Low engine idle speed whilst under electrical load

[bag 'o' bones]

Our beta engine is equipped with a secondary 12 volt alternator feeding a 230v 1800 watt inverter.

 

When the boat is stationary and we use the microwave (750w), the engine idle speed drops to a point where it sounds strained and laboured.

 

Now, I am aware that generator sets incorporate a governor device to automatically regulate engine speed depending on the electrical output.

 

It appears that boat engines do not have such a device, other than the one that prevents the engine from running away.

 

In my mind it seems to make sense that if you place a AC load on the engine whilst stationary, there should be a device to increase fuelling to maintain the engine speed?

 

Is it a case of in ideal world the engine could have one fitted but you can get away with not bothering (even though it probably not particularly healthy for the engine)?

 

Edited

 

Microwave is 1300w rated power. 750w cooking power.

Inverter is actually 1800 watt not 1200 as originally stated.

We don't have a washing machine on board!

Edited February 19, 2015 by bag 'o' bones

[pearley]

About three years ago we shared the Ribble Link locks with a boat that had adapted an aftermarket car cruise control to keep the engine revs at a set Kevel whilst he was using his washing machine.

[Chalky]

When things like air conditioning and power steering are designed into a car its usual to add some form of idle jack. This increases the engine speed as the load is applied to prevent poor idling etc.

[Paul C]

 

 

When the boat is stationary and we use the microwave (850w), the engine idle speed drops to a point where it sounds strained and laboured.

 

 

 

 

It might just sound it, but actually be okay. I noticed this too the other day, normally if/when we run our motor (not just for electricity, but water heating and central heating too) I normally raise the revs to around 1200rpm. I can't remember what revs exactly, is idle, I think around 750-800 though? I'd say there's nothing inherently wrong with a lower speed, except possibly a too-high vibration and the possibility that the oil pump doesn't work very well at that speed and lead to low oil pressure/lack of proper lubrication. The other thing is, is it still adequately providing electrical power at those revs? I know our (12V) alternator's best output is at around 1500rpm, lower than this with high demand, its output will be lower too in proportion to the revs.

[Keeping Up]

Surely the inherent feature of ALL diesel engines, including the Beta 43, is that they operate solely by means of a governer ?

[nicknorman]

Yes, the beta's fuel flow is controlled by a governor. However all mechanical governors work on the principle that it is the difference between the target rpm (in this case, the desired idle speed) and the actual rpm, that increases or decreases the fuel flow. In other words, the fuel flow will only increase when the rpm is below that desired. When a load is applied, the rpm drops and the governor adds more fuel. As the rpm starts to rise again in response to the increased fuel flow, the fuel flow therefore starts to decrease again and the result is that it settles at an rpm below the no-load rpm. You can increase the sensitivity of the governor (ie add more fuel for less drop in rpm) but it is a fundamental principle of physics that if you increase this sensitivity too much, oscillation and instability (ie hunting) will be the result.

 

There is only one way to deal with this and that is to raise the desired / target rpm. As chalky says, with electronic systems in cars this is routine, but on a mechanical Diesel engine governor the only way is to mechanically move the throttle (for it is the throttle that sets the target rpm). Therefore the solution is simple - just raise the rpm a bit by increasing the throttle (in neutral of course, if you are tied up). Running the engine too slow under load is bad for it, and not particularly good for the travel power either as you maximise the drive belt load and the heating of the alternator.

[David Mack]

When you use the engine to move the boat, you don' t just put it in gear (although a single lever control may give that illusion), you increase the revs as well. So you should do the same when applying a heavy electrical load.

 

Just as in you car, when you let the clutch in, you have to have press down on the accelerator to maintain the engine revs.

[bottle]

Simple answer, do not run engine at idle whenever charging batteries or an electrical load.

 

Suggestion run engine (in neutral) at a minimum of 1,000 rpm whenever doing previously mentioned.

[Guest]

Yes, the beta's fuel flow is controlled by a governor. However all mechanical governors work on the principle that it is the difference between the target rpm (in this case, the desired idle speed) and the actual rpm, that increases or decreases the fuel flow. In other words, the fuel flow will only increase when the rpm is below that desired. When a load is applied, the rpm drops and the governor adds more fuel. As the rpm starts to rise again in response to the increased fuel flow, the fuel flow therefore starts to decrease again and the result is that it settles at an rpm below the no-load rpm. You can increase the sensitivity of the governor (ie add more fuel for less drop in rpm) but it is a fundamental principle of physics that if you increase this sensitivity too much, oscillation and instability (ie hunting) will be the result.

