Topic: anyone know about diodes?????

[J.Webster Designs]

ok.... here is the short version....

I am using an LED array as a tail light on my 1976 CB750F... since I am running an LED, i have to wire the system as a single filament system instead of a dual filament that came stock ( putting the running light wire and the brake light wire together to get a single output).... i also have turn signals that are functioning as run/brake/turn and are controlled by a module... the module is getting back feed current from the running light wire (brown wire) through the brake light wire (green yellow wire). This back-feeding current is causing the module to think that the brakes are being actuated which in turn makes the turn signals turn on to the brake light function.... I am stopping this with a 1N5400 diode which i believe is a 3Amp 50Volt diode.... The diode is doing its job by keeping the back-feeding from happening.... however... because of the .7 forward voltage drop, it is not allowing my LED brake light to reach full brightness (intensity) when the brakes are activated...

SO I am switching to a schottky diode... These diodes have between .15 and .45 forward voltage drop... however, I am not sure if i should go with a 3 amp 20v diode, or if i can use a 1N5817 schottky diode that is rated at 1Amp 20Volts... i know that the 20Volts will be plenty enough as the back-feeding will not reach anywhere near 20Volts.... but i am wondering if the 1 amp will be enough? how can I measure if 1 amp will be enough? or does the rear running light system on a '76 CB750F even see 1 amp?

[mystic_1]

TwoTired is you man on the diode questions but...

since I am running an LED, i have to wire the system as a single filament system instead of a dual filament that came stock ( putting the running light wire and the brake light wire together to get a single output)

Wouldn't doing this effectively mean that your taillight would be on at full intensity all the time, regardless of whether or not you were stepping on the brake?  Or am I misunderstanding how you're wiring up the run/brake/turn module?  Which module are you using and how exactly are you wiring it up?  Got pics?

mystic_1

[Laminar]

TwoTired is you man on the diode questions but...

since I am running an LED, i have to wire the system as a single filament system instead of a dual filament that came stock ( putting the running light wire and the brake light wire together to get a single output)

Wouldn't doing this effectively mean that your taillight would be on at full intensity all the time, regardless of whether or not you were stepping on the brake?  Or am I misunderstanding how you're wiring up the run/brake/turn module?  Which module are you using and how exactly are you wiring it up?  Got pics?

mystic_1

I read it as the taillight is at full intensity all the time, and the turn signals act as the brake light because of the run/brake/turn module. If this is the case, I don't know why the brake lead needs to be connected to the tail light at all.

But of course, I could be misunderstanding.

You can put a multimeter inline with your taillight to determine its current draw - unhook the +12V wire from the taillight, put one multimeter lead on the taillight and the other lead on the +12V taillight lead. Now when you turn on the light, the multimeter should read out the current draw (be sure you're using multimeter settings that can handle several amps - you don't want to fry your multimeter).

[Laminar]

If your reading end up close to these, it sounds like the 1 amp will be enough:

On a side note here are some Amp readings i took before and after :
STOP light: 2.07A (1157)
Tail light: .550mA
(old setup licence plate light would get MUCH dimmer when brake was off)

LED light:
STOP light: 255.7mA
Tail light: 161mA
 BOTH: 389mA

From this thread.

[jessezm]

Does this help at all?

http://www.bareasschoppers.com/dualcircuit/

[mystic_1]

The run/turn/brake controller may take care of that, depending on which one is being used.

mystic_1

[Bodi]

Some LEDs will take over one amp, but they are expensive super bright ones that need a heat sink. I think one amp is plenty for your use.
Also: LEDs are current devices with a fixed operating voltage drop. In a LED 12V circuit, there must be a current limiting resistor. The 0.6V forward drop of a normal junction diode should not be an issue... with a single LED the resistor will be dropping around 9V and the difference between 9V and 8.4V should be negligible (although visible). If you've wired a LED array in series to get the total voltage drop close to 12V then the 0.6V will make a larger difference, but normal voltage variation in the battery circuit - from 12V to 14.5V or so - will make a huge difference in brightness. And possibly overdrive the LEDs and cause them to fail in a short time. It's best to have no more than 3 LEDs in series for a 12V automotive circuit, I would recommend 2 in series. This leaves the resistor with a 6V drop at 12V (most hi intensity LEDs have a 3V Vf). If you use resistor values so that the Imax is at 14.5V then all should be safe, and brightness at 12V should be good. The other option is to use an active current regulated supply, a simple LM117 3 terminal regulator IC can be wired to do this easily, and there are specialized ICs to do this job as well.

