Prelude conversion project - some questions

Technical discussion on converting internal combustion to electric
francisco.shi
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Re: Prelude conversion project - some questions

Post by francisco.shi »

The energy density of your pack will be really good.
I always wondered if you could seal the ends of the cells to the plastic plate could you run coolant thru the gap? This would be the ultimate cooling system.
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Re: Prelude conversion project - some questions

Post by jonescg »

Yeah like Novec or some non aqueous material. It still needs to be set in resin for vibration protection though, but you could focus on just setting it on the top and bottom.
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Re: Prelude conversion project - some questions

Post by jonescg »

Populating a module is the easy bit...
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Spent today unboxing the remaining cells and cutting up sheets of G10FR4 for the enclosures. Once the modules are fully terminated I'll build an enclosure around it and fill 'er up with resin.
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Re: Prelude conversion project - some questions

Post by jonescg »

Well the nickel plating didn't happen before Christmas, which means nothing will happen until after January 4th. After spending the last two days indoors with the aircon on full blast (and not drawing from the grid - thanks to solar ;) ) today was cool enough to attack the Prelude battery again.

I spent today looking up waterproof multi-pin connectors as these modules will need an external wiring loom to the BMS. I went to Altronics and bought four of the universe's most expensive Amphenol 18-way connectors, only to realise I actually need 8 of them. At a cost of $500 in connectors, I won't be pursuing this approach.
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So I think the next best option is a waterproof 37- pin D-sub connector, or maybe not even use connectors - just run the cables out and hope the potting works?

Also, I had to remove the 100 mm square section and replace it with a pair of angle-aluminium channels since the connectors can only feasibly come out the inside edge of the modules. Good opportunity to clean up the plate and water-proof all the bolts which go through the floor.
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Re: Prelude conversion project - some questions

Post by brendon_m »

How many pins on each module do you need?
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Re: Prelude conversion project - some questions

Post by jonescg »

25 pins for the cells and 8 for the thermistors. So minimum of 33 pins.
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Re: Prelude conversion project - some questions

Post by 4Springs »

jonescg wrote: Sat, 26 Dec 2020, 19:57 25 pins for the cells and 8 for the thermistors. So minimum of 33 pins.
Sounds like a job for a DB25 and a DB9.
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Re: Prelude conversion project - some questions

Post by coulomb »

Remembering that these are unfused battery cell connections, I'd be more comfortable with pins spaced a bit further apart than with a DB25. The thermistors should be ok on something like a DE-9.

And of course, you need excellent reliability, in the face of vibration, heat, humidity, and the rest of it. Not a trivial design decision.
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Re: Prelude conversion project - some questions

Post by jonescg »

I've concluded that the best approach is to use a cable gland and run the leads directly to the BMS modules. The battery modules will be potted anyway so it should all be hunky dory internally at least.
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Re: Prelude conversion project - some questions

Post by nuggetgalore »

I only just now stumbled onto this thread.
Wow what job.
In reference to the iMiEV battery cell replacement, I wonder if the cells should be capacity tested and sorted into modules with equal capacities. Or would that make it worse if a whole bunch of cells are lower or higher than a neighboring bunch? Testing at least might find some bad ones to weed out.
The news re the 60 Ah cells is not really good, with the one exception on a hot day the performance is disappointing, already the cell volt drop and volt difference is as bad as the original ten year old LEV50s under moderate load.
More in the other thread later on.
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Re: Prelude conversion project - some questions

Post by jonescg »

Since everything is on a go-slow I figured I might as well get busy with the other parts of the project I'd forgotten about, or at least would soon discover they were unfinished...

