Parallel 2x router UPS

[cavedog]

So ChatGPT says no I must not do it because a voltage drop on one ups will cause the one with higher voltage to backfeed into the other one potentially damaging it.

My question though. Both UPS output 12V and both UPS's battery packs have a BMS for cutoff and both UPS cuts off when the battery dies so it not like 12v will gradually drop as the batteries get drained. From my understanding both UPS will supply 12V until the batteries are drained.

Am I correct and is this setup a problem?

Basically, the background is I got a bunch of these faulty router UPS that gets thrown away and some have board issues, some transformers and other batteries but I managed to put together a few working ones.

Attached image for reference. As it stands it's working as expected when both are on and both on battery standby but as you can see both indicate the batteries are full. I'm yet to see what happens when the battery is at 50% or lower.

 

[Herr der Verboten]

Noob: why not serie?

 

[WAslayer]

I think you can add a diode after each of the 12v outputs, which will prevent feedback if there's a voltage drop, but adding a diode does introduce a drop in voltage, which may or may not be significant enough to prevent your router from running..

 

[wingnut771]

Does the voltage drop though? Surely the output is constant?

 

[wingnut771]

Noob: why not serie?

Series doubles voltage.

 

[airborne]

As long as the capacity of each unit is close and they start at the same state of charge it should be fine, the problems start when one drains faster than the other and can eventually go into reverse polarity but then again the bms should prevent that.
You can prevent having issues by never discharging the units by too much, the issues really start when they start getting deeply discharged.

 

[wingnut771]

As long as the capacity of each unit is close and they start at the same state of charge it should be fine, the problems start when one drains faster than the other and can eventually go into reverse polarity but then again the bms should prevent that.
You can prevent having issues by never discharging the units by too much, the issues really start when they start getting deeply discharged.

Is the output not going through a dc to dc converter?

 

[denmendez65]

So ChatGPT says no I must not do it because a voltage drop on one ups will cause the one with higher voltage to backfeed into the other one potentially damaging it.

My question though. Both UPS output 12V and both UPS's battery packs have a BMS for cutoff and both UPS cuts off when the battery dies so it not like 12v will gradually drop as the batteries get drained. From my understanding both UPS will supply 12V until the batteries are drained.

Am I correct and is this setup a problem?

Basically, the background is I got a bunch of these faulty router UPS that gets thrown away and some have board issues, some transformers and other batteries but I managed to put together a few working ones.

Attached image for reference. As it stands it's working as expected when both are on and both on battery standby but as you can see both indicate the batteries are full. I'm yet to see what happens when the battery is at 50% or lower.

ChatGPT is talking nonsense. It will work fine.

 

[B-1]

The 12v will be from some 12v regulator or dc-dc buck converter and unless its a really bad design won't allow back feed. I guess gpt is playing it safe.

 

[repitah]

From what I've seen from my ancient APC router UPS, is the inrush current to start the devices might be more than it can supply (from dead start, pure UPS mode) -- so worst case is unplugging 1/both device, start the UPS and plug the other device(s) in after a few seconds. Otherwise if you have the right voltage and the general use current doesn't exceed the capability of the UPS, a multiway splitter works. Just note that run time obvious goes down when using more power.

 

[denmendez65]

From what I've seen from my ancient APC router UPS, is the inrush current to start the devices might be more than it can supply (from dead start, pure UPS mode) -- so worst case is unplugging 1/both device, start the UPS and plug the other device(s) in after a few seconds. Otherwise if you have the right voltage and the general use current doesn't exceed the capability of the UPS, a multiway splitter works. Just note that run time obvious goes down when using more power.

The 2 will be in parallel. Load shared by both and split 50/50 if both UPS are the same capacity. Unless he is supplying quite a bit of routers I dont see the problem. Googled random UP (AC12000) and its a 5G one. Uses only 1A. Thats nothing.

 

[denmendez65]

The 12v will be from some 12v regulator or dc-dc buck converter and unless its a really bad design won't allow back feed. I guess gpt is playing it safe.

