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Discussion Starter · #1 ·
Hi All,

I just wanted to create a thread for my upcoming project. I hope to modify a VX220 (Opel Speedster) using a Tesla SDU, with a focus on light weight, fun, and open source where possible.

The parts I currently intend to use:
  • Vauxhall VX220 2.2L NA
  • Tesla SDU
  • Openinverter Tesla SDU controller
  • LG Chem 16S packs (96s2p total)
  • 6.6kW 400V+ charger with CAN (brand undecided)
  • DIY central controller to link together inverter, charger, BMS slaves, EVSE, and OEM Vauxhall gauges
  • Appropriate replacements to power the cabin heating system and brake assist / ABS.

I have obtained the car, and fingers crossed, the Tesla SDU will fit. I will be getting professional assistance with the mechanical fitment, as my expertise is with electronics rather than mechanics, but hopefully I will be learning the latter as I go along.

I hope to program my own controller to link everything together, using CAN where possible. My main question for now is about how I will integrate the battery modules (whether I can use the LG OEM BMS slave modules, or whether I'll have to replace them). I hope to update this thread as I progress in the coming weeks (months?!).

Any advice on the general setup would be welcome, and any information about the LG Chem BMS slave protocol would be greatly appreciated.

Tire Wheel Sky Plant Car
 

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Which LG 16S modules are you planning on using? Have you looked at the price of these batteries vs something like modules from Zero-EV? (to be clear I work at Zero-EV and have used certain LG 16S modules in the past)
Zero-EV 6S Module
 

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Discussion Starter · #3 · (Edited)
Which LG 16S modules are you planning on using? Have you looked at the price of these batteries vs something like modules from Zero-EV? (to be clear I work at Zero-EV and have used certain LG 16S modules in the past)
Zero-EV 6S Module
Thanks, your modules are marginally higher capacity (2.2 vs 1.8kWh, at the same weight 12kg) and do look like they'd be a good option for me. I'll compare prices wen I can as I haven't had firm information about the price / availability yet. I was hoping I might be able to use the OEM BMS slave boards included on the LG modules, but if not, then those CALB modules may be the better choice, so thanks for the pointer. Are the connectors to plug into the cell taps readily available? If so, I'll look at BMS options.

Edit: I ignored your first question. Please see this post too: Unknown LG 16S pack with water cooling
 

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Discussion Starter · #4 ·
PS. I'd need a minimum of 16 of these modules, to achieve 96s, vs only 6 (but realistically 12) of the 16s modules, so this will be a factor too, but will of course also depending on my current draw requirements and available space. I think I want 600A peak for the Tesla SDU, so 16 of your 6s modules might be spot on!
 

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Discussion Starter · #6 ·
Hi, I'm new.
Does SDU mean single drive unit?
It means "Small Drive Unit". Tesla Model S comes in various configurations, using some combination of "Smal Drive Unit" (approx 200kW) and "Large Drive Unit" (approx 400kW). I believe 4-wheel-drive versions use one of each.
 

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It means "Small Drive Unit". Tesla Model S comes in various configurations, using some combination of "Smal Drive Unit" (approx 200kW) and "Large Drive Unit" (approx 400kW). I believe 4-wheel-drive versions use one of each.
Yes, but...
  • 2WD Model S had one large drive unit in the rear (the large unit was used only in the rear)
  • the first AWD Model S had small drive units at front and rear, while Performance AWD versions had a small unit in the front and the large unit in the rear (the small units were used only in AWD vehicles)
These are all the original Model S/X induction motor drive units; they are no longer used in current Tesla vehicles, but they are what can be found in salvage and they're what most people mean when they talk about conversions using "Tesla motors" or "Tesla drive units". They are what all of the aftermarket controller modifications are for. There are now different drive units first introduced in the Model 3 and Model Y, with variations of them now used in the Model S (and presumably Model X) as well.
 

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For those (mostly in North America) who are unfamiliar with the Speedster and VX220, these are the GM versions of the Lotus Elise. It's an aluminum-framed mid-engine car.
 

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If I understand this correctly, the LG Chem 16S modules that are being considered are not the ones used in the Chrysler Pacifica Hybrid and widely sold by conversion suppliers such as EV West. Those appear to now be unavailable from those sources (allegedly due to legal action by LG Chem).

The appeal of a low Ah capacity - and so a lot of cell groups in series for the size of the module - is to keep the total size of a ~360 V pack down. By the same logic, any plug-in hybrid is a potential source of a suitable small high-voltage battery pack; this is one reason that Chevrolet Volt packs were popular. The LG Chem 16S modules in the linked thread were apparently from a Volvo XC90 T8, an example of a plug-in hybrid.

The problem if you go too small in cell group capacity is that - as in this case - there isn't enough capacity and you need to parallel strings of modules, increasing the complexity of battery management.
 

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These appear to be in the VDA 355 format, sometimes called the "shoebox" size. There are a few choices of manufacturers and sources of modules in this format; an example is the OX Drive series from Electric GT. The relatively small size is good for flexibility in arrangement, and in the 6S version the total pack size is moderate so a high-voltage pack might fit in a small car like the VX220.
 

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With a Tesla SDU sitting mostly behind the rear axle, and most of the battery presumably in the original engine compartment, the result is going to be even more rear-biased in mass (weight) distribution than the original car. That's not necessarily a problem (and it has been done before in similar vehicles), but needs to be considered when making selections such as tire sizes and spring stiffnesses.
 