The new battery modules will call for new busbars and cable links, so I spent a bit of time planning out the main fuse and cables lugs. Since discovering Bussmann do a fuse cradle for the 200 A fuses I decided I might buy a few. I'm mounting the fuse on the side and have cut a 140 mm x 100 mm access hole in the base of the battery pack which will mean the fuse can be repaired or inspected with a quick hoist. It will need a decent waterproof seal though!
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Don't be too alarmed by my 'fuse' in the images - it's just a placeholder while I get the cable runs right.
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Re: Prelude conversion project - some questions

Post by jonescg »

The new location for the BMS will be down the middle, with all of the BMS fly wires hanging downwards in a water-draining kind of way.
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Also, I have decided the correct clamping method should involve folded, laser cut sheet metal. This is the most compact and reliable method I think. Maybe galvanised steel at 1.2 mm thick, and powder-coated? I can put bits of foam in there to take up any slack. And speed holes of course :)
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Re: Prelude conversion project - some questions

Post by jonescg »

Today I spent a bit more time catching upon the things I'll need to do at some point, but ahead of the battery re-installation.

I was most excited to see this magnificent widget on the ZEVA website: https://www.zeva.com.au/index.php?product=142
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This is what we've been nagging Ian to build for the last few years - credit to him he's built it! Thanks @zeva !

The beauty of this thing is that it talks to the TC charger and takes signals from the EVSE the car is plugged into. If the EVSE says it can offer 32 A at 240 V AC, then the widget tells the TC charger to up the power. If the EVSE is limited to 15 A, it will automatically turn the charge power down. It's a lot easier than changing the settings before plugging in. It even has an LED output for letting you know the charge is progressing, or has stopped! Luckily I wired one of these up and tested it today:
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But critically, it looks to replace the ACV2 which is already working fine for Type-1 public chargers, provided they are OK with being run at full power (32 A). The issue I need to reconcile is the charge/drive interlock. I was using the output of the relay on the ACV2 to power the DPDT relay preventing +12 V from reaching the inverter. The new ZEVA unit will need to do something similar, perhaps using the charge enable output to drive the relay? So long as it's got the current to power a coil it should be an easy fit. New wiring is as shown:
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(edited to correct NO output)

I will be very interested to see if the Zeva unit works well with other Type-2 chargers like the Schneider's and Tesla destination chargers.

This all means I need to tidy up the charge control box and update the wiring diagrams should I ever forget. So I got rid of the thermal management Arduino and relay board, as they were completely redundant now. I've wired it so the battery coolant pump and the inverter/charger/motor coolant pump are always on whenever the car is powered on or charging. If we ever go back to installing a cooling loop in the battery (shudder) we can re-use it easily enough.
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Re: Prelude conversion project - some questions

Post by zeva »

jonescg wrote: Thu, 31 Dec 2020, 10:58The beauty of this thing is that it talks to the TC charger and takes signals from the EVSE the car is plugged into. If the EVSE says it can offer 32 A at 240 V AC, then the widget tells the TC charger to up the power. If the EVSE is limited to 15 A, it will automatically turn the charge power down.
A quick amendment for anyone interested in in the technical details.. This device can't actually talk to the charger directly because it doesn't know the DC pack voltage, which is needed for calculating DC current limit. Instead it sends maximum available AC power to the EVMS (aka BMS master controller, etc), which knows the DC pack voltage and so can dynamically adjust the DC current limit accordingly, also allowing for 10% loss in the charger, which will usually mean a few % safety margin. It is new functionality in the EVMS so people retrofitting the EVSE Interface will also need a (free) firmware update on their EVMS.

