Renard's BMW

Post up a thread for your EV. Progress pics, description and assorted alliteration
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weber
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Post by weber »

Hi Renard,

Back In December 2012 I decided I wasn't getting any work done so I turned off all my AEVA thread watches. Coulomb just referred me to your latest post re low vacuum switch to remind me we have yet to install ours.

I then discovered I have been missing some great stuff in your thread. Congrats on the BMS. And kudos to Nevilleh for making a successful minimal BMS.

And congrats on the neat dash work including the forward/reverse buttons. And for isolating the charger control circuitry. It's ridiculous that that isn't done by the charger designer/manufacturer.

Please excuse me for responding to some old posts below.

In our engineer's case, not cutting out the tyre well (or boot floor) was about the bracing it supplied between the chassis rails rather than the spare tyre. He's fine with a "patch-kit-in-a-can". And if the battery box itself can be shown to restore that bracing (e.g. some diagonals in the lid) there should be no problem.

I'm sorry to tell you I have seen several of those Australec (made in China) DC circuit breakers failed in PV systems. You find them with one side of the lever sagging and floppy and open-circuit, with signs of overheating. It should not be possible for just one side to trip, as it will only have a 220 Vdc rating in that case. Linking the toggles is not enough.

It is not possible to make a DC circuit breaker with that voltage rating in that space without it being polarised. That's because they need to use permanent magnets to deflect the arc into a long curved path thereby making it easier to cool and break. The magnet on one side is flipped relative to the other side. If the DC current is flowing the wrong way, the magnet holds the arc at the contacts and makes it worse than if there was no magnet at all. So the polarity markings are about direction of current flow, not voltage polarity. Or putting it another way, they must agree with the voltage polarity on the source side and not the load side, and they can't be used in cases where current can flow both ways.

Polarised DC breakers have been banned from new PV systems now because installers sometimes didn't understand this and wired them backwards. So electrical suppliers like Ideal Electrical are selling them off cheap now, and they have more reputable brands like ABB. I recommend you grab one of those.
Nevilleh wrote:I think that you will wonder why anyone bothers with thru-hole stuff once you've successfully made some smd boards.
Actually, when I'm placing SMD parts and trying not to bump the one's I've already placed, or when I'm carrying the fully placed board oh-so-carefully to the frypan/oven, or when I watch parts tombstoning or leaping off the board completely, then I think, "One day someone will invent a system where the parts have wires that go thru holes in the board, so they can't move."
Renard wrote:Fortunately, I have an oven of just the right size sitting in the shed.
(Oh wonderful cornucopian shed that has such things within it!)
As you no doubt intended, that resonated in my mind with some famous quote I couldn't quite place. But Google to the rescue:
Shakespeare, The Tempest, Act 5 Scene 1, Miranda:
    O, wonder!
    How many goodly creatures are there here!
    How beauteous mankind is! O brave new world,
    That has such people in't!

Nothing like a bit of kulcha. Image
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Post by Renard »

Hi Weber,

I have just realised you have posted here -- thanks for your detailed responses, always helpful.

Weber wrote:

"In our engineer's case, not cutting out the tyre well (or boot floor) was about the bracing it supplied between the chassis rails rather than the spare tyre. He's fine with a "patch-kit-in-a-can". And if the battery box itself can be shown to restore that bracing (e.g. some diagonals in the lid) there should be no problem."


When I considered the thinness of the sheet metal I was cutting out and the awkward profile of the wheel well, I decided that it was not doing much at all to brace the rear end, particularly as the panelling didn't even contact the RH rail. (See post for 3 Nov 2012.)
And with the brackets I made for the rails and the box fixed firmly to the brackets I thought I had a much stronger arrangement than before.

Now about the DC circuit breaker: I can see from what you write that I need to investigate more carefully.

Today I have assembled the two battery boxes which go under the rear seat.
These two boxes are filled from one end, and the cells are held in place laterally (with respect to the box) by the close fit -- there is less than a millimetre of play, longitudinally by packing the end of the box, and vertically by a wooden lathe between the cell tops and the supporting bolts. (Top LH corner of the photo.)

Image

The photos also show the BMS modules and their comms leads. The clear rigid film that seals the top of the box has not yet been siliconed and screwed down -- that happens after the cables have been connected.
These boxes will be the trickiest to install. The supporting method is shown in the post of 1st Sept 2012.

