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Old 11-27-2018, 02:12 AM   #11 (permalink)
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Originally Posted by cRiPpLe_rOoStEr View Post
That's a good point. Well, some engines used in conversions may eventually not be meant to be directly reversible, and then a transmission becomes a must. I don't remember when it was done, but someone converted an Opel Astra to electric here in Brazil with a 20hp engine and claimed to have retained the transmission mostly because the engine wouldn't operate properly on reverse...
That's interesting.

I wonder how much you can save, in terms of electricity, going for a smaller motor? Looking at charts, it seems like EV kwh use varies more by weight than power or performance.

Possibly most of the savings are in upfront costs and weight and packaging penalties.

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Old 11-27-2018, 02:55 AM   #12 (permalink)
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The torque falls off as the motor gains RPM. All electric motors have peak torque at stall. A continuously variable transmission, keeping the motor near stall with acceleration, would give the best acceleration.
Not true if you control peak current electronically like all EVs do. With a motor controller capping peak amps at, say, 450A (in my Electric Booger), torque remains constant from zero rpm up to the rpm where the amount of voltage required to maintain said current is equal to pack voltage. In the Electric Booger this is 4000 rpm and 68V (pack voltage sag @ high current). Electric motor current is proportional to torque.

An AC motor's huge advantage is lack of back EMF, so voltage required to maintain a set current does not rise with rpm, which allows for a massive rpm range. If you look at the torque curve on many available AC motor kits, they are flat from nearly zero to very high rpm.
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Old 11-27-2018, 10:42 PM   #13 (permalink)
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Originally Posted by niky View Post
I wonder how much you can save, in terms of electricity, going for a smaller motor? Looking at charts, it seems like EV kwh use varies more by weight than power or performance.

Possibly most of the savings are in upfront costs and weight and packaging penalties.
Well, that engine was not too big, but IIRC it was quite low-revving.
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Old 11-27-2018, 11:12 PM   #14 (permalink)
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Originally Posted by cRiPpLe_rOoStEr View Post
Well, that engine was not too big, but IIRC it was quite low-revving.
The smaller motor does weigh a bit less. IMHO it is more important that it fits into a smaller space.

The motor will have a certain rating for 1 hour or 2 hour use ... likely what I'd use for a conversion ... the continuous rating would be lower. But the extra torque for accelerating would be less, so running through the gears may make it more fun to drive.

An 1800 rpm, 4 pole, AC induction motor used in industry has a minimum current ... just spinning with no load .. around 1/3 amps. I have not measured .. or read about .. any similar minimum current on AC motors used in cars. ASS U MING (not a good idea) that there is a similar minimum, there may be a marginal advantage to using a smaller motor. It might be hard to separate the contributions of lower weight from lower max rated current in real-world testing ...
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Old 11-28-2018, 06:05 AM   #15 (permalink)
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Not so fast, GM!

At least not if Trump has his way:
https://twitter.com/realDonaldTrump/...gm-layoff-plan

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Originally Posted by POTUS
Very disappointed with General Motors and their CEO, Mary Barra, for closing plants in Ohio, Michigan and Maryland. Nothing being closed in Mexico & China. The U.S. saved General Motors, and this is the THANKS we get! We are now looking at cutting all @GM subsidies, including.... ....for electric cars. General Motors made a big China bet years ago when they built plants there (and in Mexico) - don’t think that bet is going to pay off. I am here to protect America’s Workers!
A subtle nudge by the POTUS, as ever.
Little chance the Congress lets him have it, but GM be warned.
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Old 11-28-2018, 09:12 AM   #16 (permalink)
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I appreciate that you posted the full quote. The media (at least CNN that I saw) doesn't do a good job of that, so you miss a lot of context.
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Old 11-28-2018, 01:13 PM   #17 (permalink)
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conversion motors and GM's EV subsidies

More context is a good thing on Trump's bluster, as GM is only 10,000 cars away from their 200,000 vehicle cap on EV tax credits anyway. The credit will go from $7500 to $3750 for the 2nd quarter after hitting that target, then down to $1875 for another 3 months before hitting zero.
https://www.edmunds.com/fuel-economy...x-credits.html There are efforts afoot to extend that credit, which is the main thing he could affect.

Now back to motors for conversions. Analogous to rotor tip speed with helicopters, the speed of the commutator under the brushes is a limiting factor on series wound brushed motors, which is proportional to the motor diameter. So a larger motor will have more starting torque, but a lower top RPM. Since starting torque is rarely an issue in EV conversions but highway passing power is, a smaller motor, or especially multiple small motors can be the best solution, as they can reach higher RPMs. Efficiency will not change appreciably between say a 6" and a 9" series motor.

My 9" series motor has externally wired fields that can be switched from series to parallel. This provides maximum starting torque in series, and then further down the dragstrip, switching to parallel provides more power at high RPMs.
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Old 11-28-2018, 03:26 PM   #18 (permalink)
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Originally Posted by jray3 View Post
More context is a good thing on Trump's bluster, as GM is only 10,000 cars away from their 200,000 vehicle cap on EV tax credits anyway.
And if I understand correctly, it's not GM that gets the tax credit, it's the person who buys the EV.
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Old 11-28-2018, 03:38 PM   #19 (permalink)
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Originally Posted by jamesqf View Post
And if I understand correctly, it's not GM that gets the tax credit, it's the person who buys the EV.
GM gets to charge more for the car, helping make it profitable, while the customer pays the same price with the taxpayer eating the difference.

You're technically correct, but practically speaking, that credit goes into GM's income.
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Old 11-28-2018, 06:05 PM   #20 (permalink)
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Quote:
Originally Posted by jray3 View Post
Now back to motors for conversions. Analogous to rotor tip speed with helicopters, the speed of the commutator under the brushes is a limiting factor on series wound brushed motors, which is proportional to the motor diameter. So a larger motor will have more starting torque, but a lower top RPM.
Actually, the rpm limit on my kostov is due to the windings not being restricted. Similar to most +13 inch series motors. The comm flies apart next.

The fix is kevlar banding, but at only a 1000 or so more rpm. Back EMF @ 6000 rpm kinda sucks big time, too

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