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Wed Feb 04, 2009 9:19 am

Fattie wrote: BTW: the bulb part # is Ba7s
do a web search.... there's plenty of suppliers of the LED type Ba7s :wink:

if anyone uses the ones in the eBay AD above.. please report back on the results installed

Are there any mods that need to be made to use the Ba7s LEDs?

Wed Feb 04, 2009 11:25 am

Sun Feb 15, 2009 12:37 pm

Fattie wrote: nope

Fattie , am I correct in thinking that they will not DIM with the switch?
Marvin

Sun Feb 15, 2009 1:50 pm

correct... they would shut off at a certain "dim" point

Fattie wrote: ... I'll get one up of mine with the "stock" bulbs with the gloss yellow painted housing.. the light now has an antiqued look to it.. best I can describe it :lol: ........but is very bright

here's how mine turned out using stock bulbs...and it wasn't completely dark during this picture

Sun Feb 15, 2009 2:52 pm

If the dimmer functions through a reduction in voltage, then LEDs will dim depending on which you use. This is the information I have been given in researching my own conversion.

Sun Feb 15, 2009 2:54 pm

Any dimmer switch should dim the LEDs. The only problem is that depending on how the stock switch's internal workings are, the difference between dim and off my only be a few millimeters, which for all intents and purposes means it will not work. I will be testing this soon enough when I do mine. I'll post results on my findings when I do.

Sun Feb 15, 2009 3:01 pm

Cuog wrote: Any dimmer switch should dim the LEDs. The only problem is that depending on how the stock switch's internal workings are, the difference between dim and off my only be a few millimeters, which for all intents and purposes means it will not work. I will be testing this soon enough when I do mine. I'll post results on my findings when I do.
You and me both!

Sun Feb 15, 2009 3:24 pm

Cuog wrote: Any dimmer switch should dim the LEDs. The only problem is that depending on how the stock switch's internal workings are, the difference between dim and off my only be a few millimeters, which for all intents and purposes means it will not work. I will be testing this soon enough when I do mine. I'll post results on my findings when I do.

You have to have a potentiometer in your dimmer that has a nice range between 6 and 0 volts if you want any decent kind of dimming. I talked about this about 6 posts down from my initial my post about LED warning lights:

http://www.thesamba.com/vw/forum/viewtopic.php?t=153718&

-Andy

Sun Feb 15, 2009 7:48 pm

Thats true if you run with the resistance thats built into the LED setups that you bought. If you build the setup from scratch using a standard LED and resistance that you control things will work out different.

LEDs work different than standard incandescent bulbs. They always drop the same voltage as long as at least that much is possible. I'll start with an example of how this works with the LEDs that I will be using on my speedo, your mileage may vary(very bad pun intended). These are 3mm "Ultra Bright" LEDs which means they run at a higher voltage than "regular" Their forward, or working voltage is between 3.2 and 3.6 volts. They will be the same voltage but it varies from LED to LED due to differences in manufacturing. Their forward or working current is 20mA. Now they can run at higher and lower current, thats what we vary. 20 is chosen because it gives the maximum birhgtness at longest burn life. Any higher than that and the LED will be bright and start dimming over its life. The amount that it gets brighter is also not a useful amount.

So by using ohm's law we can find the optimum resistance to use for these LEDs: Voltage=Resistance times Currrent

Since the LED drops what I'll say is 3.5 Volts to give a nice roundish number in the range they're designed. And the voltage available is 12V we know that the resistor we add in serious with the LED is 8.5 Volts. so we have 8.5V=20ma times Unknown resistance, simple algebra gives us a resistance of 425 Ohms.

Now that we have that setup the important question is ask is what is the range of the stock dimmer switch? That range will greatly impact the brightness curve of the LED.

Since I don't know what the range of the Potentiometer is in a stock beetle(mines 40 miles away so I can't check) I'm going to say that its a 10k ohm linear pot. If someone could hook an ohm meter up to their and give me the actual numbers so I can redo the math for this that would be great. I also don't know the degrees of rotation but we'll go ahead and say that its 360. again if you have the correct answer please let me know so I can fix the information here.

What this means is that every degree you turn the knob, the resistance increases by 28 ohms. When a certain low amount of current passes through an LED it will no longer light. A dim LED will be carrying less than 1mA of current. So we do the math again to find what resistance we would want. So 8.5V/1ma gives us a 1k ohm resistance. Subtract the 425 we've already put inline and we find that for the potentiometer in your dimmer to dim these to nearly out. Now 425 divided by 28 ohms per degree, and we find that the knob has 15 degrees of rotation that are useful for us. Thats about 1/24th of the rotation of our knob. Thats not very useful, and is I think what makes people think that the LEDs don't dim in a stock instrument cluster.

Again if anyone can provide me the accurate numbers that I need above, I'll recalculate this so that its not based on my educated guesses.

