12v 7.2mah lead cell battery

I have acquired several old UPS batteries rated at 12v 7.2ah. I broke out the multimeter and they tested out a-ok. Obviously my first
thoughts are using them for my launch system. My second thought was, how to charge them.
Is this something that could be done with a automotive charger or would I have to purchase a dedicated lead cell charger?
Ted Novak TRA#5512 IEAS#75
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IN GENERAL, an automotive trickle charger set on the trickle setting (not 'boost' or anything else) will work. Charging at a very slight charge at a constant voltage is okay for these.
David Erbas-White
P.S. In general because some systems will try and 'force' a certain current, raising the voltage too high. If you connect it up and measure the voltage, it should be around 14.0 VDC. If so, you're probably okay.
tdstr wrote:

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David Erbas-White wrote:

That's exactly what the guy told me at Batteries Plus. Basically he told me that I would make certain that the amperage would be low. Apparently 2.7ah would be ideal.
Ted Novak TRA#5512 IEAS#75
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writes:

I assume the subject is a typo, and that your battery is 7.2 AH, not 7.2 mah. If so, 2.7A (not AH) is too high a charge current. The rule of thumb is c/10 for the charge current, and c/100 for trickle charge current. For your 7.2 AH battery that would be 720ma and 72ma respectively. These numbers are much smaller than you're going to get out of an automotive battery charger.
You said you had a bunch of these batteries. How many in a bunch? Something like 3-5 of them in parallel would give you a battery pack that you could safely charge with the very low setting (2A) on an automotive charger.
And here's a trick I use with various battery chargers. I get one of those plug in 24 hour lamp timers that has the little removable tabs used to set the on and off times. For general charging, I remove the ON plug completely, and just set the off at 12:00. Then I dial the time setting so that the appropriate amount of time is between where I set it and the 12:00 OFF tab. Flip the little tab to ON, and it automatically will shut off and stay off at the programmed time.
Another trick is to use the same timer with both tabs to set the shortest possible ON time every day. [make sure it's ON then OFF, and not OFF then ON!] That gives you something on the order of 15-30 minutes of charge each day, enough to keep a battery form draining itself down over a period of non-use. This turns a regular charger into a trickle charger.
One cute trick I picked up years ago (from a DEC notes file IIRC) is to connect a battery charger to the light on the garage door opener, and use it at the LOW setting on your lawn tractor (or rocket launcher) battery. Every time you open and close the garage door, you get 5 minutes of charge to keep the battery fresh during the winter.
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Bob Kaplow wrote:

Yes, a typo that I noticed about 1/1000000 of a second after I hit send :)

Looks like I'll have a total of four. I could have decided to keep all 16 of them but just hauling them would've killed me ;/

Actually my dad taught me the trick years ago and thankfully, you helped jar my memory.

PDP11 faq :)
Ted Novak TRA#5512 IEAS#75
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kaplow snipped-for-privacy@encompasserve.org.mars (Bob Kaplow) wrote in writes:

One warning about this;a company I used to work for had a costly FIRE started while charging banks of SLAs. Something to keep in mind.
Make sure you use fuses and have a working smoke detector.
--
Jim Yanik
jyanik
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Jim Yanik wrote:

I have three of these cells in parallel and simply take them out of the tupperware container and charge separately.
Kurt
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Don't use a car charger for a sealed lead/acid gel battery. You need to limit the current and a constant-ish voltage charger isn't good enough. Something like this is ideal
http://www.mascot.no/pdf/9640.pdf
Chris
--
Chris Eilbeck
MARS Flight Crew http://www.mars.org.uk /
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Chris Eilbeck wrote:

Thanks for the link Chris. It looks like that charger would be about perfect for me except for one thing...I didn't see anything pertaining to US power specs :)
But it did give me aprox charge values and that info is pretty handy.
Ted Novak TRA#5512 IEAS#75
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The 9641 is the 120V AC version for use in the US, says at the top of the sheet. It's UL approved too. These things are usually just based around one chip so if you can grab something similar, that'll probably work really well for you.
Chris
--
Chris Eilbeck
MARS Flight Crew http://www.mars.org.uk /
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wrote:

