Prelude conversion project - some questions

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

Post by jonescg » Sun, 06 Jan 2019, 20:34

I have finished the rear pack subframe. Well, I think it's done. Seeking advice, but I think this will be sufficiently rigid and plenty strong to support a 120 kg battery pack. If push comes to shove I can add additional rails which bolt back onto the main frame rails.
Subframe done.jpg
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I mounted an MDF mock-up of the floor of the battery pack and clamped it in place. Then I went around and drilled 26 holes at 6 mm diameter. I wasn't sure if I would use Riv-nuts or weld M6 nuts to the top of the rails, so I welded the M6 nuts anyway. If for some reason this doesn't work out, I can still put Riv-nuts on the underside. The next step is to metal-prime and paint it black.

As for the battery itself, I will use the MDF as a template for the holes which will go through the aluminium composite sandwich panel. As amazingly light and strong as this stuff is, it's got some quirks which if not done properly, make it worse than useless. All holes need to be hollowed out and potted with epoxy, then drilled again. Normally you would use oversized washers but the clearance is rather tight, so I may end up using countersunk screws.

Before I attempt to bolt it up, I need to make the fiberglass lid (upturned tub) for the pack. I figure this should be fairly straight forward, and hopefully I can get away with using a selection of cloth and cling-wrap over the battery as the 'mould'.
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Re: Prelude conversion project - some questions

Post by jonescg » Thu, 10 Jan 2019, 15:36

After watching the Weber Auto video https://www.youtube.com/watch?v=_ILkLUE3Zxc on the three coolant loops on the Chevy Bolt, I'm starting to reconsider my approach to cooling the battery with a radiator.

The Bolt EV uses a liquid coolant circulated through the battery pack, however it doesn't pass the coolant through a radiator at the front of the car - instead it chills the coolant exclusively with the aircon refrigerant via a small (much smaller than mine) heat exchanger (18:26 on the video linked above). I was wondering why they do it this way, when a radiator would be able to get the temperature right down to ambient.

Well sometimes ambient is more than the battery wants, and it needs more cooling power. But passing coolant through a radiator at the same time would only serve to heat the coolant up if it's above 30'C on the day. Moreover, if the aircon is employed to chill the coolant via an exchanger as I plan to, the heat from the Aircon condensor will also serve to heat up the battery radiator - a bit like piping the hot exhaust air from a home split system back into the room you're trying to chill.

So what's the best option here?

1. Abandon the aircon heat exchanger and just cool to ambient?

- Key drawback here is that ambient is probably still well above the battery's happy zone. Also, if the people inside the cabin are feeling warm and turn the AC on, the condensor at the front of the radiator will start to shed heat, which in turn heats up the battery radiator behind it, further preventing the cells to cool down.

2. Exclusively chill the battery with aircon?

- Chevy and Tesla do this, so it's not too crazy. It does mean the aircon system will see a greater workout, even on a mild day.

3. Introduce a battery radiator bypass loop when it's very hot.

- This means leaving the approach as I have drawn it, but including a bypass loop which cuts the radiator out of the picture once the aircon compressor kicks in. So it cools to ambient using the radiator up to about 27'C without the aircon, but above 27'C, the aircon compressor kicks in and passes refrigerant through the heat exchanger, further chilling the battery. But, it also cuts the radiator out, meaning mildly warmed coolant leaving the battery pack is not warmed up by the ambient air - coolant simply circulates back to the refrigerant heat exchanger again. Sounds complicated, but would be less energy intensive than using the aircon only.

Any thermodynamics experts here care to chime in?

The maximum heat generated by the battery will be 6-8 kW for a few minutes. Otherwise, it's more like 700 W most of the time.
Maximum heat generated by the motor, inverter and charger is going to be about 1-2 kW, on a bad day. So we're not talking about a lot of heat, but getting rid of efficiently it would be nice.
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Re: Prelude conversion project - some questions

Post by francisco.shi » Thu, 10 Jan 2019, 15:51

I am having the same issues.
I considered using the air con to chill water which can then be used to run thru the cabin cooling or the battery. Each curcuit would have a pump. This way you can control the two temperatures independently. In certain cases you can use the cabin as a heat sink.
The heat from the evaporator will run thru the heater in the cabin and then thru the external radiator so I can use the air con to provide heating.

