To test that my alternator is charging should I be able to find 14.2 volts etc when I put the multimeter on the terminals when engine is running?
At the moment I'm only finding the current battery reading which is 12.4 and decreasing after start ups as the alternator charge light won't go off when I reach 1000 rpm?
I'm thinking maybe it's not charging I would think I should be able to find the charge rate on one of the terminals when over 1000rpm?
Any help would be great..... Cheers
When the motor is running then the battery voltage should charge to between 13.8 and 14.2 volts.
If not, it can be something as silly as the aternator light in the dashboard blown. Some cars need the charge indicator globe to be working for the alternator to work How dumb is that?
Anyway, first check is to make sure the alternator warning light comes on when you switch the ignition on and the motor not running.
If not, change the globe.
Is this in a car or are you running one separate to charge up all your lithium batteries?
Na mate in a boat but its the same principle what I'm saying if I disconnect the 3 wires from the alternator and then test the terminals Should I find the charge rate there when the engine is running? Kinda do my own bench test
There's a regulator in there somewhere that could complicate things when you disconnect the 3 wires.
If the regulator is still in circuit you should see the 14 odd volts.
If it's not then you could get anything, from a small voltage, if there's no current being fed to the field coils, to high if there is.
Alternator light on and only battery surface voltage present shows the alternator is not charging. Run the engine and give the side of the alternator a sharp tap where you can,t damage the stator or connections. This may free up the brushes spring tension if they are getting short. If you have one plug with 3 wires then you possibly have an external regulator. If so bridge power from battery positive terminal to the "F" terminal and see if the alternator charges flat out (14-18v) depending on engine revs. Or take off both units and get them to your local auto electrician
Your alternator, as its name suggests, outputs AC electricity. The diodes, mentioned above, form a full wave bridge rectifier, thereby outputing DC electricity. After that there's a regulator which should regulate that DC at around 13.8VDC to 14.2VDC (something in that neighbourhood). I don't really know, but I would guess that that the AC output, directly from the alternator windings, would go well over 100VAC at high revs - just guessing. There should be some generic automotive charging system testing procedures on the net - I haven't looked.
Thanks guys I will try and give it a tap while she's running....this alternator is on a Diesel engine on my yacht it's my 3rd in 5 years it seems the battery charger is cooking my alternator over a extended period when I leave the boat.
The battery charger will boil you batteries but won,t damage your alternator. Do you get your alternators marinized before you install them to stop any internal salt corrosion issues. Also what's size batteries are you running. If the output of the alternator isn't, high enough it may struggle to recharge batteries that have been flattened which shortens the life of the alternator.
The engine rooms on yachts are sealed to keep salt water out..... I spray my alternator with light lanolin oil anyways...... It's a 40amp alternator and I have 3 x100 amp hour battery's...... The battery charger is 20 amp and goes to float mode when the battery's reach fully charged.... But for some reason I suspect it ruining my alternator.
Not so much salt water directly but rather condensation from engine room temp. You need to get a larger output alternator if you have 300ah worth of batteries. A 40a alternator is too light for the job required of it especially if you flatten the house banks. The alternator can,t get damaged by the battery charger as the diodes in the alternator protect it from this problem.
I haven't read all of this thread, I can't be bothered it's like being at work but to answer your question.
Briefly and in the situation you have described, voltage should be 14.2v +/- 0.2v, anything less than this will only maintain your batteries state of discharge. This is why your battery voltage is at 12.4v. A fully charged battery in good condition should be 12.6v.
A good quality battery charger with a maintenance cycle will not boil batteries if left on permanently.
Edit: Type of battery, or computer controlled alternators may change the basics mentioned above.