 

There is only one way to deal with this and that is to raise the desired / target rpm. As chalky says, with electronic systems in cars this is routine, but on a mechanical Diesel engine governor the only way is to mechanically move the throttle (for it is the throttle that sets the target rpm). Therefore the solution is simple - just raise the rpm a bit by increasing the throttle (in neutral of course, if you are tied up). Running the engine too slow under load is bad for it, and not particularly good for the travel power either as you maximise the drive belt load and the heating of the alternator.

What he said ^ move the revving stick up a bit.

Simple answer, do not run engine at idle whenever charging batteries or an electrical load.

 

Suggestion run engine (in neutral) at a minimum of 1,000 rpm whenever doing previously mentioned.

Agree. I don't like using my engine thus, but if I do, find about 1100 RPM to be fine in my case (Vetus 4-15).

[b0atman]

So you fit a controller that auto accelerates for load .

Well that's tick over past boats finished with unless you go into neutral.

Washing machine on and boat accelerates down the cut.

[OldGoat]

 

It might just sound it, but actually be okay. I noticed this too the other day, normally if/when we run our motor (not just for electricity, but water heating and central heating too) I normally raise the revs to around 1200rpm. I can't remember what revs exactly, is idle, I think around 750-800 though? I'd say there's nothing inherently wrong with a lower speed, except possibly a too-high vibration and the possibility that the oil pump doesn't work very well at that speed and lead to low oil pressure/lack of proper lubrication. The other thing is, is it still adequately providing electrical power at those revs? I know our (12V) alternator's best output is at around 1500rpm, lower than this with high demand, its output will be lower too in proportion to the revs.

 

 

No, absolutely wrong, sorry to disagree (Well not actually,) all the good advice is that you should NOT charge your batteries at tickover speed BECAUSE there are torque impulses at low speeds (because there is not a smooth supply of power) and in time these WILL create wear in the crankshaft keyway. My engine failed on that two years ago and I had to buy an new engine (it not being economical to replace the crankshaft).

Apparently Beta had a lot of problems with this, so developed a better way of adapting the extra pulleys needed for multiple alternators.

 

Simple answer, do not run engine at idle whenever charging batteries or an electrical load.

 

Suggestion run engine (in neutral) at a minimum of 1,000 rpm whenever doing previously mentioned.

 

Depends on the engine size (power) to some extent I was told 1200 rpm plus and that's for a 50HP engine.

 

If the OP sets the control lever rignt - takes a bit of trial and error - the engine speed will only increase slightly as the washing machine heats the water.

Hardly worth changing the governor / messing around with the existing arrangement.

[Paul C]

Fair enough - if a modern high speed diesel has been designed to operate at a certain rpm, then I see what you mean in that something lower might not be good. I was thinking in very general terms, where diesels may run at much slower speeds, for example a Kelvin K4 is a 4 cylinder engine which idles at something around 100rpm or lower. It is designed to operate at this speed.

[by'eck]

Our beta engine is equipped with a secondary 12 volt alternator feeding a 230v 1200 watt inverter.

 

When the boat is stationary and we use the microwave (850w), the engine idle speed drops to a point where it sounds strained and laboured.

 

Now, I am aware that generator sets incorporate a governor device to automatically regulate engine speed depending on the electrical output.

 

It appears that boat engines do not have such a device, other than the one that prevents the engine from running away.

 

In my mind it seems to make sense that if you place a AC load on the engine whilst stationary, there should be a device to increase fuelling to maintain the engine speed?

 

Is it a case of in ideal world the engine could have one fitted but you can get away with not bothering (even though it probably not particularly healthy for the engine)?

 

 

 

I don't think there is anything too surprising in what is happening here. Modern engine management systems can ramp up the fuel delivered to engine to maintain a particular idle speed but only up to a point. This would take account of air-con compressors and the like on a car which present a load with engine at idle but surely an engine manufacturer can't be expected to cover the load when a high geared large alternator (or two) is added and asked to perform with the engine at idle, which is bad policy anyway.

