[Dameon]

I started this project many years ago... acquiring parts as they came up. In the meantime, electric vehicles have become much more popular and pervasive. Therefore, more parts in the junkyard for cheap.

For my project, I have everything but the batteries. Controller, motor, etc. I am debating "starting over" and using a plug-in Prius, Volt or Tesla battery pack, motor, charger, etc.

What system is easiest to "hack" in order to fit the components into my conversion? Feel free to speak at a highly technical level. I got that. I'm looking for the groups experience in the more common factory platforms and how they can be dissected and reused.

Thanks.

 

[brian_]

If you're breaking down an OEM battery to the original module level, and you are going to assemble these modules to reach a reasonable voltage level, then you will have a large battery. Most OEM batteries for current EVs and plug-in hybrids run close to 400 volts, so - for instance - if you want to run half of that voltage you'll be using half of the full OEM pack, which is a big pile of battery when it is half of a Tesla Model S pack. This might be a challenge to fit in the Spyder, especially with an older motor and original Toyota transaxle taking much of the engine compartment space.

I suggest a look at specific module sizes and voltages, keeping in mind the voltage for which your motor and controller are suited.

 

[Dameon]

The motor I currently have is a DC motor with a max input voltage of 144 (I think, it's ben buried in my shop for months and months).

I believe the Spark EV uses three 48v packs. I don't know how they are wired in the Spark, but I could wire them in series and get 144v. That would be a perfect match for my current motor and controller.

A Tesla battery pack is a bit more complicated, but I think it would work. Tesla uses 3.6v cells and they combine 74 cells in parallel into a module which should be ~21.6v. They have about 20 of these modules in series to get to ~450v. Getting this level of battery detail is convoluted as Tesla doesn't post the exact pack details. I think the information is generated by enthusiasts that have disassembled them personally. If the modules are even 25v each (hot off the charger), then I could run 5 of them and should have enough space in the MR2 for that. I guess I'd have a lot of spare modules. Maybe I could put a few packs in my Gem.

Trying to get the best options, learning from the group's experience, so I don't make the same mistakes as others might have.

 

[Duncan]

Hi Dameon

Forget about the motor voltage - the controller will vary that to suit the rpm and your current requirements
You can't overvolt a DC motor

What you can do is over-rev and over-current one

The limiting factor is the controller voltage

 

[Dameon]

Forget about the motor voltage - You can't overvolt a DC motor

That's an interesting statement. If that is the case, why do the motor manufacturers label the motors with maximum voltage limits?

What you can do is over-rev and over-current one

Yes, that is the limiting factor. Internal wiring and bearing over race on the output shaft(s).

I have a Curtis controller... the ol' 1231C and it is rated for a maximum of 550 amps and 144 volts.

 

[Duncan]

Hi Dameon

With a DC motor you control the current - for a given current and RPM there is only one voltage that "satisfies" the equation

So you can't "overvolt" a DC motor without either or both over speeding it or over currenting it!

My motor is rated at - 10 Kw , 206 Amps, 48 v and about 1400 rpm

I am using 340 volt battery and 1200 amp controller - at the end of the 1/8th mile I'm doing 4700 rpm

So I'm overvolting it over currenting it and over revving it - so far so good - next year sticky tires to try and get a faster time

 

[Dameon]

Yeah, I see your point now. W=VA... can't change the variables without changing the output of the equation.

 

[brian_]

I believe the Spark EV uses three 48v packs. I don't know how they are wired in the Spark, but I could wire them in series and get 144v. That would be a perfect match for my current motor and controller.

The Spark is uncommon - it was essentially GM's "trial project" before the Bolt so there aren't many of them, and they tried at least one unusual feature... the relatively low-speed/high-torque motor with only a single reduction gearing stage. Despite the odd motor, it would be strange if they used only 3x48 V nominal voltage; that seems at least a factor of two too low.

The Spark battery pack apparently changed significantly between the first version of the Spark (2014: cells by A123) and the second (2015: cells by LG Chem) The LG pack apparently has 192 cells - could that really be four in parallel and so only 48 cells in series? It's more likely that it resembles a second-generation Volt pack. GM's published 2016 specs say "p296s", which was presumably meant to be 2p96s (for a nominal pack voltage of 360 V, typical of recent EVs especially from GM)... so if there are only three modules they must each be 2p32s, and so 120 V (nominal) each, not 48 V. If they run around 48 volts per module, there are likely more modules. If the earlier pack with cells from A123 really ran at much lower voltage, there would have been motor and inverter changes between 20114 and 2015 as well... unless the inverter went from voltage-doubling to not doubling.

