NO CHARGING on 82 L6 90hp Merc....

S

ST

Petty Officer 2nd Class
Joined
Jul 25, 2005
Messages
192
The battery keeps getting weak, even after cruising a while. :confused: At home, I notice that the Battery voltage didn't go higher than 13.20 Volt (with nothing else turned on) even with RPM increased to about 2500 or so; while at rest it measures 13.10 Volt.(Just off the charger).<br /><br />Would someone(s) guide me to a charging troubleshooting procedures with this motor, please? It's 1982/83 s/n 06186364. Sorry, I wish I have the service manual/wiring diagram. But let me link you with a photo of the starboard side (where the most wirings are); hopefully it's legible and someone(s) be kind enough of pointing me to the right direction. Thanks! :) <br /><br />
IMG_1945.jpg
<br /><br />021606: image edited...st.
 
E

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: NO CHARGING on 82 L6 90hp Merc....

That little square puppy at the top of the upper switchbox is the rectifier. Typically the cause of a no-charge or low-charge problem.<br /><br />Before condemning the rectifier, though, take a resistance reading with your meter on the (2) yellow stator wires which connect to the rectifier. Be sure to disconnect both wires before taking a reading, and be mindful that the red wire connected to the rectifier is constant +12V as long as the main control harness is hooked to the battery.<br /><br />The stator resistance will be a fairly low value, what you don't want to see is an open stator (infinite resistance). If you move the flywheel with your hand in a clockwise direction you should see a change in your meter which indicates the stator is generating electricity.<br /><br />Seems to me the procedure for metering out the rectifier has been posted online before, try doing a keyword search and you'll probably find it. I got 8 pages of results by searching this forum for "rectifier test". Here's a good thread:<br /><br /> http://forums.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=020391#000000 <br /><br />This charging system is quite simple and if the stator's good, it's very unlikely to be anything but the rectifier. This of course barring any unforseen wiring harness issues. If you have +12V battery power at the rectifier on the red wire, that pretty much rules out anything else.<br /><br />One other thing you can do is idle the motor, and with your meter set on AC voltage, meter across the yellow leads. This is AC component which the rectifier turns into full-wave DC. Also check the DC output of the rectifier, to engine ground. You should see a rise in voltage with increase in engine speed, if you don't see anything significant the rectifier's shot.<br /><br />You can get a good deal on a new one at the Boatfix.com site, here's the Sierra parts section:<br /><br /> http://www.boatfix.com/searchsierra.asp <br /><br />HTH...........ed
 
Clams Canino

Clams Canino

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Re: NO CHARGING on 82 L6 90hp Merc....

You can almost bet it the rectifier.<br /><br />-W
 
S

ST

Petty Officer 2nd Class
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Messages
192
Re: NO CHARGING on 82 L6 90hp Merc....

Hi Ed Mc. and Clams;<br />superb professional responses! So far, I only checked for the stator resistance reading; it's got continuity: 2 Ohms. <br /><br />I don't want to start the noisy 2 strokers tonight (it's 10PM now) in the backyard (I have neighbors closeby...); so I'll do the other testings possibly tomorrow pm. <br /><br />Thanks a lot! Woohoo!
 
S

ST

Petty Officer 2nd Class
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Re: NO CHARGING on 82 L6 90hp Merc....

More test results this morning:<br />1. Engine running: measured about 35 to 36 VAC at Stator leads.<br /> 2. At the Red Rectifier terminal: 12.5V with engine stop.<br /> No increase in voltage with engine running, even with increase of RPM.<br />Didn’t those results indicate that the rectifier is bad; isn’t it?<br />Just for curiosity:<br /> 3. I went on to remove the Red wire off from the Rectifier, (engine stop):<br /> With positive red meter lead to red terminal; Black to ground: no continuity.<br /> With meter leads reversed: shows 1060 to 1070 Kilo ohms. What do you think about this last test result? I was hoping to see: open and open or short and short on a bad diode.<br />Thanks again for the inputs, gentlemen!<br /> :)
 
S

ST

Petty Officer 2nd Class
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Re: NO CHARGING on 82 L6 90hp Merc....

