Small (15kva) UPS upgrade to larger batteries - wire size question

[Linwood]

I changed an office UPS to use an AGM battery and had great luck. It had relatively small load and I just used the same size wire as was in the UPS, now about 2' each way vs 6".

I'm doing another for a network closet, it has a larger UPS partly because it also does a garage door, and the UPS is a sine wave.

I have a wiring question: This is a 1500va, 1000watt rated UPS. It uses two 12v batteries, call them 12.5 to make the math easy and it's about 60amps at full load (right? You use the before-power-factor number, not the 1000?).

It is wired with 10AWG stranded now. 60a seems high for #10 regardless of insulation type (and it's Chinese and unlabeled so not sure temp rating). It's a CP1500PFCLCDa if anyone is curious.

I went back and checked the first, it was also #10 but a single 12v system, 1000/600, so actually a bit worse now that I think about it.

Am I missing something here? Do UPS manufacturers just grossly under-size their wire? Except Cyberpower claims UL listing.

I was about to put #6 wire on it, but it looks kind of silly fastening #6 to #10 (and I haven't figured out how to open the case up to get to the PCB so I think I'm stuck fastening to their battery connectors).

Are they allowed to assume that the brief runtime at full load is brief enough that it can't actually do damage (rated runtime is 2.5 minutes at full load)?

I am not all that concerned -- the purpose of the UPS on the opener is for a one-time open with the power out (the garage has no other entrance, and inside is my generator). Make runtime is one cycle which is probably about 30-45 seconds, and at a guess 500 watts (with some starting surge) though I have not measured it.

But... why are the wires so tiny in a UPS? Is there an "out" for short duration (minutes) at way over typical ampacity?

Linwood

 

[robbob2112]

They generally are using silicone sheath wire depending on the vendor... all metal enclosure and brief runtime.... The table below - ignore the red, it isn't me... but they allow 140amps...

And they also assume nobody actually ever uses the full current avalible - they assume you will use something like 1/2 or so ... and their charger generally runs at a fraction of the max discharge current.

 

[MakeMePower]

that unit is wired in 24v, mine is. which makes the gauge appropriate

 

[Linwood]

They generally are using silicone sheath wire depending on the vendor... all metal enclosure and brief runtime.... The table below - ignore the red, it isn't me... but they allow 140amps...

And they also assume nobody actually ever uses the full current avalible - they assume you will use something like 1/2 or so ... and their charger generally runs at a fraction of the max discharge current.

Yeah, the charger is very low current, it was the max output that concerned me.

May I ask where you got that table? Is that manufacturer specs, or does it represent some kind of standard?

 

[robbob2112]

just generic specs googling for 'silicone wire ampacity'

NOTE - I have silicone 200c wire for my BMS project - but I would never run it at that spec....

 

[Linwood]

that unit is wired in 24v, mine is. which makes the gauge appropriate

The one noted is, but I changed out at a smaller unit (CP1000AVRLCD) which is one 12v battery and 1000va, which would put (let's use 12.5v) which would be 80a +/-, and it also had #10 wire, even worse than the 60a above.

I did my external wiring with THHN #6 wire on this second one. The first I used #10 wire from Powerwerx I had lying around. It's described as GTP PVC and rated to 80C. Normally that would be about 35a, so 80a is a lot worse. I'm not all that concerned as that UPS just runs about 120watts, so even if it was doubled would be well under the #10 normal usage.

I guess I am just surprised to find such potentially high amperage allowed by UL./NEC/whoever controls this.

 

[Linwood]

just generic specs googling for 'silicone wire ampacity'

NOTE - I have silicone 200c wire for my BMS project - but I would never run it at that spec....

Well, if it is outside, you couldn't need to clear it of ice and snow.

 

[MakeMePower]

cp

The one noted is, but I changed out at a smaller unit (CP1000AVRLCD) which is one 12v battery and 1000va, which would put (let's use 12.5v) which would be 80a +/-, and it also had #10 wire, even worse than the 60a above.

I did my external wiring with THHN #6 wire on this second one. The first I used #10 wire from Powerwerx I had lying around. It's described as GTP PVC and rated to 80C. Normally that would be about 35a, so 80a is a lot worse. I'm not all that concerned as that UPS just runs about 120watts, so even if it was doubled would be well under the #10 normal usage.

I guess I am just surprised to find such potentially high amperage allowed by UL./NEC/whoever controls this.

CP1000AVRLCD is a 600w unit, which puts it at 45A, with prolly less then a 2 minute runtime, based on that and the sheathing, the battery will be dead before the wire is even hot.

 

[Capt Bill]

I changed an office UPS to use an AGM battery and had great luck. It had relatively small load and I just used the same size wire as was in the UPS, now about 2' each way vs 6".

I'm doing another for a network closet, it has a larger UPS partly because it also does a garage door, and the UPS is a sine wave.

I have a wiring question: This is a 1500va, 1000watt rated UPS. It uses two 12v batteries, call them 12.5 to make the math easy and it's about 60amps at full load (right? You use the before-power-factor number, not the 1000?).

It is wired with 10AWG stranded now. 60a seems high for #10 regardless of insulation type (and it's Chinese and unlabeled so not sure temp rating). It's a CP1500PFCLCDa if anyone is curious.

I went back and checked the first, it was also #10 but a single 12v system, 1000/600, so actually a bit worse now that I think about it.

Am I missing something here? Do UPS manufacturers just grossly under-size their wire? Except Cyberpower claims UL listing.

I was about to put #6 wire on it, but it looks kind of silly fastening #6 to #10 (and I haven't figured out how to open the case up to get to the PCB so I think I'm stuck fastening to their battery connectors).

Are they allowed to assume that the brief runtime at full load is brief enough that it can't actually do damage (rated runtime is 2.5 minutes at full load)?

I am not all that concerned -- the purpose of the UPS on the opener is for a one-time open with the power out (the garage has no other entrance, and inside is my generator). Make runtime is one cycle which is probably about 30-45 seconds, and at a guess 500 watts (with some starting surge) though I have not measured it.

But... why are the wires so tiny in a UPS? Is there an "out" for short duration (minutes) at way over typical ampacity?

Linwood

I just configured an Ampinvrt unit: pure sine wave 1200 Watt Inverter w an ac battery charger capable of 25 amp charge . I thought it was great deal on Amazon for $175 (might be promo price). Got to look closely if you order to try one, because some Ampinvt are Inverters only (with low tier solar options too)