Select email exchanges between members of REVOLT Custom Electric during the conversion process:
7/2009
I didn't cover the topic of clutch grip as thoroughly as I should have while you were here. There are two things that affect it (primarily) -- material choice and spring pressure. Not talking about the springs in the hub of the clutch disk anymore, this time I'm referring to the springs in the pressure plate assembly itself, that force the ring-shaped plate onto the side of the clutch disk when you release the clutch pedal.
With the higher torque from the Warp11 at 2000 amps, there is a chance that the stock clutch will slip. If it does, then this is a situation that will cause the clutch disk to more quickly degrade over time, but the rate of additional wear would be uncertain and whether this would be a problem at all depends on what kind of torque the stock assembly is already designed to handle. A racing pressure plate, in addition to being lighter, will have stiffer springs to provide more clutch grip. In addition, aftermarket clutch disks are available that provide different materials like ceramic or carbon based pads, to provide more grip than the stock part. Mark went with one of these ceramic disks in his MR2, and it solved his problems with clutch slip (with a 1000A controller and a 10.7" Kostov motor that's shorter than yours).
Unless we can find more data about the stock parts and at what torque they're known to begin slipping, we're really sort of in the dark about the decision. The racing parts may give a definite benefit in reduced weight, but beyond that you'd essentially be purchasing "insurance" against having to disassemble the powertrain again to install improved parts later. I've been thinking that the Porsche parts might be enough and generally aiming to err on the side of keeping the project costs down; perhaps this is unwise as a policy.
Chris
--------------------------------------------------------------------------
2/2010
At his point, it looks like we'll be placing one string each in the front trunk, the engine bay (split on either side of the motor), and then also in the rear. This should allow for us to service the blades from above without a great deal of parts removal. I am doing some final modeling to make sure that the rear most box will not extend below the car too much. It may take up a significant chunk of the rear trunk though.
Aaron
--------------------------------------------------------------------------
6/2010
At this point, the boxes have been built with an inch of air gap above and below the cells and we will be seperating the cells by about a 1/16 of an inch. We're told that this should be sufficient on its own to prevent them from overheating and our experience with the Mazda project seems to show that the cells shouldn't heat up much under load. So, for now, there won't be any penetrations in the boxes. If it proves to be an issue, we can add holes to allow more airflow through the boxes. If that isn't sufficient, we can add fans to do forced air cooling. That's not worth the expense if they aren't necessary.
Aaron
--------------------------------------------------------------------------
The boxes look sturdy and well made. They will probably be safe in a collision, which was a concern of mine. They are not exactly on track for the rear box and say they will need to split it into 3 boxes to make them fit. They hope to get that done in the next few days, and I think they will need to get busy to make it so.
Will there be a temperature sensor in the boxes to detect overheating? There is a surprising amount of space still left above the motor and lateral battery boxes. Are the plans to mount the Zilla, Manzanita and or DC/DC converter above the battery boxes and motor? Do you have the DC/DC converter yet? What are plans about power steering?
--------------------------------------------------------------------------
The boxes look sturdy and well made. They will probably be safe in a collision, which was a concern of mine. They are not exactly on track for the rear box and say they will need to split it into 3 boxes to make them fit. They hope to get that done in the next few days, and I think they will need to get busy to make it so.
Will there be a temperature sensor in the boxes to detect overheating? There is a surprising amount of space still left above the motor and lateral battery boxes. Are the plans to mount the Zilla, Manzanita and or DC/DC converter above the battery boxes and motor? Do you have the DC/DC converter yet? What are plans about power steering?
There are two temperature sensors per blade. One is monitoring the board temperature ( to make sure the resistors aren't heating up too much) and another to monitor the temp of the cells that comprise the blade. We'll have plenty of monitoring to detect temp issues.
The battery boxes are set so that we can load them from above. Also, as you suspect, the controller and a fair amount of electronics, wiring, contactors, breakers and such will be installed above them. It is that install that we will be working to complete by end of July.
