Opinions on 24 Volt Instrument Lights

[Sharecropper]

An inherent problem with this model of GM trucks and blazers has always been the less-than-ideal lighting of the instrument panel. There have been numerous threads on SS and other sites regarding ways to increase the brightness, all with varying levels of success. One method which seems to provide the best solution so far is the replacement of the incandescent bulbs with LED bulbs. A while back I was reading an unrelated article about replacing the OEM 24 volt rear light assemblies of military trailers and other vehicles, which are incandescent, with newer-technology LED assemblies. The article stated that LED bulbs would work with 24 volt or 12 volt without any issue, the only difference would be the light output of the LED itself. Then it occurred to me, would it be possible to replace the incandescent CUCV instrument and accessory bulbs with LED bulbs, then feed the instrument lighting circuit from the 24 volt outlet on the fuse panel?

Has anybody ever thought about this? If LED bulbs can indeed handle 24 volts, why not increase the illumination by feeding the circuit with 24 volts? Of course, only the illumination bulbs could be powered with 24 volts, as the indicator bulbs for the Oil, Temp, GEN 1 & GEN 2, 4WD, etc would stay on their specific circuits with their specific bulbs. The headlight switch rheostat would still adjust the brightness of the LEDs as required, as well as powering the accessory light over the transmission tunnel.

If this would work, it could be the final solution to one of the design deficiencies of these trucks. I invite comments from all the master-minds on this site to chime in.

 

[MarcusOReallyus]

Then it occurred to me, would it be possible to replace the incandescent CUCV instrument and accessory bulbs with LED bulbs, then feed the instrument lighting circuit from the 24 volt outlet on the fuse panel?

Possible? Yes, possible. Theoretically.


Easy? No, I don't think so. You'd have to change all of the instruments, too. Think about changing a fuel gauge, for example. And it gets worse. See below.

If LED bulbs can indeed handle 24 volts,

Some can. It depends on the packaging. All LEDs must have the correct resistor in place to limit the current, or it will burn out almost instantly.

why not increase the illumination by feeding the circuit with 24 volts?

LEDs only need a few volts (2v - 4v) to operate at full brightness, so I can't see any advantage in increasing the supply voltage. At 12v, it's already more than needed to get full brightness. You still have to drop the current down with the proper size resistor to keep from frying it.

Of course, only the illumination bulbs could be powered with 24 volts, as the indicator bulbs for the Oil, Temp, GEN 1 & GEN 2, 4WD, etc would stay on their specific circuits with their specific bulbs. The headlight switch rheostat would still adjust the brightness of the LEDs as required, as well as powering the accessory light over the transmission tunnel.

If this would work, it could be the final solution to one of the design deficiencies of these trucks. I invite comments from all the master-minds on this site to chime in.

I haven't looked at the schematic of the dash panel, but I suspect the lights are run in parallel. That's not recommended with LEDs (because of the need for current limitation), so you'd wind up completely re-wiring the dash.


I think this would be far more trouble than its worth. Putting in a few extra 12v LEDs would likely be far easier.


Some quick reading:

http://electronicsclub.info/leds.htm

Avoid connecting LEDs in parallel!

Connecting several LEDs in parallel with just one resistor shared between them is generally a bad idea.
If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it. Although identical LEDs can be successfully connected in parallel with one resistor this rarely offers any useful benefit because resistors are very cheap and the current used is the same as connecting the LEDs individually.
If LEDs are in parallel each one should have its own resistor.

 

[ralph3162]

I used the 6" led strips from Walmart that are 12v stuck them strategically on the back of instrument cluster and made a big difference. That being said it was easy because I have a 24v and separate 12v system in my deuce.

 

[98G]

LEDs only need a few volts (2v - 4v) to operate at full brightness, so I can't see any advantage in increasing the supply voltage. At 12v, it's already more than needed to get full brightness. You still have to drop the current down with the proper size resistor to keep from frying it.



m

Not to derail the thread, but here's some experience I've had with LEDs.

