Opinions on 24 Volt Instrument Lights

[tim292stro]

...It seems the older I get, the less my brain wants to work...

With the wear and tear you apparently do to yourself - I think you've earned a few "easy ways"

...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...

It won't affect the efficiency much at all - the part of the rheostat that touches the coil (which is aptly called the "wiper") is designed to mechanically clean the contact surface as it moves. If the rheostat has dead spots or the wiper isn't doing its job any more, it's best to just replace the light switch ($17 at LMC, probably cheaper elsewhere...).
[EDIT:] I wanted to point out that for low-current potentiometers like what you'd find in a stereo volume control, yes cleaning would be useful every once in a while. However, this is a higher current potentiometer (one one leg of the resistance element is hooked up so it is called a rheostat). For higher current contacts, they are designed to self clean with the power that is transmitted across the terminals. Different alloys are used with different current levels, gold/carbon/conductive-plastic for very low currents (20mA and below), copper and copper alloys for medium currents (20mA to about 100Amps), and silver and silver alloys for much higher currents (100A +).[/EDIT]

If your dash lights are dim, start with replacing the bulbs or converting them to LED - 1Watt of LED is much more light than 1Watt of incandescent (>90% of that 1Watt is infrared with an incandescent bulb). If you find that is still not enough, you can disassemble the cluster and re-paint the insides with fresh satin white (Krylon Fusion 2420) as they may have yellowed over the years of exposure to bulb heat. You have to fully disassemble the cluster, contacts and flex board to keep from covering anything important with paint. Only takes about 10 minutes to do.

 

[tim292stro]

...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 ways, 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.

"Error free LEDs" (eBay search term) should work here. If the point is to get a bright pure color out you can still do the LED. An "Error Free LED" basically puts a resistor across the whole LED circuit of nearly the same resistance as a bulb filament- and a resistor is non-directional.

 

[cpf240]

"Error free LEDs" (eBay search term) should work here. If the point is to get a bright pure color out you can still do the LED. An "Error Free LED" basically puts a resistor across the whole LED circuit of nearly the same resistance as a bulb filament- and a resistor is non-directional.

And when the current flow is reversed? I know there are bi-directional LEDs, but with the common uni-directional ones, it would have to be installed with the polarity correct to work the exciter circuit to at least get the alt charging, but would not light in the over-charge condition.

 

[tim292stro]

It won't matter. The voltage regulator gets its power from the battery+, which is the same place the gen light gets its power. If the voltage regulator doesn't take action against the over-voltage and shut off the field by letting it desaturate to regulator ground like it should, the LED or incandescent lamp will have positive voltage on both sides. Because both the regulators supply and the lamps supply are the same voltage, if the system overvolts the only way you'll know is if the voltmeter tells you that.

For a properly functioning voltage regulator, if it detected an over-voltage situation it SHOULD try to lower the drive current on the field coil of the rotor, eventually this will lower to the point where it's completely off and the lamp will light up since it's grounded through the field coil (at the current level required to light a bulb or LED the field coil is more of a wire than a strong electromagnet). Of course this also relies on the other side of the filed coil being properly "grounded" to the regulator and system ground (for the upper 12-24 alternator the isolated ground would be at +12). If you have bad brushes, or some other short (like field coil control to + terminal), there's no way for the lamp or the regulator to indicate failures or control the system.

Figured I should back this up with a graphic (PLEASE ignore the diode polarities - I have a terrible Google Images starting point). Note the Orange line is the positive supply AND the charge output from the alternator:

What the regulator is doing is watching the Diode + input from the alternator's output and varying how much power it sends to the field terminal from the Diode+ input.


I offer the Error Free LED as a potential solution as some regulators do not use the + regulator supply but rather use the idiot lamp circuit to show the ignition is turned on, and the detection circuit is not a high enough load to make the LED conduct. Simply having the resistor across the whole LED makes the ignition voltage visible and the regulator will go active.

 

[cpf240]

If that does indeed work, I'd be happy to know it, as one of these days I'll be replacing my dash lights with LEDs, and would like to do a clean sweep. I've seen many posts here saying that the LED won't work in the GEN lights, and I can understand why. This error-free LED is new to me. Thank you for the info!

 

[tim292stro]

The Error Free LEDs were originally intended for vehicles that have a bulb health check. Some vehicles (especially those with CAN busses) will blip a ~1V pulse across the bulb to see if a measureable current passed, if it did not, it'll throw the Lamp Failure Warning on the dash board. Obviously if you have an LED that doesn't draw as much power as an incandescent bulb, it'll fool the computer into thinking that the bulb is out - so they add a resistor that increases the current draw close to what a normal bulb would have done, and the computer is happy

A M416 trailer LED mod I helped a friend with, had this problem when connected to a Land Rover Discovery. In that case the pulse was 5V and was high enough to pulse the LEDs on the trailer (which would have been bad) - so we put relays as buffer between the trailer plug and the lights so that the drive voltage had to be high enough to turn on the relay (>9V) before the relay would pass power to the LEDs. Only cost two cube relays and three minutes of time to explain it to my friend (member here pfab).

The trick is to find the characteristic of the LED that is breaking the circuit design and Work-ARound it (what we call a WAR in tech).

 

[The HUlk]

Tim - 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.

If you are looking for brighter then pay attention to any brightness, intentisy, lumens, etc. rating during the new bulb/LED selection process. Also bear in mind that your dimming characteristics may change considerably with LED as opposed to incandescent type lamps.