White Gauge and LED Converstion / Making the Rheostat work with LEDs

[Tripdawg 10]

I recently converted my old gauge cluster bulbs to LED, which I do like by the way. However, i decided to save some money by buying the cheaper bulbs that to not dim with the rheostat (its either fully power or off). I have now decided to change the gauges to a white face by buying the gauge covers. I am afraid though that they might be too bright and having a dim capability may be wanted. Has anyone converted to the blue LEDs and white gauge faces? Were they too bright? Or, has anyone figured out how to rig the rheostat to work with the regular LEDs? Maybe there is an electrical engineer in the forum that would like to tackle that one for us.

 

Thanks.

[rangerdoc 22]

If I recall from a previous post the cheaper bulbs won't work because of something to do with voltage requirement for the bulbs vs the expensive ones (forgive me, but I'm terrible with electrical stuff). I wonder if there is something your could add inline to change that???

 

Could you just return the bulbs and get the expensive ones? Probably cheaper in the long run.

[69RavenConv 286]

Well, I am an electrical engineer and the short answer is that dimming LEDs in this application is not that easy.

 

Real bulbs, because they are little more than glorified resistors, can be dimmed by lowering the voltage across them, which in turn lowers the current flowing thru them. For reasons that aren't important here, LEDs don't work the same - lowering the voltage doesn't lower the current. So you have to add circuitry to lower the current in proportion to the lower rheostat voltage

 

Rangerdoc is on the right track, I suspect the expensive LEDs have a built in current regulating circuit that allow them to dim. Installing one or two real bulbs can have a marginal effect on dimming the cheap LEDs but not much.

 

FWIW, I also went with the cheap LEDS and am living without the dimming.

[Tripdawg 10]

Thanks for the responses guys. I can understand why getting the rheostat to work is not trivial. I guess the manufacturer of the LEDs would have included a cheap fix if it was that easy. I seem to remember seeing a picture of the other bulbs and it did look like the bulbs actually had circuitry built in. I am sure that I can live with the brightness that the white gauge covers might create. And I can always buy the more expensive bulbs later down the road. Thanks again. Maybe Ill try to take some before and after pics for guys that may be thinking of doing the same.

[danno 128]

I am also an electrical engineer, and as Raven mentioned, there is no easy way. But having said that, it does remain possible, just not easy. All you need to do is add a resistor in the wire to your instruments that supplies voltage to the LED's. It should be the blue-red wire to the instruments. Determining the value of resistor, though, will be difficult. If you want to give it a try, I will work with you on it.

 

The resistor solution will probably not work to dim the LED's more as you twist the light switch knob, but if all you want is to dim them when the dash lights are on at normal full brightness, then the resistor solution will work. The resistor solution, if needed, will cost about $1 to purchase the resistor.

 

You will need to measure the current in the this blue-red wire when the lights are on. You will need an current meter to do this, most all new voltmeters also have a function to measure current. If you ( or anyone else with LED's) can make this measurement as a place to start, then we can go from there to the next step.

[69RavenConv 286]

The resistor solution will probably not work to dim the LED's more as you twist the light switch knob, but if all you want is to dim them when the dash lights are on at normal full brightness, then the resistor solution will work.

 

Yep, that would work. I interpreted your question to mean you wanted to dim up and down with the rheostat like the conventional bulbs do.

 

When I first bought LEDs (eBay) I got single LED bulbs that were so dim I couldn't read the gauges. So I spent more money on bulbs that had 4 LEDs per bulb and they are passable ... so that's another way to adjust the overall brightness, buy lower or higher rated LED bulbs. Generally, the more LEDs per bulb, the brighter.

[buening 63]

Which LEDs did you buy? Keep in mind that a standard focused beam LED would most likely produce less light than a standard bulb, because the dash lights rely on light filling the entire housing. There are inverted wedge bulbs which focus the light out the sides of the bulb, which I purchased, but they are about on par with standard bulbs. I'm looking into multiple LED wedge bulbs, but the only down side is they are too big and would have to be installed from inside the gauge housing.