Ed Mc.;<br />Thanks! I got one rectifier on order now to boatfix. :)
 
P

phatmanmike

Captain
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Oct 24, 2003
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Re: NO CHARGING on 82 L6 90hp Merc....

radioshack has rectifiers that are far superior to oem in every way and only cost 3 dollars.<br /><br />just ask for a 25 amp, full wave, bridge rectifier. <br /><br />3.29 and your done. i use them on ALL my motors. i buy spares and keep one on the boat just in case.
 
Clams Canino

Clams Canino

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2,179
Re: NO CHARGING on 82 L6 90hp Merc....

True... but you need to "custom mount" them a bit. <br /> <br />-W (uses one in my Merc 800)
 
S

ST

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192
Re: NO CHARGING on 82 L6 90hp Merc....

An update/alternate rectifier source:<br /><br />Ed Mc; I did order from boatfix, but then I cancelled it (sorry...) after I read what myoutboard said. On my way to a Radio Shack store I stopped by at an Electronic store instead (Orvac.com), and bought 2 rectifiers there. It looks pretty solidly build, and it's only $3 something; here's how it looks like:<br />
IMG_1985.jpg
<br /><br />You notice, it has 4 terminals instead of the usual 3. The 4th terminal is dedicated ground (I found out later); so I needed to run a seperate lead to ground. I drilled small holes through it's blade terminals and use tiny nut/bolt to attached the original wires to them. As for mounting: this rectifier has a built in hole in the middle and the casing are solid metal (aluminum?), I think it's for heat sinking purpose. <br /><br />SO, I simply use a longer bolt that matches the original tread and using one of the original screw hole to mount it. <br />
IMG_1975.jpg
<br /><br />Here's the reading after the rectifier replacement:<br />13.5 VDC at idle (950rpm) and 14.1 VDC at 2500rpm.<br />Turning on my bilge pump didn't decrease the voltage at all; hope that's normal reading...<br /><br />021606: images edited...st.
 
E

emckelvy

Commander
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Jan 16, 2004
Messages
2,506
Re: NO CHARGING on 82 L6 90hp Merc....

Sam, that's a nice clean job on the install, it looks factory! Also good idea to drill holes in the blade terminals for bolted connections, a lot more solid than using slip-on connectors.<br /><br />Your voltage readings sound spot on, too. You're getting quite a bit above battery voltage, and you'll find the output will be higher yet, once you get it in the water and run it up above 2500 rpm in gear.<br /><br />Guess I better get down to the Rad Shack and stock up!!!..........ed
 
S

ST

Petty Officer 2nd Class
Joined
Jul 25, 2005
Messages
192
Re: NO CHARGING on 82 L6 90hp Merc....

Ed Mc; thanks again! Btw, I also found that the 2 rectifier leads insulator coming out from the bundled sleeve crumbled. I temporarily taped them up, it's going to be one of my week end projects! I wonder what other problems or surprises might be in store for me on this oldie "Tower of Power?" (along with the same era boat and trailer!) <br /><br />I really don't know what Radio Shack's rectifier looks like; the 1st one I went to didn't have it; if you need them, please let me know...
 
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phatmanmike

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Oct 24, 2003
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Re: NO CHARGING on 82 L6 90hp Merc....

radioshacks look exzcatly like those youve got. good job! nice install!<br /><br />i always buy extras and carry a spare on each boat. for 3 bucks you cant go wrong. i got the idea from clams about 3 years ago!
 
M

MercFan

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Dec 31, 2005
Messages
347
Re: NO CHARGING on 82 L6 90hp Merc....

Question: I can get those exact same rectifiers locally aswell. I actually use 2 of them in parallel on a power supply I built for something else. The reason I don't want to use them in my boat is because they don't have any regulation. Do you guys use a seperate voltage regulator? Or is it ok as is? I'm just scared of over powering my ignition or toasting the battery.
 
S

ST

Petty Officer 2nd Class
Joined
Jul 25, 2005
Messages
192
Re: NO CHARGING on 82 L6 90hp Merc....

Mercfan,<br />I am pretty sure my old 1982 Merc 90 has no factory voltage regulator, maybe the newer models do. Hopefully someone would elaborate more on this...
 
P

phatmanmike

Captain
Joined
Oct 24, 2003
Messages
3,869
Re: NO CHARGING on 82 L6 90hp Merc....

no regulators on the stock motors. you dont need one, as when i tested my 1150's output, it never went above 15 volts. most any battery can handle that.<br /><br />at idle it made about 13.5 volts
 
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