Bodywork, Paint, Interior, Trim, & Wiring

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rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

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Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 19, 2014 06:35PM

Take a look at the attached diagram. For those who weren't around when I wired my car, I have 12V power going to the ground pin on the headlights lights & then I switch ground to control headlights on/off & high beam/low beam per the diagram.

I've had a blue LED for high beam indicator but it's never worked right. I need to get it working because my inspection is expired & they won't pass me again w/o fixing it. Since I had to take the dash off to get at the wiring, I got a bi-color LED & want to wire it so it comes on green when the low beams are on; blue when high beams are on.

I didn't draw the resistors, but I have the right resistors on the LED for it to work with 12V and it works fine if I direct wire it to the battery.

"Logically" it seems like the LED wiring (circled with the black dotted line circle at the bottom of the picture) should work... but, it doesn't so I'm obviously missing something. What's happening is the LED lights up green when I first turn the headlights on. When I flip to high beam, green stays lit & blue comes on. When I flip back to low beam, both green & blue stay lit. Anyone see why that would occur?
Headlight wiring Diagram.jpg


63BlueMGB
Nick B
Kansas City, Mo.
(96 posts)

Registered:
01/16/2011 05:17PM

Main British Car:
1963 MGB

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Re: Why doesn't this LED circuit work?
Posted by: 63BlueMGB
Date: April 20, 2014 07:23AM

To better answer you question I need to see how and were the resitors are hooked into the Circuit


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 20, 2014 09:20AM

Hi Nick - I didn't draw it originally because it's a bit more complex, but here it is. Note that:

a) the forward voltage & forward current for the green & bue legs are the same. They are different
for the red leg hence the extra resistor on the red leg of the fan circuit.

b) The LED's all work properly wired as shown when not tied into the headlight circuit. In other words,
with the ground wired direct to my battery. I can connect & disconnect any combination of the color
leg annodes to the + side of the battery and the LEDs light &/or turn off as expected.
And, I can adjust the intensity (within a reasonable range) with the potentiometer.

c) The fan LED is working properly in the car. Only the headlight side is giving me grief.
LED Wiring diagram.jpg



Edited 1 time(s). Last edit at 04/20/2014 09:23AM by rficalora.


63BlueMGB
Nick B
Kansas City, Mo.
(96 posts)

Registered:
01/16/2011 05:17PM

Main British Car:
1963 MGB

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: 63BlueMGB
Date: April 20, 2014 02:40PM

Hi Rob-

While I am not an expert on wiring and LED stuff but it appears there is more current on the side of the LED so it is keeping your relay closed. To overcome that current you might try hooking a resistor in line with your controlling ground and switch to pull that relay back open, when you switch from hi to low or vice versa. I Think that the Red works okay because you have a bigger resistor on that leg when it switches from hi to low speed. You could check the Milliamps on those circuits with a multimeter to confirm this when it goes high to low before trying my suggestion.



Edited 2 time(s). Last edit at 04/20/2014 02:45PM by 63BlueMGB.


flyinlow
Kevin .
Elko NV
(84 posts)

Registered:
01/25/2011 04:52PM

Main British Car:
1964 Spitfire Ford 5.0

Re: Why doesn't this LED circuit work?
Posted by: flyinlow
Date: April 21, 2014 06:52AM

You most likely have diode suppressed relays so try switching terminal 85 & 86 since they are polarity sensitive and wired reverse of standard.

If the led lights correctly with relays bypassed then that part should be fine. No current is needed to open the relay, an internal spring opens the circuit and the coil closes it. Typical Bosch type relays don't care what's down stream from them on the load side balanced or not as long as iit's not overloaded which an LED wouldn't be able to do.



Edited 1 time(s). Last edit at 04/21/2014 07:36AM by flyinlow.


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 21, 2014 10:11PM

I swapped 85/85 but that didn't change anything. Interestingly, I measure 12V at 86 on the headlight relays when the headlights are off. That doesn't make sense to me. See the diagram below where I've simplified it down to just the low beams.

