How Does Alternator Charge Circuit Work?

[Matt Bachand]

There are 2 wires that go the alternator and of course the one charge wire.

I assume one wire sends the tach signal, how does the turn on work? I know it has a voltage regulator internally, does it automatically know when to 'charge' and when to not?

When I swapped my alternator, i noticed the 2 wires were alittle worn down insulation wise, they still looked connected, I cleaned em with electrical cleaner, and retaped them, as I wasn't sure If i popped the connector open It would go back together.

The tank of fuel I had (100 miles worth) when alternator failed, internally bearings shot and tach stopped working. I netted 15 mpg.

The 100 miles before was around 9-10.

I installed new alternator, and I have noticed sometimes my volt gauge is well above 14, higher than I've ever seen it. It settled a little above 14, but was much higher than 'normal' from memory anyhow.


Next 100 miles, MPG 11.


I don't know if alternator stuck charging would driop mileage that much, or if its my injectors or what, but figured I'd talk a little alternator to figure out how it works.

I'll have to get new batts for my dig volt-tester and check for sure whats coming out of it.

I also added 2 ground wires from each battery to each side's frame, I don't see how that could interfere with anything electrically though. Before I did this, my old alternator worked, and MPG's were up around 16.

 

[mfgguru]

I think you need to look back to VSSB or whatever it is. May have screwed up your mileage by trying to correct the speed due to tire change. Alternator shouldn't affect mileage to that extent, and if it was continually charging you would boil a battery or fry the alt or something of that nature.

 

[Acesneights1]

Overcharging usually smells like burning mud. Should be ideally around 13.5 don't trust Dash gauges. Use a meter. Drop in MPG maybe coincidental and another issue.

 

[Matt Bachand]

I think you need to look back to VSSB or whatever it is. May have screwed up your mileage by trying to correct the speed due to tire change. Alternator shouldn't affect mileage to that extent, and if it was continually charging you would boil a battery or fry the alt or something of that nature.

My alternator failed before I touched my VSSB, and I was able to record the 15mpg multiplying odo by 1.07, VSSB is extremely close, When truck reads 65, GPS says 66. So damn close.

You bring up a good point about batteries, mine are 4-5 year old interstates, perhaps I should check them. A bad battery would have the alternator constantly charging?

 

[Matt Bachand]

Overcharging usually smells like burning mud. Should be ideally around 13.5 don't trust Dash gauges. Use a meter. Drop in MPG maybe coincidental and another issue.

I think so... I'm overdue for injectors, have a questionable sock in my tank, could be partially starving IP at times... who knows, I have alot of PM i need to get done on the rig as soon as a little more cake flows in... Still playing 'catch up' on some important bills for a few more weeks before I'm not in the red anymore. The good news is, work is here, and its jam packed all of a sudden. I expect it to stay this way till winter again.

 

[schiker]

Here is my understanding. 3 wires for diesel (3rd is tach drive) usually 2 wires for gassers. One wire is charge wire the other is warning light.

Internal to most alternators is a voltage regulator which measures battery voltage. This controls amperage output to charge batteries on the charge wire.

The warning light recieves power from the battery goes to warning light bulb then to alternator for ground or a lesser potential to induce current and turn on the warning light. When the alternator is working and creating voltage this line looses ground or gains potential and looses current through the warning light which has a diode inline somewhere and bingo either you have a charge light/battery warning light come on or you don't when the alternator is good and everything is working correctly. If the alternator can't build a charge the warning light will come on because the battery has more potential and finds a path for current to ground and lights the warning light. Or it works cuts off the warning light.

Not sure but its an alternator not a generator and as such has alternating current and diodes to transform AC to DC some kinda of way. So the voltage regulator senses battery voltage and outputs a corrective charge to equalize the potential energy postive lead to ground. But I think the warning light is a one sided device and won't recognise overcharging. That's why an amp gage is useful vs only a volt gage . You want to see 13.8 +/- volts all the time (minus some dips) but that doesn't tell you if the alternator is overcharging. You only want to see amps when voltage is down or an accessory is on pulling amperage. Ideally you could see both voltage and amps. And you could monitor a slight drop in voltage on starting. Then corresponding dip in voltage and increase in amp output. This would recover to once 13.8 volts amperage would decrease unitl somewhat equalized.

 

[ak diesel driver]

most alternators I've been around usually run at 14.5 +/-

 

[schiker]

Hmmm, learn something new everyday. Makes sense it would have to be higher voltage to flow current to battery. I thought a 12V battery was typically 13.8V +/- depending on actual cell temperature when fully charged. But can see the alternator putting out 14.5 volts again to have higher potential and flow current to charge battery.