[69RavenConv 286]

Which LEDs did you buy? Keep in mind that a standard focused beam LED would most likely produce less light than a standard bulb, because the dash lights rely on light filling the entire housing. There are inverted wedge bulbs which focus the light out the sides of the bulb, which I purchased, but they are about on par with standard bulbs. I'm looking into multiple LED wedge bulbs, but the only down side is they are too big and would have to be installed from inside the gauge housing.

 

Yes, LEDs are highly directional and this can be a drawback in indirect lighting applications like an instrument cluster. The first ones I tried had a frosted diffuser lens shaped like a conventional 194 bulb. It diffused a bit but not bright enough. The new ones are straight-ahead but are so bright they do a good job. I imagine the wedge-style you describe would be even better

 

I'm using white LEDs behind the stock blue gauge lenses.

[buening 63]

These inverted wedge are similar to what I purchased. I made the mistake of buying blue ones, which have the lowest lumen rating of all bulbs. You can see from the lighted picture how the light goes out the sides rather than focused at the center.

 

What I mention above about multi-LED wedges is something I really haven't seen anyone use for our instrument clusters, but here is a 28-LED bulb that is the 194 wedge bulb style. It would have to be installed from inside the cluster with the holder on the outside, due to the increased diameter of the bulb. I don't think its tall enough to interfere with the gauges.

 

Another idea I've been throwing around is getting the LED plate style with the 194 bulb connector, such as this It is directional like standard LEDs, but you could place the plates anywhere inside the housing with some double sided tape. You could even tilt them towards the outer edges of the gauge housing, to aim the light beams towards the outer edges of the gauges.

 

These are merely brainstorms and I haven't pulled the trigger yet. I may end up doing an Autometer conversion, so the larger LEDs may not be possible.

[Black_69_FB 49]

Giving this thread a bump in case someone still needs info and/or for future searches...

 

I used the 5X LED kit from NPD, page 16 of their 2010 catalog. They claim that the rheostat will work with these. They do look MUCH brighter/better than stock to me. I can actually see the gauges very clearly now.

 

However, I can't confirm that they work with the rheostat, because my headlight switch is acting up. Specifically - I believe - the rheostat.

 

P.S. - This looks like the same kit I got from NPD (5X, blue-green):

HiPo Parts

[Black_69_FB 49]

Well, I've got a new headlight switch on the way, so hopefully I will be able to give an update toward the end of the week as to whether the LEDs dim with the rheostat or not. In the meantime I took a pic to show what they look like:

 

 

My camera isn't too good in low light conditions, they look a a bit better in person.

[Tripdawg 10]

The LEDs I bought were out of the NPD catalog, the single LED bulbs for like $25. What I have ended up doing was painting the inside of the gauge cluster a metallic silver and switching to white face gauges to get the brightness I wanted. I think I am pleased with the overall look but come to think of it I spent just as much now as I would have had on the 5X LEDs. I do have white guages now, which look pretty good in daylight.

 

I think I will steer away from trying to fabricate the dim feature once given by the Rheostat. I do appreciate the feedback though on how to possible make it work.

 

I meant to take a picture of the cluster lit up by the LEDs with black gauge faces no metallic paint on the inside, after the paint, and finally with the white gauge faces. I forgot though and now have to just take one of the finished product. I will try and get a pic and post for whomever is interested.

[Jurisd 10]

FWIW, I spend the extra $25 and bought the "5X dimmable" bulbs. And although there is a small but noticable change in brightness when using the stock rheostat, it is by no means as wide a range as you see with modern cars, or even with the incandescent stock bulbs.

 

So my advice is to avoid the brain damage of making a rheostat, since you will probably spend more that $25 in parts and aggravation, only to find out that LEDs don't dim well, regardless.

 

As a practical solution, why not use the LEDs you have, install the stock blue/green covers, and then use the white faces? Since your LEDs are "2X" and my "5X" bulbs are comfortable to view at max brightness, I would bet you will be happy with the result.

