Battery Boost Charging Current

This is determined by the battery manufacturer....typically ~1.5v per cell...

Donno, but try googling: "NiCd boost charging current" I see there's a ton of documents(PDF's) on the subject. Also note that this could possibly be dangerous to perform. And this does sound like a 'school' question...

Are you sure they are NiCd batteries?

That is a HUGE battery, I have never seen one so big. Did it come off a submarine or something? And you have TWO of them!!!!

In comparison, I recently replaced my car battery with one 40% larger at 92 AH and it is Lead Acid.....the engine is a diesel which requires a lot of cranking amps.....a real lot!!!

I am guessing here but I suspect your batteries are FAR smaller than you wrote and probably also Lead acid, which are easy to charge.

If you are right and they are NICAD, then you have to be an expert with expert knowledge to avoid turning them into a small bomb.....

Leave well alone is my advice.

You already have the answer in your question. The rectifier chargers are rated to 150% of the demand factor on your battery bank. If you have a load demand of 80 amps per bank, all you need to have is a rating of 200 amps max output of your chargers. Rule of thumb in electrical, never take a load more than 80% of the circuit supply. And it does not matter if you use 90% of the battery during an outage, the charger is designed by the OEM to regulate its own output and time to charge the load. Battery chargers are set as a current control output. Being your rectifier is built to have a constant of 48Vdc, the demand factor, being Resistance in the circuit, will regulate the actual current output to charge. As the batteries close the gap on their rated potential, the charger takes sample readings of the resistance in the circuit and the current draw.

As for the boost, you need to understand the math involved for the actual number you are searching. Each battery has a voltage and current rating. You need to actually have the life reading of each battery in voltage to have the definite answer to your question. As a battery is depleted, the voltage used off each battery is different from the one forward and after that battery, plus all the batteries are set in a series/ parallel condition too. So you need to know the formulas on series/ parallel circuitry too. The answer requires precise numbers for a correct answer. 8-)

Maximo

Thank you Mr. Maximo for your reply, maybe i missed out some information.

Presently there are 2 chargers whererin each charger is connected and charging independantly to each NiCd 2x770A (2.4V i.e 2cells each battery) series/parallel connected battery bank and their output is connected to the common 48V DC bus. Each charger is rated for 492A at 61.6V, the nominal voltage is 48V. I understand the high rating of 492A is because of the the high current taken by the batteries during boost charging.

Now I am only replacing the chargers but retaining the existing batteries and I am changing the system wherein each charger is charging both the battery banks and supplying the load of 80A incase 1 charger is out of service unlike before.

Therefore inorder to size the new charger, I just need to know the current taken by the NiCd batteries during boost charge considering the batteries are discharged to 10% of their capacity. As a thumb rule please can you advise what will be the boost charging current for the NiCd batteries.