But since there are draws of power and such almost always some current (and some state of charge less than perfect) and of course temp fluctuations you'll see just above 12 to 14 +/- depending with most measuring devices and dash gauges at or just off the the battery terminals. I have never measured volts at the alternator. The temperature fluctuations come from ambient, engine, and chemical reaction heat of charging or discharge and current flow.

I have measured amperage output on a single wire alternator and amps rise and fall according to battery/system voltage. A single wire alternator doesn't have warning light or other output. It just has a built in voltage regulator and senses voltage or potential energy of system vs the potential from the alternator itself. If it senses less than 13.8? volts battery it outputs current to correct. The lower the voltage the higher the current.

So how does one tell if alternator is overcharging with voltmeter only? If at or above 14.5 or at 14.5 continuously?

It all depends on the truck and accessories. What is typical amp usage for normal conditions I am guessing 10 to 15 amps just to run minimum electronics and lift pump? So if you had an alternator outputting say 20 amps or more all the time it would be overcharging the battery and "cook" out the electrolyte.?.

 

[DieselCash]

Here is a good website if you want to learn how it all works.

http://www.bcae1.com/charging.htm

Enjoy! :thumbsup:

 

[THEFERMANATOR]

A fully charged 12 volt battery is roughly 13.2 volts at 100 degrees as a wet cell in a battery is 2.2 volts and a 12 volt battery has 6 of em. Now it takes a 1/2 volt differential average to push current into the storage cells in a battery, so 13.8 is the common accepted voltage for a charging system. When a battery is cold it can take MUCH more current so that it can rapid charge quickly, but after about 12-15 minutes it begins to get hot and the current must drop down or else it will boil over. On a 30 degree day I have seen alternators charge at 15.6 volts, but when the battery is 150 degrees it would only charge at 13.1-13.2 volts. GM's new style regulators use rapid charge technology so that vehicles that get driven short distances don't get dead batteries. This means that they will charge at roughly 14.6-14.8 volts for the first 5 minutes or so and then drop back to 13.2-13.8(depending upon under hood temps at the regulator) over the next 10 minutes.

 

[schiker]

So I think my understanding is ok and the website was helpful. According to it clipped...

Current demand and flow:
If you have an alternator that can produce 120 amps of current (max) and the the total current demand from the electrical accessories (including the battery) is only 20 amps, the alternator will only produce the necessary current (20 amps) to maintain the target voltage (which is determined by the alternator's internal voltage regulator). Remember that the alternator monitors the electrical system's voltage. If the voltage starts to fall below the target voltage (approximately 13.8 volts depending on the alternator's design), the alternator produces more current to keep the voltage up. When the demand for current is low, the full current capacity of the alternator is not used/produced (a 120 amp alternator does not continuously produce 120 amps unless there is a sufficient current draw).


So how do you tell if its overcharging with only a voltmeter or can you. If system voltage is above 14.5? volts at idle? (once cranking amps are replaced). Or do you have to measure voltage of battery and current output too. If above 13.8V or 14.5V at battery (system) and you still have appreciable current out of the alternator to battery its overcharging??? I think you would need to know typical system draw and compare charge amperage to know for sure.

At 60amps 12V the altenator would draw what about 3ish hp.

 

[Matt Bachand]

Well, here's the other side of the story that I kept to myself.

When the voltage was reading high, my truck felt super peppy. I don't fully understand how voltage affects the PMD, but I know when I limped it back with a dead alternator last winter, it gradually got slower and slower and slower as the batteries were dying, until i was able to get to the driveway doing about 5mph.

So, would a DS-4 powered circuit somehow put out more fuel at higher voltage? It defanately outputs less fuel at lower voltage, as proven by gradually getting slower as batteries are dying. And when my volt guage was reading well higher than 14 (now its back to 14 where it should be BTW) The truck felt extra peppy.

I know my truck, and I know this was not in my head.

 

[94K30]

all of the sensors feeding info to the ECM are voltage dependant. they work by varying the voltage that goes through them. If you feed them a low voltage, they cannot put out the correct reading, so the ECM gets incorrect info, which would get worse as the voltage drops lower and lower. This is also why grounds are so important.......

 

[Acesneights1]

Interstate Batteries..Hmmm...probably part of the problem right there. JMO But ever thing I ever got with those in it including most recently my Tahoe they were junk. I tossed them last fall and threw a couple Die Easys in and it was like night and day starting. I'm sure some will disagree but I personally hate them.