 

[brian_]

A Tesla battery pack is a bit more complicated, but I think it would work. Tesla uses 3.6v cells and they combine 74 cells in parallel into a module which should be ~21.6v. They have about 20 of these modules in series to get to ~450v. Getting this level of battery detail is convoluted as Tesla doesn't post the exact pack details. I think the information is generated by enthusiasts that have disassembled them personally. If the modules are even 25v each (hot off the charger), then I could run 5 of them and should have enough space in the MR2 for that. I guess I'd have a lot of spare modules. Maybe I could put a few packs in my Gem.

Although Tesla details can be hard to find, a lot of people (not me!) have put a lot of effort into literally tearing the components apart to understand them. Yes, my understanding is that the Model S/X have many 18650 cells in parallel, then six in series per module; the 16 modules are identical, and all connected in series. This means that several modules are need to hit a desirable voltage, but on the other hand some people are piling that amount of battery into original VW Beetles (apparently enough for a low-voltage motor can stack up behind the rear seat, under the window).

 

[brian_]

As a technically oriented auto enthusiast, I find it hard to see functional and nicely balanced sports cars turned into front-heavy things with no trunk space, so the typical mid-engine conversion with modules filling the front, engine, and rear compartments is what I would watch out for.

I assume that the Spyder continues the tunnel-mounted fuel tank of the first two generations of MR2; it would be nice if some modules could fit in that space, but it's pretty tight for modules not designed to fit there. Ideally, a low complete drive unit (almost any of them mount the motor around axle height, with only inverter and sometimes charger stacked on top) would be nice, allowing modules to be stacked on top without being excessively high. For a bizarre alternative, if the inverter/controller and motor could fit in the tunnel and be connected by a shaft to a final drive (differential) from front-engine/rear-drive car (a single-ratio system), with the charger in the front compartment, perhaps all of the required battery could fit in the original engine space.

Since no one has the development budget of the auto manufacturers, the best setup (if the wiring and software issues can be managed) would be the complete powertrain (battery to final gearing) of a production EV transplanted into the desired body and chassis, but that's not practical for many DIY builders.

 

[Dameon]

The Spark is uncommon so there aren't many of them

Yes, that's the widget in the works. I've only found 6 of them in recent months on the various auto auction sites. Most of them are on the left coast. There are a couple in Houston (flooded of course), but I'm not sure that would be a wise candidate. Batteries don't care to be submerged in water and electric engine windings typically freeze up from rust. If I can get a wrecked/flooded car cheap enough, I'll consider it.

The Spark battery pack apparently changed significantly between the first version of the Spark (2014: cells by A123) and the second (2015: cells by LG Chem)

The facts I read were on the A123 pack. I didn't know they changed packs in mid-run. Coincidently, one of the models on auction is a 2014.

 

[brian_]

The facts I read were on the A123 pack. I didn't know they changed packs in mid-run. Coincidently, one of the models on auction is a 2014.

An article about the change (GM Shifts 2015 Chevy Spark EV Battery Production In-House – Pushes A123 Out) showed the Spark battery, and it has six modules, not three... but that is apparently the 2015 pack with LG cells. These modules look very much like Volt modules - with the coolant manifolds low on each side - because they are GM's in-house assembly with the same or similar cells.

An earlier article (Aug 2013, so it must be for the A123 battery) compares the Spark EV and Volt: Spark EV versus Volt Battery. This early Spark appears to have four modules, each running the width of the box (almost the width of the car). This article says there are 336 cells, in a 112s(3p) configuration, so the modules are 28s(3p) each.

A classified ad offered A123 Spark modules:

I have 4 A123 5.37KwH battery packs. These are made with genuine A123 20Ah batteries. The spec sheet says they can do 18C. The modules are 97V and 60Ah.

That means that a roughly 48 V (nominal) group of cells would be only half a module. If you can physically arrange that, you could series three groups of 14(3p) each, for a 3s(14s(3p)) or 42s3p arrangement of 146 V and 60 Ah nominal capacity... or 8.7 kWh (nominal). Detailed specs for this pack give a 21.4 kWh capacity (rated), and you would be using 3/8ths of it, so the rated capacity appears to be 8.0 kWh; the pack usable capacity says 17.3 kWh, so 3/8ths of that would be 6.5 kWh. If you could use 192 V (nominal) from two very long modules, it would be a lot easier to keep the modules intact.

