HV Box (Tesla LDU) Feedback Requested

[BlueHorizon]

Hi,

After having purchased a V2 Tesla LDU board from Damien years ago and after waiting for bodywork on my 1980 911 to be complete during COVID, I'm finally getting back to planning my EV conversion!

Specifically, I'd like to get some feedback from the board members and input on the way I'm putting together my high voltage box that will house the main contactors and other bits. I should state up front that I am not an electrical engineer, but have a background in software engineering so I am learning lots as I go which, honestly, was the whole purpose of the project.

Please see attached what I'm thinking as far as the various components are going to be connected, in part based on Damien's docs but I tried to make it a bit simpler for my brain to comprehend as I start building these parts. I think most of the diagram is correct, however..

I decided to opt for the ZETA precharge unit and am a bit uncertain how that wires in. Specifically pin 3 and 6. I have pin 3 going to the ground input of the ZETA which is likely wrong and then pin 6 is going to the main (positive) coil contactor, which I *think* is correct.

Also, the ZETA unit I went for is considered for higher voltage (160-320 Volts) which I assumed is correct for this application, but again would appreciate thoughts. Details here on the unit: https://www.evwest.com/catalog/product_ ... cts_id=299

Let me know your thoughts. Also, I'm going to try to document as much as I can and am happy to contribute to any wikis.

All the best,

Garry

[EV_Builder]

Hi,
2P6S but you don't tell us how many in series in each pack.

My self I would try to 4P6S in that way you omit cable length differences. But maybe I'm wrong...

Regards

[BlueHorizon]

@ev_builder

It's 16s in a pack as I'm using LG Chem batteries (see here: https://www.evwest.com/catalog/product_ ... cts_id=481. Due to the shape and size of these batteries and taking into account the space restrictions of the frunk and engine bay of an old 911, this is a common setup to use. Basically 6 batteries in the front and 6 in the back.

EVWest's original Tesla conversion matched this and so does BisiMoto's amazing 959, you can hear him talk about the LG battery setup at 12:15 here: https://www.youtube.com/watch?v=VfRHud2W738.

Why the concern about the different cable length?

[Isaac96]

Different cable length can cause inductive issues in some cases. Basically, one pack is 'further away' electrically and so it will lag the other pack a little. This may or may not cause problems.

Do you have 12 LG Chem modules? I can't see two 2p6s packs fitting (that would be 24) in a 911.

Two packs, one front and one back.

Here's what I'd do.

Front would be 2P3S - that's two strings of three.
Rear would be 2P3S - two more strings of three.

So that's 12 modules total at 360v (and 90Ah).


Or go 1P6S in front and rear, using separate contactors for extra safety. (This is recommended by people like the Orion guys).

My car has 2P3S of LG Chem on each side of the engine. It works well so far.

[BlueHorizon]

@Isaac96 - you are completely right, I made a mistake on labelling the diagram. I have 12 LG Chem batteries in total and was intending to go with 1P6S in both front and back. I'll have a think about the 2P3S setup.

On the cable front, I'm not sure how I can avoid running a longer cable from the frunk to the rear of the car where the motor is. Perhaps I could simply run a longer cable from the back battery pack although I'll first try it with regular length to see if I run into any troubles.

Regarding the ZEVA precharger, how am I looking there? Should I skip this and just go with a standard relay / 100W 50 Ohm resistor combo?

[Boxster EV]

I think you’ll find that the pre-charge process is handled by the drive unit logic board (assuming the early boards assimilate the later boards) . You just require an appropriately rated resistor and contactor set-up.

[Isaac96]

1P6S - sweet. If you do end up with issues then switching to a 2P3S front and rear would remove the cable length differences (since the packs would be in series).

[BlueHorizon]

@Boxster EV - I was looking through your build thread and it looks like you are using 2 x 100w 30 ohms precharge resistors rather than a single 100w 50 ohms as what was in Damien’s original documentation. Is that right?

@Isaac96 - when you noted having another 2 contractors for safety, are we talking both pack’s + go to a contractor before the next positive contactor and same for negative?

