[Duncan]

Hi Bigmouse

If you lock the rears then you won't be going in a straight line!!!

You should always set a car up to lock the fronts BEFORE the rears, locking the fronts is not too scary

locking the rears is very very scary

The reason is -
If you lock the fronts you lose front grip, you tend to plough straight on, letting the brakes off immediately restores front grip

Locking the rears drops the rear friction and the rear starts to overtake the front,
Even if you immediately let the brakes off you are now not pointing in the direction of motion and the car is massively unstable

All cars are set up to lock the fronts first
(motorbikes are a different issue)

 

[bigmouse]

Hi Bigmouse

If you lock the rears then you won't be going in a straight line!!!

You should always set a car up to lock the fronts BEFORE the rears, locking the fronts is not too scary

locking the rears is very very scary

The reason is -
If you lock the fronts you lose front grip, you tend to plough straight on, letting the brakes off immediately restores front grip

Locking the rears drops the rear friction and the rear starts to overtake the front,
Even if you immediately let the brakes off you are now not pointing in the direction of motion and the car is massively unstable

All cars are set up to lock the fronts first
(motorbikes are a different issue)

My understanding of car brake systems is that when you first apply the brake, the rears get the pressure first to stabilize the car, then as you press harder, the fronts get more pressure. This is because the weight is transferred more to the front wheels when braking so they do more of the work (they're also physically bigger for this reason).

If the rears lock up (for example, pulling the handbrake or the transmission or diff locking up in a straight line), with no braking on the front, they act like the feathers on an arrow. If the fronts are braking as well when the rears lock up, then they have more friction than the rears (as you said) and will want to trade places with the back.

Regardless, if you're in a corner and lock up either axle, you're having a bad day ;-)

 

[bigmouse]

When I took the sawzall to the floor of the back seat of my car, I was sweating a bit more than would have been justified considering the temperature. That was the most visible indication of the scale of what I'm doing to this poor BMW. The holes that were left when I finished were jagged and uneven.
And they still are! But now there are the beginnings of battery boxes sitting in those holes. And those battery boxes actually hold batteries!

We only dropped the cells in to test-fit. The next steps are to fill in the gaps in the sheet metal around the boxes, paint them, and install panels in them to make them water tight. We'll also make some passages for the HV cables and coolant lines as well. Once that's complete, a rack for the upper portion of the rear battery will be built on top.

​ Here's a photo of the rear battery that will sit on top. It's actually the rear module of the Chevy Volt pack with part of another module attached to it. It's 10kWh all up and about 1200mm (4ft) long.

I also spent some time getting the charge port installed. Here it is before painting. It's held in with pop rivets. It will get a coat of sealant, a drain hole drilled at the lowest point, and some black paint.

 

[eldis]

...
I've heard that the original Prius inverters are easy to control. You might be able to match one of those up with Eldis's UMC and use both inverters in parallel with similar results as you would get with the Lexus inverter.

Sorry if I misled you about how easy it might be to use the Lexus inverter.



Rears locking up is fine as long as you're going in a straight line. Fronts locking up is bad no matter what, you lose all steering control.

Bigmouse is right. Prius inverter (2nd gen!) is quite easy to interface with custom controllers, as it was designed with motor controller being outside of the inverter (old automotive guys and their weird ideas..) Just like there are many Prius inverters, there are also many Lexus inverters. The oldest versions (can't remember the name), followed the Prius 2nd gen logic and had compatible interface, accessible from the outside. Those would be possible to reuse. The new ones (like the one bigmouse has) are not supported from my side and probably never will.

Anyway, UMC Drive is not ready yet to be shipped as plug&play solution. There is a big step between making few units run on your table/in one car, and being user-proof, with a PDF showing wires here and there. With high voltage (even if lower than 600V) being the main concern.

Bigmouse, who makes that white data connector on Lexus inverter? The same one is on 3rd gen Prius. The closest thing I could find was this
http://www.jst-mfg.com/product/detail_e.php?series=234

 

[ETO]

Hi bigmouse , did you plan to connect additional motor to this transmission in future, and use like double motor?
If its possible to convert original Lexus?
I understand should be same voltage and synchronized controllers work, but just like idea to share the load.
because your project amazing, but just cover on engine space make looks empty.