Should be fine. He must just measure to see the output of both if both are the same or within 0.1V.

 

[denmendez65]

Otherwise spend 56 rand and get a relay with a NO and NC contact. No worries about voltage drop with diodes even though that is the cheaper and neater method. Relay will allow the output of only 1 at a time. Also the 2 outputs will never interact.

Edit. I did draw it a bit kak. But basically wire the positive of one to the coil and the same positive to the NO. When the battery of the UPS dies and the output goes off, the other UPS output will go through the NC contact of the dead relay. The router might actually not switch off during the transition as the transition should be quick enough.



This is from Micro-robotics. Can look for cheaper ones with at least 5A rating.

 

[Tomtomtom]

The 2 will be in parallel. Load shared by both and split 50/50 if both UPS are the same capacity.

Unlikely. The buck regulators on the outputs will not be perfectly matched and the one with the higher setpoint, even by a tiny amount, will take all the load. That's the best case.

In the worst case they'll oscillate and overheat.

You would be better off paralleling the cells themselves for more capacity. Or split the load physically - each device on its own UPS.

 

[denmendez65]

Unlikely. The buck regulators on the outputs will not be perfectly matched and the one with the higher setpoint, even by a tiny amount, will take all the load. That's the best case.

In the worst case they'll oscillate and overheat.

You would be better off paralleling the cells themselves for more capacity. Or split the load physically - each device on its own UPS.

I have done it a couple of times with no issues at Uni. Maybe I was just lucky but I never had issues.

If really worried he can use the relay method. Opening the units causes its own problems also.

 

[AnimateX]

Just piggy-backing on this thread and seeing if someone might know.

So I bought a Gizzu Mini-UPS recently because my old brick one is only keeping about half as long as it used to. Can I daisy-chain them? Like put the 12v output of the Gizzu into the 12v input of the brick and then take the output 12v of the brick into my router?

Searched a bit on the internet and it seems to be a rarely discussed topic and AI gets confused between power stations and mini-UPSs.

 

[airborne]

Just piggy-backing on this thread and seeing if someone might know.

So I bought a Gizzu Mini-UPS recently because my old brick one is only keeping about half as long as it used to. Can I daisy-chain them? Like put the 12v output of the Gizzu into the 12v input of the brick and then take the output 12v of the brick into my router?

Searched a bit on the internet and it seems to be a rarely discussed topic and AI gets confused between power stations and mini-UPSs.

I don't see why it won't work, it may be a little energy inefficient but if it works it works.

 

[AnimateX]

I don't see why it won't work, it may be a little energy inefficient but if it works it works.

Cool. What sort of energy loss would there be? It will essentially be all DC:

Gizzu => 12V DC => Brick => 12V DC => Router.

So there shouldn't be any conversion, but I'm not too knowledgeable about electronics. In my mind I can't see why it won't work either, just don't want to damage anything. Will give it a shot tomorrow.

 

[denmendez65]

Just piggy-backing on this thread and seeing if someone might know.

So I bought a Gizzu Mini-UPS recently because my old brick one is only keeping about half as long as it used to. Can I daisy-chain them? Like put the 12v output of the Gizzu into the 12v input of the brick and then take the output 12v of the brick into my router?

Searched a bit on the internet and it seems to be a rarely discussed topic and AI gets confused between power stations and mini-UPSs.

Does the brick charge itself from the 12V input? Or does it just pass it through? Either way, the Gizzu will die first and then the brick will take over. Just not as effective as running them one at a time if the 12V input does actually charge the brick. It may not be worth it if the losses are high which i suspect only some 80% efficiency if you lucky.

 

[airborne]

Cool. What sort of energy loss would there be? It will essentially be all DC:

Gizzu => 12V DC => Brick => 12V DC => Router.

So there shouldn't be any conversion, but I'm not too knowledgeable about electronics. In my mind I can't see why it won't work either, just don't want to damage anything. Will give it a shot tomorrow.

The Gizzu batteries native output won't be spot on 12v and neither will the bricks battery charge input and output so there will be buck/boost conversion losses there.