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Discussion Starter · #12 ·
With a Tesla SDU sitting mostly behind the rear axle, and most of the battery presumably in the original engine compartment, the result is going to be even more rear-biased in mass (weight) distribution than the original car. That's not necessarily a problem (and it has been done before in similar vehicles), but needs to be considered when making selections such as tire sizes and spring stiffnesses.
Thank you very much for your replies. With regard to the SDU, I had hoped it might be possible to run the SDU either upside down, or in reverse, so that it could sit where the original engine did. I'm told both of these may have implications for lubrication / cooling. Do you know if either is feasible, or whether I'll definitely have to place the motor behind the axle? In either case, I hope to put at least some of the batteries in the front compartment (in place of the radiator) to partially rebalance the weight, though I won't know for sure what is possible until I choose battery modules and pull the car apart.
 

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Discussion Starter · #13 ·
These appear to be in the VDA 355 format, sometimes called the "shoebox" size. There are a few choices of manufacturers and sources of modules in this format; an example is the OX Drive series from Electric GT. The relatively small size is good for flexibility in arrangement, and in the 6S version the total pack size is moderate so a high-voltage pack might fit in a small car like the VX220.
Thanks for the additional battery module suggestion. Looking at the OX-Drive datasheet, they appear to have plenty of options, but in order to get the 600A peak current, I'd need 24 x 4s modules. I'll definitely need to give some serious thought to how many modules I can fit, and how much current I actually need. If I reduce peak current to 410A, I could use 16 x 6S modules, which may be a little saner. I'll look at the available space and see what makes sense.
 

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Discussion Starter · #14 ·
The problem if you go too small in cell group capacity is that - as in this case - there isn't enough capacity and you need to parallel strings of modules, increasing the complexity of battery management.
I agree entirely. I think a potentially cheap source of a small number of the 16S packs may be a false economy. I'd need a minimum of 2 strings in parallel, and future maintenance could well be painful. I'll look more at the 6S options, and measure space to see how much capacity I can realistically fit.
 

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With regard to the SDU, I had hoped it might be possible to run the SDU either upside down, or in reverse, so that it could sit where the original engine did. I'm told both of these may have implications for lubrication / cooling. Do you know if either is feasible, or whether I'll definitely have to place the motor behind the axle? In either case, I hope to put at least some of the batteries in the front compartment (in place of the radiator) to partially rebalance the weight, though I won't know for sure what is possible until I choose battery modules and pull the car apart.
The usual approach is to keep the drive unit the same side up, and turn it around so it rotates in opposite to the usual direction, but perhaps turning it over is also possible with suitable lubrication modification. A Model 3 drive unit has a better motor, and places the motor ahead of the axle line, but it's not as well supported by aftermarket controllers.

To me, the problem with putting the motor ahead of the axle line is the loss of space for battery modules... and there isn't enough of that to start with. :(

You can't entirely eliminate the radiator if you are using any modern drive unit (they're all liquid-cooled) or liquid-cooled battery... although you could use a much smaller radiator, and could place it differently.
 

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Discussion Starter · #16 ·
You can't entirely eliminate the radiator if you are using any modern drive unit (they're all liquid-cooled) or liquid-cooled battery... although you could use a much smaller radiator, and could place it differently.
That's a good point. This is why I come here for sanity checking! Your approach is probably the correct one then, putting the batteries as far forward as possible in the engine bay.
 

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Discussion Starter · #17 ·
It occurs to me that I really don't actually need to draw 600A at 360V unless I want to reach the moon, so I can definitely sacrifice either some voltage in the battery, or sacrifice some peak current capacity in the battery.

If I understand correctly, both options will essentially have the same effect, limiting the amount of current I can draw at high RPM, the only difference being the programming of the inverter.

In both cases, there will be less peak power available and hence a reduced top speed. If I use 6S cells, which seems like the leading option right now, I could fit as many as I can, which may end up with a reduced voltage, but performance should still be quite impressive. Is there a power vs weight vs top speed calculator for such decisions?
 

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It occurs to me that I really don't actually need to draw 600A at 360V unless I want to reach the moon, so I can definitely sacrifice either some voltage in the battery, or sacrifice some peak current capacity in the battery.
True, 180 kW is more than the VX220 should need to match the original performance.

If I understand correctly, both options will essentially have the same effect, limiting the amount of current I can draw at high RPM, the only difference being the programming of the inverter.
Close, and valid at lower speeds. Since the controller can only reduce voltage from the battery to the motor (with a corresponding increase in motor current versus battery current), the battery voltage is a limitation on how much voltage can be delivered to the motor. Higher motor speed requires more voltage (due to back-EMF... good to look up, if not familiar with this), so reduced battery voltage is a limitation on high-speed performance.

Certainly something less than the normal battery voltage for a production EV motor is still usable.
 

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Is there a power vs weight vs top speed calculator for such decisions?
Not really, in part because the power required to keep moving at any speed depends more on aerodynamics than on weight.

In most modern EVs,
  • top speed higher than any normal highway speed so it doesn't matter, and
  • top speed is limited by the motor's top speed and gearing, not by power.
 

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This should be a good build.

A suggestion for one of your points - 6.6kW 400V+ charger with CAN (brand undecided)

Its the same as the unit from StealthEV but direct from the manufacturer in china. I bought mine from them, but if your in the US, the StealthEV unit is probably better suited to you as the supplier and support is 'local'. Cost wise, its about the same. It combines the charger and DC-DC converter into one compact unit, which is a bonus when space is a premium.
 
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