I bought 12v LED tow lights from the tractor place. I've used them on my (obviously 12v) dodge ram, and I've also hooked them 1 wire at a time into the 12 pin connector on 5ton trucks.

They are noticeably brighter on the 5ton trucks (receiving 24v).

If minimal voltage is all that's required to reach maximal brightness, then this shouldn't happen.

Observed phenomena trump theory every time

In all seriousness, educate me....

 

[True Knight]

Not to derail the thread, but here's some experience I've had with LEDs.

I bought 12v LED tow lights from the tractor place. I've used them on my (obviously 12v) dodge ram, and I've also hooked them 1 wire at a time into the 12 pin connector on 5ton trucks.

They are noticeably brighter on the 5ton trucks (receiving 24v).

If minimal voltage is all that's required to reach maximal brightness, then this shouldn't happen.

Observed phenomena trump theory every time

In all seriousness, educate me....

If they are 12v only lights, then they are not wired to handle more than 12v. So 24v will make the LEDs burn brighter, however the life of the LED will be greatly reduced.

If the light is designed to run on 12v or 24v (usually says something like 9-26v) then the lights are wired with the proper set up of voltage regulators to make sure the LEDs don't get too much voltage. If you take these same 24v rated LED lights and feed them with 36 volts, for example, they will burn much brighter as the 12v LEDs being given 24v did, again with greatly reduced bulb life.

 

[True Knight]

And as MarcusOReallyus said, LEDs only need a few volts to run at their best efficiency- bulb brightness + bulb life.

Have you ever seen the OEM led lights on vehicles and a section of LEDs are out? This is because it's cheaper to wire in a few bulbs in series and then a smaller resistor is used to lower the remaining voltage not used by the LED bulbs. For example, if each LED needs 3.2 volts to operate at it's full potential and you are running 12v to the circuit, then you could run 3 LEDs in series and the proper size resistor to take up the extra 2.4 volts. However with this wiring type, if one bulb goes out the other 2 will soon follow. It gets a lot more complicated than that, but that's a whole other level of electronics.

 

[The HUlk]

It gets a lot more complicated than that, but that's a whole other level of electronics.

It's really pretty simple after the design and it's intent are understood.

As was mentioned LEDs require a resistor in the circuit to limit the amount of current(power) they draw. If they draw too much they will will burn out.

When a large number of LEDs are used they are placed into seperate series circuits(banks) of say three or five LEDs as an example. Each bank uses a single resistor which reduces the number of resistors required. This reduces cost and space required on the circuit board allowing for miniturization.

If any part of a bank goes bad, such as a solder joint(most common), or component failure then the entire bank will go out due to lack of a complete circuit. This is why you typically see sections of LED strips go out rather than individual LEDs.

 

[The HUlk]

There are replacement "bulbs" available for automotive applications that have LEDs and resistors built into them. You just swap them out like you would an incandescent type bulb.

 

[MarcusOReallyus]

Observed phenomena trump theory every time

Only if you understand what you are observing.


Since a fixed-value resistor is used to drop the current down for 12v operation, putting 24v to it will cause more current to flow, thus giving you a brighter light, and (as mentioned) shortening its life.


But since the 12v is already way more than is needed, why bother putting 24v in there? Just use your existing 12v and use a smaller resistor, if you don't mind burning out the LEDs sooner.


But really, the best answer is right here:

I used the 6" led strips from Walmart that are 12v stuck them strategically on the back of instrument cluster and made a big difference.

 

[True Knight]

It's really pretty simple after the design and it's intent are understood.

As was mentioned LEDs require a resistor in the circuit to limit the amount of current(power) they draw. If they draw too much they will will burn out.

When a large number of LEDs are used they are placed into seperate series circuits(banks) of say three or five LEDs as an example. Each bank uses a single resistor which reduces the number of resistors required. This reduces cost and space required on the circuit board allowing for miniturization.

If any part of a bank goes bad, such as a solder joint(most common), or component failure then the entire bank will go out due to lack of a complete circuit. This is why you typically see sections of LED strips go out rather than individual LEDs.

