Alternator regulation

[Cstoliker]

I just replaced the alternator with a Tough One 92520 (130 amp) on my 2000 XLT SOHC.
I'm not sure its working as it should. While driving with all electrical components on and battery fully charged the voltage gets as low as 13.6.
at idle it can even get below 13V.
Does anyone have any idea what the voltage regulator should regulate to?

 

[my98nnj]

If you're above 12, full load at idle and not more then 14.xx with no load, I'd say it's doing it's job.

 

[SoNic67]

13V is NOT good.
The lead batteries need to be charged at 14.2..14.4V - that is with High beams on, 1000rpm. At idle, alternator voltage might drop, bun never below 14V. Period.

If they are fully charged, 14V might be sufficient and some of the newer PCM-controlled alternators will do that (to "save" gas). But the 2000 Explorer don't have that, they have a regular alternator.

I replaced an alternator that was giving 13.6V just because it was messing up the Camshaft Position Sensor (P0340 code).

Go to the store to check the alternator - I know that Advance Auto Parts have a portable tester that can test alternator and battery for free.

 

[Cstoliker]

Advanced auto has no idea how to use their tester.
This alternator was the third one. The first was DOA (drive works) . The 2nd (the tough one) I had them test before I left with it and it faild.
This one (the third) passed the test. Before I took it home.

This was at 3 different stores because no single store had more then one In Stock.

I asked advanced auto what this model regulates at and their response "it is a 12v alternator"
Another advanced auto rep told me the voltage at the battery should never read more then 12.6
So they are useless.

 

[imp]

Missing a Point

The voltage regulator of an alternator "senses" the battery voltage at all times, and increases the alternator's output voltage to a level higher than that of the battery, thus ensuring that sufficient current (amperage) be made available to supply ALL energy-using accessories, plus maintaining the battery's own level of charge.

To answer your question, the regulator will always attempt to keep the battery's output voltage at that of a fully-charged battery, about 12.5 volts.

The kicker is that alternator output voltage is dependent on it's SPEED, so at idle speed, if lots of current demand is present because of accessory load, the alternator may be UNABLE to meet that demand, and the battery must supply some current of it's own. If that happens, the batt. is discharging. Most newer vehicles have adequate capacity built in to provide enough alternator output at idle speed, to meet average requirements. The assumption is that the engine will not idle for very long periods of time with lots of electrical load being demanded; stopped at traffic lights, for example, or stuck in traffic. Special use vehicles like cop cars often have SMALLER alternator pulleys than usual vehicles, in order to meet long-term idling demand without draining the battery.

Does this help? imp

 

[Cstoliker]

It does help. What I'm concerned about is at idle with full load the battery does discharge some. Most vehicles I've owned will maintain at or more then 14 volt.
I never tested the explorer prior to changing the alternator so I don't know what the norm is for this vehicle.
When I first start the truck it runs 14v with everything on at idle. After it warms up is when it starts dropping. I would think the regulator would increase output as the battery tops off.
Maybe the best thing to do is get it warmed up, turn everything on and see if it stalls.

 

[imp]

It does help. What I'm concerned about is at idle with full load the battery does discharge some. Most vehicles I've owned will maintain at or more then 14 volt.
I never tested the explorer prior to changing the alternator so I don't know what the norm is for this vehicle.
When I first start the truck it runs 14v with everything on at idle. After it warms up is when it starts dropping. I would think the regulator would increase output as the battery tops off. Maybe the best thing to do is get it warmed up, turn everything on and see if it stalls.

14 V. after starting should only appear when the battery state of charge is fairly low, OR, the battery has become borderline unable to accept a full charge. Let's say a fully-charged battery starts an engine, fairly quickly, just a few seconds cranking. That process should lower a good battery's output by maybe a volt or two, this being it's voltage right after cranking the eng. stops. System voltage might then jump to 14V., this being provided by the alt., as it provides both re-charge current, and eng. running current. (current is Amps.). It should take no more than about 10 seconds or so to bring the battery back up to full voltage, at which time the measured voltage should have dropped back down to perhaps 12.8 or 13, where it should STAY pretty much, regardless of changing loads imposed by accessories.

(bold). Actually, just the opposite; system voltage SHOULD drop a little while after starting, as the charge has been returned to the batt. The discharge of the batt. imposed by starting, having dropped it's output to maybe 11V, requires a differential of voltage to be imposed, several volts MORE than the batt. voltage, to cause current flow backwards, that is, BACK into the batt. That difference in voltage between batt. and system (alternator) decreases as charge is returned to the batt. Once full-charge is back in the batt., system voltage remains EQUAL to batt. voltage, thus no current leaves or enters the batt. A sudden need for more electrical energy, like switching on headlights, results in alternator instantly meeting that added current demand, while batt. sees no change.

If alt. cannot meet the demand, for whatever reason, batt. must then make up the difference, resulting in discharge of the batt. The thing making this difficult to picture is that YOU can't measure the battery's output voltage SEPARATE from the alternator's output. The voltmeter only shows SYSTEM voltage, once the eng. is running. The only way to absolutely know if the batt. is getting current (charging), or supplying current (discharging), is to have an AMMETER in series with the battery. The old-time cars and trucks had 'em, and one could always see if the batt. was being discharged or not.

