combining AC backup devices

Posted on
Fri Sep 07, 2018 8:16 pm
kw123 offline
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combining AC backup devices

a little trick: how to combine 3 AC backup devices to extend the available power of AC backup systems.

You can only get up to 1500 Wh battery power AC backup systems for a reasonable price.
Here a way to combine 3 to triple the available power:
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. The relay is ON when system delivers power. When A is empty it switches to B. The switching AC interruption is covered by system C. When System B is empty ,system C will deliver the power. Hence you have 3* 1500 Wh available.

The relay is a simple 120V (or 220V) relay with 2 independent switches. They switch both Line and Neutral from A and B to C. If A delivers power it is switched to A, once A done, the coil loses its power and it goes to off mode and routes B to C.

Seems to work fine.

If you try this make sure that everything is well isolated.


Karl

Posted on
Fri Sep 07, 2018 8:28 pm
mundmc offline
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Re: combining AC backup devices

Any links to the relay you use/recommend?

Posted on
Fri Sep 07, 2018 8:45 pm
kw123 offline
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Re: combining AC backup devices

I use this one:
https://www.amazon.com/gp/product/B07CT ... UTF8&psc=1 ~$24

12 Amp. is enough for my devices.

make sure it has : Double-Pole / Double-Throw Relay with 120VAC coil,

Karl

Posted on
Sat Sep 08, 2018 10:05 pm
kw123 offline
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Re: combining AC backup devices

here the finished box.

You MUST pay attention that Neutral goes to Neutral (white) and Line goes to Line (black).
This is why the black and white wire cross (neutral is the one with the longer slid 3rd pic ... in the US).

Karl
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Posted on
Mon Sep 10, 2018 10:13 pm
mundmc offline
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Re: combining AC backup devices

I know this is probably really dumb, but I’m gonna ask it:
Why not just plug the three UPS’s into each other in series?


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Posted on
Tue Sep 11, 2018 5:00 am
kw123 offline
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Re: combining AC backup devices

Where is the fun in that? Yes you are right

Some advantage is that you have one that is not used Might live longer.


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Posted on
Tue Sep 11, 2018 5:45 am
mundmc offline
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Re: combining AC backup devices

DIY line voltage relays for fun! You’re too much

Posted on
Tue Sep 11, 2018 6:35 am
Turribeach offline
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Re: combining AC backup devices

mundmc wrote:
I know this is probably really dumb, but I’m gonna ask it:
Why not just plug the three UPS’s into each other in series?


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See this article, connecting UPS' in series is not a good idea. I think you should connect all 3 UPS' in parallel or split the devices connected to the UPS to spread the load.

Posted on
Tue Sep 11, 2018 6:38 am
Turribeach offline
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Re: combining AC backup devices

Also this article from APC.

Posted on
Tue Sep 11, 2018 6:42 am
Turribeach offline
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Re: combining AC backup devices

APC doesn't even recommend connecting them in parallel either, but I wonder how much science is in that statement.

Posted on
Thu Sep 13, 2018 9:25 pm
kw123 offline
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Re: combining AC backup devices

I have spend some time on it .. and it does not work with the regular APC devices ~<$200.. With the $500 it would work.

The cheaper ones do not deliver a proper sin wave output and the down stream APC interprets this as no power.

The more expensive ones " pure sin wave output" SHOULD work.

Putting them in parallel should NOT be tried as the 2 APC's will be out of sync and will destroy each other.

Final solution: buy the APC 1500PRO (BR1500G) $180 and the Battery extension BR24BPG $150. That extends the capacity by a factor of 3.
For my mac pro 2012 the single one gives 20 minutes and adding the battery extender gives ~1 hour total power

Karl

Posted on
Thu Sep 13, 2018 9:55 pm
lanbrown offline
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Re: combining AC backup devices

There are also PDU's that offer dual input and they will switch over to the other input when power is lost. This would accomplish your original goal.

Posted on
Fri Sep 14, 2018 8:45 am
ELWOOD offline
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Location: Ramsey, NJ

Re: combining AC backup devices

Have a few UPS that used 12 volt 7 ah batteries, when it came time to replace the batteries I used 12 volt 12 ah battery. The bigger battery does not fit
in the original UPS box, just have the batteries next to the UPS. This defiantly gives longer stand by time. Have been tempted to try the same thing using
a car or even larger truck battery. This might require a separate trickle charger to keep the big battery at full charge. Also have to keep in mind with a
car battery there might be out gassing from the battery that would cause trouble in a confined area.

Elwood

Posted on
Fri Sep 14, 2018 4:11 pm
roussell offline
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Re: combining AC backup devices

I did the car battery mod several years ago, used a sealed lead acid deep cycle inside a battery box that was vented outside via a 1/2” tube. The box was a leftover from my drag racing days. The ups worked well with crazy up-times. I’ve got a few 2200VA rack mounts that all need new batteries so I’ve thought about doing it again, if time ever permits...

Terry


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Posted on
Fri Sep 14, 2018 6:24 pm
DaveL17 offline
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Re: combining AC backup devices

We modified our UPSes with a 15kW natural gas generator. Not really that cost effective from a UPS standpoint, but they only need to last about 20 seconds. :D

Seriously though, we bought it after losing power for 3 or so days during the winter. The inside of the house got down to about 40°F and our basement became our indoor swimming pool (from ground water seepage). If I can manage it, every house I ever own will have a backup generator.

I came here to drink milk and kick ass....and I've just finished my milk.

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