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Alternator Speed on Slow Revving engine


steve.sharratt

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1 hour ago, IanD said:

But then you might get slipping on the flywheel side (no grooves), the tension in the belt is the same at both pulleys -- you might be lucky though because the flywheel is so much bigger diameter.

 

Even without this, a polyvee belt running on the tips of the vees on the flywheel is likely to wear them away quickly... 😞

 

I am not sure what you say agrees with basic physics. I agree the wear rate of running it Ved side down sill increase the wear rate but I don't see how t will transmit less torque. The "down force" will be the same flat or V side down but the point contact force will be far higher on the peaks of the Vs so they will transmit more torque before slipping. However, the total torque transmitted should be the same.

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10 minutes ago, Tony Brooks said:

 

I am not sure what you say agrees with basic physics. I agree the wear rate of running it Ved side down sill increase the wear rate but I don't see how t will transmit less torque. The "down force" will be the same flat or V side down but the point contact force will be far higher on the peaks of the Vs so they will transmit more torque before slipping. However, the total torque transmitted should be the same.

 

The vees on the belt sitting in the vees on the pulley increase the frictional force for a given belt tension because they're at an angle, the steeper the angle of the sides of the vees is the bigger the increase in the torque capacity at a given belt tension. The factor is 1/sin(angle), so 2x if the sidewalls are at 30 degrees to vertical.

 

If you run the polyvee belt points-in on a flat pulley you don't get this advantage, just increased force per unit area on the belt tips (maybe 5x?) which will increase the wear rate compared to a flat belt.

Edited by IanD
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Just now, IanD said:

 

The vees on the belt sitting in the vees on the pulley increase the frictional force for a given belt tension because they're at an angle, the steeper the angle of the sides of the vees is the bigger the increase in the force.

 

Yes if we are discussing a pair of Vd pulleys but we are not. We are discussing on Vd pulley on the alternator and a flat surface on the alternator. In that configuration it should not affect the torque transmitted whichever way up the belt is on the FLYWHEEL because the flywheel has no corresponding vs for the belt to sit into.

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6 minutes ago, Tony Brooks said:

 

Yes if we are discussing a pair of Vd pulleys but we are not. We are discussing on Vd pulley on the alternator and a flat surface on the alternator. In that configuration it should not affect the torque transmitted whichever way up the belt is on the FLYWHEEL because the flywheel has no corresponding vs for the belt to sit into.

 

I don't think we're disagreeing here... 😉

 

It all depends which has the lower torque limit, polyvee on vee pulley on the alternator or polyvee on flat pulley on the flywheel. With a big diameter flywheel the alternator pulley will probably set the limit, which is fine (but a 180 degree wrap on the alternator is needed). If the flywheel is big enough then the faster wear due to running on the tips of the belt (about 20% of the area) should also be fine -- but both these should be checked with Balmar.

Edited by IanD
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Since, on the V pulley the drive is taken by the angled flanks of the ribs, wear of the tips (from running on the flat flywheel surface) should not be problem until the extent of the tip loss is quite large. So while the belt life may be less than if running on two polyvee pulleys, it should still be a workable solution.

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3 minutes ago, David Mack said:

Since, on the V pulley the drive is taken by the angled flanks of the ribs, wear of the tips (from running on the flat flywheel surface) should not be problem until the extent of the tip loss is quite large. So while the belt life may be less than if running on two polyvee pulleys, it should still be a workable solution.

Agreed -- but the obvious thing to do is ask Balmar since I'm sure they'll have encountered this case before, they'll probably say something like "all OK so long as the flywheel pulley is (example only) 5x bigger than the alternator pulley".

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If you want to really transmit more torque without undue wear of vee belt points, use a toothed belt, like a cam belt, with an idler on the plain side. It will take years to wear to any degree.

The original belt driven cam engine I came across was the Vauxhall sloper in the Victor and CF van. When first released, they were offering a life time of use without belt replacement. They did find out that this was not so, quite quickly, as the high mounted oil pump and filter caused cam seizure on cold starts.

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We used to run a poly v belt biggest profile we could get with an hb3 , with custom made pulleys, on to a 110 amp alternator. We had 800 ah of leisure batteries.

It was ok if we were careful to let the alternator charge for a while before winding up, (if the batteries were less than 60% ,) but a quick get away with revs on used to cause smoke and screaming from the belt.

