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?
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.
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.
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
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
MARS Flight Crew http://www.mars.org.uk /
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.
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.
MARS Flight Crew http://www.mars.org.uk /
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.
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.
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.
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.
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.
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.
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
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.
- 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
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 :)
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