UPS's that use them are often tossed or (hopefully) traded in. See if you can find one someone doesn't want and use that to charge it. Also a low current charger that is used for keeping boat batteries charged when the boat isn't in use are good for them.
Phil
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The ones that I've gotten from hobby stores have little block transformers (the AC power supplies that come with small consumer electronics, but with alligator clips instead of coax plugs) for chargers. They act as trickle chargers. Someone else can probably tell you the right size to get.
Roy nar12605

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tdstr wrote:

I charge mine with a small wall-wart battery charger from Axe Man. 300ma on charge, 100ma on float (it has 3 LEDs for power on, charge and float). It switches to float based on the battery voltage, it appears.
Any battery charger that specificly says it will charge sealed lead-acid batteries (gell and AGM [advanced glass matt]) will work. You can't charge a SLA battery at more than a small percentage of it's capacity (1-2% as I recall) before bubbles in the gel will form, at which point the battery capacity begins to degrade and short, at which time the battery charger will dump lots of current into the battery which will heat up and swell up.
I found The Battery FAQ was a good place to start to learn about batteries.
Glen Overby
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Glen Overby wrote:

I completely forgot about Ax Man! And I just so happen to live within 3 miles of Ax Man.
Before xmas shopping this Friday I'll stop by Ax Man and look for that charger. Any other physical details you could offer about this charger? As you already know, there's a good chance that Ax Man would probably have a 100 different chargers to choose from.
Ted Novak TRA#5512 IEAS#75
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tdstr wrote:

That would be a dangerous place for me to live!
For those of you in Chicago, this place has the same stuff as American Science Surplus but with a better name ;-)

Sorry - I forgot to look up the name on it last night.
It's approximately 3" x 4" x 2" (width, height, thick) and has an AC plug prongs on the bottom. It has 3 LEDs (Yellow, Green, Red) along the top to indicate it's state.
The cord has a weird connector on it, but I chop that off and put an Anderson Powerpole on it, since all my ham radio gear uses that.
Glen
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Glen Overby wrote:

Don't I know it. My neighbor and I try to keep our trips there down to two, maybe three times monthly.

And Ax Man has a sense of humor :)

That's good enough description for me. As a matter of fact, I think I know exactly which charger you speak of. Thanx!
Ted Novak TRA#5512 IEAS#75
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Glen Overby wrote:

Just got back from Ax Man and I scored a 12v 350mah charger with the three led's. It's a bit smaller than the one you have; 3*1.5*1.5". Got the last one for $3.95 so I'm happy about the deal. I'll have to cut the connector off and put on some clips. No biggie.
I also scored some other stuff(what a surprise). I don't know what is with Ax Man but *everytime* I leave that place I end up spending more that I wanted :)
Before I forget, they had some kick butt 2" and 4" thick walled cardboard tubes made by Unite. This isn't the typical cheap cardboard mailer tubes that you usually see and these tubes would work VERY well for airframes. Better than LOC tubes for sure.
Ted Novak TRA#5512 IEAS#75
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I acquired several a few years back from work. I don't know how they were used, in a UPS probably. They were right there in the junk pile. But they were all perfectly good and only one needed a charge. And they work fantastic for my relay launcher
I bought a charger from Batteries Plus specifically for sealed lead acid batteries. $22. It's the small black box type with alligator clips as previously mentioned.
tdstr wrote:

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I just finished building a heavy duty fused 30 amp relay launcher utilizing my 12v 7.2mah lead cell battery. Just got done testing it out with a variety of ignitors and I'm impressed with the results.
The results:
- one AT Firstfire ignitor = instant ignition - three AT Firstfire ignitors = instant ignition of all ignitors - one 2" piece of .032(I think) nichrome = vaporized! - one AT Copperhead = instant ignition - three Copperheads = instant ignition! - one Novak 2000 ignitor (cat5, IM pyrogen nichrome wrap) = instant ignition
Now for the big test....THREE Novak 2000 ignitors = ALL three lit immediately!
I modified a the original UPS wiring harness to hook up 2 of these batteries in parallel but I don't think I'll need it :)
Ted Novak TRA#5512 IEAS#75
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the notorious t-e-d wrote:

I have three of those in parallel and am quite happy with it. Used 10Ga. wire.
Kurt
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