I have underdrive pulleys and my voltage at idle is around 12 volts. It goes up right away when I hit the gas. Any thoughts on this method to raise voltage?

http://www.zzperformance.com/grand_p...les1.php?id=48

"By installing a 1 amp diode in the orange 12 volt reference wire you can raise your system voltage by 1/2 a volt. Cut the orange wire and install the diode in series with the stripe facing the alternator."

 

As a technician still in school, I seriously do not remember using diodes being used to increase any voltages. They are primarily used to turn AC into DC by only allowing the current to flow one direction, and even then almost always use 2 diodes so that there is a solid DC output, instead of a choppy one. Think of a check valve allowing air to flow only one way.

The site also fails to mention what type of diode you would need, seeing there are several types, including one called a zener that actually limits voltage, and should be installed in the reverse direction or normal diodes.

Also, diodes do not generate free electricity. In reality, they actually require voltage to operate, generally around 0.6V depending on the type of diode material (silicon, germanium etc.), so it USES 0.6V before it allows the electricity to flow.

I believe this guy has it completely backwards. I feel that he is measuring the 0.6V drop across the diode, and thinking that this is an extra 0.6V that he can add to the voltage that is coming out of the alternator. You will be losing power if you add this to your system.

Also, always question a site that shows you a "free" mod, but then gives you a link to their product, that is the exact same thing, except for $16. Diodes are 15 cents a piece.

 

This is a cheap, easy, & ok way to raise the voltage if you have a 13.8V generator and live in a cold area where 14.4V would be more preferable, instead of exchanging the internal regulator.
I do however question your reasoning in this regard, because you say you have underdrive pulleys and too low low voltage at idle. Well, the question is not your idle voltage because the generator is out of regulation at the low rpm it gets then, and inserting the diode will not enable the generator to perform any more than it already does. It will however make a difference when you hit the gas, but that isn't where you say your problem is.. What is it at speed? If you already have 14.4V then it would only kill the battery and bulbs..
Your only solutions are: reduce current consumption in the car, or: reduce the diameter of the generator pulley, or: get a generator that puts out more amps at low rpm's than your current one does.
Notice that a hi-amp generator doesn't neccessarily give more amps at low rpm's..

 

 

Fullsizewagon,

May I ask how you have come to the conclusion that this device works? Not trying to flame you, but genuinely interested seeing that diodes USE UP aka drop voltage before they allow current to flow. Also wondering what type of diode you used, seeing there are many different types that are made from several different types of material.

Electrical laws cannot simply be broken or ignored.

To increase the voltage of the entire system, you need to either increase the source voltage (the generator, or alternator), use a step-up transformer, or use a voltage multiplier circuit. The total voltage for the circuit remains the same whether there is a diode in the circuit or not. The diode will act as a small resistor and actually drop voltage that could otherwise be used elsewhere in the system, therefore, theoretically, reducing the voltage to your lights, radio, fan etc. By adding the diode, you are doing nothing more than redistributing the voltage throughout the circuit.

And even though you can use step-up transformers and voltage multipliers to increase the voltage, you reduce the current. If I have a total of 50 watts being supplied, but at 2 volts, there is a total of 25 amps. If I use a transformer to step-up the voltage to 25 volts, my current drops to 2 amps. The formula for these calculations is Power = Voltage x Current. This is all considering perfect conditions with 0 losses, which is simply not possible, so actual results will be vary.

If you want to research all of this for yourslef, check these links I found on Wikipedia. Note that I did not just look up this info so I could post, this is for those that want to learn more about this subject.

http://en.wikipedia.org/wiki/Ohm_law
http://en.wikipedia.org/wiki/Transformer
http://en.wikipedia.org/wiki/Diode

 

Phatfiddler, check out how an externally referenced or "adjustable" linear voltage regulator works. Something like an LM317, maybe.

 

I think the lm317 voltage regulator would require a higher input voltage than output. In order to have a steady output voltage of say, 14 volts, I would need an input of around 16V or so. I'm guessing you are referring to figure 1 on page 7 of the datasheet, which shows how to set it up using 2 diodes and a potentiometer for adjustment. So the diode D1 is providing a sort of "feedback" mechanism for the regulator, sort of like how some op-amps are set up?

So maybe adding the diode affects the way the feedback mechanism works?

 

Yes, the diode simply lowers the sensed voltage so the regulator thinks it's lower than it actually is. The generator will do everything it can to keep the sense input at it's original specified voltage. The sense input just goes to an internal resistor voltage divider (pretty much like a volume control) so knowing it's resistance one could also use a variable resistor instead of the diode and get an adjustable voltage out from the generator, even to the point of getting a 24V unit out of it. I wouldn't warrant it's durability at that kind of overvoltage though.. It would also need twice the rpm to reach that voltage (given the same current draw).
One could also imagine using an NTC instead of a diode, and place it onto the battery to sense it's temperature, and so get a higher voltage and better charging in the winter, without cooking the battery dry in the summer.
You will find electronic diagrams of the internals of generators on the internet. Not all generators are made the same though, so this sensing input capability doesn't apply to all of them.

 

Ok, I gotcha. Makes more sense now that I know the internal circuitry of the generator and that it uses feedback to vary it's output accordingly. Yes, I thought about using a potentiometer instead of the diode after I realized what Apeiron was hinting at. I guess as a generic fix for most makes/models the diode would work best because you know there is 0.6V there regardless of the resistance within the generator itself. Thanks for the clarification!

 

Electronics aside (and I really struggled through circuits ii), I'm thinking no1kicker would still essentially defeat the purpose of his underdrive pulleys by increasing the output of the alternator. It's been a while since thermo but the increased output (not JUST voltage as voltage is a measure of potential difference) would still require more mechanical energy and increase efficiency loss. More output ~ more drag.

 

Yes, I completely agree that when you install underdrive pulleys you do it to free up some horses, and knowingly accept some minor side effects.
I guess underdriving is most beneficial for a heavily cammed engine that struggles enough as it is at idle, and where the fractions at the track matters. Applying things where it matters is the name of the game.
But of all accessories I guess the alternator draws the least horsepower.?

 

I just find it silly when underdrive pulleys are combined with a high output audio system. Kinda defeats the purpose. Maybe I'm old though, I remember installing an FM modulator in my first car way back when. The under-dash 8-track came later.

 

I have posted many times about this problem. Even a brand new vehicle will not provide the current to charge a battery at low RPM, the reason is it's NOT designed to do that. The charging current is dependent on the stator size, RPM level and setpoint of the internal regulator. However, you are trying to do something that the gen simply cannot do. The gen will not keep up with current demand at idle, and even with todays improved gen's like the 130D output at idle with heavy current demand is impossible. In order to do that you would need a gen probably at least twice the size and the load on the engine would be sizable. The diode pack cannot withstand the heat of a constant high charge rate. Forget external reg IC's, some laws of electronics you can't change.

 

As has been said, this would not help you much. It's takes a given amount of mechanical energy (speed and torque on the front of the alt.) to make a given amount of electrical energy out of the alt. This method of using a diode to raise the output voltage is only really useful when using a diode battery isolator with a duel battery setup to compensate for the 0.7V drop across the diode isolator.

 

Thanks for all the replies guys. My alternator has no trouble putting out enough voltage when the engine revs a bit higher. It's only with the headlights on combined with heat and the radio that the voltage goes to around 12V. I noticed a very nice gain from the pullies, so I'll pass on this and leave it as is.

Thanks again.

 

Getting a small diameter pull would help some.