts out more
(unlikely)

Not likely. Worst it will do is "eliminate" the little charger.The 12
amp charger should not be an issue.

in

power

Just put a diode between the UPS and the battery - then the charger
can't put any power to the batteries.

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<clare at snyder.on.ca> wrote in message

     There are two considerations here, and (respectfully) you are missing one
of them.

1) Protecting the UPS and its wiring:   Here, you are correct, you need nothing
over 40 amps.

2) Protecting the batteries and their associated wiring:  Have you ever seen a
battery start smoking seconds after an accidental short circuit?  (Example: You
accidentally touch the + & - cables together.  They make a neat spark while
welding themselves together, then instantly turn red hot)  Here, the currents
can get very large and it takes a suitable device to interrupt that much
current.  They don't make them small.  It is impossible for fuses to protect
against every possible situation, particularly against an internal battery
short, but we do our best.  In the case of a two-battery string I have always
placed the fuse on the jumper between the two batteries.   The other "device"
that you use to protect against battery shorts is a good battery box.

Vaughn

 

On Sun, 22 Apr 2007 00:30:39 GMT, "Vaughn Simon"


You missed where I said toput the fuse AT the battery. No fuse will
protect against dropping a crowbar across the terminals. FUSE THE
CIRCUIT. Not the supply.

--
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