[rangerdoc 22]

Well, I've got a new headlight switch on the way, so hopefully I will be able to give an update toward the end of the week as to whether the LEDs dim with the rheostat or not. In the meantime I took a pic to show what they look like:

 

 

My camera isn't too good in low light conditions, they look a a bit better in person.

 

Did you keep the stock defusers in or did you remove them?

[Black_69_FB 49]

Did you keep the stock defusers in or did you remove them?

 

Kept them. The instructions said the bulbs were designed to give the correct color with the stock diffusers in place.

 

As a practical solution, why not use the LEDs you have, install the stock blue/green covers, and then use the white faces? Since your LEDs are "2X" and my "5X" bulbs are comfortable to view at max brightness, I would bet you will be happy with the result.

 

I agree, 5X bulbs are fine on max (to me). I see no reason to dim mine. They were dim before, that's why I went with LEDs :biggrin:

[rangerdoc 22]

Thanks! I kept mine on but accidentally threw away the instructions so I wasn't sure :)

 

I also agree with your second statement. My 5x bulbs are perfect at max. I don't see myself dimming them, but I can see how 2x bulbs might be too dull.

[ForceFed70 14]

Well, I am an electrical engineer and the short answer is that dimming LEDs in this application is not that easy.

 

Real bulbs, because they are little more than glorified resistors, can be dimmed by lowering the voltage across them, which in turn lowers the current flowing thru them. For reasons that aren't important here, LEDs don't work the same - lowering the voltage doesn't lower the current. So you have to add circuitry to lower the current in proportion to the lower rheostat voltage

 

Rangerdoc is on the right track, I suspect the expensive LEDs have a built in current regulating circuit that allow them to dim. Installing one or two real bulbs can have a marginal effect on dimming the cheap LEDs but not much.

 

FWIW, I also went with the cheap LEDS and am living without the dimming.

 

 

You're way off base here.

 

LED's don't dim quite like regular bulbs, but they still dim just fine.

 

The real reason why they don't dim properly is that the resistor value of the rheostat is all out of wack. LED bulbs use about 1/5 of the current that traditional lamps use. 1/5 of the current means that you only get 1/5 of the voltage drop across the rheostat. Instead of dropping up to 9V across the reostat, you end up dropping only 1-2 volts. If you were able to increase the resistance sweep of the rheostat, the LED's would dim just fine.

 

The fancy "dimmable" LED bulbs just draw the same current as traditional bulbs. Usually this is achieved through a combination of more/brighter LED's and a built in resistor that shunts current to ground.

 

One could fix the dimming by installing a resistor to ground (of proper wattage) to increase the current to what would normally be seen with traditional lamps. The dimming wouldnt' be linear due to the nature of LED's, but it would still work.

Edited September 24, 2010 by ForceFed70

[69RavenConv 286]

You're way off base here.

 

No, I'm not way off base. You are correct about lower current draw and reduced rheostat effectiveness, but some your conclusions are oversimplified.

 

The fancy "dimmable" LED bulbs just draw the same current as traditional bulbs.

 

I'm quite certain they don't. If they did they would be huge, or dissipate great amounts of heat. It's more likely they stack 4 or 5 LED dies in series, along with some passive resistance. The usable voltage range of an LED is very small, something like 1.5V-3V. Below that, they are off; above it they vaporize. Stacking multiple LEDs across, say 9-13V, splitting it up just right might allow some dimming. Really a poor way to do it, but maybe good enough for a car.

 

One could fix the dimming by installing a resistor to ground (of proper wattage)

 

As Danno already pointed out, adding resistance (in series, not parallel) may offer some dimming but it's still a poor solution that may or may not even work, given the quirkiness of many, many, LEDs used in combination. And adding resistors to the dash light circuit (especially the large ones required) is not easy. So I stand by my initial statement that it is not easy, and any results would probably be disappointing anyway.

[ForceFed70 14]

You're way off base here.

