One of the often things overlooked in an electric car conversion are the accessories. Sometimes these are called creature comforts since they include air conditioning, cabin heater, power steering, and brake assist. Most people would think you’re crazy to go without these features nowadays, but it is an option for you to have in your EV conversion.
All of these previously mentioned accessories are driven off the engine using the serpentine belt. The exception is the brake assist which uses the vacuum that occurs with the internal combustion to provide assistance with the brake booster. If you have ever tried to hit the brakes a few times with the engine off you will notice that it gets harder to press the brake pedal down, which is due to the vacuum being equalized with atmospheric pressure.
The accessories running from the engine are all designed for the 12-volt system. The interior cabin controls for the radio, and even the lights, would fall under the accessories as they also use the 12V circuit. This component is called a voltage step down converter, or buck converter, to provide adequate 12V power for an inexpensive cost.
Even though with internal combustion engine has a 12V starter battery, this is only intended to start the engine, and the alternator generates the electricity for the accessory system. The alternator is really powering the engine as the primary focus and the accessories are secondary.
When you’re talking about removing the alternator and the engine for an EV conversion, there needs to be something put in its place to retain functionality. With an electric vehicle there is a large battery pack with a higher system voltage than the original 12V. This is to reduce the size of the cable used as there is a relation between voltage and current to get to the total power required to propel the vehicle. If the battery pack voltage was 12V then the current would have to be much higher to handle the load on the electrical cables. With a higher current the electrical cable size needs to be increased to be under the cable rated thermal capacity.
No matter which battery pack system voltage is selected, whether it is 72V, 96V, 144V or any other, this voltage needs to be stepped down to the original 12V system voltage.
You might be thinking that you can just create a connection to one of the batteries that have 12V to dedicate to the accessories. The issue with this solution is that the battery units that make up the battery pack are out of sync. It might not be noticeable at first but as time goes on, and there is a higher use of the accessory battery in either summer or winter, it will become more noticeable.
There are actually two components that do the same function, the linear voltage regulator and the buck converter. The linear voltage regulator is very cheap but it is inefficient. How inefficient? Well the regulator generates a lot of excess heat to help with the voltage drop. This is a big issue if you want to use the 12V on a continuous usage. Since there is a temperature limit to the voltage regulator, it will shut down until it is back into a safe temperature range.
On the other side, there is the buck converter which is also known as the voltage step down converter. This uses a small circuit board to drop the voltage down in an efficient manner. The temperature generated from the voltage change is consistent and manageable.
Here is a buck converter that I like from Amazon which has an input range between 72V and 144V with the output at 12V. It really isn’t that expensive of a component but it is quite useful. One thing to note is that the buck converter board does not come with an enclosure. I recommend this IP65 enclosure that the buck converter fits into for protection.
When you use a buck converter that is connected to the entire battery pack, it allows the 12V accessory system to have the benefits of a large capacity battery. This way the lower voltage 12-volt automotive system has the ability to provide power for all of the creature comfort components as you need them. This will draw the power from all the batteries at the same time along with the driving of the electric car. Mind you the power used by the accessory system will be much lower than the electric motor or motors.
Now that you have a supply of 12 volt DC to power the accessories, you need to use different components. The air conditioning, heater, and power steering need to be replaced since they were driven from the internal combustion engine. These will now need to be powered using the 12V power supply.
The power assist brakes, or brake booster, operates with the assistance of a vacuum to help apply the brakes by adding more force so the driver doesn’t have to. One of the outcomes of the combustions in the internal combustion engine is the generation of a vacuum. This was discovered as a side effect that wasn’t being used, so it was added to every vehicle with an engine as it does not draw any extra power from the engine to operate.
Now with the EV conversion, a separate vacuum pump runs on 12 volt DC power supply. Here is a Electric Vacuum Pump Kit that includes everything you would need to set up the power assist brakes.
It might not seem immediately obvious at first, having the accessories running off the main electric motor, but you would lose essential functions when the electric car comes to a stop. This would leave you without power steering, brake assist, and to a less functional component like the air conditioning or heater. If you have ever experienced either power steering or brake assist failures, you would know how big of a difference they make. It instantly shoots you back 50 years with turning becoming a struggle for most adults. It’s best to avoid this type of situation.