Sorry this is somewhat lengthy - I didn't want to eat up your entire Saturday reading it. But I’m in need of a sanity check here…..

Several months back we were discussing the weak instrument lighting in my 1800ES. I don’t know if I mentioned at the time, but I have verified that the dimmer is NOT introducing any noticeable resistance when it is turned to full speed. I asked about the possibility of converting to LEDs and a couple of you responded that would likely be the way to go. Then I dropped the ball, thinking I would just live with it as-is. Also, I wasn’t sure I could find an LED dimmer that would fit in the same position as the original. But since I still have the steering column, seats, center console, etc out of the car I’m rethinking the whole thing and the fact that it would be much easier to do now rather than later. (I’m 6’-3”, 225 lbs.)

So I’ve located a couple different 12v LED dimmers that should fit nicely in place of the original dimmer. I’m leaning toward one in particular as it incorporates a small heat sink and more circuitry than the other one. (Chris’ theory: More circuitry equals better switch. Lol.) I think I can mod an original knob to fit the new dimmer’s knurled shaft.

Researching data on the original 3W incandescent bulbs, it looks like they produce anywhere between 12 and 25 lumens, depending on who you believe. I’m thinking about doubling, tripling , or even quadrupling the lumens and let the dimmer do the limiting. Maybe something like 50-75ish lumens on each LED bulb? Looking at all of the bulb choices out there it appears that 2W per bulb would be the max wattage I would ever incur, and that’s a bulb that produces up around 100 lumens. So I theorize that even if the lumens were up in the 50-100 range, the level of heat produced would be = or < the incandescents. I would bench test them for a couple hours just to see how hot they get. The dimmer I’m considering says it can handle up to 6 amps. One consideration is that I need to be cognizant of the bulb’s overall length so that it doesn’t bottom out inside the instrument. Another issue I see is that many of the bulbs I say “non-dimmable”. Hmmmm.


Possible Dimmer Switch:
https://www.oznium.com/switches/led-dimmer-knob#photos

Another Dimmer Switch (questionable?)
https://www.amazon.com/gp/product/B01C4UBMY6?pf_rd_p=d1f45e03-8b73-4c9a-9beb-4819111bef9a&pf_rd_r=MEJKGAN0G30Y1ES6FZQP

Possible LED Bulbs:
https://www.amazon.com/Bonlux-Replacement-Malibu-Landscape-Lighting/dp/B0732VKYCQ/ref=sr_1_2?s=hi&ie=UTF8&qid=1537021480&sr=1-2&keywords=12v+wedge+base+led+light+bulbs+warm+white+lumens

or....
https://www.aqlightinggroup.com/lightbulbs/led-light-bulbs/led-wedge/12v-1w-warm-white-led-cob-t10-wedge-light-bulb-10w-equivalent/?msclkid=340ab06100471d83bf92ebfc3b97e3d9

or…
https://www.amazon.com/Bright-Interior-Lights-Courtesy-License/dp/B07D3P9ZCN/ref=pd_sim_263_3?_encoding=UTF8&pd_rd_i=B07D3P9ZCN&pd_rd_r=80246c26-b8fc-11e8-940e-2fb2dccbe537&pd_rd_w=mzx4u&pd_rd_wg=wJJjx&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=18bb0b78-4200-49b9-ac91-f141d61a1780&pf_rd_r=5F919K36WPXV3M5RGFG1&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=5F919K36WPXV3M5RGFG1

So what do all of you electronically savvy folks think? Am I even close to being on the right track?

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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (STILL not road worthy!)

No reason it should not work.

Some LEDS with internal electronics can be dimmed by reducing the supply voltage. Other LEDs which are generally listed as non dimmable will operate at a relatively constant illumination level as the supply voltage drops and then all of a sudden go out (once the voltage drops below the diodes forward voltage). PWM modulates the LED output by switching the LED off and on at full voltage (which is at or above the diodes forward voltage); but, varying the on time to adjust the illumination level. As such, even a non dimmable LED should light up and dim successfully with a PWM dimmer.

Something to be aware of with LEDs. Some have internal circuitry that allows the LED to be inserted in the socket without regard to + or -. Others require that they be wired up / inserted in the socket with the appropriate terminals connected to the + an - supply.

Planning to bench test the completed set up in the instrument cluster is a good plan. There can always be some hidden factor that crops up and you want those sorted out before the cluster is back in the car. You may also find that even with dimming, some high power LEDs may still be too bright when the dimmer is on minimum. Not all dimmers can dim to zero pulse width.