Does this help more? Glad you answered. Makes my effort feel worthwhile! imp

 

[Cstoliker]

When the truck is first started I get 14.3v with everything electrical on. After it warms up it drops to below 14. But by this reasoning if I have the truck warmed up, at idle and turn all electrical devices on the voltage should increase to confiscate for the higher load and system voltage not discrease

 

[SoNic67]

Well 14.3V at cold is correct. The alternator will put out less voltage if is "hot" outside of it, because will have to protect the battery.
Battery charging voltage changes with temperature. It will vary from about 2.74 volts per cell (16.4 volts) at -40 C to 2.3 volts per cell (13.8 volts) at 50 C. This is why alternators have temperature compensation because battery is subject to wide temperature variations.

 

[imp]

When the truck is first started I get 14.3v with everything electrical on. After it warms up it drops to below 14. But by this reasoning if I have the truck warmed up, at idle and turn all electrical devices on the voltage should increase to confiscate for the higher load and system voltage not discrease

What you must understand here, is that added electrical loads do NOT require an increase in system voltage, only an increase in current (amps) delivered by the alternator. The actual voltage which the alternator "puts out" is determined by the state of charge of the battery, not the amount of accessory load.

Think of the battery and alternator as two sources of electrical power, each connected to the other in parallel. That is, either one, or both, can supply power to the vehicle's electrical system. The idea is, the battery supplies starting power, since the alternator is not being driven yet, the engine starts, thereby spinning the alternator into action, and it then supplies ALL the power needed to replace back into the battery that used by starting, AND all the rest needed by accessories, IF the alternator is turning rapidly enough. Sometimes, at idle, some alternators cannot deliver enough; during that time, the battery supplies the difference, and it discharges under those conditions. imp

 

[Cstoliker]

Yes I know the voltage should remain constant. Voltage would not increase with load. But it does seam to decrease with load which would mean the alternator is not put out the nessisary current or is was at or near capacity before introducing the load.

I disconnected the battery when it was running. Turned everything on and it did not stall. The voltage did drop below 13 at idle though. It was idling very slowly so I turned the throttle close limit screw to raise idling speed and it now keeps in the 13.6-8 with everything on and 14 while driving.

 

[pugulis]

I think there's a little confusion on how Voltage and current work. Current is not supplied, it is drawn from the alternator. So when you have a 130 amp alt, that means, at max, you can draw 130 amp. So the amps (current) being drawn from the alt can vary greatly depending on the load. Voltage, on the other hand, should remain constant. You may see a dip or rise by a volt, but not much more. You should see roughly 13.5 volts + or - 1 volt. Less then 12.5 or more than 14.5 is bad. The voltage regulator does not regulate voltage based on load, but on speed. Remember, your alternator is seeing variable speeds as you run the engine faster and slower. So it is actually has a higher potential voltage the faster the engine is turning. The regulator, does exactly what it says. It regulates the voltage so it stays a the roughly 13.5 volts the system needs to operate. If you are seeing a swing of more than 1 volt (1.5 on the outside most) there is something wrong with the voltage regulator. Now I'm assuming that you are using an actual volt meter and not the one in the dash. The dash gauge is a worthless piece of crap. With all this said, if you're idling with all accessories on and you're seeing over 12.5 volts you're fine. And as you said, you were able to run all the accessories and disconnect the battery without the engine dying. If you can do this, the system is functioning.

A little more on voltage. You have to remember, all the accessories (especially the computer) are expecting 12 volts constantly. You can go slightly higher, but much higher than 14 will fry components. Hence the reason for the voltage regulator. You could have 100 accessories hooked up and it will still produce 12+ volts.

A little more on amperage. Accessories will only draw what they are designed to draw and no more. That's why you can hook up a 90amp, 100amp, 130amp alternator with no effect on the system. And why, if a component goes bad, you blow a fuse. Usually it's because the bad accessory has a short to ground and is instantly trying to draw more amps. And again, you could hook up 100 accessories as long as their combined draw is no more than 130amps (your alt). This is why, if you have something like a sub woofer hooked up, it will dim all the lights. It is trying to draw more than the alt can handle. But even if you hooked up more than 130amps worth of accessories, you'll still only be producing 12+ volts.

Hope some of this helped. I tend to ramble on a bit.

 

[imp]

Yes I know the voltage should remain constant. Voltage would not increase with load. But it does seam to decrease with load which would mean the alternator is not put out the nessisary current or is was at or near capacity before introducing the load.

I disconnected the battery when it was running. Turned everything on and it did not stall. The voltage did drop below 13 at idle though. It was idling very slowly so I turned the throttle close limit screw to raise idling speed and it now keeps in the 13.6-8 with everything on and 14 while driving.

This is exactly what should happen. It shows the alternator is working properly, but does not reveal anything about the condition of the battery.

One thing you can do to get some insight to the battery condition is to hook a voltmeter across the batt. terminals, disable the ignition by pulling the ignition coil high voltage wire out of the coil (to prevent starting), then crank the eng. while watching the voltmeter. If it drops much below 8 or 9 volts while cranking, the battery is struggling. After cranking 5 seconds or so, the voltage should rebound back up to maybe 12 volts or more. If it does not, trouble is brewing. It might read a bit lower than before the test began: this reflects the battery's voltage drop due to the discharging of the battery. The voltmeter should be connected directly to the battery posts, not to the terminals surrounding them, which carry current to the cables. This is because some voltage may be dropped between the post and terminal. That particular area is a most common source of trouble: the posts & terminals should be kept clean and lubricated to prevent corrosion. imp