Discharging Capacitors Prior to ESR Meter Probing

I just use about a 20w 1K ceramic power resistor from a scrap unit with some leads soldered to it. Probably a little higher value than needed for audio work and a little lower than optimal for TV HV, but it is a good compromise that works fine for everything so far.

One thing that I like about the Atlas and Sencore meters over the DSE (I have them all) is that you don't have to worry about it. Actually, I use the Atlas more than anything in the field and for protable applications. I like the size and the fact that you can get cap value readings. I still like to discharge the large PS caps and CRTs just for safety, but for the lower capacity and lower voltages I just let the meters designed to do so discharge them. You can get a dischage update for the DSE, IIRC.

Leonard

I soldered in two 600 volt diodes back to back across the probes input connectors on my Dick Smith ESR meter. About 1 or 2 amps rating would be OK. Connect one diode with the anode toward one probe connector and the other diode with the anode toward the other probe connector. I haven't had any problems in the 3 years I have been using my meter. The diodes do not seem to affect the meter reading. Hope this helps. John

"I just use about a 20w 1K ceramic power resistor from a scrap unit with some leads soldered to it. Probably a little higher value than needed for audio work and a little lower than optimal for TV HV, but it is a good compromise that works fine for everything so far. "

Like one of these?

"I soldered in two 600 volt diodes back to back across the probes input connectors on my Dick Smith ESR meter. About 1 or 2 amps rating would be OK. Connect one diode with the anode toward one probe connector and the other diode with the anode toward the other probe connector. I haven't had any problems in the 3 years I have been using my meter. The diodes do not seem to affect the meter reading. Hope this helps. "

I saw this modification in the documentation that came with the unit. Let's say I placed the meter with this mod across a filter cap on a

When I used to repair PC monitors it was often necessary to discharge the SMPSU primary side reservoir cap, which could be charged to as much as 320V! The device I found best to dump this charge was a NTC thermistor, most monitors and some TVs have these as inrush surge limiting devices in the mains input circuit, the ratings vary considerably depending what you salvage them from, the cold resistance can be anything from a few hundred Ohms to about 12K, as the discharge current heats the NTC thermistor it's resistance falls to typically less than 10 Ohms and discharges the cap in a controlled manner - rather than blowing chunks out of the PCB track like when shorting it out with a screwdriver.

There's a slight possibility one of the diodes might fail S/C - but it should protect the ESR meter.

I have been reading this, and I guess your talking about two parallel reversed diodes, not back to back series diodes, right?

greg

The problem with this solution is that there is no limitation of the discharge current. Exceed the dv/dt rating of the capacitor being tested at your own risk. You may create a bad cap instead of just finding one.

John

Just check any caps that might be charged with a volt meter. If they are charged, use a large resistor to discharge them. Adding back to back high current diodes to the ESR meter isn't a bad idea to protect it from the occasional cap you forget to discharge, but don't rely on the diodes to discharge caps. Andy Cuffe

snipped-for-privacy@gmail.com

"Just check any caps that might be charged with a volt meter. "

You can do this with any digital multi-meter on any sized cap? No danger of damaging it, even when reading a power supply cap?