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Low alternator ouput at startup?

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iaff284

Contributing Member
I have a 1995 Crownline with 350 Mag and an Alpha drive. The Engine serial number is OF354207. I have been chasing a low voltage/hard start issue since I rebuilt the engine last summer. After I run the blower for 15 sec., the voltage at the key switch will drop from 12.5 to 11.5. When I try and start it it will kickback against the starter and then start but the alternator will not charge until I rev the engine to 1100rpm. Then the voltage will jump to 13.9 and stay there. If I turn the blower off the voltage will go to 14.2. After running for a minute if I shut it off and don't turn on the blower and try and start it the volatge at tge key switch is 12.5 and it will start immediately without kickback and the voltage will jump 13.6. It appears as though when the voltage drops below a certain point the alternator won't charge without a slight rpm increase. It also seems that the blower is drawing alot of voltage and draining the battery. I have had the alternator and battery tested and both are supoosed to be good. I have swapped the battery with a known good battery with similar results. I am at a loss as to where to test from here. Any help is appreciated.
 
Replace the 18 year old blower to start...new blower motors draw lower amperage. How old are the battery cables? Old boat wiring can corrode internally causing a voltage drop. If you strip back some insulation near a wire terminal and find blackened wiring that is corrosion. Are you using a single wire alternator? I seem to remember some alternators don't charge below 1000 RPM. You can perform a voltage drop test from the battery to various compnents. Most important would be to check both sides of the slave solenoid when it's activated. Its internal cotactors get burned after awhile and increase in resistance causing a volt/amp problem. Also check for a voltage drop from the alternator output stud to the battery. You don't want more than 0.02 vdc drop between major components.
 
Guyjg, Is there any way to test the amp draw from the blower. I checked the resistance on the battery cables and cleaned the cables and there was no resistance. I don't understand why the alternator won't charge with a low initial voltage. It is a five wire mando alternator that tested with a 14.4 output
 
Guy is spot on about making the voltage drop measurements but you shouldn't see more than 0.2 VDC drop on any of the high current carrying connections...The alternator may be fine but the wiring (harness) may not be...in particular check the voltage drop between the battery's GND terminal and the alternator case...bad ground for the alternator can inhibit the initial startup (charging)...

As far as checking the current draw, use a clamp on amp meter...the 'cheap' ones only work on AC circuits and are pretty useless on a small boat...

Checking the "resistance" of a high current carrying conductor won't tell you anything about its internal condition...most ohm meters use a current value of less than a miliamp...use the voltage drop test, with the 'normal' current flowing thru the wire...
 
Makomark, what is the best way to check the voktage droo betweeen B- and the alternator case? I am assuming that I put the VOM on dcv and the neg on B- and the positive lead on the alternator case.
 
You have it...most digital meters are auto ranging so the "which lead goes where" isn't that important, as long as you understand what you are measuring...

And if you can't find the alternator's ground wire that's a good indicator to expect a large voltage drop...

BTW, the one-wire setups are notorious for needing the rpm's to be raised to get them to start charging...that's 'normal' for that setup..
 
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Makomark, I will check the volatge drop and report back. I know the ground wire is there as I just had it off to test the alt Thanks for the help. Let me know if there is anything else I should check
 
I don't understand why the alternator won't charge with a low initial voltage.
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Your alternator tested fine out of the boat but won't charge until you increase RPM. That statement leads me to think there is a problem w/the exciter circuit that turns the alternator on to start charging. I don't have a manual anymore and don't remember the specs. The best thing you can do is perform the VD test and then examine every wire and termination point for continuity and corrosion. Look on the alternator where the wires connect...each point should be labled for reference. Make sure the engine to alt. ground is clean and tight.


I had an 87 Baretta w/the 3 wire alt. I had a similar problem and ended up replacing the output wire and several crimped wire terminals to remedy it due to old wire corrosion. Again, I'll state if you find blackened copper wire of any gauge it needs to be replaced for perfect operation.

Maybe someone can chime in on the voltage specs for the exciter circuit.
 
I think that Mark is giving you some great advice here.


It seems odd to me that a bilge blower motor could draw that much current to the point of lowering amperage or voltage elsewhere.

Try disconnecting the actual blower motor, and excite the blower motor circuit.
See if there is a load on this circuit in the absence of the blower motor.

And if you replace the blower motor..... say no to these noisy, low flowing, worthless and short lived In-Line or Turbo style blowers........




