I have posted the discussion so far below. Please note I have changed the order or replies slightly to improve readability.
mizlplix wrote: One thought to ponder:
The Prius only uses the electric drive up to a point (not sure), when the I.C.E. motor takes over.
So even when you got it working OK alone, you will have at best a 30-35 MPH car.
If you can over freq. the motor, you might pick up some RPMs there too.
If rewound to 6 or 4 pole to pick up torque, it would worsen the problem.
(Not trying to put a dampner on it)
I would like to try one myself.
BigMouse wrote: The ICE never "takes over" in the Prius. It only comes on above certain speeds, and always works with the electric motors. The big motor (MG2) is coupled to the drive wheels by a fixed gear ratio, so rotational speed isn't an issue. The motor is capable of spinning (and commutating) at any speed the car is capable of. Otherwise it wouldn't be able to regen at freeway speeds.
The purpose of the rewind would be to lower the voltage in order to maintain constant torque to a higher RPM. It's not really over freq'ing the motor because it commutates at these speeds anyway during normal use, just not with as much current. The rewind would just push the torque fall-off knee to a higher RPM.
I would suspect that the motor can't be rewound to a different number of poles because the rotor has 8 poles with permanent magnets.
mizlplix wrote: Cool, I am far from knowledgeable on these.
I DO know, there are several converters in California doing the plug in thing by removing the ICE and related stuff and adding another pack to the car. So, I would assume the electric motor will RPM just fine.
The first group to do this is a bunch of engineering students. I guess the hardest part was a new VCL for the controller, which they wrote.
(And I suck at)
After reading that PDF on the operation, it seems that a planetary is instrumental in keeping the electric motor within it's RPM range no matter what the ICE does.
It acts as a priority power flow divider and each power trane can operate at it's own speed without interference from the other.
Like the ICE can shut off locking it's input source allowing the Electric motor to provide 100% of the motive force. OR both can operate allowing the power flow to combine to one output source.
If this is correct, then the electric motor will not throttle up and down with the ICE, but run within it's own range. I wonder what that is?
The Prius transaxle has two electric motors. One (the big one and the one of interest for EV conversions) is coupled to the differential via a fix gear ratio. It always spins at a constant multiple of the wheel RPM.
The smaller electric motor isn't much use for an EV conversion. It's just there to start the ICE, and transfer the ICE's torque to the wheels when required. It is coupled to the differential via the planetary gears and its RPM is a ratio between the ICE RPM and the wheel RPM (determined by the planetary ratio). It's what gives the transmission its "continuously variable" nature, and serves a role similar to a brake band in a normal automatic transmission, but does its job magnetically rather than through friction.
In a PEV conversion of a Prius, the ICE would be removed, and the smaller electric motor would either be removed as well or the planetary would be welded to allow the two motors to work together. This seems like way more work than it's worth as you'd need a second controller for it and it wouldn't add much power.
Johny wrote: Just in case you haven't seen this, it may be a helpful visualisation aid.
Scroll down the page a bit - then play with the controls.
PlanB wrote: Tnks for the rewind info offer Miz. The tritium controller I'd use is 450VDC and 368ADC input and 320VAC and 300Arms output. The IPM is currently 8 poles & I'm not sure that's alterable because of the permanent magnets?
coulomb wrote:BigMouse wrote: In a PEV conversion of a Prius, the ICE would be removed, and the smaller electric motor would either be removed as well or the planetary would be welded to allow the two motors to work together. This seems like way more work than it's worth as you'd need a second controller for it and it wouldn't add much power.
I don't know why you'd want to ignore a motor that is 60% of the power of the main motor (30 kW verses 50 kW, though it's hard to find definite numbers for MG1). 50 kW peak, with much less continuous, is pretty light on for a Prius sized car with an EV sized pack. 80 kW peak is much more reasonable.
It's a pain having to drive the two motors with two controllers, but the car comes with two water cooled inverter back ends already matched to the motors (before rewinding, of course). So if you can deal with a 500 VDC pack (you'd need 650 VDC on later models), you get two inverter back ends for free. You do need to provide the inverter front ends, but that's "just software" and a microcontroller.