Sun Feb 15, 2009 7:55 pm

glutamodo wrote: You have to have a potentiometer in your dimmer that has a nice range between 6 and 0 volts if you want any decent kind of dimming. I talked about this about 6 posts down from my initial my post about LED warning lights:

http://www.thesamba.com/vw/forum/viewtopic.php?t=153718&

-Andy

I read your posts on the subject. The question is: how do we know if our dimmers qualify?

Oh, Andy, I did end up receiving the speedometer I bought. I've been doing the clean up/prep work for the LED conversion, and... Good news! My rubber holdie thingies for my gels are in good shape! Took out the old gels, bought the folder tabs, and now just need to find a store that isn't out of stock on 1000 grit sandpaper so I can scuff them up. 600 grit and scouring pads are way too course. I might try some #0000 steel wool just for S&Gs but I don't have high hopes.

Lastly, I followed your instructional on dismantling and other misc. speedo lore. I'm to the point now of reseting my odometer. For the record, I have a brass gear that runs along the main drive gear. You mentioned popping out the pin that holds the odometer gears in place. I don't see what is holding it in, but do we just push it out with force? Should it be turned a certain way first? Pushed in a particular direction? I'll put plenty of tape along the gears to ensure they don't go flying, just in case, but before I go bending, manhandling, or otherwise beaking anything :oops: , I need to understand how this shaft slips out.

Thank you, friend Andy!

Sun Feb 15, 2009 8:08 pm

Cuog wrote: A bunch of stuff!
:shock: ... Whoa.

Sun Feb 15, 2009 8:10 pm

'69Custom wrote: Cuog wrote: A bunch of stuff!
:shock: ... Whoa.

I'm currently in school majoring in Electrical Engineering, my future depends on knowing how to do all that stuff, and tons more :roll:

Sun Feb 15, 2009 8:12 pm

Cuog wrote: I'm currently in school majoring in Electrical Engineering, my future depends on knowing how to do all that stuff, and tons more :roll:
And our projects benefit greatly from it! :D

Sun Feb 15, 2009 8:17 pm

Anyone know how many bulbs are in a 73 Super speedo? Thanks.

Sun Feb 15, 2009 8:20 pm

GatorJZ pm puddlepirate, he's got an extra laying around, but if I recall correctly, there are 2 that are for backlighting, plus for the warning lights.

Sun Feb 15, 2009 8:54 pm

GatorJZ wrote: Anyone know how many bulbs are in a 73 Super speedo? Thanks.
I'm thinking a total of nine, counting the often unused ATF indicator.

Sun Feb 15, 2009 11:52 pm

GatorJZ wrote: Anyone know how many bulbs are in a 73 Super speedo? Thanks.

My '73 Super speedo has 6... if I remember right! :oops:

Mon Feb 16, 2009 12:05 am

mine has 6 to but we dont have ATF or defroster lights here

but one thing to bear in mind, u CANT use an LED for the alternator light
LEDs dont have enough of load to get the alt circuit charging and its a good idea to stay regular bulb for the oil light to as LEDs are either on or off, they dont glow faintly which is what oil lights can do sometimes

ive just been thro and replaced every single bulb in my bug cept for the oil and charge lights and the 2 h4 headlights
aside from those everything else in my car is now LED and the load thats gone off my electrical system now is incredible

Mon Feb 16, 2009 9:52 am

Yes you can use an LED for the alternator light. If you need more of a current draw for that circuit you can add a resistor in parallel with the LED. VW did use LED warning lights on watercooled models after all and their circuit panels have resistors in them - each LED warning light on the dash had one in series to protect the LED (which was just a plain LED and not a 12V component back then), but the alternator LED spefically also had a 2nd resistor in parallel with the other LED and resistor for more of a current draw to that circuit.
-Andy

Mon Feb 16, 2009 9:58 am

Buggin_74 wrote: mine has 6 to but we dont have ATF or defroster lights here

but one thing to bear in mind, u CANT use an LED for the alternator light
LEDs dont have enough of load to get the alt circuit charging and its a good idea to stay regular bulb for the oil light to as LEDs are either on or off, they dont glow faintly which is what oil lights can do sometimes

ive just been thro and replaced every single bulb in my bug cept for the oil and charge lights and the 2 h4 headlights
aside from those everything else in my car is now LED and the load thats gone off my electrical system now is incredible

LEDs do light dim. They are NOT on/off devices. The reason they're not good for a dimming circuit in a VW is because of the way they work in comparison to an incandescent bulb. An incandescent will vary its brightness very well when you adjust its voltage. An LED however needs its current adjust to control brightness. An incandescent draws a lot more current than an LED as well.

Now the reason that an LED is not favorable in things like the alt circuit and oil light is because both of those circuits were designed with the characteristics of an incandescent bulb in mind(obviously since LEDs didn't exist then)

When modifying a circuit to utilize LEDs it is important to keep in mind what the circuit originally did to make sure that when you put in extra resistance and limit the current flow, that the rest of the circuit will still operate properly.