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Discussion Starter · #1 ·
Hi there.

I aim Tim. Next year my current ride will be sold. So i aim starting my search for the perfect car to convert into my dreamcar.

The idea:
Front wheel drive hybride.
With the possebility to add a motor with differential to the rear wheels. Target power of the rear electric motor is 100-150Kw.
I will be using 18650 lithium cells. At the moment i have collected 800 cells. Around 6,5kWh. I will have somewhere between 15 and 25kWh of battery to trow in the trunk. Activation of the rear motor is with on/off switch to activate the system (failsafe) and 2 noss style type buttons on the steeringwheel. 1 for around 30Kw (adjustable) 2end for 80kW or so. And both for full power! With 25kWh i think i can get away with 250A x 96 serie cells x 3,7V = 90kW Where do i get or how do i make a bms for this battery?
What cars have space at the rear wheels to put a motor there?
What motor/controller should i use?

Thanks.
 

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assembling a DIY battery out of 18650's is a lot of work. I know Tesla makes it look easy but they have mass manufacturing equipment and lots of strict quality control and a good plan for dealing with cell failures.

I hope all your cells are the same age, capacity, chemistry, quality, and manufacturer. Otherwise you are probably going to have a lot of problems.

There are a couple different BMS manufacturers you could buy from. Elithion and Orion are the two most common right now that would probably be workable for your application. Some of the more intrepid among us have built our own as well.

110kw is about 150hp. Do you want a system that will deliver that continuously? That will be a pretty tall order and completely unnecessary in most vehicles, even high performance ones. But there are certainly AC and DC setups that can do that (or more) on an intermittent basis. The AC vs. DC tradeoff often comes down to cost per performance. You can look at the many other threads for the benefits tradeoff. I always recommend AC these days. Siemens or REMY motor and suitable inverter.

DIY hybrids are a challenge because you are keeping the original drivetrain and trying to integrate an entire second drive train to it. This means you don't get to make any space from removing ICE stuff to make room for batteries and your motor. For that reason you are probably going to need to look at a larger vehicle to have enough space to do it. In the USA an older midsize SUV or midsize AWD vehicle like a subaru or such might work. Other possible options are 4WD vanagon or similar vehicle. Furthermore the big challenge with a hybrid is being able to control the mix of power from ICE or Electric to optimize efficiency. Unless you are just trying to boost power which it sounds like might be the case.

Very few if any people have tried the DIY-Tesla pack and very few people have tried the DIY-hybrid.

Note there are AWD hybrids out there, and some actually do work by having an electrically propelled rear axle already. So perhaps you can just buy what you want. If you are a good CANBUS hacker you might even be able to directly control the electrics separately, then add a bigger battery, and have a greater chance of success than starting from scratch.

Good luck.
 

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Note there are AWD hybrids out there, and some actually do work by having an electrically propelled rear axle already. So perhaps you can just buy what you want.
Yes, such as a Toyota Highlander, Toyota RAV4, Lexus versions of those two, and Honda Pilot (and Acura MDX).

I think this is an excellent point, and brings up a question which would apply to most potential DIY projects: what do you want to accomplish by building instead of buying? A unique technical configuration for an existing vehicle type (probably not very workable), a unusual type of vehicle (sure, if there really isn't one available), a unique appearance (that's reasonable), saving money (only possible with salvaged parts and no value on your time and effort)...

110kw is about 150hp. Do you want a system that will deliver that continuously? That will be a pretty tall order and completely unnecessary in most vehicles, even high performance ones.
Another good point. For instance, the Highlander Hybrid's rear power unit's motor (the MGR) can run about 50 kW, and only intermittently because it doesn't have the cooling needed for even that output continuously. The same motor can run that power level continuously, when it is used in the liquid-cooled front transaxle (as the MG2).

I do see where one might want a lot of rear power, sustained for at least the longest acceleration run anticipated or repeated frequently while lapping a race track, to provide a power balance with substantial rear bias. In practice, production parallel hybrids putting a lot of power to the rear drive the rear with the engine - not the front - minimizing the power passed through the electric system.
 

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Activation of the rear motor is with on/off switch to activate the system (failsafe) and 2 noss style type buttons on the steeringwheel. 1 for around 30Kw (adjustable) 2end for 80kW or so. And both for full power!
I read this yesterday and "noss" didn't register any meaning with me. I read it again today, and realized that of course this means NOS, as in nitrous oxide injection system. So I now get the idea, but it's scary. If the intent is drag racing then maybe on/off power is okay, but the effect on handling balance of crudely switching substantial power to only one axle while cornering is not safe. At the very least, how about putting in a switch which only enables this kind of boost while the accelerator pedal is fully applied?

Personally, I wouldn't add this much hardware for only occasional bursts, but that's the joy of DIY projects: people have different desires and so build unique things. :)

So, since rear motor is only to be a later addition, the intent is for a front drive motor/generator as well, right?
 

