I'm looking to add a small gasoline engine (5hp) to charge a 48 vdc electric manlift during and after operation. Trying to figure out best, economical way to do this. I understand most auto alternators will put out 60 volts without ruining diodes, stator windings. Can I use an automotive type remote mounted regulator set to ~14.2 volts to control field voltage if I use taps off the first two batteries for voltage sensing? The battery pack consists of 8 6-volt golf car batteries in series. I'd be happy with even 30A. It would be nice to supplement the battery pack during operation. Electric motor on manlift is rated at 6hp and runs mostly intermittently. Permanent magnet rotors are available for delco alternators with windings and diodes made for 48 volts, but how would I control voltage after batteries charged. The people who use these for wind generators usually dump load into a big resistor (water heater) after battery voltage reaches about 56. I guess I could use a voltage sensing relay and a soleniod to idle down at this point. I'm seeking suggestions and experience. I've thought also about just getting a small genset and a 48 volt charger, but I'm concerned the charger would take a hit if I ran the lift while charging. I could put in a disconnect relay that would take the charger off line when the lift runs. Would it be better to switch the input or output in this circumstance, or would this ruin the charger?

 

My advice to you,
Use the proper charger and operate the equipment in a safe manner.

 

I recommend a small motor-AC generator powering a 48V charger. That way you don't have to try to kludge up a 48VDC regulated motor-generator. A good charger should limit it's output current to safe levels, even if the lift is being operated while charging.

I would think you could just use the charger that already charges the batteries from the mains.

 

I'm not going to second guess you on why not use mains as suggested, but it is dooable as I have done it. " We " did a seismic exploration job on Lake Erie involving setting instrument dog house down on a tug boat, which then required power to recharge two sets of 14V batteries. I removed the cable reel and put in a B & S 5 hp belt driving a 100 A Lese Neville[sp ?] 100A alternator, selinium rectifier with fan, & reg. With fingers crossed all went well. For 48 V, will need a 48 V regulator, tapping @ 12 V will give 12V out. Hope there are some regulator experts here.

 

Thanks for input. Cannot use mains as project where machine will be used and stored (mostly) is served only by a 135kw genset which would not be running when lift would be charging. Machine came with two cheap 24volt chargers which I do not yet trust to maintain battery pack--plus use of these requires splitting pack into two sets for charging. I'm leaning toward use of 120vac charger with small suitcase generator. I know cheap chargers use auto reset cb's for oc protection and I couldn't leave them on while machine was being used, so I would have to leave machine with a small generator running out in the middle of the vineyard and hope that the genset would run out of fuel shortly after batteries reached full charge--still not ideal. I'm trying to "Mac'giver" a solution. I have a 5hp Honda engine and a Denso alternator that has a bad regulator. What I want to try is to isolate + and - outputs and brush connections on alternator. Then I would connect alternator outputs to battery pack (through diodes) and would use a new external regulator to control rotor field using the first two of the 8x6-volt batteries for control sensing. Is this feasible? If I'm only to be rewarded by a big ZZZZT! and a flash (somehing I do enjoy), then maybe I should just skip ahead and build a a credible hybrid generator system using a pm motor (for starting and generating) and a real controller. This kind of equipment will eventualy be used in the project I am involved with, so I do need to learn more about it. Any suggestions as to how to proceed with this would also be welcome.

 

You would want to control sense from the 48V of all the batteries, not just from two of the batteries.

If you want to use the Honda engine then I would recommend buying a 48V alternator/regulator. You could possibly get the Denso working but it would take a lot of work to build you own regulator. Better to buy a 48V regulator for it. A 12V regulator might possibly work but you would need a voltage divider to reduce the 48V to 12V for the regulator input.