Pre-Charge
Battery Components
High Voltage/Power resistors to Pre- Charge any Capasitive load from 50,000uF to 1F!
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Why Pre-Charge Resistors
• Safeguards the BMS from Tripping or Damage: A Lithium Battery Management System (BMS) is designed to shut down at the first sign of a sudden current spike, treating it like a short circuit to protect itself. In severe cases, this spike can wreak havoc, frying the internal MOSFETs or other vital components of the BMS.
• Prevents Arc Damage and "Welded" Contacts: When you engage a high-voltage switch or relay, the initial rush of current can create a fierce electrical arc (spark). This arc can erode or pit the contacts, potentially causing them to weld together. In an emergency, this could make it impossible to safely disconnect the battery.
• Prolongs Capacitor Lifespan: Inverters and motor controllers are equipped with large filter capacitors that function like "empty buckets" waiting to be filled with energy. If they are charged too rapidly at the battery's full power, it can lead to excessive thermal stress and physical strain, drastically shortening their lifespan.
• Prevents Blown Fuses: That massive initial surge of energy can easily surpass the ratings of main system fuses, resulting in frustrating and costly "nuisance trips" every time you try to power up the system.
How the Process Works
1. Stage 1 (Pre-charge): We kick things off with a small, high-resistance path known as the pre-charge resistor. This clever component lets current gently "trickle" into the capacitors, slowly raising their voltage until it approaches the battery's—typically reaching a comfortable 90–95%.
2. Stage 2 (Bypass): As soon as the voltages are nearly aligned, the main Relay springs into action, sealing the deal with a full, low-resistance pathway for seamless operation. With the voltage difference now minimal, we avoid any dramatic sparks or current surges, ensuring a smooth transition.
2. Stage 2 (Bypass): As soon as the voltages are nearly aligned, the main Relay springs into action, sealing the deal with a full, low-resistance pathway for seamless operation. With the voltage difference now minimal, we avoid any dramatic sparks or current surges, ensuring a smooth transition.
Why use the big Pre-Charge resistors
For 12V or 48V packs, you can use a 20 Ohm 100W resistor. The current is 2.4 Ohms and the power is 115W for a very short time. Most of these resistors can handle 3-4 times that power, meaning 300-400 Watts.
However, with a 600V pack, things change a lot. With a 600V and a 20 Ohm resistor, the current is 30A and the power is 18000W !!
So, we will increase the resistance to 150 Ohm, giving a current of 4 Amps, but that still means 2400 Watts for a very short time.
However, with a 600V pack, things change a lot. With a 600V and a 20 Ohm resistor, the current is 30A and the power is 18000W !!
So, we will increase the resistance to 150 Ohm, giving a current of 4 Amps, but that still means 2400 Watts for a very short time.
There are however a lot of other calculations to be made to match the correct resistor to the Capacitance:
- Voltage 24 V to 1500 V
- Resistance 20-250 Ohm+
- Load Capacitor size. 30 000 uF to 1 F
- Power 1 Watt o 30 KW
- Pre-Charge time 0.5 Sec to 10 sec
- Dissipated energy 100 J to 100 MJ
Just mail the support team and they will be happy to assist
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High Voltage/Power resistors to Pre- Charge any Capasitive load from 50,000uF to 1F!
