Instrument cluster lights are dim

[BeMyWay]

As we all know...3rd time is a charm....Are LED's dimmable?  

 

I just placed a mat on the ground for my knees and reached up under the dash and found the nuts holding the assembly and the speedometer cable and pushed it out.  

 

Edited March 14, 2017 by BeMyWay

[Tsingtao_1903]

It's depends.

 

LEDs are current sensitive devices.  There is a minimum voltage threshold where they will power up.  There is also a maximum voltage threshold where they will burn out.  Typically, lowering the current will cause the LEDs to be less bright; increasing the current will cause the LEDs to be more bright.  With that said, whether they are dimmable or not depends on the power supply and/or the driver circuit or chip.  I have replaced all incandescent bulbs in my '02.  They were all dimmable.

 

Below is the chart showing the typical relationship between Ir(forward current) and brightness (relative luminous intensity).  The higher the current (resulting from the higher voltage - this relationship is dependent on the power supply or the driver chip), the brighter the LED up to a point. 

Edited March 14, 2017 by Tsingtao_1903

[Mike Davis]

Thanks for the feedback. Now how many l.e.d.s are in the cluster, what light # and where to order?

 

[beammmer]

14 minutes ago, Tsingtao_1903 said:

It's depends.

 

LEDs are current sensitive devices.  There is a minimum voltage threshold where they will power up.  There is also a maximum voltage threshold where they will burn out.  Typically, lowering the current will cause the LEDs to be less bright; increasing the current will cause the LEDs to be more bright.  With that said, whether they are dimmable or not depends on the power supply and/or the driver circuit or chip.  I have replaced all incandescent bulbs in my '02.  They were all dimmable.

 

Below is the chart showing the typical relationship between Ir(forward current) and brightness (relative luminous intensity).  The higher the current (resulting from the higher voltage - this relationship is dependent on the power supply or the driver chip), the brighter the LED up to a point. 

Good to know, I think. The reply still doesn't answer the question.

 

LEDs in our cars = dimmable= yes/no?

 

Don

 

 

As questioned before, are the LEDs dimmable in our cars?

 

Don

 

[Tsingtao_1903]

15 minutes ago, beammmer said:

LEDs in our cars = dimmable= yes/no?

It depends on how the specific LED bulb is constructed.  

 

In my case, I asked the sellers before I purchased;  They were all dimmable.

[Tsingtao_1903]

On 3/14/2017 at 6:39 PM, Mike Davis said:

Now how many l.e.d.s are in the cluster, what light # and where to order?

If memory serves, 4 bulbs for instrumentation lighting.  1 for the brake light, 4 for the indicator lights.

 

In my case, I used 5 blue LEDs: 4 for the instrumentation lighting, 1 for the high beam. 1 amber for ignition on, 1 red for charging and 1 for the brake light indicator, 1 green for turn signal indicator.

 

Search for T10 wedge LED.  Ask the sellers and go from there.

 

Good luck.

Edited March 16, 2017 by Tsingtao_1903

[Healey3000]

30 minutes ago, beammmer said:

Good to know, I think. The reply still doesn't answer the question.

 

LEDs in our cars = dimmable= yes/no?

 

Don

 

 

As with many things, the answer is "that depends".

 

LED's like to be pulsed (PWM), not driven DC.  To dim them, you lower the duty cycle.  In our cars, there is no provision for PWM, just a rheostat that lowers the voltage to the bulbs.

 

If the illumination bulbs are wired in parallel, as they most probably are, simply replacing them with LED's can create issues.  One should always put resistors in series with LED's if they are to be ganged in parallel.  The reason being that as LED's warm up, their forward voltage (Vf) drops.  Since LED's are not matched in their Vf values, the one with the lowest Vf will draw the most current.  As that happens, it warms up more than the rest and its Vf drops even further.  You see where this is going...

 

Using the stock rheostat is fine if you can put resistors in series with each LED.  While it's not the most efficient way to drive the LED's, in practical terms, it ought to work just fine.  Make sure you know the resistance of the rheostat, and that at the max brightness position it isn't going to apply 12 volts directly to the LEDs.  That may burn them out.

 

I would suggest putting all the illumination LED's in series, if that's possible with the cluster.  A single resistor to protect them and you're good to go.  LED's in series have the added advantage of seeing the same current, yielding more uniform brightness.

 

Therefore, it depends :-)

[Tsingtao_1903]

1 minute ago, Healey3000 said:

If the illumination bulbs are wired in parallel, as they most probably are, simply replacing them with LED's can create issues.  One should always put resistors in series with LED's if they are to be ganged in parallel.  The reason being that as LED's warm up, their forward voltage (Vf) drops.  Since LED's are not matched in their Vf values, the one with the lowest Vf will draw the most current.  As that happens, it warms up more than the rest and its Vf drops even further.  You see where this is going...

Absolutely correct.  I did not even know where to begin to explain this.  

[rmoore007ri]

Back to your original question. The original dash bulbs were type  2821  and easy to find at places like AutoZone.  They have a Sylvania two-pack long life version for $4.99.  Replace them all at once . . .

[rmoore007ri]

Automotive LEDs have an internal resistor to limit the maximum continuous current.  A typical max current rating is 35 ma. A typical internal resistor is around 300 ohms. That is the only way they can be sold as 12 VDC bubs.
 

The max current is  specified as typically something like 30 ma.  BUT this can be time averaged.  In an instrument we manufacture we run pulses of current MUCH higher than that using a pulsed constant current source.  We then use frequency modulation (rather than the much more common pulse width modulation) for technical reasons. We use a pulsed constant current source (a single point on the curve provided by Tsingtao_1903 above) to achieve luminous linearity with frequency over a broad range.  (We work with frequencies up to 300 KHz . . .)

The big problem with LEds is getting rid of the heat generated by high currents. 

 

ymmv, mcd

[rmoore007ri]

You can find "wedge base" LED bulbs with resistive current limiting and polarity protection from vendors like Allied. See
http://www.alliedelec.com/jkl-components-corporation-le-0504-01w/70314433/?mkwid=sFQxBG5rL&pcrid=30980760979&gclid=CNr6h-mq19ICFQ-Bswode9AGmA

 

bob

[Healey3000]

1 hour ago, rmoore007ri said:

You can find "wedge base" LED bulbs with resistive current limiting and polarity protection from vendors like Allied. See
http://www.alliedelec.com/jkl-components-corporation-le-0504-01w/70314433/?mkwid=sFQxBG5rL&pcrid=30980760979&gclid=CNr6h-mq19ICFQ-Bswode9AGmA

 

bob

Excellent.  I didn't know such existed.  Thanks!

[Tsingtao_1903]

1 hour ago, rmoore007ri said:

You can find "wedge base" LED bulbs with resistive current limiting and polarity protection from vendors like Allied. See
http://www.alliedelec.com/jkl-components-corporation-le-0504-01w/70314433/?mkwid=sFQxBG5rL&pcrid=30980760979&gclid=CNr6h-mq19ICFQ-Bswode9AGmA

 

bob

So, are they dimmable?

 

 

 

 

Just kidding.

[rmoore007ri]

So I just ordered a handful of these LED "wedge" LED lamps and will report back in a bit on fit and dimmability (is that even a word)

(good thing I have three spare clusters to play with)

:-)

 

[BeMyWay]

Thanks rmooredoublenought7ri aka bob...appreciate your advice and for checking out the "dimmability" of these  LED bulbs. 

 

Edited March 15, 2017 by BeMyWay