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I was speaking from memory and i have to make a correction, the rheostat is 1000 Ohm cos it appears "1E3 Ohms" in the diagram and thats 1000/1K ohm for the voltage divider not 1.3 Ohm (or 3 as i wrongly remembered)... that 1E3 side is a rheostat which is not well shown in the diagram cos the dimmer is not only a two position switch, it's variable.... i edited my other post accordingly, it would work with a 10 Ohm rheostat as well just that it won't be so sensitive and not dim so much
So, i counted the interior illumination bulbs and on the fully equipped ones there are 30 x 1.2 Watt bulbs so the load is 36W, in this case the simplest way is to use a 50W rheostat cos it can bear that load without getting too hot and simply connect it in series on the feed circuit(the highest it's power is the coldest it will stay so a 100W one will not get so hot like a 50W one and the load of the circuit will be the same), i might try that on mine soon and report
I agree. From the schematic a 5 ohm linear potentiometer should do the job. If a I put a 1.3 ohm resistor in series, it should prevent any overload potential and set the maximum brightness to the right level.
Aaah. I wondered about the 1K ohm to 5 ohm ratio for a simple switch setup. So I made the mistake of reading 1E3 as 1.3 ohm [its been a while since I did my electronic theory :) ] But if R1 is a potentiometer then it makes more sense. I assume then that the switch would then be for just the automatic dimming function?
From the D2 WSM...
Attachment 104972
A pwm signal is a far better way to dim the lights than using a potentiometer to dissipate power.
Seem to be a bunch of PWM dimmer controls for LEDs on ebay, like so
DC12V 8A PWM LED Strip Light Switch Dimmer Brightness Adjustable Controller TXPD | eBay
Would need some repackaging, but this one is capable of handling 96W to dissipate 1W, so wouldn't get hot.
I can't magnify that pic what ever i do... i dont say that dimming lights with PWM signal is not good as long as the whole circuit is built for that and the controll is on the earth path but on this particular interior illumination circuit which is a simple switch on a feed to some bulbs i can't see how a PWM generator would work instead of that bypass on the header.... in which section of the D2 WSM is that page you posted?
that device from ebay is more complicated to be addapted on the existing circuit cos it needs it's own feed then the interior illuminatio circuit must be fed through it and it's not alone there, the feed for interior illumination is common with the side lights.... the original setup on D2 for that was through a variable resistor and that's what i emulated not a new circuit through a PWM generator
Opening the picture in a new tab in my browser provides a full screen view of the picture. Without reloading the WSM to find the page, its in the instruments section.
The control is on the power supply path to the instrument back lighting only. That the power is common to side lights is immaterial because the modulated feed is only to the 3 backlights. Npte that the warning lights/LEDs are not dimmed.
The wiring schematic smacks of someone having measured the resistance between the switch wires when doing the documentation as the 1K and 5 ohm circuit is nonsense. A single 1.2W globe has a resistance of around 120 ohms so feeding its supply through a 5 ohm resistor will have nil visible effect and the 1K to ground will do absolutely nothing.
The ebay item will generate a much higher frequency signal than needed for incandescent globes but that should still be OK because the pwm signal simply supplies power for only a percentage of the time. The 3 back-lights, if indeed 1.2W as previously reported (not be me), will consume less than 4W so a mini version of the ebay device is all that is needed. (connect its o/p negative to earth/its input earth).
Ok, but what's wrong with that extremely simple to do scheme i made though... other than it's a bit old fashioned but functional?
Nothing wrong with using a potentiometer.
It is less efficient power wise, but 50W of power lost via heat is nothing in the grand scheme of things. As long as ambient temps aren't too high.
On the pro side of a pot, it's very simple.