Worse when the ardvec cut in.

we were changing the belt twice a year and using belt spray. The dust and mess from the wear was a big problem.

If I had kept the boat I would have double pulleyed it. 

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When running the alternator geared up like this, consider adding a switch to disable the field during cold starts. A cold low-revving diesel will quite possibly fail to accelerate at all if it's a loaded by an alternator producing that best part of a kilowatt at normal idle speed. Starting without load avoids that and allows the oil to circulate before adding load. On my FR2 with a 70A A127 and belt around the flywheel I always start from cold with the field off. It's not necessary with a hot engine.

 

MP.

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8 hours ago, Tracy D'arth said:

Even with matched belts, one is always going to be tighter than the other.

 

 

Initially yes, but I reckon the slightly tighter of the two will wear faster and eventually they will match perfectly. But yes one nice wide multi-vee belt would be a million times better anyway. 

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5 hours ago, dmr said:

If you have the rib side on the alternator then you will also have the ribs on the flywheel, not the flat side 😀. I think the idea of using the flat side refers to idlers as in the picture above.  An issue with a big pulley or flywheel is that it results in very poor wrap at the alternator, unless you include an idler. I have seen installations where this is partly solved by mounting the alternator some way from the engine rather than on the engine.  mtb???.

 

 

Mine (now sold) was a 24v 30A alternator running on a 2.5" single vee alternator pulley and a 30" diameter Taperlock crankshaft pulley. 

 

Worked fine except when the engine had just been started and was stone cold, as the alternator sucked 100% of the engine power for a few minutes with no spare torque available to turn the prop! 

 

The most interesting thing was when the vee belt was gripping well, the 30A alternator would happily deliver 40A into the lithium battery bank. 

 

 

 

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We have a Kelvin J2 which is about the same hp as a Lister JP2 and pretty similar on revs. It is fitted to a remotely mounted 160A alternator - yes I know this is ridiculous but it's how it came and that particular bit hasn't broken, and enough other things have to keep me busy without interfering with something that isn't broken. It runs on v-pulleys and I am currently running a single standard v-belt. The reasons we get away with this are 1. It has switches to switch out the connection from the alternator to the batteries when starting. Bear in mind this is a petrol start so it runs for a few minutes on petrol and then a few minutes on diesel before I switch on the alternator and in theory I can switch on the starter and domestic batteries separately if I needed to keep the load down and 2. We have never let the batteries drop significantly. I couldn't tell you the percentages but the starter battery runs at very low duty due to the petrol start which fires on the magneto within one revolution and I always rotate the flywheel back by hand before starting to give the maximum 'run up' to compression to keep the current to a minimum and the boat has minimal electrics, only using 10 LEDs and a water pump for the taps on the sink. This means the batteries do not drop by more than natural loss so whilst I can't read the charging current, it is never going to be anywhere near the capacity of the alternator. Once I get the solar panel set up to trickle charge it will do even less work.

 

The point being, if you fit a very big alternator because you need one, you need to figure how to drive that much power in to it, but if you never have it working very hard then you may be OK (or you could just fit a smaller alternator, if you have nothing else in need of more urgent attention...)


Alec

Edited by agg221
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12 hours ago, MoominPapa said:

When running the alternator geared up like this, consider adding a switch to disable the field during cold starts. A cold low-revving diesel will quite possibly fail to accelerate at all if it's a loaded by an alternator producing that best part of a kilowatt at normal idle speed. Starting without load avoids that and allows the oil to circulate before adding load. On my FR2 with a 70A A127 and belt around the flywheel I always start from cold with the field off. It's not necessary with a hot engine.

 

MP.

we had switches on each battery bank and if the batteries were really low ( we could live a week between charging no solar in those days).would turn off a couple till we had been running for a while. Good excuse for a 9 hr day.

depends how involved you want to be manual or automatic!

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There is another aspect -heat. Our current set up 75 a alternator 330 ah system has to heat a 12 v marine calorifier. ( yes i know but its an h series and a tiny cabin). We never but the water heater on until the advrc has cut out, but once on the 30a it draws obviously heats the alternator too.

A standard alternator is designed for short engine battery charging, not prolonged high outputs. 

