Alternator issue

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DannyS

DannyS

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May 27, 2004
933
Beneteau 393 Bayfield, Wi
I admit that my knowledge in this subject is lacking so please help me out here, I recently added a Victron battery monitor so I can see just how much (or little) charging my alternator is pushing back into my battery bank. I've never seen more than 5 or 6 amps being pushed back into the bank, even when the bank is down in the 70-75% range.
I assume the alternator is original to the Universal M-25 engine. From what I can see, the alternator is a Motorola but I don't know what the output level should be; the info plaque on the alternator had been painted over.
So I think I've determined that I have a charging issue so my question is what is the procedure for rebuilding my alternator or should I be looking for another alternator?
 
JoeWhite

JoeWhite

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Mar 6, 2008
1,498
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
Remove the alternator and take it to an automotive shop - they can test it. Considering the size of your boat and engine I expect that the alternator should output about 50 AMPS at about 1000 RPM. I have M35B Universal and it has a 51 AMP alternator. The alternators have internal regulator. You should be able to connect the alternator directly to the battery or through the monitor and see how much current it is putting out. Also the batteries may be bad.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Danny,

Stop! Before you do anything, please tell us what size battery bank you have on your boat and what your use is.

If you have a small bank and small needs, that charge from an internally regulated alternator is just fine.

Step-by-step before answers can be useful to you.
 
Douglast

Douglast

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Jul 18, 2009
274
marine clipper 21 ft santa ana Southern Lakes,Yukon
x2...5/6 amps.output just might be ok.....most little household chargers are 2 amp min and 10 max..
 
whatfiero

whatfiero

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Oct 30, 2011
542
klidescope 30t norfolk
put a load on your altanator then check your victron use a lot of lights or 12v heating unit motor load something to demand power to check out put
 
DannyS

DannyS

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May 27, 2004
933
Beneteau 393 Bayfield, Wi
More info...I just replaced the house bank batteries, two Costco marine group 27's at 115 amp hours each for a total house bank of 230 amp hours. I have 9 interior cabin lights that I've been slowly replacing bulbs to LED, chartplotter/radar/speed/depth, refrigeration. At any one time, I'm only pulling out 5-7 amps, usually when the fridge is running. Without the fridge, 2-4 amps depending on what electronics I have in use and which cabin lights my kids left on.
I just got back from a 4-5 day trip away from shore power and at times the battery monitor was showing at it's lowest state of charge to be about 70-75% and a consumed energy amount of about 65 amp hours. The battery bank was showing 100% SOC when we left. There were days that we motored for 4-5 hours and still only brought the bank up to the low 80% range and at the end of those long day of motoring, I was only seeing 1-2 amps going in.
 
Snotter

Snotter

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Sep 25, 2008
615
Morgan 415 Out Island Rogersville, AL
do you have a diode based battery isolator hooked up?
 
heritage

heritage

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Apr 22, 2011
974
Hunter 27 Pecan Grove, Oriental, NC
DannyS said:
More info...I just replaced the house bank batteries, two Costco marine group 27's at 115 amp hours each for a total house bank of 230 amp hours. I have 9 interior cabin lights that I've been slowly replacing bulbs to LED, chartplotter/radar/speed/depth, refrigeration. At any one time, I'm only pulling out 5-7 amps, usually when the fridge is running. Without the fridge, 2-4 amps depending on what electronics I have in use and which cabin lights my kids left on.
I just got back from a 4-5 day trip away from shore power and at times the battery monitor was showing at it's lowest state of charge to be about 70-75% and a consumed energy amount of about 65 amp hours. The battery bank was showing 100% SOC when we left. There were days that we motored for 4-5 hours and still only brought the bank up to the low 80% range and at the end of those long day of motoring, I was only seeing 1-2 amps going in.
Click to expand
To check the output of the alternator without removing it from the boat, the batteries need to be depleted somewhat.... the more the better. Also, it would help if the frig were running when you do the check. Start the engine and run it at mid rpm range, immediately check the amp input to the circuit. If you don't see at least 20amps, I would remove the alternator and have it checked at a shop.

