Battery discharge time

Hello, I have had the fortune (Or the misfortune, if you ask my wife) of inheriting some sealed lead-acid batteries from a computer room that was dismantled. The batteries are made by C&D Technologies and are model Liberty 1000 Series LS 2-600, made in June 2001 and put in production in 2002.

Each battery (I have 8 of them) consists of two 2.17v cells, each of which is rated at 600Ah. My plan is to use a UPS that is defunct because of its battery (APC 1400) to keep six of these batteries connected in series charged at all times. Six batteries with two compartments would yield 24v. I would then tap the 24v to power a DC-DC PC power supply and some lights to power my house.

Eliminating the lights from the equation, assuming that my PC uses about 150 watts when connected to 110vac and that the PC-PC power supply has the same efficiency of the current PC power supply, how much backup can I expect out of these batteries? I have calculated

150w/24v=6A, and that my batteries will have 600Ah@24v, I should have about 100 hours. Is that correct?

Also, assuming that the batteries have been taken care of, how long of a life can I expect from them? The batteries are in my garage and the temperature will reach about 40F during Winter. Is this really bad for these batteries?

Finally, should I use a relay to disconnect the batteries from the UPS during a power failure, or should I go with a circuit?

If anyone has done something like this before, I'd be interested in knowing some details, too.

Thanks, Ross.

Reply to
rnaheed
Loading thread data ...

assuming you have usable voltage remaining at the bottom of discharge cycle.

my UPS MFR recommends replacement after 5 years.

The batteries are in my garage and the

it does not seem excessively cold to me. it would be best to check the makers recomendation.

you mean the charging supply? probably not needed... it can "float"

i have my feet on a similar system. two 12V deep cycle battery in parallel being charged by a tripp lite 200W inverter. a low cost 1000W inverter is handy if i need serious power.

Reply to
TimPerry

You are getting them for free. I would ASSUME that they are being replaced for one of several reasons. Age, or testing showed bad cells. Before construction I suggest you buy or build a battery test bench and test every cell. Loose all that are not close to spec. Then you can decide if your idea is plausable.

I am doing a demo of a building. The owner showed me a bank of batteries then asked me what they were worth. I told him since they were all low on fluid, and corrosion was eveident on most of the terminals, SCRAP. I will not even test them. They have been sitting in a unconditioned space for most of an Arizona summer.

The batteries are in my garage and the

With proper electrolite in the cells probably ok.

Relays take time and cause spikes. I suggest that you read on line about "active" and "passive" UPS's. The you will be able to make that decision. I personally do not like passive/switching UPS's. I am willing to pay the extra IMO, for the "better" active units.

Reply to
SQLit

Probably not. They're lead cadmium, intended to be used in high current, short duration discharge. You could check the manufacturer's discharge curves to try to get some form of baseline estimate.

formatting link
Fudge factoring in the 4 year age of the batteries of unknown condition belongs to the mystic arts.

I think you'd be better off building a circuit to test the discharge time. Use a comparator -> transistor ->2 relays, one DPDT and one SPST heavy duty. Wire the test load (6A) to the battery through separate wiring and the heavy duty relay contact. Connect an analog clock to one of the DPDT the relay points, and Vin to the comparator through the other. Use a momentary switch to energize the relay. It energizes and stays energized until Vbatt (Vin) drops below Vref. When that happens, the relay drops out, disconnecting the load, the clock and the comparator circuit. The clock records the time. To make it entirely hands off, you need an analog clock with a calendar, otherwise you need to check it once a day.

Not if you maintain the charge properly. It shouldn't be stored more than 3 months without being re-charged.

I wonder if the duty cycle of the UPS is more important than how you disconnect. Seems to me that the UPS should already have circuitry to stop powering the load when the Vbatt drops to some particular level. But with these mosnsters (600 ah), the on time for the UPS might cook it. A small ups using say 7 aH batteries is self-limiting - it'll run for some relatively brief time before the battery is exhausted. With the big guys giving essentially unlimited time, there is no (relatively brief) self-limiting.

One other point - you would need to make sure that your UPS charging circuit properly charges these batteries. If you did run them for an extended period, they might want far more charging current/duration than the UPS can provide. Also, the charging voltage levels might be different.

Ed

Reply to
ehsjr

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.