The only problem with this is there is no heating for the battery and if the weather gets very cold the battery could end up too cold.
For now this is what I will do because in QLD the weather doesn't get cold enough.

I did consider running a hot water circuit to the condenser and run either the hot water or the cold water thru the battery or cabin depending on requirements but I think this getting a little complicated. The coolant for the hot and cold circuits would be the same I would just run the coolant thru the one with the right temperature.

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Re: Prelude conversion project - some questions

Post by jonescg » Thu, 10 Jan 2019, 16:04

I'm not too worried about heating the battery - like Brisbane, Perth is pretty mild and it will warm up in operation before too long. I can choose to not circulate the pumps below 22'C.
One option could be to put the battery radiator in front of the aircon condensor since it's shedding less heat?
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Re: Prelude conversion project - some questions

Post by Johny » Thu, 10 Jan 2019, 16:09

It's my understanding that Tesla runs the battery heat control system even when the vehicle is off. I have found that the amount of time that the battery pack sits in an over temperature environment while the vehicle is not in use (parked) WAY exceeds any time when it is in use.
So, IMO, if your are not going to run air-con cooling all the time (even when vehicle off) I don't see much gain in cooling with it - just cool to ambient.

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Re: Prelude conversion project - some questions

Post by francisco.shi » Fri, 11 Jan 2019, 04:16

As far as I understand one of the problems with the Nissan Leaf was that it could not cool the batteries below ambient. So if the ambient temperature got too hot it would cook the batteries. If the car is parked under the sun it could potentially get hot enough to damage the batteries. So what I was going to do is use the air conditioner to cool the battery and the electronics but only if it got too hot. My guess is that the cabin temperature needs to be within the limits of what the battery is going to need. So if you need air con chances are the battery needs it too and if you need to heat up the cabin then the battery and electronics can provide some of the heat just by not running the compressor.
The benefit of all this is that you only need one radiator so you don't need to worry about one radiator heating the other one up. The condenser runs close to 100°C on the inlet (worse case). I do not have enough data to do any better for the moment.
Another thing I was planning to do was to put solar panels on the roof and a retractable section to cover the front windscreen when parked to act as a shade. I can get 6 250w panels which I think would be enough to keep the air conditioner running to keep the battery cool without draining the traction battery. I just haven't worked out if it is worth the extra weight.

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Re: Prelude conversion project - some questions

Post by jonescg » Fri, 11 Jan 2019, 10:06

I finally got around to testing the cooling system on this battery module. To be honest I'm disappointed, but it's not all bad. Let me explain.

First up, this is a 4.4 C discharge on a cell which is nominally 1-2 C and 5 C burst - so I'm fairly hammering it. At 330 amps, the busbar linking the two half modules is not rated for this sort of continuous rate (neither are the cells, but that's not what I was testing).

Secondly, the cells were still warm from the day - they have a specific heat capacity of about 2000 J/kg.K so they retain heat fairly well. The cooling loop was bringing them down to ambient slowly before I started the run, hence the higher starting temperatures for the cells.

Finally, the thermal epoxy application on this particular module was poor - the cells to the rear of the module have very little contact with the potting material, while the ones at the front were OK. This is evident in the difference in temperatures of the two probes I had in the pack. I applied the thermal material with a spatula, rather than squeezing beads out with a gun like I did for the others. So there would definitely be better contact and heat transfer in the later modules.

Still, the delta T on the inlet and outlet was at best 0.6 'C with a flow rate of 3 litres per minute.
temp plot.JPG
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So at the point where the cells are as hot as they can be, the water in the cooling loop was removing heat at a rate of about 120 W. At this point the cells are generating about 1000 W of waste heat, so they get hot fast. They cooled down once the load was removed at a rate which was OK, but when I turned the pumps off for the night and went to bed, the rate of cooling was not much slower.

