Monitoring Alternator Output

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Ifixyawata

Ifixyawata

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Some of you may have seen my previous thread. Today I will be replacing the alternator on my Focus and I want to know what the most reliable way to monitor it's output voltage is.

Currently I am planning on using my smartphone and Torque Pro ODBII app to monitor the system voltage at the adapter. I have watched it when the old alternator was failing and it seems to be pretty closely representative of the alternator output and matched the numbers I was getting at the battery.

Is this a sufficient way to monitor the health of the alternator and charging system?
 
Install a voltmeter.

Edit: you can get small clusters and also mount coolant temp, oil pressure, trans temp, oil temp, etc in the same housing.
 
Last edited:
DC Clamp meter?

Most clamp meter cannot do DC though so be careful when buying the meter.

Assuming you know the cable going from the alternator to the battery, although, it is probably easy to id.
At idle speed, alternator suppose to produce the lowest amp.
The higher the speed, the higher the amp up to the highest limit voltage determine by voltage regulator.
 
Last edited:
Originally Posted by Trav
Install a voltmeter.

Edit: you can get small clusters and also mount coolant temp, oil pressure, trans temp, oil temp, etc in the same housing.


I think I should do this soon, I was sort of wondering if the voltage at the adapter (as reported through the software) is at least a ballpark reliable figure.

Originally Posted by JMJNet
DC Clamp meter?

Most clamp meter cannot do DC though so be careful when buying the meter.


I'm looking for a permanent in-car solution. I will probably go with a voltmeter. The question is, where/how do they wire in?
 
Wire it into any circuit that's live with engine on or accessory circuit on. For example if it's going to be in the dash there is the radio supply, just pick the one that is for main power not for memory for clock and radio stations/etc., so it's not draining the battery unnecessarily when the vehicle is off. The drain is not much for the minimum function of most voltmeters but might as well not have it with vehicle off.

It just gets wired to its supply wire and any chassis ground or ground wire. Do use quality sealing splices or solder and heatshrink tubing, not just twisted and electrical tape which can fall apart later.
 
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Get a 3 wire voltmeter. The third wire usually yelow or white is voltage sense. Ru. It and a ground wire.with some 22awg zip wire to battery. Fused at battery with waterproof atc fuse holder

Wire.red wire to a circuit live. When you wantvoltmeter it live.

I like.seeing battery terminal voltage during starter motor application.

Use fuse tap.to cleanly tap a circuit for the voltmeters red wire

Voltmeter with only two wires.will read voltage wherever you tap power from. Which can be far different than the battery terminals depending on loads.on the circuit tapped.

There is a bayite ammeter/voltmeter combo that uses a hall effect ing sensor. With a 3/4" inner diameter. That one can slide over a single wire to see amperage with a 0.2a resolution .
 
Originally Posted by Dave9
Wire it into any circuit that's live with engine on or accessory circuit on. For example if it's going to be in the dash there is the radio supply, just pick the one that is for main power not for memory for clock and radio stations/etc., so it's not draining the battery unnecessarily when the vehicle is off. The drain is not much for the minimum function of most voltmeters but might as well not have it with vehicle off.

It just gets wired to its supply wire and any chassis ground or ground wire. Do use quality sealing splices or solder and heatshrink tubing, not just twisted and electrical tape which can fall apart later.
You could just run a add a circuit off the fuse box, no need to hack up the factory wiring.
 
Hook it to an ignition circuit as WRX alluded. It'll be off with the car off and you can see how low it dips when you crank.

I'd get something like this guy and hole-saw through some lower dash trim to install it.
 
Originally Posted by wrcsixeight
Get a 3 wire voltmeter. The third wire usually yelow or white is voltage sense. Ru. It and a ground wire.with some 22awg zip wire to battery. Fused at battery with waterproof atc fuse holder

Wire.red wire to a circuit live. When you wantvoltmeter it live.

