Weber and Coulomb's MX-5

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Post by coulomb » Wed, 24 Mar 2010, 05:33

We've been distracted lately with the "charge using AC controller" idea, but this week's hands-on EV day, after showing off the partly completed car to no less than three visitors, was spent preparing to bolt in the two battery cages shown painted on the previous page.

They are the middle level that fit in the space behind the seats, basically where the petrol tank was. The chassis has a hole here with a rounded end, where we had to keep some rounded reinforcing.

Image

You can see that the boxes are staggered vertically a little, to clear the differential subframe at the back, and to keep the cells as low as possible for the best (lowest) centre of gravity. The two cages bolt together.

We fit 14*3 + 10 cells at this level. There will be cells below (on either side of the tailshaft) and above it (the well-restrained "neck snappers" Image ). We counted today that we will have 10 battery cages in all.

In the above photo, we're preparing the 45° pieces of flat 20 x 3mm bar that will bolt the front of the cages to the chassis, onto those pieces of 50x50 mm angle.

There are also two other pieces of 20 mm flat bar that we welded to the chassis today, which will carry more M6 bolts to hold these cages down. One of them is that bright white strip of metal at the right (not in its correct position). You can see a little of the left one (not painted) sticking out at the left of the picture.

We have to use a lot of M6 bolts instead of a smaller number of M10 bolts, since the flanges we have on the vehicle are quite narrow and won't take larger bolts. This is approved by our engineer.

The front one of the two cages is one of the easiest to get in and out, so we might fill it with cells soon to sort out exactly how the cells will fit in the cages, how they'll be held down, how much room there is for cables and BMUs, etc. Also, it's fun, and we need something to spur us on to finish more cages. We've completed 3, almost installed 2 of those, designed 2 more, and just have 5 more to do after that   Image !

Edits: grammar; number of cells (I was a bit optimistic there!), designed in conjunction with engineer, not entirely by him, and reason for the split level; link to previous page.
Last edited by coulomb on Thu, 20 Mar 2014, 18:13, edited 1 time in total.
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Post by coulomb » Thu, 01 Apr 2010, 17:27

We considered a simple DC/DC discrete converter (since we can't find a module to do what we want). Either capacitively coupled or inductively. Capacitive is really out, because the voltage from one side to the other isn't a defined constant, and any glitch in that voltage would glitch the output voltage. Plus, it would be at least a tingle hazard. Not good.

So it had to be inductive, using a small toroid or the like. I did some simple experiments using a 74C14 hex schmitt trigger inverter, but couldn't get anything out of it. I'm pretty sure I need a lot more turns:

Image

The white thing in the middle of the toroid is just a piece of insulation I found that keeps the primary and secondary physically separated.

The project is so behind, that we'll have to abandon the idea of a DC/DC for now; wiring 12 V to each cage won't be such a hard thing.

Speaking of taking too long and getting behind, we took most of a day just getting little strips of zinc plated steel (with much of the zinc removed for welding) prepared with M6 nuts welded to them. This is because once the cells are installed into our cages, the nuts will be inaccessible.

Another lesson: 6 mm holes are not adequate for M6 bolts. The slight misalignments and angles of the holes, exacerbated by the inaccessibility of most of the holes (we needed a right angle drill adapter and a cut-down drill bit) meant it was very difficult to do up the nuts. When we drilled them out to 6.3 mm (with a strange old drill with markings something like "1/4"), things went much better.

I think we've really learned our overall lesson: 3 battery boxes maximum! 10 is insane! But there isn't anything we can do about it now, except get on with it.

We did our first trial packing of cells as well. This, as expected, brought up some problems. The cell strapping hardware supplied by Sky Energy, which is a pair of coated metal brackets and long pieces of stainless steel M5 threaded rod, was too wide to allow our cell rows, which are packed at 124 mm spacing, to be inserted from above. They have to be inserted from above because we can't get to the nuts when they're in the cage.

We considered cutting the brackets to the width of the cells (116 mm), and using many cable ties "in series". We would need about 10 ties in series for a typical row of 14 cells. That seems excessive, a lot of work, and not very strong.

