Dummy Load Build

[TACAMO]

Hi, I have a capacitor bank that stores 2300 joules of energy when charged to 400 VDC. I need to build a "dummy load" to safely dump the energy. I was thinking of putting a few of those 50 watt resistor in series. What do you think? Thanks.

 

[Ratchit]

Tamco,

Hi, I have a capacitor bank that stores 2300 joules of energy when charged to 400 VDC. I need to build a "dummy load" to safely dump the energy. I was thinking of putting a few of those 50 watt resistor in series. What do you think? Thanks.

Any idea what the value of your discharge resistance is going to be? How long do you want to wait for the capacitor to deenergize?

Ratch

 

[TACAMO]

I don't know what the discharge resistance is going to be. The dummy load is going to be for safety. It dosen't have to drain instantly, 45 seconds sound good.

 

[Ratchit]

TACAMO,

I don't know what the discharge resistance is going to be.

We'll figure it out.

The dummy load is going to be for safety.

Irrelevant with respect to the calculations.

It dosen't have to drain instantly,

It won't.

45 seconds sound good.

We'll see.


Let's look at what you have now. ½CE² = 2300 ===> C = 0.02875 farads

Let's be conservative and use the resistor at 25 watts instead of 50 watts. Then,
E²/R = 25 ====> R = 6400 ohms. The resistor will dissipate less power as the capacitor de-energizes down to a lower voltage.

The time constant is RC = 184 seconds.

In three time constants, the voltage will be down to 400*exp(-3) = 20 volts

So, in about 9 minutes, the voltage will be down to a safe level. Is that what you want? If not, can you figure out what you need to do to change it?

Ratch