Newb Asks: Can I connect a generator to a motor the same way you connect an alternator in a regular car?

[Scrappyjoe]

Hello,

So, in a regular car, you connect the ground terminal of an alternator to the ground, the positive terminal to the positive terminal of the battery, the battery ground to ground, and then you have a simple circuit. The other stuff in your car taps into the positive loop and grounds as well.

Now, with an EV, if you have a generator, which is an ICE coupled with an electric motor, pushing out 300V DC via its inverter, and you have a 300V battery, and a 300V DC inverter driving your traction motor, can you just wire it up in a similar fashion? Obviously we won’t ground everything, we will use an insulated negative cable.

I’ll take my bashing in the comments please.

[Aragorn]

In very general terms, if power is pushed into the DC Bus from any source (Charger, Traction inverter doing Regen, Your ICE/Generator unit) it will end up in the battery (assuming nothing else has consumed it first).

How the rest of the cars systems react to this power magically appearing from "nowhere" is where the problem lies, the cars electronics might decide something weird is happening and shut down or otherwise generate a fault code. Or it might just accept it and your battery charges up.

As an example there was a retrofit rapid charging kit developed for the Merc B250e which essentially used this principle. You had to "start" the car, so the cars systems were all on. Then the CCS bits simply tapped into the main DC bus and stuffed charge in, which the car happily accepted.

[Scrappyjoe]

Ah, ok. So, this is a closed 300V DC loop. It has no other stuff on it, just a generator, battery and motor. So the rest of the car (all on 12V bus) would be unaware of this.

On a 12v alternator system, the lights don't care whether they are getting juice from the battery or running alternator. They just shine. In a system where the generator is putting out 300V, and the battery is at 300V, does the traction motor care where it gets juice from? Will it just run happily?

Since voltages are never identical, would I be correct in assuming that the traction would pull energy from the source with the highest voltage?

[arber333]

Ah, ok. So, this is a closed 300V DC loop. It has no other stuff on it, just a generator, battery and motor. So the rest of the car (all on 12V bus) would be unaware of this.

On a 12v alternator system, the lights don't care whether they are getting juice from the battery or running alternator. They just shine. In a system where the generator is putting out 300V, and the battery is at 300V, does the traction motor care where it gets juice from? Will it just run happily?

Since voltages are never identical, would I be correct in assuming that the traction would pull energy from the source with the highest voltage?

Hm... you may want to include DCDC into this link just so that your 12V is steadily supplied.

In general yes the power from the generator is unloaded on your system and its voltage needs to be regulated. This is how your amps flow in the direction of lesser voltagge. When the system is unloaded generator will supply voltage and very small current to the battery to keep it topped up.
When any load appears on line generator voltage will immediately dive and battery will take the load. Gas engine/generator combo is unable to process quick load changes and this is why you need that HV battery in Prius. Only when engine torque will stabilize it will be able to supply the load AND to fill the battery back up.

[Scrappyjoe]

Thanks arber333. In the time since I started this thread, I have received my 2x outlander rear drive units. My focus right now is getting one running on the bench (refer my other thread where I asked about how to build a test battery).

Once that is done, I'll start getting it into the vehicle. But already it is pretty clear that getting hold of enough HV battery to power my vehicle will be prohibitively expensive (probably ~EUR12000 or so). This is why this thread is relevant to me as a speculative option.

Basically, one outlander motor coupled to diff. One high C rate, low amp hour battery (perhaps harvested Prius modules). One outlander motor coupled to an ICE engine - perhaps a BMW k75 engine, an old Nissan 1400, or even perhaps a beetle engine. Battery serves the function you mentioned above. So a classic series hybrid.

From what I can gather, the Nissan ePower ICE engines have two rpm settings, one at 2500, one at 4000. The ICE chooses between those depending on the battery SOC. The actual amps generated by the generator would be determined by, I am guessing, a regen setting that seeks to cover the required energy from the traction motor.

[Scrappyjoe]

But, as I say, speculative. I would far prefer the simplicity of 2x old leaf packs and save the second outlander motor for another project

[arber333]

......
From what I can gather, the Nissan ePower ICE engines have two rpm settings, one at 2500, one at 4000. The ICE chooses between those depending on the battery SOC. The actual amps generated by the generator would be determined by, I am guessing, a regen setting that seeks to cover the required energy from the traction motor.

I think there is a third RPM setting a 1500RPM start setting to get the engine heated up and oil flowing.
EV will allways be lighter and more efficient than hybrid.

If you could get a WV Golf GTE battery you could go the way of Volvo V60 hybrid with normal front engine and install Outlander motor and battery in the rear. That way you can still drive the same its just 4x4 now . Earth will take car of the connection between both systems and you can simply drive along to regen your pack.

[Scrappyjoe]

The vehicle is actually a VW T3 Syncro - so 4WD, ICE in the back.

Through the road hybrid is indeed another option I am considering - simply swapping out the front diff (remember, it’s rear engined) with the Outlander drive unit. I think three modes would be best - full EV (fwd), full ICE (rwd) and ‘slave’ hybrid, where the electric motor compensates for the load on the rear engine to try and keep the torque load to the back constant. But I have no idea how to implement that. In theory it sounds smart, but it violates the principle of removing complexity when converting to EV - sounds like I am adding complexity to an already quite old car!