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Old 10-30-2020, 06:32 AM   #1 (permalink)
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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%.

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Old 10-30-2020, 07:19 AM   #2 (permalink)
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One problem with your suggestion is that you cannot induce DC indefinitely.

Voltage is induced by the change of magnetic field, voltage will be zero even with a constant magnetic field present.

And voltage will be negative while the field is removed, even without the field ever being reversed.
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Old 10-30-2020, 08:05 AM   #3 (permalink)
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Hi Crashy.
Electric and hybrid cars must use something like this now for regeneration. I assume they use active rectification (?) I think we will see this soon in conventional cars too. Auto makers are always looking for lower production costs and higher performance, including better efficiency. I assume it will look like an alternator with internal electronics. Probably operate at a few hundred volts, with a buck converter down to 12. Or 48 if that "standard" ever gets adopted.
I don't think we'll see lithium batteries as the 12 volt source until their low temperature performance and cost are better than lead.
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Old 10-30-2020, 09:33 AM   #4 (permalink)
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24v vs 12v

It has been years since I did serious work with electronics, though I graduated from Elkins Institute as a TV-Radio tech. I have always wired my cars from scratch so I know how it is routed. Now that we have electric power steering, I have read companies are looking at electric Air-Conditioning to remove the compressor drag on the engine. I am still debating if I should install a standard Air-Conditioner in my Sunbeam or hold off for total electric AC. My fear is it will be a 24v system...though I can convert if necessary. Just a thought.
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Old 10-30-2020, 09:53 AM   #5 (permalink)
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Old 10-30-2020, 10:26 AM   #6 (permalink)
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Quote:
Originally Posted by Charlie Cheap View Post
It has been years since I did serious work with electronics, though I graduated from Elkins Institute as a TV-Radio tech. I have always wired my cars from scratch so I know how it is routed. Now that we have electric power steering, I have read companies are looking at electric Air-Conditioning to remove the compressor drag on the engine. I am still debating if I should install a standard Air-Conditioner in my Sunbeam or hold off for total electric AC. My fear is it will be a 24v system...though I can convert if necessary. Just a thought.
Prius has electric air conditioning. Has electric everything actually as there are no fan belts.
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Old 10-30-2020, 11:58 AM   #7 (permalink)
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Scrap the alt altogether, replace with a similar sized BLDC motor, run regen when you need to or it's most beneficial, run assist for the same, converter to 12v off the battery pack, if you have one.

Hmm...sounds familiar.
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Old 10-30-2020, 03:06 PM   #8 (permalink)
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ecomodder.com: Controller mods or build for E-assist altermotor

Quote:
Originally Posted by Charlie Cheap
I am still debating if I should install a standard Air-Conditioner in my Sunbeam or hold off for total electric AC.
DDG: heat pump in electric car with buck converter.
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Old 10-30-2020, 06:50 PM   #9 (permalink)
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Have you heard of something called money?

I looked into the price of active rectification. It would cost around 70 dollars in parts to retrofit an alternator with active rectification. An OEM could probably do it for 50 (Bosch has done this already on some alternators).

24V means adding DC-DC converters to power switches and lights and such. You would need to spend around 100 dollars.

They could also use thinner laminations to gain a little bit more.

The fuel economy difference would probably be well under 1% for all three combined, and no one would ever notice, so the manufacturer chooses to pocket the extra 200 dollars.
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Old 10-30-2020, 11:18 PM   #10 (permalink)
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Who are you talking to?
Did you even read the thread before commenting?
I said NOT to use active rectification, instead use AC rotor current rectification.
I said use a 24v alternator and convert it to 12v. I never suggested changing everything in the vehicle to be 24v.
The fuel saving will not be 1%, we already know alternator delete saves 10%, and an alternator is 50% efficient, so a 100% efficient alternator would save 5%. But you have made the silly assumption that fuel economy is the only incentive. It can pump out 400A when required.

Have you heard of money?
I'm willing to bet that my design would be cheaper to manufacture. If you kept the same 50A output, you could do it with far less copper for a start. No fan, less aluminium, smaller bearings etc. It would be 1/4 the size

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