I would like to know a general value & wattage rating for bleeder
resistors. I do occasionally recapping of vintage radios and would
like to build a unit with a resistor and alligator clips to attach to
the electrolytic leads to discharge them. The electrolytics I come
across mostly are rated for 200 to 600 volts.

Thanks

In article
<4ef304f5-23d0-4a0c-853f-5f332eb8997e@i29g2000prf.googlegroups.com>,
"Dave.H" <the1930s@googlemail.com> wrote:

> I would like to know a general value & wattage rating for bleeder
> resistors. I do occasionally recapping of vintage radios and would
> like to build a unit with a resistor and alligator clips to attach to
> the electrolytic leads to discharge them. The electrolytics I come
> across mostly are rated for 200 to 600 volts.

A bleeder is generally always in place, low wattage, high resistance,
may take quite a while to bleed down (RC of a minute or more), so that
it won't load the circuit too much when running.

A shorting stick (applied to caps without a bleeder) is generally not
"alligator clipped on both ends" since it is generally a poor idea to be
quite that close, and is usually a lower value, high-wattage resistor.
Exact figures depend on the caps in question - figure a reasonable time
constant (ie, you'll hold the shorting stick on the capacitor for 5 or
10 seconds, and want it to be down to, say, 6 V - about 5 RC time
constants, so a time constant of 1-2 seconds) for 600V on the largest
typical capacitor you work with. One side has a clip and lead, the other
side has some sort of stiff electrode, and an insulating stick handle
leads back to the operator.

Remember that an easy method to up the power is to use multiple
lower-resistance resistors in series - it may be much simpler to find 10
2 watt resistors than 1 20 watt resistor. You can also use a light bulb,
(nice low resistance 100W [or whatever you buy] resistor, easily found)
but in that case you need to check that it has not broken, and/or use a
resistor in parallel with it so that you have some discharge even if the
filament does break.

Once the cap is shorted, if there's some chance of stray charge pickup,
a two-alligator clip lead (no need for a resistor, but there can be one
if it makes you happy) can be installed.

--
Cats, coffee, chocolate...vices to live by

> Remember that an easy method to up the power is to use multiple
> lower-resistance resistors in series - it may be much simpler to find 10
> 2 watt resistors than 1 20 watt resistor.

I prefer to parallel higher resistance ones for more wattage ratings,
like if I wanted a 10k 2 watt, I parallel 2 20k 1 watt resistors
together. Which makes it easier as Dick Smith only sells 1/4,1 watt
and 5 wa

In article
<a14cbb6f-e71d-48e1-a81a-866417318bc2@s8g2000prg.googlegroups.com>,
"Dave.H" <the1930s@googlemail.com> wrote:

> > Remember that an easy method to up the power is to use multiple
> > lower-resistance resistors in series - it may be much simpler to find 10
> > 2 watt resistors than 1 20 watt resistor.
>
> I prefer to parallel higher resistance ones for more wattage ratings,
> like if I wanted a 10k 2 watt, I parallel 2 20k 1 watt resistors
> together. Which makes it easier as Dick Smith only sells 1/4,1 watt
> and 5 wa

I come from a high voltage background - in that context, the reduction
of voltage across each resistor (when in series) is beneficial for
inexpensive parts. At the voltages the OP is working with, makes no
difference, either series or parallel would be fine.

--
Cats, coffee, chocolate...vices to live by

On Sun, 10 Feb 2008 05:14:51 -0800 (PST), "Dave.H"
<the1930s@googlemail.com> wrote:

>I would like to know a general value & wattage rating for bleeder
>resistors. I do occasionally recapping of vintage radios and would
>like to build a unit with a resistor and alligator clips to attach to
>the electrolytic leads to discharge them. The electrolytics I come
>across mostly are rated for 200 to 600 volts.
>
>Thanks

Something like a 10 watt, roughly 100 ohm wirewound resistor works
fine.

John

On Feb 11, 2:16 am, Ecnerwal <LawrenceSM...@SOuthernVERmont.NyET>
wrote:

> Remember that an easy method to up the power is to use multiple
> lower-resistance resistors in series - it may be much simpler to find 10
> 2 watt resistors than 1 20 watt resistor. You can also use a light bulb,
> (nice low resistance 100W [or whatever you buy] resistor, easily found)
> but in that case you need to check that it has not broken, and/or use a
> resistor in parallel with it so that you have some discharge even if the
> filament does break.

I will do this, I have a couple of old bakelite bayonet lamp sockets,
I can use one of them, what value resistor would I put in parallel? I
regular 240 volt 100 watt light bulb tests at around 42 ohms.

In article
<d8fc3fb8-d0dc-4983-8dab-b6e899994767@e23g2000prf.googlegroups.com>,
"Dave.H" <the1930s@googlemail.com> wrote:

> I will do this, I have a couple of old bakelite bayonet lamp sockets,
> I can use one of them, what value resistor would I put in parallel? I
> regular 240 volt 100 watt light bulb tests at around 42 ohms.

Whatever's handy - probably a couple of hundred ohms. If you simply
check (with an ohmmeter) that the filament is sound after you've
discharged things, and before you reach in and grab stuff, you can do
without it. Unless you drop it, the bulb should hold up for years in
this application, as it never should get hot.

--
Cats, coffee, chocolate...vices to live by

On Feb 12, 12:35 am, Ecnerwal <LawrenceSM...@SOuthernVERmont.NyET>
wrote:
> In article
> <d8fc3fb8-d0dc-4983-8dab-b6e899994...@e23g2000prf.googlegroups.com>,
>
> "Dave.H" <the19...@googlemail.com> wrote:
> > I will do this, I have a couple of old bakelite bayonet lamp sockets,
> > I can use one of them, what value resistor would I put in parallel? I
> > regular 240 volt 100 watt light bulb tests at around 42 ohms.
>
> Whatever's handy - probably a couple of hundred ohms. If you simply
> check (with an ohmmeter) that the filament is sound after you've
> discharged things, and before you reach in and grab stuff, you can do
> without it. Unless you drop it, the bulb should hold up for years in
> this application, as it never should get hot.
>
> --
> Cats, coffee, chocolate...vices to live by

I'll just use a clear bulb, so the filament is easily visible. Think
I may have one lying around somewhere, probably with those lamp
sockets.

On 2008-02-10, Dave.H <the1930s@googlemail.com> wrote:
>
> I prefer to parallel higher resistance ones for more wattage ratings,
> like if I wanted a 10k 2 watt, I parallel 2 20k 1 watt resistors
> together. Which makes it easier as Dick Smith only sells 1/4,1 watt
> and 5 wa

There's a "learn to solder SMT" QRP dummy load kit out there that's
around 44 2k2 SMT resistors to make one 5W 50R load.

--
Ben Jackson AD7GD
<ben@ben.com>
http://www.ben.com/