RX400H transaxle

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Post by Johny » Wed, 13 Jun 2012, 20:52

coulomb wrote:
Johny wrote: This graph of power vs speed supports the torque "knee" at around 2730RPM.
Leaf 2 Dyno runs

Johny, I'm getting a protection error on that link. Can you check a box or something that says others can read it, please?
That's weird - I have't got special access - anyway - replaced with image.

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Post by Johny » Wed, 13 Jun 2012, 20:53

I got that Leaf Dyno run info here:
http://www.mynissanleaf.com/viewtopic.php?f=27&t=5323

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Post by coulomb » Wed, 13 Jun 2012, 21:15

Johny wrote: So while the Leafs 2222/1530 => 1.45 power-to-weight looks good, it only pertains to up to 40kmh.
Well, that would be a "torque to weight" ratio. If we take the peak power as 105 HP, or 78 kW, it's 78 000 / 1530 = 51 W/kg.
After that the torque must be dropping off or the power wouldn't be basically flat.
The power only drops to say 97 HP = 72 kW at top speed, so that's still 47 W/kg. That's a pretty impressive power-speed curve, actually. No 1/f fall-off there.
Edit: Replaced link with image

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Post by Johny » Wed, 13 Jun 2012, 21:28

coulomb wrote:The power only drops to say 97 HP = 72 kW at top speed, so that's still 47 W/kg. That's a pretty impressive power-speed curve, actually. No 1/f fall-off there.
Yes I understand that there is not a significant power fall off. I was making the point that they don't design for maximum torque to 100kmh. It's in constant power region from about 40kmh.
Contrast with my project where I designed for constant power from about 80kmh.
Food for thought.

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Post by Tritium_James » Wed, 13 Jun 2012, 22:34

PlanB, you don't get something for nothing by dropping the voltage :) Yes, switching losses are proportional to voltage, but they're also proportional to current! So designing your system for say 400V/100A the switching losses in the controller are going to be about the same as a system using 100V/400A, for the same power throughput. The efficiency gain comes with being able to *vary* the DC voltage.

Also don't forget the losses in the motor are in large part resistive losses in the copper, which are proportional to current *squared*. So motor copper losses are 16x higher in the 100V/400A case compared to the 400V/100A situation.

I don't see why you'd want to run a lower voltage if you have the option to run higher. You've got 600V silicon as the most commonly available option, might as well use what you've paid for and run it as high as it will go.

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Post by PlanB » Wed, 13 Jun 2012, 23:56

Your preaching to the converted here TJ (I'm the guy who purchased the 650v transaxle). I get what you're doing with the Sew, taking advantage of it's x8 starting current ability at one end & pushing it to 6000RPM at the other.
It was just that I thought I saw something between the lines in T2s posts on low V/F motors in that they could be an alternative efficiency to varying the DC supply & I wondered if something like this might be an alternative?
I do take your point though, there is no such thing as a free lunch &, if there was a better way of doing it, chances are folks would be doing exactly that already.

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Post by T2 » Fri, 15 Jun 2012, 07:55

Also don't forget the losses in the motor are in large part resistive losses in the copper, which are proportional to current *squared*. So motor copper losses are 16x higher in the 100V/400A case compared to the 400V/100A situation.

- T-J, I know, hard to believe, but you may have made an error here. You may want to think and repost.

If not perhaps someone could come forward with the argument that dispels this mistaken perception. I'd rather not come off as being the know-it-all on this site. Also I just got "volunteered" to help a friend move house. Getting some exercise may be a better use of my time was the argument. How lame is that.
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Post by Canberra32 » Fri, 15 Jun 2012, 12:27

Is that calc right?
That would mean I have 346w/kg.
I know it's a big motor I got but that seems a tad high.
Also remember to adjust the weight ratio calc for taking parts out and adding the new.
Public weigh bridge and a car trailer is a easy way :) go get the trailer and weigh it on way home then stuff all your goodies on it and go weigh it again :)

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Post by Tritium_James » Fri, 15 Jun 2012, 15:54

T2, yeah you're right, my bad! Motor resistance is 1/4 in the lower voltage case. Losses in all the cabling are 16x higher though, but that's not such a big deal...

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Post by PlanB » Sun, 17 Jun 2012, 02:26

Some feedback please on 2 x RX400H transaxles running in parallel from one VFD for AWD. The guys with long multi motor conveyor belts seem to get away with it but I'm not sure how it would go with IPMs in an EV? I guess if I connected the resolver from the more lightly loaded motor to the VFD that might be more self balancing than the other way round?

