Hi Tom,
Do agree with all the replies. You need to know the battery capacity. If you are looking for the output of the charger make a provision of about 12 to 14% of the battery capacity for a 12 hour charger or 20 to 22% for an eight hour charger. Of course 12 hor charger is cheaper. We have these 2 types of chargers working in Singapore. The time taken to recharge the battery depends on the state of discharge. However, if I am not mistaken companies in the U.S. like to use the 8 hour charger. Of course the charger output must be the 36 VDC type, in your case

1. Yes, you need to determine the battey amp hour capacity. The battery may have a name plate that will give you this, if not remove one of the inner cell connectors near the the positive battery cable (the red one) you will find a number like 18-125-13. Take a way 1 from the last two digits & divideby 2 then multiply the result by the middle set of numbers this will = the AHC of battery at a 6 hour rate (in Europe & Asia & probably the rest of the world - use a 5 hour rate). In my example 13 minus 1 divided by 2 = 6 times 125 = 750 AHC.

2. Charger should have an Amp Capacity + or - 20% max of teh battery AHC no more or less - personnaly I like to size the charger by plus or minus 10%. The Amp Capacity of the charger will determine the Charger out put. Most 36 volt charger will have an out but of 130 amp or greater.

3. The next thing you need to know is if the charger is Single Phase or Three phase. A Single phase charge can be wired into a 3 phase power supply but a 3 phase chager cannot be wired into a single phase power supply - with out cahnging the charges transformers = too much $$

4. Finally, you need to know if the battery is a gel or maintenance free type battery - the require a SCR type charge (do no confuse that with a GNB SCR FLK charger - all that means for a few hunder bucks you can convert teh charger to full SCR otherwise they operate liek a ferro reonate charger) as a different charge profile for these batteries is required.

I'll stop right here - you question is a good one but right sizing a charger to the battery is very important. If you get a charger too big you will basically microwave the battery to an early death. I had a customer that the local "lean to" type forklift dealer sold him. He was "cheaper" than my proposal. He got a truck with a 595 AHC, 48 v battery & a 1200 Amp charger. I have since sold him 1 new battery & late last year when the battery died after 2 years in a low usage (1 - 2 hours per day) operation sold him a newer truck and a right sized battery charger package. Pay them now - then pay me more later - luv it.

DaveUK is dead-on, ideally the charger size should be calculated based on the amp/hour rating of the battery.

That being said, so long as you get a charger that has dv/dt controls (difference in voltage/difference in time) with an output of 110+Amps, you should be fine.

If the charger is too small, it will never ever fully charge the battery, which will lead to sulfation.

The dv/dt timer is important to make sure the battery recieves only the charge it needs.

Hi Tom, to calculate charger size you will need to look at the battery data plate and check what the AH/C rating of the battery is. (Ampere/Hour Capacity) usually stated as being at a 5 hour rating) Then as it is a 36v battery it will be easy for sombody to work out the charger size for 3 or single phase. We have 240 single and 400 3 phase in the UK so our calculations will be inacurate for the US. But I am sure if you post this info one of the other guys will come back yo you when they sober up after the holiday.......Happy New Year everybody, Dave