Now we're looking into plastic strapping, probably with hand tools for tensioning and crimping a seal on them. If we get 12 mm strapping, it will fit in the 14 mm "channels" of the cells. We'll still need the metal brackets, cut to 116 mm and with somewhat rounded corners.
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Post by Nevilleh » Thu, 01 Apr 2010, 18:00

Here I am,oozing sympathy.
(Really!)
Have you looked at the SEPIC converter? If not, National Semi AN1484 will show you how. (here: http://www.national.com/an/AN/AN-1484.pdf#page=1)

I eventually discarded the SE battery clamps and made my boxes (only 3) to be a snug fit for the number of cells that I installed. Fairly easy to install until I came to the last row and found they are very snug indeed. The blasted ribs on the cases get in the way something terrible, but a little judicious application of the angle grinder allowed me to eventually get them all in. Only needed a mm or so here and there.

In your case, it might be possible to also do away with the SE clamps and then fill the left over space with wooden blocks? They could be cut to fit quite nicely, I think. I wish I had allowed a little more room and done just that!

Not sure about the clamps, they didn't have much tension and the tight fit in the boxes will - I hope - stop any cell expansion. Probably better than the clamps as the cells are contained over the whole surface, not just at two places.


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Post by coulomb » Thu, 01 Apr 2010, 19:27

Nevilleh wrote: Here I am,oozing sympathy.
Thanks, Neville.
Have you looked at the SEPIC converter?
Yes, unfortunately it has the same problems as a capacitively coupled converter.
I eventually discarded the SE battery clamps and made my boxes (only 3) to be a snug fit for the number of cells that I installed. Fairly easy to install until I came to the last row and found they are very snug indeed.
I wonder if you'll ever be able to remove the cells again, if needed. They will presumably swell a little, which means that the present tight fit may become impossibly tight in the future. You might have to ruin a box and repair it or build another one just to get one cell out.
In your case, it might be possible to also do away with the SE clamps and then fill the left over space with wooden blocks?

Interesting idea, but the wooden spacers would have to be somehow collapsible or they'd have the same problem. Perhaps wedge shaped, yet somehow causing even loading.

Our idea of lowering in strapped rows, while a bit of work and expense, does allow for later removal even in the presence of a little swelling.
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Post by Nevilleh » Thu, 01 Apr 2010, 19:42


Have you looked at the SEPIC converter?
Yes, unfortunately it has the same problems as a capacitively coupled converter.
Not sure what those problems might be. The coupling method, whether it be inductive or capacitive will transfer energy in exactly the same way. Current spikes in one winding of the transformer will appear in the other, same as voltage spikes on one side of the cap.
I wonder if you'll ever be able to remove the cells again, if needed. They will presumably swell a little, which means that the present tight fit may become impossibly tight in the future. You might have to ruin a box and repair it or build another one just to get one cell out.
Yes, I wonder too! But I have already had to remove a cell and it came out quite easily - and went back in again. The whole purpose of the clamping is to stop swelling, after all. Admittedly, the battery hasn't seen much use yet   Image

My thought about wooden blocks was to use a couple of opposed, wedge-shaped pieces of say high density particle board. Driving them in fairly gently would provide compression for the cells and they would be easy to remove later if you had to. If ever I make another battery box, that is what I will do.
Last edited by Nevilleh on Thu, 01 Apr 2010, 08:45, edited 1 time in total.

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Post by Squiggles » Thu, 01 Apr 2010, 19:59

Maybe the boxes/racks need to be made in two separable pieces that can be released to allow batteries in/out.

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Post by coulomb » Thu, 01 Apr 2010, 20:53

Squiggles wrote: Maybe the boxes/racks need to be made in two separable pieces that can be released to allow batteries in/out.

Well, they are, there is the lid. But I suppose that the split could be made more 50/50 so that the cells can be more readily strapped.

