Possible to parallel 2 UPS's?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
185
Hey my fellow DIY'ers,

Strange question that I think I already know the answer too...

Is it possible to put 2 UPS's (uninterruptible power supplies) in parallel for high output capability?

I have a bunch of old UPS's that I use basically as 12v inverters. I was wondering if you could parallel their outputs.

I'm pretty sure this is not feasible though. I understand that some UPS's can be Daisy chained but I would be using two completely different UPS


Thanks
 

MisterBill2

Joined Jan 23, 2018
18,167
Some models of some brands of inverters have provisions for parallel operation. Tghat requires a synchronizing signal cable. If the UPS devices that you have do not have this feature, the answer is NO, you can not put them in parallel, it will not work.
 
It's possible but kinda expensive, the company I work for makes UPS's. I am an apprentice for their testing program and one of the units I am being trained on is a type of sync control that can sync up 4 or 5 large UPS's. Unless my understanding of this control is incorrect but from what the engineers and my trainer were telling me that what this sync control is for. Unfortunately I am not at the point where I can involved in the full test of the control with the UPS's but I hope to be one day.
 

MisterBill2

Joined Jan 23, 2018
18,167
It's possible but kinda expensive, the company I work for makes UPS's. I am an apprentice for their testing program and one of the units I am being trained on is a type of sync control that can sync up 4 or 5 large UPS's. Unless my understanding of this control is incorrect but from what the engineers and my trainer were telling me that what this sync control is for. Unfortunately I am not at the point where I can involved in the full test of the control with the UPS's but I hope to be one day.
Alpha, I am presuming that the UPS devices that can be synchronized are all the same model and power rating, and that there is some sort of additional connection between the units. Perhaps the designers can verify that this feature is an addition to the design, not a common capability. That would not be giving out any secrets.
 
Alpha, I am presuming that the UPS devices that can be synchronized are all the same model and power rating, and that there is some sort of additional connection between the units. Perhaps the designers can verify that this feature is an addition to the design, not a common capability. That would not be giving out any secrets.
I am only an apprentice, so I am a bit limited atm, but I do know that all the UPS's are from the same product line. The sync controls are a somewhat rare product that we have built on top of the fact this one was a custom design so the testing procedure we normally follow was tweaked a little bit so it will probably be awhile until I see another like this one. Also there was some additional connecting units to the sync control for this set up, and as I said this was fairly expensive the entire project itself from what I was told was in the millions. I wish I could of gotten pictures of it but there is a very strict no photo policy in test. So I would say your presumption is most likely spot-on.
 

MisterBill2

Joined Jan 23, 2018
18,167
That is exactly what I was thinking. As each UPS includes an inverter circuit of some kind, phase locking the inverters is not likely to be possible without a bit of additional circuitry. But this does bring up an interesting possibility, which is a number of separate UPS devices all feeding separate rectifier bridges, providing a single much higher power DC source, which could then feed a single switching type converter to deliver a higher power AC output. It would functionally be a high powered switching supply but with an AC sine wave output. Not a pure sine wave, but fairly close. Probably it would include a PWM system plus a low-pass filter. Certainly not a simple solution.
 

MisterBill2

Joined Jan 23, 2018
18,167
Another option would be to use one UPS as a master and run the additional ones as slaves, their function being to run as externally driven inverters. That would be simpler than my other idea but it would require modifying only the slave inverters.
 

nsaspook

Joined Aug 27, 2009
13,079
That is exactly what I was thinking. As each UPS includes an inverter circuit of some kind, phase locking the inverters is not likely to be possible without a bit of additional circuitry. But this does bring up an interesting possibility, which is a number of separate UPS devices all feeding separate rectifier bridges, providing a single much higher power DC source, which could then feed a single switching type converter to deliver a higher power AC output. It would functionally be a high powered switching supply but with an AC sine wave output. Not a pure sine wave, but fairly close. Probably it would include a PWM system plus a low-pass filter. Certainly not a simple solution.
We need the hot swap redundancy to reduce single point of failure. The critical online UPS power bus at a typical SEMI plant is must have close to 100% reliability with Very high efficiency ( typically 99%) and Very high fault capacity compared with a standard UPS.
 

Reloadron

Joined Jan 15, 2015
7,501
Hey my fellow DIY'ers,

Strange question that I think I already know the answer too...

Is it possible to put 2 UPS's (uninterruptible power supplies) in parallel for high output capability?

I have a bunch of old UPS's that I use basically as 12v inverters. I was wondering if you could parallel their outputs.

I'm pretty sure this is not feasible though. I understand that some UPS's can be Daisy chained but I would be using two completely different UPS


Thanks
Based on your post in a word no you can't parallel them for all the reasons already mentioned.

On a side note it was maybe 25 years ago my department, Assembly and Test inherited a large APC UPS from the IT Department. Big and heavy with hot swap drawers where each draw was in sync with the others. Had like 5 big roll out drawers. I forget what each drawer capacity actually was but you could have a drawer or just a blank cover panel. We had testing going on where a loss of control power could be catastrophic waiting for the backup generator to come online. Anyway it's not like the technology is new for industrial applications. All the batteries were in the bottom shelves and like the top shelves you could add more battery power. The backup generator was a 100 KW unit and an old Kohler generator. When I retired there was a 200 KW unit on order powered by Cummins.

Ron
 

MisterBill2

Joined Jan 23, 2018
18,167
Redundant hot backup is by far the most reliable, but also by far the most expensive.
We have not heard from the TS as to how reliable the system needs to be, and so while it has been an interesting discussion, it is waiting for more TS input.
 
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