 

[Matt Bachand]

Interstate Batteries..Hmmm...probably part of the problem right there. JMO But ever thing I ever got with those in it including most recently my Tahoe they were junk. I tossed them last fall and threw a couple Die Easys in and it was like night and day starting. I'm sure some will disagree but I personally hate them.

... They were in the truck when i bought it and are stamped 12-04.... One is a little wet up top by teh seal....

Always starts any temp, even -8 on 7 cylinders unplugged... No issues so far. Every year or so I read this from you Kenny lol...

Would liek to replace them, but so far no need too. Should buy a cheap batt load tester though...

 

[schiker]

I believe most voltage reference are from 5 volts. Because there can be a lot of voltage fluctuations between 9-13.8 due to loads, temperatures, connections, charge variation, and connection health etc etc.

My understanding is the fuel metering solenoid is like 120V and the PMD/FSD steps up the voltage from the 12V system and switches the current according to the PCM commands. Thats why is considered the driver. The sol-D seemed to have promblems when system/battery voltage dropped to 9 or under. The stanadyne seems to work ok a little under 9. Not sure when it quits.

I wouldn't think the PMD/FSD would over fueling from a bit higher voltage as it and engine RPM's are controlled by PCM. And the PCM filters and conditions the

5V references for sensors etc.?. Maybe with new alternator and connections you are getting a bit more performance (because the PMD/FSD likes clean 12V power) and its now delivering fuel like its suppose to and you were unaware you had a slightly underperforming system before?

I would monitor a couple more tank fills then avg to see if averages out. I know I sometimes get caught enjoying the feeling of peppiness on a tank of good fuel and good weather and the MPG suffers some.

 

[Matt Bachand]

True... when all systems go right it always feels good to 'stretch her legs out'.... So true

Last tank was around 14, and my voltmeter settled at 14. Perhaps it just took that long to top my batteries off again from driving it 45 miles or so in traffic too with no alt...

Should have let my charger sit on them overnight, but didn't. I have a lifetime warranty on this alternator, and planning on having my core rebuilt by a locAl guy who does great work as a spare. Lifetime warranty wont help me none if the alt goes when its working hardest (plowing) and in the middle of the night when stores are closed. Only a spare would keep the cAshflow coming.

Plus I think a quality rebuilt by hand alternator is 10x better than my 'made in mexico' autozone lifetime warranty special.

Perhaps I'll talk to him about winding it differently to output more amps at less RPM too. These things are rated at 6000 rpm, my truck never sees over 2500, and when plowing doesn't even see 1500 often.

Core charge was only 10 bux, and for him to rebuild will be around 100, so if it saves me 1 1/2 of plowing i'm ahead of the game. If it doesn't, I'll always have the spare, easy enough job to change it out.

 

[schiker]

Perhaps I'll talk to him about winding it differently to output more amps at less RPM too. These things are rated at 6000 rpm, my truck never sees over 2500, and when plowing doesn't even see 1500 often.

Make sure you check what rpm they are talking about alternator rpm or engine?

Maybe they are rated at 6000 because that's what they will spin at anticipated engine at ~2000 rpm ? ( avg cruising speed) with the pulley sizes. They generally will make a little more current the faster you spin'em within reason. I don't THINK you have to redline your engine to get rated current.

I believe most factory hi idle settings will get you most of the rated current from the alternator and what was max GM hi idle 1650 rpm???.

Not sure how much increase in current potential from the alternator there is between 2200 to 3400 rpm at crank. I think the voltage regulator and control logic adjust the current output so that its not linear from idle to redline and somewhat independant of rpm its more a voltage regulation thing. I THINK its a steeper curve then tapers off so that it has good current potential around cruising speed. Kinda along the fast charge logic that was mentioned earlier.

On a single wire alternator..... I can't remember what powermaster told a friend of mine but you could get something like 20 more amps above the "rating" out of their alternator if you could spin it faster without getting silly on rpms I think that was with 2000 or 3000 rpm increase iirc.

Some guys will race their engines really fast when boosting another vehicle but all you need to do is go to a typical hi idle in my opinion (1300-1600 rpm) after that its just noise.

 

[hereismylife]

Hey matt did you ever get it figured out?

 

[Matt Bachand]

Apparantly it was settling in, or I was overanalyzing (probably it).... Everythings running great, charging right around 16 or so estimated from gauge and never drops below 14 even with all my lights on blower motor etc. All my extra grounds can only help me thinks.