 

[67BGTEV]

I think it's important to point out that the Lexus inverter won't work on its own without a bunch of custom electronics and some modification.

In order to get the controller working, you need a control board for it, or figure out how to control the stock one. I designed the control board I'm using and I don't plan on selling them separately.

There are more modifications required for the inverter to get it to work on its own. Specifically, the HV input needs to go directly to the inverter block rather than the converter block.

Since this system uses upwards of 600vdc, I'm very hesitant to provide anything for sale. The inverter is only part of the system anyway. You need a BMS that works with a 600+v battery. At these voltages, you need to be extremely careful with precharge, safety interlocks, leakage detection, etc. I've designed all of these functions in to my own BMS. This is a whole different ball game from a 144v DC conversion.

Depending on which version of the motor you have, you may be able to use one of Eldis's UMC boards and a Chevy Volt inverter to drive it with a standard EV battery. I'm using the full voltage to ensure that I get the most performance out of it that I can. That would work on the lower voltage version of the HVH-250.

If you have the high voltage version of the motor, the Lexus inverter would be a very good candidate to drive it, but you still need to get it to run.

I've picked up a several tips from the forum - one of them is Honda Insight DC-DC converter, which has worked great for me.
Before I placed an order for GS450H Controller, I did read the Controller tear down articles. Due to a lack of my knowledge about power electronics, I failed to realize the complexity of using this controller. Now that I received my controller, time to see how to make it work. May be GEVCU

or a Raspberry Pi may work. I'll start a different thread. Appreciate if you guys can share the knowledge.

 

[Karter2]

If the rears lock up (for example, pulling the handbrake or the transmission or diff locking up in a straight line), with no braking on the front, they act like the feathers on an arrow. If the fronts are braking as well when the rears lock up, then they have more friction than the rears (as you said) and will want to trade places with the back.

Ahh..No !
once the rears lock, by definition they have lost grip and can do nothing for directional stability. ( the very essence of a handbrake turn , and how Rally drivers and Drift racers set a car up sideways for a corner)
As Duncan says, if anything is going to lock, you always want the fronts to lock first....
Very noticeable with F1 cars...and i think they know a bit about how to set up braking .

 

[bigmouse]

Hi bigmouse , did you plan to connect additional motor to this transmission in future, and use like double motor?
If its possible to convert original Lexus?
I understand should be same voltage and synchronized controllers work, but just like idea to share the load.
because your project amazing, but just cover on engine space make looks empty.

It doesn't make much sense to add another motor to the front of the transmission as the torque that motor can transmit is limited by MG1 anyway. It would have no advantage over using MG1 as a motor on its own. The only reason it works in the original car is because the engine is gas driven, so it adds power to the system.

Ahh..No !
once the rears lock, by definition they have lost grip and can do nothing for directional stability. ( the very essence of a handbrake turn , and how Rally drivers and Drift racers set a car up sideways for a corner)
As Duncan says, if anything is going to lock, you always want the fronts to lock first....
Very noticeable with F1 cars...and i think they know a bit about how to set up braking .

Those examples are all in corners, which I agreed with. Notice in the example I gate I specifically stated "in a straight line" and "no braking on the front". Locked up rears will have more drag than free-wheeling fronts. As soon as you enter a corner, or the fronts begin braking, that doesn't apply anymore and what you're describing is true. I'm approaching this question from the point of view of what happens if my rears lock up from regen while I'm not on the brakes (single-pedal driving).

 

[Karter2]

...
Those examples are all in corners, which I agreed with. Notice in the example I gate I specifically stated "in a straight line" and "no braking on the front". Locked up rears will have more drag than free-wheeling fronts. As soon as you enter a corner, or the fronts begin braking, that doesn't apply anymore and what you're describing is true. I'm approaching this question from the point of view of what happens if my rears lock up from regen while I'm not on the brakes (single-pedal driving).

