I need a tempory battery back-up system, 48v, 3000Ah. The batteries being considered are 16v, 925watts/cell 15 minutes. How do I translate watts/cell into amp hours (for a layman?)
Thanks in advance DESK
925 W gives (925/16 = 57.8 A). And 15 mins is 0.25 Hrs. So you have 57.8x0.25 = 14.5 Ah
Calculating Ah in this way is approximate and you need to consider a lot of other factors like charging / discharging rates / heat / amp profile over time , etc.
But at the first glance your battery is waaaaaay small for this application.
3000Ah is better served by a generator. A typical Prius battery is about 1200Ah - so you need like 3 Prius batteries if you go that way.
Damn, I was hoping I was doing the math wrong; that’s what I was coming up with.
As for a generator, there are multiple ones on site. The people I’m working for have 8Hr @3000A of battery back-up. 1 system is being replaced. While that system is off-line, they’ll only have 7 hours. Despite the generators, they’re insisting on having 8 hours at all times.
Oh well, placating them is for my higher-ups.
deleted, incorrect
Three thousand amps!? That’s an enormous current. At 48v, that’s 144 kilowatts - which equates to 193,000 horsepower.
Yipes.
(I’m tempted to think this might actually be 3000 ma.)
Let me try that again…
I agree, if a battery can provide 925W @ 16V for 15 min, that’s a 14.5 Ah capacity.
3 of these batteries in series will provide 48V, but only at 14.5 Ah capacity.
So you need about 200 sets of 3 batteries to provide 3000 Ah at 48V.
Or thinking of it in terms of energy, 925W/15 min battery has a capacity of 925W * 0.25h = 231 Wh = 0.231 kWh. You need 3000 Ah * 48V = 144,000 Wh = 144 kWh of energy. So you need 144/0.231=623 of these batteries.
Sorry - hp equivalent above is 193, not 193,000.
If we take this as 3000 amp-hours over 8 hours, that yields a current of 375 amps, which at 48v implies 18kw (24 hp).
This page says the ‘06 Prius has a 288V 6.5Ah battery. thats’ about 1870 Wh of energy. You need 80 of these to meet the OP’s requirements.
That page has two cites and they are both broken links. The numbers are wrong.
Wikipedia says the Prius has a 4.4 kWh (4400 Wh) battery pack. Toyota agrees with that number. So does AVT.
nm
I saw your correction about 193hp, not 193,000hp. Just for the curious though, I’m talking “bank/hospital/data center back-up,” not “something to plug my PC into” back-up.
Individual 2V cells that are 2V, 3900Ah, 715LBS and are seriesed together into a 48V, 3900Ah system. Seven of them are paralleled into a redundant system that, if everything works correctly, provides 3,412.5AH (for eight hours) of back-up. Take one off line and you only have (GASP!) 2925Ah of back-up for eight hours.
But my question has been answered. Thank you all for your help.
Peace - DESK