# Switching DC between traction and generator



## trukr (Mar 17, 2013)

This is meant to be for a direct drive parallel DC set up with seperate controllers for each motor.

Is it possible to use a netgain motor as a generator?

I've tried to understand why DC cannot really be used for regen, but is it more a controller issue than an issue with the motor itself? In that case is it the inverter that allows regen more easily with AC?

My thinking is to uncouple the rear motor from the diff and bypass the controller straight to a charger. I would use the rear pulley with a belt drive to a motorcycle engine to spin the netgain. The front motor will then be the only traction motor, while the rear becomes a generator. 

The motorcycle engine is meant to be a removable highway extender. I only want enough power from the ICE to maintain hwy speed plus say 20% for a slow charge. All acceleration, hills, and headwinds would have to draw from the pack. I'd be able to get away with a smaller ICE spinning at a steady rpm but my acceleration would drop dramatically.

Option 2 would be to keep the motor coupled to the diff. The controller would be the only component bypassed. The ICE can spin the diff through the motor so the rears can remain a drive axle. With the motor switched to a charger instead of the controller, would it not become an effective generator? I'm thinking with this set up, the ICE would have to bump up from ~45hp to ~100hp, and I would need to keep the motorcycle tranny.

I understand there will be a lot to figure out, especially with matching both axles, but if it's possible, then this could be one way to run a removable range extender without needing a full genset on a trailer.


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## major (Apr 4, 2008)

trukr said:


> This is meant to be for a direct drive parallel DC set up with seperate controllers for each motor.
> 
> Is it possible to use a netgain motor as a generator?
> 
> ...


Hi trukr,

DC motors can be used as generators. In fact, DC generators were widespread on combustion engines before alternators (AC generators) became popular. There are probably millions of DC generators in use today in various industries.

Netgain DC EV motors are series wound. Most DC generators are shunt wound (or separately excited). The series wound DC machine makes an unstable generator because the field is excited by the armature current. When the load increases (as with a perturbation), the field excitation increases which increases the voltage which increases the output current which increases the field which increases the voltage which increases the current and so on. Control methods get messy real fast. It is just not worth trying to use series wound DC machines as generators. It can be done, just not worth it.

You might be able to use separately excited (SepEx) machines as motors and generators but there are no controllers available for EV size SepEx. The only reasonable approach IMO is the AC drive. The AC motor and associated AC inverter (controller) would be fully capable of bidirectional operation (motor/generator).

Regards,

major


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## trukr (Mar 17, 2013)

Thank you very much Major. This is exactly what I was wondering.

It's not what I was hoping to hear, but it is what I needed to hear.

Thanks again


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## trukr (Mar 17, 2013)

Ok so now that I've done a copy and paste of a whole new set of concepts to study for later, I can think about an AC set up.

I'm guessing a single AC set up wouldn't work because of the nightmare handling and fuel economy you'd get from the fronts dragging and the rears driving. It would have to be a properly integrated hybrid system, so not removable.

A twin set up could still work... with double the components at AC prices. Ouch.

Maybe a single mid-mounted motor with a rear-mounted engine. 30hp to maintain highway speed and another 30hp to spin the AC. Direct belt drive with a clutch for the 60hp aircooled ICE should work. There would be no handling issues other than the added weight behind the axle, and it would still be easily removable. An ignition kill switch could be used at around 90-95% charge.


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## Duncan (Dec 8, 2008)

Hi Trukr

Why not simply drive the diff using the electric motor as a driveshaft?

This avoids the inefficiency of converting "work" into electricity - storing it in the battery and then converting electricity back into work


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## PStechPaul (May 1, 2012)

The most efficient and easiest setup may be to use a 4WD setup with an electric motor for the front wheels and an ICE for the rear wheels (or vice versa). Thus it would be possible to get maximum power by driving both together, or you could use either one separately. When the battery pack is mostly depleted you can kick in the regen for the electric motor when braking and going downhill. The electric motor system will be most efficient for stop and go driving, while the ICE is best when used at its "sweet spot" of peak efficiency. You might even be able to add the electric motor to the load when cruising if the added torque and RPM are at a more efficient point for the ICE.

Of course this may involve some tricky mechanical ingenuity to decouple either the ICE or the electric motor from the driveshaft and differential. It might be as simple as a clutch or a transmission with a neutral position. The pros and cons of series and parallel hybrids have been talked to death, and there are also the considerations of extra weight and complexity when you combine both types of propulsion. But having both systems gives you an emergency backup in case of failure of either one, and may provide an awesome 4WD capability. However, synchronizing the two systems may be a nightmare and a safety issue.

I think AC is the way to go in any case, especially compared to series wound DC motors and a desire for regeneration (or simple generation). I have found some information on making a series motor perform (re)generation, but it seems to be risky in terms of safety as well as brush and commutator deterioration.


