Battery bank breakdown 1

[vanskat]

I have station battery bank (56 2.22V cells @130Vdc) that is breaking down rapidly. Replacement batteries are on order but I need an interim measure to survive until then.

Any thoughts on using a deep discharge inductrial battery in the cirucit? What are pros and cons?

 

[MikeHalloran]

You need an electrical engineer's handbook from the late 19th or early 20th century. That will teach you how to take proper care of storage cells. In the meantime, any battery is better than a broken one.

That said, real deep discharge batteries are meant to be run to exhaustion and then recharged. If your duty cycle works like that, then deep discharge batteries are indicated. One good example of deep discharge is starting a helicopter; the battery is typically able to spin up the rotors and the engines to light-off speed exactly once, at which point the battery needs to be fully recharged. NiCd batteries thrive in that environment.

If on the other hand your duty cycle discharges just a little of the battery capacity and then recharges it, or discharges and recharges it continuously, you want a 'float' battery. Lead-acid batteries do well in float service.

Sears sells 'deep discharge' lead-acid batteries for trolling motor and similar service. They're constructed so as to have some probability of surviving an occasional deep discharge cycle that would kill a regular lead-acid battery. The market exists only because NiCds are expensive.



Mike Halloran
Pembroke Pines, FL, USA

 

[nukeman]

Need a little more information to understand your problem. What do you mean the whole bank is breaking down? Has the bank started to show signs of degradation (low cell voltages, plate shedding, internal corrosion, loss of electrolyte, etc.). What kind of cells are you talking about (NiCd, lead calcium, etc).

The fix depends on the problem. If you have a few cells that are bad (internal shorts, contamination, cracks, etc) you can jumper around them and take them out of the circuit. This is not ideal but at least you can get some of the battery bank back online. You will have to adjust your charger to the new float voltage since you now have fewer cells.

The question should be asked why are the cells going bad. Are they the correct type for the usage? Are you floating them at the correct rate? Have you been performing the proper maintenance? Have you performed a capacity discharge test to see what condition the cells are in? Have you been taking cell voltages and if so are they fairly close in value? How old is the battery? What was the expected life (warranty) of the battery? These are just some of the questions you need to answer to determine why you are having problems.

 

[digitrex]

vanskat,
At least you are monitoring the condition of the batteries and detected their failures. I had experienced failures of recombination type lead acid batteries for UPS and substation batteries. We have parallel banks in all these batteries and we swapped around the good batteries to make one of the banks working while new batteries are on order.

For new replacement batteries, I suggest you change the single bank to parallel banks in the future.

Meanwhile, any car or lorry batteries will do. Since they are the substation battery(for switchgear control) and they are kept on float charge all the time, I don't think you need deep discharge batteries.

 

[ScottyUK]

I think he said 'station battery' rather than 'substation battery' - if this is a power plant application it could be over pretty much any size. Our station batteries are over 1400AH at 110V (55 cells). It would help immensely if the OP had included a bit more information about the size of the battery and the nature of the loads it serves.

We've run our station batteries with a few defective cells bridged out without any problems to the loads supplied. If you do this then obviously you must drop the charger voltage to compensate.

What is the failure mode? How critical is the load? If the battery is the last line of protection for an expensive item of plant like a turbine generator, I'd be advocating shutting it down if the battery is unfit for service, in writing if need be. Let the top brass overrule you if they wish - if things turn out well they can pat themselves on the back for their brilliant decision, and if it goes wrong you are reasonably in the clear.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[vanskat]

Batteries (lead calcium) are 25yrs vs the 20yr projected life for switchgear control. Preventive maintenance over the last few weeks revealed sudden and repetitive breakdown. Haven't done the investigation as yet but physical evidence include:
1. plate shedding
2. corrosion and cracks

Bank is C&D KCR-13 with 56 cells at a float voltage of 2.22Vdc. Cell voltage meaurements are at 1.87Vdc

My concerns with using an industrial battery are:
* effect on charge rate/current
* position in string
* current distribution etc...

 

[digitrex]

Your new batteries are on order. If the delivery time will be in 3 months, no harm to use car battery as temporary measure to replace all the old batteries. It won't be damaged within 3 months. You can temporary layout the batteries on the floor until you have your new batteries arrived.

You can connect the car batteries (9pcs or 10pcs) in parallel strings such that the temporary AH capacity is 50% of the original. I don't think the charging voltage will need to be adjusted to suit the car batteries because they are going to be used for 3 months.

Just my personal opinions.

 

[fsmyth]

25 years?? Certainly have licked the goodie off
that bank!! I have trouble with 7 year cycles.
<als>

 

[easpe]

Use golf cart batteries, more amp hr and deep discharge rated.

 

[nukeman]

I just read your reply which gave the recorded cell voltages as low as 1.87V. WOW! If the voltages are that low then the battery is shot, you probably have internal shorts causing the low voltage. I would not rely on this battery to perform its function. I would remove them from service and initiate a temporary fix as suggested by digitrex until your replacement cells arrive.

25 years is a long time for a battery to be installed. You might want to verify the sizing requirements have not changed over the years. Have any additional loads been added or removed? If so, you need to re-verify the battery size for the application. IEEE 485 should be consulted for sizing requirements.