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Crashy · 10-30-2020, 06:32 AM

Alternators are basically unchanged over the last 60 years. Still the same crappy diode rectification with 10% volt drop across them. Still the same crappy method of rotor current regulation. They are 50% efficient and nobody seems to care. Then we throw it into a lead acid battery which is in itself only 50% efficient. Oh wow, 25% efficiency. It's 2020 for gods sake.

Replace the diodes to Schottky and halve the rectification losses. There's active rectification, but that's actually less efficient at high current.

How about eliminate the rectification entirely? Why have AC produced in the first place? Rotor current is DC. Instead of alternating the current, just alternate the poles in the rotor. Use AC in the rotor. It doesn't even have to be sine wave, square wave is probably better. I'm sure a hall sensor and a few simple components could synchronise the rotor poles with the stator, thus producing DC. Basically BLDC in reverse.

I2R losses. Buck converters are a thing. Stop making low voltage. Make high voltage with low current, and convert it to low voltage after its left the alternator. With no rectification losses, and much lower I2R losses inside the alternator, the stator can handle much more current. And, a cooling fan is no longer required, further improving efficiency. I've played around with circuit simulators and a 50A alternator is capable of putting out 3kw with these modifications. But why not use a 24v one? Half the current again, much lower I2R losses.

And forget star or delta. Put the 3 windings in SERIES. Reverse one of them, and now you have a sine wave of higher magnitude. Now you can reduce current even more.

In summary:
1. Use a 24v alternator instead of 12v
2. Remove the rectifier
3. Change the windings to series
4. Convert the rotor to AC
5. Remove the fan
6. Run the high voltage through a buck converter
7. Use a lithium battery

It should now be possible to run the alternator ONLY when braking, and have sufficient energy recovery (like 400A) to keep the battery around 80%.

10-30-2020, 06:32 AM	#1 (permalink)
Crashy EcoModding Lurker Join Date: May 2018 Location: New Zealand Posts: 30 Thanks: 14 Thanked 1 Time in 1 Post	A much more efficient alternator Alternators are basically unchanged over the last 60 years. Still the same crappy diode rectification with 10% volt drop across them. Still the same crappy method of rotor current regulation. They are 50% efficient and nobody seems to care. Then we throw it into a lead acid battery which is in itself only 50% efficient. Oh wow, 25% efficiency. It's 2020 for gods sake. Replace the diodes to Schottky and halve the rectification losses. There's active rectification, but that's actually less efficient at high current. How about eliminate the rectification entirely? Why have AC produced in the first place? Rotor current is DC. Instead of alternating the current, just alternate the poles in the rotor. Use AC in the rotor. It doesn't even have to be sine wave, square wave is probably better. I'm sure a hall sensor and a few simple components could synchronise the rotor poles with the stator, thus producing DC. Basically BLDC in reverse. I2R losses. Buck converters are a thing. Stop making low voltage. Make high voltage with low current, and convert it to low voltage after its left the alternator. With no rectification losses, and much lower I2R losses inside the alternator, the stator can handle much more current. And, a cooling fan is no longer required, further improving efficiency. I've played around with circuit simulators and a 50A alternator is capable of putting out 3kw with these modifications. But why not use a 24v one? Half the current again, much lower I2R losses. And forget star or delta. Put the 3 windings in SERIES. Reverse one of them, and now you have a sine wave of higher magnitude. Now you can reduce current even more. In summary: 1. Use a 24v alternator instead of 12v 2. Remove the rectifier 3. Change the windings to series 4. Convert the rotor to AC 5. Remove the fan 6. Run the high voltage through a buck converter 7. Use a lithium battery It should now be possible to run the alternator ONLY when braking, and have sufficient energy recovery (like 400A) to keep the battery around 80%.