Yup, that's what I was attempting to say!

 

[latvius]

I changed mine to LED and am glad I did not choose the brightest ones because it is plenty bright. About the only thing I might still do is add a strip at the heater controls as it only has the one bulb.

The picture is at dusk so at night if they were any brighter they would be irritating.

 

[True Knight]

I changed mine to LED and am glad I did not choose the brightest ones because it is plenty bright. About the only thing I might still do is add a strip at the heater controls as it only has the one bulb.

The picture is at dusk so at night if they were any brighter they would be irritating.

Any specific brand of bulb or were they generic ones?

 

[tim292stro]

I missed this thread this weekend. Nuts.

So Sharecropper, I have a solution for you. Yes, LEDs require a specific voltage to overcome the semiconductor barrier, but once they get past that threshold they will conduct power to their own destruction. As others have said you need something to limit the current - a series resistor is the most comon in cheap lights - the Omni-volt type LED fixtures you were asking about use a current regulator to limit the current through an LED or series LED string.

This type of requlator will vary the amount of voltage it "consumes" in order to regulate the circuit current to the set-point. A regulator like the CL220 will regulate a cicuit to 20mA (one of the most comon low power LED currents) and doesn't require any othe external parts. A device like this means you can run the LED from any voltage between the foward voltage of the regulator+LED to the power disipation limit of the regulator itself (varies by device package).

As it happens I am planning on doing a revesible mod to my M1009 to allow for white LED light in service mode and NVIS-A Green in blackout mode. Just bought sockets to modify so I don't screw with the factory flex-circuit. Regulator gets soldered into the socket, and the LED gets soldered and glued to the top of the socket second circuit gets wired through the back of the socket.

I'll be posting that effort in my ride's thread when I get to that.

 

[latvius]

Any specific brand of bulb or were they generic ones?

This is what I ordered from superbrightledsDOTcom

QTY DESCRIPTION PRICE AMOUNT
11 WLED-G-120: Green 120 Degree $1.39 $15.29
1 WLED-A-120: Amber 120 Degree $0.79 $0.79
5 WLED-R-120: Red 120 Degree $0.79 $3.95
5 WLED-W-120: Cool White 120 Degree $1.39 $6.95
17 T3.25S-TW: T3.25 Socket $1.19 $20.23
1 BA9S-G-120-12VAC: Green 120 Degree 12V $1.98 $1.98
1 67-G15: Green $6.95 $6.95

 

[Recovry4x4]

I've pondered may different solutions on this but I'm going to try a different route here soon. I will be hot gluing EL Wire to the back of the metal light deflector that surrounds the gauges. Problem with EL is it's not that easy to dim. Should be an interesting experiment.

 

[tim292stro]

EL is as easy to dim as LEDs - use PWM.

EL is driven by AC voltage - usually around 90-120V AC, and the light gets better with higher frequency. Incidentally you can build a circuit that generates both an AC pulse (square wave) and does PWM with only a few parts. You can do a 555-timer based oscillator to generate the AC signal which you send to one leg of a transformer coil, and then use the pulse output to drive a counter, then with the outputs of the counter you can use a resistor ladder on the outputs to generate a saw-tooth wave (ramp) which you compare to a potentiometer voltage in order to drive a FET on the low side of the transformer coil. The transformer steps up the voltage, and the comparator will turn on and off when the voltage generated by the resistor ladder goes above or below the voltage set by the potentiometer. This simple circuit will stop output pulses when the saw-tooth signal gets higher than the dimmer set-point.

I'll draw up a full schematic later today when I have a moment. You can adjust the frequency of the whole circuit by speeding up the 555-timer circuit, and you get essentially what ever bit-depth of dimming your counter IC supports (and you can daisy chain them to get more).

For instance an 8-bit counter will give you 255 levels of brightness. The trick here is running the counter at a high enough speed to not see flicker, you can't really see a TV's individual frames at 60Hz, so double that (120Hz) * 256 = 30,720Hz or 30.72kHz. That's above the frequency of sound so you wouldn't likely hear the whistle of the EL either - you just need to make sure the transformer is rated for 30-40kHz. They make those for switching power supplies so they are easy to get.

