Topic

Can the heater control panel back-light be replaced with LED lamps?
If so, which lamps do I need?

Are there any potential flickering issues when the dimmer is used?

Interesting question, now, let me make sure I'm referring to the right person, yours is the LE500 isn't it. Unless the 500 uses a different circuit, the incandescent lighting would be controlled resistively , which would be less than ideal with LEDs. LED control is usually done by switching at high(ish) speed with the controller altering the mark space ratio, which is nob speak for the frequency of switching & the time gap between the LED being switched on. There will be some strobing but whether it can be detected in this application I don't know but I've a PWM controller in the workshop & enough LEDs to create my own mini illuminations. I've just completed a design project & can forget about that, until he blows it up, so after the dentist & while articulation returns to the numbed face I'll do a lash up & report back.
M

The workshop part of this review went very well, the posting of the results less so, I’ll start afresh shortly.

As half expected the addition of pictures has yet again be my undoing. I’ll start with those first & then I’ll clarify later.

I’m hopelessly outclassed by my camera, two minutes into a photographic bout & its got me on the canvas with my arm up my back.
Anyway the tests were successful & I might think along the same lines. The board I’ve been using is smaller relative of the one I used on the heater fan speed control & it was £2-59 so not too larger strain on the wallet & like a lot of my experimental bits it comes from eBay. It doesn’t extinguish the light completely but that could be due to the small amount of current being draw, I’ll look at that later, but it takes the lamp up to fill brilliance. You mentioned strobing, I set a matrix display next to it whilst I was doing the tests, these are addressed in rows & columns & can be notorious for flicker, but although there is was barely perceptible.
There are some more examples of over exposure & out of focus but I doubt they would convey anything useful, so I’ll leave it there.
M

I have just found a ragged hole in our plans. The output from the board is in effect positive earth & we require negative, this is to do with output devices polarity. There are N channel power FETs & P channel, N are cheaper & more robust therefore they are chosen for inexpensive controllers, they also create positive earth topography.
The dash lights are a battery bulb circuit, if the supply can easily be isolated from the lamps the jobs back on. I’ll have a look later.
M

Right, my assumption that the dimming circuit would be resistive was incorrect although two out of the three sets of diagrams I have show it as such. I had a good look through my spare parts & turned a dimmer module up & stripped it down, only to find a circuit almost identical to the one I illustrated. I intended to rig it to make sure it behaved correctly but it was cast aside due to it being knackered.
And finally after wasting your time on a wild goose chase, chose the LEDs you fancy, observe their polarity & if they are not optimised for 12v wire in a current limit resistor, one per device preferably, 1k for 12v is a useful can do most value.
Sorry it’s taken so much buggering about but although a circuitous route we arrived. Whether we’ve got there yet is a philosophical question.
M

Hi Mike, so if I am reading this correctly, the LED's should work ok if I add a 1k resistor.
Is this to each lamp?
Is this in series or in parallel?

Final question is, what is the type of lamp used in the heater control panel. I have pulled one out, but cannot accurately determine the part number/type/size. I assume that it is a T5, but there seems to be a big selection of these.

Obviously the 1k value is a good general value, in actual fact it depends on the forward voltage of the device & the current it draws. If you want the idea value you would be able to calculate it for 12 or any voltage by knowing those perimeters, I say 1k because it’s a better limiter of current & easier to remember than the 680 ohm which if I recall correctly is nearer the ideal value.
And I consider it good practice to use one per LED & in series with the positive (usually the longer of the two leads). Due to manufacturing differences, especially at the budget end of the market one device can draw a more than others & you can end up with one bright & others not do.
A case I point; I use U/V activated adhesive, the better the U/V source the better things go all round. I made my own after the commercial device provided did not to have the correct frequency of light.
I bought a batch of devices “selected” to be right, & arranged them in a matrix without resistors & although the frequency might be right some are much brighter than others.
Moral of this; follow your own advice.
The illumination of the heater panel. I have been in there within the last six months doing other things but didn’t take any notice of the lamps & although you mention T5 I really have no clue, sorry.

I determined that the lamps are T5 286.

You just pull out the halogen one out of the holder and replace with led types.

The ones I got already have resistors for CAN systems. These seen to work ok with the dimmer.

And that’s the outcome we we’re looking for. It might have taken me a long time to reach the conclusion that you could indeed stuff any old T5 wedge LED in the bayonet adapter & providing the polarity was correct you wound up up & running. Great.
M

Here's a photo of them turned to the brightest setting. Much better than they used to be.