I might try to cool the busbars above with airflow as they are in direct contact with the core of the cells. It may end up being as effective as the liquid cooling :cry:
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Re: Prelude conversion project - some questions

Post by jonescg » Mon, 21 Jan 2019, 09:25

A little more progress to report.

The rear pack subframe is painted and bolted in position. The battery pack can now be offered up to it and bolted in place. Just need to finish the battery pack :)

All the modules are done, and the BMS + thermistors have been set into position. I need to get some 2-position C-grid terminal connectors for the ZEVA BMS so I can connect the thermistors.

The battery pack floor has started, with the drilling, reaming out and potting of the voids. Once everything is set I can jigsaw the final shape out.
Battery floor.jpg
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I have also glued a sheet of 0.8 mm thick G10FR4 to the aluminium panel to be doubly sure they can't find a high potential path to ground.

The three modules will be held in place with M6 threaded rods and a clamp over the top with T-sections between each module. It doesn't leave much room for coolant tubes or busbars / cables but I'll find a way.
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Re: Prelude conversion project - some questions

Post by jonescg » Sun, 27 Jan 2019, 17:08

Today was a moment of truth day - did I account for the height and footprint of the rear battery pack or do I have a mountain of work ahead of me? Bit of both, but my estimates were correct at least. The sandwich panel has been potted all the holes ready to be drilled out. I was tempted to use countersunk bolts to save on ground clearance, but it might not be a big deal. Perhaps just for the more central bolts?

Anyway, I put all 6 modules in position, and lowered the car over the top of it, taking great care to ensure the busbars didn't touch something they shouldn't.
Pack fitment1.jpg
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Pack fitment2.jpg
Pack fitment2.jpg (174.92 KiB) Viewed 1110 times
The 4WS is a fair way to the left so I might need to shuffle the modules across a bit further still. At least the modules on the drivers side can come across a long way. Reassuringly, there is enough clearance for the module clamps and the battery cover tub.
Pack fitment3.jpg
Pack fitment3.jpg (184.28 KiB) Viewed 1110 times
There's room for equipmenbt like a contactor down the tunnel, but I just need to be conscious of the cross-member there. At least a Gigavac contactor will still fit underneath it.
Packfitment5.jpg
Packfitment5.jpg (169.67 KiB) Viewed 1110 times
Not fully lowered, but about 4 mm away from the end location. I'm a little more relieved now.
Pack fitment6.jpg
Pack fitment6.jpg (195.04 KiB) Viewed 1110 times
Prior to this I have installed three thermistors in each module - two for the ZEVA BMS and one for the battery's independent thermal management system. Next step is to hook all of these thing together and mount the HV connectors and busbars.
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Re: Prelude conversion project - some questions

Post by francisco.shi » Sun, 27 Jan 2019, 17:45

It is looking good. 👍
How are you going to make the battery water tight?

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Re: Prelude conversion project - some questions

Post by jonescg » Sun, 27 Jan 2019, 18:09

Plan is to seal the battery lid/tub to the floor with a semi-permanent mastic or silicone. So it seals, but not permanently glued there. Alternatively I could find some closed cell foam and stick that down, but I'd feel better about the goo to be honest.
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Re: Prelude conversion project - some questions

Post by jonescg » Tue, 29 Jan 2019, 08:47

Picture of the battery modules as they sit on the floor of the pack:
Prelude battery layout.jpg
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Re: Prelude conversion project - some questions

Post by Richo » Wed, 30 Jan 2019, 12:47

jonescg wrote:
Sun, 27 Jan 2019, 18:09
Alternatively I could find some closed cell foam and stick that down...
EVA would work but would really need to be a continuous piece.
So you would have to buy a big sheet just to cut a wired skinny shape o-ring.
~$20 for 2200x1100.
I think Clark rubber used to have it on rolls you could buy the meter.

