Testing 24v alternator output

[sailor Martin]

Hi All

I'm trying to obtain a tool for load testing an either 12v or 24v alternator.

I was wondering if I used the normal 12v load tester for a 24v systrm, would it burn the tester?

Alternatively could I possiblely use two 12v testers in series so that each receives 12v while I test the output with Amp clamp?
If this is possible, perhaps (in order to avoide buying two testers) I can hook up something else in series . But I suppose it'll have to be something big and uncomfortable with the same low resistance as the load tester?

BTW I'm not interested in the electronic testers as I understand they cannot test current output.

Cheers
Gal

[Sherpa17]

Fluke makes meters tested to 60V. I imagine there are others.

[tkeithlu]

The crude old-fashioned load tester for batteries is nothing more than a resistance coil and a volt meter. The coil will handle 24 volts, and the meter could be sacrificed and then substituted by any multimeter. On the other hand, modern electronic testers have gotten a lot cheaper than they used to be; they don't all cost as much as a Fluke. Here's one:

https://www.amazon.com/TOPDON-100-20...s%2C208&sr=8-8

[CharlieJ]

Deplete the battery bank that is fed by the alternator you want to test. Start the engine and, after about a minute, race it to 2000 rpm and then set it at a fast idle. Use a DMM and check voltage at the output post on the back of the alternator. It should be >14.2VDC. Use a clamp on ammeter to measure the current flowing out of the alternator. It should be about 80% of the rated capacity of the alternator. Test complete.

If you don't have either a DMM or a clamp on ammeter, this meter does both and will not break most banks: https://www.bluesea.com/products/811...imeter_-_AC_DC. It is available for $148 here: https://tinyurl.com/y4ge83xb

[GordMay]

What CharlieJ said.
You might also be interested in a much earlier discussion:
BASIC Alternator Testing ➥ https://www.cruisersforum.com/forums....html#post1264

[RaymondR]

Originally Posted by tkeithlu

The crude old-fashioned load tester for batteries is nothing more than a resistance coil and a volt meter. The coil will handle 24 volts, and the meter could be sacrificed and then substituted by any multimeter. On the other hand, modern electronic testers have gotten a lot cheaper than they used to be; they don't all cost as much as a Fluke. Here's one:

https://www.amazon.com/TOPDON-100-20...s%2C208&sr=8-8

Another use for the push bike spoke variable resister.

[Cowpoos]

run the leads into the sea so both ends don't touch, a foot or so away from each other and put a clamp meter on the leads. Put a voltage meter on the leads at the alternator end.

Don't run this test for too long as alternators are not rated for continuos duty and they over heat.

[stormalong]

Originally Posted by Cowpoos

run the leads into the sea so both ends don't touch, a foot or so away from each other and put a clamp meter on the leads. Put a voltage meter on the leads at the alternator end.

Don't run this test for too long as alternators are not rated for continuos duty and they over heat.

Don't do this! As already said the way to test an alternator is to check the voltage and current into a battery that is partly discharged. You can turn on additional loads to increase power load. An inverter with a space heater is a good additional load.

[Cadence]

You might use a dead battery as a test load.

[Cowpoos]

Originally Posted by stormalong

Don't do this!

Why not? A partly discharged battery is not enough of a load to test an alternator and get accurate results.

[stormalong]

Originally Posted by Cowpoos

Why not? A partly discharged battery is not enough of a load to test an alternator and get accurate results.

Because this is a crazy way to produce a resistor. What is the resistance you are aiming for? What evidence do you have that a foot between electrodes will produce the intended resistance? What is the surface area of your bare wire electrodes? Have you done anything like this? It is an uncontrollable experiment. On the other hand there is a boat full of load that can be switched on.

It is very easy to produce controllable results so why play around with some unknown wild ass guess on making a proper load.

Testing an alternator is not difficult. First measure the battery voltage, then power the voltage regulator. Did the voltage rise? If yes the alternator is producing power. How much power? Use a clamp on ammeter. Turn on loads. Use your inverter, run a microwave, an electric stove or electric heating element on a water heater. No inverter and microwave, stove or water heater? Why do you have a 24 volt electrical system? Spin your windlass without chain. Turn on the refer. Turn on every light, fan, etc on the boat. That makes a controllable measurable load.

[RaymondR]

A bike spoke makes a very good high wattage variable resister.

[Cowpoos]

Originally Posted by stormalong

Because this is a crazy way to produce a resistor. What is the resistance you are aiming for? What evidence do you have that a foot between electrodes will produce the intended resistance? What is the surface area of your bare wire electrodes? Have you done anything like this? It is an uncontrollable experiment. On the other hand there is a boat full of load that can be switched on.

It is very easy to produce controllable results so why play around with some unknown wild ass guess on making a proper load.

Testing an alternator is not difficult. First measure the battery voltage, then power the voltage regulator. Did the voltage rise? If yes the alternator is producing power. How much power? Use a clamp on ammeter. Turn on loads. Use your inverter, run a microwave, an electric stove or electric heating element on a water heater. No inverter and microwave, stove or water heater? Why do you have a 24 volt electrical system? Spin your windlass without chain. Turn on the refer. Turn on every light, fan, etc on the boat. That makes a controllable measurable load.

Go and google Liquid resistors and Liquid rheostats....you might learn something.

[stormalong]

Originally Posted by Cowpoos

Go and google Liquid resistors and Liquid rheostats....you might learn something.

OK, so go out and experiment with a resistor of your own making when there are plenty of loads readily available.

I am not going to research liquid resistors. Do any of the references talk about running cables into open sea water? How much cable would you need? What is the cost of that cable and the terminals attached to the inboard end? How much time will you spend on this? Once you have put the ends of wires into salt water capillary action will suck the water up into the cable so you cannot reuse the wire.

I have to call BS on cowpoos.

[Cowpoos]

Originally Posted by stormalong

I am not going to research liquid resistors.

Well good for you, but you then can't tell someone they are wrong if you have no knowledge of a subject.

Because that my friend is very dangerous on an internet forum such as this.