Well, unless you are in a perfect straight line, on a perfectly even level surface, with no side wind, etc etc, I can assure you from experience ...(I used to be a "hoon" in my youth, and specialised in use of the handbrake for no good reason other than to scare people !) ...that the back end will step out on you at the slightest oportunity once those rears are locked up.
The only way to keep control is to have a front drive car and apply more power.
Watch some go karts, the one with rear brakes only, if those rears are locked
For more than a second, it will spin ...even on a straight, ..unless the driver is ready to catch it !

 

[tylerwatts]

Karter

This statement of yours is physically impossible and you are not mentioning a few variables that would also be involved to make this happen. Even locked brakes have drag and unless the vehicle mass is experiencing a sideways force (turning) or greater drag on the front axle (braking or force elements of steering) the back will not kick out. On a fwd car your engine braking can be greater drag than locked rear wheels and weight distribution and transfer also alter the physics involved but for a typical rwd sports car you need to be aggressive (steer hard or sharp or swerve) or have poor traction to lose sufficient rear drag to cause a spin from only locking the rear wheels whilst coasting on the front.

I agree with the circumstance and outcome you describe and I believe bigmouse does also. But your cause is incomplete. No need to argue over it though, lesson is be mindful of the slowing force on the rear wheels as locking up is bad.

 

[Duncan]

Hi Tyler
I agree with Karter on this - locking up the backs is awful
And YES you can swap ends so fast it makes your eyeball spin!

The problem is any tiny imbalance goes straight into positive feedback and becomes a major imbalance,

I have also seen (and been driving) karts that spin on a straight - both from an excess of power and an excess of brakes

 

[F20A2-t]

Here in The Netherlands, a car that locks up the rears before the fronts, fails its mandatory yearly road-worthiness test.
If you just lock up the rear wheels, without braking force on the front, the car will continue in a straight line as long as the road surface is flat and level, the car's suspension / wheel geometry is set-up properly and you were already driving perfectly straight.
If the car is already braking with the fronts and weight has been tranfered (nose dive), the car will try to turn when the rears lock up. This is also due to the brake force never being perfectly devided 50/50 between the front brakes and having less weight on the rear axle.

You could take a FWD car and put two plastic trays under the rear wheels to see what happens

 

[wujekptack]

do you have a full schematic of the inverter including driver chips IGBT?

I would also need pin input and output descriptions. I'm building a vehicle based on a Prius. I have a gearbox from a prius, I have some stuff from Aigo.

Love your work, please help me out.

Thanks

Ptack

 

[bigmouse]

Sorry for the long delay since my last update! Work has been continuing, though was a bit slow through January as I had a lot of other things taking up my weekends. While the car is at a friend's place for the mechanical work, I can only work on it one day a week.

That doesn't stop me from working on things at home though. I've been getting a lot of questions about my Chevy Volt battery BMS ECU. I'm still working on it, and it's been getting a bit more of my attention recently as it'll be one of the first electrical systems to go in to the car once the mechanical work is done. So I want to have it as far along as possible by that time. I spent a full day last weekend coding on it. It's going to be very nice. So far I've got the J1172 interface working and tested. Precharge and contactor weld detection coding is done. The framework for the main state machine is in place as well.

Mechanically, the rear lower battery boxes are still coming together. The sheet metal cut from the car is all closed in now, so all that's left to make it water tight again is to skin the flat sides of the boxes. That will be the last thing that gets done before painting, once the structure for the rear upper battery is complete.

Here's a photo of one of the rear lower batteries in its home.

The tubes mounted above it will have feet which press it down in to the box, securing it in place. There's a channel in the bottom that fits with the stock clamping point on the battery to keep it from sliding rearward. The top battery will rest on top of the structure, also on its side, with a channel on the rearward steel box section serving the same purpose as in the lower batteries. The top battery will be held down by a strap/frame which uses the same mounting points as the lower battery tie-down.

Here's the assembled rear upper battery.

