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Discussion Starter #1
We have built an EV! Lopified.blogspot.com
We have used the stock 5 speed manual transmission.
The motor is rated at 10k rpm, the car tachometer goes to 6500 redline, 7500 max. Is the redline for the transmission or engine?
Redline @ 6500 in:
1st gear = 29mph
2nd gear = 53mph
3rd fear = 81mph

Endline @ 7500 in:
1st gear = 34mph
2nd gear = 61mph
3rd fear = 94mph

The power needed to push the car through the air at 45mph is the same independent of the gear I am in. I know with the ICE I shift gears to keep the engine near the most efficient operating range. I know that with the motor 3rd gear will pull more amps than 2nd, but the overall power output is the same. More amps = more heat. The transmission will churn less at lower rpm, but high torque at low rpm can break gears.

SO, how do we know if we should be running 2nd gear at 5000rpm to do 40mph, or 3200rpm in 3rd?
Similarly 5500 = 70mph in 3rd, OR 3500 in 5th?

The motor has enough torque to pull them all, the amps just go up...
 

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The redline shown on a car's tachometer is for the engine, but the transmission has an upper limit to input speed as well - you just don't know what it is, other than something higher than the engine's redline.

You are presumably referring to current into the motor, not current out of the battery. You can't assume from just motor current how much power is being used - you need current and voltage. While the same power is needed to move the car (at the same speed) in either gear, different motor and controller efficiency will mean different power. If you know the power consumption, you can shift for efficiency just as you do with an engine.
 

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Discussion Starter #3
Yes, current to the motor. We are running a 2013 Leaf battery to an Azure 645 controller to a Siemens 1PV5135 4WS14 AC Induction Motor. Our dash output is not currently showing kW output, and does not have enough visual resolution yet in V or A to calculate. My best guess at the moment is keep the rpm under 6500 and the motor and controller as cool as possible, therefore high rpm. I do recognize that once we can resolve the V and A better that is an easy calculation, I was just hoping for more general insight into running a motor vs and ICE w.r.t transmission rpm.
 

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You should be concerned about smoking your synchros in the transmission by running the revs too high. The difference in RPM between gears is what they work against and that increases with input shaft RPM. You may also run into lubrication issues with higher input revs.
 

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You should be concerned about smoking your synchros in the transmission by running the revs too high. The difference in RPM between gears is what they work against and that increases with input shaft RPM. You may also run into lubrication issues with higher input revs.
Yes, while shifting the synchronizer rings act as clutches to match speeds, so big speed differences mean more wear. This assumes - I think a safe assumption for any DIY EV - that you are not rev-matching during shifting.

Once you are in gear (any gear) there is no synchro wear.

This could be considered an argument for avoiding shifting, unless you need to shift up to avoid overspeeding the motor or transmission input shaft, or need to shift down for adequate torque to the wheels, or will be in the newly selected gear for a substantial time so the efficiency or cooling benefit is worth the transmission wear.
 

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Discussion Starter #6
Thank you for the syncro insite, I had not considered that. I tried to watch motor current and voltage today along straight roads, no good data to speak of.
True, in the future there will be automatic motor speed matching for shifting, but not yet. We generally pick the gear need for the next segment of driving, neighbourhood = 1st, city = 2nd, over 40mph =3rd all chosen on the premise of keeping the transmission under 6500rpm. Rough scale, 1st =x2.2 therefore 30mph=6500rpm. 2nd=x1.2 53mph=6500rpm 3rd=x0.8 82mph=6500.
 

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Hi,
Try to monitor the motor and inverter temperature. Usually whatever produces less heat is better. Also don't depend on the power readings from the DMOC, a separate ammeter & voltmeter is more reliable and accurate.

I have a 1PV5135 (with Chevy Volt inverter) in my Boxster conversion. With the DMOC, there is constant torque between 0 and 4000 revs, then constant power past that point (decreasing torque).
Thus I think efficiency is highest at or about 4000RPM -- that is the point of maximum voltage and thus minimum current per Kw/HP.