Of course GM would not have chosen to change battery suppliers after only a year, especially to a substantially different cell design; they went with A123 and that fell apart as A123 failed. They even ended up with six Volt-like modules a bit awkwardly packaged (extra space in the box), because they're in a box sized for a different configuration of differently-sized cells. I think I would be hesitant to put a lot of work into accommodating the A123 modules for the Spark, knowing that that they will always be rare, even compared to the LG modules for the Spark. I can only guess that the LG modules are six identical units (unlike the Volt, which as two different lengths and voltages of module).

The A123 and LG Chem cells have different chemistry, so charging and management details will be different.

I suppose I shouldn't be surprised, but for a relatively obscure EV there's a substantial amount of detailed discussion of the A123 Spark EV in this forum... just do a Google search for "A123 Spark" in DIYElectricCar.

 

[Dameon]

I think I would be hesitant to put a lot of work into accommodating the A123 modules for the Spark, knowing that that they will always be rare, even compared to the LG modules for the Spark.

Lot's of great information and links. As much as I've dug up in various holes, there's always more available. Thanks for your effort.

Your point is quite valid. Why design battery boxes, wiring and connections for a battery pack that is going to be hard to source? I don't think Tesla is going away any time soon. There are dozens of cars available at auction. They are a good source for batteries, chargers/BMS and engines... if the system can be fully dissected and hacked apart. If it isn't already, it probably isn't far off.

I'll stick with Tesla auctions.

 

[tylerwatts]

Hi Damien

Any progress on your build? My Spyder is waiting in lock-up for the event drivetrain sitting in my garage. Just another project I haven't enough time to crack on with.

Someone asked about battery location in the Spyder, it is transverse in front of engine/behind seat tubs beneath the storage bins. Unfortunately it is separated from the engine bay by a sturdy cross member, others you could probably fit 4 Tesla modules stacked in a box, maybe only 3 to be safe. And you could fit more in the storage space with a new bulkhead behind the seats. I envisaged a cassette case slotting in from underneath the car into the storage space like Riperton's bike battery or the Renault Fluence EV.

My donor is a Mitsubishi i-MIEV and I plan to mount the drivetrain further rearward by making a tubular subframe for the suspension to gain space and hopefully fit the battery repackaged in a box in the fuel tank and under the cross member up into the front of the engine bay. Fortunately the entire drivetrain with controller, charger, cooling pump etc is all mounted on a subframe that I can bolt into the engine bay.

I don't want to hijack your thread though. Apologies.

One critical limitation in the Spyder is space especially for batteries, without cutting the shell. Then you must split the pack. Most effective packaging I believe is as I said, removing the floor of the storage bins and sliding a cassette style battery case up into the space from beneath. I believe you could fit 8 Tesla modules in that space which would be too much for your controller, or stacking Leaf modules vertically and side by side would give similar results with a simpler implementation method and more flexibility to achieve your required voltage.

I look forward to both our progress.

 

[Dameon]

Any progress on your build? My Spyder is waiting in lock-up for the event drivetrain sitting in my garage. Just another project I haven't enough time to crack on with.

Same here. Just last weekend my MR2 saw the light of day. Something it hasn't seen for probably 3-4 years. Everything is still in good shape. Spiders had taken over inside the car. It was a bit creepy to even sit inside it. I also noticed that the soft top is dry rotting around the top corners of the rear window glass. Sucks because I just had the top replaced before I stored it 6 or so years ago. That's a bit surprising as I stored it cleaned and treated and it's been under cover, in my shop, since then. Other than that, no further progress.

I also haven't secured any auctions for donor EV's. I've been watching Copart for months and months, but nothing won. The salvage cars are going for very high rates. I suspect shill bidding from the organizations selling them or some kind of "back end" reserves. I'm not in a big enough town to have anything local. My best bet in Houston or, less likely, New Orleans.

I envisaged a cassette case slotting in from underneath the car into the storage space like Riperton's bike battery or the Renault Fluence EV.

My desire/hope is to create a "standard" sized box that contains the batteries and can be lifted in and out from above with a forklift or engine crane. I could change battery technology fairly easy that way. I could also swap between two boxes easily. Have one as a charging spare to reduce potential charging delay. I haven't disassembled the car yet to determine the feasibility.

Fortunately the entire drivetrain with controller, charger, cooling pump etc is all mounted on a subframe that I can bolt into the engine bay.

I was going to put all "management" components in the front trunk. More as a "showcase" measure than a convenience factor. In fact, to do that will require a great inconvenience to me for installation.

I don't want to hijack your thread though. Apologies.

