Runtime shown in NMC and UPS via Hyperterminal is different from the actual runtime of the UPS.

[BillP]

This question was originally posted by Joseph on APC forums on 11/3/2016

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Hi! I've always noticed that the runtime on the NMC and Hyperterminal will not always be equal to the actual runtime of a UPS. I have an SURT2000RMXLI, One external battery pack and an NMC (AP9630). The Load is at 90% (I used a load bank set to PFC=1) and the runtime show by the NMC and Hyperterminal is at 18minutes. When I run a pull plug test, it took 24 minutes until the UPS turned off. I would like to know if this is normal and how accurate is NMC and UPS in calculating the runtime? 

[Brad_C_apc]

This was originally posted on APC forums on 11/4/2016

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The NMC has nothing to do with calculating runtime, it simply reports what the UPS tells it. The runtime estimation is performed by the UPS, and it is an estimation rather than a calculation. The problem is the runtime will vary depending on battery age, condition, and even temperature on the day. The UPS does a fairly good job of tracking battery condition over life and it can put together a reasonable estimate of runtime performance, but if you understood the variables involved you'd see it's all very handwavy. One thing it does try very hard to do is not overestimate runtime, so it'll always try to err on the conservative side.

It's not an exact science and the behaviour of SLA batteries (particularly under extreme loads) can be fairly hard to accurately model, particularly as they age.

[BillP · Accepted solution]

This reply was originally posted by Joseph on APC forums on 11/5/2016

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Hi Brad, 

Thank you for helping out in my query.

Kind regards, 

JC