It seems that series hybrid systems are often discussed and rarely built. I think the realities of the series hybrid configuration dawn on potential builders before they get very far.
Posts by brian_
1 - 6 of 13 Posts
It will be easier to select components when you have a more clear idea of the required power and operating voltage.
I can only guess that the reason to consider this combination is that you want DC power at some voltage over 12 volts, so off-the-shelf engine-generator sets are not directly usable.
The generator included in a modern inverter-type portable engine-generator is a three-phase PM machine.
I don't understand why older EVs would use these. They're EVs, so their only need for a generator would be to produce low-voltage power from the high-voltage battery, inefficiently (because modern DC-to-DC converters were not available)... but aircraft typically have 24-volt systems and a car would want 12-volt power.
If you don't need much power, a commercially produced consumer generator set is the obvious way to get a generator set. Of course they are set up to produce 120 V AC single phase power (or up to 240 V is a larger unit). The old-style constant-speed designs are not very efficient or compact, so an "inverter" type would likely be preferable. You might look at intercepting the power before the built-in inverter, then using a DC-to-DC charger to regulate power to the battery.
A typical automotive alternator is not likely a highly efficient generator. I had to search for a what a "HF predator motor" might be, and it turns out to be a basic small gasoline engine from Harbor Freight. I can pretty well guarantee that's about the least efficient and most noisy thing you can get to burn gasoline and turn a shaft.
I can only guess that the reason to consider this combination is that you want DC power at some voltage over 12 volts, so off-the-shelf engine-generator sets are not directly usable.
Okay, although not highly efficient... but with what engine driving it?
Yes, 3-phase permanent magnet motors make good efficient 3-phase generators, but you need to be able to control it. It may be sufficient to just rectify the output and manage the engine to control out voltage. And there's still the question of what engine to drive it.
The generator included in a modern inverter-type portable engine-generator is a three-phase PM machine.
I think this fits in the same category of "it's not very good but it's what I can get cheap" category as forklift motors to drive EVs... except that those old aircraft units are probably no longer cheap or even readily available.
I don't understand why older EVs would use these. They're EVs, so their only need for a generator would be to produce low-voltage power from the high-voltage battery, inefficiently (because modern DC-to-DC converters were not available)... but aircraft typically have 24-volt systems and a car would want 12-volt power.
Just as the most effective components for a DIY EV conversion come from production EVs, it makes sense that the most effective engine and generator set for a DIY series hybrid conversion would come from a production series hybrid. The only pure series hybrid car (rather than truck or bus) currently available in most of the world is the BMW i3 REX, although Nissan now sells them (the e-POWER Note and Serena) in Japan, and some production hybrids have a series mode (a current Honda Accord runs as a series hybrid at all but highway speeds).
Anyone wanting to follow the same design as the i3 but without buying the BMW system could buy a scooter engine (BMW uses a 650 cc 2-cylinder engine from Kymco) and attach a generator, but if the i3 system is the right size for the intended application, and the moderate efficiency is sufficient, it would be hard to beat this production system's packaging and cost.
Again, a clear idea of required power will guide the choice of engine-generator set from a production EV. The i3 unit is relatively small for a car, but still too large for a golf cart. The e-POWER systems are even larger (twice as powerful), and packaged with a drive motor (the same one as a Leaf). The Accord engine is even larger, and also includes the drive motor and a clutch to connect the engine and generator to the drive motor and final output to the wheels.
They work well, but compared to modern EV equipment I doubt they're efficient - maybe fine for what is essentially an educational project.
Delco Remy promotes their higher-efficiency alternators, publishing a white paper on the subject (Improving Alternator Efficiency Measurably Reduces Fuel Costs), yet the specs for one of those high-efficiency units claims only 72% efficiency.
Why remove the stock diodes? They just form a rectifier, which is what you want, right? Yes, the regulator controls the field current, and for better control you might want to use your own regulator.
Ah, I was thinking of the 3-phase synchronous PM motors typically used in EVs, not realizing that permanent magnets were common in large brushed motors. I don't know what a typical application would be for a PM motor - brushed or AC - of that size.
That's the start of the discussion of the i3's motor, which is not specific to the REX version. Try starting at 15:25 for about one minute about the engine-generator set (no internal details, but he mentions that the generator is used as the starter motor) and then Damien's plan to build a BMW E39 as a series hybrid with it (no other details).Damien is planning to use a BMW i3 REx in an upcoming project... great way to get a cheap ~20kW (iirc) generator with ICE attached
Some info in this video (start at 13:14);
1 - 6 of 13 Posts
