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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
If you can't keep the batteries outside, google 'marine regulations for battery enclosures on boats', or something similar. Lloyd's Rules should provide suitable guidance.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I would build a battery box for his local outside enviroment,put 10 car batteries in parallel, allofthe same group size. the inlcude a charger, and then your SMPS can be inside home/business with the server.
thats just my crazy oppinion.
Sealed lead acids are better for "living" or "occupied' spaces.
Registered Member #1262
Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451
I've already taken safety, original application, etc into account choosing car batteries.
The fact is they should not gas during normal operation. They'll be sitting in a 20x30 well ventilated room in my basement, and recharged at a fairly slow rate, never seeing the "magical" 13.8V.
Considering the marginal cost increase per amp hour going from car batteries at a junk yard to new marine batteries, I'm better off simply buying more car batteries and discharging them less deeply, by around at least a factor of five.
I'm mostly interested in picking the best group, I'm highly leaning towards 31 at 100+ Ah (probably a good bit higher at low discharge rates seen in my application).
Even if I never take them past 50% depletion, you simply can't beat $0.50/amp hour with a new deep cycle.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Backyard Skunkworks wrote ...
Considering the marginal cost increase per amp hour going from car batteries at a junk yard to new marine batteries, I'm better off simply buying more car batteries and discharging them less deeply, by around at least a factor of five.
Even if I never take them past 50% depletion, you simply can't beat $0.50/amp hour with a new deep cycle.
I totally agree.. as for group size im going to have to research that abit... my memory is fuzzy at the moment.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Ash Small wrote ...
Patrick wrote ...
If you regulate with diode drops from 12.6V down to 3.3V, at 30 Amps, you will waste (12.6 -3.3) = 9.3V x 30A = 279 watts wasted for 99 watts passed, thats 26% efficient.
.
I think you've missed something here Patrick. You regulate the voltage with a string of capacitors (capacitive divider), the diodes are just to parallel the capacitors.
similar circuits (with diodes) are used to charge 6V batteries (from a 6V supply) while they are connected in series for 24V, but without the capacitors.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Anders M. wrote ...
. Capacitive dividers do not work for DC.
Yep. You're right. I've been puzzling over it all morning, but I might construct a circuit to see what happens. I don't think any current will flow, though.
EDIT: FWIW, I think it could be done with strings of capacitors across an H-bridge, with bridge rectifiers across each capacitor. Not sure how efficient it would be though (switching losses, etc.)
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
One thing to keep in mind is that normal car batteries do not like being 'deep discharged' and even running them down to 11v will do significant damage to them. They are sized to give enough current to start the engine, by the time you have a battery big enough to run a starter motor you already have plenty of capacity to handle the small load the car has when the engine is not running (and the alternator is not charging).
That said, if you can get them for $25 they are probably still cheaper than buying proper gell cells.
Bjorn does have a good point, you are going to need to have enough batteries to get 300v or so to keep the PSUs happy, because the way the AC-DC conversion inside the power supply is most likely configured to step the voltage up to a 330v DC bus.
Also, how do you plan to charge this huge bank of mismatched cells? I would not recommend just hooking 300v up to the whole series bank, because some batteries will overcharge and some will under charge due to the varying capacities/ages of the batteries.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
So you're planning on using old batteries of the wrong type simply because they're cheap. Sounds like false economy to me. You would be much better off investing in a new deep cycle battery, with a small genny for extended operation.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
2Spoons wrote ...
So you're planning on using old batteries of the wrong type simply because they're cheap. Sounds like false economy to me. You would be much better off investing in a new deep cycle battery, with a small genny for extended operation.
If he uses 10 car batteries in parallel, he can discharge them more shallow then a single deep discharge battery.
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Best car batteries for server backup?
