Poecheng
Well-known member
Agree re the chicken and egg, which is why I know I don't know enough about diesel engine fueling and management.
Yanmar engine issues
- Thread starter Rhubarb
- Start date
Fr J Hackett
Well-known member
I hope the OP comes to a satisfactory solution to this and gets a definitive answer because it's an interesting conundrum
bristoljim
Active member
The simple standard way of making a large alternator work on a small engine is to fit a switch in the field or exitation wire,start the engine to nearly max rpm then close the switch. The 28hp is developed @ max revs not at starter/starting revs.
Jim
jwilson
Well-known member
I'm with Poecheng: it's a hell of a alternator belt setup that will absorb most of 18 hp. The diesel governor will try and pump more fuel in to get to the revs you set with the throttle.
I have a 3YM30 27hp with a standard 65? amp alternator. There is no discernible difference between a cold start with near-flat domestic batteries and fully charged ones: in both circumstances full revs are availble within a second or two of starting and putting into gear. Not that I do that that often.
I have a 3YM30 27hp with a standard 65? amp alternator. There is no discernible difference between a cold start with near-flat domestic batteries and fully charged ones: in both circumstances full revs are availble within a second or two of starting and putting into gear. Not that I do that that often.
Adjag
Member
I think it does reach an equilibrium, at these speeds (<1000rpm) the engine power is roughly proportional to speed (ie the torque curve is flat). But the alternator power rises v quickly with speed, actually there's a cut in speed where the power is 0! See Alternator Output Curves - Balmar for example.It would be amazing if the extremely high load created by the oversized-alternator with no soft start was so perfectly balanced as to permit the engine to idle (but not stall) and yet not allow the revs to rise at all for a fixed period, when all of a sudden it can then rise as much as you wish it to.
I am not suggesting it is nothing to do with the alternator but it would be quite a feat to achieve such an unusual equilibrium simply by the application of load.
Being a bit dim here but, if the output matches the load, the application of the throttle brings about an increase in output - the load doesn't prevent revs rising unless the load itself increased massively to strangle the engine down. Though I don't know how you strangle a diesel engine down back to idle revs by application of load.
It is as if there is a soft start, just that it is on the throttle not the alternator
So with the load rising v rapidly with speed & the power not so much it'll find a balance point. In Rhubarb's case this balance point is probably just below normal idle speed, so the governor is giving it full fuelling - that's why the engine won't listen to the lever on max - it's already trying it's hardest!
Poecheng
Well-known member
The other thing to factor in is that the engine is at idle revs therefore the alternator will not be giving out 125A. The charge curve differs from alternator to alternator but the Hitachi ones are likely to be low-ish at idle compared to a HD Balmar or Prestolite (probs the same thing).
It is probably only giving out 30 or 40 A at idle ??? 14.3v x 40A = 572w or 0.6KW or 0.8hp.
If it was 60A - which would surely make it one of the best 'standard' alternators available at idle - that is 0.85kw or 1.14hp
If we say the V at the alternator is 16v (in order to get 14.3v at the battery albeit it is not battery sensed so probs generous ) then the figures are 0.65kw/0.9hp and 1kw/1.34hp. It will make other outputs (heat) and so even if we added 50% for inefficiency, it is still not explaining how the engine is being held back.
Or is it.................?
It is probably only giving out 30 or 40 A at idle ??? 14.3v x 40A = 572w or 0.6KW or 0.8hp.
If it was 60A - which would surely make it one of the best 'standard' alternators available at idle - that is 0.85kw or 1.14hp
If we say the V at the alternator is 16v (in order to get 14.3v at the battery albeit it is not battery sensed so probs generous ) then the figures are 0.65kw/0.9hp and 1kw/1.34hp. It will make other outputs (heat) and so even if we added 50% for inefficiency, it is still not explaining how the engine is being held back.
Or is it.................?
Adjag
Member
I think it might be. Taking yr 1kW alternator output at (say) 800rpm idle. Alternators aren't v efficient so adding 50% makes 1.5kW load on the engine. It's hard to get power curves at such low speeds but I'd guess abt 4kW. So the alternator is taking nearly 40% of what's available. But with a cold engine (high friction with cold oil) you could easily lose 2kW so the engine becomes only a 2kW one. All these numbers are rough so that doesn't leave much spare over the alternator's 1.5kW thirst...
Poecheng
Well-known member
i have looked at the power graph for the Yanmar 20 but it commences at about 1600rpm which is no use for this issue.
The Beta 20hp graph shows that at 900rpm the crankshaft output is at least 2hp, at 1000 rpm it is c.3hp and and at 1200rpm it is just above 5hp: https://betamarine.co.uk/wp-content/uploads/2020/07/B20-HE-Power-Graph.pdf
I take Adjag's point in #65 but the power of the alternator and the engine are not rising at the same values, even if they are increasing at the same rate. I think the Balmar curve will differ considerably to the Yanmar Hitachi alternator output curve - the Hitachis are pretty crap in overall output and throttling back etc.
