[Heavy49]

.Hello everyone I am new to the ev world and have been doing a lot of reading but I have some questions I have not found the answers for.

I want to make a hybrid car. I have an Audi TT 225 Quattro and have been playing with the idea of removing the rear drive shaft and haldex system (and tune out the haldex from the ecu) to replace it with an electric motor. So my questions are:

I know that the warp 9 hv goes up to 5000rpm but I would like to mount it driectly to the rear diff so is there is a way to rev it higher safely?

Since its going to be a hybrid will 1 warp 9 be enough for the load (about 3000lb) or should I go with 2?

Thanks

 

[brian_]

What about the rest of the hybrid system... where does the power come from for this motor?

I know that the warp 9 hv goes up to 5000rpm but I would like to mount it driectly to the rear diff so is there is a way to rev it higher safely?

Why would it need to run faster? Do you know the ratio of the gearing in that rear final drive (diff)? Unless it has a high reduction ratio, 5,000 rpm would be more than enough... and a VW/Audi Haldex usually has a near 1:1 ratio.

Since its going to be a hybrid will 1 warp 9 be enough for the load (about 3000lb) or should I go with 2?

What are you expecting the electric motor to do? Unless you are running only the electric motor, it isn't accelerating the whole 3,000 pounds. Also, especially after replacing a Haldex clutch with a motor, controller, and battery, 3,000 pounds for the vehicle with passenger seems very optimistic for a TT Quattro.

 

[Heavy49]

Hello brian_ and thanks for your reply. My plan is to race the car and yes the rear diff ratio is 1 to 1. Sorry if i sound like an oximorron (dont know much about transmissions or gear ratios) but my thinking was that both the gas engine and the electric motor should be able to rev to the same range am I wrong?

And currently my car's weight is 2900lb with me in it (the car is mostly gutted on the inside) but I know I can take at least another 160lb out of the inside and that is before I get Lexan windows. On top of that there is some stuff in the engine I dont really need that is also coming out in the near future.

 

[brian_]

... yes the rear diff ratio is 1 to 1.
...
my thinking was that both the gas engine and the electric motor should be able to rev to the same range am I wrong?

The engine's output goes through a transmission, with several different ratios, then a final drive reduction. If the electric motor were connected directly to the engine's crankshaft it would need to match the engine's speed, but you are talking about connecting the motor's output directly to the diff input, so the speed ranges are different.

If the engine is running over 5,000 rpm, it's not connected to the axles with a 1:1 ratio. It's likely that none of the transmission ratios is 1:1, but even if you were in a 1:1 transmission gear, the output of the transmission goes through a final drive reduction (in the transaxle, at the front differential) of roughly 4:1 before doing to the front axle, and through shafts and 1:1 gearing to the rear axle. Your motor won't be going through the 4:1 final drive reduction, so it won't be turning nearly as fast as the engine.

If the tire size is (for example) 225/40R18, the overall diameter is 25.1" so the tires turn 830 revolutions per mile. So at a mile a minute (60 mph) that's 830 rpm... at the tires, the axles, and (because the rear final drive unit has 1:1 input gearing) the motor. 5000 rpm would be 361 mph. The TT is quick, but not that fast.

These common brushed DC motors work best (highest power and efficiency) somewhere around the middle of their speed range, so if that's 2500 rpm then it would happen at a road speed of 160 mph. It looks like you need a motor suited to much lower speeds, or a reduction gear to allow the motor to run fast enough to be useful.

The annoying thing in this case is that while a traditional final drive unit has a roughly 4:1 ratio which would put a 5000 rpm (max) motor in the middle of its speed range at 45 mph and allow up to 90 mph road speed, this particular AWD system has 1:1 gearing which is all wrong for a motor directly driving it.

 

[Heavy49]

I see, then what about scratching the use of the 1.8t from the car and instead using the just 1 electric motor maybe the warp 11 and a small motorcicle engine (maybe 125cc) to run an altrenerator? (To charge the batteries)
Good or bad idea?
How big of a battery pack would ineed?

 

[brian_]

I see, then what about scratching the use of the 1.8t from the car and instead using the just 1 electric motor maybe the warp 11 and a small motorcicle engine (maybe 125cc) to run an altrenerator? (To charge the batteries)
Good or bad idea?

That's a configuration called a "series hybrid". Due to the inefficiency of converting all of the power to electricity (in the alternator) and back to shaft power (in the motor) it is very difficult to make this setup as efficient as other designs (a parallel hybrid, or just an engine mechanically driving the vehicle with no hybrid or electric element at all). With a relatively inefficient engine, home-brew electrical system, and a crude motor the overall efficiency would be very poor.

