Multiple UPS's from a single battery

[SparkyLarks]

I have 3 UPSs, all 400V. Two are 40KVA and one is 30 KVA.

The Load that they are feeding is 50KVA.

I want to set the UPSs up in a Duty/Standby so if one of the UPs fails I'll still have the other two powering the Load.
I also want to use the common battery Bank for all three of them.

I also have 68 100Ah 6V Batteries,

I Plan to connect the three UPSs in Parallel across the batteries, but I'm concerned about the charging Phase. Would it be better to see if I can set the UPSs up so only one of them will charge the batteries?

Will I have an issue with the Synchronizing of the AC Supply from the Inverter of the three UPS?

 

[waross]

Redundancy will give added dependability. You may lose much of your redundancy by using a common battery bank and a single charger.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Bad idea! for what Bill said. Now the battery becomes single point of failure.

Rafiq Bulsara

http://www.srengineersct.com

 

[KiwiMace]

The UPS's cannot be connected at the AC output without paralleling switchgear, or if they are all the same make and capable of being configured into a multi-module set up, which is unlikely.

Anyway, with a load higher than any individual UPS, a single UPS failure will cause the remaining unit to trip to bypass.

What you need to do is split the 50kVA load out into separate 30/20kVA panels, assuming these are not one big load.

Also:

1. Find out the kW rating of your UPS - often only 0.8 of kVA, whereas an IT load will be nearer 1.0 and the kW will limit your capacity.

2. Limit each UPS load to 90% of the rated capacity. Allow some headroom to recharge batteries under load.

 

[Noway2]

First off, be VERY careful with your attempts. The 400V DC links in a UPS and the battery banks can be explosively lethal and are much more dangerous than live 480Vac systems. A wrong connection could be disastrous.

Unless the UPSes are designed to operate in parallel for power your arrangement will not work. As was pointed aout above, when designed to operate in a parallel, some form of control mechanism must be built into the UPS. This can be done with a synchronizing communication circuit or using techniques such as droop control on the output. Without consulting with the manufacturer there is no way to tell if you have this capacity or not.

You may have problems connecting the DC-links to a common battery bank too. It really depends on the design of the rectifier / chargers (assuming that they don't have separate chargers) and whether or not any protective diodes and / or SCRS are between the DC-link and the batteries. Again, unless the system were designed for it, you shouldn't do it. You will need to consult with the manufacturer.

 

[SparkyLarks]

Thanks.

I had though that that would be the case.

Thanks for the rest of the tips too.

 

[DanEE]

First of all, DITTO "Noway2" and other's remarks above.. You need to be asking the manufacturer of the UPS system if this is possible..

There are a few systems, typically smaller scale, using a design architecture of N+X modular design driven by master sync clocks, with paralleled outputs, but they are designed from the ground up for this type of operation.

It would also be helpful if you indicated the type of equipment being supplied by the separate UPS systems..

For example, if this is an IT network, CISCO, HP and many other manufacturers use a dual rail power system design concept in many of their products, designed to be fed from 2 different power sources to achieve high availability.

One of our customers has a completely parallel, but separate, system of dual generators, UPS systems, battery banks, UPS distribution panels and branch circuits to the the using equipment.

Their dual rail server and network equipment systems have power feeds from each system, so if one side fails for whatever reason, the feed from the other side will keep the networks and servers running.

 

[peebee]

The battery is the weakest link in a UPS system. It would make much more sense to parallel 3 batteries on one UPS, that would be much more reliable than 3 UPS's on one battery.

And as DanEE suggests, it'd be even better to have two UPSs, each with their own battery, feeding dual-cord (dual power supply) equipment.