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| Thread ID: 55858 | 2005-03-21 06:24:00 | Sealed Lead-acid battery charging in a PC | george12 (7) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 336464 | 2005-03-21 12:57:00 | Or, a not so high tech design: elecdesign.com |
zqwerty (97) | ||
| 336465 | 2005-03-22 02:52:00 | You have shortened their life by getting the batteries hot. The cells are not totally sealed: they have rubber caps which will lift if you get too much pressure, and the gas will escape. That's the water of the "captive" electrolyte that you have lost. Adding water does not restore them. :( For maximum life, you could regulate the supply at 13.8V. That's the recommended CV value for float operation. 14.4 is OK (it's the manufacturer recommended value for deep cycling). I have two chargers (these are commercial 8A regulated supplies); one set at 14.4V, the other at 13.8 and choose depending on the state of the batteries. Of course you are working them fairly hard anyway. For lead batteries (including gel) the Ah rating is a 20 hr one ... so a 4Ah battery will give 200 mA for 20 hours. If you pull amps from each, the time to end point (10.5V) would be much shorter. The Jaycar catalogue and web site have charts of voltage versus time at various currents. Unfortunately the plots are reduced and the numbers are unreadable ;) but you will get an idea. If you let them get below 10.5 V, you will permanently damage the batteries. Switching is a problem. All the clever ideas I have come up with in a few minutes won't work.:D The ideal would be a switchmode which would both buck and boost. I don't think there is one. You could make one which would switch to double the battery voltage, then switchmode that down to 12V. Or the suggestion I made at first ... a 230V ac inverter, then a standard PSU. |
Graham L (2) | ||
| 336466 | 2005-03-22 04:57:00 | I've decided just to stick some caps in the PSU to let it run for about half a second with no power input. Then I will have a simple circuit that switches it over using a relay when the power goes out. That way the charging and running the PC will be separate and won't conflict in any way. Thanks for the help. I'm sure every one of those batteries are permanently damaged, but scooter operation had them down around 8 volts on a daily basis and they still work great, so they must just be tougher than usual. They'll do the job :) |
george12 (7) | ||
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