Plastimo Compass light - dont cut the red wire - Why

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mark1882

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Hi
I have been doing some work on my binnacle whish necessitated removal of my Plastimo Olympic 135 steering compass the compass slipped and the light/bulb cable sheathed in red broke as it pulled out of the connector, it does have solid metal piece on the end not bare wire like the black cable has.

No problem I thought just re-join it, I then noticed a label on the cable that says do not cut the red cable.

What does this label mean ie why should you not cut the red cable, I have broken mine. Its not the end that is attached to the bulb but the end where you connect it to the electric feed

Any advice would be appreciated.

Thanks

Mark
 
Curiouser and curiouser....

Must admit, I'd just repair the break - worst that can happen is that you'll find out why they stipulate not cutting it. Perhaps a certain length is needed in the test rig at the factory or allows it to be fitted in certain installations? I'll admit to having cut or extended a number of cables which had such dire warnings, some allegedly tuned lengths, etc. Mostly I believe that they just didn't want to field warranty claims if the joint was poorly made.

Rob.
 
The bulb in mine is not an LED but a little "grain of wheat" bulb which may well have a resistance wire to keep it from being blown by the voltage of a system on charge. Long before LED's were available such bulbs were sold to provide lighting on model railway layouts. I remember them as being easily blown. I am a bit surprised that LED's are not now used, and supplied as replacements, but when I looked to get a replacement for one of miner the new ones was still appear to be tiny conventional bulbs. http://marinestore.co.uk/Merchant2/...re_Code=mrst&gclid=CKyPmLi5hskCFYhAGwodaywMyA
 
mark1882 said:
.... do not cut the red cable.
Click to expand...

'Juggernaut', Richard Harris is the bomb disposal expert parachuted into the Atlantic ocean where he boards a cruise liner with bombs on board. He was instructed not to cut the red cable by the dastardly villain who had now been caught and forced to divulge what cables to cut to disarm the bomb. Harris goes to cut the green cable but at the last second ignores the advice and cuts the red cable thus saving the day. I may be getting my films mixed up!

I know, pointless trivia.
 
JumbleDuck said:
LED (or other low voltage lamp) and resistive wire as ballast?
Click to expand...

Very unlikely I would think in this context. However resistive line-cords were certainly used on mains equipment in the past as a cheap solution to drop the voltage ...... until that is someone shortened the cord and/or it caught fire!

I still regularly use a mains fluorescent (8w) inspection lamp which has a resistive mains lead as the ballast. (Crazy concept since more energy is wasted in the line-cord (which gets quite warm) than used by the lamp. I also recall domestic 4ft fluorescent fittings which used an incandescent bulb as the ballast :disgust:
 
BlowingOldBoots said:
'Juggernaut', Richard Harris is the bomb disposal expert parachuted into the Atlantic ocean where he boards a cruise liner with bombs on board. He was instructed not to cut the red cable by the dastardly villain who had now been caught and forced to divulge what cables to cut to disarm the bomb. Harris goes to cut the green cable but at the last second ignores the advice and cuts the red cable thus saving the day. I may be getting my films mixed up!

I know, pointless trivia.
Click to expand...

I have the movie on DVD! I might have to watch it now... "Fallon is the champion!..."

W.
 
Norman_E said:
I am a bit surprised that LED's are not now used, and supplied as replacements, but when I looked to get a replacement for one of miner the new ones was still appear to be tiny conventional bulbs.
Click to expand...

LED require a voltage regulator circuit. Cheap circuits emit RF noise which is spurious electromagnetic waves that can impact the precision of a very sensitive compass needle nearby. In addition such circuits require protection from water and salt. You can get a potted circuit with low RF noise emissions, but it would add significantly on production costs. You may understand thus why for these application the traditional bulb is still better indicated.

The length of wire is used as a resistance to reduce the current flow through the bulb. This increases its life and reduces the working temperature. If shorten the wire or try a normal bulb you will likely melt the plastic cover in the summer as it is fitted right next to it.
 
Last edited:
We are all speculating here but I doubt that the wire is resistive. For an LED or even a current limitter for a garin of wheat incandescant bulb I think a ressitor is more likely than resistive wire.
However being in a compass the wire carrying Dc is likely to produce a small magnetic field around it.
My speculation is that the wire its location, length and current have been taken into account in adjusting the compass for accuracy.
However a simpler way to solve this problem is to twist the 2 wires together.
So still no likkely answer. good luck olewill
 
Reviving an old thread for good reason.
last week (in Australia as it happens olewill) I bought an old stock plastimo mini contest compass. This is the older one not the mini contest 2 now being sold.
Brand new though and a good price.
Fitted it today to replace the old leaking silva that i had.
My installation instructions said nothing about not shortening the red wire so when i got a wire break pushing the wires through the too small hole in the plastimo supplied gasket, i just cut and stripped the wire. Connected up and switched on and got one brief flash from the light as it flared and died.
Turns out that the light is LED and inside the heat shrink on the tail of the wire was a 2 k ohm resister.
(Why didnt they put this at the LED end? No shortage of room. Why didn't they have this in my documentation?)

Not to worry, i fitted an LED to my old Silva compass, I will jsut repeat that as i am not likely to return to the vendor anytime soon, and for the component cost its hardly worth the warranty claim time and aggravation.
My question is this:
My Old compass was OK in half light, but too bright in full darkness. Has anyone here connected compass LEDs with a rheostat/pot to vary the brightness?
Tips or advice or better yet full specs would be appreciated.
Thanks
John
 
John the kiwi said:
Reviving an old thread for good reason.
last week (in Australia as it happens olewill) I bought an old stock plastimo mini contest compass. This is the older one not the mini contest 2 now being sold.
Brand new though and a good price.
Fitted it today to replace the old leaking silva that i had.
My installation instructions said nothing about not shortening the red wire so when i got a wire break pushing the wires through the too small hole in the plastimo supplied gasket, i just cut and stripped the wire. Connected up and switched on and got one brief flash from the light as it flared and died.
Turns out that the light is LED and inside the heat shrink on the tail of the wire was a 2 k ohm resister.
(Why didnt they put this at the LED end? No shortage of room. Why didn't they have this in my documentation?)

Not to worry, i fitted an LED to my old Silva compass, I will jsut repeat that as i am not likely to return to the vendor anytime soon, and for the component cost its hardly worth the warranty claim time and aggravation.
My question is this:
My Old compass was OK in half light, but too bright in full darkness. Has anyone here connected compass LEDs with a rheostat/pot to vary the brightness?
Tips or advice or better yet full specs would be appreciated.
Thanks
John
Click to expand...
Bump - anyone?
 
According to the installation notes for my Plastimo compass as follows :” Lighting….Compasses fitted with LED can be connected onto 12v or 24v. A resistance is cabled under the red sheath. Hence, the length of threads must ot be cut and shortened in any case. Polarity must be respected (+ on + red) and (- on black).”
 
Re dimming the light easiest might be to fit a switch that adds another 2000 ohms resistor in series or by passed. Or fit a 5000 ohm potentiometer. (rheostat) variabl;e resistor preferably a wire wound type. for variable light intensity. I can only say to land in Australia you did wander off course by a fair bit. Bet you won't do that again.
ol'will
 
I dimmed my compass light, it was too bright by fitting a 24v bulb instead of the original 12v. Works well and it should last a long time. (it was an incandescent bulb not led)
 
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