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Post by BigMouse » Sun, 17 Jun 2012, 03:13

PlanB wrote: Some feedback please on 2 x RX400H transaxles running in parallel from one VFD for AWD. The guys with long multi motor conveyor belts seem to get away with it but I'm not sure how it would go with IPMs in an EV? I guess if I connected the resolver from the more lightly loaded motor to the VFD that might be more self balancing than the other way round?


Since IPM motors are synchronous, I doubt running two on the same VFD would work (at least at low speeds). Induction motors don't mind though.

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Post by Canberra32 » Sun, 17 Jun 2012, 03:52

It could be like running hub motors. Run a controller for each motor.
Easiest Awd is run a Subaru drivetrain with a bigger motor.
I thought of running in hub motors and every company other than brusa told me balance between front to back is an issue.
Brusa have some serious tech controlling it but at the price they charge I would expect it.

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Post by PlanB » Tue, 26 Jun 2012, 17:11

I've been ogling EVO motors & Rinehart inverters but I keep coming back to the 'local product with local support' notion, which is TJs Wavesculptor & his Sew motor. What's the collective wisdom on coupling the motor straight to the differential? Apparently MX5 diffs are available up to 5:1 for ~1200 RPM & ~1200Nm at the wheels but Weber reckons a Eurodrive poking up through the parcel shelf wouldn't be a good look?

The Sew is 250mm in dia (only a bit bigger than the diff) but 517mm long so I take Dave's point. I really want the drive up the back so I've got the engine bay entirely for batteries but it's not lookin' easy. Meanwhile my mate has gone & bought his charging station & I think the Leaf is next, if I don't get a wriggle on all my EV experiences are going to be vicarious.

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Post by Johny » Tue, 26 Jun 2012, 17:50

The SEW directly coupled will give you 0-100kph in just over 10 seconds if we go on what TJ reckons he get get out of it in torque - AND you don't make the car too heavy.

However, to get the revs up for more power. Mount the motor just out of the engine bay in the transmission tunnel (assuming that the MX-5 have one of those?). Then place a Lenco 1.7:1 single ratio transmission on the diff and run the tail shaft from motor to Lenco. The Lenco - because other threads have mentioned around $2000 for single ratio so it looks possible.
That would give you around 7:3 final drive and sub 6 seconds from 0-100kmh (according to the hairs on my wrist). Motor doing around 6700RPM at 100kmh. That assumes a 4.3 diff, do even better with over 5:1 diff.

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Post by PlanB » Tue, 26 Jun 2012, 19:35

I should have posted a bit more about the Sew sorry, 6000RPM max & 63kg.

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Post by weber » Wed, 27 Jun 2012, 04:27

The MX-5 transmission tunnel is too small for a 132-frame motor near the diff. Nothing that couldn't be fixed with lots of cutting and welding.
PlanB wrote:... but Weber reckons a Eurodrive poking up through the parcel shelf wouldn't be a good look?

Actually, I wrote that it "would look pretty radical". By which I meant good (but unusual).
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

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Post by Johny » Wed, 27 Jun 2012, 16:09

weber wrote: The MX-5 transmission tunnel is too small for a 132-frame motor near the diff. Nothing that couldn't be fixed with lots of cutting and welding.
I meant place the Lenco near the diff and the motor in the transmission "hump" not the tunnel - sorry.

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Post by Tritium_James » Wed, 27 Jun 2012, 19:15

Johny wrote: I meant place the Lenco near the diff and the motor in the transmission "hump" not the tunnel - sorry.


This also has the advantage that you get a potentially lighter driveshaft than the motor -> lenco -> driveshaft -> diff option, since the driveshaft is in the lower torque part of the system.

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Post by PlanB » Fri, 29 Jun 2012, 21:37

If I go wavesculptor I need to recharge a nominal 450v pack (380v working under load). Looks like this is a bit short of the mark voltage wise?
Is it fair to say that any single phase 10kw charger is going to struggle to charge a 450v pack? Does this mean I need to go 3 phase?

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Post by Johny » Fri, 29 Jun 2012, 21:50

PlanB wrote: If I go wavesculptor I need to recharge a nominal 450v pack (380v working under load). Looks like this is a bit short of the mark voltage wise?
Is it fair to say that any single phase 10kw charger is going to struggle to charge a 450v pack?
No. Time-to-charge from any given power source depends on the pack capacity - not voltage. It can produce 450 VDC from just about any input voltage.
It says that it can do up to 700 VDC with mods.
"Fully assembled and tested PFC charger unit, ready to plug in. Capable of charging batteries up to 350VDC (up to 700VDC with slight modifications)"
Does this mean I need to go 3 phase?
For 10kW you'll need 3 phase but the charger has only a single phase input. You don't need a PFC input when using 3 phase, but a full wave bridge will produce around 600 VDC which the charger was not designed to cope with.

