Prelude conversion project - some questions

[jonescg]

Hi All,

I have been asked to do a conversion on a 1988 Honda Prelude. The owner of the vehicle contacted the AEVA and asked around, and while many people reasonably suggested she spend her money on a used Leaf, she was adamant that she wanted to convert her car to electric, and cost (although significant) was not a major barrier. So good on her I say! I've enlisted the help of Matt Lacey because there is no way this is a one-person job, even with a generous timeline. With the owner's permission I will start a build log, but this might be a good spot for the technical discussion about certain aspects of the build. If it rapidly turns into the build log, we can move it to Members Machines forum I guess. So the project:

1988 Honda Prelude (yes the one with mechanical 4-wheel steering). It's in reasonably good condition, but has had several panel jobs done over it's life. The owner has had the vehicle from 40,000 km - 26 years, hence the emotional attachment and desire to convert. Perfectly irrational - that's why we do it hey?

We've sourced a Greatland motor and controller from EV-Power, so 30 kW continuous and 60 kW peak. We will keep the gearbox out of convenience, and the clutch to make changes smoother. This motor-drive package will accept up to 400 V DC, so the battery will be a 96s Li-ion pack.

Battery - as space is constrained, we will be using some rather energy dense cells. I'm putting the battery pack together using 7000 mAh pouch cells which will be liquid cooled - more on that later. But 25 kWh and 110 kg worth of cells is pretty good going. The liquid cooling will be a product I intend on developing for future applications as well, and will call for some interesting control features.

Like the battery on Voltron, it will be completely self-contained with nothing coming out of the sealed enclosure but coolant lines, HV lines, and a low-voltage input connector with all the BMS and contactor supplies. So I have started to draw up the main traction circuit and I'm wondering if putting a contactor on the negative is worth the trouble. Seems all production EVs do it, so it might be worth it?

Drawings to come...

[Rusdy]

Nice one! Any fancy charging capability? I presume planned for basic J1772, or straight to Mennekes 22kW?

What's the plan for air-con? I wonder any products out there these days for EV converts to do variable power air-con (instead of full ON-OFF)? That's what I've found very good with OEM EV (especially the remote ON).

[jonescg]

The original Honda air conditioning equipment is still connected but not working. Probably needs a reconditioning and re-gassing. However we will probably fit an ESC and small brushless motor to it. Ideally we would use the HV supply to run a VFD-motor and keep the loads off the 12 V system if possible - any tips or leads here would be appreciated.

Charging - hoping to go for a 6.6 kW charger, single phase, but use a Type-2 connector should we want to upgrade. Ovartech made a promising liquid cooled charger, but it's price doubled in the last 6 months so we're likely to be using a TC charger or similar for now.

We can put a heat exchanger on the battery coolant line so that refrigerant can be used directly to cool the battery pack. I'm inclined to think that a fan-forced radiator to ambient will suffice, but we do get some unpleasantly hot days through summer in Perth. Shouldn't be too hard to plumb in if necessary.

[Richo]

I had one of my cars for 14 years - was sad to see it go.
So 26 years is very impressive.

I'd still go with both contactors.

[Rusdy]

We can put a heat exchanger on the battery coolant line so that refrigerant can be used directly to cool the battery pack. I'm inclined to think that a fan-forced radiator to ambient will suffice, but we do get some unpleasantly hot days through summer in Perth. Shouldn't be too hard to plumb in if necessary.

I do wonder though with 'small'' powered motor and no fast charge, will there be any benefit going liquid cooled? How much cost extra going liquid cool system? Or is it due to your pouch configuration that it becomes necessary?

After monitoring my Leaf religiously (which is closer to air cooled pouch type?), the only time the batt temp went really high, was when I went to South West. In the space of 6 hours, I stopped 4 times for fast charging. At the very end of the trip, one of the batt sensor hit 49C (ambient around 30C). The fastest temperature incline was during fast charge (understandable, since 30-ish kW get into the battery, where as doing 110kph consumes just under 20kW)

At other times, even in 40C summer heat, the difference in ambient never exceeds 10C.

Anyhoo, looking forward for the detailed story!!

