Charge light

Hi Guys,

My Charge light is constantly on but dim. It started two years ago, when starting the car the light didn't extinguish as usual, and my voltage display confirmed that the battery wasn't being charged. I looked under the bonnet and the belt was still there and tight so I continued driving. After a few miles the voltage gauge displayed that the car was charging the battery again, and has continued to charge properly since- but the 'charge' light has been on since, albeit dimly.

I've been driving around for the few years no problem but it's kinda getting on my nerves now. I've checked the voltage regulator and main positive coming from the alternator (sandpaper the contacts) on the weekend but that did nothing.

Anything else to look for? I had a similar problem on my other car whereby the positive contact of the alternator was a bit rusty and cleaning that fixed that car so that was the first thing I thought of.

With ignition on (engine off) the charge light illuminiates to full brightness, and acts the proper way that it should as do all the other dash lights (for example when cranking over, and extinguishing when engine started), but it just doesn't quite turn off.


Any other ideas? Thank you. Matt.

 

cock roaches like getting inside the alternator where is warm and cozy but it shorts out the bridge or the tri-diode like CJay said.

Fernando

 

Thanks guys. Just wondering what other people would look at foremost before looking more closely at the alternator internals. Yes, I have the manual here which i've used in the past so when I get time i'll have a look and take the alternator apart again (last done in '16). It could also be something as simple as a poor earth connection between the alternator itself and the body though? Simple tests such as that but besides what I did on the weekend i've yet to test first before decideding to remove it from the car completely.


ftp://blurredmanswebsite.ddns.net/Vehicle_Documents/Delco%2010-SI_Alternator.pdf



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Interesting mix of cars and bikes - what voltage do you get with a handheld multimeter at the battery with the engine running?

 

Assuming that you are referring to a GM Delcotron, the diode trio is very replaceable. I don't know about now, but 20 years ago most decent auto parts stores had them in stock. That should tell you something...

If you decide to tackle it and you haven't done one before, there is a trick to getting the brushes back in place when attaching the rear housing. It involves a toothpick. You should be able to figure the rest out.

 

I have just finished a trip of over 2,000 miles going to france and germany and the charging system never faultered other than the charge light being on slightly the entire time (charge voltage 13.7v when idling in drive with the voltage meter). The voltage gauge I installed in the car corresponds to this, and indeed on my trip the voltage never went highter than it should have.

However, now that it needs the rest- when it's in the garage I'll take the time to remove the alternator fully and take it apart to do the testing of the diodes. Thanks.

 

Finally got time to take apart the alternator.

I don't have a diode test function on my multimeter and the book I had previously linked doesn't contain any figures for one to do on the bench resistency checks so I did it the easy way and test each diode terminal with a battery inline with a bulb. One of the diodes does not allow the bulb to get voltage (either way) so presumably this is the problem. I'll look to be ordering a replacement at somepoint soon and updating thread if/when works. But I have other things I need to buy for the car yet so I won't make that order yet (I'm in Britain- the postage is expensive!).

Additionally I noticed the brushes are quite a bit more worn than I might expect them to be for a genuine 38k mile vehicle/alternator. The one in particular (to the rear) is particularly worn, and more dust than I might expect. Curious. The sliprings however seem perfect and not grooved- brush springs themselves seemed fine too at a glance as did everything else.

 

From the picture, it looks like you have a 27SI alternator. Replace the diode trio when you replace the diode assembly. Also be sure the connection at the other end of the metal bar (not shown in the pic) is clean and tight. They have a tendency to burn there. Just for curiosity, which diode is bad? looks like it may be the one on the lower left.

 

Hi, I always thought I had a 10SI looking at various pictures. Perhaps I was wrong.

I don't know of any test for the rectifier itself- I was talking about the black component that links all three of the phases and passes the voltage to the regulator.

 

That would be the trio. Check the other six diodes or just replace it when changing the trio. Look at the numbers stamped on the case. If you see a stamp 80A or 100A it is a 27SI. or post a pic of the entire inside of the case. The diodes and trio are different on a 10Si than a 27SI.

 

Use an ohm meter to check the rectifier bridge. Remove the diode trio and bend up the six tabs touching the three studs. Put pos lead on the stud and the other lead on the aluminum heat sink you should have continuity one way and not the other. Then check for continuity to the other heat sink. Do that on all three studs and both heat sinks. then switch the leads, put the neg lead on the stud and check for continuity from each stud to each heat sink. You shouldn't get continuity in both directions on any stud to any heat sink and you shouldn't have any open. You're taking 12 readings.

 

Thanks guys. Will check.

 

Okay. Thanks 1973gs. I'm getting 40-44ohm each on the rectifier and only one way. so it seems that checks out. Though I was only getting those figures reading on the copper bit- I was getting nothing on the terminals themselves either way. From what I read on-line none of the instructions for testing seemed to tell the user to bend up the tabs to seperate from the posts.

Can confirm. 80amp alternator

 

I had same issue, took it to the alternator shop and they replaced the diode like 17 years ago and it never did it again. Except I think my idiot light says "ALT"

 

I don't have experience with these, (which i can tell Stellar does), but If the left leg of that trio is supposed to be grounded to the heat sink, that blob of solder looks super sketchy to me. Do you re-solder those blobs when you replace the trio?

 

It's not solder that you are seeing. It is melted plastic. The trio is not grounded and should not be. At one time I used to rebuild the rectifiers. In the pic you can see two heat sinks. The lower is the pos and the upper is the neg. The neg is grounded with the 2 screws upper left and right. The pos is insulated from ground with plastic at the base. On the left above the half bar visible on the pos rectifier ( bar goes to pos output post not visible in the pic) you will see a plastic lock with angled corners. There is a lock on the other side also. The narrow rectangular piece of plastic in the center of the plastic lock is what keeps the lock tight. You can knock that piece out and the two halfs will separate. Without the diode trio there you can bend the copper tabs that fold to the 3 posts straight up The rectangular black piece encapsulates the 3 posts. It can be pried up past the copper diode tabs. The melted plastic that you thought was solder is there to hold black piece in place.

 

I don't recommend anyone trying to rebuild the rectifier unless you are very good at soldering. The heat sink is aluminium and the diode has a copper base on both sides. one side is soldered to the heat sink and the other side is soldered to the copper tab. The heat sink needs a lot of heat to melt the solder, but too much heat and the diode will be damaged. The trio can be rebuilt also. Grind the top of the plastic trio off to reveal the diodes. Grind them out and solder in new diodes. Pretty easy actually.

The rectifier and trio are not expensive, so it would be better to replace with new ones unless it is desperate times and nothing is available. The original poster should replace everything while it is apart. Diodes,trio,regulator,brushes and bearings. It is obvious the stator and rotor are good as it charged as it should with one bad diode in the trio. (meaning charging at 13.7V) as he mentioned. With the new trio he could expect to see about one volt higher.

 

I purchased some very nice items from Stellar. He does great work on these and starters.