[ArabiGaming]

So im planning to convert a car to electric

I want to get 150 - 200 miles of range

Im looking into getting chevy volt batteries and getting an orion bms 2 with it and using a chademo charging port

I live in northern virginia so if i get an average of 250wh/mile using the Warp 9 dc motor ill need 50kwh of batteries of battery to get 200 miles. That would be like 400 cells.

So do i use a slave board for each battery module since the bms is yet to be hacked for the volt or am i better off using tesla batteries

Id like to hear your opinions on the best route to take with this conversion

 

[brian_]

First, I think 250 Wh/mile (156 Wh/km) is quite optimistic, unless you are driving slowly, and especially with a brushed DC motor and no regeneration. That's comparable to the urban energy consumption of the lower-consumption production EVs available; highway is higher than that for all of them, and they're using the most efficient motor and controller technology available... plus regenerating on stops and descents.

I understand the appeal of the Volt modules, but they're intended for a plug-in hybrid (so not a lot of capacity) running 360 volts. To pile up 50 kWh worth, you're talking about more than three complete Volt packs worth of modules, presumably configured for less than half the usual voltage, so that's something like six sets of modules in parallel. This seems like it would be a lot easier with larger cells, using modules from a battery-electric vehicle rather than a plug-in hybrid. Lots of people use Volt modules in their DIY conversions, but not usually for long range.

A first-generation Volt has 288 cells (in a 96S 3P configuration); a second-generation Volt has 192 cells (in a 96S 2P configuration). So those cells are different sizes (the second are more than 50% larger capacity). Which cells are you thinking you need 400 of? Even 400 of the larger cells wouldn't likely be enough... so were you thinking of four complete Volt packs, thinking that they have only 96 cells each?

 

[ArabiGaming]

Yeah the more i think about it i find it more unrealistic
Do you think a nissan leaf motor can get me to 250wh/m or do you have any other recommendations
For the batteries im probably going to go with model s batteries

 

[MattsAwesomeStuff]

Do you think a nissan leaf motor can get me to 250wh/m or do you have any other recommendations

It's not so much the motor. It's the shape of the car.

The reason that it takes energy to move a vehicle is because of the tires squishing and the need to move air out of the way. It doesn't matter what is powering it, those numbers won't change.

Knowing that range is an issue on EVs, OEM EVs are engineered for a fairly optimum aerodynamic profile. And their battery packs and bodies are engineered around each other so that they're compact.

I think what Brian was saying was that, since your demands are for it to be as good as OEM EVs, you've got to be doing everything at least as good as OEM EVs can do it. So even if you could get a vehicle just as light (difficult with using Volt cells) and aerodynamic, you'd also have to have the motor be just as efficient. If you're starting off with even a slightly less efficient motor, now you have to be even lighter and more aerodynamic than the best that world-class engineering and manufacturing can produce, which isn't likely.

Motor choice is only going to make a few percent difference, but you've got a big challenge to match the physics to get it to the right ballpark.

 

[john61ct]

A pickup truck with the whole bed full of big prismatic batteries might not be so efficient, but will get you that range.

 

[swoozle]

To correct a couple of errors/misconceptions above (though it may not change the way you're going):

The Volt BMS has been completely cracked. It'll do voltage monitoring, temp monitoring and balancing but it has restrictions on the number of cells you have to plug into each slave.

Although the number of cells in a (for instance) 1st gen pack is 288, it's fairly impractical to break it down to that point. It's more standard to think of it as 12S and 6S modules totaling 96 "cells".

The other large differences between Tesla and Volt packs that weren't mentioned are cost and energy density. An equivalent kwh Volt pack is ~1/2 the cost but significantly heavier/bulkier than a Tesla S module.

 

[brian_]

Although the number of cells in a (for instance) 1st gen pack is 288, it's fairly impractical to break it down to that point. It's more standard to think of it as 12S and 6S modules totaling 96 "cells".

I agree that it is not very practical to reconfigure within the modules, but just don't call a group of three cells a "cell", because it's not.

It could be that ArabiGaming wanted to use four 96S strings (for 4 x 96 = almost 400) cell groups... but that's why I was asking what was intended.

 

[brian_]

Yeah the more i think about it i find it more unrealistic
Do you think a nissan leaf motor can get me to 250wh/m or do you have any other recommendations

The motor from a Leaf - or any other production EV - would do better, but only significantly better if you effectively use regenerative braking. Even then you're talking about matching the efficiency of a modern EV, and as Matt explained that's tough. Looking at the published energy consumption values for the various Tesla models, even the tire size makes a substantial difference.

For the batteries im probably going to go with model s batteries

Technically any series combination of multiple cells is a "battery", but in EV terminology "battery" is reserved for the vehicle's complete battery, and the smaller chunks of multiple cells in a package are called "modules". A Tesla Model S or X uses 14 or 16 (depending on model variant) modules. These discussions are much easier is common terminology is used.

So, you could use a Tesla battery (if your vehicle has the space and weight capacity to carry all of that), or just several Tesla modules. Tesla tends to claims higher energy and (especially) power ratings that other manufacturers for their EV batteries, but much of that is just Tesla's willingness to push them harder.

 

[brian_]

A pickup truck with the whole bed full of big prismatic batteries might not be so efficient, but will get you that range.

Yes, and if it's compact pickup it won't be able to carry much of anything other than those prismatic cells.

A CALB CA 180 LFP cell has a capacity of 180 Ah at nominally 3.2 V, for 576 Wh of energy capacity. 100 of those would provide 57.6 kWh... for 560 kg (1235 pounds), plus the support structure, housing, wiring, and BMS. Lots of DIY conversions have used CALB prismatic cells, but usually about of quarter of that capacity... because they are running low voltage by current standards (e.g. 120V) and not trying for such long range.

 

[john61ct]

> truck with the **whole bed full** of big prismatic batteries

yes I explicitly meant exactly that

 

[john61ct]

These discussions are much easier is common terminology is used.

Yes very much so,

I like

cell/group

for the 1S-voltage, lowest unit monitored by a BMS

To me "group" explicitly means parallel

String meaning connected in series, most packs / modules being a string of groups

but sometimes a string of cells, hence the usage

"with a BMS monitoring each cell/group in the string"



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