Image
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Post by Renard »

I had a little trouble with the Driver Controls Unit recently. I had successfully loaded the Weber-modified program, but somehow I managed to disturb - I've no idea how - a component within it.
But James fixed it for me. Great support!

Now I have been running the firmware through Tritium's DCTest program which allows one to set the WS speed to see what happens to the requested current.
I set the regen control at maximum (0.25 of the current maximum of 300A) and have run it at various pedal settings.
The graph below shows the requested current on the y-axis as a percentage of maximum current. This result is for a pedal position of 34% of full.
We can see that regen occurs at speeds in excess of 2087rpm.
( 0.34^2 - (0.34^2 - 1) x 0.25 x 2087/4000 = 0)

Image


The DCTest screen shots are requested-current examples of this formula for two different speeds set in the WS box.

ImageImage


I would plot the results for current as a function of p (holding s constant) except that determining p from the position of the potentiometer is imprecise, and in any case, the actual accelerator pedal potentiometer parameters will be a bit different again. (Love that alliteration!)
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Post by Renard »

I have now installed the two under-seat boxes. I jacked up the car, positioned the boxes roughly underneath their correct place, attached nuts to two of the fixing studs that suspend the boxes from the seat base, and connected two lengths of M8 threaded rod to the nuts. The rods passed through the mounting holes and acted as guides. I lifted the box by the rods while an assistant moved a trolley jack under the box. Then the boxes could be jacked up into the correct position, and the rods and nuts removed just at the right moment.

The photo shows the location of the boxes; note the conduit joining the two boxes passing beneath the drive shaft. The conduit also touches the hand-brake cables, but there should be no mutual movement between them.

Image

More pictures -- without cells -- appear on P3, post for 1st Sept. 2012
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Post by BigMouse »

That's great stuff! What were the final dimensions of these boxes? The P3 post says they're all 240mm tall. Does this fill the entire space available under the seats? Is there any space left to expand the boxes toward the rear at all? I've done my best to measure the space available on my car, but I still have my fuel tank installed as it's still my daily driver.

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Post by Renard »

BigMouse wrote: The P3 post says they're all 240mm tall. Does this fill the entire space available under the seats? Is there any space left to expand the boxes toward the rear at all?

The height of 240mm is the most that would allow the bottom of the boxes to be flush with the floor panelling.

One box is 480mm long, the other, 550mm. The longer box has an offset portion at one end in order to fit an eighth cell. With hindsight it was probably not worth the extra trouble of a complex shape.

If you wanted to put more cells in the tank space, you could do so, but only by putting cells on their sides -- that would permit several more on each side -- but I hesitated to do that as I didn't want to risk any leakage. Perhaps my concerns were groundless -- I don't know.
It's true that moving some cells from the boot to the tank space would improve the weight balance etc.
My other concern was that by keeping those two boxes to seven and eight cells, I could still physically manage them by myself without a vehicle hoist and special equipment.
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Post by BigMouse »

Renard wrote:If you wanted to put more cells in the tank space, you could do so, but only by putting cells on their sides -- that would permit several more on each side -- but I hesitated to do that as I didn't want to risk any leakage. Perhaps my concerns were groundless -- I don't know.


I'll be using much smaller cells than you. 114 CA70FI cells, so hopefully I'll be able to tetris a larger portion of my pack under the seat. I'm trying to leave the interior untouched if possible, though I've also considered deleting the rear seat (one reason I bought the coupe) and just having it registered as a 2-seater after engineering. I'd probably be able to put most, if not all of my pack in that general location and leave the engine compartment above the motor clear for a Tesla-style "frunk".

Also, supposedly you can lay the cells on their side, as long as they're still "upright". So on the narrow edge rather than laying flat. There's a post on the EVTV site that demonstrates why. I'll be keeping all mine upright though.

Thanks again for your excellent documentation. I'm really looking forward to getting started on my E36, though it's been pushed back 6mo (for good reasons).

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Post by Renard »

BigMouse wrote:

I'll be using much smaller cells than you. 114 CA70FI cells.


70? I didn't know there was such a beast. But CA60 cells are 245mm high. They would have to go on their sides unless you chop the rear seat base out.
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Post by BigMouse »

Renard wrote:
BigMouse wrote:

I'll be using much smaller cells than you. 114 CA70FI cells.