[jonescg]

@Richo - It does make for a slightly more complicated initiation though; one more contactor to pull in but at least it can be powered by the same source that energises the precharge relay. Hopefully I have room for all the bits!

@Rusdy - It's about longevity. The Nissan battery might have only got up to ~50'C but it would have stayed at ~50'C for several hours afterwards. The longer a battery sits at elevated temperatures and states of charge greater than 50%, the more degradation will occur. It's a cumulative effect. So for a >$20k investment in batteries, an extra couple of grand for a cooling system is sound insurance in my view. It might seem okay for the first year, but capacity loss starts to rear its head over several years. One Tesla in Sydney has clocked up 200,000 km and it's lost barely 4% of its original range. This all comes down to good thermal management.

I'm pretty excited about how it's coming together!

[Richo]

Yeah doesn't need to precharge on the second just on/off - i'm sure you have a line to tap into that will do it.
Safety first...

[jonescg]

My thoughts on the HV wiring side of things.

HV Wiring plan.jpg (147.92 KiB) Viewed 873 times

Just wondering if the charger should be connected to the battery with it's own contactor... and I'm wondering what input is the most appropriate for the negative contactor - If I stick with this layout, it needs to close whenever the charger is needed. I could power the negative relay with some OR logic - if the charger is plugged in, the (-) contactor closes, but the precharge and main (+) contactors are prevented from closing. Yet when the precharge contactor is closed, so too is the (-) contactor.

[Johny]

Looks OK but 2 comments.
1. It needs a fuse to the inverter.
2. If you are thinking of using a contractor on the charger DC side ensure the charger can handle being re-connected without damage. Some chargers can not connect without pre-charge.

[antiscab]

The Tc chargers have internal output relays, so don't need Pre charge.

Johny - why would the inverter need a separate fuse? I haven't seen that before. The battery fuse is usually sized to protect the wires between battery and inverter. I could understand if there's multiple major loads, but the inverter is the biggest device by at least an order of magnitude

[Johny]

You're right. I missed the fuse in the middle of the pack.
I have mine so the main traction fuse and aux fuses come off the pack - not fuses in series. That's just a preference though. Good that the charger has O/P relays. All good.

[jonescg]

Here are my thoughts about the battery cooling system.

Lithium cobalt batteries are a lot like humans. We like it when the temperature is between 20 and 30 degrees Celcius; we don't like working too hard; and when we get too stressed, we explode in a fiery rage .

So the plan is to have a water-glycol coolant circulating through the cooling plates of the battery and having this heat removed to the atmosphere through a radiator. This is great when the ambient air is at or below 30 degrees, but when we get our signature hot days in Perth some more cooling is required.

airconsystem.jpg (102.83 KiB) Viewed 798 times

I figure a heat exchanger just before the blower is a good place to chill the battery coolant. Being tied directly to the air conditioning, whenever the driver is hot enough to need AC, the battery will get some of it too.

Importantly, the coolant will have to continue to circulate well after the car is parked, and on a very hot day, perhaps even run the AC compressor.

[4Springs]

I figure a heat exchanger just before the blower is a good place to chill the battery coolant. Being tied directly to the air conditioning, whenever the driver is hot enough to need AC, the battery will get some of it too.

I'm no expert, but my thought is that having the heat exchanger after the blower would be better for the driver. The cabin air is then cooled with the coldest refrigerant, before it moves on to the heat exchanger. The heat exchanger will be much more efficient than the blower at heating up the refrigerant, so if it is first there might not be much 'cold' left over for the driver.

The heat exchanger will add resistance to the circuit though, and it may be better to put it in parallel. That way you can use a valve to decide exactly how much refrigerant goes to each evaporator.

[jonescg]

Hmm good point. I guess we should look after our humans before the batteries...

I don't think the battery coolant would be getting more than a few degrees over ambient, but as you say the heat exchanger will be pretty good at warming up the refrigerant. I'm wondering if a thermostat can be set up so that if you're parked in the sun all day, the AC can come on if needed. Seems quite energy intensive though.

[4Springs]

I'm wondering if a thermostat can be set up so that if you're parked in the sun all day, the AC can come on if needed. Seems quite energy intensive though.

