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Battery backup - chemistry

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Full Member level 6
Aug 18, 2012
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The following post is similar to what I'm trying to accomplish. I was going to resurrect the thread, however a pop-up message suggested I start a fresh thread because the original thread is so old.

Design a battery powered uninterruptible power supply 12V, 0.4A

Load is normally powered via a 120Vac to 12Vdc power supply, however the 120Vac will drop out from time to time for up to 2 hours. Outage is unpredictable, but will likely occur once every 5-10 days, but could be as infrequent as 6 months.

Battery technology has progressed since the original thread was posted, I'm not sure lead-acid is still the recommended technology for this application?

  1. So what battery technology would you recommend for this application?
    [*]Recommended circuits for the power switch-over?

For my backup power system (in 1999), I chose lead-acid golf cart batteries. They're designed to take abuse.

* If you wish to spend more on AGL (Absorbed glass mat) lead-acid, that is more robust than plain lead-acid.

* Although newer types (ex., lithium) have emerged, these require extra care. They have higher energy density per cubic inch. A mistake with these types could be expensive. Li-ion type is in the news due to occasionally exploding and causing fires.

* Gel cells are great because they are suited for indoor use. You can turn them upside down. They don't leak. However you must not charge them at too high a rate, because bubbles can develop on the plates. Once formed, the bubbles do not go away. The battery's performance drops.

I inherited an ailing UPS (Radio Shack). Its batteries were 4 gel cells. One was bad. I went to a motorcycle shop and purchased a small 6V lead acid battery. It worked okay with the remaining 3. However I had to be careful not to tilt or jostle the unit.

for a storage capacity of 10 Watt hrs at 12V perhaps you can run at 11.1V with three 3.7V Lipo Cells for short durations or perhaps 4 cells with an LDO wired in parallel.

But I might consider running off a central car battery distributed like phone wire to any peripheral or emergency light using the unused Line 2 pair of wires if that is avail.

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