Measuring Alternator output

[bagmaker]

Hi all,
how can I measure the output of my (24v) alternator?
Is there a simple way?
There does not seem to be any stickers or markings on it and I am uncertain if it is an original item.

cheers,

edit - after the amps, not just the volts

[Mrcoolabah1au]

Have you try a multi meter?


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[BruceS]

Most auto electricians would have a test bench to run it up to maximum output.
I realize it'd mean you having to remove it from your vehicle though.
What vehicle is it in?
Only other way would be to install an amp meter on the output and after nearly flattening your battery (headlights on for an hour?) start the motor and give it half throttle!!
Probably need a 100A meter if it's a big sucker!
http://www.ebay.com.au/itm/New-100A-DC- ... 58bb4abfa4

[jon_d]

The easyway is to use a current clamp meter

With the motor running at a reasonable speed, clip the current clamp over alternator wire and then start turning everything on.

Lights, high, low, wipers, heaters and a flat battery.

[supersparky]

The easyway is to use a current clamp meter

With the motor running at a reasonable speed, clip the current clamp over alternator wire and then start turning everything on.

Lights, high, low, wipers, heaters and a flat battery.

The method that Jd has described will tell you what it can output, it won't tell you its maximum output. Some alternators have metallic labels and some are stamped into the stator housing. However, I wouldn't want to load an alternator anywhere near its max output for very long. Can you get a pic of the unit.

[jon_d]

But..... If you keep switching things on and the current doesn't go up, the output might be the maximum.

As Dave says, the label is the only way to really know the true spec of the unit.

[bagmaker]

thanks guys, I will check for a label first and try the "load up" method.

[T1 Terry]

Connect a clamp meter to the alternator output and a volt meter. Start engine and run at a fast idle, wait 10 mins, read the voltage, turn on a load, read the voltage and amps, continue doing this till you notice the voltage drop more than usual, this is the limit of the alternators 100% output, or the point the belt starts to slip, either way, that is maximum output. You will probably need to connect an inverter and start adding loads after you have gone through the lights and other accessories, you can hold this max output for 10 mins, watch the amps and voltage and see if they stabilise, add a load and see if the amps increase or the voltage drops further. 60% of that maximum reading is as much as you can draw continuously, after you turn the loads and the motor off, carefully touch the alternator and you will see why you can not run it at full load for more than about 10 mins, it will be quite hot

T1 Terry

[bagmaker]

OK, makes sense, thanks- but wouldn't the crank battery add a fair bit to the readings?
And if not, wouldn't it be slightly flattened at the end of the test?

[T1 Terry]

The load will pull the voltage down, the alternator will try to bring the voltage back up. When the alternator can't add more amps than the load, the voltage will start to go down but the amp readings will remain the same, within a few amps anyway. Reduce the load until you can maintain 12.8v, give or take a bit, hold that for 10 mins and see if the amps are still the same, give or take bit. This will determine the max you can draw from the alternator. Make sure the belts are in good condition before you start the test, this will put max load on them and if they are a bit on the weak side it will shred them in mins. You will be able to smell the belts slipping if the alternator is over sized for the belts, back the load off till the slipping stops. If the belts are shiny inside the V, they have been slipping and need replacing.
Gates make the best belts, Dayco aren't bad, the rest are fairly much the average, some better than others.

T1 Terry