PRECHARGE

Pre charge ensures that the intermediate circuit is pre-charged to at least 95% of the actual TS accumulator voltage before closing the second AIR (Accumulator Isolation Relay). If the pre charge is not present, the capacitor present inside the motor controller will receive maximum voltage (80V in our case) at time t=0 resulting in high inrush current. Nearly all of the accumulator voltage will be across the closing contacts. If a pre charge resistor is not used, this could damage the motor controller as large amount of current will flow through it. Therefore, a pre charge circuit is used to allow slow charging of capacitor before the relay contacts are closed.

Supplies

LM358 (Op-Amp)

LM331 (Voltage to Frequency Convertors)

LM7805 (Voltage Regulator)

PC817 (Optocoupler)

Precision Resistors (6.8k, 12k and 100k)

Resistors (47, 560, 10k, 100k)

Capacitors (0.01uF, 1uf)

2N7000 (MOSFET)

SPDT

Arduino Nano

Supply 12V

Step 1: Parts of Circuit

The circuit can be divided into two parts, high voltage side and a low voltage side. At HV side, two inputs are taken, one at the motor controller and one across the terminals of the accumulator. The inputs are given to unity gain operational amplifiers and the outputs of the two op-amps are converted into frequency signals using LM331, a voltage to frequency convertor. An optocoupler is used to send signals to the Low voltage side while maintaining isolation. These two signals are then compared on the LV side using an Arduino Nano. When the capacitor is charged to 95% of the accumulator voltage, it will short the contacts of AIR 1 and pre charge relay will be opened. If the voltage across the capacitor is less than 95% of the accumulator voltage, AIR 1 will remain open.

Step 2: Reference

EV5.7.1 A circuit that ensures that the intermediate circuit is pre-charged to at least 95% of the actual TS accumulator voltage before closing the second AIR must be implemented. Therefore the intermediate circuit voltage must be measured. EV5.7.2 The pre-charge circuit must use a mechanical, normally open type relay. All pre-charge current must pass through this relay

Step 3: Ordering the PCBs

Now we have got the PCB design and it’s time to order the PCB’s. For that, you just have to go to JLCPCB.com, and click on the “QUOTE NOW” button. JLCPCB has sponsored this project. JLCPCB (ShenzhenJLC Electronics Co., Ltd.), is the largest PCB prototype enterprise in China and a high-tech manufacturer specializing in quick PCB prototype and small-batch PCB production. You can order a minimum of 5 PCBs for just $2.

To get the PCB manufactured, upload the Gerber file you downloaded in the last step. Upload the zip file or you can also drag and drop the Gerber files.

After uploading the zip file, you’ll see a success message at the bottom if the file is successfully uploaded. You can review the PCB in the Gerber viewer to make sure everything is good. You can view both the top and bottom of the PCB.

After making sure our PCB looks good, we can now place the order at a reasonable price. You can order 5 PCBs for just $2 but if it’s your first order then you can get 10 PCBs for $2. To place the order, click on the “SAVE TO CART” button.

My PCBs took 2 days to get manufactured and arrived within a week using the DHL delivery option. PCBs were well packed and the quality was really good.