Uses for Old UPSes

I have two Minuteman units I rescued from work. Both just needed batteries. I opened them up so I could get to the battery while they were plugged in and checked the charging voltage. It was something over what the battery was rated, 13 volts and a 12 volt battery, so I figured that the charging circuit was ok. The UPS worked as far as running a load when unplugged, but they had no reserve capacity so I took a chance and put batteries in them. Greg

Beware that some UPSes refuse to start without A/C voltage present. Kind of stupid, but it's reality. That could hinder their use for emergency.

12V is a very low voltage and you need big cables. Your battery can produce a lot of amps intermittently, so with it, you could run loads that are not too high on average.

For example, on 70 amps, you could run about 700 watts of power (after considering all losses). That's enough to power up the furnace and a few fluorescent lights or the TV. Maybe even a refrigerator.

Since your truck recharges the battery as it runs, the battery acts as a buffer/smoother of your alternator's output and can help produce power without frying the alternator.

i

He wants to run house equipment from 12V.

To run, say, 500 watt, he needs about 50A of current. Cannot do that well on 12 gauge. 10 gauge, maybe if the run is not too far.

i

Assume the UPS was designed to properly charge the batteries. Look up the battery manufacturer's recommended charge rate. As a practical matter, that's probably the best most people can do when the UPS specs are not available.

Well, if you happen to have a high wattage fully adjustable load (not very damn likely) and the wherewithal to fool the UPS into "thinking" that a battery is connected (with a variable supply and a diode or maybe a big 'lytic), you could plot a charge curve by measuring the current through the load and the voltage across it.

Ed

Those older Fortress units are EXCELLENT

216 volt battery pack??? I don't think so.

If you have any Best Fortress 1420s of the older model with the 4 digit display, I might be interested in purchasing them sans batteries to save on shipping if the price it right.

Pete C.

You can call APC. As for Best, I blew one Best trying to use a different battery.

Better check first if the UPS can handle a log term run of a battery. It might be that it was designed for a short term, just to give you enough time to power everything down properly. Longer runt time might cause some marginal designs to overheat.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

Not very common on a unit as small as 2kW, but very common on units in the double digit kw range. If he meant 20kW instead of 2kW, it almost certainly had a high voltage battery string. Much more efficient to have the higher voltage at much lower current to convert to the high voltage AC. On a 20kW unit that would put your battery current in the 85A range for a 2xxV battery string vs. 850A range for a 24V battery string.

Pete C.

No, quite possible and makes some design sense - they would not need a heavy output transformer in the unit boosting the voltage of a 36V or 48V battery string after converting it to a sine wave AC, as 216V would be right around the sine wave peak voltage of 120VAC. Just run the battery DC through two sets of power transistors to let through a reconstituted sine wave - one for the positive half of the output waveform, the other negative.

And it cuts the current the transistors have to pass.

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Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700 
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address:  Remove the python and the invalid, and use a net.

Sell them to FedEx? ;-)

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Cheers!
Rich
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 "Grain grows best in shit." 
   -- U.K. LeGuin

Bruce, this also sounds like a simple approach to generating 3 phase out of DC. Without the noise and weight of rotary phase converters. What are your thoughts on that?

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Quite Plausible, but when you add the caveat of reproducing 3-Phase power the engineering just got really complicated, and more than likely rather expensive. And I'm NOT a high-powered electronics drive wonk by any means, the best I could do for fixing them is look for the obviously crispy components and swap out the blown boards - or swap the crispy parts and diodes that fail a VOM test and see if that does it.

With a single phase inverter, they're just doing a push-pull on one

240V lead, relative to the center tapped neutral. When you try 3-phase, there's going to be constant voltage, current and capacitance interaction between all three sets of "hot AC" switching transistors (or Triacs, or whatever). And the load's resistive, inductive and capacitive components are all going to come into play.

The resulting inverter would need to be built rather robust, and be able to overcome drive issues with brute force where finesse won't do. Compared to that, RPC's are the KISS method. And RPC's aren't a bad way to go, if they are well balanced and have cooling air you can tuck them away in a closet.

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Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700 
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address:  Remove the python and the invalid, and use a net.

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Right. As you know, I recently made a DC -> AC inverter myself.

Yep.

You are right. I am going to redo my RPC into a 17.5 HP RPC. (two motors, 10 and 7.5 HP). Right now I have a 10 HP RPC.

Someone offered me a Semikron 6 IGBT drive, with which I could make a

3 phase inverter. That sort of made me interested. i

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Get your hands on a large, like 30kw or better, used as in "please take it out of here", three phase, online UPS from a computer room installation. As long as you can supply adequate power to the DC bus the inverter portion will happily generate your three phase power with no issues with designing and inverter or trying to synchronize three inverters or duty cycle problems. It's a DC - 3 phase AC continuous duty inverter, ready-to-go.

Pete C.

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A 30 kVa UPS would weigh approximately a ton. That's without batteries. It is beyond what I can handle.

Since it needs a system for producing DC, it would be comparable to what the UPS already has.

That means that I would have a monster that weighs a ton.

I almost bought a 15 kVa UPS though.

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No way, I put in a 30kw 3 phase UPS (Best Unity/1) and it was close to a ton with batteries. Without batteries (when I moved it across a raised floor with a pallet jack) it was far under a ton.

It has a system for producing DC, it's just setup for three phase input. Depending on how it is configured it could be quite easy to rework the input section for single phase. The more modular the design the better and you might get lucky and find three discrete DC supplies, one fed from each phase, that couldn't care less if they were actually 120 degrees apart.

That would mean you have all the clean sine wave three phase power your shop could need, uninterruptable no less, and heat for the winter.

The building I used to work in had about six monster UPSes in the basement, each feeding a 600A 208/120V 3 phase buss duct running up through the building to multiple PDUs. They had the nice 5 gal size glass cased batteries in the strings. Also had five 800KW diesel generators with paralleling switch gear and 40,000 gal of fuel supply. Redundant utility feeds as well. Place would have made a nice house if it was in a better location :)

Pete C.

Thanks for the input! I'll get out the Fluke and download the .PDF and see what I can find before I burn the place down :) I was sort of hoping to be able to replace the stock batteries but they are so insanely expensive, hacking the box for batteries I have no use for (Still in the plastic wrap and caps on. got them in a barter) Get this- Mercedes wanted $430.00 to replace my battery for P/M- Yea right, my car now has a Optima yellow in the trunk and why a factory (much smaller and lighter too) battery would be junk after two years blows my mind.

Thanks for the info and help!

Rob Fraser

Fraser Competition Engines Chicago, IL.