I have looked here and on the web. I think I am ready so much I am confusing myself. I have 4 devices that are 48v dc and pull 200w each. I am looking for battery backup if I loose power. I have four 100 amp hr batteries run in series to get to the 48v. What will run time be? my number keeps coming up low. Or will I be better off getting a AC to DC 1000w power supply. Then run it off a UPS inverter. Then I could put my 4 batteries in parallel
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Battery Run Time
- Thread starter sroka2011
- Start date
rlitman
Well-known member
You are positively better off running the DC directly. Running it through an inverter may cut your run time in half.
That being said, what is the model number of your batteries. That will make a big difference on your projected run time. You cannot expect to get the full 100 Ah of energy out of the batteries, as that number comes from a 20 hour discharge rate. You'll need to find out the discharge rate at 200 watts per jar.
That being said, what is the model number of your batteries. That will make a big difference on your projected run time. You cannot expect to get the full 100 Ah of energy out of the batteries, as that number comes from a 20 hour discharge rate. You'll need to find out the discharge rate at 200 watts per jar.
BillK
Well-known member
st,
400 watts at 48 volts is 8.33 amps. The batteries are 100 amp hours so you would have 12 hours run time. That is in a perfect world if the batteries are able to stay at the correct voltage you need for their entire 100 ah capacity.
watts=amps x voltage . . . amps= watts ÷ by volts
400 watts at 48 volts is 8.33 amps. The batteries are 100 amp hours so you would have 12 hours run time. That is in a perfect world if the batteries are able to stay at the correct voltage you need for their entire 100 ah capacity.
watts=amps x voltage . . . amps= watts ÷ by volts
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rlitman
Well-known member
He's asking for 800W, not 400W (200 x 4 = 800). That's 16.67A at 48V. That works out to 6 hours on a 100Ah of energy, however, the real run time will probably be under 4 hours, because as I mentioned above, the amp-hour rating of a battery is derived from a 20 hour run rate, and you get less energy out at higher rates. Additionally, the voltage will be under 12 V per jar for much of that run time, so the current will be higher (unless these devices are simply passive elements, such as resistive heaters).
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BillK
Well-known member
He's asking for 800W, not 400W (200 x 4 = 800). That's 16.67A at 48V.
Doh, I missed it. You are correct.
MikeF2316
Well-known member
He's asking for 800W, not 400W (200 x 4 = 800). That's 16.67A at 48V. That works out to 6 hours on a 100Ah of energy, however, the real run time will probably be under 4 hours, because as I mentioned above, the amp-hour rating of a battery is derived from a 20 hour run rate, and you get less energy out at higher rates. Additionally, the voltage will be under 12 V per jar for much of that run time, so the current will be higher (unless these devices are simply passive elements, such as resistive heaters).
I explain the run rate to people all the time, and they give me a blank stare. A 20 amp-hour battery performing up to specs will give 1 amp for 20 hours, but not 20 amps for 1 hours. Then it is considered dead, generally this is 1.75 volts per cell on a lead-acid battery. (So a 12 volt battery at 10.5 volts is considered dead.)
Plus, as mentioned, using batteries to power an inverter, then using that to power a UPS will introduce a lot of inefficiency that will seriously impact run time.
theoldwizard1
Well-known member
Any one wanting a long run time pn lead acid batteries should be looking at TRUE deep cycle batteries, like golf cart batteries. Yes, they are 6V and you would need 8 to make 48V. At 25A discharge rate (well above what the OP stated) GC2 batteries should get about 7 hrs. At 17A, you probably get about 10 hours.
8 GC2 batteries at Costco or Sams Club will cost you $700-$800. These are your best bang for the buck. If you need longer run, you will be looking at stationary/solar batteries. MUCH MORE $$$ ! Of course you could buy another string of 8 and double your run time.
8 GC2 batteries at Costco or Sams Club will cost you $700-$800. These are your best bang for the buck. If you need longer run, you will be looking at stationary/solar batteries. MUCH MORE $$$ ! Of course you could buy another string of 8 and double your run time.