I like.seeing battery terminal voltage during starter motor application.

Use fuse tap.to cleanly tap a circuit for the voltmeters red wire

Voltmeter with only two wires.will read voltage wherever you tap power from. Which can be far different than the battery terminals depending on loads.on the circuit tapped.

There is a bayite ammeter/voltmeter combo that uses a hall effect ing sensor. With a 3/4" inner diameter. That one can slide over a single wire to see amperage with a 0.2a resolution .

I like this idea but my battery terminals are pretty 'full' with extra grounds and an Amp power wire.

Originally Posted by eljefino
Hook it to an ignition circuit as WRX alluded. It'll be off with the car off and you can see how low it dips when you crank.

I'd get something like this guy and hole-saw through some lower dash trim to install it.


I like the price point on that one for sure.
 
You can get a volt meter that plugs in cigar lighter. EBay or Amazon. Check accuracy with a regular volt meter.doesn't matter if it's a little high or low as long as you know
 
You can get a volt meter that plugs in cigar lighter. EBay or Amazon. Check accuracy with a regular volt meter.doesn't matter if it's a little high or low as long as you know
 
If your car has regular halogen (not HID or LED) headlights and is wired so that the lights stay on after you turn off the engine, something you can do for zero dollars is pay attention to what happens when you park at night. The lights should dim slightly from the voltage drop when the engine stops.
 
Originally Posted by maxdustington
You could just run a add a circuit off the fuse box, no need to hack up the factory wiring.


So you have a fuse sticking up higher and wire hanging out of your open fuse box, running to wherever the voltmeter is, and still needing to run the ground wire somewhere else? That seems like a messy solution, and one that is prone to failure after miles of the wire vibration and stacked upper fuse adding stress to the fuse contacts.

If done right there is nothing negative about splicing into existing wires. It is the right way to go for something that is permanently installed and low (ultra low in this case, could be no more than 15mA if that, depending on the display type LCD vs LED) current consumer so it doesn't need its own dedicated, fused circuit.

On the other hand if it is not meant to be a permanent installation then a cigarette lighter plug based voltmeter is a good option, but many vehicles have always live cigarette light outlets, though some with multiple outlets have one that goes off when the accessory circuit times out, but it may not be in a convenient, line of sight location. Some are under $3 delivered on eBay. Another option is add an additional lighter outlet in line-of-sight that shuts off with accessory power, do run that to the battery with an inline fuse, through a relay activated by the accessory power circuit, then it is available for anything you want to use it for whether a few mA voltmeter or something using up to the rating of the outlet and relay.
 
I have a ScanGauge and I monitor it via that. A Cigarette lighter volt meter can be had on the cheap on Ali-Express / E-bay
 
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Why do you need to monitor it full time? Why not just after the new alternator is installed? If it's working properly you should get many years before it's a possible issue.

My Dad took heavy wire and ran the battery charging circuit into the dash and installed an ammeter. It was a 1960 Chevy wagon. Might have had a generator vs alternator.

I think measuring it once and awhile using a batter & charging meter that can detect ripple (bad diode) would be best idea.
 
Originally Posted by JMJNet
DC Clamp meter?

Most clamp meter cannot do DC though so be careful when buying the meter.

Assuming you know the cable going from the alternator to the battery, although, it is probably easy to id.
At idle speed, alternator suppose to produce the lowest amp.
The higher the speed, the higher the amp up to the highest limit voltage determine by voltage regulator.



A clamp meter is not going to measure voltage via the clamp . It would probably measure voltage if it comes with leads & has a voltage scale .

I have used my Fluke T5 from work to verify voltage on a car .

https://www.fluke.com/en-us/product/electrical-testing/basic-testers/fluke-t5-1000

But a DIY'er can probably get buy with a HF VOM .

https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore%2Cf%2CEAFeatured+Weight%2Cf%2CSale+Rank%2Cf&q=volt+meter
 
Originally Posted by Donald
Why do you need to monitor it full time? Why not just after the new alternator is installed? If it's working properly you should get many years before it's a possible issue.

