Prelude conversion project - some questions

[jonescg]

The new jig spacer makes a much more convenient half-module assembly. The cordless driver with torque settings helps a lot too

Module assembly2.jpg (190.19 KiB) Viewed 2191 times

Module assembly3.jpg (197.76 KiB) Viewed 2191 times

I assembled another two enclosures this afternoon (^on the lower shelf of the workbench). I seem to have a system down now. With any luck I'll get the last one perfect

[francisco.shi]

How much does the brick weigh and how many kwh do you have per brick?

[jonescg]

The two row module weighs 18.6 kg and stores 3.2 kWh as a complete unit. So each brick of cells like the one above is about 9 kg.

[tidalev]

I used an off-the-shelf controller for this, mine uses a 0-5V signal (from memory) to control the speed based on the temperature of the coolant.

Do you have any more info on this? I'm looking at a similar setup

[4Springs]

Controller info in this post.
viewtopic.php?f=18&t=5249#p64990
There are simpler controllers around if you just run the thing flat out.

[jonescg]

Not exactly a gigafactory, maybe a kilofactory?

3 modules worth.jpg (179.38 KiB) Viewed 2094 times

[jonescg]

Managed to get a little help from Mike to bring the hoist up the hill. The Hyab truck they use to deliver and install wouldn't fit through the carport, so we had to unload it and roll it down to the shed. While we could have driven all the way back, we then wouldn't have a means to get it off the truck...

We can solve these minor issues

Hoist arrives.jpg (136.95 KiB) Viewed 2024 times

[Richo]

I'm lost - what's that for

[Johny]

I'm lost - what's that for

Looks to me like Chris is going to lower the car onto the battery pack
It's awfully big

[jonescg]

It's a car hoist. It will be installed in the workshop ahead of the Prelude conversion. Since the battery is going where the fuel tank used to be, the hoist will make the whole job a lot easier.

It's a clear-floor type, so they are taller than the regular 2-post hoists.

[francisco.shi]

Have you done any measurements on the cooling system for the battery pack?

[jonescg]

I've not yet set the modules up for testing, but I will have several tests to do by the weekend. The one module have already built is to be the 'spare' module, and it's just as well because the thermal epoxy doesn't have the sort of coverage I'd like it to have. It's probably 90 % as good as it needs to be.

However I found some Tesla pack data:

Tesla pack water temp graph.JPG (77.87 KiB) Viewed 1964 times

So this is a 1.2 C discharge on a Tesla Model S module. The measured internal resistance is about 100 mOhm per cell (remembering there are 74 in parallel and 6 of these in series - so the overall internal impedance of the pack is 0.0081 Ohm. At 297 amps it was generating 715 W of heat - for the first 30 seconds anyway. It dropped off as the voltage dropped.

The heat generation is plotted, as is the delta T in the coolant. From the delta T in the coolant we can infer the heat absorbed by the coolant.

Tesla pack water heat flux.JPG (70.94 KiB) Viewed 1964 times

It's rough, but should give some idea. Hope to have my data soon.

[francisco.shi]

Where did you get the data from. I would like to read a bit more about what other tests they did.

[jonescg]

I should add this was based on a measured DC IR of 100 mOhms per cell, which is probably higher than it really is. But not a lot higher. It's a used pack, so the DCIR has no doubt increased from new (which is supposed to be 60 mOhm).

[jonescg]

Potted my first complete battery pack with thermal epoxy. Next step is to wire up the BMS and test it

Potted pack.jpg (134.71 KiB) Viewed 1925 times

[jonescg]

And then there were two.

2nd module done.jpg (141.05 KiB) Viewed 1902 times

[mikedufty]

Is that a zero motorcycle in the background?

[jonescg]

Yes, Daniel Klemm's bike. Still has problems and we're trying to re-flash the firmware to make it go. Currently a 50 km/h limited bike with 5 km range and won't take a charge...

[mikedufty]

Bummer

[jonescg]

I seem to have about a one-a-day sort of productivity right now.

Prelude modules.jpg (290.06 KiB) Viewed 1845 times

And now there are four (and a spare).

4 done and a spare.jpg (220.67 KiB) Viewed 1798 times

[rhills]

Well, they look pretty professional IMHO.

How do you think those screws into perspex will hold up against vibration?

[jonescg]

It's polycarbonate which is tougher than perspex. The screws are also glued in place by virtue of the seal it goes through. I reckon they will be okay.

[francisco.shi]

Is the potting compound only on the bottom of the cells?

[jonescg]

Is the potting compound only on the bottom of the cells?

Correct. The bottom face of the cell stack represents about 20% of the total surface area, and it's all in the plane of the electrodes, so thermal conductivity is at it's highest.

Screenshot from a video I'm preparing:

potting screenshot.JPG (129.06 KiB) Viewed 1792 times

[jonescg]

Almost ready to start work

Hoist installed.jpg (228.25 KiB) Viewed 1758 times