[TangentialTorque]

Its a 2WD but automatic so I'm probably tossing the transmission with the motor, but the basic gist of the matter is the van has a very nice interior, and I have a title. Used cars are criminally expensive in my area, and the engine is blown again. It's the third engine the dealership put in there (warranties huh) and at this point the warranty ran out of time.

I've researched the topic quite a bit, and Astrovan conversions have been somewhat unfeasible in 2012, many forums opining the difficulty of battery capacity and a motor large enough to regeneratively brake a vehicle that weighs 4000 lbs when the electric conversion is factored in.

A decade later, batteries CAN be sourced at $100/kWh, and finding a used AC motor for basically free is not too difficult. I'd like some help with some of the general math and safety margins, although I am well practiced with repairing vehicles, and physics, I've worked in enough factories to know that there's a huge difference between theory and practicality.

To that point, I have calculated that a roughly 60kW motor should take the van up to around 50 MPH, but I assume something around 80kW is a lot more reasonable.
Reasonable efficiency suggests I could get a 50 mile range with 35-40 kWh of LiPO4 batteries, but once again, when factoring in AC conversion from DC, and the efficiency of whatever beefcake VFD powers the 80kW 4 or 6 pole AC monster.

So I'm fairly well aware it's a bit of an undertaking for a first conversion, but jumping into the deep end is a frequent habit. Basic specs suggested by math are as follows, please feel free to call me a fool and correct me.

35 kWh of LiPO4, exact arrangement depends on voltage and current requirements of controller
70kW 4 or 6 pole AC motor (probably an old Siemens motor)
Some VFD, here I need a lot of help. I am very familiar with some crane and machine VFDs, but those don't have capability for regen-braking, and I wouldn't even know where to look!

Likely to be direct drive (a dream of mine) but I do realize the regen braking from a 4000lbs vehicle is INTENSE, basic physics calculations suggest that any reasonable amount of breaking power is likely to generate 60-80 kW, which is a lot of power. I have been known to make large capacitor banks, so that may be a decent way to dump current from breaking and bleed it into the batteries, but also LiPO4 batteries are very capable of high current.

 

[remy_martian]

Industrial AC motors are super heavy and bulky because they run at low speed. VFD is not well suited to automotive environments and most use resistor braking that I've seen.

So your math looks ok, your conclusion on battery sizing is off by about 50% imo, but your for-nothing choice of an industrial motor will likely be worth what you're paying for it in this application....worthless. I know a company in Thailand that used industrial motors with direct drive on small campus buses which are rougly the size of your van....25mph and slow AF on hills....they did that design about 30 years ago.

It's the battery and accessories that are the big cost. Motor and inverter can be had these days for ~2000 or less. Your propulsion choices here are about three decades behind the times....you can do better, but they're your choices.

 

[TangentialTorque]

Industrial AC motors are super heavy and bulky because they run at low speed. VFD is not well suited to automotive environments and most use resistor braking that I've seen.

So your math looks ok, your conclusion on battery sizing is off by about 50% imo, but your for-nothing choice of an industrial motor will likely be worth what you're paying for it in this application....worthless. I know a company in Thailand that used industrial motors with direct drive on campus buses which are rougly the size of your van....25mph and slow AF on hills....they did that design about 30 years ago.

It's the battery and accessories that are the big cost. Motor and inverter can be had these days for ~2000 or less. Your propulsion choices here are about three decades behind the times....you can do better, but they're your choices.

I hadn't really considered that. I was looking more at asychronous AC motors simply for cost and applicability for regen braking. With a 4000lbs vehicle, regen braking is a very good thing to increase range, but I really don't want to have to design a circuit to energize the armature to generate 3 phase AC at 60kW that I then have to rectify to the batteries. What kind of controllers should I be looking at?
Also RPM for 22in tires at 70MPH is about 700-800RPM, which most of the AC asychronous motors I've looked at are around 1200 to 2400 RPM at 60kW, which would need some kind of reduction for reasonable torque at the low end.
Most of the AC motors for 'sale' around here are from large industrial plants that are being taken apart for hipster housing, so the cost of the motor is more "please take this 400lbs motor away from me", just becuase the investors who bought and somehow rezoned a warehouse know nothing of the value of the equipment housed within. One was selling a 20ft bed, ~4ft swing royal monarch laythe for $2k, motor included, still running.
What kind of motor would you recommend for this type of vehicle? I don't really want a top speed higher than 65mph, it can feel pretty terrifying with the raised roof and all!

 

[remy_martian]

Most inverter designs already have the rectifiers built in, so the DC link never sees AC from the motor. A Prius inverter might work...

 

[TangentialTorque]

Most inverter designs already have the rectifiers built in, so the DC link never sees AC from the motor. A Prius inverter might work...

Oh geez I don't even need a specific charging circuit for the breaking? That's pretty fantastic. Do you think the drive of the 60kW Prius drive train would work to motivate such a large vehicle? Scrapping them can be very affordable, afaik, supplemented with a real battery, could you not just rip out the inverter and drive-train and franken-rig it to the diff of the van? I have some limited machining capability.

