I'm attempting to convert 32 VAC to 24 VDC, sourced from a steam driven turbo generator.
It's on a steam locomotive with AC lighting, but needing 24v DC for radio and speedometer. 24 VDC is currently sourced from 2 x 12v deep cycle lead acid batteries wired in series; charging them up after each day's travels. The aim is to keep the batteries charged, or at least slow the depletion rate, whenever the locomotive is 'live'.
I've made a partially succesful prototype using a bridge rectifier (BR354), filtering the output using a 100v 10000uF electrolytic capacitor, then into a 150W DC-DC converter. I've set the output at 27.2V (battery float voltage).
It seems to work, however there are some problems and concerns.
1/ Current spiking due to the filtering capacitor. This concern arises from circuit simulation showing approx. 90amp peak (albeit abrubt) each charging cycle of the capacitor. The turbogenerator is rated at 16A (500W @ 32VAC). Is that magnitude of current spiking correct? Could current spiking cause excessive heating/damage to the loco or generator wiring ahead of the rectifier?
2/ The DC-DC converter drops offline about half the time. I believe this is because as the turbo RPM drops depending on electrical load (and varying steam pressure), rectified voltage drops below the DC-DC converter minimum input of 30V to function. I also think 150W might be too much to bleed off. Does 75W seem like a sensible 2nd attempt? Is a wider range DC-DC converters eg 18-60V worth a shot?
3/ Longevity of the capacitor - I'm not sure it's going to last with the ripple it's getting. The current cap was really only meant to be interim to prove the concept. What capacitor choice would be appropriate?
4/ Is the significant voltage/current ripple output from the rectifier likely to damage the DC-DC converter? Is there a better way to filter?
5/ Is 27.2 VDC output to the batteries the correct choice?
I've looked at PWM / switching AC-DC converters, but they don't seem to handle significantly varying AC frequency, which I assume to be the case, or AC voltage's much below about 90 VAC so discounted that solution. Are there converters that can handle varying frequency? Searches so far have been fruitless.
I would greatly appreciate any assistance with this project. Any advice welcome.
It's on a steam locomotive with AC lighting, but needing 24v DC for radio and speedometer. 24 VDC is currently sourced from 2 x 12v deep cycle lead acid batteries wired in series; charging them up after each day's travels. The aim is to keep the batteries charged, or at least slow the depletion rate, whenever the locomotive is 'live'.
I've made a partially succesful prototype using a bridge rectifier (BR354), filtering the output using a 100v 10000uF electrolytic capacitor, then into a 150W DC-DC converter. I've set the output at 27.2V (battery float voltage).
It seems to work, however there are some problems and concerns.
1/ Current spiking due to the filtering capacitor. This concern arises from circuit simulation showing approx. 90amp peak (albeit abrubt) each charging cycle of the capacitor. The turbogenerator is rated at 16A (500W @ 32VAC). Is that magnitude of current spiking correct? Could current spiking cause excessive heating/damage to the loco or generator wiring ahead of the rectifier?
2/ The DC-DC converter drops offline about half the time. I believe this is because as the turbo RPM drops depending on electrical load (and varying steam pressure), rectified voltage drops below the DC-DC converter minimum input of 30V to function. I also think 150W might be too much to bleed off. Does 75W seem like a sensible 2nd attempt? Is a wider range DC-DC converters eg 18-60V worth a shot?
3/ Longevity of the capacitor - I'm not sure it's going to last with the ripple it's getting. The current cap was really only meant to be interim to prove the concept. What capacitor choice would be appropriate?
4/ Is the significant voltage/current ripple output from the rectifier likely to damage the DC-DC converter? Is there a better way to filter?
5/ Is 27.2 VDC output to the batteries the correct choice?
I've looked at PWM / switching AC-DC converters, but they don't seem to handle significantly varying AC frequency, which I assume to be the case, or AC voltage's much below about 90 VAC so discounted that solution. Are there converters that can handle varying frequency? Searches so far have been fruitless.
I would greatly appreciate any assistance with this project. Any advice welcome.