lets talk about voltage regulation...

[colbystephens]

went camping this weekend out in the mountains and on the way there my alternator went out on me. for about a year and a half it's been putting out too much voltage (according to my guage), so i've always driven with an accessory on to make sure it's under the "red limit" line of the voltmeter. well, it was not that big of a deal for my alternator to go out because my diesel uses nearly no electricity to run, so i just drove it for the weekend without an alternator.

picked up a high out-put alternator today and installed it. when i romp on the fuel, it sky-rockets my guage WAY into the red - almost pegging out the guage, whether or not i have accessories running. so i went down to the parts store and they put a meter on my batteries - now, my batteries are low to begin with: about 10volts i think. well, they test my charging system and say it's just fine - never puts out too much voltage or too little, always between 13.1-15.5V. by the way, i'm fairly certain that my alternator is internally regulated.

they tested it by way of the battery. is it just my guage that's inaccurate? i hope so. tell me whatchy'all think.

 

[4X4HIGH]

First off, an alternators job is to maintain the charge in the battery(s) NOT to charge the battery(s). If the battery was low on voltage and you just swapped in a new alternator without first fully charging the battery(s) on a slow trickle charger that is the best way to fry the new alternator since the low voltage in the battery(s) makes the alternator work way beyond what it was designed to do.

When the charging system is operating properly the volt meter should read anywhere between 13.5-14.5 volts. Anything less and the battery(s) aren't maintaining enough charge and anything more and you start to cook the battery(s).

 

[BKinzey]

I think it would be a good idea to test your guage

 

[colbystephens]

First off, an alternators job is to maintain the charge in the battery(s) NOT to charge the battery(s). If the battery was low on voltage and you just swapped in a new alternator without first fully charging the battery(s) on a slow trickle charger that is the best way to fry the new alternator since the low voltage in the battery(s) makes the alternator work way beyond what it was designed to do.

When the charging system is operating properly the volt meter should read anywhere between 13.5-14.5 volts. Anything less and the battery(s) aren't maintaining enough charge and anything more and you start to cook the battery(s).

this is great info. i've got a trickle charger on it that i'm going to leave on all nite.

how do i check my guage?

 

[wasted wages]

A battery with a dry cell will make an alternator overcharge...
make sure you don't have hole in the battery and drained one cell.

also the overcharging may have boiled the battery dry in one or more cells.

just something to look for..

 

[Blue85]

First off, an alternators job is to maintain the charge in the battery(s) NOT to charge the battery(s).

One of the primary functions is to charge the battery. I think you mean that its job is not to recondition, repair or compensate for a faulty battery.

I guess it's a catch-22 because you can't start the engine if the voltage is too low anyway. First you have to bring it up with a charger or a jump start. In theory you could disconnect a dead battery and start the engine with a second battery, then switch back to the dead one. I agree this is attempted homicide for something in the vehicle, be it the battery, the alternator or some other electrical part you kill with the transients. There is always some risk to running without a battery, but it is much greater if you disconnect it while the battery is charging.

 

[Blue85]

If your gauge was running in the red a lot, you would be going through bulbs at a frantic pace. I would get a hand-held voltmeter and check it. It's possible your voltage was too low most of the time before and only acceptable at high rpms. As long as it maintains 13-14V, the alternator is fine. Then test that battery.

 

[4X4HIGH]

One of the primary functions is to charge the battery. I think you mean that its job is not to recondition, repair or compensate for a faulty battery.

You are dead wrong. You better go do some searching on what the alternators job is.

Also, disconnecting the battery while the engine is running could easily blow the diod trio in the alternator as well. And even if that did not happen and you hooked a dead battery back into the system with the engine running that is going to make the alternator work it's hardest and will no doubt kill the alternator.

Once again, the alternators job is to maintain the charge that's in the battery, NOT to charge the battery.

 

[Blue85]

You are dead wrong. You better go do some searching on what the alternators job is.

Interesting choice of words. What research do you recommend?

What is your definition of charging? It's a chemical battery, so talking about something like a zero voltage state doesn't make any sense.

So I start my truck via the starting motor, which draws current from my battery. How does the battery ever get that energy back? They discharge and charge every time you operate the vehicle. It's just normal operation.

