Author Topic: higher charging voltage from 350 UPS  (Read 2412 times)

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Harold in CR

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higher charging voltage from 350 UPS
« on: November 01, 2015, 09:45:37 AM »

 I have a 350W APC UPS and use a small bank of LiFePO4 3.2V Nominal batteries with it, instead of Lead batteries.

 I'm about to replace it with another bank of LiMn02 3.8V nominal voltage. This will increase the voltage needed to charge the battery from 13.5 or so, to 17.5 or so. The bank will be 1980 Whr, but, I will seldom pull it down much over 1000Whr. It feeds my laptop and modem for now. Trying to stop lightning and power surges from outages is where I am headed, as soon as I get the axial flux alternator finished and installed in the Lenz2 VAWT.

 How can I check the output of the charger inside the UPS, to see if it can handle this chore?

 The specs I found do not state the charge voltage of the internal charger, only how long it takes to charge >15 seconds for the small SLA typical UPS battery.

dnix71

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Re: higher charging voltage from 350 UPS
« Reply #1 on: November 01, 2015, 10:28:48 AM »
Lithium cells are quickly damaged by overcharging. The max voltage I see for LiMNO4 is 4.5. The APC will overcharge a 3 cell stack and undercharge a 4 cell stack. If you had a 3C charger for LiMNO4 then you could charge 3 cells in series and use them to power the APC. Otherwise this won't work.

Harold in CR

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Re: higher charging voltage from 350 UPS
« Reply #2 on: November 01, 2015, 12:19:13 PM »

 As usual, my lack of info.  ::)

  I have 4 modules of 4S1P Nissan leaf battery cells. All are wired as 12v (16.2) actual at full charge, into 1 large pack. I have other ways to charge the pack, but, was wondering if the UPS charger would keep the cells close to 3.8V Nominal (15.2V. These cells are good to 3.4 Low voltage cut off, and, rated at 3.8V Nom.

 I have low voltage alarms I can add as needed, also.

 I don't know if the higher voltage will affect the UPS. At the AC input, it is rated at 88V-135V. This is why I would like to measure the charge voltage, or, if it might be adjustable in any way ?

dnix71

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Re: higher charging voltage from 350 UPS
« Reply #3 on: November 01, 2015, 01:19:36 PM »
If the APC is working correctly it will cut off at 14.5 max. I don't think you can change the charge voltage, just the total battery capacity (external battery vs. internal).

These were made to run from agm lead batteries. I used to have a Lithonia backup light that was made for either lead or nicads. It had a trim pot for adjusting charge voltage.

Harold in CR

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Re: higher charging voltage from 350 UPS
« Reply #4 on: November 01, 2015, 06:14:01 PM »

 Thanks David

Harold in CR

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Re: higher charging voltage from 350 UPS
« Reply #5 on: November 02, 2015, 07:01:19 AM »

 Would there be a way to add a voltage booster after the charge voltage output, like a transformer or something, to boost the output to 16-16.5V to the battery?

dnix71

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Re: higher charging voltage from 350 UPS
« Reply #6 on: November 02, 2015, 07:33:16 PM »
These are lithium batteries. They need to be charged according to the type and size. A homemade unattended charger will most likely undercharge or overcharge. I don't think these will catch fire like their cobalt cousins, but you could destroy them easily by overcharging.

The APC won't operate from a 16v battery pack anyway. My inverters don't like anything above 14.5 to 15.

The electrolytic caps inside the APC and inverters are rated 16v MAX, so anything above 15v is going to damage the caps in the long run.

16 and 35 are common voltages for electrolytic caps. 16v is for 12v nominal applications and 35 is for 24v nominal apps.

Harold in CR

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Re: higher charging voltage from 350 UPS
« Reply #7 on: November 02, 2015, 11:26:42 PM »

 Thanks again, David.  I just don't know anything about electronic stuff.