Mazda MX-6 build thread (EV conversion)

[mechman600]

Originally Posted by freebeard

Hydraulic clutch? If you remove the engine and transmission, what does the clutch attach to?

You don't remove the transmission. You make an adapter plate to mount the electric motor to the transmission, and the flywheel to the output shaft of the motor. DC motors have a relatively narrow efficient operating RPM, so we keep the transmission and use maybe three gears to get the best acceleration in every situation.

mechman600 -- Is there a second reason for retaining the clutch? Because I watched a Youtube video of a Porsche EV conversion, and as he was driving he'd say, "Oops, there goes the clutch...there goes the clutch."

Won't a switch like they put on the outside of race cars substitute?

Not sure why he said that. He likely was using the old original clutch which couldn't handle the increased torque of a ginormous DC motor.

You always need redundant safeties build in, like a contactor or two. Rule of thumb: engineer it so that if ANY two devices fail, you will be able to stop the car.
For example, a failed closed controller & failed closed contactor - without a clutch you are screwed, flying down the road in a runaway condition, which is why it is recommended to use TWO contactors in a clutchless DC powered EV.

[thingstodo]

Originally Posted by freebeard

Are you weighing the stuff as you remove it? Would it be a spoiler to estimate the weight lost and gained?

I have 296 lbs removed from the front so far, 50 lbs from the back.

I can't find the weight for the gas tank, so the rear weight will rise a bit.

Netgain Warp 11 is 229 lbs. The adapter plate and coupler from CanEV were 12 lbs from the shipping carton - I can't find video where I weighed it so maybe 10 without packing. Netgain industrial controller 23 lbs from the web site.

As I put stuff in I'll be weighing it.

The motor weight may be a problem as it weighs more than the original ICE!

The left/right weight balance will likely be off. I was planning to mount the controller above the motor, but maybe it should be above the transmission to try to balance things out a bit more?

The rear spring and shocks may need an upgrade. I intend the battery pack to go beneath the back seat, where the gas tank was, plus a smaller pack right behind the back seat taking up part of the trunk. The batteries are just over 400 lbs, plus frame, plus insulation, plus battery heating, plus supports. So the car may drive like I have 2 sumo wrestlers sitting in the back seat!

Contactors, wiring, inertia switch won't be much - 30 lbs

Liquid cooling will be significant - maybe 50 lbs for coolant and pump

DC/Dc converter and small 12V battery will be another 20 lbs up front

Charger is another 50 lbs in the back

Did I miss anything?

[freebeard]

So the transmission is going back in; makes sense. Has anyone posted a comparison of shifting and just leaving it in top gear? I was thinking that torque gets you off the line and horsepower limits the top speed.

I think you're right about the 'old, original clutch'.

The reason I ask is I'm following http://ecomodder.com/forum/showthrea...mgr-29878.html and wonder about the downside of a single-speed, clutchless, electric reverse drivetrain.
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I need to educate myself about contactors. I noticed in Paul Holmes VW conversion he had a lanyard to pull on a shorted plug. But thread like http://ecomodder.com/forum/showthrea...ack-29765.html have it in the trunk. Better to have it accessible from the driver's position?
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thingstodo -- For whatever reason your post doesn't have a Thanks button. Thanks.

[Astro]

Originally Posted by freebeard

I think you're right about the 'old, original clutch'.

Could also be caused by the increased torque due to most EV drivers choosing a single gear for most driveing. 2nd or 3rd. Taking off from a stand still in 3rd gear, even though the electric motor has the required torque it may exceed the clutches torque handling abilities. An worn clutch would be even worse.

Originally Posted by freebeard

The reason I ask is I'm following http://ecomodder.com/forum/showthrea...mgr-29878.html and wonder about the downside of a single-speed, clutchless, electric reverse drivetrain.

I believe the MGR is an AC motor which is much less likely to fail full on. The controller needs to continue to do all its very complex math and timing to keep the motor turning. Maybe if the accelerator pot failed full on it may cause the motor to full on. Luckily Paul thought of that and in Paul's controller (maybe other controllers too) he checks for 100% pot output and detects it as a fault and shuts down the motor. I think full throttle is designed to be reached at 95% (or something around that) so that 100% throttle can be set as a fault condition.

