How do you test alt output?

[Goebeler]

I am a novice and will most likely catch some crap for asking...how do I test the output (if any) of my alt. I installed a high output last year and I am now going on my second redtop Optima. I don't think it is charging for sht. It sat for 6-7 months due to an injury and now is ready to be beaten again. I charges it up and it jumped to life but after two starts, it is dead the next day. There is no other drain on the battery while the key is off that I can find.
What should I look for?
My bigest concern is that it is an auto trans and I don't want to be stranded in the woods without a jump start. Should I put some type of battery didconnect on for when I shut the truck down?

Any advice?

 

[Stone]

It could very well be your battery that's the problem and not the alternator. Do you know if you had a good battery before you put it in storage (I would have disconnected the ground cable if I knew Iwas storing it for that long)? If its a serviceable battery, do you have enough fluid inside or is it dry? Etc. etc. If you have a stereo, alarm system, or a clock hooked up in your vehicle, there's always a tiny draw even when the vehicle is turned off (radio memory, clock memory, etc.).

Take a voltmeter to your battery when the vehicle is turned off, it should read somewhere around 12v (maybe slightly under).

When you have the vehicle running, put the voltmeter to your battery again, and now it should read a few volts higher with the alternator charging the battery (between 13.5-15v).

Easiest way I can think of testing if your high output alternator is putting out enough Amps is to look at your accessories and add up the number of Amps that they use up and turn them all on while your vehicle idles, then look at your voltage.

Hope you feel better from your injury...6-7 months off probably meant it was a fairly serious one.

 

[IDave]

That, and you can pull the alternator and take it to NAPA and they'll test it for free.

 

[Landpimp]

volt meter, check(when running) on the main post(the one with the nut) on the alt for voltage, should be 14volt-ish, then check the battery should be the same(or real close)

yeah you might have a voltage draw. Alt might also be overcharging the batts causing them to fry and die.

I just started using the Deltron Bettery Tenders, it keeps the batts at a perfect level without over charging, $33 each, got em hooked up to 4 rigs that don't get much use, the units I got are waterproof.

my guess is the alt is dead.......and you are just running on the battery alone, can drive for a day or 2 if you don't have much stuff on......I know I have

 

[LT]

Just going through what you are, I went and had my alternator tested at Auto Zone and it was DOA. I bought the damn thing back in August, Napa Reman. Quality

 

[toddslater]

One other little tid bit...when checking your alt output. Don't just check it at idle. Push it up to 2,000/2500 rpm and check it as well. Alt's can put out the correct voltage at idle but if the reg is not working properly, I've seen 16-17 volts. And that will cook your optima post haste.

 

[Goebeler]

I just put a new Optima in the cruiser and it jumped to life. I will test the output as soon as I find a volt meter. I was curious about one other thing. I have a single wire going from my Alt (powermaster) to the hot terminal on the battery. I assume this is where it goes? I assume the alt, if working correctly should be charging through the positive terminal? As you can tell, I am no genious with this crap, but willing to learn!
Sounds like the voltage meter is a must right now. The Napa won't check the high output alts. Not sure why but they said no.
Another interesting thing is that when I raise the rpms on the engine, the alt gauge goes the wrong way. ..to the left? When I turn lights or accesories on, it goes to the negative side, but shouldn't it go to the positive side if the rpms are racing and thus charging the battery?



Again sorry for the stupid ??'s but I am easily stumped.

Goebs

 

[mr_manny]

You will forever be in the NEGATIVE, as long as the original white/blue wire from original harness is not incorporated into your upgraded alternator system

It's no big deal, several fellow cruisers don't really recommend sending all those amps under the dash...

at idle, test your voltage at the battery...raise rpms to apporx 2k and re-test.

hope this helps,
manny 72fj40

 

[treerootCO]

Two things you can always try if you don't need a real answer. Pull the pos/neg with the truck running. If it dies, the alt isn't working. You don't need a battery for the truck to run. Also, the alt becomes a magnet when it is working. Stick a screwdriver to the back of it, where the post is that everything spins on. If your screwdriver sticks it's doing something. All this really tells you is if it isn't working. Anything else it might be working.

 

[JohnL]

You will know right away if you lean against the fender and stick your finger into the connectors at the back of the alt.

 

[Landpimp]

I think that a safe test for old school alts but new alt and cruisers it can kill stuff

Two things you can always try if you don't need a real answer. Pull the pos/neg with the truck running. If it dies, the alt isn't working. You don't need a battery for the truck to run. Also, the alt becomes a magnet when it is working. Stick a screwdriver to the back of it, where the post is that everything spins on. If your screwdriver sticks it's doing something. All this really tells you is if it isn't working. Anything else it might be working.

 

[mr_manny]

If he wanted to see the positive side of the amp-meter, would it be as simple as attaching the current alternator output lead to the white/blue stripe (heavy gauge) wire from original alternator harness?

I believe he currently has the output going straight to the Battery (original external voltage regulator would be removed from wiring harness)...

manny 72fj40

 

[Goebeler]

I liked Treeroot's ideas but am thinking I ight damage something if I remove the terminals while running. Thus I guess I am left with finding a volt meter and learning how to test the volts at idle and rpms increased. May be a good tool to add to the collection.
Thanks and hope I can solve this once and for all.

Goebs

 

[lovetoski]

Get a digital multi-meter at Radio Shack or Sears. Read the following website, and you're good to go!

http://www.shadetreemg.com/multimeter.htm

 

[72cruiser]

doin the same thing goebeler...
borrowed my bro-in-law's multimeter and have been goin to town on all my wiring.

actually starting to understand some stuff (by 'some' i mean extremely small amounts of very basic electrical theory....ha ha, should have paid more attention in physics a couple semesters ago...)


malphrus

 

[Goebeler]

The new Optima tests at 12v and when running it is at 14.1-14.7. Seems to be charging fine and running well. I might have had a bad wire to the engine coolong fan cause when I turned it on the engine almost stalled and then came back to full idle. I removed the wiring and ran it directly to the battery with an inline fuse and now when I turn it on the idle remains the same. Could that have been drawing down the battery?

The Optima I took out tests at 4.5 volts. How do you charge an optima red top or should I take it somewhere to have it checked to see if it is dead.?

Goebs

 

[JohnL]

Charge with any charger.

Here's a related ?...

What does it mean when you check you battery with a volt tester and it momentarily reads 14v, then immediately goes to 0? I'm getting ready to start her up tomorrow after 5 months in rehab (the FJ, that is!) and my 5 year-old optima red top has been sitting that time. I topped it off with a charge and when I checked it with a voltmeter, that's what I got.

Oh yeah, my multitester has been being a bitch lately.

 

[Stone]

Are your meter leads in good shape? Maybe there's a loose connection inside...unscrew the plastic cover from the probe and make sure the wires inside are still securely soldered. Also, just make sure you have good batteries inside your meter if it's acting up generally.

 

[JohnL]

Mine is making a continuity connection inside teh case itself, so if I press lightly or jar the case, the continuity "tone" goes off. Generally don't trust it 100% anymore.

Have you seen voltage readings like that before?

 

[Stone]

I have seen that and have generally attributed it to bad contact to the current source or a loose connection in the meter somewhere. I'd suggest a new meter which cost less than $20 these days (for a basic one). Cheers.