142,

Thanks for the reply - it's encouraging.

Note that I have individual Smiths gaugec rather that an instrument "cluster".

I've sent an email to the switch vendor to ask if it will work (dimmable) with a particular LED that they also sell. In the mean time though, in reading the questions and answers on their web page, it looks like I may not be able to ground the bulbs back to the switch via chassis ground like the old incandescents. If that's the case I may have to devise a way to insulate the bulb holders' ground-to-gauge body contact and somehow add a (-) ground wire running from the bulb holders back to the switch.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

I saw that reference to ground switching which I found a bit confusing. I am wondering whether it was related to the fact that on modern cars, certainly Japanese cars, the practise is to have the +12v side of the device permanently connected and then control by switching the ground connection on the bulbs. Implementing the dimmer on this type of arrangement would be more complex because the dimmer needs a switched supply on its source and the original 12v 'source' to the bulbs needs to be isolated from the bulbs.

The 'other' dimmer was a three wire device. I expect: 1) +12 v source, 2) common ground, 3) PWM output to the LEDs. In such case, the dimmer ground would be connected to chassis ground. The + terminal of all the LEDs (assuming they are polarity sensitive) could be commoned and connected to the dimmer output and I presume that the individual gauges lights already use chassis ground? The dimmer with the 4 terminals can probably be set up just the same by connecting the two ground terminals together and then connecting to chassis ground. Connect the dimmer input to switched 12 v power and the output directly to the LEDs.

I'll probably try sticking with the existing chassis ground setup first and see how/if it works. But I'm prepared to string a dedicated ground wire, just like the + power wire, from bulb to bulb and running home to the dimmer switch - if need be. I was looking at one of the bulb holders and figured out it's fairly easy to convert them from chassis ground to a wired ground. (The chassis ground path would be severed.)

I'll report back but it will be a little while....

Thanks.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (STILL not road worthy!)

Chris;

I'm following this thread with interest, and since you're already getting good advice from other posters, I didn't feel the need to chime in and possibly confuse the issue...
...but now that it sounds like you're unclear and discussing chassis vs wired return paths, I did want to add clarification...either one is acceptable as long as long as all possible current paths are considered...in other words, chassis can only be the return (negative) node...so inspect all panel mounted switches and modules carefully to assure their panel connection is return only.

Cheers

Can you please let me know how the rheostat was removed. I have a replacement. I’ve tried to remove from the back but the ignition piece is stopping it.

I'm thinking you should be able to loosen the ignition lock assembly where it attaches to the steering column and then slide it down the column a little bit. Oh yeah, you'll have to drill the pinch bolt out as it will be a snap-head bolt if it has never been loosened before. You shouldn't have to move it very far in order to get the dimmer switch out. You may have to turn the key on in order to retract the column lock pin before it will slide down the column. If that's the case, then disconnecting the battery would be advised.

Are you doing an LED conversion or are you just replacing a faulty dimmer with an original one?
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

How into home-brew are you? I made a useful PWM switch to check LH2.4 and Regina idle valves using a Toko TK75005. It does all the way to 0% duty cycle (max about 89%) but you'd have to invert the output and use a P-channel mosfet, I think, to drive your instrumentation lighting ground referenced. The pot to control the brightness could be any size you want physically. My circuit is simpler, using an N-channel driver, but it switches the battery side.

Can't help with the myriad of new LEDs with integrated electronics and modular controls. I'm stuck in the 80's I guess.





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Art Benstein near Baltimore

When everything's coming your way, you're in the wrong lane.

Art,

You're WAY over my head! I'm mildly challenged to get the batteries in the flashlight the right direction. Well, maybe it's not quite that bad.....

(Ooops, there's "it's" again!)

I got a reply from the dimmer switch and bulb supplier. They say what I'm proposing should work. A $50 investment for switch and bulbs and a few days shipping time will be required to finally see if the plan is thumbs up or thumbs down.

Thanks!
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Guess I was inspired to jump in by 142 guy. Admittedly, I gave up some time ago trying to enhance the stock instrument lighting (240 small clock for example) seeing how young folks didn't find it inadequate, and the ophthalmologist seems to think my cataracts are still short of necessary clarification. I find myself feeling under dressed without a flashlight clipped on my belt and spending my free time lurking in the lighting department at HD admiring the high-output fluorescent and LED fixtures.

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Art Benstein near Baltimore

Birthdays are good for you. The more you have, the longer you live.