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Old 29-06-2015, 20:27   #16
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Re: Blowing 12 Volt Bulbs

As has been said charging voltage can be as high as 15 volts depending on your battery type. Trojan specify bulk charging voltage of 14.8 volts for their flooded lead acid batteries. There are some on this forum that know a hell of a lot more about the subject than I that say that 15 volt bulk charge is good for the battery bank. Adjusted of course for temperature.
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Old 06-07-2015, 04:31   #17
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Re: Blowing 12 Volt Bulbs

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I don't know where you learned your electrical theory but I think you need to go back and reread your books. A lamp, which is a resistance, will not draw more current if there is a high resistance in the wiring. A high resistance in the wiring may cause a fire but it will not be the cause of the bulbs burning out. A lamp does not "draw" power. The current running through the lamp is a product of voltage and resistance. Note that the resistance is of the whole circuit not the lamp alone.
hmmmm. You're right. My apologies! V=IR so of course an increase in resistance will result in a decrease in current...... ignore what I said before!
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Old 06-07-2015, 07:14   #18
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Re: Blowing 12 Volt Bulbs

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Originally Posted by DeepFrz View Post
I don't know where you learned your electrical theory but I think you need to go back and reread your books. A lamp, which is a resistance, will not draw more current if there is a high resistance in the wiring. A high resistance in the wiring may cause a fire but it will not be the cause of the bulbs burning out. A lamp does not "draw" power. The current running through the lamp is a product of voltage and resistance. Note that the resistance is of the whole circuit not the lamp alone.
hmmmm. You're right. My apologies! V=IR so of course an increase in resistance will result in a decrease in current...... ignore what I said before!
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That statement is right. but any circuit run for long enough periods at higher or lower voltages of their rated range will burn out. Also a light bulb designed for 32 volts will use less amps at the same wattage as a bulb designed for a 12 volt range. Use "PIE" you'll see. Hence a wire with Higher resistance due to corrosion and or broken strands or any form of resistance in a circuit will generate heat, due to the increased amps needed to cross the circuit.
If your bulbs are burning out prematurely it is due, more than likely, to low voltage, causing more heat. Hence the word "burned" out. You can get deeper into the Physics of impedance, energy and potential and cause all kinds of confusion or you can Keep it simple and check for voltage. A 12 volt circuit has a range of 11.5 to 15 volts. Continuos voltage out side this range will cast premature failure. No if, ands or buts.
start at the battery and work your way along the circuit, up the pos side and down the neg. side using a known good ground, separate from the circuit being tested until you find the voltage drop. replace that component, wether it be a wire a socket, switch or connector. It's a very simple process, altho accessibility will determine how easy it is to do the job. ;-)
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Old 06-07-2015, 18:51   #19
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Re: Blowing 12 Volt Bulbs

Thanks for all trying to help here, finally had a chance to check alternator output this weekend while engine running 15 volts and old chevy unit we rebuilt believe its a 10si.
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Old 06-07-2015, 20:20   #20
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Re: Blowing 12 Volt Bulbs

When I first got my boat in 2003, it blew out 12 volt bulbs left and right. Finally I learned that I was shutting down the diesel engine using a wrong sequence.

To shut down the engine I was (1)turning off the key (nothing happens) and then (2) pulling the tit (engine chugs to a stop). I learned that when I shut off the key, that stopped the alternator sending a big voltage spike through the electrical system, burning out whatever bulbs were on.

The proper way to shut down the diesel is (1) pull the tit and the engine chugs to a stop. The alarm siren comes on to let you know it works. (2)Turn off the key.

No more problems with bulbs burning out.
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Old 06-07-2015, 21:25   #21
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Re: Blowing 12 Volt Bulbs

A Delco 10si will never put out more than 14.4 volts unless there is something wrong, typically a bad regulator.


Ask Delco (ACDelco or DelcoRemy now) or any other automotive alternator maker. The only reason that all the light bulbs blow out real fast no matter how often you replace them? Is because they are all nominal "12" volt bulbs intended to run at 14.4 volts from an alternator (13.8 from a cheaply regulated one at idle) and they all say the same thing in their diagnostics.


High voltage blows the bulbs. Then it blows all the electronics shortly after.


There's a GE 6V automotive headlight that used to be common in dive lights. Ikelite used to run it on 9 volts instead, which made it really super bright. Except, on 6 volts the bulb has a 50-hour lifetime. On 9 volts, that's cut down to 3 hours. Two dives, and you buy a new $20 bulb, because it will burn out on the third one.


