Alternator/Charging question

[dk6164]

I have a 1990 3.0 with a Mando alternator. I had a current draw that drained my old battery last season and put a new one in. The alternator seems to be always charging. Even with a fully charged battery you can hear it charging. It lugs the motor down even at idle? I wonder if the regulator could be bad and how to check it? I put a voltmeter on the battery with the engine running it's showing 14.9 volts. I don't want to smoke the new battery so any advise would be greatly appreciated!<br />Thanks

 

[Bt Doctur]

Re: Alternator/Charging question

try this: turn everything off, remove the pos. cable and touch it the pos. post. any spark is a current draw. most likely a bad diode in the alt. most are preset to about 14- 14.6V. the regulator may be an adjustable type,remove 4 screws, move adjustment counterclockwise.

 

[dk6164]

Re: Alternator/Charging question

Bt Doctur-Thanks, I know somethings drawing current after shut-down. I'm gonna install a battery switch to (hopefully) get rid of the draw Do you think the Mando's are worth getting rebuilt? Or should I replace it with something else. I noticed in alot of the older posts you seem to think it's better to replace the Mando with a GM 1 wire!<br />I'll pull the cover first to see if it's adjustable.

 

[Bondo]

Re: Alternator/Charging question

With the motor Running,+ a Fully Charged Battery,........<br /><br />You Should be seeing 13.6V on a Gauge or Meter.........<br /><br />Whether you go with the Mando, or the Delco,.......<br />Get the Right 1,.. The 1 that's For Your 3.0l Merc.......

 

[dk6164]

Re: Alternator/Charging question

If I can rely on the volt guage in the dash, it would drop down to about 10 volts and then the alternator would kick in. Now it's always charging<br />and it's reading 14+ volts. I was given to understand that the alt. wouldn't charge at idle, it would kick in at, or around 1000-1200 RPM. I can't even set up the idle speed because it depends on weather the alt. is charging or not. There's a difference of about 300 rpm. I see that ebasic has the Mando on sale for $99.00 right now but I don't want to buy one if mine is still good!

 

[bruceb58]

Re: Alternator/Charging question

An alternator can charge at idle, it just can't put out its full cuurent at idle.<br /><br />What do you mean that you can hear an alernator charging? Need to measure its voltage to see if its charging or measure the current coming out of it with a current clamp loop meter. <br /><br /><br />14+ volts at your dash guage doesn't tell me anything until you verify with a meter that it is accurate. i don't trust dash guages except for gross differences in voltage.<br /><br />When do you see 10V?<br /><br />As far as your current draw is concerned with everything supposedly off, get your hand held meter, start off in the 10A range, remove the negative terminal and measure the current between the cable and the negative terminal of the battery. Once you determine it isn't a huge amount of current, put it at a lower range. A 50 ma current will drain down a 50 Amp/hour battery to half its capacity in 500 hours or around 20 days.<br /><br />If you have an excessive current draw, start pulling fuses one at a time until you find the culprit circuit. Be aware that radios meant for cars can draw a fair amount of current when they are off but still have power to its inpurs. In cars, the ignition turns off power to the radio.

 

[johnbo]

Re: Alternator/Charging question

When I got my new (to me) boat, it had a flat battery. I did the same chase looking for the current path to ground. Eventually I determined that the current (with key off) was going into the B+ terminal on the Alternator. It was about 500 ma. <br /><br />I had the alternator rebuilt by a local auto-electrical place for about $75 including a new voltage regulator (internal). Totally cured the problem.<br /><br />One thing that can kill the diodes in the alternator is disconnecting the battery while the engine is running. In my boat, I think that the wing nuts on the battery had loosened. I've now removed the wing nuts in favor of something a bit more stable. <br /><br />The previous owner had dropped a whole handful of wing nuts into the bilge over time. As well as installing a battery switch, and a brand new battery right before I bought it. I suspect that they lived with this problem for some time, until I 'bought' the problem and fixed it.<br /><br />Just another piece of data.<br /><br />Later,<br /><br />johnbo

 

[dk6164]

Re: Alternator/Charging question

bruceb58- when I say I can hear it charging what I guess I mean is, I can hear the engine rpm's drop in the engine and hear a slight whine which coincides with the volt guage climbing from 10V to 14V. The whole charging issue was intermitent last season and I used to recharge the battery b-4 going out. But now with a new battery I would like to put the issue to bed. I will track down the current draw b-4 installing the battery switch but I really would like to fix the alt. (if it needs it). The 10 volts was shown after the boat sat for about 4 days without being ran. The draw pulled a fresh battery down that far! When I first started it it wasn't charging at all so I bought a new belt (the adjustment was all the way to the end of the slot) after installing the new belt and charging the battery fully I fired her up and that is when the alt. started doing it's "running all the time" thing while reading 14V. A reading on the battery terminals showed 14.9 Volts with the engine running and the alt. charging! One thing I did notice is that the Trim curcuit is live without the key being on. Are you supposed to be able to operate the trim pump with the key off?<br />Thanks for all the replies!!

 

[bruceb58]

Re: Alternator/Charging question

Yes...normally the trim circuit is always alive.<br /><br />I think your alternator is fine. 14.9 is a little on the high side but only by around 0.2V.<br /><br />Is 10V while you are cranking because that is normal.<br /><br />As your battery charges, the voltage should drop a bit. Should go down to 14.0V or so.<br /><br />One possibility is that your alternator is damging your battery if it is trying to charge a fully charged battery at 14.9V.<br /><br />On the back of your alternator, there are a few terminals. make sure the wire going to the S (sense) terminal is at 12V with the engine not running. If this sense line is open, I believe the alternator may go to full output.<br /><br />There are a few other tests you can make but I would be having you do those if you had a low voltage condition.

 

[dk6164]

Re: Alternator/Charging question

The 10 volt reading was after the engine had started. The alternator wasn't charging and I couldn't get it to charge even after turning all the accesories on! That's when I changed belts. Now, with the new belt on and the battery fully charged, the alternator won't shut off! I think I need to get the whole "Volt Meter" straight in my mind- I've always had Amp. meters. The reading you see on the guage indicates what? the action of the alternator(i.e.-putting out 14+volts) OR the status of the battery- 14+volts?<br /><br />I'll check the reading on the alternator as suggested after I attend to the "honeydew" list the Admiral has for me-gotta LOVE the weekend! <br /><br />Thanks for all the help, I really appreciate it!

 

[bruceb58]

Re: Alternator/Charging question

Thats the voltage of your battery/alternator. Should be the same since they are all connected together.<br /><br />That 10V you get is very odd. The spec for the Mondo alternator is that it can source 20 amps at 600 RPM.<br /><br />It sounds like the regulator is not working properly or the Sense terminal is not hooked up.