I think that only makes a real difference where there is one row, though.
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Post by Squiggles » Thu, 01 Apr 2010, 22:15

I was thinking more left and right not top and bottom.
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Post by Tritium_James » Thu, 01 Apr 2010, 23:33

Coulomb I can't recommend the nylon strapping - you can break that pulling on it by hand as you tighten it. It breaks where it folds back on itself going through the clamp piece. Maybe if you had a thermal sealing machine where the tape didn't get folded it would be a lot better.

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Post by coulomb » Fri, 02 Apr 2010, 00:30

Tritium_James wrote: Coulomb I can't recommend the nylon strapping - ... It breaks where it folds back on itself going through the clamp piece.

TJ, does this apply only to buckle arrangements?

We were thinking of this type of tool pair:

Image

From the first video on this page: http://www.getpacked.com.au/strapping.htm (in the PLASTIC HAND STRAPPING section). Lower down you can see references to "seals" and "buckles". It looks like you can get a hand tool that uses a "seal" rather than a "buckle". These seem to use "friction welding". [Edit: and they don't seem to fold the strapping at all.]

Would using a "seal" like this negate your warning?
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Post by antiscab » Fri, 02 Apr 2010, 00:30

Nevilleh wrote:
I wonder if you'll ever be able to remove the cells again, if needed. They will presumably swell a little, which means that the present tight fit may become impossibly tight in the future. You might have to ruin a box and repair it or build another one just to get one cell out.
Yes, I wonder too! But I have already had to remove a cell and it came out quite easily - and went back in again. The whole purpose of the clamping is to stop swelling, after all. Admittedly, the battery hasn't seen much use yet   Image


installing rope between and under the middle cell in each group will get around this issue. that and brute force if swelling does cause you grief :D

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Post by coulomb » Fri, 02 Apr 2010, 00:47

Nevilleh wrote: Not sure what those problems might be. The coupling method, whether it be inductive or capacitive will transfer energy in exactly the same way. Current spikes in one winding of the transformer will appear in the other, same as voltage spikes on one side of the cap.
Sure, but the SEPIC and other capacitive isolation schemes have a capacitor between the input and output sections. In fact, the SEPIC assumes a common ground between the two, so really it's not isolated. If the voltage between input and output sections suddenly changes by 200 V, then a capacitively coupled system will try to add that 200 V spike to the output. A transformer coupled one would not.
I have already had to remove a cell and it came out quite easily - and went back in again. The whole purpose of the clamping is to stop swelling, after all.
I think you were lucky that there wasn't significant swelling in the short time you had those cells in service. Or maybe you charge at relatively low currents (less than 2C), and swelling just isn't as much of an issue then. I think what will eventually happen is that swelling will occur and shrink the gap to zero with a pressure on it. The strapping prevents the cells from swelling any further, but they'll have expanded enough to make your snug fit very tight. I hope that doesn't happen to you.
My thought about wooden blocks was to use a couple of opposed, wedge-shaped pieces of say high density particle board. Driving them in fairly gently would provide compression for the cells and they would be easy to remove later if you had to. If ever I make another battery box, that is what I will do.

Ah, sloped that way, yes. I just couldn't picture it before. As long as the wedges stay in the box, they should stay tight. With the lid off, they are free to slide up and take up less width. I think it could work well, but you have to have designed the boxes for this.

We actually have some boxes where we'll have wooden separators, but that's to clear chassis rails or other obstructions, so I don't think we could use the idea there.

But for next time... it's certainly worth considering.

I suppose with a thin enough pair of wedges, we could consider it for the current boxes. We would have (guessing) about 12 mm (6 mm at each end) to clear the brackets and nuts. Maybe as much as 20 mm. So it may be possible. Thanks for the idea!   Image
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Post by Tritium_James » Fri, 02 Apr 2010, 02:04

Yeah, I think with that kind of tooling you'd be a lot better off. We are using the buckles - for box packing & shipping, not batteries!

I'd still be a bit dubious about the nylon strap, the breaking strain isn't that high and I suspect swelling batteries can generate a lot of force. Maybe if you've got a lot of strapping (one per 'recess' in the battery?) you'd be OK. I guess the only way to know is to try it and find out.