We do have the dc/dc. It is an iota high voltage unit. We ordered an mr2 (electric) steering pump for the power steering. It should be here shortly. We need to order a couple of pumps for the cooling loop and some vaccum hose and some liquid line. That should be about it aside from some wire and electrical connectors that will come up as we get things put together.
Aaron
I realized I got side tracked during our conversation and we never completed discussing the DC/DC. Our preference would be to use the Iota 55amp 220V Converter as a DC/DC. I have a new one handy, and
the size is about right to fit near the 12v battery up front. If you want to explore other options just let us know. I don't have much data on using the Vicor modules, so any pointers would be helpful.
Mark
The AC normally is pretty easy with a "close clutch"signal from the climate system. Right now that signal never appears to be triggered. My guess is the climate computer won't try to turn on the AC clutch unless the engine is idling, maybe? Seems odd, the signal doesn't go from the climate system straight to the clutch, it
passed thru the Engine computer which decides when to close the clutch. One would think the ECU could disable the clutch if the engine wasn't running. There is two signals going to the hot/cold mixing valve that we might be able to use instead, but it means disassembling the dash enough to tap that signal... not fun.
Alternative might be to put a tiny three position switch on the dash for the heater/AC or off.
Mark
Finally figured out the AC control circuitry. I've been trying to figure out why the climate control computer never asserted the signal line asking for the AC compressor to be turned on even when set to max
cooling. My suspicion was that it was waiting to see the engine running, and tonight I figured out a way to fake an idle signal to the dash using a speed sensor and my cordless drill.
The good news is that it works, once it sees the engine idling for about 30 seconds it starts pulsing the AC demand line.
Bad news... the pulsing won't turn on the Masterflux compressor, I need some circuitry to convert the pulsing signal to a continuous on signal for the masterflux controller. Other bad news... our motor doesn't idle, so the AC won't turn on until your going down the road and might turn off at traffic lights. So we probably need to build a circuit that sends a false "idling" tach signal to the dash when the motor is stopped. I'm going to ask Otmar if he might be able to add this to the Zilla software, it would be really easy for him. Otherwise I have to design a circuit and send out to have the PC board made. (Time consuming)
Mark
--------------------------------------------------------------------------
If it is a 205V pack, and we can output a max of 960A, I am wondering what the motor will actually see on early acceleration? Can the controller convert extra voltage not used at lower motor rpms into amps for the motor???
Rob
The large inductance of the motor and the switching of the controller produces what electrical engineers call a "buck" DC/DC converter. A Buck converter can step output voltage down and output current up. At low speeds the motor only needs 80-100V, so the output or motor amps might be double input (battery) amps. But the controller's 1000 or 2000amp rating is on the motor side. (Mostly the freewheel diodes, which work the hardest at slow speeds) As speed increases the motor wants to become a generator, so the motor side voltage has to go higher and higher to force amps into the motor and amps start falling off. Top speed is limited by how much voltage you can use to stuff
So in general, a 1000amp motor controller will never draw 1000amps on the battery side. At the most it will draw about 800, and usually more like 600-700.
A 2000 amp controller could draw up to 1200-1500 battery amps... but there are few batteries out there that can produce that for more than a second or two.
Mark
--------------------------------------------------------------------------
According to the 10C discharge curve on the web site I sent you, a mid-way discharged pack will drop from 3.2V to 2.4V under 10C load which is actually a 25% sag. That would give us 153V at presumably a full 960A. If we are using 100V, then we convert the extra 53V into a relative increase in Amps, which may be an additional 333A. So total, at 100V, we have 1293A to the motor, even more at lower speeds. Based on this concept, at low RPM, could we give the full 2000A capability of the Z2K to the motor with our pack? Acceleration will taper off as motor rpms increase due to higher voltage diminishing amp capability of the controller.
Rob
Its very complex, and difficult to model. The exact curve the batteries give will be a big factor. 20% sag may be optimistic, though these cells might surprise us. Since we have the option to try it first, lets see what the the difference is. We could even put the car on a dyno with each controller and see if there is a difference.
It may also be that a 1k produces the acceleration you want.
Mark
No comments:
Post a Comment