How to test a Dynamic Braking Resistor?

I have a vector drive faulting out. Manual says inspect and test the Braking Resistor. I have never done this procedure before.

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From Google searching I came up with:

1. remove resistor from circuit.

2. set fluke to ohms, put a probe on each end of the resistor

3. compare values of meter and resistor rating.
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Is that correct?

KingPresident said:

I have a vector drive faulting out. Manual says inspect and test the Braking Resistor. I have never done this procedure before.

===
From Google searching I came up with:

1. remove resistor from circuit.

2. set fluke to ohms, put a probe on each end of the resistor

3. compare values of meter and resistor rating.
===

Is that correct?

Click to expand...

Hi, well you'd definitely need to remove it from the circuit, at least one end, anyway. That way there is no possibility of getting a false reading on the meter.

You could of just done it and compared the Fluke Ohms reading with the Ohms reading on the side of the breaking resistor!

Most breaking resistors (dynamic brakes) have a thermal switch in them to protect the device from melting or catching fire. While you're checking the resistor you should check the switch as well.

What is the Fault that's coming up "Buss Over voltage"
if it fault pops up on power up try powering up without the DB resistor
Check the DB Transistor i have seen them shorted usually when that happens the resistor burns up
Also when working with the DB resistor one end is connected directly to one leg of the DC Buss (750 VDC)

New install or is this a drive that has been running and now just faulting out?

yes, but

Lynx777 said:

Most breaking resistors (dynamic brakes) have a thermal switch in them to protect the device from melting or catching fire. While you're checking the resistor you should check the switch as well.

Click to expand...

The braking resistors that I've seen installed in the past few years do have a thermal switch (Kl****, for us old-timers), but it is not in series with the resistor by any means. It will typically be mounted near the resistor, but be wired independently. But, yes, it should be checked if the designer included it in his design...to drop out the hardwired contactor in series with VFD supply.

jdbrandt said:

The braking resistors that I've seen installed in the past few years do have a thermal switch (Kl****, for us old-timers), but it is not in series with the resistor by any means. It will typically be mounted near the resistor, but be wired independently. But, yes, it should be checked if the designer included it in his design...to drop out the hardwired contactor in series with VFD supply.

Click to expand...

this. looks like a small nickel sized sensor (about 1/2 in thick) with two wires off it (usually fork connectors). Normally closed if circuit is good (continuity between both terminals). Most of the time the switch is ignored anyway because a stopping load is more important than a resistor. You are looking at 50 ohms or under usually for breaking resistors.

0949er said:

this. looks like a small nickel sized sensor (about 1/2 in thick) with two wires off it (usually fork connectors). Normally closed if circuit is good (continuity between both terminals). Most of the time the switch is ignored anyway because a stopping load is more important than a resistor. You are looking at 50 ohms or under usually for breaking resistors.

Click to expand...

The thermal switch's function is to monitor the temperature of the mounting bracket of the dynamic braking resistor. The idea is that if the DB resistor overheats, the mounting bracket will heat up, as well. The reason this is important is because the DBR can overheat, if there is a malfunction. Because of this, the manufacturer of VFDs will generally recommend a mechanical contactor in series with the VFD power.

Yes, stopping the motor is important....but it is surely important to prevent dynamic braking resistors from bursting into flames.

I worked at a place where the factory nearly burned down because of a faulty dynamic braking circuit. It was scary, but at least nobody got hurt. The machine was destroyed, but that's all.