charging not working on Merc 850 1974

fishjumped

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i have checked my rectifier it ohms out directionally polarity wise diodes are working and the stator has around 7 ohms start and run motor and it dosent show charge on my meter thought the stator resistance was too low at 7 ohms what should it read
 

fishjumped

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Dec 27, 2005
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i have checked my rectifier, it ohms out directionally polarity wise diodes are working and the stator has around 7 ohms start and run motor and it doesn't show charge on my meter thought the stator resistance was too low at 7 ohms what should it read?
 

racerone

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I think 7 ohms is way too high for the battery charging part of the stator.----Should read like 1/2 ohm or less.
 

racerone

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I think 7 ohms is way too high.----Should be more like 0.5 OHMS ( 1/2 ) or less
 

Chris1956

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Did you check all 4 diodes in the bridge rectifier? They all need to be good for the battery to charge. If one diode is shorted to ground or open, the motor will not charge.

You can check for an AC voltage at the rectifier, motor running, from the stator wires to prove the stator is good or bad.
 

fishjumped

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Dec 27, 2005
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had set for DC voltage meter on ground and on + of the rectifier it went crazzy reading bouncing and diappearing
 

fishjumped

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i have rectifier out now and reads meter set to diode neg lead on +of rectifier and Neg of meter to Chassis ground reads .983 and move + meter lead to each of the leads for stator that is not connected they read .515 and .530 if I have red meter lead on + I have no reading to chassis ground or stator connections at the Rectifier
 

fishjumped

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i have rectifier out now and reads meter set to diode neg lead on +of rectifier and Neg of meter to Chassis ground reads .983 and move + meter lead to each of the leads for stator that is not connected they read .515 and .530 if I have red meter lead on + I have no reading to chassis ground or stator connections at the Rectifier
that sound ok? have the same on another rectifier used
 

Chris1956

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Look up Bridge rectifier to see the 4 diode configuration. On your Mercury rectifier, you have 3 connections and ground. So you need to check all the rectifiers for continuity one way and open the other way. Some digital meters have a setting for diode checking. Analog meters usually have built in polarity for checking diodes.

So check +DC to AC; +DC to other AC; -DC (ground) to AC; -DC(ground) to other AC. 8 tests. 4 of them should show 0 resistance, 4 tests should show infinite resistance.
 

fishjumped

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Dec 27, 2005
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Look up Bridge rectifier to see the 4 diode configuration. On your Mercury rectifier, you have 3 connections and ground. So you need to check all the rectifiers for continuity one way and open the other way. Some digital meters have a setting for diode checking. Analog meters usually have built in polarity for checking diodes.

So check +DC to AC; +DC to other AC; -DC (ground) to AC; -DC(ground) to other AC. 8 tests. 4 of them should show 0 resistance, 4 tests should show infinite resistance.
so what else could it be? nothing right?
 

racerone

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There is a stator.-----There is a rectifier.-----There are wires.-----Wires on that era Mercury is known to be defective,-----Rotten to the core so to speak..-----Inspection on your motor required.----Rectifiers are cheap.
 

dwco5051

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oops it read .6 ohms on stator
When you are reading the resistance of the stator you are just measuring a long length of copper wire. Depending on the accuracy of your meter and the temperature of the stator it will vary so it seems to be withing specs. Like raceone said those old mercs are good motors but known for brittle insulation and corrosion of the wiring. Time to start cleaning connections, wiggle wires while checking for continuity.
 

racerone

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Not just " copper wire "-----It is called ----" magnet wire " -----That would be wire with a clear varnish type coating.-----So a simple check with an ohmmeter does not always indicate the true condition of the windings !!
 

sam am I

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Jun 26, 2013
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Unless you have a low ohms meter and you're measuring strictly the stator's windings, you're looking more or less for an open circuit or a short to the iron core more than anything else, would be tough otherwise to really know if some windings were shorted to each other........

BUT even enameled copper wire (magnet wire) still has the normal resistance in ohms/ft of regular copper wire....LOL, because it is normal copper wire! Just painted....

Say the stators coil is 1000' total in length or 10AWG solid core copper wire @ 0.6282 ohms/1000ft @ 20C, with no shorted windings to themselfs, you'd measure .6282 ohms.

And if the stator was shorted in half? It'd be 0.3141 ohms and almost impossible to tell with even a good STANDARD Fluke DMM.

You can try to use the "REL" setting if you have one and you have a decent meter, short the leads out to one another firmly, hit the REL button to zero out any lead/meter inherent resistance and re-try the stator again...If you see 0.2 or 0.3 ohms and the wire is 10AWG, I'd bet the statos windings are good(see example above, you have approx 400/500' of good still insulated wire which is more than reasonable for a coil)

Thinking though and again for example with a 10/20A stator, it will be more like 100' of 10AWG...........something like 0.06282 ohms, though read even with a REL setting.
 
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