Sizing up my UPS cables

[drummerdimitri]

I have a UPS with external batteries but I am not sure how thick I should go on the wiring of the batteries.

It is rated at 700W 220V and pulls around 80A under full load.

I did some voltage drop calculation and with my current 3 AWG wires of 1m, i get a voltage drop of around 0.1V under full load.

Do you think this is reasonable? Will it decrease my runtime?

I have access to 1/0 cable but they seem overkill for such low loads. Voltage drop would be about half as much but is it worth the extra $?

[BradC]

It entirely depends on how your ups measures battery voltage and calculates runtime.

[cowana]

Will it decrease my runtime?

80A * 0.1V = 8W dissipated in cables

That's roughly 1% of the total power draw - meaning that if you completely eliminated cable loss, your gain to runtime would be around that.

Doesn't seem worth spending any more on thicker cables to me!

[Siwastaja]

Will it decrease my runtime?

80A * 0.1V = 8W dissipated in cables

That's roughly 1% of the total power draw - meaning that if you completely eliminated cable loss, your gain to runtime would be around that.

Doesn't seem worth spending any more on thicker cables to me!

In addition to this 1% loss, low-voltage cutoff happens 0.1V earlier than otherwise - as a crude approximation, this is about 5% difference in state-of-charge (i.e., assuming linear 100% = 13.0V, 0% = 11.0V), so expect about this much loss in the runtime.

Also, according to the wikipedia table, 3AWG wire has ampacity rating of 85A at 40 degC temperature rise.

So you are at minimum cable sizing right now, with some (approx 5%) loss in runtime, and cables that will run quite warm, but not dangerously so. It's OK, but I might consider going one or two notches up in size. "1/0" size is approaching overkill.

[drummerdimitri]

I can set my voltage cut-off and currently it's at 10 V even though the UPS shuts down when my my DMM value reached around 10.3 V or so.

I and currently only used 400 W and pulling 45 A from the battery but though it would be better to size up for the maximum power capacity for future-proofing.

In the manual, they say that 4 AWG is the minimum required thickness for the conductors. Knowing this and only having access to 3 AWG and 1/0 AWG, would the run-time from the cut-off voltage difference due to voltage drop make any significant difference in run-time? 5% is worth it if the cables run cooler.