There are significant numbers of large UPS that now don't have transformers in the input or output these run with a 800v battery centre taped and connected to Neutral.... and they hurt if you catch hold of them wrong !!! Steve -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Dwayne Reid Sent: 03 May 2009 20:39 To: Microcontroller discussion list - Public. Subject: Re: [EE] Dry vs Wet Cell Lead Acid Battery Charging At 01:06 PM 5/2/2009, Hasan A. Khan wrote: >The concern >about deep cycle issues is still there since the batteries will be >discharged to about 80% of full charge atleast twice a weak. Given that >the batteries are well taken care of otherwise, will they last two years >with that frequency of deep discharge? I think the batteries will fail fairly quickly. You are far better off adding more battery capacity so that the batteries don't discharge so deeply. You say the batteries that you are using are quite inexpensive - add 3 or 4 times as many as you have now (go from 2 to 6 or 8 batteries) and discharge down to 75% instead of 20%. >Also I was not aware of the fact that 220V can appear on the battery >terminals. I don't understand how that can happen. Its the battery charge circuit that is the problem here. You will notice that the UPS doesn't weigh very much with the batteries removed. That's because there isn't an isolation transformer inside - they are using a simple off-line convertor without isolation for battery charging. I should clarify that: *MOST* UPSs don't include isolation transformers. Certainly none of the inexpensive consumer units that I've had apart have isolation. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist