Looking for a 2.5ohm 50W resistor...

greywolf224 · Apr 24, 2015

...Anyone want to get rid of one? Need it for a small project I am working on. Dont care if its ceramic, metal can or open wire wound.
If so let me know how much you want for it. A small envelope and a few stamps should cover shipping.

Have looked at a few places but shipping cost is twice as much as the resistor.
May run up to radio shack to see what they have.

souNdguy · Apr 24, 2015

50w is plenty of dissipation, look for this to be aluminum cased with heatsink fins.

U wouldn't be looking for a CSI resistor for an I/o engine would you?

Marine supply places sell them, but cost is 30-40$ due to the power dissipation. Ratschacke usually has 5-10w ceramics.

Cdi-121-br50-2.5. Should be a good part number.

For wire wound flat, 55w, 2.5ohm # (rwf) hl55-2.5. 7$ from surplus sales of nebraska

greywolf224 · Apr 24, 2015

(quoted from post at 14:09:07 04/24/15) 50w is plenty of dissipation, look for this to be aluminum cased with heatsink fins.

U wouldn't be looking for a CSI resistor for an I/o engine would you?

Marine supply places sell them, but cost is 30-40$ due to the power dissipation. Ratschacke usually has 5-10w ceramics.

Cdi-121-br50-2.5. Should be a good part number.

For wire wound flat, 55w, 2.5ohm # (rwf) hl55-2.5. 7$ from surplus sales of nebraska

That is one of my go to sources for parts but their shipping is a bit high for a single small part like that.
The resistor I need s/b the same that folks use when putting a 6v square can coil on a 12 volt system.
I saw one in pep boys yesterday for $25 but passed.

souNdguy · Apr 24, 2015

You can get by with a lot less than 50w rating.. if you are just ballasting that coil..

greywolf224 · Apr 24, 2015

Maybe I am assuming incorrectly. I thought those white ceramic resistors that you put in series with a ballast resistor are rated at 55watts?

souNdguy · Apr 24, 2015

Like adult underwear, it depends on which ones you buy.

People shopping at RadioShack are likely buying 5-10w jobs.

10w2d7 is a 2.7 ohm 10w rs resistor. If you need 2.5 on the nose, series a 1 and a 1.5 10w... etc..

JMOR · Apr 24, 2015

(quoted from post at 15:16:31 04/24/15)
Maybe I am assuming incorrectly. I thought those white ceramic resistors that you put in series with a ballast resistor are rated at 55watts?

talled, points closed, maybe 55W, but the average current with engine running is much closer to 1 amp than 4.5 amps. Or about 3 or 4 Watts.

souNdguy · Apr 24, 2015

Yup.. duty cycle..

greywolf224 · Apr 24, 2015

Thank You both for the input. I was going off of constant max current rather than normal current draw.

I need to protect the coil and points on a test jig I setup.
Using a 12volt battery connected to a 6 Volt round coil. Coil has a 1.1 ohm reading. So adding a 2.5 ohm resistor in series should get me to where I want to be with about 3.6 amps.

Charles Krammin · Apr 25, 2015

Try junk yards. Some older cars, used ceramic resistors in start-run. You may have to put some in series to get 2.5 ohm. I bought mine at compatetion antique tractor site. I run 12 volt generator and 6 volt coil on 2N. Have a 12 to 6 volt ceramic dropping resistor and ballast resistor in series. 4 years same points and coil, with fast start and positive ground.
Charles Krammin SW MI

Hobo,NC · Apr 25, 2015

When I set those up to test I use a VR1 voltage reducer and the appropriate resistor for the coil...

VR1 is a standard number for NAPA are most parts stores.

Dune Country · Apr 25, 2015

Have you considered using a auto headlight switch?
You could wire it through the dash light dimmer circuit(rheostat)
it would be adjustable.
Don't know if it would get 50w though.

greywolf224 · Apr 25, 2015

Quick run to RadioShack and $5.19 later I picked up 2 one ohm resistors rated at 10 watts and a .47 ohm resistor rated at 5 watts. Connected them in series and ohmed out at 2.6 ohms.
Perfect.

Wanted to get 3 eight ohms resistors rated at 25 watts and connect them in parallel but they only had 2 left.

greywolf224 · Apr 29, 2015

2.5 ohm 50 watt resistor.
Not Bad for $3.24 although shipping was $5.25
And it works :roll:

JMOR · Apr 29, 2015

"AS pictured", that is a 20 Watt resistor. Needs 291 square inch heat sink or equivalent to be rated at 50 Watts.

greywolf224 · Apr 29, 2015

Thanks.
Brass plate that the jig is mounted on is a 12"x12"x.25". It will have to do.
Not to mention, I doubt I will draw more than an amp or two at any given time while testing unless I forget to hit the off switch when I walk away.

Now if I can only find my 30 year old pint size paint can of heat sink paste.

JMOR · Apr 29, 2015

(quoted from post at 14:09:19 04/29/15) Thanks.
Brass plate that the jig is mounted on is a 12"x12"x.25". It will have to do.
Not to mention, I doubt I will draw more than an amp or two at any given time while testing unless I forget to hit the off switch when I walk away.

Now if I can only find my 30 year old pint size paint can of heat sink paste.

f can't find HS paste, just put some bacon drippins under it & it will smell good during testing.

Looking for a 2.5ohm 50W resistor...

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