Originally Posted by freebeard

I need to educate myself about contactors. I noticed in Paul Holmes VW conversion he had a lanyard to pull on a shorted plug. But thread like http://ecomodder.com/forum/showthrea...ack-29765.html have it in the trunk. Better to have it accessible from the driver's position?

I was toying with the idea of getting the park brake mechanism from an overseas version of my vehicle. Driver on the opposite side, so park brake on the opposite side of the tunnel. Paint it red and mount it on the passenger side of the tunnel. As my battery pack will be at the back under the rear passenger seat (where the petrol tank was) the cable end will be right near the batteries and should be able to join to a shorted Anderson connector. Anderson connectors come in 350amp types and have nice screw holes for attaching one to the end of the cable and the other to the body.
So in an emergency, not just a runaway motor but also a fire or after a collision. Simply pulling the red park brake will cause a physical disconnection of the battery from the rest of the vehicle.
This would be in addition to the emergency stop buttons in the cabin and engine bay. Which are wired in series along with an inertia switch, to the main contactor energise circuit.

[thingstodo]

Originally Posted by freebeard

Has anyone posted a comparison of shifting and just leaving it in top gear? I was thinking that torque gets you off the line and horsepower limits the top speed.

I have not seen one. I would be interested as well.

Talking it through, I would expect the acceleration to be a bit less unless your motor and controller are over-sized .. and your transmission/axles/etc can handle the boosted torque.

The siemens motor on the single-speed borg-warner transmission for the Ford Etransit is rated over 100 kw. The motor used by the Coda is(I guess WAS) also over 100 kw, using a different gear ratio on the same borg-warner gearbox.

The original beetle was no speed demon, but it got by with under 60 hp (45 kw or so)

The reason I ask is I'm following http://ecomodder.com/forum/showthrea...mgr-29878.html and wonder about the downside of a single-speed, clutchless, electric reverse drivetrain.

I am no expert. My opinion is that the downside is a bigger controller and a bigger motor to get good performance. My standard transmission weighs under 75 lbs. I hope that the MGR gives decent acceleration. I hope to use it in a WIKISPEED car. I hope it gets GREAT performance on a 1400 lb car

Since Toyota designed the motor, gearbox and axles I would expect them to be well matched, with decent safety factors. My clutch is a mechanical fuse for my system. I can turn up the torque until I smell clutch. The MGR should not need anything so crude.

I need to educate myself about contactors. I noticed in Paul Holmes VW conversion he had a lanyard to pull on a shorted plug. But thread like http://ecomodder.com/forum/showthrea...ack-29765.html have it in the trunk. Better to have it accessible from the driver's position?

The contactor opens when 12V is no longer applied. It can be wherever you like. If you have a pull switch or cable, you have fewer options on where it can go since the cable must be routed.

I have two contactors, one for the precharge and one for the main enable. That gives me minimal redundancy. I need to figure out a visual indication that both contactors open each time.

In the case that the contactors BOTH fail AND the controller fails ON to full throttle, there will also be a cable connected to a DC breaker under the hood. Similar in function to the shorted plug you discuss. Pull the cable (I hope it looks like an old style choke) and the breaker (like the breaker in your house panel, but BIGGER and it can open on 500A of DC) the controller loses power. That should be paranoid enough for most people.

And lastly, if all else fails, I press the clutch and let the motor overspeed until it tears itself apart .. but it stops and I don't die. Perhaps I am hurt by the motor shrapnel, likely not. The warp11 is big and sturdy.

Watch out .. reading posts by paranoid people may be hazardous to your health .. paranoia is catching!

[oldtamiyaphile]

Originally Posted by freebeard

So the transmission is going back in; makes sense. Has anyone posted a comparison of shifting and just leaving it in top gear? I was thinking that torque gets you off the line and horsepower limits the top speed.

Accelerating in top gear will pump a lot more amps. You can get away with a smaller controller if you use the gears. Easier on the motor and gearbox (input shaft etc) too. Electric motors have the very real capability of breaking gearboxes as often they're torque rating isn't much above what the OE ICE produces.

