BE550G battery voltage low

[DaveH52]

My BE550G is not fully charging its battery. The charging voltage is only 12.5V. My other UPSs (BE750G) have battery charging voltage of 12.7V. Is there a simple adjustment inside the unit that I can use to set the voltage?

I found a schematic and I think this is the circuit that controls the charging voltage by adjusting VR1.  I'm a retired EE and have plenty of meters and scopes and stuff, and I'm not afraid to open it up and poke around, but I thought I'd find out if others have run into this problem first.

[Teken]

How was the battery voltage taken?!?

Based on the reading you have provided it would seem it was taken while the battery was disconnected from the system.

As the float voltage would be 13.5 ~ 13.8 VDC. While equalize charging the input voltage would be 14.4 ~ 15.XX VDC.

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[DaveH52]

Teken thanks for replying.

That was the charging voltage with the battery connected and measured with a Fluke 87 DMM. To make matters even worse, I had another battery that had been charged to 13.7V. When I installed it into the BE550G, the serial app said it was 13.7V which is what I expected. What I did not expect was that a day later, it said 13.5V. I have another BE550G, and I tried the same experiment. It started at 13.7V, and a day later it was at 13.5V. I opened one of the BE550Gs to see if there was a voltage adjustment, but I could not find anything to adjust anywhere inside. Apparently, it's set in the UPS firmware, and I have not seen any firmware files anywhere. So, I'm seriously considering trying to sneak a small surface mount regulator board inside both units that I can set to 13.8V so the battery takes more charge. Unfortunately, empty space inside will be a challenge.

[Teken]

A 13.5 VDC float voltage is perfectly fine as this is within the battery makers charging specifications. 

Any voltage that is above 12.80 ~ 12.90 VDC will fully charge and saturate a battery cell. 

Being on the lower floating threshold has the benefit of extending the battery service life as it will not boil out the electrolyte. 

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[DaveH52]

That does make some sense, at least about the electrolyte. However, it seems that the BE550G tells me that I've got a considerably longer run-time when the battery has been charged at 3.7V, as opposed to 3.5V. Perhaps I'm just so used to automotive batteries that charge at 13.8V

[Teken]

13.5 ~ 13.8 VDC is the Float voltage not the charging voltage.

The operational runtime seen  / displayed is reflective of the load, battery health, and temperature.

A 13.5 VDC Float charge has absolutely no impact whatsoever on the operational runtime.

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[DaveH52]

OK next issue. 

One of my BE550Gs does not seem to be showing the % load. 

What I've been doing is plugging another computer into a battery-backed outlet, waiting for Micro$oft and all the other start-up SW has settled down and until Task Manager says it's idling at about 1% CPU then telling my browser to reload the page, which also causes the APC software to update. 

So this particular BE550G says that it has 475 minutes of runtime and that there is 0% load on it. Now I don't think an intel i7 cpu, spinning HDD, and everything else in that box is capable of running without drawing any power.

Do you know how the power consumption or % load is measured inside the BE550? Is there a torroid or other kind of current sense transformer in the BE550 that might have an open winding or a bad solder joint?

What I'd really like to get my hands on are schematics for the BE550G and the BE750G UPSs.

Again, thanks for putting up with me!