..... and purchase a good squirrel cage blower motor.


As for the alternator..... what you describe regarding the RPM needed for it to excite, is very typical of the Delco 10si single wire alternator..... but
apparently you do not have this alternator.

Also, your engine rpm is not necessarily your alternator rpm. Our alternators are typically over-driven due to the difference in belt pulley diameters.
IOW, an engine at 1k rpm, may actually spin the alternator at 1.5k rpm.


As for the testing.... the shop's test machine is very likely not capable of simulating low engine RPM.
The test machine's electric drive motor most likely turns at either 1,750 rpm or 3,450 rpm.... and these are over-driving the alternator just as your engine does (again, due to the difference in belt pulley diameters).

So I would question as to how the shop was able to check low RPM excite function.


Edit:

Also..... make sure that your alternator has a good chassis negative connection to the engine block.
All of our Negative cables, conductors and connections are equally impotant.
What travels throught the Postive side, must also travel through the Negative side, and of an equal current value.

Perhaps pull your hull harness/engine harness interface connection apart, and examine and/or clean the contacts.




.
 
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Sorry for the delay all, here are the results of the testing.

Alt. ground stud to B- 0 resistance
Voltage at red/purple stud on alt.- 12.20
Voltage at purple stud on alt.- 11.71
Voltage at Orange stud on alt.- 12.20
Voltage at tie strap stud on alt.- 0.26

All voltage readings were taken with key on and using the B- stud on alt.
Based on these readings there is a problem with the voltage regulator on the alt. Correct? Can I just replace the
Regulator or does tge whole alt. have to be replaced?
 
Edit....sorry just reread the merc test procedure and it states that a reading of .75 - 1.1V indicates an open or short in the rotor field. My reading is below that and way below the range of the other tests......now what?
 
did you see my post about the test results and the rotor field?
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Yes...don't have anything specs. for reference. Were those reading taken while the engine was runnning or off?
 
The link from boat tech above has the specs. I performed the test as specified in the link from the merc manual. All readings were taken with the key on engine off. My reading was .26V which was below the lowest spec of .75V.
 
Sorry...link won't open. The 0.26 vdc reading is not in the range of a "failure" thereby the circuit must be good. See what the reading is if you trace that specific wire to a junction point. If not the same then that could be part of the issue.
 
Guyjg, the test states that an acceptable range is 1.3-2.5, .75-1.1 is range for open circuit, and 6.0-7.0 is the range for a regulator failure. My reading of 0.26 is way below the acceptable range and below the range for an open circuit. My question is whether there is more testing I can do to check the alt. For open circuit
 
FWIW, the manual can't provide every combination of voltage readins based on failure modes and operating conditions....the "low" voltage indicates something is wrong in the field circuit...it could be the regulator or it could be "inside" the alternator...A "high" volatage indicates an open in that circuit...and that's assuming you made the measurements according to the procedure in the linked data...

There are more tests that can be used to help you isolate the fault....the way I see it you have three choices: 1) do the rest of the tests and determine bad part and replace, 2) start throwing new parts at it until it "works", or 3) remove the alternator and take it to a good electrical shop and just pay them...
 
Makomark, I would like to test and replace the defective part. I appreciate the numerous voltage readings that could exist. Guyjg was indicating that my readings were within spec. Which according to the merc manual link posted above for testing a mando alternator my reading is not within spec. I perfomed the tests as stated in the link above. I realize that the possiblity to perfom the measurements incorrectly exists I am confident that my process of key on engine off, black lead on meter to negative terminal on alt. And red lead on meter to link bar terminal is exactly how the manual says to perform the test. That being said what is my next step in the testing process?
 
the initial indicator points to the exciter circuitry and your voltage measurement confirms a concern...

that being said, the alternator appears to "work"...I understand the problem is that the alternator turns on "late".

If the alternator delivers enough energy, I would do a comprehensive voltage drop test across both sides of the alternator wiring as I suspect you don't have an alternator test bench...if the voltage drop test shows no issues, the regulator is about all that is left...
 
That is correct, if the voltage on the battery stays above 12v the alternator will charge immediately at idle . If I run the blower which seems to be drawing an excessive amount of voltage, and the battery volts drop below 12the alternator will not start charging immediately at idle. I have to bump the throttle up 200-300rpm and then it will charge anywherd from 13.9-14.4 depending on wgat elseis turned on. Is there a link to the voltage drop test for alt.? Is it listed in the charging system manual from Merc.?
 