They do mention that you can run it from a DC source (rectified 3 phase gets close) so you would have to ask whether it can be modified to cope with 600 VDC.


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Post by PlanB » Fri, 29 Jun 2012, 23:04

Something gave me the idea they are just using a bridge so the output voltage limit is the single phase mains peak? They do mention on one of their other pages that it can take rectified 3 phase or voltage doubled single phase derived DC as an input.
I had to smile at the bit about using another EV as the charger input. Given the struggle to shoe horn a decent sized pack into any EV with current battery technology I can't see any EV owner being inclined to share?!

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Post by antiscab » Fri, 29 Jun 2012, 23:15

a boost stage is part of any active PFC powersupply/charger

the internally DC bus is generally 400vdc from 240vac, but can really be as high as you like

if output voltage is higher than the rectified mains, you can do away with the buck stage completely

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Post by BigMouse » Fri, 29 Jun 2012, 23:17

I have heard of people using tired battery packs as DC charging sources for their EVs. Charge the tired pack using a standard slow charger, then use it as a high-current DC power source through a suitable quick charger. Maybe this charger could be used like that?

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Post by Johny » Fri, 29 Jun 2012, 23:28

PlanB wrote: Something gave me the idea they are just using a bridge so the output voltage limit is the single phase mains peak? They do mention on one of their other pages that it can take rectified 3 phase or voltage doubled single phase derived DC as an input.
Trouble is they are talking about US home 3 phase which is 220V phase to phase, Australian 415V phase to phase. (Assumption here that you are in Oz). Output voltage can exceed input voltage with a PFC front end but that's not an issue for you if you use 3 phase and the charger can handle it.
I had to smile at the bit about using another EV as the charger input. Given the struggle to shoe horn a decent sized pack into any EV with current battery technology I can't see any EV owner being inclined to share?!
I can imagine a meeting between EVers or a small rescue where one EV goes to the rescue of another and provides a get-home charge.

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Post by T2 » Wed, 04 Jul 2012, 08:52

T-J    I was not intending to rejoin this thread but your response Motor resistance is 1/4 in the lower voltage case is close. But no cigar. At least not yet anyway !
It does however give me another opportunity to get the message out there regarding rewinding for re-rating motors. The following can't be repeated often enough so here goes.

TTAM The Truth About Motors.

Compared to a 400Vac motor a 100Vac motor of the identical frame size has one quarter of the turns so the path length is one quarter and therefore so is the resistance. So far so good.
But then, the slots would only be filled 25% after removing all those turns, therefore it makes sense to replace existing wire with wire of four times the cross section therefore bringing the slots back to 100% fill capacity. This makes the motor resistance one quarter yet again. The 100Vac motor therefore has one sixteenth the resistance of the stator of an identical frame size 400Vac motor.

The 100Vac motor will require four times as much current to compensate for having one quarter of the turns. Having four times the current but in one sixteenth the resistance makes the I2r copper losses in the 100Vac motor identical to those of the 400Vac machine. Bottom line, when this is done both machines will still develop the exact same torque but of course with wildly different stator currents as noted.

But now, supposing we take the 100Vac machine and speed up the inverter frequency in step with voltage.

The 100Vac machine is now running four times the rpm with 400Vac across its terminals and we will assume that the torque remains unchanged since the stator current has not been allowed to increase.

The mechanical power must have therefore increased four fold which is what having four times the speed with the same torque will get you. Of course with 400Vac across its terminals and that necessary 400% current increase it is not surprising that the electrical input has gone up by four fold also.

However the copper loss did not increase it remains the same since the current was held constant the motor case temperature will therefore not increase either.

We can therefore say that - neglecting the iron losses - the motor must therefore have a continuous rating of four times that previously. And BTW this has been verified by ACMOTOR with a 104V rewind somewhere on these forum pages about two years ago.

To recap, since the motor underwent its rewind the current has been four times greater as previously noted but now with the original 400Vac across its terminals it is now absorbing four times the electrical power and producing quadruple the power.

But what about iron loss ? In the event of full disclosure that does modify the continuous rating by exponential 0.7 but this is empirically determined for only one motor. In this case 4^0.7 =2.6

So I want all those bitching and complaining about spending $800 on a rewind and perhaps a $100 rotor balance to know one thing. The rewind increased your motor performance by 2.6 times. You entered the store with a motor of 1.0 rating and came out later with one of 2.6. Nearly two extra motors worth but weighing the same as the one you took in. So give me a break about this low voltage rewind stuff . It's one of the best deals going.
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