 

Simple answer is to increase throttle a little in anticipation of heavy load not after. Its a win win situation then as alternator will spin faster aiding cooling, and both engine and alternator will perform more efficiently.

[Bobbybass]

A 850 watt microwave....if that is the microwave power...will probably draw about 1100- 1200 watts.

 

Study the power label on the back carefully.

[Roger Crown]

A 850 watt microwave....if that is the microwave power...will probably draw about 1100- 1200 watts.

 

Study the power label on the back carefully.

 

Very true.

The O.P. may also like to consider that running high loads at idle speed for long periods

i.e. washing machines etc , can easily cause the alternator to burn out.

 

Beta marine engines can happily be run stationary at 1200 to 1400 rpm .

This helps prevent the bores of the engine from glazing whilst also getting plenty of cooling air around the alternators from their built in fans.

Edited February 19, 2015 by Roger Crown

[Neil Smith]

You cant run a washing machine on a 1200watt inverter that the op has got,

 

Neil

[bag 'o' bones]

Got the ratings a bit mixed up

 

 

Microwave is 1300w rated power. 750w cooking power.

 

 

Inverter is actually 1800 watt not 1200 as originally stated.

 

 

We don't have a washing machine on board!

 

Sorry for the confusion.

 

[bag 'o' bones]

Cheers for the replies.

 

With the present set-up, the only way to raise the revs is to put the engine in gear. Perhaps fitting an ancillary throttle that can be operated whilst the engine is in neutral would be the way forward. Old style JCB excavators had a separate hand throttle in the cab to rev the engine to the required level to operate the rear back-hoe hydraulics, so not a new idea. Would be important to incorporate some sort of lock out whilst the boat was moving however.

 

Seems that fitting an automatic speed up like those found on a generator would be difficult as someone pointed out you would risk the boat speeding up or slowing down unpredictably whist underway.

 

Running the engine at low revs is definitely not good for an engine that is designed for high speed.

 

If anyone is reading this and thinking about having a boat built. I reckon it would be well worth fitting a gen-set Beta engine with the electric motor drive. so you can have the best of both worlds.

[Timleech]

Cheers for the replies.

 

With the present set-up, the only way to raise the revs is to put the engine in gear. Perhaps fitting an ancillary throttle that can be operated whilst the engine is in neutral would be the way forward. Old style JCB excavators had a separate hand throttle in the cab to rev the engine to the required level to operate the rear back-hoe hydraulics, so not a new idea. Would be important to incorporate some sort of lock out whilst the boat was moving however.

 

Seems that fitting an automatic speed up like those found on a generator would be difficult as someone pointed out you would risk the boat speeding up or slowing down unpredictably whist underway.

 

Running the engine at low revs is definitely not good for an engine that is designed for high speed.

 

If anyone is reading this and thinking about having a boat built. I reckon it would be well worth fitting a gen-set Beta engine with the electric motor drive. so you can have the best of both worlds.

If you have a normal single-lever speed/gear control, the gear linkage can be disabled to allow engine speed to be varied without engaging gear.

If it's some sort of twin lever control, there's no problem anyway.

 

Tim

[OldGoat]

Strange, I've never seen (a NB) setup where you couldn't disengage the gearbox control. Most ? have a button in the throttle arm.

If not would it be practical to fit one which does?

 

Mine looks like this:-

http://www.midlandchandlers.co.uk/Catalogue/ProductDetail/single-lever-control-tx700-ss-172103-sid?productID=b42667b6-7319-4119-a4ab-59400eed33eb&catalogueLevelItemID=6c5ecf69-c429-438b-8e65-b1ac3008dce9

[Neil Smith]

On my morse you pull the lever out to disengage the gear box, then rev up engine by pushing forwards but there is nothing on it to tell you, so if you didn't know you might think you can only increase revs while in gear.

 

Neil.

[frangar]

but on our CanBus equipped car it does alter the idle speed as electrical loads appear as the computer knows whats being switched on and off…as well as the aircon & power steering loads….all far too clever for its own good in my opinion…fine when its working but just more to fall over when it goes wrong.

 

On a boat I would keep it as simple as possible….just lift the engine above tick over when you aren't moving.

 

Cheers

 

Gareth