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Post by coulomb » Fri, 02 Apr 2010, 03:40

Tritium_James wrote: I'd still be a bit dubious about the nylon strap, the breaking strain isn't that high ...

Is it literally nylon? We're seeing mostly polypropylene (mostly blue) and polyester (e.g. green); the latter seems about twice as strong.
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Post by Nevilleh » Fri, 02 Apr 2010, 12:08

I had some TS cells that I originally used to power a scooter and found that just sitting on the bench for 3 months caused considerable swelling. The nominal 46 mm thickness grew to about 55mm in the middle.
I didn't have any "proper" clamps at the time, so I clamped them in groups of 4 with a large G clamp and two blocks of wood. I found that I could re-tighten the G clamp every morning for about 3 days by which time they were back to the original shape. I didn't use a lot of pressure, certainly the clamp was only hand tightened. None of the pressure vents popped.

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Post by Tritium_James » Fri, 02 Apr 2010, 15:27

I think it's actually polypropylene. I suspect you'll get away with it if you use that strapping machine.

We used stainless steel strapping in the Civic, and while I'm certain it's strong enough, it's difficult to do and quite dangerous too, with whippy 2m long bits of conductive strap waving around near 100s of cells. The tooling was also really expensive.

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Post by weber » Tue, 06 Apr 2010, 22:56

Coulomb posting:

Well, we thought we'd have a quick positive feedback hit and try the motor in Rotor Flux Control mode (RFC - sensorless vector mode on other drives). In the book, it looked really easy: select vector closed loop mode, set 3.24 to 1 to select RFC mode, and set 3.40 to 0 (it was already).

Well, first off, parameter 3.24 to choose RFC mode just wasn't on the menu. It skipped from 3.18 to something more than 3.24. (That's one of my pet hates with user interfaces: disabling an option with no obvious way of finding out why it's disabled).

Turns out I need to reset the drive to make the mode change stick, but then it goes back to open loop mode. Turns out that a mode change is a big deal; the only way to do one is to first reset all parameters to 50 or 60 Hz defaults, then change mode, then reset, and then it stays in the mode you select. Fine.

I selected RFC submode, entered the basic drive parameters (rated frequency, current, voltage, speed), set 0.40 to 2 for a rotating auto tune, enable and run. Weber was standing on the motor in case it decided to walk about, as it sometimes did. It was the roughest auto-tune I'd ever come across, and ended up with a trip PH (phase lost or other cause of excessive capacitor bank ripple).

This may have been because the pot was set to about 2/3, but I think it's not supposed to go from auto tune to real run mode without enable coming off and on.

I had selected extra slow ramps, and with an unloaded motor, that should not be necessary. So I set the ramps back to normal, and for good measure, set the motor maximum speed to just 2500 or so. This time it worked fine. We set the max speed to 4500, and the auto tune succeeded again. Success. Cos phi measured at about 0.87 (nameplate says 0.88).

With the pot set to zero, and Weber drawn to his full height, we toggled enable and slowly advanced the speed. The motor made awful sounds and shuddered violently. We disabled it quickly.

We tried one more time with slightly quicker acceleration, but no better. Ick.

We'll wait for Ross Pink, our local drive expert, to sort this one out for us.   Image
[Edit: drive shuddered -> motor shuddered]
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Post by coulomb » Sun, 11 Apr 2010, 03:11

The prototype digital BMU (battery management unit - the part on each cell) boards arrived recently, and we (mostly) populated them yesterday:

Image

You can see that the boards have shrunk a bit since the early versions, especially the part that fits over the terminal posts.

On "top":

Image

This is how we test it when we need access to the component side of the board:

Image

Handily, a pair of 5W resistors is just the right size to stand the boards off the cell terminals.

You can see that we drilled the holes for the LEDs before we looked at their physical size; the holes are way too big for these versions. Normally, the board would be routed with appropriate slots that accept the larger square bodied LEDs we got last time. So the LEDs tend to fall out of alignment after they are soldered.

Alas, we don't have facilities yet for JTAG programming the micros on the cards yet, so there isn't much exciting we could do. We measured 2.502 or so volts at the output of the 2.5 V regulator; that's a good sign. Also, the voltage dividers seem to working OK.

