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Old 24-09-2020, 18:55   #1
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Yanmar 3gm30f starter electrical requirement

The boat is on the cradle until the spring and I need to start the motor to winterize it. My batteries are pretty much dead and not holding a charge. I do have a very beefy power supply that I can plug-in but I can't find what the power requirements are for the starter. I want to make sure the power supply can handle the load.

Any guess how many amps a "standard" starter motor draws?
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Old 25-09-2020, 00:37   #2
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Re: Yanmar 3gm30f starter electrical requirement

No need to guess, here are the numbers from the Yanmar 3GM30f manual.

However by using the decompression levers, you can start a 3GM30 with 'near' flat batteries.

Decompress all cylinders, engage the starter motor and wait a few seconds while the engine rpm builds. Keeping the starter engaged, compress one cylinder and usually it will fire. If so, introduce another cylinder and if it fires, you are almost there! Release the starer at the same time as bringing the third cylinder in.

The starter motor does not require huge amps to spin over a decompressed engine and the energy stored in the flywheel does all the work.
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Old 25-09-2020, 06:29   #3
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Re: Yanmar 3gm30f starter electrical requirement

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...

Decompress all cylinders, engage the starter motor and wait a few seconds while the engine rpm builds. Keeping the starter engaged, compress one cylinder and usually it will fire. If so, introduce another cylinder and if it fires, you are almost there! Release the starer at the same time as bringing the third cylinder in.
I saw that in the manual and unless I'm reading that wrong, 460 amps?

I have started it that way and it works well if you have an assistant to turn the key.
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Old 25-09-2020, 14:18   #4
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Re: Yanmar 3gm30f starter electrical requirement

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I saw that in the manual and unless I'm reading that wrong, 460 amps?

I have started it that way and it works well if you have an assistant to turn the key.
Yes, 460 amps or less. Starter motor current draw is proportional to the torque required as can be seen on the graph below the specifications.

A second starter switch either mounted near the engine or on a fly lead is a great help in this situation! At a guess, you probably get away with less than 80A when decompressed.
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Old 26-09-2020, 16:43   #5
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Re: Yanmar 3gm30f starter electrical requirement

If it is in good shape using the decompression levers you should be able to use a auto battery charger with a 50 amp boost. It is good for 5 to 7 seconds of boost before it cuts out.
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Old 26-09-2020, 16:47   #6
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Re: Yanmar 3gm30f starter electrical requirement

This is a cheap version of a charger booster

https://www.harborfreight.com/10250A...QaAvVcEALw_wcB
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