Billion Watt Load Bank Build

[WOPL Sniffer]

Here's an EBAY link for the switches I used. EBAY link To clarify the listing appears to be the same as what I used. Have to be careful using a switch on the bleeder resistor. Contacts rated for 100 volts DC are rare. I don't have a switch on my bleeder.

Thanks for the link Don. I'll figure out the bleeder switch and resistors to keep from smoking the switch. I have a meter for monitoring the DC Offset so after the voltage drops when I turn off the amp, I can then switch the bleeder resistor on as long as the cap voltage is under 100VDC. These 2 switches are momentary and not used during amp testing but at idle.

 

[J!m]

Use a contactor for the switching and a switch to close the contactor.

 

[wattsabundant]

For discharging caps there are plenty of options available. If some kind of a mechanical switch is to be used, the contacts must be rated for the DC voltage applied. Any ice cube relay is rated for 250 VAC and 32 VDC. The reason for only 32 VDC? When the contacts open, arcing occurs as any inductance tries to keep current flowing. With AC, the current goes to zero each half cycle and the arcing stops. With DC the current doesn't drop and it sustains itself. The contacts must move far enough apart to stop the arcing.

For the same reason it is common practice to use a 0.01uf 1kv ceramic cap across power switch contacts to minimize the arcing. See the attached document.

 

[Vynuladikt]

Had an old Navy shipboard electrician tell me about WWII ships with a DC system.
Never try to screw/unscrew a lightbulb while under power. Welds itself in the socket!

 

[WOPL Sniffer]

For discharging caps there are plenty of options available. If some kind of a mechanical switch is to be used, the contacts must be rated for the DC voltage applied. Any ice cube relay is rated for 250 VAC and 32 VDC. The reason for only 32 VDC? When the contacts open, arcing occurs as any inductance tries to keep current flowing. With AC, the current goes to zero each half cycle and the arcing stops. With DC the current doesn't drop and it sustains itself. The contacts must move far enough apart to stop the arcing.

For the same reason it is common practice to use a 0.01uf 1kv ceramic cap across power switch contacts to minimize the arcing. See the attached document.

I looked at the PDF you posted, Not sure which one I should use so until I figure that out, I'll just use my Bleeder setup if I need to discharge the bulk caps. The document said if all else fails, use a .1uf and a 100 ohm resistor (both of sufficient size), a QC100 and put it across the contacts and look at the scope. Don, you probably already have the specs for a WOPL in your head to know what to use. If I have to use my Navy Math.................... Maybe one of the brainiac's here will chime in. Maybe Joe has an idea too. Maybe it's easier to just skip the switch and put my bleeder kit inside the LB on a set of naner jacks and when I need to discharge, hook a cable to go from the bulk caps to the jacks. ???? I'm thinking it will be easier to just skip that feature. I can still use the momentary switch for monitoring the offset at idle between tests.

 

[J!m]

Big, gnarly knife switch!

 

[Vynuladikt]

Since you are "making" the circuit, not "breaking" it, much less concern. Or do you need to do both under load?
As long as it is made quickly without bounce, arcing is a minor issue. Breaking a DC circuit on the other hand, you have an arc welder.

 

[Gepetto]

What is it you are attempting to do with a bleeder Perry. I thought this was about a resistor load bank?

I have not been keeping up...

 

[WOPL Sniffer]

What is it you are attempting to do with a bleeder Perry. I thought this was about a resistor load bank?

I have not been keeping up...

I was just trying to cover all my bases. I wanted to use my cable and bleeder resistor and have the ability to hit the Momentary switch and bleed off the bulk caps but it aint worth all the extra work. I can still look at offset before and after testing at idle and I figured bleeding off the caps would have been nice. Damn Buffalo Bob has me wanting to do some gadgets but I'll skip the bleed. I thought that after shutting the amp off it wouldn't have been an issue with arcing switches since it bleeds down fairly quick.

 

[Gepetto]

I was just trying to cover all my bases. I wanted to use my cable and bleeder resistor and have the ability to hit the Momentary switch and bleed off the bulk caps but it aint worth all the extra work. I can still look at offset before and after testing at idle and I figured bleeding off the caps would have been nice. Damn Buffalo Bob has me wanting to do some gadgets but I'll skip the bleed. I thought that after shutting the amp off it wouldn't have been an issue with arcing switches since it bleeds down fairly quick.

As in the bulk caps in the amp under test?

What's the issue? Should be easy to do.

 

[Gepetto]

It is just a switch and a resistor

 

[J!m]

Just the DC arcing when it is broken under load. As long as you "hold" until there is no current, the switch will be fine as said above.

 

[Gepetto]

Just the DC arcing when it is broken under load. As long as you "hold" until there is no current, the switch will be fine as said above.

This gets a Perry Huh??

This bleeder will be attached to a capacitive load (the bulk caps in the amp) not an inductive load. As long as you don't have miles of wire creating inductance and a resistor in line to dissipate the energy stored in the capacitors, this is an easy task--the voltage is the voltage.

We all do this often to bleed off the caps, a pair of jumper wires with alligator clips with an appropriately sized resistor in between. No drama has ever been involved for me while doing this.

 

[WOPL Sniffer]

It is just a switch and a resistor

That's what I thought. I wouldn't even hit the switch until the amp is off.

 

[WOPL Sniffer]

This gets a Perry Huh??

This bleeder will be attached to a capacitive load (the bulk caps in the amp) not an inductive load. As long as you don't have miles of wire creating inductance and a resistor in line to dissipate the energy stored in the capacitors, this is an easy task--the voltage is the voltage.

We all do this often to bleed off the caps, a pair of jumper wires with alligator clips with an appropriately sized resistor in between. No drama has ever been involved for me while doing this.

That's what I was thinking. I'll make a nice cable with my big clips and the 2 resistors I have been using. I never even get a spark when I bleed them so.....

 

[Gepetto]

That's what I was thinking. I'll make a nice cable with my big clips and the 2 resistors I have been using. I never even get a spark when I bleed them so.....

Pretty much any old switch will do Perry...just rate it for the current involved. If you are discharging the 100V caps on a 700 with a 470 ohm resistor, you will need a switch rated for minimum of 1/2A.

 

[WOPL Sniffer]

Pretty much any old switch will do Perry...just rate it for the current involved. If you are discharging the 100V caps on a 700 with a 470 ohm resistor, you will need a switch rated for minimum of 1/2A.

Got it, thanks Joe.

 

[Gepetto]

Got it, thanks Joe.

Just don't have miles of wire Perry...

 

[wattsabundant]

Big, gnarly knife switch!

Try slowly opening a knife switch with 100 VDC and watch the fire ball. With care you can sustain a very nice arc, right up until it melts down into a puddle.

My bleeder resistor is hard wired to test probes. When you make the connection to the charged cap, jam it on there and leave it for a few seconds. If you pussy foot around with it you can draw a nice arc, especially if there are bus bars in close proximity to each other. The ringing in your ears will help you remember to do it the right way the next time.

 

[WOPL Sniffer]

Just don't have miles of wire Perry...

I'm doing wireless wires Joe