70? I didn't know there was such a beast. But CA60 cells are 245mm high. They would have to go on their sides unless you chop the rear seat base out.
Yup, the 70ah cells are shorter and fatter than the 60 and 66, that's one reason I've chosen them.

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Post by Renard »

Following on from Weber's comment about dodgy Chinese DC circuit breakers, I found an explanation of the markings on polarised units, which made clear how they should be wired -- which is not entirely apparent from the little + and - signs on the breakers themselves.
Doing some web research, I found a Moeller PLS6 10/2DC from sparkydirect.com.au for a modest cost. This is a 2-pole polarised 10A DC breaker rated at 250V DC per pole. My wiring to the heater (max. 4A) and DC/DC converter (max. 1.5A) is 1sqmm, so the 10A breaker is best suited.

Image

The boot boxes are finished and covered up with 3mm ABS.
The picture of the cells in the place of the lead-acid battery shows the auxiliary 17Ahr gel-cell battery just forward of the four cells.
In the big box, some heatshrink-covered aluminium strips hold the cells down.
The most central cell has a lift-out strap looped under it.
With the former carpet restored, who'd know there's anything there?

Image

Image

Image
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Post by Richo »

Renard wrote: The boot boxes are finished and covered up with 3mm ABS.


Are you sure it's ABS?
Most people use for polycarbonate
So the short answer is NO but the long answer is YES.
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Post by Renard »

Umm, no, not sure. Clear, rigid stuff from the hardware store.

Edit: 22 April. Yes, it's acrylic. Seems adequate just as a cover.
Last edited by Renard on Mon, 22 Apr 2013, 07:07, edited 1 time in total.
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Post by Richo »

Come to think of it I haven't seen clear ABS.
Acrylic is cheaper and more common at hardware stores.
I'd still recommend the use polycarbonate over Acrylic for an eV.

So the short answer is NO but the long answer is YES.
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Post by woody »

Ha, I thought ABS and Polycarbonate were the same thing, I was wrong

Renard - looking great!
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Post by Renard »


Step by step -- progress.
Yesterday I wired up the front, lower 16-cell box, and this morning I hoisted it into place. I decided to assemble this box out of the car for ease of work, and that was a good decision. It dropped in quite nicely.
It's held in position with four M10 bolts into threaded, re-inforced holes.

Image

Image
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Post by Renard »

At last, after an intense burst of many days of work, all the cells are in and the BMS installed and working. All the HAZV cabling is in place and the WaveSculptor wired up and plumbed in.

Of course there were the usual problems of pieces not quite fitting in place, bolts in hard-to-fix positions, wiring having to be pulled out and re-positioned etc etc.
A plug and socket BMS connection pulled itself apart and I had to take out the cells from the front box to fix it -- an hour or two wasted there.

Now the last work under the bonnet is to wire up the ELV circuits. That's all the mess in the top right hand corner of the second photo.
The first photo shows the complex of connections to the WaveSculptor.

Image

Image

There's no spare room over the fuse box (that's the one with the clear lid) or the WaveSculptor: the bonnet comes down quite close to both, although the insulation makes it hard to tell just how close it gets.
Last edited by Renard on Thu, 09 May 2013, 13:57, edited 1 time in total.
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Post by jonescg »

Looks very neat mate! Well done! So does it turn a wheel?
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Post by Renard »

Yes, indeed it does. I've run it off 60V, rear wheels off the ground.
Tomorrow I'll run it from the full 374V.
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Post by unheardofinstruments »

Well done Renard, thanks for all the photos and explanations, I learned a lot reading this thread, great to see a local EV just about up and running, interested to see how the engineer likes it, certainly raises the bar for neatness and attention to detail, best of luck there and congratulations on reaching the home straight. Beautifully done.

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Post by Johny »

Really neat job Renard. Getting close...

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Post by Renard »

unheardofinstruments wrote: …. I learned a lot reading this thread... .


I have learned much from others on this forum, and so although a major part of the reason for writing up this account was for my own record, I'm pleased that others find it useful too. This is what makes a community. (Administrator, please receive a bow.)
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Post by Renard »

Except for a little tidying up, I've completed the under-bonnet wiring.

