[Kevin Sharpe]

Any input would be of great interest!

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);

 

[brian_]

Just wondering if anyone has done a DIY hybrid project? What I mean would be a series hybrid not a parallel hybrid.

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.

 

[brian_]

It will be easier to select components when you have a more clear idea of the required power and operating voltage.

1. household portable generator

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.

2. High powered Aumobile Alternator driven by a HF predator motor.

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.

3. Brushed sepex DC Motor used as a generator.

Okay, although not highly efficient... but with what engine driving it?

4. Large heavy duty PM motor.

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.

5. WW2 aircraft generator used on older EVs

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.

 

[brian_]

Damien is planning to use a BMW i3 REx in an upcoming project...

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.

 

[GE11]

It will be easier to select components when you have a more clear idea of the required power and operating voltage.

1. household portable generator

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.

2. High powered Aumobile Alternator driven by a HF predator motor.

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.

3. Brushed sepex DC Motor used as a generator.

Okay, although not highly efficient... but with what engine driving it?

4. Large heavy duty PM motor.

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.

5. WW2 aircraft generator used on older EVs

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.

Well I’m each of the case I was wanting to use a Harbor freight engine to keep cost under control. Once I had the concept I could then go more expensive...

I was looking at something like a golf cart at 35mph for starters then go maybe to a VW beetle

1. Household generator—- I was planning on using this with a bridge rectifier and either a nice bank of capacitors or a small 120v battery bank... then use a 144V controller to top switch the voltage down to 36V for the golf cart motor... just a DC to DC concept.

2. The alternator——
Now I have done a lot of experiments with this. One of the keys is which one you use. The large case GM alternators work the best. You take all the regulators and diodes out of the the unit where you have only the three phases and field exposed. Then run the three phases to a three phase bridge and you can control the current output through the field. It quit remarkable because this three phase synchous machine works like a current source and not like a voltage source! It really seems rather efficient !

The DC brushed motor— I have not tried this yet but it would basically have an armature where the main power would come and then control the field. But unlike the Alternator (synchronus Machine) the brushes sep ex generator would be a constant voltage machine.

The PM DC—- now I was thinking of using a big 45lb 4 pole low RPM brushed motor like the imperial 36v motors they have for Sale on eBay from floor burnishers. But a 3 phase dc Motor seem interesting... where would I get one that could handle 6KW of power?


Anyway Brian I hope you and others continue to chime in this very helpful! I need to pick a direction and go that way..

 

[Emyr]

Build the EV part first, then add the generator. Plenty of people struggle just to build the EV.

Also, if you permanently install a combustion motor, your local vehicle licensing/registration authority may refuse to call it an EV, so you'd lose out on any low-emissions tax breaks.

 

[brian_]

2. The alternator——
Now I have done a lot of experiments with this. One of the keys is which one you use. The large case GM alternators work the best. You take all the regulators and diodes out of the the unit where you have only the three phases and field exposed. Then run the three phases to a three phase bridge and you can control the current output through the field. It quit remarkable because this three phase synchous machine works like a current source and not like a voltage source! It really seems rather efficient !

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.

 

[brian_]

The PM DC—- now I was thinking of using a big 45lb 4 pole low RPM brushed motor like the imperial 36v motors they have for Sale on eBay from floor burnishers. But a 3 phase dc Motor seem interesting... where would I get one that could handle 6KW of power?

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.

 

[brian_]

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);

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).

 

[GE11]

2. The alternator——
Now I have done a lot of experiments with this. One of the keys is which one you use. The large case GM alternators work the best. You take all the regulators and diodes out of the the unit where you have only the three phases and field exposed. Then run the three phases to a three phase bridge and you can control the current output through the field. It quit remarkable because this three phase synchous machine works like a current source and not like a voltage source! It really seems rather efficient !

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.

Wow this is extremely informative! I did Not realize these things were this inefficient. I typically get 3600 watts with a predator 212 with is close to what this engine is rated as...usually the alternator does not get that hot.. but this white paper Is eye opening!

THanks again!

 

[CanadaLT28]

I have the VW 1.9TDI for my REX and it will be coupled to another Leaf motor to directly charge the batteries. I just have to get a speed increaser set up so I can run the TDI at less than 2000 rpm (within its best torque range) and the generator at perhaps 6000 RPM. It is a bit of an experiment of course. I am very curious how Damien controls all this. It is helpful that he has a complete unit so that wheel does not need to be re-invented.

 

[GE11]

I have the VW 1.9TDI for my REX and it will be coupled to another Leaf motor to directly charge the batteries. I just have to get a speed increaser set up so I can run the TDI at less than 2000 rpm (within its best torque range) and the generator at perhaps 6000 RPM. It is a bit of an experiment of course. I am very curious how Damien controls all this. It is helpful that he has a complete unit so that wheel does not need to be re-invented.

I would plead with you to keep us updated on your project on this thread I really would like to see how you do this!