 

[brian_]

Also RPM for 22in tires at 70MPH is about 700-800RPM, which most of the AC asychronous motors I've looked at are around 1200 to 2400 RPM at 60kW, which would need some kind of reduction for reasonable torque at the low end.

Did you mean 32 inch tall tires? A 22" tall tire is for a tiny car, not an Astro. The stock tire is P215/75R15, which is about 28" in diameter or 750 revolutions per mile, for 875 RPM at 70 MPH.

Presumably you would connect the motor to the stock axle, which has reduction gearing (the pinion and ring gears), likely something between 3.23:1 and 4.10:1. That means when the wheel speed is 875 RPM, the shaft speed is 2826 to 3588 RPM. That's slow for any reasonable motor, mostly because the speed is proportionately even lower at lower road speed, so a good conversion would typically have an additional reduction gearbox or at least swap the axle ratio to the most extreme reduction available; Strange offers up to 4.56:1 for the GM 7.5"/7.625", which would result in 3990 RPM @70 MPH.

 

[TangentialTorque]

Did you mean 32 inch tall tires? A 22" tall tire is for a tiny car, not an Astro. The stock tire is P215/75R15, which is about 28" in diameter or 750 revolutions per mile, for 875 RPM at 70 MPH.

Presumably you would connect the motor to the stock axle, which has reduction gearing (the pinion and ring gears), likely 3.23:1. That means when the wheel speed is 875 RPM, the shaft speed is 2826 RPM. That's low for any reasonable motor, mostly because the speed is proportionately even lower at lower road speed.

Yessir, I did mean 32, I am about as smart as I am literate, so I should make a great engineer! All joking aside, yeah I figured direct drive would be a little low for most of these motors without more gear reduction, but I am hesitant to make a gear myself that will be transmitting 60kW of energy mechanically. Some of those AC motors have fantastic amounts of torque at 0 RPM but of course the current requirements are phenomenal, which further motivates me to include a capacitor bank for starting from 0 and storing current from regen breaking.

 

[remy_martian]

You can't afford the cap bank needed to store that much energy.

 

[brian_]

... Some of those AC motors have fantastic amounts of torque at 0 RPM but of course the current requirements are phenomenal, which further motivates me to include a capacitor bank for starting from 0 and storing current from regen breaking.

Capacitors are an unnecessary distraction. Any battery with sufficient energy storage capacity to be useful for the Astro will be able to handle the power requirements.

Remember that current and voltage between the inverter and the motor are not the same as the current and voltage between the battery and the inverter. The power is about the same (the inverter loses a few percent of the power on the way through), not the current.

 

[brian_]

Yessir, I did mean 32, I am about as smart as I am literate, so I should make a great engineer!

Okay, replace my example speeds with lower wheel and shaft speeds due to the larger-than-stock tires: about 630 revolutions per mile instead of 750 revolutions per mile.

 

[TangentialTorque]

You can't afford the cap bank needed to store that much energy.

Whoever buys capacitors for a bank that large is a fool! If you don't know how to make multi-farad systems, you have no business manipulating or installing them. They are not too terribly difficult to manufacture, given access to the right supplies and a safe and solid understanding of chemistry. Although as I said and as brian_ said, LiPO4 batteries can handle frankly disturbing amounts of current.

 

[TangentialTorque]

Capacitors are an unnecessary distraction. Any battery with sufficient energy storage capacity to be useful for the Astro will be able to handle the power requirements.

Remember that current and voltage between the inverter and the motor are not the same as the current and voltage between the battery and the inverter. The power is about the same (the inverter loses a few percent of the power on the way through), not the current.

Yeah, I just assume the current the batteries will get will be much larger than the motor gets, at least for AC systems. Now there is a guy around town who converted a big-ole pickup (a ram 1500 I believe) using a bunch of deep cycles and an old forklift drive motor. I think AC systems can be a lot more efficient, however.
Is there any particular concern with setting up the batteries to produce high-voltage DC, something north of 300V? I have a feeling battery cells are more sensitive to high-voltages rather than high-current, but limiting voltage at 60kW can lead to some very thick bus bars!

 

[remy_martian]

You clearly have a bunch of reading and catching up to do on this site.People here regularly assemble cells and modules in the 400VDC nominal range.

Also, watching somebody build a "supercapacitor" on Youtube using a microscope slide is a joke. "All you gotta do is..."

"They are not too terribly difficult to manufacture, given access to the right supplies and a safe and solid understanding of chemistry." Neither is a nuclear reactor.

We try to look at pragmatic stuff here.

If the supercaps are, indeed, "not too terribly difficult to manufacture", stop f*cking with a beater van and go set up a factory to make the caps for everybody who has no clue how to make them cheaply or to store high amounts of energy in a given volume needed for mobility applications.

There are some supercap buses in operation, but you have to throw bags of money at them and their charging stations are not well grounded in today's Lithium battery reality.

 

[Jordan325ic]

If high power and high speed is not a concern, the most cost-effective EV solution at the moment is a Nissan Leaf motor/inverter. Thunderstruck-ev sells a (more or less) plug and play kit I believe.

