10w 100 ohm resistor

[sam67]

Hi i have a few 100 ohm 10w wire wound resistors .. how much voltage can these take ,say for discharging a cap ..or would i need summat in the 1.8k range.. Just wondered that's all as i thought i might be able to use em rather than chucking em..I measured the spec with my dvm and they are in spec.

cheers

[stj]

Re: 10w 100 ohm resistor

depends on the make & series.
pretty sure it will be 300+ though.

you want to put a number in series for discharging big caps btw.

[sam67]

Re: 10w 100 ohm resistor

Hi the caps are in an lcd monitor ,i was thinking of getting a couple of 10w 2k wire wound resistors and use one of em to touch both ends of the cap leads on the underside of board...i know some discharge after you shut them down but i wanna make sure using a volt meter also..it's an lcd what i am just practicing on with some soldering and what not ..So this method should be ok right for the bigger caps ?..I have not opened it up yet but will be going to just to get a few good parts off.

cheers

[PCBONEZ]

Re: 10w 100 ohm resistor

The voltage rating will depend on:
Ohm and Watts [do the math]
-and-
How thick the insulating materials are [arcing through the insulation].
There is no way to find the second one out if you don't have a PN & Datasheet or markings on it that tell you.
.

[larrymoencurly]

Re: 10w 100 ohm resistor

I've been told that the maximum across a resistor shouldn't be more than about 500V, and I have a Panasonic CRT monitor with several identical resistors in series that seem to confirm that.

[kikkoman]

Re: 10w 100 ohm resistor

for wirewound resistors, vishay says max voltage is (P x R)^0.5.
since this is for continuous operation, the limiting factor is the power dissipation.
for a 10W resistor that gives you 31.6V.
if you put 4 in series, that gives you 126V; 5s give 158V etc.
i'm sure though you can go well beyond the ratings if it's just a pulse like from discharging a cap.

[stj]

Re: 10w 100 ohm resistor

worth adding that a big cap could dump 3-6amps into that resistor when it's fully charged.

i'd rather make a discharge lead with a few 1meg high-voltage resistors in series in it.
that would act slowly enough to even discharge a 30kv crt safely if you use well insulated wires.

[sam67]

Re: 10w 100 ohm resistor

Hi guys, i have this guys lcd monitor repairs and other stuff ,he reckons doing this will be ok.. http://www.electronicrepairguide.com...discharge.html

Seems theres lots of people have different methods.. p.s he recommends a 1.8 to 2k resistor either 5w or 10 also for SMPS he says either a 2.2 or a 4.7k will work ..