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Old 06-03-2012, 06:50   #16
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Re: YANMAR 2GM20F STARTING AMPS

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Originally Posted by cal40john View Post
That's the inrush current. I'd think you'd want to have an idea how long that lasts to select a fuse. The Blue Seas link posted above showed maybe 40 msec of high inrush, then 2x to 3x for another 200-400 msec.

I'd be interested in seeing the fuel shutoff pulled while turning over the engine to get the steady state current draw while loaded.

John
That particular motor is wired with 1/0 cable and fused with a 200A ANL. The difference in starting between the old 2GA wire and the 1/0 is quite noticeable. In-rush does not really affect the fuse as the trip curves require a duration considerably longer with an MRBF, ANL or Class T fuse.... The average current of that starter is about half, or slightly less, than the measured in-rush..
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Old 06-03-2012, 08:40   #17
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Re: YANMAR 2GM20F STARTING AMPS

I think I worded my last post poorly, but now you're making exactly the point I was trying to bring up. You posted a video showing the inrush current with no other information. Circuits are usually fused on the steady state, not inrush currents. Blue Seas does have the trip time vs overload graphs for the MRBF fuses, and an example of inrush currents of a starter motor on a scope screen.

John


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Originally Posted by Maine Sail View Post
That particular motor is wired with 1/0 cable and fused with a 200A ANL. The difference in starting between the old 2GA wire and the 1/0 is quite noticeable. In-rush does not really affect the fuse as the trip curves require a duration considerably longer with an MRBF, ANL or Class T fuse.... The average current of that starter is about half, or slightly less, than the measured in-rush..
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Old 06-03-2012, 08:52   #18
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Re: YANMAR 2GM20F STARTING AMPS

Starting circuits are important! This is no place to guess or to skimp on wire size. Inrush current typically can exceed 1,000 amps, then drop to several hundred amps.

Typically, starter cables on boats are way undersized, in my experience. As Maine says, the difference between AWG2 and AWG1/0 cable is very noticeable.

I would not wire ANY starting circuit with less than AWG1/0. For longer runs (over 15' round trip) I would use AWG2/0.

The proper ANL or MRBF fuse size for a small diesel is in the 200-300A range. I'd prefer the upper figure and, on my boat with a 4-108, have a 400A ANL in a start circuit with AWG 2/0 cable.

And, I would NEVER solder lugs or crimp connections on a boat. Good crimpers are available (they're a bit pricey but WELL worth it). Be sure you have a crimper which is designed for the type of lug or terminal to be used.

There are numerous threads on crimping and soldering which provide great info and pictures.

Bill
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Old 09-03-2012, 03:28   #19
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Re: YANMAR 2GM20F STARTING AMPS

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Originally Posted by btrayfors View Post
Starting circuits are important! This is no place to guess or to skimp on wire size. Inrush current typically can exceed 1,000 amps, then drop to several hundred amps.

Typically, starter cables on boats are way undersized, in my experience. As Maine says, the difference between AWG2 and AWG1/0 cable is very noticeable.

I would not wire ANY starting circuit with less than AWG1/0. For longer runs (over 15' round trip) I would use AWG2/0.

The proper ANL or MRBF fuse size for a small diesel is in the 200-300A range. I'd prefer the upper figure and, on my boat with a 4-108, have a 400A ANL in a start circuit with AWG 2/0 cable.

And, I would NEVER solder lugs or crimp connections on a boat. Good crimpers are available (they're a bit pricey but WELL worth it). Be sure you have a crimper which is designed for the type of lug or terminal to be used.

There are numerous threads on crimping and soldering which provide great info and pictures.

Bill
I have been meaning to get back to thread but work just keeps getting in the way .

It is not often that I disagree with Bill's comments but I have to say I don't share his concern about starter cables being way undersized. Sure larger sized cable is always better (assuming lugs etc will fit on the terminals and such) but mostly we use larger cable to eliminate voltage drop to voltage sensitive devices or to increase efficency of circuits that are mostly turned on.

A starter motor is very tolerant of low terminal voltages due to being series wound. In this instance I referring to the voltage present at the terminals of the motor, not the battery terminals. It is used for a few seconds at a time so efficency is not an issue.

What it is not tolerant to is low current capacity of the supply source (the battery). Providing the battery can deliver its rated CCA, some extra resistance in the wiring will only cause a voltage drop at the motor terminals.

A 12 volt, 1 KW series wound motor will deliver 1KW (almost) when connected to 6 volts (but drawing twice the current and having a lower RPM). Of course there are limits, mainly due to winding restraints and overheating but even at a full 12 volts, there are limits (mainly overheating).

I am not recommending to go small in wiring size but likewise I don't believe in going oversize just to keep the motor terminal voltage near to battery terminal voltage and yes, to repeat again, big IS better but not always necessary. This is a case of don't sweat the small stuff - IMO.
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Old 09-03-2012, 05:08   #20
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Re: YANMAR 2GM20F STARTING AMPS

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Originally Posted by Wotname View Post
I have been meaning to get back to thread but work just keeps getting in the way .

It is not often that I disagree with Bill's comments but I have to say I don't share his concern about starter cables being way undersized. Sure larger sized cable is always better (assuming lugs etc will fit on the terminals and such) but mostly we use larger cable to eliminate voltage drop to voltage sensitive devices or to increase efficency of circuits that are mostly turned on.

A starter motor is very tolerant of low terminal voltages due to being series wound. In this instance I referring to the voltage present at the terminals of the motor, not the battery terminals. It is used for a few seconds at a time so efficency is not an issue.

What it is not tolerant to is low current capacity of the supply source (the battery). Providing the battery can deliver its rated CCA, some extra resistance in the wiring will only cause a voltage drop at the motor terminals.

A 12 volt, 1 KW series wound motor will deliver 1KW (almost) when connected to 6 volts (but drawing twice the current and having a lower RPM). Of course there are limits, mainly due to winding restraints and overheating but even at a full 12 volts, there are limits (mainly overheating).

I am not recommending to go small in wiring size but likewise I don't believe in going oversize just to keep the motor terminal voltage near to battery terminal voltage and yes, to repeat again, big IS better but not always necessary. This is a case of don't sweat the small stuff - IMO.
The importance of using larger cables in the starting circuit has to do more with the speed of cranking the motor.

If you want to turn over your motor as fast as the available voltage (at the battery) will allow -- and thereby realize a faster engine start -- then larger battery cables rather than 'the small stuff' will do the job for you.

Of course, if you're just sitting at the dock this may not be important.

So, I agree with Wotname....'big is better but not always necessary'.

:-)
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