Attn Bob M ~ Super C wiring/Charge Indicator Lights

Hello All,

I've recently got around to installing an I9 Dash on my Super-C, to house my charge indicator light and hour meter. Since I don't really like the looks of the rather large, automotive-style bulb that was on the tractor when both I and the previous owner (TractorSam) purchased it, I decided that I'd do something about it. I work with LED's a lot, and figured an LED Indicator would work just wonderfully in this situation..

Looking at Bob M's wiring diagram #5, I see that I need to have a ~200mA draw across that bulb. It's my understanding that the automotive-style bulb thats in there now is one of the recommended ones thats supposed to draw about 200mA. The LED I'm working with is 25mA and 2.1V, so I calculated that I needed a 470-ohm resistor to allow the LED to survive 13.4V.

When I fired the tractor up tonight to test everything out, I noticed that, despite me throttling up to activate the alternator output, the LED stayed lit. I shut it down, and started it again, and noticed that the LED stayed lit even after the automotive-style indicator bulb had shut off.

Anyone have any helpful hints or suggestions? I like to think I'm decent with electronics, but events like this sort of leave me standing there thinking "Wha?".

Thanks everyone!
AR

I think Bob has some data concerning just how many amps of current flow is required to excite an alternator, buttttttttt I can tell ya one thing till him or Jim arrives, an LED may be??? wayyyyyy toooooooo high in resistance (i.e. it dont allow sufficient current flow to excite the alternator) and thats why a regular lower resistance incandescent bulb is used in an alternators excitation circuit. Some use a diode there but I prefer at least a 10 ohm resistor to limit current and a small incandescent bulb limits current even further buttttttttttttt Im afraid an LED is simply too high in resistance such that theres NOT ENOUGH current flow.....

Im sure Bob M or Jim can give you more exact specs or resistance or current values but if she fails to excite using an LED you may have to switch to a small incandescent indicator light.

It dont take much current to make an LED glow, maybe thats why it stays lit buttttttt still if its wired off the Ignition switches IGN terminal or the coils input there shouldnt be any voltage present with the switch off so it shouldnt glow regardless IFFFFFFFF all is wired correct and the alternator is okay

Sure its wired correct???????????

John T

Andrew - John T's identified the problem: The LED does not draw enough current to "turn on" the voltage regulator. (It takes a minimum of about 200 ma to turn the regulator....)

Solution is to add a bypass resistor wired in parallel with the LED/470 ohm resistor. The parallel resistor should have a resistance between about 12 and 40 ohms, and should be rated for at least 5 watts.

Or...wire a #168 indicator lamp in parallel with the LED/470 ohm resistor. Then hide the bulb inside the ammeter box. A bit crude perhaps - but it will work!

Bob,
Thanks for the input. I am unsure exactly what automotive bulb I have, though as I said, it worked in the past, so I figure it's suitable. It's currently still inside the box, in this case, a dash off an I-9...the LED is just a "prettyification" for a more finished look. The Automotive bulb still exists, and the LED is wired in parallel with it.

Like I said, this has me stumped...I figure it should work perfectly as I have it wired. I was getting cold, so I didn't troubleshoot tonight. Thats my first step tomorrow. I figured I'd ask here and see what people thought the problem might be. Since your widely respected as a Farmall Wiring Guru, I figured this would be right up your alley.

Thanks again!
AR

Would placing a 10 or 20 Ohm resistor, parallel to the diode, help?
Just a thought. Hendrik

Yep, cuz the result of two resistors in paralell is less then either, so if say a 90 ohm is in paralell with a 10 ohms the result is

90 x 10 / 100 = 9 ohms

The lowered resistance should then allow sufficient current to excite the alternator and the LED in paralell with the resistor makes up a a current divider, so when the alternator isnt producing voltage the current out of the switch will flow thru thAT current divider on its way to the alternator and lite the lamp assuming its sufficient enough current..... Buttttttttttt then when the alternator gets excited there will be too low voltage across that LED and it should go out.......

I think thats right?? The wife is callin me to breakfast and Im in a hurry lol if Im all wet (wont be first or last time) Bob can correct my errors........

John T

As John T and Bob M indicate it is the ability to pass some 200 Plus MA on the wire that counts. To do it place the 10 ohm resistor in the wire. (the charging system will work as is this way. To see a LEd indicator light on the panel, measure the volts across the 10 ohm resistor with the key on and tractor not running. This dropped voltage will be what your LED will see if hooked across it Use appropriate resistance to keep it below its max operating voltage.
When the tractor is stopped, the alternator terminal is electronically ground. Lighting the light when 12v is placed on it by turning on the ignition. When it is effectively excited, the regulator internal to the Alt. puts charging voltage on that terminal (~14volts are now on both sides of the bulb, or resistor) no flow, alternator runs and will continue to do so until its output goes to zero when stopped. Then the #1 terminal goes to ground again.

If the resistor is not used, (or a diode is used and installed backwards) the 14 volts of the alternator will back feed the ignition switch, making the ignition stay on, not letting it shut off. Thus the resistor/lamp/diode. is needed. JimN

Bob,
Do you have a simple wiring diagram for a 1957 International 650 Diesel or a source other then the manuals which are sometimes hard to make out?
Thanks!
KJ