If the top was acrylic or polycarb you could route a channel and use an o-ring.
Or fill it with silicone etc and let it set - then it becomes removable.
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Re: Prelude conversion project - some questions

Post by jonescg » Wed, 30 Jan 2019, 16:00

Richo wrote:
Wed, 30 Jan 2019, 12:47

If the top was acrylic or polycarb you could route a channel and use an o-ring.
Or fill it with silicone etc and let it set - then it becomes removable.
This could be the easiest option - just Dremmel a groove the whole way around the inside of the flange and fill it with silicone. However, a single bead of silicone on a flat surface should achieve much the same thing. I think fibreglass will be the material of choice for the lid, particularly given it will add strength to the assembly.
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Re: Prelude conversion project - some questions

Post by rhills » Wed, 30 Jan 2019, 22:32

What dimensions do you need for your fibreglass lid? I happen to have two or three sheets of vinylester fibreglass made up for me by Custom Mouldings in Henderson for a boat project a while back. We didn't need anywhere near as much as I'd anticipated.

Two of the sheets are about 1200mm square x 5mm thick and are white gel-coated on one side.
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Re: Prelude conversion project - some questions

Post by jonescg » Thu, 31 Jan 2019, 06:33

Thanks Rob, but the lid will be more like an upside down tub. Flat sheets won't be much use.
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Re: Prelude conversion project - some questions

Post by rhills » Thu, 31 Jan 2019, 12:27

Easy enough to make into a "tub". Our project was a fresh water tank for our yacht, two compartments, baffle plates, complex shapes. Kaye and I constructed it ourselves after some "training" from our nephew who is a professional shipwright specialised in fibreglass fabrication. Doing a rectangular "lid" would be very easy. That said, Custom Mouldings could probably make one up for you for a good price. I found them to be very reasonable and good to work with.
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Re: Prelude conversion project - some questions

Post by jonescg » Thu, 31 Jan 2019, 13:20

I guess all they need is an accurate 3D drawing? Or a mould since that's the most expensive and time consuming part.
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Re: Prelude conversion project - some questions

Post by rhills » Thu, 31 Jan 2019, 14:59

A mould would be worthwhile if you were going to do more than a couple of these I'd imagine. If you're only doing one or two, I think it would be quicker/cheaper to just fabricate it. It's not too hard to fabricate a shallow fibreglass box. You'd just do a timber frame that sat neatly and accurately on top of your existing battery box, lay it on your main fibreglass sheet and then glue and glass on the sides around the frame (using releasing wax, gladwrap or greaseproof paper around your frame so you could get it out again without destroying it). Quick tidy up with the angle grinder/flap sander and a couple of coats of epoxy for a nice finish and it's all done :-)
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Re: Prelude conversion project - some questions

Post by jonescg » Fri, 01 Feb 2019, 13:41

For those who are keen, electric pickup truck maker Rivian have filed a patent on their rather sophisticated (complicated) thermal management system.
Like the Konas thermal management system (see here: https://electricrevs.com/2018/12/20/exc ... nt-design/) they have left open the option of heating the battery to ambient on cool days using a conventional radiator.

Some heavy reading here: http://images2.freshpatents.com/pdf/US20180086224A1.pdf
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Re: Prelude conversion project - some questions

Post by francisco.shi » Fri, 01 Feb 2019, 14:35

They look like the same cells I am using.

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Re: Prelude conversion project - some questions

Post by brunohill » Fri, 01 Feb 2019, 22:46

francisco.shi wrote:
Fri, 01 Feb 2019, 14:35
They look like the same cells I am using.
And they are the same size.

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Re: Prelude conversion project - some questions

Post by jonescg » Tue, 05 Feb 2019, 20:20

Just arrived - Type-2 inlet with 32 A, three phase cable. I ordered a second one for my car :)
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Re: Prelude conversion project - some questions

Post by francisco.shi » Tue, 05 Feb 2019, 21:49

Where did you buy the plug from?

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Re: Prelude conversion project - some questions

Post by jonescg » Tue, 05 Feb 2019, 21:56

francisco.shi wrote:
Tue, 05 Feb 2019, 21:49
Where did you buy the plug from?
These guys:
https://evconnectors.com/index.php?rout ... ption=true

It took a while because their supplier sent the wrong one to them in the UK, but luckily I wasn't in a huge rush. Once they got the right part it arrived within days.
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