With one of the boards, we could get the bypass transistor to come on by connecting a multimeter (in volts mode) between 2.5 V and the gate (I/O pins default to open circuit). Putting the voltmeter between the gate and ground turned it off. Alas, the other one didn't turn on hard this way, and we didn't pursue the matter.

One of the new boards has the "end of row only" logic, but we're still waiting on a couple of parts for that. The tiny dual inverter will be a challenge to solder.

The micros seemed to solder OK, though one ended up with a pair of shorts between adjacent pins. A touch with a soldering iron (with an ultra fine tip) seems to have fixed it up no problem; well, at least the short is gone.

So the next job is to adapt one of the development boards to become a JTAG programmer. It should be straightforward enough.
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Post by Nevilleh » Sun, 11 Apr 2010, 13:20

Much, much prettier than my home-made prototypes!

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Post by Tritium_James » Sun, 11 Apr 2010, 15:03

Needs more flux! You'll be kicking yourself for how hard you've made your life up until you try it :) I'd suggest some NC254 gel flux, get it here: http://www.okay.com.au/okay2009/product ... ts_id=3433

For 200 boards you two should really consider solder paste and a reflow setup. Details here: http://www.sparkfun.com/commerce/tutori ... ials_id=58 It's about 3x faster than doing it by hand with an iron.

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Post by coulomb » Sun, 11 Apr 2010, 20:07

Well, JTAG programming turned out to be pretty easy:

Image

You can see the 6-pin (only 4 used) connector at the bottom of the picture that connects to the processor board. It's 1/20" spacing and very thin pins; I don't think I'd have much luck getting a matching socket. So I soldered a short piece of 4-wire ribbon cable, which is also 1/20" spacing, to the board, and soldered a 1/10" spacing header to the end, which mates with the JTAG connector on our BMU boards:

Image

When I get near an electronics store, I should perhaps get some gold plated pins, though then there is the issue of different metals in contact. What I have now seems to me mostly-tin to mostly-tin.

I fired up the free embedded workbench software, and told it to download the bootstrap loader (bootstrap bootstrapper). It warned me that the project is set for a MSP430-2013 device, and it had detected an MSP430-2012 device, continue or cancel? I pressed continue, it downloaded, I ran the program, and it seemed to work (I didn't notice the LED flashing, but it's on a different pin to that of the development boards). So two trivial changes to the software and it should be perfect.

Now that the bootstrap program is running, I can no longer turn on the bypass transistor by putting a multimeter (10 M impedance) from 2.5 V to the gate of the bypass MOSFET. In other words, the bypass output is programmed as an output now, as it should.

I worry that sometimes not all 4 of the wires will make contact, but it worked this first time. [Edit: The connector can't go further in, because there is a 5W resistor behind it.]

Progress!

Now I need to arrange a serial port connection to the BMU board, to talk to the master software, though that's mostly not written yet.

Edit: 1/50" -> 1/20" inch (1/50" would be pretty amazing)
Edit: had 2012/2013 microcontroller part numbers swapped
Last edited by coulomb on Mon, 12 Apr 2010, 04:50, edited 1 time in total.
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Post by Nevilleh » Sun, 11 Apr 2010, 21:14

Yes, its a great feeling when you build a board with a micro on it, program it for the first time and it actually runs!
Congratulations.
My master unit is nearly done but in abeyance while I rebuild my motor controller.

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Post by EV2Go » Mon, 12 Apr 2010, 03:09

what language do you program them in?

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Post by coulomb » Mon, 12 Apr 2010, 03:15

EV2Go wrote: what language do you program them in?

Basically assembler for the BMU code, and C for utilities and master code. Some of the BMU code is tokenised Forth-like code.

Edit: capitalise Forth, to distinguish from fourth generation language.
Last edited by coulomb on Mon, 12 Apr 2010, 06:02, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, PIP-4048MS inverter, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

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EV2Go
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Weber and Coulomb's MX-5

Post by EV2Go » Mon, 12 Apr 2010, 03:16

As in a 4GL?

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