Battery & Charger Requirements for Stand-By Generator Starting

[GRAEE]

We have a 132 kVA, 3-phase,60-Hz, 240 volts-AC, with pf=0.8 stand-by generator. we're on the process of specifying the battery and charger system for genset starting purposes. It has a 12 volt-DC starter motor.

can you give us inputs and guidance on how to do the specification?

thanks,

 

[GRAEE]

In addition, what are the considerations in designing a battery & charger system to be used for generator starting?

 

[racobb]

Can't you ask the manufacturer?

Alan

 

[ctpt]

The battery and Charger System generally comes along with the DG set as a standard vendor design.
Following is generally specified by customer:
-the number of consecutive starting attempts
-Input supply voltage/ frequency to the charger
-any metering/ lamp requirement on the charger
-cable entry to charger (top/Bottom)
-charger enclosure type

 

[rbulsara]

See NFPA 110, even if it is not an emergency unit.

Rafiq Bulsara

http://www.srengineersct.com

 

[catserveng]

If you're looking for non vendor specific info, try this,

http://www.egsa.org/LinkClick.aspx?fileticket=1i36Vs-HefE=&tabid=228&mid=674

http://www.egsa.org

also has a standard for batteries. go to their donwload standards section for more info.

Hope that helps.

 

[waross]

what you can expect based on a genset that would be common for your size. This will have a 12V automotive type alternator to charge the battery whenever the set is running.
A> No battery charger and infrequent starts one month or more between starts:
This battery will fail the soonest. As a battery deteriorates it starts to discharge internally. As the battery ages the internal discharges get worse until, when the battery is called upon to start the engine it no longer has enough charge left.
B> No battery charger and starts once a week or more. Similar to A but the battery may last a year or more longer than scenario A.
C> The unit has a small internal battery charger to keep the battery at peak charge. This arrangement has the longest battery life. Unfortunately the failure mode is often a battery explosion. I have cleaned up from enough exploded batteries that I no longer spec internal chargers and I disconnect them when I encounter them.
Disclaimer: These sets were all privately owned and had little maintenance other than regular oil changes and overfilling of the cooling systems. A set under the supervision of a building manager with a PM schedule may fare better.

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

 

[edison123]

Bill - regarding those exploding batteries - any idea what sort of protective measures to be taken for personnel safety ? Grilled enclosures ?

Muthu

http://www.edison.co.in

 

[GRAEE]

Guys, thank you for your valuable inputs.

GRAEE

 

[alehman]

Bill - why are the batteries exploding? My clients have lots of these (albeit with some level of maintenance). I haven't seen that problem.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[waross]

The batteries are typically located at the front of the base frame. The battery will have a hold down strap or clamp. No special protection. The explosions typically leave the battery case intact but remove the entire top.

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

 

[edison123]

Ok. Thanks Bill. That's a relief.

Muthu

http://www.edison.co.in

 

[waross]

Hi Alan;
This is a guess only, by the time get there there isn't much left of the battery and acid splashed around the area.
I believe that the batteries may have a low electrolyte level. I suspect the batteries are generating hydrogen. I have seen batteries exploded from steam pressure and batteries exploded by hydrogen. A heavy overload to the point of steam pressure will take the end out of the battery case. That is the largest weakest area for the pressure to work against.
Hydrogen will collect in the area above the plates and explodes so violently that the battery top is gone before pressure builds up on the case ends.
These go from hydrogen. I speculate that the electrolyte level may have been below the top of the plates and the starting current caused an arc between plates of opposite polarity. Possibly a flake of plate material may have bridged across between the plates and caused an arc or hot spot. It doesn't take much to light off a hydrogen oxygen mix.
In a lot of years I been there when one battery exploded from pressure build up due to shorted cables.
I was starting an old Pinto when the battery exploded from hydrogen. I was safely in the car at the time. The hood or, if you prefer, bonnet had an area of small dimples from the inside out caused by the fragments of plastic that used to be the top of the battery. I try to remember to keep as much of my body as possible away from above the battery when I have to work on one.
I am open to suggestions from anyone who has more familiarity with battery chemistry than I.
Another possibility is that the charger may have failed in such a manner as to cause over charging. Probably not. When a new battery is installed the charger seems to work properly but to tell the truth, I haven't wasted much time checking the charger. I just cut the leads and forget it. If a battery fails quietly the customer often does not call me to replace it. (I cost too much for a simple battery replacement job.) When a battery explodes I get a call. All exploded batteries have had chargers.
Comments and suggestions welcome.

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

 

[alehman]

Interesting. Thanks for the info. When you said explosions resulting from chargers, I was envisioning explosions happening when sitting on float. That would seem unusual to me.

Explosions when the engine cranks are much more common. Dried out electrolyte is common due to lack of maintenance, overcharging or both. Clearly cranking current while dry or low could lead to arcing and kaboom.

Either way, your safety cautions are good advice.

IMO though, it is important to maintain proper float voltage with some sort of charger unless the engine has a battery charging alternator and runs quite regularly. It must be quality charger with a properly set, stable, temperature-compensated voltage regulator to prevent battery abuse.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[waross]

Good points Alan.
But you will probably agree that a set that works about once a week and will not get any maintenance until it won't start may be better off without the charger. All sets do have automotive alternators.
When the battery won't hold a charge for a week it will be replaced. It is still some time before an explosion is imminent.

In an environment where maintenance happens even semi regularly, I would re-evaluate my position re float chargers.

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