Capacitor discharge probes
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From: Shaun on 17 Jun 2010 20:55 Hello, I recently bought a Blue ESR meter and assembled it and it is working well. In the instructions it mentions making a jig with a 100 ohm 5 watt resistor attached to some probes for discharging capacitors before testing them with the ESR meter. How does one calculate the required resistor wattage for different capacitor values. Say I wanted to discharge a 63 volt cap at 500 microfarads, would 5 watts be enough. Right now I've made a probe jig with four 100 ohm 3 watt resistors for a total of 100 ohms at 12 watts. thanks in advance, Shaun
From: Tom Biasi on 17 Jun 2010 21:27 "Shaun" <rowl(a)nomail.com> wrote in message news:yuzSn.62258$mi.39337(a)newsfe01.iad... > Hello, > > I recently bought a Blue ESR meter and assembled it and it is working > well. In the instructions it mentions making a jig with a 100 ohm 5 watt > resistor attached to some probes for discharging capacitors before testing > them with the ESR meter. > > How does one calculate the required resistor wattage for different > capacitor values. Say I wanted to discharge a 63 volt cap at 500 > microfarads, would 5 watts be enough. Right now I've made a probe jig > with four 100 ohm 3 watt resistors for a total of 100 ohms at 12 watts. > > thanks in advance, > > Shaun > Hi Shaun, I could say a few words here but Sam can provide you with much more info. See here: http://www.repairfaq.org/sam/captest.htm Tom
From: Shaun on 17 Jun 2010 22:22 "Tom Biasi" <tombiasi(a)optonline.net> wrote in message news:4c1acb9e$0$5016$607ed4bc(a)cv.net... > > "Shaun" <rowl(a)nomail.com> wrote in message > news:yuzSn.62258$mi.39337(a)newsfe01.iad... >> Hello, >> >> I recently bought a Blue ESR meter and assembled it and it is working >> well. In the instructions it mentions making a jig with a 100 ohm 5 watt >> resistor attached to some probes for discharging capacitors before >> testing them with the ESR meter. >> >> How does one calculate the required resistor wattage for different >> capacitor values. Say I wanted to discharge a 63 volt cap at 500 >> microfarads, would 5 watts be enough. Right now I've made a probe jig >> with four 100 ohm 3 watt resistors for a total of 100 ohms at 12 watts. >> >> thanks in advance, >> >> Shaun >> > > Hi Shaun, > > I could say a few words here but Sam can provide you with much more info. > See here: http://www.repairfaq.org/sam/captest.htm > > Tom Thanks for the link, there is alot of information there but not what I was asking for. How do you calculate resistor power rating required to discharge a capacitor of x volts and y microfarads? Shaun
From: stratus46 on 17 Jun 2010 22:33 On Jun 17, 7:22 pm, "Shaun" <r...(a)nomail.com> wrote: > "Tom Biasi" <tombi...(a)optonline.net> wrote in message > > news:4c1acb9e$0$5016$607ed4bc(a)cv.net... > > > > > > > "Shaun" <r...(a)nomail.com> wrote in message > >news:yuzSn.62258$mi.39337(a)newsfe01.iad... > >> Hello, > > >> I recently bought a Blue ESR meter and assembled it and it is working > >> well. In the instructions it mentions making a jig with a 100 ohm 5 watt > >> resistor attached to some probes for discharging capacitors before > >> testing them with the ESR meter. > > >> How does one calculate the required resistor wattage for different > >> capacitor values. Say I wanted to discharge a 63 volt cap at 500 > >> microfarads, would 5 watts be enough. Right now I've made a probe jig > >> with four 100 ohm 3 watt resistors for a total of 100 ohms at 12 watts. > > >> thanks in advance, > > >> Shaun > > > Hi Shaun, > > > I could say a few words here but Sam can provide you with much more info. > > See here:http://www.repairfaq.org/sam/captest.htm > > > Tom > > Thanks for the link, there is alot of information there but not what I was > asking for. > > How do you calculate resistor power rating required to discharge a capacitor > of x volts and y microfarads? > > Shaun The vast majority of capacitors will be discharged by the time you get your test probes ready to use. I've been doing ESR stuff several years and only once did I damage a meter by sending power into a Capacitor Wizard. It was a small value (around 10 ohms) resistor that fried and only took a few minutes to replace. Or do you just want formulas? G²
From: George Herold on 17 Jun 2010 23:02
Shaun wrote: > "Tom Biasi" <tombiasi(a)optonline.net> wrote in message > news:4c1acb9e$0$5016$607ed4bc(a)cv.net... > > > > "Shaun" <rowl(a)nomail.com> wrote in message > > news:yuzSn.62258$mi.39337(a)newsfe01.iad... > >> Hello, > >> > >> I recently bought a Blue ESR meter and assembled it and it is working > >> well. In the instructions it mentions making a jig with a 100 ohm 5 watt > >> resistor attached to some probes for discharging capacitors before > >> testing them with the ESR meter. > >> > >> How does one calculate the required resistor wattage for different > >> capacitor values. Say I wanted to discharge a 63 volt cap at 500 > >> microfarads, would 5 watts be enough. Right now I've made a probe jig > >> with four 100 ohm 3 watt resistors for a total of 100 ohms at 12 watts. > >> > >> thanks in advance, > >> > >> Shaun > >> > > > > Hi Shaun, > > > > I could say a few words here but Sam can provide you with much more info. > > See here: http://www.repairfaq.org/sam/captest.htm > > > > Tom > Thanks for the link, there is alot of information there but not what I was > asking for. > > How do you calculate resistor power rating required to discharge a capacitor > of x volts and y microfarads? That's a bit of a weird question. Most times caps aren't charged (much) just sitting on the bench. So any old resistor will do. (Is there some danger just using a peice of wire?) The energy stored in a cap is 1/2 CV^2. If you discharge it with a resistor R it'll take something like the time constant RC. So the power is energy/time ~ V^2/R. (Hmm the C goes away?) anyway, if the RC time is short the resistor won't have time to heat up much and you could use a smaller value. So what's a short time? at a guess anything shorter than 1 s or maybe 0.1 s. George H. > > Shaun |