Doesn't sound too hard, you'll need a thermostat anyway in normal running.
If you need it to run when nobody is in the car it would be much more efficient to cool just the battery and not the the greenhouse that is the cabin. You'd want a good source of coolish air though, it wouldn't be good to have the condenser source air from under the bonnet if you are going to run it when parked.

What sort of temperatures will damage the battery? And what sort of temperatures are experienced underneath a car in Perth in summer?

[jonescg]

The cells are at their happiest at 20 degrees C. However as long as their average lifetime temperature and state of charge is as close to 20 degrees as possible, they will live a long life. While they might have a maximum operating temperature of 60 degrees, you would want to minimise the time spent up there.
I can't upload files other than images here, but this is a link to a good paper on what charging regime gives the most cycles:
https://endless-sphere.com/forums/viewt ... 14&t=93512

[Paul9]

Just in regard to TC Chargers.

My last upgrade included adding two new TC chargers. They have a new model available which is roughly half the weight and size of the old models. I bought two to fit to my car. The first problem was that the chargers have very small pin and socket fittings and the manual does not clearly say which pin is connected to which socket. Emails to TC chargers solved that problem. Secondly the sockets that go over the pins are not very tight. The socket fitting wobbles a little. Thirdly you don't get any spare pins which means if you drop one in a crowded garage there is a great chance you won't find it. I tried to buy some spares (just in case) and I could not find spare pins anywhere.

The long and short story is that, after triple checking I had everything wired up correctly, I turned on the power and was greeted by a loud bang and a 6 foot high shower of sparks. Result was one dead charger! Melted pins and black sockets.

I hooked up the second charger the same way but added small pieces of rubber between the pins in case there was some sort of arcing between the pins. The pins are very close to each other. Turned on the power and nothing happened. No lights or noises. No sparks either. Just nothing.

Took both chargers over to my electrician brother in case I had done something stupid - always a strong possibility. He wired up the unexploded charger turned on the power and again nothing happened.

I then bought two of the old models and wired them up. They use normal IEC connectors. Both these chargers worked fine and still are.

Just a warning!
Good luck
Paul

[Richo]

..and when we get too stressed, we explode in a fiery rage .

No that's only when ppl are on extremis

[jonescg]

Quick question for the high voltage converters - how do you heat your cabin / demist your windows?

I found this kit online, and I doubt I could engineer something better for much less money:
http://www.electriccarpartscompany.com/ ... p_712.html

Looks to be two of the usual AC heating elements in series. Since we'll be using the existing vehicle blower/AC unit this will no doubt be sufficient. Switching a non capacitive load like a pair of heating elements at 8 or 9 amps shouldn't strain a contactor too much.

[Richo]

It looks quite good.
I ended up with some instant in-line under sink water heater from fleabay.
For that voltage I'd have to use 2 - add the pump, control etc doesn't work out much cheaper than that kit.

[jonescg]

http://www.engelaustralia.com.au/produc ... ctid=21607

Now this looks interesting. Assuming your vehicle doesn't have an AC system already, I wonder if this would be a practical option?

[reecho]

For the saloon cooling that wont have enough BTU's. The Masterflux compressor is much more suitable. But for battery cooling it might be ok.

[jonescg]

All good - since found a supplier of gas/liquid heat exchangers which are easily incorporated into the car's AC.

[Richo]

I thought it was for the battery cooling.

[jonescg]

It was for the battery cooling, but if I can plumb into the car's AC it should be more effective and take up far less space.

I've devised a bit of a flow-chart for how the battery thermal management system will work.

Battery thermal management program.png (32.32 KiB) Viewed 284 times

In essence, if the temperature is below 22 degrees, not even the coolant will circulate because if it did, the battery would be a little too cold, and you would lose range.
If the cell temperature goes above 22 degrees, the coolant pumps kick in. If any cell temperatures exceed 32 degrees, the car's AC compressor will kick in which ensures sufficient cooling to get them back into their happy zone.

I'm thinking about have this set up so it can work whenever the vehicle is plugged in, as well as when the car is in use. That way the thermal management can do it's thing with out running the battery down. However if you drive somewhere on a hot day and park up, it would be ideal if the system kept working for another half an hour or so just to get the cells down to ambient.