If we take the 120A Balmar though, at 1000rpm engine and 2000rpm alternator, it is giving 14.3 (they say 13.5v) x 80A (cold) = 1.15kw = 1.55hp and at 1250rpm engine, 2500rpm alternator, it is giving 116A (cold) = 1.66kw=2.22hp.
At those revs, the Beta engine is producing 3hp and 5hp+ at the crank.
I have (reasonably) assumed the Beta is roughly the same as the Yanmar and (unreasonably) assumed the Balmar 120A is the same as the Hitachi, and it still doesn't show how this can happen IMHO. The engine power at the crankshaft is at all times greater (2 x) than the alternator load. They may both increase as the revs rise but the increase in engine power is greater than the increase in alternator load at all stages.
The Beta 20hp graph shows that at 900rpm the crankshaft output is at least 2hp, at 1000 rpm it is c.3hp and and at 1200rpm it is just above 5hp: https://betamarine.co.uk/wp-content/uploads/2020/07/B20-HE-Power-Graph.pdf
I take Adjag's point in #65 but the power of the alternator and the engine are not rising at the same values, even if they are increasing at the same rate. I think the Balmar curve will differ considerably to the Yanmar Hitachi alternator output curve - the Hitachis are pretty crap in overall output and throttling back etc.
If we take the 120A Balmar though, at 1000rpm engine and 2000rpm alternator, it is giving 14.3 (they say 13.5v) x 80A (cold) = 1.15kw = 1.55hp and at 1250rpm engine, 2500rpm alternator, it is giving 116A (cold) = 1.66kw=2.22hp.
At those revs, the Beta engine is producing 3hp and 5hp+ at the crank.
I have (reasonably) assumed the Beta is roughly the same as the Yanmar and (unreasonably) assumed the Balmar 120A is the same as the Hitachi, and it still doesn't show how this can happen IMHO. The engine power at the crankshaft is at all times greater (2 x) than the alternator load. They may both increase as the revs rise but the increase in engine power is greater than the increase in alternator load at all stages.
Poecheng
Well-known member
I am (sadly) finding this fascinating.
The Balmar power curve clearly shows a much higher amperage at cold alternator. I take your point about engine efficiency at cold start.
Is there a weird crossover point where, although the alternator won't start getting hot by that stage (and thus reducing the load), the engine might have got itself going and the oil circulating and warmer and then can push its way past the deadlock???? Which is what somebody probabl
y said 50 posts agoAdjag
Member
How nice to have a good technical conversation (I wonder if we're boring everyone else?) I think you've missed the inefficiency of the alternator in these calcs. They're not v good , maybe 70% at best and only 50% at low (or high) speeds What makes automotive alternators so inneficient relative to other applications?. So at 1000rpm the Beta makes abt 2kW (3hp), the alternator outputs 1.15kW but needs 2.3kW to drive it (50% efficient) so we're in debt...
Rhubarb
New member
Well I’ve enjoyed your calculations, I’ve tried similar sums myself, but far less informed.
The 2 sets of marine engineers (one of whom was appointed by Barrus) both concluded that the alternator is slowing the engine (via their various tests). They are equally stuck for a way forward as it’s a new engine with the factory fitted alternator and they struggled to believe that Yanmar / Jeaneau had not tested this before lots of boats were made.
One of the difficulties in trying a smaller 70amp alternator is that the drive belts and pulleys have all been scaled up to drive the 125amp alternator and so there is not a direct smaller replacement.
Allegedly Yanmar Europe have kicked Barrus off the case and are arguing directly with Jeaneau Europe regarding solutions/ responsibility. That doesn’t bode well for a quick solution for us as I suspect they’re factoring the consequences for several hundred other boats.
The 2 sets of marine engineers (one of whom was appointed by Barrus) both concluded that the alternator is slowing the engine (via their various tests). They are equally stuck for a way forward as it’s a new engine with the factory fitted alternator and they struggled to believe that Yanmar / Jeaneau had not tested this before lots of boats were made.
One of the difficulties in trying a smaller 70amp alternator is that the drive belts and pulleys have all been scaled up to drive the 125amp alternator and so there is not a direct smaller replacement.
Allegedly Yanmar Europe have kicked Barrus off the case and are arguing directly with Jeaneau Europe regarding solutions/ responsibility. That doesn’t bode well for a quick solution for us as I suspect they’re factoring the consequences for several hundred other boats.
Rhubarb
New member
I did email Theo Stocker to see if YM would be interested in a story of the problems.
6 weeks and no-reply so I think we can assume Theo is more worried about his advertising income from Yanmar rather than a story of interest to sailors?
6 weeks and no-reply so I think we can assume Theo is more worried about his advertising income from Yanmar rather than a story of interest to sailors?
Fr J Hackett
Well-known member
They won't like it but suggest that they fit a decent smart alternator that can be configured to allow the engine to run up and I bet your problems but not theirs would be solved, they may find a cheaper alternative.
greeny
Well-known member
If they have lots of boats giving the same problem then it's clearly a design problem and all the discussion about faulty this or that is irrelevant. Have Yanmar/Jenneau admitted there is a problem with the setup and it's an issue on all boats fitted with this system, or is all the discussion going on between them just about your boat?