No, quite the opposite. I really value your comments and input. Please continue to share at your convenience.

Then you must split the pack.

I have no unreasonable aspirations for range in this car. Strictly for "fun runs" around town and maybe an occasional show. I have a Model S for more serious trips.

I believe you could fit 8 Tesla modules in that space which would be too much for your controller

By module, do you mean the 22.8v module? If I had 8 of those, I'd wire 6 of them up and look for 4 more for a second pack for the front trunk. Another factor driving Tesla modules is that I already have a Tesla HPWC installed in my garage. I also have a second one installed in my shop. It'd be nice to utilize my home charging infrastructure for both cars.

stacking Leaf modules vertically and side by side would give similar results with a simpler implementation method and more flexibility to achieve your required voltage.

Yes, the 7.4v modules would be much easier to place and would get me much closer to 144v output. I'd probably series 19 of them in my "battery module" box.

I look forward to both our progress.

I hope to learn from your experiences. I expect you will finish before I will.

What have you done for the more common accessories? A/C? Vacuum? Power steering? Dash gauges (Speedo, Gas - wired from SoC, RPM)?

 

[Dameon]

Since this was brought to mind (thanks tylerwatts), I did a bit more battery shopping. Just using eBay, Leaf and Tesla cells appear to be a rarity. I did find lots of Prius modules though. This one is a tested and warrantied module. 7.2v @ 6.5Ah. I would need 20 which would give me 144v and 130Ah. That converts to W=VA which is W=144x130 or 18.7Kw. 20 modules would be right at $1000 plus shipping.

The manufacturers curb weight for the MR2 is 2195 pounds. Assuming the weight remains similar (removal of engine, exhaust, fuel tank, etc. and addition of electric motor, batteries, etc.) and a general calculation of 250wh per mile (pack wh x wh/m), I should get 74 miles from a full charge. An 80% charge would be right at 60 miles. Almost exactly what I'm going for.

I can get the 3rd gen battery from the same group. It's a little more expensive at $1100 for 20 modules. They are both NiMH, so I'm not sure of the value of the newer modules.

I can get the Tesla Li-ion from EVWest, but it is very expensive. I would need 6 of those to get to about 136v (so I lose a little power) which would cost me $9480, but I get 31.8Kw of range. That's almost twice the range, but 10x the cost. If I could find Tesla modules for MUCH less, I would seriously consider them. Longevity isn't a discussion because I can replace the failed/worn NiMH 10x for each Li-ion and I doubt Li-ion has 10x the life.

 

[Kevin Sharpe]

If I could find Tesla modules for MUCH less, I would seriously consider them.

Don't forget that some vendors offer the 12S converted Tesla modules which are nominally 50V

http://www.diyelectriccar.com/forums/showthread.php/tesla-parts-buy-188490.html

 

[Dameon]

Don't forget that some vendors offer the 12S converted Tesla modules which are nominally 50V

Good information at that link, backed by forum user experience. Don't know how I missed that one.

Edison "has" the 12S modules for $1525. Since they are wired for 48v @ 5.4Kw, I could use 3 to get to 144v which would give me about 16Kwh of range. That's my desired minimum range at about 60 miles and is only $500 more for batteries over NiMH. That makes my "battery module" box pretty small. I could have two slots in my car and they would be in parallel. I could run them both or keep one as a spare to resolve range anxiety. There's a 99% chance that wherever one box got me, the other could get me home... assuming I didn't drive down a steep grade for most of my initial trip.

Edit: Forgot to multiply by 3 for the modules. $4575 in battery cost, not $1525. 4x the cost for basically the same performance (not accounting for battery weight or discharge rate) and the same range.

 

[zsnemeth]

Since this was brought to mind (thanks tylerwatts), I did a bit more battery shopping. Just using eBay, Leaf and Tesla cells appear to be a rarity. I did find lots of Prius modules though. This one is a tested and warrantied module. 7.2v @ 6.5Ah. I would need 20 which would give me 144v and 130Ah. That converts to W=VA which is W=144x130 or 18.7Kw. 20 modules would be right at $1000 plus shipping.

There is your problem. 20 modules will give You 7.2V @130Ah or 144V @ 6.5Ah.
Not both! You'll need 400 of those modules for 144V @ 130Ah.

 

[Dameon]

There is your problem. 20 modules will give You 7.2V @130Ah or 144V @ 6.5Ah.
Not both! You'll need 400 of those modules for 144V @ 130Ah.

Precisely right. w=vA. If you take from one, it has to come from the other.