VRLA Battery Sizing

[CircuitSolver]

I am specifying a 125 VDC VRLA battery that will be connected to a distribution bus that provides standby power for a UPS as well as 3 125 VDC loads. The battery operating voltage range is 105 - 140 VDC. The VRLA battery will supply standby power for 2 hrs. for a constant load of approximately 350 Amps. Vendors have returned quotations each with 60 cell battery strings. The two batteries specified were Absolyte GP model no. GNB 100G19 and BAE OPzV 600. I am trying to verify that the battery is adequately sized. I haven't been able to locate the required information to perform the calculation online. I was wondering if anyone had this information available and could provide assistance.

 

[Jebb]

Get the battery technical specification sheets from the manufacturers. This will have all the discharge data, and with some simple math you'll have your answer!!!

 

[ScottyUK]

From a quick glance at the 2-hour rate the OPzV 600 isn't big enough in a single string but in dual string configuration it is probably about there. The GNB 100G19 is also too small in single string configuration but likely a little over-sized for dual string unless you require a fairly shallow discharge and a large aging factor.

Bear in mind that a UPS is a constant power load, so the discharge current increases as the battery voltage falls.

Ring the manufacturer as jebb suggests, and have details of the loads available.

 

[iceworm]

ike -
The two basic documents are IEEE 485 on sizing and IEEE 1188 on VRLA selection.

These two discuss margin, aging factors, recommended practice for calculating required capacity. And they even discuss converting constant power to constant current.

I'd highly recommend getting and reading those two. And yes, you will need the mfg discharge data.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[ScottyUK]

That's what I love about IEEE standards - they are helpful! Totally different to the majority of IEC standards which appear to be written for lawyers, not engineers.