The first photo shows the auxiliary box, of which I can't say I'm at all proud. Some parts were made ages ago and I would do things differently if I felt I had the time to re-work it. But when I look at the entrails BMW have stuffed into their fuse box I don't feel quite so bad.
Bottom left (in the photo) is an auxiliary fuse block for the vacuum pump relay, the motor fan, the coolant radiator fans, the coolant pump.
Next to it is the power steering control circuit. In the middle is a board I made a year ago controlling the motor fan and the coolant fans. It also monitors the ELV level and the coolant flowmeter. The instrument cluster battery light comes on when ELV < 11.5V, and a LED comes on when the coolant flowmeter output is less than 5Hz.
To the right (separated by an insulating barrier) is the heater control circuit. I set up a PWM facility, but as it turns out, I need not have bothered as with 370V, the ceramic heater draws only 4.5A for a 1600W approx. output.
I've had quite a bit of trouble blowing IGBTs even though I feel as though I've been reasonably careful with static control.

Image

In the main contractor box, there are a few additions to the 14 January post.
To the LH side (as one views the photo) of the fuse can be seen the incoming charge cable - 16mm^2 to cope with possible high charge rates in the future.
To the RH of the fuse is the HAIS100 current transducer encircling the incoming positive lead from the battery pack. This transducer operates from 5V and provides an output of 2.5±1.875V corresponding to a current of ±300A, or 6.25mV per amp.

As it turns out, I could have used a bigger box for the main and accessory contactors. This one feels slightly more crowded than I could have wished. Still, it all fits in, and it couldn't have been any deeper as it would not then fit under the bonnet. I'm getting to the stage where I'd rather get things finished than have them ideal.

Image

The layout in this space.
Image


For the late model E36 owner, I'm putting some wiring information in a separate pdf file. It lists details of X20 and X69, the two principal connectors that link the motor wiring harness to the rest of the vehicle. The BMW Electrical Manual, while admirable in its detail, does not collect all this information in one place, and the wiring to these two connectors requires modification, and not simply disconnection.

BMW_Engine_Connectors.pdf
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Post by weber »

Awesome work Renard. I wouldn't worry about what that auxiliary box looks like. We've just started one (12 volts only) that will probably end up looking very similar. Spaghetti junction. However, we won't be putting a transparent lid on it. Image
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Post by BigMouse »

Engine connector file saved, though I'm not sure how applicable to my 1992 E36 it'll be. Thanks for putting in the effort though!

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Post by Renard »

BigMouse wrote: Engine connector file saved, though I'm not sure how applicable to my 1992 E36 it'll be. Thanks for putting in the effort though!


You're welcome.


I need a little help with my IGBTs please.

I followed Johny's heater control circuit, except that I used two IGBTs (one for each side) and 600V 40A ones for my lower voltage. I put 0.47uF caps across the IGBTs, 15V zeners from gate to emitter, and am careful to install them with pins shorted. Well, they work for a short while, then go short collector-emitter, and in doing so, take out the opto.
I wonder what I'm missing here.
My fall back position is to simply put in a contactor since I don't need any PWM, but that seems inelegant.

Apart from that problem, everything seems to be working so far: BMS, warning lights, JLD. The wheels spin - off the ground. All ready to try moving under its own power.

About the current transducer, I should say that the output, together with the 2.5V reference, is fed into the non-inverting and inverting inputs respectively, of an op-amp wired as a differential amplifier, with ±5V supplies furnished by a DC/DC converter. The op-amp circuit reduces the voltage by a factor of 25 so for an input range of 0.625V to 4.375V the output is ±75mV which is sent to the JLD404 which accepts an input of -15mV to 75mV. This corresponds to a current of -60A to 300A. It seems accurate - at least up to 5A which all I've drawn so far.
[Edit: I used an op-amp rather than a voltage divider because I didn't want a high impedance input to the JLD404.]

Now supposing the vehicle descends a 1 in 10 slope at 20m/s (72km/hr). With the vehicle weight 1500kg, pack 370V, and allowing, say, 7kW to overcome air and rolling resistance forces, the gross energy into the motor is 22.4kW and at an efficiency of 85% motor and controller combined we have about 50A regenerative current. This will be within the range of 0-60A of the JLD's negative range.

The JLD404 is powered by the contactor circuit so that it will also be switched on whilst charging and so record charged amp.hours as well as amp.hours expended. I'm not proposing that it should read pack voltage, as I don't want to bother with the extra circuitry to deal with ground isolation issues. Pack voltage is reported by the BMS master.
Last edited by Renard on Mon, 20 May 2013, 15:11, edited 1 time in total.
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