'85 Mercury Charging problems

[amichael]

Have a '85 Mercury 35hp s/n 6628776. I replaced the rectifier but still its not charging. Reading 12.26 volts at the battery terminals + & - running or not. I checked the stator at .8 ohms, but cant find any specs on it. Any help appreciated.

 

[Barnacle_Bill]

Re: '85 Mercury Charging problems

Were the 2 yellow wires disconnected when you checked them? Did you check to see if they were shorted to ground?

 

[amichael]

Re: '85 Mercury Charging problems

Thanks for the input. Yes yellow and grey (stater) wires disconnected. No ground present. Any idea what that coil (stater) should ohm out at? I don't find that info in my service manual, or internet.

 

[Texasmark]

Re: '85 Mercury Charging problems

Stator resistance wire to wire is in that area, temperature dependent. The service manual uses vague terms for the value as it varies; but they are all very low. Between the wires and ground (battery -) should be an open circuit, or as mentioned in another thread awhile ago, at least 60k ohms.

Mark

 

[schematic]

Re: '85 Mercury Charging problems

Have a '85 Mercury 35hp s/n 6628776. I replaced the rectifier but still its not charging. Reading 12.26 volts at the battery terminals + & - running or not. I checked the stator at .8 ohms, but cant find any specs on it. Any help appreciated.

Is it possible you have the battery connected backwards?

if not:


connect the wiring back up and check for a/c voltage across the stator wire while running. If you have >14v and still no rise at battery, the rec. is bad.

 

[James R]

Re: '85 Mercury Charging problems

Could be you have a bad battery and it is dragging the charging system down.

 

[schematic]

Re: '85 Mercury Charging problems

Could be you have a bad battery and it is dragging the charging system down.

He's not seeing any rise at all. 12.26v running or not

 

[amichael]

Re: '85 Mercury Charging problems

Stator resistance wire to wire is in that area, temperature dependent. The service manual uses vague terms for the value as it varies; but they are all very low. Between the wires and ground (battery -) should be an open circuit, or as mentioned in another thread awhile ago, at least 60k ohms.

Mark

Could be you have a bad battery and it is dragging the charging system down.

Is it possible you have the battery connected backwards?

if not:


connect the wiring back up and check for a/c voltage across the stator wire while running. If you have >14v and still no rise at battery, the rec. is bad.

Thanks guys,
This really helps, I like this site. The battery is good and is connected correctly. I have rechecked the rectifier. But not sure of the input voltage, I checked it before i replaced the rectifier, which was bad, but don't remember
the result. I'll re check that soon as it stops raining, we've had 3+ inches in the last 24 hrs.
Thanks again for the help
Michael

 

[jslu]

Re: '85 Mercury Charging problems

Have a '85 Mercury 35hp s/n 6628776. I replaced the rectifier but still its not charging. Reading 12.26 volts at the battery terminals + & - running or not. I checked the stator at .8 ohms, but cant find any specs on it. Any help appreciated.

Michael:

At what RPM are you checking the voltage? I have a similar 35 HP Merc and I've noticed that you do not see any evidence of charging until about 2000 RPM.. It is thoroughly evident at WOT. Did you use an OEM replacement rectifier or a much better Radio Shack full wave bridge rectifier costing around 5 bucks. You will have to modify your engine wiring for this product from ring terminals to push on lugs, but well worth the effort. In either case, be sure to scrape away painted surface on the engine mounting area & use thermal transfer compound at the mounting interface.

John

 

[schematic]

Re: '85 Mercury Charging problems

Michael:

I've noticed that you do not see any evidence of charging until about 2000 RPM.. It is thoroughly evident at WOT.

John

Ditto

 

[Texasmark]

Re: '85 Mercury Charging problems

My service manual uses 2000 rpm as the current set point for the rating. For my 90 hp engine with the red 16 amp alternator 2000 rpm is where you should read 16 amperes when doing the test. Above or below that the current varies per the rpm.

The rms ac voltage will be about 70% of the dc output reading. So, if the rectifier/regulator is supposed to be putting out 14.5v at 16 amperes at 2000 rpms into a charged battery the rms ac voltage will read about 10vac yellow wire to yellow wire.

Mark

 

[amichael]

Re: '85 Mercury Charging problems

Not sure of the rpm. guess i'll tach it and see, but at about 1/4 to 1/2 throttle I have 13-14 vac, still don't see any dc out put above the 12+ volts that I have with out the motor running. I used the OEM rectifier, read about the radio shack one but didn't heed the advise. You use a term I'm unsure of "WOT" probably I'm gona feel real STUPID but... Any way thanks for the help and I'll get back to you when I find out the RPM and "WOT"

 

[schematic]

Re: '85 Mercury Charging problems

WOT = wide open throttle


Do you have an ammeter or the amp function built in to your meter? Or maybe an amp clamp?

You should check the current output of the stator. If it is zero when you are reading 12 - 13 vac and the rpm is 2k or higher, the stator is bad.

 

[CharlieB]

Re: '85 Mercury Charging problems

That charging system isn't very large, you may not see much voltage rise at the battery for quite a while.

It may be easier to pull the fuse, pull start the motor, then check voltage on both sides of the fuse holder, one side will read the battery voltage, the other will read the charging output voltage.

Shut the motor off before re-installing the fuse.

 

[Texasmark]

Re: '85 Mercury Charging problems

That charging system isn't very large, you may not see much voltage rise at the battery for quite a while.

It may be easier to pull the fuse, pull start the motor, then check voltage on both sides of the fuse holder, one side will read the battery voltage, the other will read the charging output voltage.

Shut the motor off before re-installing the fuse.

On my engine the output of the regulator goes to one of the large terminals on the solenoid (junction point) and to the fuse and battery. If you pull the fuse, the down wind side would be zero volts I would think. The output of the regulator goes to the battery regardless of fuse or no fuse and the battery is loading the output. I guess the SM uses current as the metric as current is what charges the battery and actual voltage is more battery charge condition related.

Mark

 

[CharlieB]

Re: '85 Mercury Charging problems

I was thinking of a pull start motor, no electric start.

In that case just disconnect the rectifier red wire and test both sides there, one side battery and the other will be charging output.

It will be small at idle and rise with RPM.