[1080]

Can you give more info on the make of the LED array/ module?

I cannot see why you must combine wires if there is a module that controls the leds?

[J.Webster Designs]

sorry... i was down in the garage working on the seat.....

The running light wire (brown wire) is resisted with a 47 ohm resistor which knocks down the voltage to give me the distinct difference between running and brakeing... when you hit the brakes, it send a jolt of 12V through to the LED array so that it goes to full brightness.....


the module allows the turn signals to function as running and brake lights but when you hit the turn signal, it over rides the running lights and brake lights so that the turn signal will blink whether the brakes are applied or not.....

Some LEDs will take over one amp, but they are expensive super bright ones that need a heat sink. I think one amp is plenty for your use.
Also: LEDs are current devices with a fixed operating voltage drop. In a LED 12V circuit, there must be a current limiting resistor. The 0.6V forward drop of a normal junction diode should not be an issue... with a single LED the resistor will be dropping around 9V and the difference between 9V and 8.4V should be negligible (although visible). If you've wired a LED array in series to get the total voltage drop close to 12V then the 0.6V will make a larger difference, but normal voltage variation in the battery circuit - from 12V to 14.5V or so - will make a huge difference in brightness. And possibly overdrive the LEDs and cause them to fail in a short time. It's best to have no more than 3 LEDs in series for a 12V automotive circuit, I would recommend 2 in series. This leaves the resistor with a 6V drop at 12V (most hi intensity LEDs have a 3V Vf). If you use resistor values so that the Imax is at 14.5V then all should be safe, and brightness at 12V should be good. The other option is to use an active current regulated supply, a simple LM117 3 terminal regulator IC can be wired to do this easily, and there are specialized ICs to do this job as well.

im not sure what you meant by all of this.... as the question isnt about resistors....  my run/brake/turn LED array has 100 LEDs. the brake light alone is 60 with 20 per turn signal...

I cannot see why you must combine wires if there is a module to control the leds?

The control module takes an input from the running (brown wire) and the brake (green yellow wire) and sends them off into the turn signals. but then over rides those inputs when the turn signal is turned on....




I hope this clears things up... I am confused by the different types of posts that I got... but I know that is because of the confusion that I caused by not explaining the module fully....

[1080]

So how many hook up wires does the module have?

[J.Webster Designs]

6 if i remember correctly.... but the module is of little concern.... everything works properly but the diode in question....

I am trying to figure out the if the diode that i have can be replaced by a shottky diode that is 1Amp 20Volt..... If i can replace it with a schottky diode, It will fix the last problem that I have with this...

[mystic_1]

the module is getting back feed current from the running light wire (brown wire) through the brake light wire (green yellow wire). This back-feeding current is causing the module to think that the brakes are being actuated

What's causing this back feed current?

Any chance you could post a rough schematic of your setup?

That aside, try PMing TwoTired with your question, he's much better versed in this stuff than most here.

mystic_1

[1080]

 If you have 6 hook-up wires then you should not be having hook up problems. I will try to post a simple wiring diagram. The turn  signals should 2 control wires, brake 1 wire, night tail light 1 wire, +12volt 1wire & common ground 1 wire. That adds to 6 wires.

[Cormac]

Suppose the real question is, HOW MUCH DO THEY COST?
If the diodes are cheap, buy them both, try the little one. If it fries, use the next bigger.

I always got my diodes at radiocrap, huge selection, cheap prices.

Oh, and feed back is typically very minimal current, so the 1 Amp should be fine.