So if I have no electrical equipment on the vehicle (let's say it's a diesel with mechanical pump, etc.) except the starter motor, I don't need an alternator? Please help me understand your terminology.

 

[4X4HIGH]

Interesting choice of words. What research do you recommend?

What is your definition of charging? It's a chemical battery, so talking about something like a zero voltage state doesn't make any sense.

So I start my truck via the starting motor, which draws current from my battery. How does the battery ever get that energy back? They discharge and charge every time you operate the vehicle. It's just normal operation.

So if I have no electrical equipment on the vehicle (let's say it's a diesel with mechanical pump, etc.) except the starter motor, I don't need an alternator? Please help me understand your terminology.

When you use the starter you are not using hardly any voltage from the battery at all, you will draw a bunch of AMPS while cranking so once the engine starts the alternator will maintain the 12.5 (roughly) volts that's in the battery. You can run a vehicle for probably a good month on the battery alone if you're not using the head lights. Let's get serious about this. If you think i don't knowwhat i'm talking about then i want you to go measure the voltage in your battery with a quality volt meter and then remove the alternator from the system and start the engine however many times you feel you need then go measure the voltage again. You'll quickly find that the starter isn't drawing hardly any voltage to start the vehicle. CHARGING a battery is when there is an exceptional low voltage and then you ask the alternator to perform a job it was never intended to do.

 

[Blue85]

If you think i don't knowwhat i'm talking about...

More and more with each post

I've seen you post a lot of stuff here and it's obvious that in general, you know your stuff. I'm sure I could learn a lot from you about machining and some mechanical stuff. This thread is another situation, however. I don't really care, except for the risk of mis-information.

How do "use hardly any voltage"? You're using all of it! The battery voltage does dip down during crank. Have you ever measured that? Every battery has an intrinsic resistance, so that voltage drop is a function of current (it's just Ohm's law - very simple). The fact that it comes back to nominal voltage after crank does not mean that the battery has not been discharged at all. You have to drain a battery very low before the no-load voltage drops a lot. Fully charged is like 12.6V (each cell is about 2.1V) and nearly dead is about 11.9V (open-circuit votages). This is just chemistry.

You are correct that putting a fully dead battery on an alternator is hard on it. Your definition of charging is just wrong.

CHARGING a battery is when there is an exceptional low voltage and then you ask the alternator to perform a job it was never intended to do

I don't think there are any sources to back this definition up.

 

[smalltruckbigcid]

Colby back on track for you. If you have a 3 wire setup measure alt voltage at the manin electrical junction point which should be a terminal to the right of the brake booster. It will have 2 screw terminals on it. 2 of the wires on it will go to the alternator, on is the big red charge wire the other is the small brown (I think thats the color) that goes to the R terminal on alternator. The function of the small wire is to tell the alternator how much voltage is available in the system so it knows where the voltage level is at, say the reg is set for 14.2 volts.

Above 14.2 volts the alternator shuts off and below that it turns on, the lower the voltage the harder the alternator charges. Because a 3 wire measures the voltage farther back in the system it can maintain a higher and more level system voltage so all the power draws can function properly.

Here's the thing, you need to measure system voltage where the alternator measures it from or you don't get the same system read the alternator uses to turn on and off. On a 1 wire system you measure voltage at the back of the alternator to see what its putting out. On either system if you measure it at the same point the alternator does you should have about 13.9~14.2 volts present. If you need more help PM me...
George

 

[dyeager535]

IIRC, the gauge voltmeter gets it's reading right off the PCB, which gets it's voltage from the fuse panel.

You can measure at the fuse panel therefore...if the gauge is off from there, it's wrong. If it's consistently wrong it doesn't really matter, just watch that it doesn't go beyond where it normally reads, but I couldn't leave something like that alone myself.

Anywhere on the truck you shouldn't lose more than about 1V from the normal 13-14V you should see at the back of the alternator. On mine there is a single red wire to the back of it, on a stud. Check voltage there to see what the alternator is putting out.

Measure with all accessories off, then everything on...heater on high, headlights on high, radio, etc. Shouldn't drop down below about 12.5V under the max load it will see.

 

[colbystephens]

thanks guys. i don't have internet regularly - so i can't post up at home. i'll have to try this stuff out!