[mechman600]

Yes, AC systems are much safer because it is impossible for them to fail full-on, unless of course it is a potbox failure, but allegedly Toyotas were known to fail that way a few years back too.

DC motors have a limited RPM range because as their speed increases, so does back EMF, which is self-induced voltage in the opposite direction that it is spinning. Therefore, voltage necessary to maintain a given amperage (amperage is proportional to torque) is proportional to RPM. At zero RPM it takes almost no voltage to reach max controller amps, and at, say, 5000 RPM it may take full pack voltage to achieve the same amperage/torque. On my 72V Electric Booger, the crossover where full pack voltage was put to the motor to maintain max amperage was at 3500 RPM. Above 3500, while pack voltage remained at the motor, amperage began to fall as the motor speed increased above that. Thank-you back EMF!

AC motors do not have back EMF to deal with, which is why you see a single speed Tesla S with a motor that delivers 300 ft/lbs of torque and revs to 14,000 RPM.

As for the above question about starting off in higher gears, here is a video I posted a long time ago about first gear vs second gear starts in the Electric Booger. As you can see, having no clutch really slows the upshift down, which is why I will do a clutch next time. This was more or less a test to show that. A third gear start with the car would have been PAINFULLY slow, so I didn't even bother to show that.

https://www.youtube.com/watch?v=OpbHJPgcVIY

[Astro]

Originally Posted by thingstodo

...
Watch out .. reading posts by paranoid people may be hazardous to your health .. paranoia is catching!

Too true.
I doubt i will use the second park brake idea, it was more appropriate when i originally thought i would only be able to afford a DC system.
But now i have the AC motor the emergency cut out button and inertia switch in the main contactor seems like it will be enough.

Somebody mentioned the pre-charge contactor circuit. I think i will put the emergency cut outs in the earth return that will be used by both the pre-charge and main contactor coils.
I don't think the pre-charge resistor would last long at full current and so wouldn't be a huge issue in a contactor fail on scenario. The pre-charge resistor would act like a fuse at full amps.
But best that both circuits are cut with the emergency cut outs in case of an electric shock scenario.

[freebeard]

Thanks all. If you are curious, visit the MGR thread; but they are "multi-phase DC" for reduced back EMF and the gearset is single speed (6.xx to 1 reduction). I'm more concerned about off-road creeping than 60 foot times.

I'm going to let this thread go back to the assigned topic.

[Astro]

Originally Posted by thingstodo

...
Contactors, wiring, inertia switch won't be much - 30 lbs
Liquid cooling will be significant - maybe 50 lbs for coolant and pump
DC/Dc converter and small 12V battery will be another 20 lbs up front
Charger is another 50 lbs in the back
Did I miss anything?

Vacuum pump if needed for brake assist.
Electric power steering pump unless you use the original pump driven off the rear shaft of the drive motor or have a manual steering rack.

Probably not very heavy items but it all adds up.

Just like you I weighed each item as i took it off and then did the same for the items i planned to put on, either weighing them if i had them or using weights from spec sheets or just by estimating.
I was shocked to find the car would be one third of a kilo lighter than factory original.
That made me feel really pleased until i bought my AC motor. Which was about 20 kilos heavier due to buying a cheaper rewound AC industrial motor rather than a purpose built car AC motor.
But then i GPS logged my commute and found that i would need much less battery capacity than i originally guesstimated. 20 kilos less, so i am back to factory weight again.
My commute is not a long distance but lots of waiting at traffic lights.

You listed 50lbs for liquid cooling.
Is this for cooling the controller?
This seems like a lot to me. Of course i have no idea what would be involved in cooling a controller but i would have thought a few of litres of coolant at the most with a nice fan assisted aluminium radiator to cool it down. Like the after market ones they sell to cool transmission fluid.

I just finished pulling the heater core out of the cabin in my car as it is to be replaced with a ceramic heater element. Maybe the heater core could be reused as a cooling radiator? That would make it zero cost. Maybe strap a couple of 12v fans from a computer on it to increase the air flow.