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How to make a safe capacitor discharge tool
Materials
(2) plastic nozzle tips with screw cap
(1) 470 Ohm 5 W resistor
(1) soldering iron tip
(1) cable gland
(1) crocodile clip
heavy duty insulated wire
heat shrink tubing
If you do not know what a capacitor discharge tool does or you do not understand how to use a capacitor discharge tool then this project is not for you.
First you need to cut the tip so it is level with the thread. Next you need to remove the plastic flange and washer from the other end see fig 1a . I am using 2 plastic nozzle tubes to make the outer case.
You will need to cut down one of the tubes to allow the wire and probe to pass through into the other nozzle please see image fig 2a
Next you need to push in the second nozzle inside so it locks tightly please see images fig 3a
fig 1a
fig 2a
fig 3a
fig 1a
In my scrap box I had an old soldering iron tip this is what I decided to use for the discharge tip.
The soldering iron tip as a hollow tube .I decided to cut an half section into the bottom end of the soldering iron , this made it very easy to solder the cable in place
fig 4a
Use a small drama multitool to cut 1/2 section out of the soldering iron tube. The cable I am using is of an old multi metre lead which is very well insulated and is very suitable for this project. Solder the cable to the inside of the old soldering iron which will now become your discharge tip
The next process is to solder on the 470 Ohm 5W resistor you want the resistor to be soldered so when you put it inside the casing you get double layer plastic around this area, also I've wrapped around some heatproof shielding
Next stage is to thread the wire + components through the plastic nozzle tubes. At the end of the cable you need to put on a small cable gland .This needs to be pushed inside the bottom of the nozzle tube. When you push the cable gland in it will lock in place, Tighten up the cable gland so the cable will not pull on the internal components. Next stage is to solder on a crocodile clip to the end of the cable,
The last stage is to slip some heat shrink tubing around the join of the two nozzle pieces. Make sure you use plenty of heat shrink tube around all the joints . I think the overall capacitor discharge pen looks professional and should last many years, and much safer than using the screwdriver technique to discharge capacitors which should not be used. For more information about discharge capacitors correctly. please go to UTube there are many videos covering the subject
Designed by Michael G Parry-Thomas
Discharging Time: It depands on the capacitor capacity. The max voltage depends on the type of resistor used . To find out the size of the resistor you need for higher Voltage and higher Power capacitors. Please follow the information on the Capacitor Discharge Calculator. And seek advice from other sources who deal with high voltage capacitors
https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-capacitor-safety-discharge
Capacitor Safety Discharge calculator
Please watch the above U tube video for more information about discharging capacitors. I have found this video very helpful and gave me the information for choosing the right components for my application .Please Note the maximum capacitor voltage I discharge is small ( max 50 V For this project )