 

[brian_]

Yeah, I just assume the current the batteries will get will be much larger than the motor gets, at least for AC systems.

Why? Or just don't worry about it... that's not going to happen.

 

[brian_]

Is there any particular concern with setting up the batteries to produce high-voltage DC, something north of 300V? I have a feeling battery cells are more sensitive to high-voltages rather than high-current, but limiting voltage at 60kW can lead to some very thick bus bars!

Each cell doesn't care about the overall pack voltage, only the voltage difference between its terminals (and between the cell case and anything that case is touching).

Yes, low voltage means undesirably high current, and that's why the most common nominal operating voltage for modern EVs (and plug-in hybrids) is 360 volts (with maximum charging voltage around 400 volts)... and double that is now appearing.

 

[TangentialTorque]

You clearly have a bunch of reading and catching up to do on this site.People here regularly assemble cells and modules in the 400VDC nominal range.

Also, watching somebody build a "supercapacitor" on Youtube using a microscope slide is a joke. "All you gotta do is..."

"They are not too terribly difficult to manufacture, given access to the right supplies and a safe and solid understanding of chemistry." Neither is a nuclear reactor.

We try to look at pragmatic stuff here.

If the supercaps are, indeed, "not too terribly difficult to manufacture", stop f*cking with a beater van and go set up a factory to make the caps for everybody who has no clue how to make them cheaply or to store high amounts of energy in a given volume needed for mobility applications.

There are some supercap buses in operation, but you have to throw bags of money at them and their charging stations are not well grounded in today's Lithium battery reality.

Woah man calm down. There's a very obvious reason you can't buy ultracapacitors, and its safety. Caps with more stored energy than a stick of dynamite are not something people should be able to buy without very specific use cases. I don't want to power the van purely off caps, because I'm not that stupid. Caps are great at smoothing high current out. At the end of the day, however, multifarad capacitors are phenomenally dangerous, and I don't want to store enough energy to move a 4000lbs vehicle 50 miles in a storage device that can dump 20kWh of energy in less than a millisecond.

Stop trying to gatekeep its embarrassing, and more than a little shameful. Most of the difficulty in making extremely high capacity banks is procuring gallons of electrolyte. Most of the electrolytes that function well are also used by unscrupulous types to make much more dangerous things, which is not great. There are no comprehensive "diy" guides on how to make capacitor banks of this size because no one is going to tell you how to procure a gallon of concentrated nitric or sulfuric acid.

The reason I'm "f*cking around with a beater van" is because I am extremely poor, which is often what happens when you have to purchase education. And don't knock nuclear reactors, they're a lot simpler than you give them credit for. It's literally just a balancing game between multi-state moderators like water, single state carbonaceous moderators like graphite, and large stable nuclei control rods. The real difficulty is always in managing relative reaction rates and ensuring the removal of neutron poisons like xenon which can destabilize some types of reactors.

Once again, the caps are suggested for storing current generated during regen braking as the current levels can be high enough to destroy a lot of motor controllers, as seen in a chevy express (note: a larger van with the same engine) converted on this site. If a cheaper controller can be used in conjunction with a "small" capacitor bank to reasonably store charge, the overall cost can be decreased, which is kind of the point. :/

 

[TangentialTorque]

Each cell doesn't care about the overall pack voltage, only the voltage difference between its terminals (and between the cell case and anything that case is touching).

Yes, low voltage means undesirably high current, and that's why the most common nominal operating voltage for modern EVs (and plug-in hybrids) is 360 volts (with maximum charging voltage around 400 volts)... and double that is now appearing.

I've just been very paranoid about Lithium cells for a long time lol, I tend to baby lithium cells in projects I utilize them in, but I haven't really played around with battery packs with higher voltage than 60 or 70V. It's good to know that I can more completely utilize the LiPO4 cells for their current capacity as well! Given a lot of what I've seen from other heavy EV conversions, a lot of the problems people have is cooking their controllers during breaking, which is partially why I am considering capacitors. AC caps are actually very versatile, and can perhaps smooth that out a little bit, allowing the use of controllers than can't handle 70kW of regen braking from such a heavy vehicle.
Honestly I don't know if there is a significant price difference between the controllers I've seen used for chevy vans, but most of those conversions were done a decade ago so much of the info is less useful than I'd like.
Thank you so much for the help by the by

 

[TangentialTorque]

If high power and high speed is not a concern, the most cost-effective EV solution at the moment is a Nissan Leaf motor/inverter. Thunderstruck-ev sells a (more or less) plug and play kit I believe.

I was considering something similar with the 60kW prius system, but my main concern is how the regen braking for smaller vehicles would work in an Astrovan, but as far as I can tell, both the nissan leaf and the astrovan have a curb weight of ~4,000lbs! So I guess it would probably work pretty well! Thank you gallons man.

 

[remy_martian]

Each cell doesn't care about the overall pack voltage, only the voltage difference between its terminals (and between the cell case and anything that case is touching).

As long as the cell/module does not fail open circuit, that's true.