DIY Electric Car Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter · #1 ·
I am starting on a ev conversation next month on a 78 mgb without the engine and transmission it weighs in at 1540 lbs
I am wanting to do a direct drive configuration if possible with a top speed of 85mph preferably 95mph since that’s just keeping up with traffic around here and a range of 270 miles I just had a few questions about hardware

AC or DC if DC I was going to build my own controller

what torque and would be required

what BMS would you recommend for a Tesla style battery pack

and I know I’m not gonna get the range I’m looking for but temporarily until I can afford it could I use golf cart batteries to power it to get around 80 miles of range
 

·
Registered
Joined
·
105 Posts
This guy might be able to help with parts, not an mgb but a sprite so similar size.


How do you plan to get such a big range in such a small car?

If you're going direct drive then definitely AC.

Also take into account a lot of modern cars have larger wheels so you won't be able to match their top speed with standard wheels (unless you go back to the idea of a gearbox)
I reckon my Mini will top out at 67mph compared to my donor i3 top speed of 93mph if I keep the same max rpm.

Sent from my moto g(8) power lite using Tapatalk
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #3 ·
This guy might be able to help with parts, not an mgb but a sprite so similar size.


How do you plan to get such a big range in such a small car?

If you're going direct drive then definitely AC.

Also take into account a lot of modern cars have larger wheels so you won't be able to match their top speed with standard wheels (unless you go back to the idea of a gearbox)
I reckon my Mini will top out at 67mph compared to my donor i3 top speed of 93mph if I keep the same max rpm.

Sent from my moto g(8) power lite using Tapatalk
I was going to cut out all the old rusted floor pans and
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #4 ·
I was going to cut out all the old rusted floor pans and
I was going to cut out the old rusted floor pans and make new custom ones with them raised up about 2 inches into the cab and the bottom edge lowered 2 inches so I will have room to pack in the required 4,224 18650 cells to get a 43kw battery pack that will weigh in at 500lbs and I was going to use the Area behind the passenger and driver seat that’s raised up to store the inverters speed controller’s, chargers and BMS and vent that compartment out the back near where the gas tank was or into the trunk I may have to make a simple constant mesh gearbox with a high and low range to get those highway speeds the idea was to extend the drive shaft all the way to the engine bay and have all the engine components there
 

·
Registered
Joined
·
105 Posts
Wow, that is a very exciting plan, can't wait to see how it all fits together. Are you US based?

Sent from my moto g(8) power lite using Tapatalk
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #6 ·
Wow, that is a very exciting plan, can't wait to see how it all fits together. Are you US based?

Sent from my moto g(8) power lite using Tapatalk
Yes I am in Texas which would explain the need for 300 miles of range my daily commute is 115 miles one way so 230 miles round trip and the nearest town with a supermarket is 70 miles away this is going to be a multi year project I am going to be doing a full restoration on the body as well and a Crome bumper conversion with the honeycomb grill
 

·
Registered
Joined
·
105 Posts
It also makes it a damn sight easier to do the major structural changes you are talking about, you'd have to have loads of testing in the UK to get it road legal.
Had you thought about rear mounting the motor then the tunnel can be used for more batteries?

Sent from my moto g(8) power lite using Tapatalk
 

·
Registered
Joined
·
6,191 Posts
I am starting on a ev conversation next month on a 78 mgb without the engine and transmission it weighs in at 1540 lbs
I am wanting to do a direct drive configuration if possible with a top speed of 85mph preferably 95mph since that’s just keeping up with traffic around here and a range of 270 miles I just had a few questions about hardware

...

what torque and would be required...
The requirement for torque depends on your requirement for performance, and assumes some specific gearing and tire size. The gearing in this case is presumably the stock final drive (3.909:1) and the tire size is presumably stock (165R14, or about 24.5" overall or 861 revolutions per mile). You can think of that in terms of actual performance (rate of acceleration), or by comparison with the original car.

The car will be heavier than it was originally. You have it at 1540 lbs without powertrain and Automobile-Catalog has the curb weight (complete, with fuel) at 2339 pounds. It's hard to see even the MG boat anchor of and engine and iron-case transmission weighing 800 pounds, but maybe assume that the converted vehicle will weigh about the same 2340 lb (1062 kg).

The stock 1978 MGB (manual 4-speed transmission version for North America) had an engine which could produce (according to Automobile-Catalog power and torque curves) more than 75 b-ft of torque over the entire engine speed range normally used in driving (1800 to 4500 RPM), and 63 HP (47 kW) as long as you shift to keep in it a suitable engine speed range for performance (4000 to 6000 RPM). That went through a transmission, so the torque was multiplied:
  • 1st gear:
    • 3.036:1, so 75 lb-ft is multiplied to 228 lb-ft
    • 1800 to 4500 RPM engine speed corresponds to 11 to 28 MPH
    • driveshaft speed for this engine speed is 593 to 1482 RPM
  • 2nd gear:
    • 2.167:1, so 75 lb-ft is multiplied to 163 lb-ft
    • 1800 to 4500 RPM engine speed corresponds to 15 to 39 MPH
    • driveshaft speed for this engine speed is 831 to 2077 RPM
  • 3rd gear:
    • 1.382:1, so 75 lb-ft is multiplied to 104 lb-ft
    • 1800 to 4500 RPM engine speed corresponds to 24 to 61 MPH
    • driveshaft speed for this engine speed is 1302 to 3256 RPM
  • 4th gear:
    • 1:1, so 75 lb-ft is unchanged
    • 1800 to 4500 RPM engine speed corresponds to 34 to 85 MPH
    • driveshaft speed is the same as engine speed (1800 to 4500 RPM)
So you can pick your road speed range and see how much motor torque you need (without any additional gearbox) to feed to the axle to get close (because the engine does up to 88 lb-ft) to matching the original car's performance at moderate engine speed... and the engine is stronger at higher engine speed.