[Boxster EV]

@Boxster EV - I was looking through your build thread and it looks like you are using 2 x 100w 30 ohms precharge resistors rather than a single 100w 50 ohms as what was in Damien’s original documentation. Is that right?

Yes, as it was all I had available at the time. I'm just having to wait slightly longer for pre-charge to complete before closing the main contactor,

[BlueHorizon]

Thanks - I managed to find a 100w 50 ohms one on Amazon so we'll see how that does.

On the 50A contactor, rather than order the one from ZeroEV, here in the US it looks like I might be able to buy the Gigavac P115 Mini-Tactor. (version BDA specifically)

[Isaac96]

@Isaac96 - when you noted having another 2 contractors for safety, are we talking both pack’s + go to a contractor before the next positive contactor and same for negative?

Exactly. That way, if a cell fails, that side of the pack can be disconnected. One, you get to keep driving, and two, the other pack doesn't dump all its power into the broken one.

[BlueHorizon]

OK, here's another basic question about designing a HV box:

What material board do you use to mount your components on inside the sealed box?

[Boxster EV]

OK, here's another basic question about designing a HV box:

What material board do you use to mount your components on inside the sealed box?

Most decent GRP boxes have steel chassis to them. My set-up is mounted on that (all of the components are insulated).

modular_polyester_boxes_combiester_system_-_eng.pdf

(1 MiB) Downloaded 133 times

[BlueHorizon]

Thanks! I’ve ordered a similar box that will hopefully arrive today.

Another thing I’ve been researching is the wiring sizes inside the HV box. Right now I have 2/0 AWG (70mm2) to run the longer lengths from the battery packs, however for the short runs from component to component (e.g. contactor to contactor), I believe I should be able to use 1/0 AWG (50mm2) or less. What are you all using for these shorter cable lengths?

Likewise I’m thinking about the same for the module to module connections in the battery pack where I have a couple of inches to bridge between the terminals, although actually bought some copper to create busbars as trying to get a decent crimped cable with ends between that is tricky.

BTW really enjoying learning throughout this whole process. For example, today I read that cutting / drilling copper (for the busbars) can be tricky, but using milk as a cutting fluid can prevent your drill bits / saw blades from clogging up!

[Boxster EV]

You need to check the wire and fuse data sheet based on what components you intend to use.

I’m using 400VDC 12 AWG for pre-charge set-up.

For DCDC and AC charger 400VDC 8 AWG I think.

70mm2 for battery.

[BlueHorizon]

@Boxster EV - That makes complete sense. I'll size things out accordingly and had a good time making copper bus bars yesterday.

Question for you: I noticed in your build for the pre-charge contactor, it looks like you are using the Zero EV 50A / 750V contactor. Is that correct?

[Boxster EV]

Question for you: I noticed in your build for the pre-charge contactor, it looks like you are using the Zero EV 50A / 750V contactor. Is that correct?

Yes, exactly. I’m also using the same model contactor to turn on my PTC heater

[BlueHorizon]

Nice! I picked one up too. Ironically shipping products from the UK to Texas was faster than items from California.

The other thing I'm debating is where to put the 400A fuse. I see it sometimes put in between the + battery leads and then the + contactor in the HV box and sometimes it is inserted after the + contactor in the HV box leading to the drive unit.

Thoughts on pros / cons for either placement?

[BlueHorizon]

OK, lots of progress today as I'm back from travel for work.

Made 6x busbars to link up the 1st battery pack (don't actually need 6 for one pack, but needed extra for the second pack later). On top of that I made a prototype HV component box setup using some wood as a base for now. I'm only focusing on 1 battery pack for now and will worry about the second one a bit later.

Also made a variety of 2/0 AWG cables to connect the battery pack to the HV box via the contactors. Thank god for hydraulic crimpers!

I think I have all the high(er) voltage cables in place, tomorrow will try to figure out the various coil wires from the contactors.

[BlueHorizon]

@Boxster EV - although not noted in the diagrams, I'm assuming I need to run the pre-charge resistor loop through a fuse. Is that how you wired yours up and, if so, what size fuse did you go for?