The blower may be drawing excess amperage but you can't tell unless you measure it....that could be due to a bad connection (an excessive voltage drop) too...

Could be the diode trio which provides the field current to get the alternator charging, too...what is the voltage on the tie strap when the engine is running?

The voltage drop test isn't explicitly called out in the manual...in essence, you start at the battery and measure each connection to the alternator and then back out...you can use the schematic in the wiring diagrams section as a guide...it doesn't show every junction though...

what is the voltage between the battery's negative terminal and the alternator's case....key on and then with the engine running (w and w/o the alternator charging)?
 
Guyjg was indicating that my readings were within spec.
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Based upon the info you posted. The problem may be twofold...exciter voltage problem and alternator problem. Makomark has you on the right track. If the alternator is 18 yrs. old why not do as he said...get it tested, inspected and refurbished by a professional. Doing that eliminates it from the equation.

Next, dig into inpecting the wiring harness on the engine. Did you strip off some wiring insulation to look for blackened copper wire? It's as simple as cutting off a connector such as the one for the exciter circuit; strip off an inch of insulation and see what you are dealing with. If it's clean and shiney copper just install a new connector. If it's blackened then replace that wire and inspect the junction point where it attaches. Then move to the next alternator wire until you have checked them all.
 
Makomark, I will check the voltage drop on each wire from the battery to the alternator and the voltage between the ground and the alt. case. I will also measure the voltage at the tie strap with the engine running with the alt. charging and not charging. I am working tomorrow but I will run the tests on Thursday and report back.

Guyjg, I listed my test voltage and the Merc specs above....my test voltage has always been below the range indicated by the Merc manual. There is a possibility that there is corrosion on the wires as I purchased the boat with a siezed engine due to the bilge plug being left in and water getting into the engine through the carb. I rebuilt the engine and cleaned every connection with sandpaper. Shouldn't a resistance test and voltage drop test show a corroded wire/poor connection? I have no problem having the alt. rebuilt but again I don't want to pay to have something repaired that isn't broken. Let me know what you think about the resistance and voltage drop test, and thank you both for your help!!!
 
Shouldn't a resistance test and voltage drop test show a corroded wire/poor connection?
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Yes it should. You will be measuring low voltage changes. Being able to interpret what you find can be a challenge. Make a drawing and write down your voltage and resistance readings for reference. Sometimes you have to just get down and dirty to find the problem. Performing a wire wiggle test can help locate brittle wires and internal corrosion. I like to watch a gauge or meter while pulling, twisting, bending and contorting every wire in the circuit. Many times doing it will cause the problem to show itself.

I still remember my first major radar repair as a 19 yr old private...1/2 dozen senior techs worked on it and could not get the video to show on the radar scope. They replaced everything they could. A simple wiggle test found a cracked wire providing the sweep trigger for the radar scope...it flashed brightly. Sometimes the simplest thing is the solution.
 
sorry for the delay in posting, I got called away for business. Here are the results of the testing,

Voltage Drop Testing
Battery to Alt. Orange-0v
Battery to Alt. Red Purple-0v
Battery to Alt. Purple-0.48v
Battery Ground to Alt. Case-0V

Tie Strap voltage when charging and running-7.33
Tie Strap voltage when not charging and running-0.43V

all voltage drop tests were done from battery + terminal to alt. stud. After the high drop on the purple wire Itested the resistance on it to battery+ and it showed 7.25 on a 20k scale. I am assuming that alot of my issue is going to be the high resistance and voltage drop in the purple wire. should I remove the purple wire from the alt. and connect a temporary from battery + to the alt. purple stud and see how the starting and charging circuit respond? Thanks again for the help.
 
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You may be on to something....the purple lead should be +12VDC from the key switch....you can just put the jumper from the + lead of the ignition coil....assuming the wiring harness is good from the key to the coil...

The purple lead is provided to the alternator to "turn it on"...if your measurement of it's resistance was done with the key on, that's were the issue is...if is was done with the key off, that may be 'normal'...

Once the alternator is "on", it no longer requires any current from the purple lead...
 
That is what I suspected. I will double check coil voltage and jumper from there to the alt. purple stud. I have the thunderbolt v ignition system and I am not sure if it will supply a full 12v to the coil, especially if the knock sensor is activated. Let me know if you think that the coil + will work.
 
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