Modified UPS with Golf Cart Batteries

[dave]

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?

 

[Vaughn Simon]

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?

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.

Would it be ok to not use any fuse?

Only if you like fire.

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?

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.

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?

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

 

[Ecnerwal]

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.

300W inverter should only be taking 25 amps off of a 12V battery. 30 if we assume a
rather terrible efficiency of 80% (probably not far wrong for a UPS, those don't tend
to be built for efficiency, just low sales price).

I'm looking for an appropriate DC fuse and cut-off switch, but the DC
fuse is not easy to find.

Not too hard to find, at least on the internet. The local hardware store may be
another matter.

The blade type auto fuses don't suit NEC (ie, "code").

Nor do some of the other automotive-type stuff you'll see for breakers on links I'm
about to list. A DC-rated breaker is typically the simplest way to have both
overcurrent and a disconnect. There are many other suppliers, these happen to be
handy:

http://store.solar-electric.com/fuandbroupo.html

OBDC 30, or OBDC 40, either $20.75 - you could go to the 50, but it seems unlikely
that 50 amp draw at 12V (600W) is really appropriate for a 300W inverter.

http://store.solar-electric.com/cipr1.html

http://store.altenergystore.com/FusesBreakersEtc/

 

[clare at snyder.on.ca]

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.

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.

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.

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.

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.

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

 

[Vaughn Simon]

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

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

 

[clare at snyder.on.ca]

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

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.

 

[dave]

Yes, that's fine. Unsurprising that the breaker would buzz under
load, as the inverter draws more power at the peak of each half cycle.

I've tested domestic type AC circuit breakers rather extensively for
use on DC relative to my electric car work. This type of breaker
interrupts what golf cart batteries can throw at it up to about 48
volts. Above 48 volts to 72 (the highest I've tested), the
interruption is accompanied with some rather violent arcing that comes
out the arc chute. The breaker still functions just fine but I'd
replace it after a short circuit interruption. It's perfectly fine
for your 12 volt system.

Thanks for all the info. I found a DC automotive-type fuse and
installed it at the positive terminal of the series connection between
the two batteries.

I decided to keep the AC circuit breaker in addition to the fuse as a
convenient way to disconnect the batteries. I'll see how it does for
awhile, at least.

I also got a separate inverter to use instead of the UPS, since the
UPS won't operate unless it was plugged in when the power went out.

 

[asfsdpk]

Can 300 watts ups

Can 300 Watts UPS charge 30-60 Amp Battery. plz tell me about it.
i have 300 Watts UPS