Diesel Generator Battery Sizing

Well, the simplest thing would be to use one of these

to contact the equipment's manufacturer directly if, indeed, the size information were not already actually stated in the user manual that was originally supplied with it.

Call the manufacturer. Of all the data you could provide so someone might be able to help in selecting a battery you gave us the most useless data.

I'll ask one question that might help. Can you tell us what is wrong with the batteries already attached to this diesel engine?

...and if they are faulty, what's wrong with exchanging like-for-like, new-for-old?

Sorry, I did not mention the battery capacity before. I am interested in verifying the existing configuration. Like I mentioned in the start of this thread - A 126 HP DG - 200Ah battery - Is it enough? If yes or no, how?

Well, does it turn the engine over, and start it?

You did not answer the question. If you ever hope to get engineering services for free, you have to answer the questions you are asked.

A battery of any size will not be enough if the starter is not working properly. IF you are having problems, make sure that you analyze the symptoms well.

Yes that is more than enough however it's the cranking amps that matter more than the amp hour rating.

On a diesel engine of that size most any good quality medium sized automotive battery would work just fine.

Is it charged or is it flat? If it is flat, then it won't be enough. If it is charged it will do it provided the rest of the starting equipment and circuit is in order.

The present battery will have a AHr value on it. If you're replacing batteries do not go below this value. As a fire pump it helps if it starts.

Just to add it seems a stupid idea to me to us a DG to drive a fire pump. Direct coupled would make more sense.

Quite. All the best ones operate when the power goes off. After all, one wouldn't want a silly thing like a blown fuse to precipitate loss of life and enhanced property damage as the fire melts the insulation on the conductors of the cables operating an electric pump, would one?

We're singing from the same hym sheet.

Tony and PW -

FWIW, where Im at, its rather standard to have a central pump house for the fire pumps, right next to (100' away for ex.) the generators. we have 3 gensets so they are redundant, and the pumps are 100hp each and also redundant. This pump house serves approx. 20 fire hydrants. There arent any water mains, except for the hydrants, so the pumps feed from a 20,000 gal tank. When they pump it dry, they are supposed to automatically shut down, although unfortunately they didnt the last time, one kept running until it burned up. Im not saying this is "best practice," but it is a common setup. BTW the pumps are soft start, star delta, each approx 150 amps @ 230/400v 3 phase. The generators run 24/7, also serving other loads. The main pumps also have a smaller "jockey pump" adjacent to them, which imho (im no plumber) serves to top off the system when pressure is gradually reduced due to leaky pipes.

Having worked in automated foundries for 15 years I'm not unfamiliar with fire pumps.

3 X 150HP diesel pumps had to be ready as needed, if the pumps started a signal went through to the county control centre, a minimum of 4 fire trucks were obliged to attend. As for the top storage tank, 650,000 gallons with a head of 120' should keep the hydrants and sprinklers going for a while.

No I don't like the idea of a DG powering the pumps.

OP, are your sure your generator doesnt require 24v = 2 x 12v batteries to start?

thats rather standard for 100 KVA or larger DGs, imho.

Well then, it turns out that there are no standards/thumb rules for selection of battery for a DG set, atleast for now.

PS:The DG was idle was the past three years. I intend to verify if the battery size is alright.

I am still searching for some document which provides a scientific approach for selecting batteries for DG sets.

No joy over the phone with the DG supplier, then?

Two 12volt truck batteries in series, assuming that your starter motor is 24volts, but you did say did ya?

As you are only three questions old in this forum..... a bit of advice... be detailed and precise in the question you ask.... otherwise you won't make it to the end of the page!

Remember we can't see what you have and for us older ones the batteries in our crystal balls run out long time ago!!

Alright, I'll do that from now.

But do you happen to know of any document I have been speaking of until now (battery sizing for DG)?

For goodness' sake ring the DG supplier, and ask directly.

There is NO generic document that would help you in this instance. You need the hand book for the gen set. If you do not have it, google the gen set maker and ask them, again back to my statement about not enough detail in your question, you have not mentioned the make of gen set, and now at this point, mentioning the manufacturer would be of no use as the answer from everyone would be the same, call, email or look on their web site for information.

The answer is actually in your hands, apply yourself, think a bit and as I suspect you found CR4 by goole-ing for the answer to this problem, google once again for your answer....