My APC Smart-UPS SMT750VA LCD 230V is running hot

[BillP]

Hello,

Today I have checked my UPS and it felt quite warm to the touch. I checked the battery temperature and it said it was just over 42 degrees Celsius. This is too hot for a battery. What could be the issue, the UPS is 1 month old and was made in February 2017. Where is the battery sensor located? The battery compartment does not fell that hot on the sides.

Kind regards, 

Luka

[BillP]

Hi Luka,

Sorry to hear that you are having some issue with your UPS,  have you checked the batteries inside the UPS?  If the batteries are the cause of the issue,  I would recommend that you call our technical support at 1-800-800-4272 to properly assess the issue.

Regards

[BillP]

hello,

The temperature inside the UPS is always higher than the room ambient temperature. My Smart UPS 750 (one generation older model than yours, but otherwise very similar in specs) usually measures 33 degrees celsius internal temperature when the room ambient temperature is 19-20 degrees celsius. So if the room ambient temperature is high, then the UPS internal temperature will raise accordingly as well.

I had to replace batteries in my unit the last summer, and before that happened, I noticed that the internal temperature has risen to 38 degrees celsius (from 33 degrees measured under normal circumstances), while the room ambient temperature remained the same 19-20 degrees. This was because the batteries had one or more shorted cells which caused them to withdraw larger charger current than the usual float charging current, resulting in more generated heat. Given that your unit is quite new, the chances of your batteries gone bad are small, but possible. Only way to tell for sure is to test their capacity.

[BillP]

Thank you Wolf for a reply, 

I've kind of resolved my issue by using an old PC fan and I just moved it towards the UPS. The temperature in the room is about 27 degrees Celsius (now, in the summer) and the temperature in the UPS was before I started cooling about 42 degrees Celsius under normal conditions. That's a delta of 15 degrees Celsius. Now the temperature in the UPS is around 29 degrees Celsius. I have also tested the capacity by unplugging the UPS, until it discharges the batteries completely and it's still the same. 

The sensor readings probably don't show the actual battery temperature, I had a feeling that the batteries aren't that hot, when I touched the side of the UPS, where the batteries are located. Could that sensor just measure the chassis of the UPS or the conversion circuit?

Kind regards, 

Luka

[BillP · Accepted solution]

If the thermistor is located in the same position as it is with older models, then it measures the inverter circuit temperature (eg. The location with heatsinks and mosfets) this location is usually warm even during non-battery operation because the charger utilizes the inverter 'in reverse'  to push current into the battery. Due to the tight space inside, the transformer runs hot as well which affects the detected temperature. 

Your ups temperature is appropriate given the ambient temperature. It is good that you put some active cooling there to increase the airflow.