Backyard Aquaponics
A place to discuss aquaponics

the best solution would be a more advanced electronic charger with float.
That way it will charge when they are down, and keep the batteries on float the rest of the time. Floating means the batteries are kept at the correct voltage not to cause gassing and so can be left permanently on the charger.

Your UPS charger should be fine once the bank of batteries is charged.
It may not cope with the charge requirements of "flat" batteries of that capacity.
As Privateer said, probably better to use the car charger first, then when it's charged, plug the UPS in

I couldnt agree with this more. People seriously underestimate the power that is contained in these batteries. When i was installing them, you were only allowed to use insulated tools. I was talking to a guy who dropped an uninsulated spanner across a 48v bus bar (actually @ 54v float). Big bang and whole lot of carbon where the spanner hit. No spanner. The fault current on the system was over 1,000,000A. Another guy had a massive burn on his wedding ring finger which he was lucky to have. I have seen terminals disappear and a whole lot of carbon on the battery on much smaller ones than pictured in this thread!

Keep your wits about you aquanoob, and find some insulation. A good one is some heat shrink and just cut of the section that the battery connects to it. Awesome score though man!

+1
Yeah short circuit current is effectively infinite.
Will try and dig up the story about the plasma ball...
Insulate everything !

http://www.evdl.org/pages/plasmaboy.html

Not sure about the authenticity by the way...

Maybe something like this ?




This one isn't so fun...

HV stuff there though.. but fault current of big batteries is the same or probably even greater than high voltage lines...

The second one is why i refuse to rack in HV before i have done my HV switching course

Below is a nice example of battery current available

well, haven't yet got zapped when touching the bus bars yet. Though i'm wearing rubber soled shoes and only touching one terminal bus bar at a time just to unscrew them to get the cell loose and test it.

I'll see about getting a suitable charger next week.

I agree, the 1.5A UPS charger probably is sufficient to slow charge or maintain a float charge once the cells have been fully charged initially.

Thanks for all the tips, and safety warnings.

Hmm, UPS was setup for 2 x 12V batt cells, with input current of max 1.5A.

If I run the UPS charging leads in parallel (so voltage is still 12V), would I get double the max charge current to 3A?

Rubber soled shoes wont do anything to stop you getting a zap unless you have earthed one side of the batteries. If you have sweat on your arms and you brush against 2 of the bus bars at the same time you will get a zap. 54v doesnt tickle but it most likely wont kill you.

You really need to try and reverse engineer it to work out what current you will get. It could be that it was 0.75A/battery giving you your 1.5 A. You will probably find the 2 cables are joined together at one end.

You will never get zapped from anything below about 40V. Skin resistance is quite high and to overcome that you need a higher voltage. you can touch the bus bars however you like with your hands. The issue is when you short the batteries with something conductive, and with a basically INFINITE current source arc flashes can be produced and the conductor can be vaporised. If you are close to that when it happens, you get very badly injured.

Having the multimeter set to the wrong setting, or even just using one that isn't rated for CATIII (?) can also start off the arc flash process.

I don't think you can do that. unless the UPS has two separate isolated 24v outputs, which I very much doubt. It will have just 24v output, and one of the wires is just to connect the 2 batteries together in series. That connecting wire might be seperate (directly from one battery to the other) or it might go back to the PCB and so it might LOOK like 2 separate wires...
That means that if you connect the outputs in parallel like you said, you might actually be putting a direct short across the batteries... bad (see above)

Please just use small 12v batteries for testing with the UPS. Don't mess around with the big suckers until you have sorted out the charger, you know it works for 12V etc.

I have blown the ends of multimeter probes and blown holes in aluminium casings while testing electronics attached to ordinary car batteries. Also make sure you wear safety goggles, bits of hot molten metal tend to go flying about when are shorting things...

If your skin is dry



Hopefully the fuse will stop this! CATII should be sufficient for 54v. As per:

http://zone.ni.com/devzone/cda/tut/p/id/5019

It should be fine.
It's the fuses capability to interrupt current without arcing. Thats why the CATIII Fluke fuses have fiberglass wound bodies, instead of the normal glass ones.. They can safely interrupt much higher currents.