I also measure 12V on the 87's of the headlight relays which, in hindsight, does make sense I think... Since the headlights are filaments connecting positve & negative, the 12V passes from the hot lead to the headlights, through them, and on to 87 on the relay. I'm wondering if that is somehow part of the problem?

Thoughts?
Headlight - low beam only.jpg



Edited 1 time(s). Last edit at 04/21/2014 10:16PM by rficalora.


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 21, 2014 11:51PM

OK, ignore that last post... thought about it some more & it makes sense that 86 has 12V on it.... 85/86 is just a coil so they're connected... so whatever's on 85 will be on 86. I need to re-look at my dash tomorrow because if I remember right, I used a single ground for all of the stuff in the dash... that means I'm back feeding 12V to my gauges (which probably explains why my speedo jumps every now & then & maybe one other gremlin I've had). So, I'm going to isolate that ground. Don't see a reason that'd fix the LED problem, but at least it should eliminate a problem and maybe has something to do with voltage differential that the LED is seeing??

If I can't figure this out soon I'm tempted to strip out the headlight wiring & rewire where the switches control the positive side.



DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

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Re: Why doesn't this LED circuit work?
Posted by: DiDueColpi
Date: April 23, 2014 02:25PM

Hey Rob,
The problem is that the headlights are feeding 12v back to the 87 terminals of both relays.
That's how it should be but it won't drive an LED indicator properly.
You can't use the 86 terminal for the same reason. It back feeds 12v from 85 as you noticed.
The best way to accomplish your goal is to use the 87a terminals on your relays. (assuming that you used the common 5 pin relay).
When the low beams are on 87a of the high beam relay will be energized.
Vise-versa when high is on the low beam 87a is hot.
When not energized the 87a terminal is isolated and won't back feed the LED at all.
You need to use a separate resistor for each LED as well, otherwise the heater LED will dominate the circuit and cause the headlight LED to be dim or flicker.
[www.kitronik.co.uk] has a good resistor calculator for your use. Make sure to use 14v as your voltage as 12v is not the running voltage of the car.
Cheers
Fred


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 23, 2014 10:37PM

Fred - usually I'm right there with you but not this time. I get the notion of the 87a's being normal closed to 30, but don't see how that helps me on this one. If I use the 87a's on the headlight relays, they'll be ground when the relay isn't engergized & open when they are energized. If you were referring to the LED relays 87a's i can see how they could be used to switch the LED indicator between low & high beam indicators by wiring the low beam LED to the high beam led's 87a and vice versa... but if I do that, one or the other LED will be on even when the headlights are turned off. What am I missing?

I do have another idea though... ignoring the "distinct resistor per LED" comment for a moment, if I flip flop the wiring between the headlights & the headlight relays by changing the constant power to the headlights to be a ground & then change the ground that goes to the headlight relay 30's to be where the 12V goes instead, the headlights should still work properly and I can then use the headlight relay 87's to also power the LED's & eliminate the LED relays completely.

I'm going to try to keep the shared resistor on the ground leg becuase I have a potentiometer there to adjust the LED brightness. Without knocking down the brightness, the LED's are too bright at night. If that doesn't work, I'll have to use two potentiometers - one for the cooling fan LED & one for the headlight indictor one.


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: DiDueColpi
Date: April 24, 2014 04:00AM

Sorry Rob,
Trying to do too many things at once I guess.
You are right, the 87a idea won't fly. And I wasn't paying attention to the LED relays that were added.
Something is tickling the back of my brain. But it's late and I can't quite grasp it.
We'll solve it in the morning.
Cheers
Fred


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: DiDueColpi
Date: April 24, 2014 08:00PM

Ok, so it's a new day and you have my full attention.
Remove the LED relays as you won't need them.
What you will need are 4 small diodes.
You will be connecting them to the 87 terms of both headlight relays
What's happening is when the lights are off you have 12v at both 87s so no current flow.
When one or the other is on, it's corresponding 87 goes to ground.
So if we use some doides to bias the current for the LED's then we're all lit up!
Two diodes go to each 87. One positive biased and one negative biased.
The two negative biased diodes connect to the negative or ground side of the LED through a dropping resistor.
The positive based diodes connect one each to the two positive leads of the colored LED
High beam 87 to green lead and low beam 87 to blue lead.
Now the LED's should work and no smoke.

