Yanmar engine issues

[Rhubarb]

Has anyone experienced problems with recent Yanmar 3YM20 engines/125A alternators being slow to achieve sufficient rpm to enable propulsion?

 

[jwilson]

At worst high charge rate your surprisingly large alternator is probably taking away a couple of horsepower, but that should not have a huge effect on practical engine power output.

 

[Rhubarb]

At worst high charge rate your surprisingly large alternator is probably taking away a couple of horsepower, but that should not have a huge effect on practical engine power output.

Thanks for your response and that was our view too but the “surpringly large alternator” is surprisingly standard fit on new Jeanneau yachts (319 and 349). I’ll try to attach our video of the engine rpm at start-up to illustrate our problem.

 

[Rhubarb]

iCloud

See link to watch our engine start, make sure you wait until the end of the video.

 

[[2574]]

On Balmar regulators there is a config to depower the alternator for exactly this reason, I think it cuts capacity by 50%. I think I’m correct in saying that a 100A alternator can take 4hp to drive it, significant on a small engine,

 

[Rhubarb]

On Balmar regulators there is a config to depower the alternator for exactly this reason, I think it cuts capacity by 50%. I think I’m correct in saying that a 100A alternator can take 4hp to drive it, significant on a small engine,

Thanks for your response. Yanmar tried a voltage regulator but it made virtually no difference as the batteries demand the 125A and the alternator tries to deliver it. Can’t believe we’re the only owner of a Sun Odyssey 319 or 349 that has this problem - any other owners in the same boat (sic)?

 

[burgundyben]

On Balmar regulators there is a config to depower the alternator for exactly this reason, I think it cuts capacity by 50%. I think I’m correct in saying that a 100A alternator can take 4hp to drive it, significant on a small engine,

100A at 12v = 1200 watts = 1.2kW = 1.6hp.

But I dunno how efficient the alternator itself is or the belt, I can see the belt being quite lossy.

100amp continuous is a lot, surely only when windlass working hard?

 

[[2574]]

I think it’s a field regulator that’s required, not a voltage regulator. Field regulator de-powers the alternator windings - but I’m no expert…..

 

[Rhubarb]

100A at 12v = 1200 watts = 1.2kW = 1.6hp.

But I dunno how efficient the alternator itself is or the belt, I can see the belt being quite lossy.

100amp continuous is a lot, surely only when windlass working hard?

The problem occurs even when there is no apparent load on the batteries (ie no windlass, fridge etc)

 

[[2574]]

100A at 12v = 1200 watts = 1.2kW = 1.6hp.

“Aa rule of thumb, 12-volt alternators use one horsepower for every 25 amps of output, or to put it another way, their ratio of output to horsepower load is 25:1.”

This comes from here: Selecting an Alternator | West Marine

 

[[2574]]

The problem occurs even when there is no apparent load on the batteries (ie no windlass, fridge etc)

I wonder if the alternator thing is a red herring. Sounds more like fuel issues to me.

 

[Adjag]

Has anyone experienced problems with recent Yanmar 3YM20 engines/125A alternators being slow to achieve sufficient rpm to enable propulsion?

I have that exact setup & find it v reluctant just after a cold start. But if you let it warm up a bit - say at 1000rpm ish for a minute or two then it's fine. The alternator is quite powerful (125A at 14V is 1.75kW and the alternator is probably only about 70% efficient so that's 2.5kW from the engine). The engine power curves I have only go down to 1800rpm where it gives 9kW, so the alternator is taking nearly 30% of the available power - hardlysuprising the poor thing feels it!

 

[Adjag]

I have that exact setup & find it v reluctant just after a cold start. But if you let it warm up a bit - say at 1000rpm ish for a minute or two then it's fine. The alternator is quite powerful (125A at 14V is 1.75kW and the alternator is probably only about 70% efficient so that's 2.5kW from the engine). The engine power curves I have only go down to 1800rpm where it gives 9kW, so the alternator is taking nearly 30% of the available power - hardlysuprising the poor thing feels it!

Just watched yr video -I think it's quite tough on the engine to start from cold at full throttle (I assume it was from cold & you don't get this problem on a hot start?) What happens if you start with the lever vertical, then after say 30s gently inch it up?

 

[burgundyben]

Why do you think its an alternator issue?

Is it a modern engine? Electronic control? Perhaps its meant to hold the revs down at first in order to start warming up?

 

[burgundyben]

And what makes you think the batteries demand 125 amps?

 

[Fr J Hackett]

And what makes you think the batteries demand 125 amps?

I would have thought it quite likely that an alternator would try to deliver its maximum output initially even to nearly fully charged batteries until the regulator sensed the battery condition and regulated the output.

 

[Rhubarb]

I wonder if the alternator thing is a red herring. Sounds more like fuel issues to me.

Nope, that was ruled out early on…

Just watched yr video -I think it's quite tough on the engine to start from cold at full throttle (I assume it was from cold & you don't get this problem on a hot start?) What happens if you start with the lever vertical, then after say 30s gently inch it up?

It makes no difference whether it’s a cold or hot start - or whether it’s full throttle or with lever vertical - it takes 45s (at least) to get more than 1000 rpm. It’s not a problem when everything is predictable but waiting 45s for sufficient rpm to move the boat is no good if you need to move or manoeuvre in an emergency.

 

[Rhubarb]

And what makes you think the batteries demand 125 amps?

Because until the batteries are fully charged, the engine rpm does not get any priority

 

[Fr J Hackett]

Because until the batteries are fully charged, the engine rpm does not get any priority

See post #16

 

[Clancy Moped]

Drive belt tight enough and in good condition?