GE and other bulb makers also publish tables that show bulb brightness versus bulb life (in hours) as the voltage supplied to them changes. Overvolt them, and they all blow faster. All the time.
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Old 06-07-2015, 22:35   #22
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Re: Blowing 12 Volt Bulbs

And finally corrosion does indeed cause heat, but it causes the heat at the point of the corrosion. That may be the socket of the bulb, or it might be at a point where 1/2 the strands of wire have broken due to flex, or it might be at the point where the wire connects to something. One way or the other, corrosion causes HIGH (er) resistance over the circuit as a whole. The voltage applied across the real load (light bulb, motor etc) WILL DROP by some amount determined by the resistance caused by the corrosion.

In DC circuits (lamps) this will usually just cause a dim light. AFAIK it would never cause a failure, other than dimming.

Electronics may or may not fail depending on the voltage supplied vs actual minimum voltage required by the circuit (regulators usually).

Motors OTOH can cause issues such as the motor not overcoming some physical load, causing the motor to stall, causing heat in the windings. (Additional) Heat in the windings is bad...
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Old 07-07-2015, 05:11   #23
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Re: Blowing 12 Volt Bulbs

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Please use a decent multimeter and measure the DC voltage while the engine(s) are running.

It should be about 12.5 VDC w/ the engines off and the batteries fully charged and 13.8 VDC while the engine(s) are running.

If the voltage is higher, then the power to the bulb goes up by the square of the voltage.
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Thanks for all trying to help here, finally had a chance to check alternator output this weekend while engine running 15 volts and old chevy unit we rebuilt believe its a 10si.
Thanks for checking. That is the problem.

The voltage regulator for a 10Si is available to swap out the bad part.
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Old 07-07-2015, 18:04   #24
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Re: Blowing 12 Volt Bulbs

where would I get a voltage regulator for this alternator, is it easy to install?
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Old 07-07-2015, 19:19   #25
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Re: Blowing 12 Volt Bulbs

Your loose wire could have caused your issue.

Google "Collapsing Field Effect"

Tesla stuff.


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Old 07-07-2015, 19:28   #26
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Re: Blowing 12 Volt Bulbs

With the 10si, if the voltage sense lead was not connected (or was connected through a corroded contact) that could also make the alternator put out excess voltage, so that does need to be checked.


The 10si was a very common part on GM vehicles. The regulator is an internal part. If you're unfamiliar with alternators, you might be better off having a shop test the alternator and replace it if needed. Or you can look around online for it. Trying to buy one "retail" might cost more than that, but you can look online for them along with instructions for how to replace it.


Easy to install? Well, they're all easy, if you're comfortable with opening up alternators.


Depending on the age and condition of the alternator, a good used 10si from a junkyard or remanufactured one with a warranty might be a better way to go. New bearings, brushes, all part of the same deal at the same time.
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Old 07-07-2015, 19:32   #27
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Re: Blowing 12 Volt Bulbs

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Originally Posted by DeepFrz View Post
I don't know where you learned your electrical theory but I think you need to go back and reread your books. A lamp, which is a resistance, will not draw more current if there is a high resistance in the wiring. A high resistance in the wiring may cause a fire but it will not be the cause of the bulbs burning out. A lamp does not "draw" power. The current running through the lamp is a product of voltage and resistance. Note that the resistance is of the whole circuit not the lamp alone.
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Old 07-07-2015, 19:51   #28
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Re: Blowing 12 Volt Bulbs

Good advice here.

FWIW, depending on where you are, it is always good to get to know a local alternator replacement company. In most places they are around since they are used in cars.


Quote:
Originally Posted by hellosailor View Post
With the 10si, if the voltage sense lead was not connected (or was connected through a corroded contact) that could also make the alternator put out excess voltage, so that does need to be checked.


The 10si was a very common part on GM vehicles. The regulator is an internal part. If you're unfamiliar with alternators, you might be better off having a shop test the alternator and replace it if needed. Or you can look around online for it. Trying to buy one "retail" might cost more than that, but you can look online for them along with instructions for how to replace it.


Easy to install? Well, they're all easy, if you're comfortable with opening up alternators.


Depending on the age and condition of the alternator, a good used 10si from a junkyard or remanufactured one with a warranty might be a better way to go. New bearings, brushes, all part of the same deal at the same time.
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