Semi-OT: Deep-cycle Lead Acid UPS Batteries for home power

Nice score!

As big an Ah charger you're willing to buy with adjustable voltage outputs. Start at 60-80A, $400 and up.

Could get away with an adjustable PSU and regulate manually, but not worth the hassle for what you'd save.

Note UPS batts aren't really designed for regular deep discharge, but they may still serve nicely for a few years.

What is each unit's capacity in AH, at the 20-hour discharge rate?

Ideally you'd load test to benchmark that now, so as they wear out you can track their SoH.

Yea, I was stoked when I got them. The racks really make everything fit together very well, and I can actually roll the whole thing around the garage, despite the weight.

Unfortunately, I haven't a clue what their capacity is; everything I know is printed on the label.

I didn't really expect too much out of them; just that if they could run our data center with dozens of 400-1000 watt servers for 25 minutes then it should be able to run the house for a couple hours. To start, I'll probably just run my server rack (another freebie from an upgrade, 3 x 300 watt servers) so that I don't lose my network when the power goes out and expand it's uses to lights and small electronics from there.

I do need to figure out the pack capacity though - based on the info displayed on the sticker, is there a formula to figure out how to convert from "284W/cell 15min" to Amp-hours/kilowatt-hours?

Thanks!

~Jon

fireyice01 said:

Unfortunately, I haven't a clue what their capacity is; everything I know is printed on the label.

I didn't really expect too much out of them; just that if they could run our data center with dozens of 400-1000 watt servers for 25 minutes then it should be able to run the house for a couple hours...

I do need to figure out the pack capacity though - based on the info displayed on the sticker, is there a formula to figure out how to convert from "284W/cell 15min" to Amp-hours/kilowatt-hours?

Click to expand...

Well, the label says 284 W/cell for 15 minutes, which with 6 cells/battery would be 142 amps @ 12V for a quarter of an hour, or 35.5 amp-hours per battery at a 4C discharge rate. That's 284 W/cell * 6 cells *0.25 hours = 0.426 kWh each. The set of 72 of them should then deliver 123 kW for 15 minutes (and half that for half an hour).

boekel said:

that's not so difficult to find... 70AH / 8hr

https://www.sure-power.com/wp-content/uploads/2014/07/DataSafe HX.pdf

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Yes, at an 8-hour discharge rate (C/8) they're 70 Ah each... as expected, much higher than the 4C rate. The 20-hour (C/20) capacity would presumably be even better.

At this slow rate, energy capacity is nominally 70 Ah * 12 V = 0.840 kWh each, and the average discharge power over 8 hours would be about 100 W each. That's 7,200 W for the whole bank to power the house, which is a lot for a house... good, because my guess is that you don't really want to discharge to 1.75 V/cell if you can avoid it.

That's 60kwh of energy.

One of the things I've been thinking of doing is setting up some old car batteries as fast-charge station for an EV. Trickle-charge them all day long at whatever rate, but if I pull in and want to juice up quick, well, they're lead acid starter batteries, I could yank power out of them fast.

And blah blah, they'd be starter batteries and not ready for deep discharge, but, a single starter battery can put out 10,000 watts. A rack of 20 or 30 will certainly be able to fast charge without straining them much at all.

If you do go to sell them, remember the scrapper principle of not turning a table into toothpicks. Items have the most value the more you preserve their complexity.

That is... if you can sell them as batteries, you'll get the highest price.

If you can only sell them as scrap, you'll get a lower price.

And one thing I found when selling batteries, more than any other scrapyard material, prices varied. You want to dump steel or aluminum at a scrapyard, you can call around but they'll all be pretty close.

I called probably 10 places the last time I took batteries in, prices varied by 500%, and that one that was 500% was double the next closest. I almost didn't even call them to find out their price that day, because I thought it was starting to be diminishing returns on making more calls.

If you're looking at ~$0.33/lb, and you've got something like 6000 lbs no? That's $2,000 of scrap. Make lots of phone calls, and tell them you're bringing in 6000lbs and shopping for the best rates. They'll give you better rates.

I really need better suggestions of how to keep these things charged/balanced until such a time that I can afford the solar/wind charge controller + inverter equipment to take advantage of these.

Click to expand...

Good news! You're already doing it!

If you keep them all in parallel they'll all stay balanced. If you keep a charger on them, they'll all stay topped up and not sulfate.

If you have some bad cells in there, they may get hot (the charger will be dumping all it's energy into a high-self-discharging cell to keep it maxed out, making the cell hot). Those ones are probably junk, so disconnect any that get hot and keep the others topped up.

Done.