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## trukr (Mar 17, 2013)

Duncan said:


> Hi Trukr
> 
> Why not simply drive the diff using the electric motor as a driveshaft?
> 
> This avoids the inefficiency of converting "work" into electricity - storing it in the battery and then converting electricity back into work


Thank you. This is what I meant by running a belt to a pulley on the tail shaft of the AC motor. The bike engine would need to be around 60hp to both maintain hwy speed and do the added work of spinning the AC in regen. (I'm just guessing that it would take around 30hp to spin the AC in order to get a decent charge.)


Since the AC is still connected to the transaxle it would effectively became a driveshaft while charging. The system would be in regen mode while the bike engine is running for traction. I think simply shutting off the regen at full charge and allowing the AC to spin freely, might be better than constantly switching between pack and ICE on the hwy for long trips.

The load on the engine would drop back down to 30hp once the regen is switched off anyways.

A simple sprocket clutch at the end of the v-twins crank would allow the sprocket to spin freely when under EV power. So you wouldn't have to deal with drag from the engine when not in use, only the added drag of the two sprockets and the belt.

edit: Now that I think about it, it might make more sense to have the sprocket clutch on the tail shaft of the AC instead. Then the only added drag would be the bearings in the sprocket clutch.


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## trukr (Mar 17, 2013)

PStechPaul said:


> The most efficient and easiest setup may be to use a 4WD setup with an electric motor for the front wheels and an ICE for the rear wheels (or vice versa). Thus it would be possible to get maximum power by driving both together, or you could use either one separately. When the battery pack is mostly depleted you can kick in the regen for the electric motor when braking and going downhill. The electric motor system will be most efficient for stop and go driving, while the ICE is best when used at its "sweet spot" of peak efficiency. You might even be able to add the electric motor to the load when cruising if the added torque and RPM are at a more efficient point for the ICE.
> 
> Of course this may involve some tricky mechanical ingenuity to decouple either the ICE or the electric motor from the driveshaft and differential. It might be as simple as a clutch or a transmission with a neutral position. The pros and cons of series and parallel hybrids have been talked to death, and there are also the considerations of extra weight and complexity when you combine both types of propulsion. But having both systems gives you an emergency backup in case of failure of either one, and may provide an awesome 4WD capability. However, synchronizing the two systems may be a nightmare and a safety issue.
> 
> I think AC is the way to go in any case, especially compared to series wound DC motors and a desire for regeneration (or simple generation). I have found some information on making a series motor perform (re)generation, but it seems to be risky in terms of safety as well as brush and commutator deterioration.


I think trying to synchronize the two differing systems on different axles would be too much for a DIY set up. Plus this is more about a removable highway extender. I wouldn't want to drag around the added weight when not needed for daily commute.

I would mount the AC motor directly to a transverse transaxle mounted at the rear. The air cooled v-twin would be hanging off the back end so that the sprocket would line up with the tail shaft of the AC motor.

This simplifies the set up quite a bit. It allows me to run regen while under power moving forward. Trying to do that with a 4wd mix set up would be a nightmare under slippery conditions. The fronts would always be dragging while the rears are trying to push.

Only allowing the regen to operate under braking and on downhills would take forever to get a decent charge going.


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## Duncan (Dec 8, 2008)

Hi Trukr

You are adding unnecessary complexity by generating electricity

If you are going on a long run you know that you are going to need the IC engine
Why not use the electric until you get out of town and then engage the IC unit and use it for main propulsion
If you do this with a mostly full battery you don't need to use expensive petrol to inefficiently charge your battery 
Simply drive on the IC unit until your remaining battery power is enough to finish your journey then shut down the IC engine and recharge off nice cheap grid electricity

If you use a brushed DC motor you will probably need to run the electric motor for the whole journey to preserve the com film
But you should be able to use it at a relatively low amperage as it will only be doing part of the job of driving your vehicle

Major will be able to advise on what "a relatively low amperage" means


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## trukr (Mar 17, 2013)

Hi Duncan,

Major was very informative in answering my original question about a switchable DC. He's made it clear to me that AC is the only way to go with a range extender with charge capability.

I'm not sure what you mean by added complexity. Are you refering to abandoning a DC system for an AC one? The only thing I would need to add to take advantage of the AC motors generative capabilities is a larger engine.

I think a 60hp air cooled v-twin with fuel injection would be ideal. No tranny on the ICE since it won't be engaged until cruising speed. 

The ultralight guys talk about 25hp 2 strokes that weigh under 30lbs. It wouldn't be enough to produce any electricity but it just may be enough to maintain hwy speed. 30lbs sounds really easy to work with. Sounds pricey too, but at 30lbs I don't think there would even be a need to remove it.

Here's a link to the ultralight guys talking about options.

http://www.homebuiltairplanes.com/f...have-about-20-30-hp-least-3-cyclinders-2.html

BTW this would not be for a conversion. I work with custom chassis' and fiberglass bodies, so the car would be designed for the removable range extender.


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