1969 Mercedes Benz /8
I’ve been looking to start a new project, and I found this beauty on Craigslist. At $500, I had to at least check it out. I went with my brother and found that it was 99.9% complete. We towed it back with the Jeep, and I got started on some troubleshooting.
It wouldn’t fire, but it turned over and sputtered. After taking off the valve cover, I found that the camshaft had seized. The engine was toast. So much for having some fun before the conversion…
This conversion is going to be AC rather than DC like the MG. I will be reusing a lot of components to make a bastard of the Mercedes, but you won’t be able to tell until you look under the hood.
The Motor and Inverter
I’m using a motor out of a Nissan Leaf for this build. It has nearly twice the continuous rating of the K11 in the MG, 80kW vs 45kW. This motor has no brushes, and it could very well outlast the car around it.
I am reusing the power stage of the OEM inverter, but I have replaced the control board with another one from Paul: Nissan Leaf Inverter Control Board. I currently have the motor running with a Prius throttle pedal and some batteries from an I-Miev. Speaking of which…
This battery pack is nearly twice as large as the one in the MG, which is reasonable for a car that is significantly heavier. At the same time, I’ll be aiming for a more comfortable and practical daily driver. No blistering burnouts for the Benz, unfortunately. Between the larger battery , regenerative breaking, and some efficiency improvements I should see significantly improved range. The battery is comprised of 88 LEV50 cells. These have a nominal voltage of 3.6v and a capacity of 50ah. The pack had eleven sets of eight and two sets or four.
Again, I got these used off of eBay, and I spent an afternoon tearing it apart and testing everything. They all tested good, and I used them to test drive the Leaf motor.
Another excellent thing about these batteries is that they include balancing boards. They are BMS slaves that will take over the critical role of keeping my batteries healthy.
Where I had to spend some significant dough to get that system in the MG, I will simply reuse these boards in the Mercedes as is with the help of a BMS master controller from Tom de Bree of DIY Electric Car Forums.
Gearbox and Adapters
For this build I will be using a transmission, though not the stock one from the Mercedes. I had an extra one that we removed from the ’66 Mustang a while back when upgrading to a T5, and it will serve perfectly in this vehicle. It’s an old school 3 speed from the same time period as the Mercedes. I will leave it in second gear to get a final drive ratio of 6.825:1. I’d like a little closer to 7 or 8:1, but this will be fine. An adapter plate will bolt to the front of the motor, which will then bolt to another adapter plate on the transmission. I have created some CAD drawings for the shaft coupler and adapter plate that I will upload later.
I have settled on a 3.3kW Lear charger from a Chevy Volt. Tom’s added that functionality to his board for me using the information already out there about the CAN protocol that it uses. It’s liquid cooled, so I’ll add it to the cooling loop for the Nissan Leaf motor and Inverter. It’s more powerful than the charger in the MG, so I’ll still charge the larger battery pack in a similar time on my recently installed level 2 charger.