Hey everyone,
I am new to the forum here, and just bought a 1993 Civic EX.Recently, the battery light has been coming on and off. When the light is on and the car is running (or not)the battery reads 12.05 V, but after it turns off it jumps to around 14V while running.The alternator-battery wiringis good (voltageat alternator.) It seems to happen more when it's hot,so I tightened the belt today butno luck. Any ideas on what to check next?

-Jim

 

Your alternator likely needs to be replaced.

 

Thanks for the reply.

Yeah, I was considering that, but even thought the car doesn't look like its been maintained well the alternator looks newer and in good condition. If I were to have it tested they would say it's good if it was during the time that the battery lightwasn't on. Would an alternator generate electricity one minute and then just stop?

 

Yes, alternators often gradually or intermittently fail before completely dying. By the way, AutoZone will test your alternator free of charge. If you have a voltmeter or multimeter, you can also test it at home. At normal idle with no electrical load, the voltage at the battery should be ~14.5V. With high electrical load (i.e., headlights ON, heater/A/C fan on high, radio ON), the voltage should not drop below ~9.5V.

 

13 to 14 +/- .4 volts is normal with a good charging alternator; anything below that is not good. Voltage readings can be battery voltage intead of alternator voltage when measuring whith a bad alternator, so dont let the battery voltage fool you. And, never disconnect a battery cable while the vehicle is running...NEVER! Dont listen to old timers telling you to do that to test the alternator.. this is dumb and the voltage spikes that you will induce when doing this would hurt your electrical system, to include your ECM, TCM and ignition componets...USE A FREAKING MULTIMETER! And also, THERE IS NOT SUCH THING AS A BATTERY LIGHT, THESE BATTERY LIGHTS INDICATES CHARGING SYSTEM. No vehicle that I know have any indication of battery state.

 

Wow. Well I figured the light with a picture of a battery on it could be described as a battery light. But yeah, Iknow what the lightrepresents.

Okay, just to be clear I checked the voltage at the battery with my trustymultimeterwithout ever disconnecting it while running. I am aware of what voltages I'm looking at and the alternator works perfectly when the light isn't on. The reason I gave the voltages on the original post with the CHARGING SYSTEMLIGHT both on and off is to let everyone know that I'm sure it's not a short and that when the light is on the alternator is actually not working. I'm not sure if its not working because it is bad, or if its a belt or wiring issue. I'm having trouble with thisproblem because it doesn't happen all the time, so its hard to know if it's fixed or not. Just throwing a new alternator at the problem considering I only paid $500 for the car seems a bit hasty so I was hoping for suggestions on what to look at (ie certain parts of the wiring) to make sure its the alternator itself that is failing... and then fixing itself... and then failing again. Also, if it is the alternator going out is there anything I can look at cleaning or replacing inside that wouldn't be quite so expensive?

Thanks everyone for your input.

 

It's almost always the alternator itself. The brushes wear down and make intermittent, and eventually no, contact with the slip rings on the rotor. If you can find somewhere to buy them, the brushes are easily replaced and you'll get considerably more miles out of that alternator.

Take the alternator off the car and take the tin cover off the back and the carbon brushes are right there. If you find they are barely touching the copper rings on the shaft, that's what the problem is.

 

Thanks mk. That's the best advice I've heard so far. That would make sense with the thing working some of the time, I'll see if I can pick some up and let everyone know if it fixes the problem.

 

Hmm... I'm finding a lot of "not-vehicle-specific" brushes and brush/holder sets but they don't all look the same. How do I know which one to get?

 

It may help you to know that Honda had two different manufacturers for its 92--95 Civic alternators: