Using multimeter to discharge filter caps

[dwinstonwood]

This was new to me, though it might be old news on the forum:

[shooter]

while it does work, it's also a good way to smoke a meter.
the cheaper method is just make a discharge box, high ohm, high watt resistor, gator clip cut in half, solder to the R, walla.


then you can safely || the meter across your discharge R to verify.


using a meter, once a cap is discharged, the meter can RE-charge the caps if left in the circuit


ALWAYS know "what to expect" before you engage in creative High voltage experimentation. ALWAYS leave room for the un-intended Consequences

[acheld]

OK, confession, I did not watch the video.

But I agree with shooter, you're risking a good multimeter.

Many us have put together a probe for this purpose.  Simple, relatively safe, and cheap.

In my case I placed 3  10k (3 watt) resistors in series within a polyethylene tube, added an audio connector pin on one end and a wire  with a 'gator clip on the other.   

This device keeps my hands out of the amp while discharging caps. 

[dwinstonwood]

Myself, I use a 3W resistor with two allegator clips to discharge caps, one end clipped to the chassis and the other onto the cap. I've never tried the method in the video. Though, it obviously works.
But, either way I'm not going to own or use a multimeter that's not safely designed to handle voltages.

[Willabe]

The B+ filter caps can be discharged through 1 of the preamp tube plate R's.

Just need a gator clip cable. Clip to tube socket side of plate R and to chassis.

[shooter]

when the probes start looking scary, that's where the fun begins 


The PS for CT X-ray tubes were 100k-140KVdc, you want to bring your A-game if it's tank diving day!

[rafe]

First tool I built 20 odd years ago two rubber coated alligator clips a 10ohm 5-watt white cement resistor and some insulated wire and shrink tube .....used it today.......nothing fancy but functional and tough   

[Willabe]

First tool I built 20 odd years ago two rubber coated alligator clips a 10ohm 5-watt white cement resistor and some insulated wire and shrink tube

Way to low in ohms. Will dis-charge way to fast.

[pdf64]

This was new to me, though it might be old news on the forum:

Connecting an ohmmeter across high voltage seems extremely inadvisable to me.
Anyone is free to do whatever they want with their own gear. Just because his meter has coped doesn't make it good practice, and suggesting others do stuff like that is a bad idea.

[rafe]

First tool I built 20 odd years ago two rubber coated alligator clips a 10ohm 5-watt white cement resistor and some insulated wire and shrink tube

Way to low in ohms. Will dis-charge way to fast.

I'm heading out the shop to test my amp....I may have misspoke about the ohms.....I'll be back soon......lol

[rafe]

No, it's a10watt 10 ohm....I am sure I didn't just come up with the ohms , I must have checked online, or seen it posted ....what harm will it cause??
It has never seemed to have caused damage ....I'm not being wise assed , I'd just like to know and what would you suggest???

[shooter]

heat will be the only cause, possibly a nice snap, it's sorta a "dead short" at big volts

[rafe]

heat will be the only cause, possibly a nice snap, it's sorta a "dead short" at big volts

Never had a spark with it ...., but I think I'll make a new one with more ohms ...........

[Willabe]

Some guys, decades ago, used to use a very large screw driver, it's shaft, to short out the filter cap to discharge it. Bam!    

Problem is it's hard on the caps insides to discharge instantly. It shocks the guts.

I wouldn't do it. And only 10 ohms, I would increase that resistance a lot.

Like I said, just use 1 of the preamp plate R's. Only need a gator clip cable, done, easy.

[rafe]

I switched it over to a 500 ohm .......from a box I found at the flea market with 5lbs of old resistors ....some of them are precision 1%  pretty cool stuff .......I

[shooter]

large screw driver, it's shaft,

ah the multi-tools


works well to jump batt volts to the starter solenoid for testing
works as "jumper wire" for testing relay contacts
opens paint cans, pry's door panels enough to scoot a coat hanger past those "sealed" upper panels
Philips works well to check the car has spark, just shove the point into a plug-wire, walk it next to some ground, snap, snap...yep got spark


and you wonder why heath care has become expensive 

[rafe]

What a shocker !!!

[Willabe]

I switched it over to a 500 ohm .......

Do what you want, But I'm talking about at least 40K/50K up to 100K. Benefit also of being able to use a lower wattage ratting. I probably wouldn't go lower than 20K.

Really, try discharging an amps filter cap bank with 1 of the amps plate R's, it works fine. Nice to have that tool around just in case for odd situations, but preamp plate R's work great.

1 less thing cluttering up the bench.

[acheld]

For my workshop, 30k ohms has been good enough. The series resistors keep it all within spec, more or less.

Draining high voltage caps is reasonably (but not lightning!) fast; lower voltages take more time than I want.

So, "good enough."

[rake]

I made mine with two 12K 7w resistors in series like 30 years ago. 
Why? Those were the biggest mamma-jammas I had on hand! 
Still works. Never blew up a cap with it so, it can stay.