Cap bleeder/Voltage probe

[martin manning]

A clip lead and a resistor works nicely for discharging power supply caps, but this is just so much more fun.

LED's indicate the voltage level and extinguish sequentially as it bleeds down, roughly 200, 120, 80, 40, and 20V. Negative voltage illuminates the offset LED nearest the tip instead of the in-line one, AC illuminates both. Three 5W wire-wound resistors dissipate the stored energy, and I see no problem hitting it with up to 700V when draining caps. Banana jacks at both ends accept test leads or a probe tip made from a banana plug as shown. No fancy circuitry, just resistors and diodes. SM/TH PCB designed using KiCad 6.

[pompeiisneaks]

That is super cool, where do I get one?

~Phil

[martin manning]

There is only one at this point, but I have more boards. If you are up for some SMD soldering, you could build one up. The diodes are pretty small, mm-size, but the resistors and LEDs are larger. It can be made simpler by soldering the clip lead and probe tip wire directly to the PCB, which would take about 0.75" of length out. I think I might rather do it that way. The board is only 6" long, but the version shown came out 8.5" across the banana jack faces.

[Roe]

you have a nice business idea here if the price is right!

[pompeiisneaks]

Ahh I'm about to put the house up for sale so all my gear is in storage, so I'll have to wait a bit... love the idea and yeah that may be a good project idea to sell.

~Phil

[martin manning]

you have a nice business idea here if the price is right!

Weber sells a cap bleeder for $20. StewMac (being StewMac) is selling what looks like the exact same thing for $30. It's just a tube with two resistors in it, a banana plug tip, and a clip lead. I guess this fancy one would have to sell for $100.

I swapped one of the photos above for one of a high voltage cap discharging test, which I repeated 3-4 times with no problems.

[bepone]

why not for 5 usd for this few components? i never understood so high prices, effect is just opposite , turns you off.
how i see there are not so many interests, electronic is not so popular these days because a lot of stupid people around who doesn't use a lot of brain. also if this is a product, selling will be limited. so maybe it is possible to put interest on those stupid mass with cheap price, and to expand little bit the joy of electronics, i'm often give for free many designs, parts or devices, also completed amplifiers...but this is only me. people just seeing the profit these days.

[martin manning]

Maybe my subtle humor isn't coming through?

[johnnyreece]

I'm not much with SMD components, but is there a way to make this with full-size parts? I could see having it mounted permanently to my bench, then I could use test probes to connect to it when needed. Either way, cool idea!

[martin manning]

...is there a way to make this with full-size parts? I could see having it mounted permanently to my bench, then I could use test probes to connect to it when needed.

Sure, I had it working on a breadboard first. If I were going to have something on the bench, I would make a simple probe with resistors in it and use a DVM as a (much more accurate) voltage indicator. Actually 2x 10k 500V resistors would be fine, and maybe connect the ground clip with a stacked banana plug to the DVM so the probe just has one 2-conductor cable attached to it.

[Phil_S]

A clip lead and a resistor works nicely for discharging power supply caps, but this is just so much more fun...

I've got a big sandblock wirewound resistor with short leads and clips soldered to both ends. And I use my meter. I'm guessing most of us do this. I agree with Martin. It works nicely. It isn't nearly as much fun.

[johnnyreece]

I've got something similar. I have a chopstick with a resistor taped to it, with one lead as the "probe", and the other connected to a wire with a clip that goes to ground. I like the LED idea, though, as my eyes have a hard time reading my meter (getting old eyes, I guess).

[martin manning]

I have a chopstick with a resistor taped to it, with one lead as the "probe", and the other connected to a wire with a clip that goes to ground. I like the LED idea, though, as my eyes have a hard time reading my meter (getting old eyes, I guess).

For a bare bones LED indicator you could just add three parts to your chopstick, on either side of the power resistor. You could even leave the 1N4007 out, as long as you never connect it backwards, or to a large negative voltage. If you did that, the LED would go out permanently, but the 1/4W 6k8 would light up.

[johnnyreece]

Fantastic! Thank you!