In applications without an EVMS, it would be possible to hard code the maximum pack voltage into this EVSE Interface device and it could talk to the charger directly, but it wouldn't be maximizing charge current while the pack is at lower voltages, and also you'd need a different way to implement BMS protection (which is otherwise handled in the CAN bus message to the charger).
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Re: Prelude conversion project - some questions

Post by jonescg »

And I trust it can be done in 500 kbps baud rate? :)
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Re: Prelude conversion project - some questions

Post by tidalev »

zeva wrote: Sat, 02 Jan 2021, 19:15
jonescg wrote: Thu, 31 Dec 2020, 10:58The beauty of this thing is that it talks to the TC charger and takes signals from the EVSE the car is plugged into. If the EVSE says it can offer 32 A at 240 V AC, then the widget tells the TC charger to up the power. If the EVSE is limited to 15 A, it will automatically turn the charge power down.
A quick amendment for anyone interested in in the technical details.. This device can't actually talk to the charger directly because it doesn't know the DC pack voltage, which is needed for calculating DC current limit. Instead it sends maximum available AC power to the EVMS (aka BMS master controller, etc), which knows the DC pack voltage and so can dynamically adjust the DC current limit accordingly, also allowing for 10% loss in the charger, which will usually mean a few % safety margin. It is new functionality in the EVMS so people retrofitting the EVSE Interface will also need a (free) firmware update on their EVMS.

In applications without an EVMS, it would be possible to hard code the maximum pack voltage into this EVSE Interface device and it could talk to the charger directly, but it wouldn't be maximizing charge current while the pack is at lower voltages, and also you'd need a different way to implement BMS protection (which is otherwise handled in the CAN bus message to the charger).
Hi Ian,
will you be publishing updated evms3 / CAN docs explaining this extra functionality?
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Re: Prelude conversion project - some questions

Post by jonescg »

Nickel plating is done, so my first task is to re-assemble the jigsaw puzzle and work out which side needs to be countersunk. Then after countersinking the fixings, spot-weld 2200 nickel tabs to them... :shock:
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Re: Prelude conversion project - some questions

Post by OzSpider »

How thick are those busbars?
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Re: Prelude conversion project - some questions

Post by jonescg »

1.2 mm aluminium, and a roughly 1 µm thick layer of nickel. So at it's narrowest point it's still about 55 mm2 in cross section.
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Re: Prelude conversion project - some questions

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I've run out of countersunk screws, so I'll have to finish that step later this week. But the packs are starting to take shape.
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The little welder will work OK, but I really need some more instant amps to get these things to stick properly.

Over the next few nights I'll start soldering the BMS wires on and running them out the corner. Then glue the sides on, and then start welding tabs on. I'll do a quick test to see that everything is playing nice and then it's time to glue the top and bottom faces on.
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Re: Prelude conversion project - some questions

Post by coulomb »

jonescg wrote:
All those reddish cells remind me of twopenny bungers (fireworks). Are you totally sure that you didn't get just one or two if those cells flipped the wrong way? :shock: 🧨🧨🧨

[ Edit: red → reddish ]
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Re: Prelude conversion project - some questions

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I'm not old enough to remember the glory days of cracker night, but a chance discovery at the Warwick rubbish dump of a suitcase full of penny bungers probably got be into chemistry as a youngfella.
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Re: Prelude conversion project - some questions

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Started to solder the BMS wiring on and routing it out to the corner. I can only do the odd numbered cells before flipping it over and then doing the even numbers.
I notice that where the nickel layer is a little oxidised the solder tends to ball up rather than wick out, which is to be expected. So it really highlights how critical keeping them clean is.
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I glued the rear panel on, but can't do the rest until all the balance wires are in.
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Re: Prelude conversion project - some questions

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Some more progress:
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Re: Prelude conversion project - some questions

Post by T1 Terry »

I'm assuming you are putting some sort of insulation sheet between the series cell groups. The cell case is part of the negative terminal so there is the cell voltage difference case to case between the parallel groups.
When we get the dead electric bike batteries in to see if we can get them going again, 9 out of 10 times the problem is the shrink wrap on each cell has rubbed through between series connected groups creating a short and destroying a number of cells. These then go zero voltage and kill the other cells in the parallel group. For some reason they consider squirting hot glue around each cell top and bottom is sufficient cell security ......

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EDIT: Forgot about the poly carbonate sheets top and bottom that the cells slot into, that should stop them from rubbing together :oops: please return to the normal program :oops:
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