Poecheng
Well-known member
True
You are correct, I hadn't added in the alternator inefficiency and so it is all getting rather marginal, at best. We might have got there - contrary to all my initial thoughts!
When I had a Beta 20hp (great engine) and the75A alternator (I think) and a polyV belt, I enquired with Beta about a bigger alternator and they advised that anything much bigger would be just too much. I didn't need it but I just like a good charging system and, in fact, I didn't even bother with an Adverc as the volts were good.
125A alternator on a 20hp engine is tending towards being a generator and seem to be reducing its core function of propulsion.
It may have worked in a warmish factory but not in the field.
OP could fit an Adverc, which has a soft start or another smart regulator which has soft start and can be programmed to derate the output or even just swap out the alternator for something like 60-75A and get it back to more usual proportions.
Fr J Hackett
Well-known member
True
You are correct, I hadn't added in the alternator inefficiency and so it is all getting rather marginal, at best. We might have got there - contrary to all my initial thoughts!
When I had a Beta 20hp (great engine) and the75A alternator (I think) and a polyV belt, I enquired with Beta about a bigger alternator and they advised that anything much bigger would be just too much. I didn't need it but I just like a good charging system and, in fact, I didn't even bother with an Adverc as the volts were good.
125A alternator on a 20hp engine is tending towards being a generator and seem to be reducing its core function of propulsion.
It may have worked in a warmish factory but not in the field.
OP could fit an Adverc, which has a soft start or another smart regulator which has soft start and can be programmed to derate the output or even just swap out the alternator for something like 60-75A and get it back to more usual proportions.
Getting there ?
burgundyben
Well-known member
I've just caught up and been thinking about it today.
Caveat. I dont do internet diagnosis, its too easy to be wrong, at work if I was facing this we'd be using a lot of test equipment, then analysis of empirical data. So what follows is idle musing based on what I've read on the thread. I do work in the design of electric turbo charging, electric supercharging, design of power electronics and of course that means I have a handle on engine development.
We're missing heat rejection out off the alternator, that is to say we dont know the efficiency of it.
Further, we don't know the losses in the belt, I suspect thats quite high too.
I suspect driving that alternator requires more hp than we realise.
Batteries in a low state of charge have lower internal resistance, since the potential difference at the alternator output is higher than that across the battery current flows into the battery, as the battery state of charge increases so does its internal resistance, so current flow reduces till we get to the point where current flow is minimal and battery is fully charged.
If we plot a curve of current flow over time we'd see a steep fall in the first few seconds, seems to me that the govenor in the injection pump at low revs cannot deliver enough fuel to increase revs as fast as the yachtie owner would like, ie load is higher than power that can be delivered.
I suspect that they've restricted the ability of the govenor in order to meet emissions regs.
You also have to take into consideration that when the engine is cold a lot of the heat from the combustion is lost in heating the engine and its coolant, so peak cylinder pressure is impacted resulting in reduced torque capability.
My summary, I suspect there's no fault as such, but its a badly optimised system.
A solution might be an aftermarket alternator control.
Caveat. I dont do internet diagnosis, its too easy to be wrong, at work if I was facing this we'd be using a lot of test equipment, then analysis of empirical data. So what follows is idle musing based on what I've read on the thread. I do work in the design of electric turbo charging, electric supercharging, design of power electronics and of course that means I have a handle on engine development.
We're missing heat rejection out off the alternator, that is to say we dont know the efficiency of it.
Further, we don't know the losses in the belt, I suspect thats quite high too.
I suspect driving that alternator requires more hp than we realise.
Batteries in a low state of charge have lower internal resistance, since the potential difference at the alternator output is higher than that across the battery current flows into the battery, as the battery state of charge increases so does its internal resistance, so current flow reduces till we get to the point where current flow is minimal and battery is fully charged.
If we plot a curve of current flow over time we'd see a steep fall in the first few seconds, seems to me that the govenor in the injection pump at low revs cannot deliver enough fuel to increase revs as fast as the yachtie owner would like, ie load is higher than power that can be delivered.
I suspect that they've restricted the ability of the govenor in order to meet emissions regs.
You also have to take into consideration that when the engine is cold a lot of the heat from the combustion is lost in heating the engine and its coolant, so peak cylinder pressure is impacted resulting in reduced torque capability.
My summary, I suspect there's no fault as such, but its a badly optimised system.
A solution might be an aftermarket alternator control.
burgundyben
Well-known member
BTW Fascinating discussion!
burgundyben
Well-known member
Exactly!
Rhubarb
New member
That’s a key question, allegedly no one else has reported the problem. Hence our interest in anyone else with the same engine/alternator and their experiences.
But if we were the only ones then you would think that they would exchange the alternator just to rule it out as a rogue.
The fact it’s being dealt with at a European level seems to imply there may be a bigger issue.
