UPS External Battery

I have several UPS units. One has a connector for an external 12V battery. I am thinking of hooking up a deep discharge marine battery to the UPS. Is there any thing to watch out for? What current rating wiring should I use? The biggest UPS is 900VA. Also, can a connector mate be found or should I just solder or attach a lug to the contacts? Suggestions please.

The UPS is signaling to the PC that I should replace the battery but running the built in test says it is still viable but probably not for a long power outage. I only want the UPS to fend off power line hickups.

Reply to
BeeJ
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Yes. Many cheap UPS units are designed to run, when at maximum load, the switching transistors at the ragged edge of their peformance, or even above, knowing that the battery is going to die in a few minutes. If you put a battery tha can handle maximum load for much more time than was originally anticipated (e.g. replacing an internal 7Ah SLA with a large 100Ah flooded cell), then the transistors can easily cook themselves the first time you have an outage.

If the output is 900VA, and we assume a terminal voltage of 12.5 volts, then the current is going to be (900/12.5)*(1/efficiency). Your absolute BEST bet would be to hook up a "about the middle" load (say a few incandescent lamps) and measure the voltage and current from the actual battery, and get a good ballpark guess for the efficiency. Add a safe margin and engineer for that amount of current. My wild-ass-guess: you are unlikely to draw more than 100 amps at 12V for the 900VA unit.

A very common connector for that application is the Anderson "Power-Pole" series connector. Here's a web-page that shows them being used in an amateur radio context:

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A google-search will lead you to mail-order sites where you can get the connectors onesey-twosey.

If you really do only need "few tens of seconds", I vigorously recommend just replacing the internal battery with the same size-and-chemistry. No power-connector or pass-transistor headaches.

A guy at a local flea-market sells "dead battery" APC 600VA units for $40 bucks, and I can buy a brand-new battery at a jobber downtown for another $20. These just have a YUASA 7Ah SLA in them. The larger units often will go to a 14Ah or 25Ah battery, which will cost more.

Here is a pic of one of the APC units that I have six of now:

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(just a random image I found off the web - no relation to Kaboodle)

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NK1G - Lawrence 
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Reply to
Lawrence Statton

Could I trouble you to disclose the maker and model number of the UPS with the connector? It might then be possible to search the manufacturers archives for information on attaching an external battery, such as does the internal battery need to first be disconnected.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

That?s probably the 5 year alarm for battery replacement. Which is about how long they last on a float charge.

Measure up the battery and go to Mouser and get a CSB replacement. It's less expensive that what APC or triplite will charge you and will last just as long.

And you don't have to worry about charging a larger battery which has its own set of problems.

Cheers

Reply to
Martin Riddle

The two UPS units are: APC BX900 APC XS1500 (label on this unit says battery pack BR24BP)

Reply to
BeeJ

No external battery connector on the rear panel. Therefore, no official method of adding an external battery. Nothing in the user manual on attaching an external battery.

There's a bit of a muddle here. APC rebranded an older unit, that was labeled XS1500 as the BX1500, but still lists is at XS1500. Worse, APC also has two different XS 1500 models for the BackUPS and SmartUPS series of products. So, rather than muddle though this mess, could I trouble you to provide the full model number, or a URL with a photo of the actual unit, which should eventually lead to the user manual, which should have instructions on how to attach the external BR24BP battery pack? My guess(tm) is that you're trying to do something like this:

I couldn't find the original BR24BP manual on the APC web pile. However, I did find this destruction manual on how to break it open and tear it apart: Note that the external battery pack consists of 4ea 12V batteries, arranged in a 2x2 24V system. I've had rather bad luck with a similar arrangement in the APC SmartUPS 1400, which killed batteries (due to current hogging) at an alarming rate. Photo of some of the 30 odd units being scrapped and on the way to the recycler: Don't parallel batteries if you have other options.

Incidentally, I have a similar BackUPS XS1000 in my office. It's major claim to fame is that it kills a battery pack every 4 years. I think it's on its 3rd set of batteries now, and is probably due for another battery transplant.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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