How can you tell your alternator is charging your batter?

[Spork]

Maybe your voltmeter in the boat is off, but on my boat @ idle it's right at 12v and underway it's 14v

[88 PS190]

Best way is to measure current, unfortunately gauges that do that are expensive, and depending how much current folks use a shunt and read the resistance across it.

[ricford]

Originally Posted by j.mccreight@hotmail.com

Maybe your voltmeter in the boat is off, but on my boat @ idle it's right at 12v and underway it's 14v

x2 don't trust your voltmeter in the boat. Check with a multimeter with boat off, then again with it running. Voltage should be right around 12v when running but definitely higher than when off. If you decide it's not charging, the most likely candidate is the alternator. You can remove it and take it to an electrical motor shop and they can test it.

[GoneBoatN]

x3 don't trust your voltmeter in the boat. For me the voltmeter gauge on the dash reads lower than using a voltmeter at the battery (about a full volt or more lower) - no big surprise there.

If your battery is not going dead (or at least being depleated), the the alternator is charging the battery. As previously mentioned, when the engine is running the voltmeter gauge on the dash should read a about a volt or two higher than when the engine is off.

A volt meter is a handy thing to have around the house. Understanding how to use one, even just the basics goes a long way.

[FrankSchwab]

First of all, don't even think about pulling one of the battery cables on anything built in the last 50 years. If the Alternator is charging, and you remove the battery from the circuit, you can get a spike of upwards of 50 volts out of the alternator for a few hundred milliseconds until it can shut down. It's called a load dump, and will destroy any unprotected electronics in the boat (ECU, Radio, etc). Most auto/marine electronics were protected when they left the factory, but the protection circuits aren't always reliable. This trick worked great on pre-integrated circuit cars (you know, when the ignition had points and the radio had a pointer on a string for station selection), but it's a good way to "Break Out Another Thousand" with anything remotely modern.

Buy the Voltmeter; Harbor Freight will sell you one for $5 ($3 on sale). We buy them by the truckload at work, because a new meter is cheaper than replacing the battery. We use them for testing the computer chips we design, so we're pretty picky. These things are plenty accurate.

Put the voltmeter on the battery. If the engine's been off for awhile (say, overnight), the battery should read 12.6 volts. Once the engine is up and running and the alternator starts charging the battery, the voltage will go up, as high as 15V but generally around 14.4V. If the battery is very low, it'll take awhile for the battery to make it up to 14.4V, but it should always be above the voltage that it started at.

[CantRepeat]

Get a cheap multimeter.

http://www.youtube.com/watch?v=arv0hutlz0Y

[JimN]

Originally Posted by j.mccreight@hotmail.com

The shade tree was is to remove the battery terminal while the engine is running, if it dies alternator is not doing its job, if it stays running the alternator is operating.

I wouldn't do that if the engine has any kind of electronic control, like an ECM. They hate voltage spikes and the ECM can be damaged by testing the alternator this way.

[JimN]

Originally Posted by j.mccreight@hotmail.com

Maybe your voltmeter in the boat is off, but on my boat @ idle it's right at 12v and underway it's 14v

That doesn't mean it's correct. At rest, a charged battery should be over 13VDC.

[JimN]

Originally Posted by 96prostar190

WITHOUT A VOLTMETER, how can you tell your alternator is charging your battery? I fired the boat up today and it was right around 13 Volts. Increasing the power to about 1500 rpm the volts jumped to about 13.5 volts. I'm sure it's working fine, but when should I become concerned it's not charging the battery? Below what volts do you guys think?

Thanks for the help!

Andy-

If you have a '96, as your name indicates, don't screw around with "shade tree" stuff. I didn't see Frank's post before I commented, but a meter is so cheap there's absolutely no reason to be without one if anyone might have even a small chance of using it. Of course, this comes with the need to learn to use it, but it's not difficult.

If you have problems with the battery being dead or depleted when you haven't run the engine for a few days, it could have a bad alternator. If it doesn't show lower voltage after running it, make sure the belt is good and it's tight enough (don't over-tighten, though).

If you have no idea about anything electrical, remove the alternator out (or have it removed) and take it in for testing. The easiest way to deal with a faulty alternator is to have the old one rebuilt- that way, you don't need to search for the same type or try to make something work when it wasn't intended for this engine.

[Spork]

Originally Posted by JimN

I wouldn't do that if the engine has any kind of electronic control, like an ECM. They hate voltage spikes and the ECM can be damaged by testing the alternator this way.

While I agree with what you and the other guys, the OP wanted a way to check WITHOUT a multimeter, yes they are cheap. Right or wrong I was merely giving what the OP wanted...