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1 hour ago, roland elsdon said:

There is another aspect -heat. Our current set up 75 a alternator 330 ah system has to heat a 12 v marine calorifier. ( yes i know but its an h series and a tiny cabin). We never but the water heater on until the advrc has cut out, but once on the 30a it draws obviously heats the alternator too.

A standard alternator is designed for short engine battery charging, not prolonged high outputs. 

Yes. My experience is that an A127 mounted high on the engine in an engine room which runs flat-out for at least half the day is that one lasts three years or so and then fails a diode. Something buried in the depths under a cruiser stern would be hotter and might not survive.

 

MP.

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10 hours ago, agg221 said:

We have a Kelvin J2 which is about the same hp as a Lister JP2 and pretty similar on revs. It is fitted to a remotely mounted 160A alternator - yes I know this is ridiculous but it's how it came and that particular bit hasn't broken, and enough other things have to keep me busy without interfering with something that isn't broken. It runs on v-pulleys and I am currently running a single standard v-belt. The reasons we get away with this are 1. It has switches to switch out the connection from the alternator to the batteries when starting. Bear in mind this is a petrol start so it runs for a few minutes on petrol and then a few minutes on diesel before I switch on the alternator and in theory I can switch on the starter and domestic batteries separately if I needed to keep the load down and 2. We have never let the batteries drop significantly. I couldn't tell you the percentages but the starter battery runs at very low duty due to the petrol start which fires on the magneto within one revolution and I always rotate the flywheel back by hand before starting to give the maximum 'run up' to compression to keep the current to a minimum and the boat has minimal electrics, only using 10 LEDs and a water pump for the taps on the sink. This means the batteries do not drop by more than natural loss so whilst I can't read the charging current, it is never going to be anywhere near the capacity of the alternator. Once I get the solar panel set up to trickle charge it will do even less work.

 

The point being, if you fit a very big alternator because you need one, you need to figure how to drive that much power in to it, but if you never have it working very hard then you may be OK (or you could just fit a smaller alternator, if you have nothing else in need of more urgent attention...)


Alec

The OP is looking at a *mahoosive* 24V 140A alternator which will generate maybe 70% more heat (and have 70% more load on the engine) than your 12V 160A one, and he's also going to use it to charge a lithium house bank -- which is a guaranteed recipe for alternator overheating since the batteries will happily accept full charge current for hours, see posts above... 😞

 

To prevent overloading the engine at low rpm and cooking the alternator the safest solution is to use a Wakespeed WS500 which can both pull back current at low rpm and has alternator temperature sensing. At these power levels it would also be a good idea to have a ducted cooling fan blowing cold air from outside onto the alternator, this will help keep the temperature down and charging current up.

 

Without these precautions the likely result at some point -- probably in hot weather in summer -- will be a very expensive cooked alternator... 😞

Edited by IanD
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3 minutes ago, IanD said:

The OP is looking at a *mahoosive* 24V 140A alternator which will generate maybe 70% more heat (and have 70% more load on the engine) than your 12V 160A one, and he's also going to use it to charge a lithium house bank -- which is a guaranteed recipe for alternator overheating since the batteries will happily accept full charge current for hours, see posts above... 😞

 

To prevent overloading the engine at low rpm and cooking the alternator the safest solution is to use a Wakespeed WS500 which can both pull back current at low rpm and has alternator temperature sensing. At these power levels it would also be a good idea to have a ducted cooling fan blowing cold air from outside onto the alternator, this will help keep the temperature down and charging current up.

As part of the install, I am including the Balmar MC624 regulator which includes alternator and battery temp sensors.  I read the install guide today and the system does control loads at startup, ramps up to max, can be programmed etc.  It also has a ‘small engine’ feature which will 1/2 the operating parameters when the engine has other priorities.  I think it simply shorts the alternator temp sensor and tricks it into an overload mode.  I have gone back to the Balmar rep with several questions including whether freewheeling is achievable if output is not required.  (I think he is beginning to hate me!)

 

My engine is mounted midships and I always run with both side hatches open so temp doesn’t vary too much to what is outside.  The engine doesn’t run very hot either.

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3 minutes ago, steve.sharratt said:

 I have gone back to the Balmar rep with several questions including whether freewheeling is achievable if output is not required.

 

I may have misunderstood but I thought that the freewheel was to do with allowing the alternator rotor to overrun the engine under certain conditions and thus minimise strain on the drive system and belt. If no output is required then either open circuit the rotor or you will need a manual clutch on the drive (I think).