My Dad took heavy wire and ran the battery charging circuit into the dash and installed an ammeter. It was a 1960 Chevy wagon. Might have had a generator vs alternator.

I think measuring it once and awhile using a batter & charging meter that can detect ripple (bad diode) would be best idea.


Its honestly not a bad idea. Even though the alternator may be working the voltage regulator can go wonky causing not only under charging that you would notice but over charging that may not get noticed for a long time but cause terminal corrosion to be heavier and cause bulbs to burn out quickly.

Many times heavy "fuzz" on the battery + terminal is written off as post to case leakage when it well be due to excessive out gassing due to higher than normal voltage.
A gauge inside the car is great for monitoring and of course it must be installed in a switched + cable, the cigarette lighter may or may not be switched especially if its an "accessory" socket, most cars today are but not all.
Amp meters were popular in the generator days and even some alternator vehicles but some were fire prone, best to leave them alone IMO.
 
Lots of vehicles today intentionally keep the battery in a discharged state. So that it can accept higher amps when the voltage regulator asks for a higher voltage wbich the alternator then produces. Usually when letting off the gas or braking.

Ignorance is bliss though. Id get irritated seeing 12.6v going down the road and only 14.7 when braking.

The ammeter allows one to see how many amps.are.flowing. where the ammeters sensor is located will show total alternator output. Or that going into, or out of the battery.

Whennone can see just how many amps the battery is accepting at a certain voltage. They can guestimate state of charge.

When one can see how many volts a battery is maintaining. Providing amperage to power loads. One can see he general health of he battery. As wel as state of charge. But comparitive observations over time are required.

My rig came with an analog ammeter. But when the alternator failed, i did not notice the needle kove 1/16" from charge to discharge. I knew the charging system was failed as the turn signal blinkers and windshield wipers moved significantly slower. A digital voltmeter would have made the failure immediately obvious. But so would a digital ammeter with a negative next to the number.

My rig uses 8.2 amps a hot idle and 12.2 amps just to run ignition and fuel pump at idle and 2k rpm.

If my alternator were to fail. The meters would give a great indicationn of how far i could drive on only the juice stored in the battery.
 
Originally Posted by WyrTwister
Originally Posted by JMJNet
DC Clamp meter?

Most clamp meter cannot do DC though so be careful when buying the meter.

Assuming you know the cable going from the alternator to the battery, although, it is probably easy to id.
At idle speed, alternator suppose to produce the lowest amp.
The higher the speed, the higher the amp up to the highest limit voltage determine by voltage regulator.



A clamp meter is not going to measure voltage via the clamp . It would probably measure voltage if it comes with leads & has a voltage scale .

I have used my Fluke T5 from work to verify voltage on a car .

https://www.fluke.com/en-us/product/electrical-testing/basic-testers/fluke-t5-1000

But a DIY'er can probably get buy with a HF VOM .

https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore%2Cf%2CEAFeatured+Weight%2Cf%2CSale+Rank%2Cf&q=volt+meter





For alternator, the proper performance measure is amperage.
How much amperage the alternator produce?
You need the clamp to measure the amp not voltage.
This is if you really needs to know how good is the alternator.

Car should have a battery logo that light up when the voltage goes below a certain threshold.
Unfortunately, it will not show if the problem is the battery 99% of the time, alternator 1% of the time.
That is why they only measure the battery and the alternator as secondary.

Measuring the volt is secondary measurement if you want to measure the alternator.
At a certain rate of amp-acity, the voltage will show sufficient and that amp-acity may be lower than what the car needs.

I agree with a post that say to measure it once in a while not continous measurement.
If I suspect there is issue with alternator in any of my vehicle, then I measure the amp-acity of the alternator.
Whether it has enough to charge the battery.
 
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