10hp mechanically works out to 7,455 watts at 100% efficiency.
If we assume the brushless generator is 85% efficient at generating electricity, this is 6,337 watts.
At the time being the average system voltage will be (12.5/battery) * 9 batteries = 112.5v DC
So 6,337 watts / 112.5 volts = 56 amps
Finally! This part of the build seemed to drag on f-o-r-e-v-e-r.
As can be seen in the above picture the generator frame is welded to the rear structure of the car. These welds were a bit tricky because the added steel was considerably thicker than the vehicle’s frame, making good penetration in one without “blowing through” the other difficult. I revised the plans to include the redundant angle section parallel to the frame in order to increase the surface area available for these critical welds.
Next step is to route the generator’s exhaust out the original location, run the necessary wiring to the front of the car to carry the ~8,000 watts of generated electricity to the motor. I look forward to my first extended electric drive, as well as a chance to really get a feel for the car’s highway capabilities.
Generator construction is under way. The 10hp air cooled diesel and the 10,000 watt generator head will be mounted in line with a lovejoy coupler. The coupler is a 3 piece design which includes a rubber insert to allow for a slight angular misalignment. I expect vibration to be an issue so all mounting points will include a rubber vibration damper. The frame is 3/16″ 2″ mild steel as used for the battery supports. I expect to have the generator module completed later today so that work can begin on mounting it in the car.
2 8″ sections of 3/16th 2″ mild steel angle were welded to the left motor support. These are many times stronger than necessary for the task of supporting the battery and are largely intended to further brace against the torque of the motor. The entire battery support frame / motor mount was coated with 3 coats of POR-15 rust protective paint. The motor mount support tubes were capped with epoxy before being coated with por-15 to seal them from interior rust.
So now I need to fab up a hold down for the 13th battery, jumper it in and re-locate the most-positive point. I am also in the process of re-wiring everything so that it will pass inspection in a few days. New wires must be run for the blinkers, brake lights and horn.
This chart demonstrates the reduction is usable energy from high amperage discharge. At the highest reported discharge current (570A) the cells deliver just 19Ah over the course of 2 minutes. I am more concerned with the 1hr and 30min specs, as these correlate with the amount of current usable for my commute with and without the ability to charge at my destination.
By plugging all the values appropriate for the 240z into this handy calculator I get a pretty good estimate for the current draw at different speeds for various incline and wind situations. It happens that the 30min draw of 96A works out to be about 70mph on flat ground, while a draw of 53A is 55mph. I also see that I can travel 30mph for 5 hours, or 90mph for just 12 minutes.
The Bussman 400A fuse just wasn’t up to the huge amp draws possible under hard acceleration so it had to be replaced. This is by far the biggest fuse I’ve ever seen.
Protective boots for the battery terminals will provide protection against a catastrophic event such as a piece of metal being dropped into the battery bay. 3,500 Amps of short circuit current is not something to play with.
A 13th battery was purchased today. This bring the voltage up to 156 volts from 144, and the total pack capacity up to 11,700 watt hours from 10,800. This is a 8.3% increase in available energy. I expect to see slightly more than an 8.3% increase in range however. This is because of something known as Peukert’s effect, which basically states that the more quickly you draw energy from an electrochemical cell the less total energy can be extracted ultimately. This holds true conversely; the more slowly you discharge your batteries the more total electricity they will provide. Say I’m traveling down the road at 50mph and consuming 100 amps at 100 motor volts.
Volts * Amps = Watts
100V * 100A = 10,000W
In this case the vehicle is consuming 10,000 Watts of energy. The batteries are not being discharged at 100A as you might expect, as the motor controller acts as a “power converter”. If we have a 144V pack voltage the amp draw from the batteries can be calculated thusly:
Motor Watts / Battery Volts = Battery Amps
10,000W / 144V = 69.4A
So 100A at 100V to the motor consumes about 69 Amps at 144V from the battery string. But now if we increase the battery voltage to 156V by adding an additional battery.
10,000W / 156V = 64.1A
The motor is drawing the same amount of power from the batteries, but because the pack voltage has increased the current required decreases.
I have begun work on the electrical subsystems. The 12v will be handled by a Iota 55Amp 96 - 190vdc DC/DC converter, along with a small auxiliary battery to power the initial contactor activation to switch the traction circuit on.
I’ve also begun etching the new battery rack/motor mount for coating with POR-15. I am also creating a new front wiring harness. I upgraded the original setup which routed the headlight power through the physical switch in the steering wheel, with a pair of relays switching straight to the 12v system’s battery. This should bring the voltage at the bulbs from the ~11.5 volts it was previously up to 13.6 volts from the dc/dc. I’ve heard this makes a significant difference with the dim old headlights of this 38 year old vehicle, as well as removing the biggest strain on the aging wiring. All front headlight and side marker connectors were replaced with OEM grade dual gasketed weather pak connectors.
I’m also etching the front and rear battery rack components. Also shown here is the contactor brackets made from 1/8″ steel flat stock.
I also fabricated a proper foot controlled throttle using a 25k potentiometer. This worked out so that the ~70* of mechanical throw from the original throttle setup became a steady linear range of 0 ohms through 5k ohms. A spring provides positive return and a very nice amount of pedal resistance.
I set up forced air cooling for the kostov motor. An automotive blower provides several hundred CFM of airflow through the motor. It was oriented as to swirl through the brushes before exiting the motor. Testing shows that even after several minutes of acceleration with many huge amp draws through the motor (600+ amps)the exhaust air was only warm, and the case barely warm to the touch. The blower draws approximently 10 Amps free air and 6 Amps when installed blowing through the motor.
The cooling setup is not finished. I must still create an end shroud for the motor to force more air to pass through the body of the motor.
Pretty cool considering I’m driving with one hand. At this point the throttle mounted to the gas pedal isn’t completed so I have a 5k pot held in my hand for control.
This car is absolutely the fastest, most fun vehicle I’ve ever driven. 1000 Amps spins the tires with ease at anything over 1/2 throttle in first, and with similar ease in second at lower speeds. I have not yet had it at higher speeds so I cannot comment on this aspect of the performance yet. 10+ Minutes of constant acceleration only managed to consume 20% of the pack’s available capacity.