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2 minutes ago, Tony Brooks said:

 

I may have misunderstood but I thought that the freewheel was to do with allowing the alternator rotor to overrun the engine under certain conditions and thus minimise strain on the drive system and belt. If no output is required then either open circuit the rotor or you will need a manual clutch on the drive (I think).

Nope, its probably me!  I thought it meant that it would spin but not engage the alternator.  Still a good question to ask though.  The regulator manual does talk about cutting power (can’t remember exactly the circumstances) but I wondered how the alternator would react to a sudden loss of demand. I assume the regulator would have some sort of microsecond wind down?

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4 minutes ago, Tony Brooks said:

 

I may have misunderstood but I thought that the freewheel was to do with allowing the alternator rotor to overrun the engine under certain conditions and thus minimise strain on the drive system and belt. If no output is required then either open circuit the rotor or you will need a manual clutch on the drive (I think).

 

 

This is my understanding too. The angular velocity of the flywheel on a one or two cylinder diesel varies widely through the complete two-revolution cycle, and in the slowest spots it is stoopid to have the alternator momentum momentarily driving the engine. Hence the need for a freewheel inside the alternator pulley like in, say, a bicycle back wheel sprocket.

 

The effect and need fades out as the number of cylinders increases. I note the OP has a three cylinder JP so the freewheel wouldn't be doing anything like as much work as a freewheel on a JP2 or JP1. 

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Just now, steve.sharratt said:

Nope, its probably me!  I thought it meant that it would spin but not engage the alternator.  Still a good question to ask though.  The regulator manual does talk about cutting power (can’t remember exactly the circumstances) but I wondered how the alternator would react to a sudden loss of demand. I assume the regulator would have some sort of microsecond wind down?

 

The basic rule of alternators is NEVER open circuit the load (charging circuit). If you do then the rapid collapse in the stator magnetic field is likely to produce a damaging electrical pulse. Any provision for clamping the pulse at a safe level should not be relied on, they can and do fail.

 

Open circuiting the rotor is done many times a second by most regulators so will not produce a voltage surge, and it has the effect of dropping the output to zero.

 

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10 minutes ago, steve.sharratt said:

but I wondered how the alternator would react to a sudden loss of demand.

 

It can easily react by turning itself into a very expensive doorstop.

 

So go to considerable effort to avoid sudden total losses of demand happening. 

 

Edited by MtB
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7 minutes ago, steve.sharratt said:

Nope, its probably me!  I thought it meant that it would spin but not engage the alternator.  Still a good question to ask though.  The regulator manual does talk about cutting power (can’t remember exactly the circumstances) but I wondered how the alternator would react to a sudden loss of demand. I assume the regulator would have some sort of microsecond wind down?

Shutting down an alternator by turning off the field current should be fine, its the correct way to do it, in fact most regulators likely work by very rapidly turning the field drive on and off.  The problem is when a load suddenly turns itself off as the main current flow has a sort of electrical inertia (inductance) so will try to continue to flow so producing a high voltage. which can damage things.    

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9 minutes ago, MtB said:

 

 

This is my understanding too. The angular velocity of the flywheel on a one or two cylinder diesel varies widely through the complete two-revolution cycle, and in the slowest spots it is stoopid to have the alternator momentum momentarily driving the engine. Hence the need for a freewheel inside the alternator pulley like in, say, a bicycle back wheel sprocket.

 

The effect and need fades out as the number of cylinders increases. I note the OP has a three cylinder JP so the freewheel wouldn't be doing anything like as much work as a freewheel on a JP2 or JP1. 

I reckon its a whole lot more complicated than that, but this would be best discused over a beer, hope to get to the K&A next summer.  I did note that on your K1 at tickover the flywheel speed got very close to zero towards the end of its compression stroke.

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1 minute ago, dmr said:

I reckon its a whole lot more complicated than that, but this would be best discused over a beer, hope to get to the K&A next summer.  I did note that on your K1 at tickover the flywheel speed got very close to zero towards the end of its compression stroke.

 

Excellent idea, other than I don't have a boat on the K&A at the moment. Might have to put that right soon....

 

And yes that was something I loved watching on the K1, the flywheel virtually stopping and only just about passing over TDC.  The K2 doesn't really do it, surprisingly. 

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