[J.Webster Designs]

this is how everything is hooked up....

the module is getting back feed current from the running light wire (brown wire) through the brake light wire (green yellow wire). This back-feeding current is causing the module to think that the brakes are being actuated

What's causing this back feed current?

Any chance you could post a rough schematic of your setup?

That aside, try PMing TwoTired with your question, he's much better versed in this stuff than most here.

mystic_1

The back feed current is caused by hooking the running wire to the brake wire... The running wire voltage is back feeding through the brake wire and triggering the module....

 If you have 6 hook-up wires then you should not be having hook up problems. I will try to post a simple wiring diagram. The turn  signals should 2 control wires, brake 1 wire, night tail light 1 wire, +12volt 1wire & common ground 1 wire. That adds to 6 wires.

Take a look at the wiring diagram I posted.... the brake light only has two wires hot and ground.... treat it as a single filament bulb....

[Laminar]

Given this new info regarding a resistor in the taillight lead and the wiring diagram, my previous post on determining current draw is correct.

[J.Webster Designs]

Given this new info regarding a resistor in the taillight lead and the wiring diagram, my previous post on determining current draw is correct.

I am thinking that your thinking about thinking that your last post about thinking that a 1 amp schottky diode is probably correct..... did that make you think?

[1080]

I think your diode if the manufacture calls for one to be introduced in the circuit should go in between the blueish wire & not between the green/yellow wire?

My diagram shows two 12 volt sources which may be wrong , but thats were your diode my have to go?

[J.Webster Designs]

the diode HAS to go between the point at which the blue wire hooks into the green/yellow wire and the tail light... if it is place anywhere else it does not do its job of preventing backfeeding.....

I appreciate your willingness to help 1080, but the positioning of the diode and the wiring of the system is not faulted... I am simply having a problem with forward voltage loss through the diode which is making the brake light not reach its full intensity.... The forward voltage loss of a regular silicone diode is .7Volts... the forward voltage loss of a schottky diode is between .15 and.45 volts depending on current.... I am just trying to figure out if a 1 amp diode is safe to use.... or if the current/amps being backfed through the brake light switch is too much for a 1N5817 schottky diode.

[1080]

Have you tried this way?

It's hard to help when you don't have all the manufacture's information

[J.Webster Designs]

yes, if you do that it does not allow the module to work properly. if you place it on the blue wire, it keeps all input from the brake wire from entiring the control module.... it would have the same effect as eliminating the blue wire all together.....

[1080]

Sorry midnight 08, but you have to post the installing wiring instructions.

Is the LED array home build? Does the manufacture of the module say that it capable of running a single filament lamp as a stop & night lamp IE. like making the LED brighter instead of running a separate night LED & stop LED?
Could it be the resistor goes after your red wire? See diagram. That way the running light led is dimmer and then when the brakes are applied the full voltage is supply throught your added diode & is not limiting your power to the module?

[Laminar]

I'm assuming the module was designed to use two turn signals to completely replace a single taillight.

[TwoTired]

In order to size a power passing diode you must know what the load or current demand is.

If the load (the LED bank) will limit its own draw below 1 amp then a diode that is comfortable handling 1 amp is sufficient.

I didn't see any specifications or reference part numbers for the lamp you've chosen.  So presently, no one can properly size a diode to match the application.

Also, I don't understand the function of the black box in your circuit drawing that is labeled "control module".  Is it meant to selectively light the turn LEDS when they aren't supposed to blink?
Anyway I don't know what circuitry is inside the black box (control module).  Did the packaging give you some idea as to what application this device is intended?

Given all that, I'm wondering if the diode simply needs to be placed in the blue wire route (or eliminated entirely, depending on just what function the "control module" is intended to perform).

[Laminar]

Here's what I understand. The black is used by someone that wants to use the rear turn signals as running lights, turn signals, and brake lights. In this case, the original poster is using that box WITH a tail/brake light, so he has to compensate for conditions that the manufacturer of the box didn't intend.