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post #1 of 4 Old 01-26-2003 Thread Starter
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Blown Balmar?

Hi, I have read the warnings about turning off the main battery switch while the motor is running. This is to protect the diodes in the alternator. Well, my daughter thought whe was doing me a favor and turned the switch off while I was running the diesel charging my batteries. I have a Yanmar 2QM20 and a 90 amp Balmar alternator and was running the engine about 1800 rpm. After about 10 minutes of running I noticed the switch was turned off. I turned it back on. My onboard amp meter still showed a positive charge rate of about .65 amps which is normal for my boat. It was charging at about 13.5 volts. Are my alternator diodes blown? Does it happen instantly like I have heard? Someone told me that when the diodes are blown, the alternator will overcharge. Another person told me that it may be able to survive for a brief period of time. Any thoughts on this?


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post #2 of 4 Old 01-26-2003
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Blown Balmar?

On the eve of the start of the single handed transpac in 94 I turned off the master switch myself. I did not have an assistant to blame. I guess I was nervous about the start of the race and flipped the switch without thinking.

I had a balmar 90 amp alternator too but the batteries were pretty well charged so it was not putting out a lot.

It instantly trashed my smart regulator but the alternator diodes survived. Stan Honey (local SF sailor and exceptional gentlemen) was in the slip next to me and took the time from his race prep to tell me how to test it.

Take the alternator control wire ( I think its the brown one) from the alternator and touch it to the positive terminal of a 12 battery. If the diodes are ok the engine will slow down as the alternator goes to full output. This should be pretty obvious on your engine. I had the earlier version of the same engine and it really slows down when the alternator loads it.

If it passes this test and is putting out amps I would bet you got off easy this time.

Check the rest of your electronics and light bulbs. My little episode trashed my cell phone. Light bulbs are especially sensitive to voltage surges so any that were turned on at the time might have been burned out. The most likely one to burn out is at the masthead!

Another idea that a friend gave me was to put a switch in the line that turns the regulator on and off. This is so you can start the engine without the load of the alternator on it. I would let the engine warm up before I switched the alternator on and forced the engine to work hard.

Those high output alternators put a heavy side load on the main bearings on your little engine. It seems like a good idea to let the bearing get well lubricated before you put that load on it.

The switch can also be handy when you want the full output of your engine for manouvering
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post #3 of 4 Old 01-26-2003
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Blown Balmar?

This is an aside on battery life:

You mentioned "put a switch in the line that turns the regulator on and off. This is so you can start the engine without the load of the alternator on it"

This suggests a strategy I have used in starting my airplane that has greatly prolonged battery life. I don''t know how your boat electrical starting system is wired, but on my plane, I have a battery switch and and alternator switch; together they are called the master switch. Normal operating procedures call for both switches ON for engine start. As the engine cranks, the sytem voltage is still well under the nominal 14 volts because the alternator won''t put out ''til at least 1200 RPM is reached. Therefore, "sensing" the lower-than-operating-voltage condition, the voltage regulator calls for more current from the battery. It will draw around 5 amps to no avail (and life-shortening to the battery). However, starting the engine on battery-only (analogous to switch you mention above) will effectively take the voltage regulator out of the picture. After, the engine reaches normal operating speed, the Alternator switch is put ON.

Though the 12-volt aircraft batteries are virtually the same as the lead-acid car batteries (slightly higher specific gravity), their life expectancy should at least be that of a car''s. The car battery is in a much more hostile environment than an aircraft battery, yet, the typical 5 year battery doesn''t last more than a couple of years. Perhaps marine batteries have similar challenges.

The best thing I have done to achieve (exceed) the design service life of the battery is not to let them get zapped at anytime and especially during initial charge. If you can do it, add the electrolyte yourself and apply the initial charge after the heat of mixing has dissipated and the solution is only slightly warm. Use a very low charging rate for an overnight charging (not the 0.5 to 2 hours typically done).

Operationally, I use the starting mode described. Also, I ensure the electrical master (and avionics master if you have one) is OFF. Also, all electrical loads, like radios and lights are off before I shut down and rechecked before start up (mostly to protect the radio from starting transients).

With normal battery maintenance, my battery lasted over 8.5 years with the engine operating an average of 150 hours per year (only 100 last 3 years).

Since marine batteries are probably similarly priced to aviation batteries (perhaps more), the increased life really, means a substantial savings.

I hope this helps you all, but of course, you should consult with the manufacturer and comply with any D.O.T., US Coast Guard, or other regulations that may apply concerning the suggestions I have made (this is to cover me).

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post #4 of 4 Old 01-30-2003
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Blown Balmar?

As previously noted, you probably got away with it.
I''d install a "Zap-Stop" diode on the Alternator output. It''s cheap & simple insurance.
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