120VDC Battery Charging

[kittydog42]

I am looking for the most efficient way to charge a 120VDC battery pack (consisting of 10 12V flooded lead acid deep cycles) from a 14.2 internally regulated alternator, operating intermittently at 140A. I don't know of any other way than to use an inverter circuit coupled with a bridge rectifier, but I don't know how efficient that is. I would like to input over 10A at 120VDC to the batteries if possible. This is not the main means of charging the batteries, only a way to replenish them during the course of the day.

 

[Nigel Goodwin]

Either use an inverter, or charge them in parallel - or at least fed individually - but the switching would be difficult!. Far easier to use an inverter!.

 

[Andy1845c]

Just curious, but what are they powering? Thats alotta battery power on tap!

 

[Leftyretro]

I am looking for the most efficient way to charge a 120VDC battery pack (consisting of 10 12V flooded lead acid deep cycles) from a 14.2 internally regulated alternator, operating intermittently at 140A. I don't know of any other way than to use an inverter circuit coupled with a bridge rectifier, but I don't know how efficient that is. I would like to input over 10A at 120VDC to the batteries if possible. This is not the main means of charging the batteries, only a way to replenish them during the course of the day.

Well the most effiecent way I can think of would be to modify an alternator by removing all it's diodes and feeding the alternators 3 phase AC voltage to a 3 phase transformer, then rectify and filter the transformers secondary, resulting in >120VDC. A charging control circuit would have to be developed but that's pretty simple. Hardest problem would be working out the transformers specifications as to the 3 phase primary input windings and the turns ratio for the secondary winding and of course the frequency range. The advantage of such a system is of course overall effeciency. Possibly some modern switching/boosting DC to DC convertor would work as well but I'm sure they don't come cheap.

I've read of ham radio operators in the distant past publishing such a alternator/rectifer project to power a 1KW tube transmitter in a car

Lefty

 

[kittydog42]

This is powering an electric car. I am trying to develop a method of regenerative braking. The idea about removing the internal diodes is a good one, but the AC voltage can be in excess of 200, of course it all depends on RPM, which will be dynamic. I would still need some sort of voltage regulator. I might be able to build a 120VDC voltage regulator and keep the diodes, but I don't know enough about how alternators or voltage regulators work. My experience so far is limited to designing ~5A 5V power circuits with switchers, caps, and inductors. How would several switching voltage regulators in series work? Would the wattage stay constant with only the voltage rising?

 

[Leftyretro]

This is powering an electric car. I am trying to develop a method of regenerative braking. The idea about removing the internal diodes is a good one, but the AC voltage can be in excess of 200, of course it all depends on RPM, which will be dynamic. I would still need some sort of voltage regulator. I might be able to build a 120VDC voltage regulator and keep the diodes, but I don't know enough about how alternators or voltage regulators work. My experience so far is limited to designing ~5A 5V power circuits with switchers, caps, and inductors. How would several switching voltage regulators in series work? Would the wattage stay constant with only the voltage rising?

"How would several switching voltage regulators in series work?

Possibly. I haven't seen any commercial DC/DC converters with much over 48vdc output. Most or many have isolated outputs so they should be able to work in series output. However a custom design might best just use two internal series stages to get the 12vdc up to your 150vdc, say 12 to 48 and then 48 to 150.

Would the wattage stay constant with only the voltage rising?"

Not constant, most switching circuits are at best at the 90% efficiency range if operated in their design 'sweet spot', but that's not bad. Recall that even a well designed AC transformer can have 5-10% losses.

Lefty