A 125 cc motorcycle engine would be working very hard to keep up with the power requirements of a car; it probably wouldn't keep up, and would be inefficient while trying. The idea of a series hybrid is usually to allow the engine to operate at its ideal speed and load, but the engine would need to be much larger than 125 cc to be able to produce enough power while running efficiently at a moderate speed.

In general, it's a workable idea, but the specific components needed are all more complex and expensive than most people seem to think. The BMW i3 REX is a (plug-in) series hybrid, uses a 650 cc motorcycle engine, costs a fortune, and gets worse fuel economy when using the engine than a common conventional car of the same size.

How big of a battery pack would i need?

This can be done with no battery at all; that's how a locomotive, or many ships, or some heavy (100 tons or more) mining trucks work. With no battery, the engine needs to immediately respond to power requirement changes, and all of the electric parts just function as an inefficient transmission that allows a continuously variable drive ratio over a broad range of speeds and down to zero road speed (infinite reduction ratio). The peak power to the wheels is just the peak power of the engine.

Basic hybrids use a very small battery, just enough to hold the energy captured in one stop of regenerative braking and to smooth out power demand on the engine. For a brief period the power output can be greater than the engine power, limited only by the electric motor, controller, and battery. With a series DC motor you won't be able to do regenerative braking. Less than one kilowatt-hour of storage works decently for a compact car without high performance requirements.

More energy storage (bigger battery) is used to allow plug-in hybrid operation, where you charge the battery at home (or wherever) and use that energy plus what the engine produces when driving. Common plug-in hybrids typically have about 16 kWh of energy storage (a couple hundred kilograms or a few hundred pounds of lithium battery).

 

[Heavy49]

Ok what about this. I believe what i imagine is not a series hybrid (or maybe i am but i misunderstood) what i was thinking was build a fully electric vehicle with batteries (for canyon riding/ track use) and have a small engine runing to charge the batteries constantly to extend range. Therefore the main sourse of power would be the batteries being charged at home and the 125cc (or maybe an actual 240v gas generator) in the car is being used to keep the batteries charged therefore extending range (I have also though of making a solar/pv roof of the car). Would this be more efficient? Or am I describing a series hybrid system?

 

[MattsAwesomeStuff]

Just buy a generator then, that should be fine. Plus, a generator you can add or remove as cargo, or, use as a generator.

 

[brian_]

I believe what i imagine is not a series hybrid (or maybe i am but i misunderstood) what i was thinking was build a fully electric vehicle with batteries (for canyon riding/ track use) and have a small engine runing to charge the batteries constantly to extend range. Therefore the main sourse of power would be the batteries being charged at home and the 125cc (or maybe an actual 240v gas generator) in the car is being used to keep the batteries charged therefore extending range
...
Or am I describing a series hybrid system?

Yes, that's a plug-in series hybrid.

Would this be more efficient?

The portion of the energy which is put into the batteries at home is used as efficiently as any other battery-electric vehicle. The portion of the energy which comes from gasoline fed to the engine is relatively inefficiently produced and handled.

(I have also though of making a solar/pv roof of the car).?

A small panel on the roof is handy to keep the battery topped up during storage. The power produced by a reasonably sized panel probably doesn't make it worthwhile to carry the panel.

 

[brian_]

Just buy a generator then, that should be fine. Plus, a generator you can add or remove as cargo, or, use as a generator.

In a pickup truck that can sort of work (having the generator in the cargo bed and running while driving), although the fuel tank needs to be separate from the generator set to be large enough to be useful. In a car I don't see how this could be workable, because the generator can't run while inside the car... the fuel can't even be stored in the interior.

 

[Heavy49]

I see, so it would be better to scratch the gas motor altogether and just have a bigger battery pack to have the extra range. Any tips or suggestions? My goal now is a fun daily driver that can be taken to the track.
So far i think the warp 11 conected to the stock transmission is my best bet but as far as controllers go im lost. I've been looking into them not really knowing what i need. I see they range between $1600 all the way to $12,000 😱 and i've read that the controller is where you dont want to be cheap but looking at thouse numbers kinda makes me fell like i should just build the existing 1.8t.

 

[MattsAwesomeStuff]

In a car I don't see how this could be workable, because the generator can't run while inside the car... the fuel can't even be stored in the interior.

Just stuff it in the car where the engine used to be, and hook it up to the original gas tank. Now you'll have an engine just as bulky, a fraction as efficient, and less than a tenth as powerful.

Hybrids are silly.

Alternatively, a trailer.