 

[Sharecropper]

EL is as easy to dim as LEDs - use PWM.

EL is driven by AC voltage - usually around 90-120V AC, and the light gets better with higher frequency. Incidentally you can build a circuit that generates both an AC pulse (square wave) and does PWM with only a few parts. You can do a 555-timer based oscillator to generate the AC signal which you send to one leg of a transformer coil, and then use the pulse output to drive a counter, then with the outputs of the counter you can use a resistor ladder on the outputs to generate a saw-tooth wave (ramp) which you compare to a potentiometer voltage in order to drive a FET on the low side of the transformer coil. The transformer steps up the voltage, and the comparator will turn on and off when the voltage generated by the resistor ladder goes above or below the voltage set by the potentiometer. This simple circuit will stop output pulses when the saw-tooth signal gets higher than the dimmer set-point.

I'll draw up a full schematic later today when I have a moment. You can adjust the frequency of the whole circuit by speeding up the 555-timer circuit, and you get essentially what ever bit-depth of dimming your counter IC supports (and you can daisy chain them to get more).

For instance an 8-bit counter will give you 255 levels of brightness. The trick here is running the counter at a high enough speed to not see flicker, you can't really see a TV's individual frames at 60Hz, so double that (120Hz) * 256 = 30,720Hz or 30.72kHz. That's above the frequency of sound so you wouldn't likely hear the whistle of the EL either - you just need to make sure the transformer is rated for 30-40kHz. They make those for switching power supplies so they are easy to get.

Tim - Wow. Your level of technical expertise is light years ahead of mine. I sincerely appreciate your comments and hope that some readers can use the information you provided.

Based on all the comments, I have decided to simply install 12 volt LED bulbs in my instrument lighting sockets. It seems the older I get, the less my brain wants to work. I do have a question for you though - do you think cleaning the rheostat in the light switch would affect the efficiency of the dash lights? I catch myself wanting to turn that darn knob just a little further each time to increase brightness.

Again, thanks for your comments.

 

[Sharecropper]

This is what I ordered from superbrightledsDOTcom

QTY DESCRIPTION PRICE AMOUNT
11 WLED-G-120: Green 120 Degree $1.39 $15.29
1 WLED-A-120: Amber 120 Degree $0.79 $0.79
5 WLED-R-120: Red 120 Degree $0.79 $3.95
5 WLED-W-120: Cool White 120 Degree $1.39 $6.95
17 T3.25S-TW: T3.25 Socket $1.19 $20.23
1 BA9S-G-120-12VAC: Green 120 Degree 12V $1.98 $1.98
1 67-G15: Green $6.95 $6.95

Latvius, would you be so kind as to explain the purpose of the different color bulbs and their location in the instrument panel?

Thanks in advance.

 

[latvius]

Latvius, would you be so kind as to explain the purpose of the different color bulbs and their location in the instrument panel?

Thanks in advance.

Sure, I got the different colors to match the color of the indicator. So green turn indicator gets a green light bulb. I realize I did not need to do this but since I had a choice of color I think it is a good idea. Also I changed the dash overall color to green, I like it better than the original white.
Also FWIW I can't remember if those sockets actually worked, I remember buying some that were too small but I can't remember if those were from ebay or superbrights.

Also changing the Gen 2 to an LED did not work for me, the batt's wouldn't charge so I kept the original bulb in.

 

[cpf240]

...Also changing the Gen 2 to an LED did not work for me, the batt's wouldn't charge so I kept the original bulb in.

LEDs will not work in either GEN light position. This will cause problems with the exciter circuit, usually resulting in no charge from the alt. LEDs are Diodes, so only allow current flow in one direction. The exciter circuit flows both was, so to speak, depending on which side has the higher potential. Thus the GEN light comes on when there is no charge, or if there is an over-charge condition.