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Discussion Starter · #5 ·
The 2 main ideas are that i extend the full electric mode. Safe fuel. Like a switch on the gass pedal maybe for continiues power of something in between 20 to 40Kw and then i can use the gas pedal to tweek the speed needed. Might ad a switch so i can choose between 2 continiues power levels. Mode 1 = for example 10Kw for low driving speeds and mode 2 = 20Kw for faster driving speeds. Of course those numbers need to be tested. What would work the best. And a switch on the pedal that activates full power mode when i press it fully down to dragrace is verry brutal acceleration on a straight. I like the Toyota Rav4 AWD but it does not have the sleeper power i aim looking for. So i might buy the FWD and add my own electric mode.

My current ride is an 2000kg rear wheel drive SUV. Witch has a little work done to it. Stock was 140hp with 300Nm. Trowed an upgraded clutch, hybrid turbo and bigger intercooler in it and has now with stock injectors 245hp and 420Nm. Every car i buy needs to be equal or better. Because of the diesel boycot overhere. The next ride is gasoline. But i miss then the instant huge torque. Thats why i choose the hybrid.
 

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No need for any power switches , just choose a controller with the output you want and fully depress the gas pedal.

The old GE controllers would engage a contactor at WOT, if that is what you are going for buy one that does it out of the box.
 

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I like the Toyota Rav4 AWD but it does not have the sleeper power i aim looking for. So i might buy the FWD and add my own electric mode.
I understand that the rear motor unit in the RAV4 Hybrid (which is presumably comparable to the Highlander Hybrid, or less powerful) might not have enough power, but it would be much easier to replace it with a larger unit than to start with a non-hybrid 2WD RAV4 and add - not just the rear motor unit - all of the front-end electric gear (motor-generator, inverter-controller) and the battery as well. These are Toyota Hybrid Synergy Drive vehicles, so the non-hybrid transaxle is completely different from the hybrid transaxle.
 

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The 2 main ideas are that i extend the full electric mode. Safe fuel. Like a switch on the gass pedal maybe for continiues power of something in between 20 to 40Kw and then i can use the gas pedal to tweek the speed needed.
So, to be clear, where is the energy for this electric mode operation coming from? The 10 kWh battery of course, but how is it getting to the battery? A continuous electrical power draw is either very limited in time (by the capacity of the battery, charged by plugging in), or it is a hybrid, with an engine-driven generator. Putting power from the engine through a generator, charge controller, motor controller-inverter, and motor (series hybrid operation) just costs energy, so I'm having trouble understanding what you are trying to achieve by extended electric operation.
 

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Discussion Starter · #9 ·
I understand that the rear motor unit in the RAV4 Hybrid (which is presumably comparable to the Highlander Hybrid, or less powerful) might not have enough power, but it would be much easier to replace it with a larger unit than to start with a non-hybrid 2WD RAV4 and add - not just the rear motor unit - all of the front-end electric gear (motor-generator, inverter-controller) and the battery as well. These are Toyota Hybrid Synergy Drive vehicles, so the non-hybrid transaxle is completely different from the hybrid transaxle.
Here in europe we can choose to buy a hybrid rav4 FWD with same preformance as the more expensive hybrid rav4 AWD. So i would start with the hybrid FWD rav4.
 

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Discussion Starter · #10 ·
So, to be clear, where is the energy for this electric mode operation coming from? The 10 kWh battery of course, but how is it getting to the battery? A continuous electrical power draw is either very limited in time (by the capacity of the battery, charged by plugging in), or it is a hybrid, with an engine-driven generator. Putting power from the engine through a generator, charge controller, motor controller-inverter, and motor (series hybrid operation) just costs energy, so I'm having trouble understanding what you are trying to achieve by extended electric operation.
Sorry, the 10+kWh battery is daily plugged in to the elektricity net. Hoping to drive as much on cheap elektricity from and to the work. (75km/47miles round trip)
 

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Here in europe we can choose to buy a hybrid rav4 FWD with same preformance as the more expensive hybrid rav4 AWD. So i would start with the hybrid FWD rav4.
Ah, thanks - that makes sense.

So the plan is the stock design of a Toyota Synergy powertrain, so the DIY part is in addition of a non-stock rear drive unit, hacking of the electric drive mode, and expansion of battery capacity.

While the rear suspension and some of the packaging of the rear area of the RAV4 will be the same whether 2WD or 4WD, there would be some cost to swapping hub components to add rear drive, as well as structural fabrication to accommodate the drive unit. I don't know what the price differential is, but it might make more sense to just get the 4WD, and modify the rear unit for more power later.

Sorry, the 10+kWh battery is daily plugged in to the elektricity net. Hoping to drive as much on cheap elektricity from and to the work. (75km/47miles round trip)
So the idea is to convert a non-plug-in hybrid to a plug-in hybrid. The RAV4 has a 1.6 kWh Ni-MH battery; it would be a challenge to replace that with vastly more capacity (of presumably some lithium variant), and make a battery management system work with it. It would certainly be possible... but it wouldn't be easy.

An alternative is to leave all of the stock 2WD hybrid powertrain alone, and add the 10 kWh battery and rear drive to run in parallel. This would take even more room, but would be technically easier to install... and a challenge to control.
 
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