Server + - My turn

Author

My turn

Supertech

2002-09-21, 6:21 pm

Can you daisy-chain UPSs?

Why or Why-not?

Lunatic Fringe

2002-09-21, 6:39 pm

Hey SuperTech...

A quick search of the APC support site found the following:

---------------------------------
Question
Can I daisy-chain UPS?

Answer
APC does not recommend that you daisy-chain two or more UPSs together. Each unit should be plugged directly into a properly grounded wall outlet for maximum effectiveness.

We do not recommend this configuration for the following reasons:

1) It is not UL (Underwriters Laboratories Inc. (UL) is an independent, not-for-profit product safety testing and certification organization) tested, and therefore, should something go wrong and damages be caused to your connected equipment, APC would not honor the claim.

2) It is a waste of money because you do not increase your load capacity in such a configuration. Plugging a Back-UPS Pro 650 in another Back-UPS Pro 650 does not give you a total capacity of 1300; Your maximum load capacity is still 650 VA.

3)Such a configuration increases the possibility of overloading the first UPS in line; if the first UPS has a load on it, and then you plug the second UPS into the first, with a load of its own, ultimately, all of the current is being drawn from the first unit. There is a potential for accidentally overloading the first unit.

4) In most cases, daisy-chaining UPSs does not allow for extra run time. If you are using a UPS that outputs a step-approximated sine wave when on battery, as soon as the fist UPS goes on battery, the second UPS will also go on battery because it will see the step-approximated sine wave as distorted or bad power. Both units will discharge together, and will not provide any extra run-time to the load.

5)This configuration does not provide any extra surge protection, because if an over voltage that is strong enough comes in, the UPS will fail open and prevent the surge from traveling further in connected equipment attached to the UPS.

If you are looking for extra run-time, we recommend one of our Smart-UPS XL products, which have the capability of adding extra, external battery packs. If you need more VA capacity than you currently have, we recommend taking advantage of our Trade-UPS program, trading up your existing your unit for a unit with a higher VA capacity.

If you are looking for a redundant solution, we recommend the following product:http://www.apcc.com/products/accessories/redundant.cfm

Supertech

2002-09-21, 6:48 pm

A good technician has RESOURCES! You don't have to know everything, you just have to know where to find it.

Good job!

twister166

2002-09-22, 2:13 pm

I always want to try that...

Good search on the APC... Job well done.

namrak

2002-09-22, 7:05 pm

Its interesting to see how books will tell you that daisy-chaining UPSs can be done. However, you are only left with that bit of info. An inexperienced technician may not know the why and why nots when considering daisy-chaining UPSs. Thanks for the search Lunatic.

Lunatic Fringe

2002-09-22, 7:10 pm

You are welcome.

cheneybros

2002-09-23, 6:46 pm

So, if you cannot daisy chain UPSs...how do you feel about daisy chaining surge protectors, then maybe back into one UPS? any feedback is welcome...8^D

cheney

Lunatic Fringe

2002-09-23, 7:19 pm

Not too sure how I feel about that, I probably would not do it.

I would worry about the types of devices I am hooking up and am I exceeding the VA rating for the ups.

I would not put anything else on the same UPS as my production server(s). I would want to avoid any possibility of a hard power down at all costs and that is what you would get if your server does not have enough time to power down gracefully.

There are a lot of inexpensive UPS systems out there that you can us for non-essential equipment.

Even on an inexpensive non-production UPS I would probably only plug one protector into each powered recepticle on the ups. Not chain the surge suppressor with each other.

Any way that is my opinion...anyone else?

Supertech

2002-09-23, 8:03 pm

I don't think you would gain any additional surge protection by daisy chaining.

APC recommends against the use of any surge protector or power strip being plugged into the output of any APC Back-UPS product. Doing so, could result in your load being rebooted or dropped during a power failure and, therefore, could void your warranty and Equipment Protection Policy (EPP). Plugging a surge strip into the output of these UPSs could capacitively overload the UPS due to its Stepped Approximated output waveform on battery causing damage to the internal circuitry of these models.

dickrwh

2002-09-26, 8:21 am

Regarding daisy chaining ups's,:
This is not recommended because of basic voltage and current considerations. Think back to basic electricity and it is obvious that essentially putting two voltage sources in parallel doesn't work unless you install some type of isolation mechanism; this is most difficult with the alternating current output of a ups unless you use mechanical or solid-state relays. This all becomes iffy.
Best to keep the ups's isolated; there would little or no advantage anyway of daisy chaining them. Best to partition the server components and run some from one ups and some from anoter ups.

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