It's a lengthened module, 10kWh total. I used threaded rod to clamp the batteries in the lower section and pallet strapping to clamp the top of the module.

At the front of the car, the hard points for the front battery are coming together. I'm using the front sway bar mount to secure the front of the front battery. These mounting points are the same points used to mount the front subframe on AWD versions of the car, so it should be plenty beefy to support the battery. The rear of the front battery will be supported by a bar which will be installed bridging the original motor mounts.

The inverter, charger(s), heater, and DC-DC will all mount to the front battery enclosure. The power steering pump and air conditioning compressor will mount to the same bars that the front of the battery will rest on. The vacuum pump (and reservior) will live in the cubby behind the passenger side strut tower.

The water pumps will mount along the bottom of the radiator.

I had some blanking plates printed for my battery coolant ports.

These will be used in the front battery as I'll be paralleling the coolant circuit with T-pieces rather than passing through one battery to the other. I have the STL files for these parts if anyone is interested. I had them printed at Seeed studio and they came out very nicely, though expensive for what they are.

This weekend we'll hopefully get the rear battery mounting structures completed so that I can start on some wiring/plumbing.

I wouldn't say it's getting close, but progress is being made! Registration for this car is due in July, so I want to have the conversion done before then so I can get the DMV to verify it doesn't need SMOG testing in time to not have to register it as non-op.

 

[gileadgarage]

Holy crap! Beautiful!

 

[mfox]

Great ,
How did you solve problems with error blinks, when you took OEM engine out?
Odometar will work after gearbox replacement ?

 

[bigmouse]

Great ,
How did you solve problems with error blinks, when you took OEM engine out?
Odometar will work after gearbox replacement ?

I haven't connected the 12V battery since the engine came out. With the DME removed, I'm hoping the cluster will only light the CEL if told to, and I know the CAN message for that. Will wait and see. Worst case scenario, I remove the light/LED.

The odometer will still work since the speedometer signal comes from the rear diff.

 

[bigmouse]

Wow, another month has gone by already!? A quick update,: we're still working on getting the rear battery installed. The mounting/clamping parts are proving to be very fiddly. The rear upper battery has been put in place and the rest for that to lay down on is being built. Then the tie-down for that as well.
The platform for the front batteries has been installed. I used some pieces of metal left over from a couple Nissan Leaf batteries that I tore down for the forward support and welded a piece of box section across the original engine mount locations for the rear support. Here's a photo of the front batteries sitting in place. You can also see the mounted power steering pump on the same supports.

For some reason, I can't get the pump to power up. I've used this same model pump before without trouble, so I think I might have gotten a broken one from the yard.


And with the front of the car on. If I play my cards right, I might have room left over in front for a "frunk", Tesla-style!

The cardboard mockup on top of the batteries behind the strut bar represents the inverter.
I've been playing with the HV cable routing. There's a photo from under the car of the HV battery cables, the AC cable from the charge port, and the beginnings of the coolant pipes visible. Don't worry, the cables will be much better supported and protected when the final routing is done. This was just a mock-up to check lengths. The coolant pipes are fairly large diameter so as not to restrict the coolant flow to the rear battery over such a long run.


I picked up a mini-lathe from Harbor Freight as well to turn up some copper spacers to bring the HV bus in to the inverter. I can't use the original connectors because the internal high voltage bus (650V nominal) was never brought out of the inverter in the original application. The photos show the copper spacers with the threaded rod installed and how the cables will connect.



I have some HDPE plastic that I intend to machine up to insulate and support these connections.

I've also still been poking at the BMS code. Spent several hours on it last night and got the CAN communications on the "powertrain" bus working. I can now monitor the BMS over CAN, request changes of state from the state machine (so I can ask it to go in to "drive" mode for example).

Still to do on the BMS:
Implement SoC monitoring
Implement isolation monitoring
Hook up to a real battery and start testing!

 

[bigmouse]

Bonus photo of the rear batteries in their homes and clamped in place. The upper battery will lay on top.

 

[mfox]

Nice. You are not afraid of such big voltage. ?? What charger and dc-dc you are using?