Racetech rainlight resistor

[andy couchman]

The little resistor in the red wire to my round Racetech rainlight has snapped its wire, so I need a replacement resistor. But I'm struggling to find out what value resistor to get and where from.

Can anyone help?

Thanks.

Andy

[andy couchman]

Anyone?

[Jonathan Kay]

Have you got a model name or number or similar?

Or the old resistor?

Jonathan

[andy couchman]

Have the old resistor Jonathan. I think the colour bands are: Red; purple; thick black; thin black (or blue); brown (or the other way up!). Very difficult to see the colours though. 

[Jonathan Kay]

You've got five bands: could you add where the bigger gap is between them.

Jonathan

[CageyH]

Red, purple, black, black should give about 270 ohms with brown giving it a 1% tolerance.

A picture would help.

[CageyH]

Running the coulours the other way gives a really big resistance of about 10^10 Ohms, so my money would be on the 270 value, if the couloirs stated are correct.

[bjw]

I don't think 270 ohms is plausible as it's far too large a value to allow a sensible current for a 'high intensity' lamp. (100-200mA?)

27 ohms seems more likely, which would imply the band that now appears to be black/blue has discoloured and was originally gold. (The metal content in the lacquer can corrode in damp/hot conditions.)

The picture below (not a Racetech branded unit) shows two 15 ohm resistors to be wired in series (i.e. 30 ohms - suspiciously close to 27.)

 

http://www.autosport.com.au/autosport-50-led-rain-light

I would think they've used two resistors to keep the dissipation down - the ones pictured look like 1/4W ones to me, so a single one would be struggling (..and perhaps discolouring through overheating?)

The Racetech light comes in two versions - a 12v and a 9v one, and I'm wondering if some suppliers are selling 9v units with added external resistors as 12v units... (30 ohms drops 3v at 100ma...)

Cheers

[andy couchman]

Thanks all. The big gap is towards the bottom (between ther last two colours) - it is just possible there is a gold band there - but it's very faded if it is. The resistor sits outside the bodywork so is fairly exposed.

[alan c]

I am fairly certain that I used a 27ohm resistor when I installed mine, I did a couple purchasing the light and resistor from Maplins but they are no longer around.

[rj]

Another vouch for the plausibleness of 27ohms from me. Plus for bjw's explanation of why to use two rather than one.

If you drop 3 volts across a 30 ohms resistor the power is 9/30W - or 0,3W which would mean a 1/4W resistor would get really hot.

Add to this, that the voltage in the car when the engine is running is more like 14V rather than 12V...

[Richard Price]

Andy,

Following your question on FB, I see that you didn't actually get an answere of where to buy here....

Based on the assumption that its actually designed to be supplied with 9V, and we assume about 0.5A, then a 27ohm resistor rated at 1.5W should do the job. You could buy 10 from RS, and chuck 9 away... 

Amazingly, RS don't charge postage, so that would be a grand total of 37p

https://uk.rs-online.com/web/p/through-hole-fixed-resistors/7078801/?fbclid=IwAR3g3C_OXVY2CJbzXkU_1I2fgMZ28xWf4tRXsZcaYyGAqVRY7IDkiZv06A8