Shunt resistor right application?

In summary, there is a 400A (125VDC) charger connected to a battery bank and several DC panels. The panels are fed from the high side of a 600A breaker, causing a potential problem when the battery is taken offline for a load test and then reconnected. To prevent a current surge from the charger to the unenergized battery bank, a properly sized current limiting resistor between the disconnect switch and panels can be used. This resistor should be shorted once the surge has passed to remove it from the circuit. An inductor was also considered, but it would not work as the battery would be too slow to respond, resulting in a longer surge.
  • #1
whodatnation
1
0
I have a 400A (125VDC) charger that feeds a battery bank and a few DC panels (critical). This poor design has the panels being fed from the high side of a 600A breaker that is between the charger and battery bank. I need to take the battery off line for a load test but the problem I'm going to have is when I reconnect the battery to the charger I will have a current surge coming from the 400A charger to the unenergized battery bank (approx. 350A). This will most probably cause a voltage drop in the DC panels which I CANNOT have (critical loads on panels). Will a proplerly sized shunt resistor between the disconnect switch and panels work for this situation?
 
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  • #2
Yes. I would not call it a shunt, I would call it a current limiting resistor. It needs to be sized for the ##I^2R## loss. Then it should be shorted once the surge has passed to remove it from the circuit.

I was thinking about an inductor for surge limiting, but no that would not work because the battery would be too slow to respond, making the surge last for seconds.
 

1. What is a shunt resistor and what is its purpose?

A shunt resistor is a type of electrical resistor that is used to measure electrical current by creating a small voltage drop that is proportional to the current flow. Its purpose is to accurately measure and monitor large currents without causing significant resistance to the circuit.

2. How do I select the right shunt resistor for my application?

The right shunt resistor for your application depends on the current range you need to measure, the accuracy required, and the power dissipation capabilities of your circuit. You should also consider the type of resistor (metal film or wirewound) and the material (copper or manganin) when selecting a shunt resistor.

3. Can I use a shunt resistor for both AC and DC applications?

Yes, shunt resistors can be used for both AC and DC applications. However, the type and design of the resistor may differ depending on the type of current being measured. For example, wirewound resistors are better suited for high frequency AC applications while metal film resistors are better for low frequency AC applications.

4. How do I calculate the accuracy of a shunt resistor?

The accuracy of a shunt resistor is typically expressed as a percentage of the full-scale current range. To calculate the accuracy, you need to know the resistance value, the current range, and the tolerance of the resistor. You can then use the formula: (tolerance/resistance) x 100 = accuracy.

5. What are the potential problems with using a shunt resistor?

One potential problem with using a shunt resistor is the generation of heat due to power dissipation. This can affect the accuracy of the measurement and may require additional cooling measures. Another issue is the introduction of voltage drops and measurement errors if the shunt resistor is not properly connected or has a high resistance. It is important to carefully select and install the shunt resistor to avoid these problems.

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