Rheostat for a Brinkman "3 Million"

[cwbycrshr]

Anybody know what Rheostat I need for my $40 Brinkman from Wal Mart?

Going to cut the cord and splice one in, just don't have a clue what the output/input would need to be or if any rheostat from Radio Shack will work.

Thanks,
cwbycrshr

 

[lctorana]

Not familiar with the exact model, but if the bulb is a 6V, 55W H3 bulb like many are, you would need a 0.33 ohm, 30 watt rheostat. This is impractically large, would run very hot, and I woud be surprised if RS would have anything like that.

With over nine amps flowing at such low voltages, the dimming options are rather limited.

Some Alternatives:

a switched chain of Si diodes

a series-fed TO36 Ge power transistor with variable base feed

a 1 ohm NTC (in case you just want to soft-start the bulb rather than turn the lumens down)

 

[cwbycrshr]

Edited for this info.
I am pretty sure it is a 12V bulb...awaiting customer service return email to verify. Does that help with options?


😕

Yep, totally lost me there.
Sooo the only way to dim down a spotlight is to have lower amps at a higher voltage...more or less?
Totally not the news I was hoping for.

I am guessing the series-fed TO36 Ge power transistor would be the easiest way to go, but I have not a clue as to where I would need to wire that in.

 

[lctorana]

No, not the easiest, definitely the hardest option. And would need a heatsink, so would be just as bulky as the rheostat. Oh, and did I mention that TO-36 GE power transistors were obsolete 35 years ago?

12V is a few more volts to play with, but the bulb is probably 100W.

The rheostat you would need to dim that would be 12^2 / 100 / 2 or about 0.75 ohms, at (100 / 12)^2 *0.75 = 50W minimum.

Impractically large.

I mentioned switched Si diodes, and that would work in theory, but you immediately would run into switch breakdown and contact resistance issues.


I'll step down now.

This needs someone far cleverer and more creative than me.

 

[SemiMan]

What you need is a pulse-width-modulation circuit (you can find lots on the web based on the 555 time) or use a micro if you know how to program. Feed that into a good low resistance MOSFET and you are set.... IRF1302 from Digikey would do the job, 0.004 ohms. You would dissipate at worst about 0.25-0.4 watts. You would only need a small heat sink.

Semiman

 

[scott.cr]

What you need is a pulse-width-modulation circuit (you can find lots on the web based on the 555 time)

Yep - dimming the light by adding resistance will murder its power efficiency. PWM is the only way to go for dimming an incandescent unless it's running on mains power.

Alternatively, you could try to source a diffusing filter to snap over your light. Output will be reduced and "softened." Better for lower-output or close-up work with a light like that.

Or you can frost the lamp with Armour Etch. This would leave you with a permanent, inexpensive compromise between a soft/dimmed light and a full-output light.

 

[lctorana]

What you need is a pulse-width-modulation circuit... ...Feed that into a good low resistance MOSFET and you are set.... IRF1302 from Digikey would do the job, 0.004 ohms. You would dissipate at worst about 0.25-0.4 watts. You would only need a small heat sink.

Now why didn't I think of that? Old-age creeping in.

I was thinking of MOSFETs, and thinking "on-off state only", and thinking of how commercial lamp dimmers work, and couldn't add two plus two.

I'm senile.

 

[RDZombie]

just hop on fleabay and search for motor speed controllers, there are many super cheap kits you can augment to fit your needs. Most of these work just as well for low voltage DC light bulb dimming as they do for PWM motor speed control