Cheers
Fred


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 24, 2014 09:30PM

Fred, sounds like that should work, but unless I'm missing something it seems more complex than rewiring the 30 pins on the headlight relays to be 12v and the current constant power to the headlights to be grounds instead. Then I can pick up power for the LEDs from the 87s without the diodes and still ditch the LED relays.

Does that make sense?


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: DiDueColpi
Date: April 25, 2014 03:00AM

For me Rob, there are several reasons to stay the course.
You're already wired that way and its a more contemporary wiring scheme.
Nobody controls power anymore. Everything has been ground switched for decades.
You have to run two wires from the 87's either way and the diode package is very small.
Changing to switched power causes it's own challenges.
The big one is back feed from the dead beam.
Power through the bulb filament will be high enough to light both LED's full time.
So back to supplemental relays for that scenario.
I know that you want to run just one current limiting resistor but it just won't work.
Wire up a few on your work bench to try it out. What you would think should work just fine won't.
The resistance to run two LED's ends up providing enough current to send one into thermal runaway.
You can run LED's in series and pull it off, but not in parallel.
If you want to run a single dimmer then you will need a ganged pot.
Or run the primary current limit resistors to the park lamps.
They will ground through the bulb filaments when the lights are off.
Giving you full brightness.
Once the park lamps are on they become neutral.
The secondary or dim resistors will run to ground.
Some fiddling with resistances will be needed to get the right brightness. but it should be pretty straight forward.

Yours in total confusion.
Fred


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: April 28, 2014 08:35PM

Fred, thanks again for the great info as usual. I got a dual gang potentiometer so will be able to get the LED's each on their own but retain a single knob to control them. I decided to swap the headlight 30/87 between power and ground. I know you recommended the capicitors, but this way seems like less failure points and parts are easily swappable on the road if necessary.

I should have it done on Friday afternoon - 1st chance to work on it - just in time to go to the Concour de’Elegance at La Toretta in Conroe TX this weekend (http://concoursoftexas.org).


rficalora
Rob Ficalora
Willis, TX
(2648 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Why doesn't this LED circuit work?
Posted by: rficalora
Date: May 05, 2014 09:55PM

Ok, Friday turned to Saturday, but got it buttoned up in time for La Toretta's Concours d'Elegance. Awesome display of cars - my wife says if I win the lottery she wants a 36 Packard dual cowl. Too many cool cars from 1910 thru modern with most being 30's.

Got to meet a gentleman named Bill Bauder whose Allard was on display. Bill is the 2nd owner and has had the Allard for over 50 years and raced it most of that time. He and his wife invited my wife and I to come visit at their ranch in Austin; I hope we get to take them up on that. Their stories were fascinating... Including one about a race Bill had with Carol Shelby back in the day...

Ok, back to my high beam indicator... Took the car back to the inspection station on Sunday. Same shop, different guy... Maybe 25 yrs old. Discussion went about like this... Do you want me to pull it in or do you need to... You can, I'm not too good with a stick. I pull it in and get out. He asks what is it... Tell him MG. He says huh, who made that. Well, um, MG did. He says does it have blinkers... yes. They work? Yes. Hazzards? Yes. Looks at my wipers. Those are tiny! Turns and fills out the sticker and sticks it on. Never drove it (they're supposed to check brakes and confirm e-brake holds to 1500 rpm)... And, of course, never even asked about the high beam indicator!!



74ls1tr6
Calvin Grannis
Elk Grove,CA
(1150 posts)

Registered:
11/10/2007 10:05AM

Main British Car:
74 TR6 / 71 MGB GT TR6/Ls1 71 MGB GT/Ls1

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Re: Why doesn't this LED circuit work?
Posted by: 74ls1tr6
Date: May 06, 2014 08:09PM

Sounds like fun Rob.....Haha, congrats getting your sticker!


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