Unfortunately, DC motor suppliers generally don't provide any performance specs in the range of speeds that you actually need... only from their maximum torque point and faster. You can optimistically assume that they can maintain that peak torque down to zero speed, perhaps without overheating.

With stock tire size and final drive ratio (3.909:1) 95 MPH corresponds to 5053 RPM.
 

·
Registered
Joined
·
6,191 Posts
Had you thought about rear mounting the motor then the tunnel can be used for more batteries?
Hopefully the motor can be mounted in the transmission tunnel, leaving the engine space free for battery.

Placing the motor at the rear axle wouldn't work with the stock suspension, which is a live beam axle. Of course the entire rear suspension could be replaced with an independent setup to accomodate a motor attached to a final drive, or more simply a complete EV drive unit (motor and transaxle), but at some point this isn't an MGB conversion but rather an MGB body on a custom chassis.

The transmission tunnel isn't a very useful space for battery modules, due to the size and shape. The driveshaft tunnel from transmission to rear axle is tiny.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #10 ·
It also makes it a damn sight easier to do the major structural changes you are talking about, you'd have to have loads of testing in the UK to get it road legal.
Had you thought about rear mounting the motor then the tunnel can be used for more batteries?

Sent from my moto g(8) power lite using Tapatalk
Yah here a inspection consists of honk your horn, turn on your headlights, “ok, you are good to go”. I just got a 350sdl Inspected that past it with no E brake, no rear brake pads, left cracked front rotors, no workin turn signals, brake lights, bad ball joints, balled tires all around but that’s Texas for you. I had thought about putting the motor in the transmission tunnel but it’s pretty tight and I was worried about ventilation. FYI yes I fixed all those things on the 350 before driving now it just has a blown head gasket :(
 

·
Registered
Joined
·
6,191 Posts
I had thought about putting the motor in the transmission tunnel but it’s pretty tight and I was worried about ventilation.
If the motor is liquid-cooled, that's not an issue. People using old air-cooled brushed DC motors often fit a shroud to it and blow in cooling air from a fan, even with the motor mounted in the open space of the engine compartment.
 

·
Administrator
Joined
·
6,293 Posts
I am starting on a ev conversation next month on a 78 mgb without the engine and transmission it weighs in at 1540 lbs
I am wanting to do a direct drive configuration if possible with a top speed of 85mph preferably 95mph since that’s just keeping up with traffic around here and a range of 270 miles I just had a few questions about hardware

AC or DC if DC I was going to build my own controller

what torque and would be required

what BMS would you recommend for a Tesla style battery pack

and I know I’m not gonna get the range I’m looking for but temporarily until I can afford it could I use golf cart batteries to power it to get around 80 miles of range
If you need 270 miles that is a big stretch - you will need to redesign the car around the batteries to get that range
I would be looking at a Leaf power unit in the rear and increasing the size of the transmission tunnel for batteries - as well as the engine bay and the boot
You will want to get a complete Tesla battery in there somehow

Golf cart batteries will be lucky to get you 20 miles range!! - Lead is dead and in its heyday cars with lead actually went about a quarter the claimed range!
 

·
Registered
Joined
·
6,191 Posts
I was going to cut out the old rusted floor pans and make new custom ones with them raised up about 2 inches into the cab and the bottom edge lowered 2 inches so I will have room to pack in the required 4,224 18650 cells to get a 43kw battery pack that will weigh in at 500lbs and I was going to use the Area behind the passenger and driver seat that’s raised up to store the inverters speed controller’s, chargers and BMS and vent that compartment out the back near where the gas tank was or into the trunk I may have to make a simple constant mesh gearbox with a high and low range to get those highway speeds the idea was to extend the drive shaft all the way to the engine bay and have all the engine components there
So, basically the old-style (not Model 3) Tesla modules under the floor, a driveshaft completely above the floor, and an MGB that looks like it has a lift kit?

If you're going to do all that, why not just put a salvaged EV drive unit in the back, changing the whole structure there, too? I don't see the point in doing an MGB-bodied custom-chassis car, but if one is going to be built then ending up with a leaf-spring beam axle rear suspension doesn't seem desirable.
 

·
Registered
Joined
·
55 Posts
Wow, for that range you'll need A lot of battery .. MGBattery vs MGBee :LOL:
 

·
Registered
Joined
·
598 Posts
270mi of range you're looking at ~800lb of battery and about $20k, unless you can stand to lose more weight and space and use 3-4 Leaf packs...One 24kWh Leaf pack will get you 80mi, and the best way to get one is to buy a whole 2014+ Leaf.

Some motor/gearbox options for ya:

 
1 - 15 of 15 Posts
Top