What your engineer wants to see

Technical discussion on converting internal combustion to electric
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coulomb
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What your engineer wants to see

Post by coulomb » Fri, 17 Apr 2009, 02:42

Weber and I had our first meeting with our engineer today. It was good though it brought is down to earth a bit.

Our tentative battery rack plan failed on several levels. He'd like to see more welding and less screws; screws can work loose and pull through metal, particularly aluminium. In fact, where screws go through aluminium, there should be a small steel plate around it to resist tear through.

There should be no aluminium on the bottom of the vehicle where it can be ripped by scrapes and stones. Battery boxes should be attached to box sections by bolts that go through all the way. The bolt should go through a "crush bush" 2 mm thick welded on both sides. The idea is that you can torque up the bolt without crushing the box section. That's way more than the Tek screws we we envisioning Image !

We can move the front sway bar from its current position where it's somewhat in the way, but it needs to be bolted to something substantial; it's not just torsion that the bar experiences, as we thought, it also gets some vertical force. We should use the existing bracket as a guide for the new one.

We are planning two long racks of cells right behind the passenger's seats, about head height. Somehow we didn't think of what would be needed to restrain those racks of cells in the event of a sudden stop like a head-on accident. Fortunately this where seat belts and roll bars are attached, so something strong can be attached there. He will calculate how strong it needs to be offline.

We are allowed to bend up or down the spot welded seams around the boot and fuel tank areas, but he likes to see "stitches" of welds a few centimetres long, especially near corners. Apparently stitches are better than continuous welds, since a crack won't keep propagating past the end of the stitch.

Special attention is needed at reinforced corners like this:
Image

We are to retain the reinforcing, but we can cut the seam nearby, e.g. where the yellow lines are. (There is an overlap of seems right near the reinforcing, hence the gap from the end of the reinforcing to the cut). The cuts should be curved as shown and stitch welded at the edges where the yellow lines are.

He made us aware that we are likely increasing the centre of gravity of the vehicle. Our original plan had more battery cells under the boot, but we put the controller there for better front to back weight ratio, but in the process raised the centre of gravity quite a bit. We have now modified our front to back spreadsheet to calculate the new centre of gravity. We believe it will go up 33 mm (from 403 mm), or about 8.5%. There isn't much that can be done about it, but it may make a 100 km/h lane change test more difficult. (We may or may not be made to take that test).

The new NCOP regulations should make it much easier for the engineer signing off. At present, there are no hard and fast rules, so it's all left to judgement and subject to controversy. With the new regulations, they can just "mark to the regs" and there is little room for argument.

In case you're wondering: that was the only photo I could find quickly with the reinforced corners.   Image
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acmotor
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What your engineer wants to see

Post by acmotor » Fri, 17 Apr 2009, 07:04

Ummm, tray back ute sounds better every day ! Image

Seriously though, good information. It will be interesting to see how you meet his expectations !
Welded rack yes, welded to vehicle no. Bolted only !
iMiEV MY12     110,230km in pure Electric and loving it !

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coulomb
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What your engineer wants to see

Post by coulomb » Fri, 17 Apr 2009, 14:06

acmotor wrote: Welded rack yes, welded to vehicle no. Bolted only !

Err, well we weren't thinking of doing much welding, as neither of us has the skill, so we really didn't ask. I think that boxes welded to the vehicle would be fine, actually. Buf if you bolt, use the crush tube through a chassis rail.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 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.

Peter C in Canberra
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What your engineer wants to see

Post by Peter C in Canberra » Fri, 17 Apr 2009, 14:59

I had a first interview with an ACT engineer recently. I showed him photos on the lap top of what I had done to date. He generally seemed happy with it all. The main area I had not yet got to at that time was also the area where I had least confidence, namely, how to attach my battery restraint to the car. I was concerned to make it strong enough but to avoid compromising anything original that should not be touched. In my case I have a total of about 150Kg occupying the lower half of the hatch space of a Daihatsu charade, mostly down into the spare wheel well. Some bits have box sections under and other bits are thin, unreinforced sheet metal. He also described the crush tube for if I were to connect into any of the box section bits. However, he said "six 6mm grade 5 bolts" would be sufficient with large washers under to stop them pulling through the thin sheet metal. I was surprise how little that was. I have a frame rather than a box of welded, slotted angle steel and he seemed quite unconcerned that that would be strong enough, although he has not yet seen my welding! I have not done it before so it is not particularly neat. The reason for using that is a good strength to weight ratio and I could use bolts to hold it together while I worked on welding it, then removing the bolts.
Also, I wanted to avoid having anything conductive over the top of the cells that could create shorts if someone ran up my rear. I sounded him out on the idea of using 'hand strap' to hold the cells down in my frame. That is the plastic tape, often blue that is used to hold large parcels together on pallets. It generally has a >100Kg breaking strain rating. I was thinking to have multiples of that in both directions over all rows of cells. He again seemed to thing that would be plenty.
Peter.
Daihatsu charade conversion 2009-18, iMiEV 2013-2019, Holden Volt 2018-present, on the ACT's 100% renewable electricity. Kona on order.

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coulomb
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What your engineer wants to see

Post by coulomb » Fri, 17 Apr 2009, 17:07

Peter C in Canberra wrote: I sounded him out on the idea of using 'hand strap' to hold the cells down in my frame. That is the plastic tape, often blue that is used to hold large parcels together on pallets. It generally has a >100Kg breaking strain rating. I was thinking to have multiples of that in both directions over all rows of cells. He again seemed to thing that would be plenty.
Peter.

Ah, that stuff has a name! Thanks.

I also asked about this, though it was in the context of strapping the cells to the anti-bulge plates. These may partially be involved with safety, I haven't thought about it in detail. Our engineer wasn't impressed with the idea. Note that some of our racks would have been 22 cells long (just over a metre of cells). We weren't proposing to use it in two directions, only one.

Your range may vary Image
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 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.

Peter C in Canberra
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What your engineer wants to see

Post by Peter C in Canberra » Fri, 17 Apr 2009, 20:34

You can also get strap that uses a tool to tighten it. Then it isn't 'hand strap'. The type with a tool can also be steel rather than plastic and has a crimped connection. I doubt if your bulge plates would move with that stuff around them.
Peter.
Daihatsu charade conversion 2009-18, iMiEV 2013-2019, Holden Volt 2018-present, on the ACT's 100% renewable electricity. Kona on order.

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