 

No, I'm not way off base. You are correct about lower current draw and reduced rheostat effectiveness, but some your conclusions are oversimplified.

 

The fancy "dimmable" LED bulbs just draw the same current as traditional bulbs.

 

I'm quite certain they don't. If they did they would be huge, or dissipate great amounts of heat. It's more likely they stack 4 or 5 LED dies in series, along with some passive resistance. The usable voltage range of an LED is very small, something like 1.5V-3V. Below that, they are off; above it they vaporize. Stacking multiple LEDs across, say 9-13V, splitting it up just right might allow some dimming. Really a poor way to do it, but maybe good enough for a car.

 

One could fix the dimming by installing a resistor to ground (of proper wattage)

 

As Danno already pointed out, adding resistance (in series, not parallel) may offer some dimming but it's still a poor solution that may or may not even work, given the quirkiness of many, many, LEDs used in combination. And adding resistors to the dash light circuit (especially the large ones required) is not easy. So I stand by my initial statement that it is not easy, and any results would probably be disappointing anyway.

 

Please. Have you actually played with this? Have you actually looked into the specifications of the "dimmable" LED's? I can tell you haven't because you are guessing (and wrongly) at the LED operating voltage. Blue LED's of the this type operate at 3-5V and if you don't believe me, actually try a test. They will be much dimmer when operating at 3V vs 5V. Of course the LED replacement lamps include LED's in series (dimmable or not). The ones I've looked at don't have stacked dies, they have multiple seperate LED's. The only difference between the dimmable and regular is the resistor in parallel. "Huge amounts of heat?" No more than the original incandescent bulbs.

 

I have played with this, I do have LED lighting, I have installed the resistor, and my LED's dim just fine.

 

The resistor needs to be in parallel, not in series. This is to increase voltage drop across the rheostat.

 

LED's do Dim, they just don't do so linerally like a incandescent bulb.

 

I know you are an electrical engineer but you have obviously never actually played with this stuff or looked into it closely. This is not complicated stuff and maybe you should actually give the other members a little credit instead of just assuming that we don't have a clue.

Edited September 25, 2010 by ForceFed70

[69RavenConv 286]

Fair enough, I stand corrected. You are right, I haven't played with it. I looked at it and decided it wasn't worth the effort. For the record, I'd love to see the mods you ended up doing and what type of leds you used.

[ForceFed70 14]

Fair enough, I stand corrected. You are right, I haven't played with it. I looked at it and decided it wasn't worth the effort. For the record, I'd love to see the mods you ended up doing and what type of leds you used.

 

I was too harsh. Sorry. :surrender:

 

My LED lighting was done back when they didn't make the lamp packages. I used 6 LED's where each lamp was located. 2 set's of 3LED's in parallel. The LED's were purchased from www.superbrightleds.com and were the standard component style. Back then they only sold 2 different types and they varied only by the viewing angle. I see that they now offer a much wider selection.

 

When I got everything back together, it worked great but wouldn't dim.

 

I played with different resistors (in parallel to groud) until I found a value that worked well. Unfortunately, this was about 6 years ago and I don't remember which one I settled on. I believe it was a 10ohm 15W resistor that worked best.

 

I have since bought one of the new lamp packages, but haven't installed them yet.

Edited September 25, 2010 by ForceFed70

[Tripdawg 10]

Here is the finished product.

Inner workings of the cluster painted metallic silver.

NPD 2X LED Kit - Part Number 13464-3AK

White Gauges from White Gauges.net http://whitegauges.net/products/1969%252d1970-Ford-Mustang-White-Face-Gauges.html

 

[Black_69_FB 49]

Looks good! :thumbup1:

[Black_69_FB 49]

Also - I forgot until now that I was going to post an update re: dimming the LED dash lights with the rheostat... I can't tell any difference :tongue:

[ForceFed70 14]

Looks great! I ended up painting the needles a bright yellow color so that they were more visable. The orange/red OEM color doesn't show up well under blue lighting.