-Isaac
 

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Discussion Starter #8
Good points, my charts are at 2003 VW Golf GL 2.0L conversion to an Electric Vehicle. Click on them to make them clear... While I agree that at maximum output the torque is constant to 3000rpm on my charts, I am not a Porsche ( I only wish I were one) and drive more like the continuous 60min output line... Thus I read that max kw is at 6000rpm but should I still be reading 3000rpm as my max torque and therefore most efficient point?
 

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The charts with the "S2 0.5M" etc. are for heat dissipation, not torque output.
This is an actual power/torque graph, measured by Azure:

Your 60m/0.5m charts show the limits of heat dissipation, and suggest that higher RPMs are better for efficiency (5-6000).
But this chart shows 4000 as the maximum point.
You should be fine anywhere between 4000-6000, even lower if you like. I generally run my Siemens at 4-5000 RPM on the highway because at that point I still have plenty of torque to accelerate (3rd gear, 60-75mph).
Just be careful about overheating the transmission. There is some power loss at higher revs due to oil (as @remy_martian noted) and temperatures will rise.

-Isaac
 

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Try to monitor the motor and inverter temperature. Usually whatever produces less heat is better.
That makes sense to me - input power which does not become output power becomes heat, so less heat is less loss.

I have a 1PV5135 (with Chevy Volt inverter) in my Boxster conversion. With the DMOC, there is constant torque between 0 and 4000 revs, then constant power past that point (decreasing torque).
Thus I think efficiency is highest at or about 4000RPM -- that is the point of maximum voltage and thus minimum current per Kw/HP.
I don't think that is a logical line of reasoning. At anything less than peak power, the same power level is available at a wide range of speeds, and the higher the speed the higher the motor voltage (and the lower the current), so even if minimizing current were the only factor 4000 RPM wouldn't be ideal at anything but full power.

What's happening at different speeds:
  • The torque is constant under 4000 RPM simply because the current is limited to a constant value by the inverter; it is not a motor characteristic, and does not indicate efficiency.
  • Above some speed (perhaps 4000 RPM in this case, but it depends on available voltage and the current limit) the available voltage is insufficient to drive the allowed current, so current (and as a result torque) drops off. This is a characteristic of the motor but again, this does not indicate anything about efficiency.
  • The power should drop off more significantly with increasing speed if the power limitation is available voltage; the power curve is so flat in this example that I suspect that it is a programmed limit of the inverter, which certainly does not indicate efficiency.
Motor efficiency depends on losses to electric resistance (which increase with current), magnetic hysteresis and eddy currents (which increase with flux and frequency, so with current and speed), and mechanical losses (due to bearing friction and fluid drag in bearings and in the air gap, which increase with speed). As a result, the best efficiency will be at some moderate speed, and the best speed will depend on load (or power level).
 

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My personal experience has been that as my motor increases rpm it's efficiency became better (according to the spec sheet) however the losses through the gearbox also go up at basically the same rate. End results (in my 2 EVs anyway) are that low rpm or high rpm makes no difference other than the noise of the gearbox.
So I run in the quieter/higher gear to save my sanity unless it's hot and the motor/controller is getting hot because I'm working it out of its efficient rpm band, at which point I'll leave it in a lower gear and put up with the noise but even though the motor is then working more efficiently, the overall power consumption per kilometre is the same because I just lose the (roughly) same energy through the gearbox instead which is less sensitive to hot weather.

Extra benefit is when it's cold and wet I have less torque (because of the higher selected gear) available at the wheels so I'm less likely to spin them.
And when it's hot and dry I can thrash the car more...
 

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My personal experience has been that as my motor increases rpm it's efficiency became better (according to the spec sheet)...
I went through a couple of pages of your AVEA Forum build thread without finding any clear motor choice, so... what motor is this, is it the Motoenergy ME1507 and do you have a link to the spec sheet showing how efficiency varies with speed?
 

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It is and isn't the motenergy ME1507. The motor in my moke build is a Me1507, but I was more referring to the kostov dc motor in my daily driver.
The mokes gearbox is noisy at any rpm...
I'm sure I had some charts but I can't remember where I found them. I'll do some digging.
 
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