I'm a little surprised that no-one seems to have done this yet. Perhaps it's the pack voltage.
Johny wrote:If I rememeber correctly the later Prius' pack is around 200 VDC and they use an up-convertor to 650 VDC. So a DIYer would not have to fiddle with the 650 VDC side. I agree - it's a little surprising that given all the reverse engineering that's taken place on the Prius that a BEV hasn't been done this way.coulomb wrote:I'm a little surprised that no-one seems to have done this yet. Perhaps it's the pack voltage.
Edit: looked up and changed battery pack voltage
BigMouse wrote: Remember that 50kW number is before the re-wind. Rewinding for even 1/3rd the voltage could push that up to 150kW. Seems hardly necessary to go through the added trouble to integrate MG1 in to it when you have a 150kW 400Nm beast of a motor already connected to the differential.
Johny wrote: ...I think I'm starting to understand (again) why no-one bothers to play DIY BEV with the Prius.
Bigmouse, that 150kW is only valid if you can use the extra Revs.
coulomb wrote:But the boost converter has a limit of ~ 20-25 kW (2004 and 2012 models respectively), as provided. I suppose you could beef up the size of the boost converter; that might be less trouble than dealing with 500 or 650 V packs (for the 2004 and 2012 models respectively).
Johny wrote:It's getting too hard isn't it. So much reverse engineering when you might as well go from scratch in a car you actually like driving. (IMHO)coulomb wrote:But the boost converter has a limit of ~ 20-25 kW (2004 and 2012 models respectively), as provided. I suppose you could beef up the size of the boost converter; that might be less trouble than dealing with 500 or 650 V packs (for the 2004 and 2012 models respectively).
BigMouse wrote:The gear reduction between the wheel and MG2 is 4.113:1 for the 2004 model (3.905:1 for the previous model).Johny wrote: ...I think I'm starting to understand (again) why no-one bothers to play DIY BEV with the Prius.
Bigmouse, that 150kW is only valid if you can use the extra Revs.
With the standard configuation and the high voltage, the rated torque of 400Nm is available until 1540rpm. Assuming a 0.3m radius on the wheel, that corresponds to 42km/hr.
A re-wind which would allow constant torque to 4000 motor rpm on a reasonable battery voltage would take you to 110km/hr and produce about 168kW.
An 8-pole motor at 1540rpm is operating at 100Hz. For 500V supply, that's 5Vdc/Hz. (note: using DC values for simplicity)
To maintain that Vdc/Hz to 4000rpm (267Hz), we'd need to supply 1335V. Therefore, if we want to accomplish this with a battery pack of say 365V, we'd need to re-wind the stator for about 1/4 the voltage. This would be 1/4 the number of turns per coil and 4x the number of wires in hand, right?
mizlplix wrote: "To maintain that Vdc/Hz to 4000rpm (267Hz), we'd need to supply 1335V. Therefore, if we want to accomplish this with a battery pack of say 365V, we'd need to re-wind the stator for about 1/4 the voltage. This would be 1/4 the number of turns per coil and 4x the number of wires in hand, right?"
Yes, but with an increase in wire gauge also. That thin wire is not up to the higher currents I am afraid. There again, 18 Ga seems the best trade off.
You can simply unwind it and count the coil turns and the in hand bundle. Divide the turns by 4 and mulitply the in hand bundle by 4.
Figure that in hand amount in circular mills and convert it to the 18 gauge wire equivalent. (Use an online chart)
Length (Turns) stays the same at 1/4 the original, inhand count gets smaller, (but really stays the same in circular mills.)
BigMouse wrote:The slot openenings through which the wire is inserted is very narrow on the prius stator. 18 guage wire may not fit.
Just a note, I'd like to concentrate on the first generation Prius if possible. Their battery packs are reaching end of life at this point (after nearly 20 years!) and so I expect the availability of used, working transaxles to improve and the cost to go down. Also, this generation had a problem with the windings that caused them to overheat as wound, meaning there are also a number of transaxles out there which are otherwise fine but have a stator in need of a rewind already. These should be the cheapest of all to obtain.