The fact that you were seeing 1-2 amps when the batteries were at 80% SOC is not that unexpected. Batteries that are nearly full will accept more charge very reluctantly.

Also, your battery monitor percentage of charge may not be that accurate when it is first installed. There is a learning curve that it creates as it sees several charge and discharge cycles.
 
B

Blitz

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Jul 10, 2007
722
Seidelmann 34 Atlantic Highlands, NJ
DannyS said:
More info...I just replaced the house bank batteries, two Costco marine group 27's at 115 amp hours each for a total house bank of 230 amp hours.
Click to expand
Are you sure your Costco house bank batteries are 115ah each? This seems a bit high.

Did you set up you Victron Battery Monitor with the correct battery capacity?

These items could be messing up your SOC readings.
 
DannyS

DannyS

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May 27, 2004
933
Beneteau 393 Bayfield, Wi
Blitz said:
Are you sure your Costco house bank batteries are 115ah each? This seems a bit high.

Did you set up you Victron Battery Monitor with the correct battery capacity?

These items could be messing up your SOC readings.
Click to expand
Yes and yes. The batteries are definitely 115ah each. I just looked at the worn out battery that was replaced. I did adjust the amp hours setting on the monitor as well to reflect this.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Danny, good added info, so far. What was the output voltage of the alternator at low charge and when the banks were close to full? With an internal regulator, it should be the same. I still don't think you have a problem.
 
DannyS

DannyS

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May 27, 2004
933
Beneteau 393 Bayfield, Wi
Stu Jackson said:
Danny, good added info, so far. What was the output voltage of the alternator at low charge and when the banks were close to full? With an internal regulator, it should be the same. I still don't think you have a problem.
Click to expand
Stu, I'm not sure I know the answer to that. Would the Victron show me the voltage output from the alternator at any given moment?
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
For the record turning on a load may not show up as current across the batteries. The alternator acts like a battery in parallel and just supplies the current as it has the higher voltage.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
DannyS said:
Digital volt meter?
Click to expand
Yup.

For learning how charging should work, try these

The Ample Power Primer http://www.amplepower.com/primer/primer.pdf

www.balmar.net and download the MC-614 regulator manual. Both will tell you how charging works.

I know you don't have an external regulator. These are for comparative purposes.

Then read Maine Sail's excellent discussion: Musings on External Regulation - http://forums.catalina.sailboatowners.com/showthread.php?t=125392

Also, what rpm where you running the engine? Around 2500 or so? If only at 1500 when anchored, you're not gonna get more than 5 or 6 amps.

I still don't think you have a problem. Hope I'm right. :)
 
jibes138

jibes138

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Jan 27, 2008
3,092
ODay 35 Beaufort, NC
Danny,
Sounds like your setup is same as mine. Alternator that came standard is a motorola 51A. I had mine checked for output voltage and it was reported as 13.6 and i was told that was low and I should rebuild or replace the alternator. I'm not sure that was sound advice but others have suggested over 14 volts as good charging voltage. I haven't had any problem with it but don't have a fridge and use very little electricity when on the hook. I tend to go to sleep when it gets dark and get up with the sun.
MaineSailes website has a great article on an externally regulated upgrade alternator that you should check out. Very good pictorial with it. Stick with Stu on this subject.
 
DannyS

DannyS

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May 27, 2004
933
Beneteau 393 Bayfield, Wi
Stu Jackson said:
Also, what rpm where you running the engine? Around 2500 or so? If only at 1500 when anchored, you're not gonna get more than 5 or 6 amps.

I still don't think you have a problem. Hope I'm right. :)
Click to expand
Unfortunately, my boat does not have a tachometer but I have run it at idle and looked at the Victron, then throttled up and have seen no increase in charge. In fact, I've even seen it drop just a bit when throttled up, not by much, less than an amp.
 
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