To run engine or not ?

[V1701]

Well FWIW I run mine up once a month under load for 1/2 an hour, no different to the normal usage of sailboat engines. What I would not do is what some canal boaters do which is run for hours on tickover with no load just to charge batteries, that's when you get glazed bores...

 

[Robih]

Well FWIW I run mine up once a month under load for 1/2 an hour, no different to the normal usage of sailboat engines. What I would not do is what some canal boaters do which is run for hours on tickover with no load just to charge batteries, that's when you get glazed bores...

Why do you do that? What is the purpose?

 

[Bouba]

After lunch we will go back to the boat and put on the generator to make a cup of coffee…but I will keep it on for at least half an hour…an use the time to charge phones etc

 

[V1701]

Why do you do that? What is the purpose?

I suppose because I think things left for months on end, especially in the winter in a harsh environment, are better used than not. I do the same with my diesel car that isn't used much, same with motorbike. Things on the bike and car start to seize - brakes, etc. I don't think I'm right and those that don't do it are wrong I just do what makes sense to me and I doubt what I do causes damage or shortens life...

 

[Alicatt]

Well FWIW I run mine up once a month under load for 1/2 an hour, no different to the normal usage of sailboat engines. What I would not do is what some canal boaters do which is run for hours on tickover with no load just to charge batteries, that's when you get glazed bores...

Why would they do that at tickover? It does not provide a good charge rate, the alternators have a working RPM range where they are more efficient at.

 

[V1701]

Why would they do that at tickover? It does not provide a good charge rate, the alternators have a working RPM range where they are more efficient at.

I suspect those that do it don't know any better...

 

[dunedin]

Why would they do that at tickover? It does not provide a good charge rate, the alternators have a working RPM range where they are more efficient at.

Actually I thought that, but the output of our alternator seemed to be pretty much the same at just a fraction above tickover vs at 1,250rpm - as measured by the Victron systems

 

[Refueler]

Actually I thought that, but the output of our alternator seemed to be pretty much the same at just a fraction above tickover vs at 1,250rpm - as measured by the Victron systems

Correct - once the 'ignition' light goes out showing Alternator is charging - even idle rpm should provide reasonable charge rate. Its one of the main reasons there was change from dynamo to alternator ...

Blimey - made me remember Dynastarts !!

 

[ean_p]

The difference of only a couple of hundred engine rpm is crucial.......have a look at the leap in output between 750 and 1000 rpm of many units........bear in mind that most engines 'tick over' at sub 1000 rates !

Alternator Output Curves - Balmar

 

[Refueler]

The difference of only a couple of hundred engine rpm is crucial.......have a look at the leap in output between 750 and 1000 rpm of many units........bear in mind that most engines 'tick over' at sub 1000 rates !

Alternator Output Curves - Balmar

The fact is that Alternators do charge at low RPM ... unlike the old Dynamos. What that rate is - is not the point ..

 

[ean_p]

The fact is that Alternators do charge at low RPM ... unlike the old Dynamos. What that rate is - is not the point ..

On the contrary....what the rate is is exactly the point. If you run the engine at 'normal' tick over which for most engines is sub 1000 rpm and generally around 600-800rpm you will get a very low output where as a very small increase above tickover will ordinarily elicit a huge increase in output. What dynamo's and Dynastarts did in your grandfathers' day are not, as far as this thread is concerned,the point. Your post 48 is wishful thinking for most engines when idling.

 

[B27]

The fact is that Alternators do charge at low RPM ... unlike the old Dynamos. What that rate is - is not the point ..

It kind of is the point.
Because alternators produce a lot of power at low RPM, they put a lot of torque load on the belt and pulley.
So it's better to use a faster idle or more.
Power = amps x Volts, Power = torque x speed x constant.

Alternators can vary a fair bit in their amps vs rpm curves, some older models have limited power at low revs, some 90s- 2000s era car alternators will produce 90% of max current at tickover.

Or maybe that's a different point?

 

[johnalison]

On the contrary....what the rate is is exactly the point. If you run the engine at 'normal' tick over which for most engines is sub 1000 rpm and generally around 600-800rpm you will get a very low output where as a very small increase above tickover will ordinarily elicit a huge increase in output. What dynamo's and Dynastarts did in your grandfathers' day are not, as far as this thread is concerned,the point. Your post 48 is wishful thinking for most engines when idling.

Just a minute. Some of us still just about alive can remember Dynastarts such as that on my Dolphin. You could get up to 8 amps if you were lucky on a good day.

 

[Refueler]

On the contrary....what the rate is is exactly the point. If you run the engine at 'normal' tick over which for most engines is sub 1000 rpm and generally around 600-800rpm you will get a very low output where as a very small increase above tickover will ordinarily elicit a huge increase in output. What dynamo's and Dynastarts did in your grandfathers' day are not, as far as this thread is concerned,the point. Your post 48 is wishful thinking for most engines when idling.

Why is it the point ... the discussion was about people charging at tick-over .. a post basically suggested that tick-over would not charge and was pointless. My reply was to say that it does charge.
The mention of dynamos was based on what appears to be some thinking that alternator at tick-over is not delivering - which was the dynamo problem.

 

[Refueler]

It kind of is the point.
Because alternators produce a lot of power at low RPM, they put a lot of torque load on the belt and pulley.
So it's better to use a faster idle or more.
Power = amps x Volts, Power = torque x speed x constant.

Alternators can vary a fair bit in their amps vs rpm curves, some older models have limited power at low revs, some 90s- 2000s era car alternators will produce 90% of max current at tickover.

Or maybe that's a different point?

I'm trying to figure out why you mention "Because alternators produce a lot of power at low RPM, they put a lot of torque load on the belt and pulley." The belt and pulley suffer regardless of RPM .... the engine will have its governor regulating fuel to maintain RPM ... so ??

My point was as I put in previous post - not what the rate is - but the fact that alternators charge at tick-over unlike the old dynamos.

As a kid - I actually drove an old banger with a dynamo system !! I boated with Stuarts - Vire - Dolphin - Lister .... with dynamos .... what a luxury to then have an alternator !! No longer thrashing the engine to get useful charge out of it ...
TBH - in those days - people avoided adding battery banks to boats not only because it was early days for mass electronics - but also the problem of getting them charged in the short engine run times ..

 

[B27]

I'm trying to figure out why you mention "Because alternators produce a lot of power at low RPM, they put a lot of torque load on the belt and pulley." The belt and pulley suffer regardless of RPM .... the engine will have its governor regulating fuel to maintain RPM ... so ??

My point was as I put in previous post - not what the rate is - but the fact that alternators charge at tick-over unlike the old dynamos.

As a kid - I actually drove an old banger with a dynamo system !! I boated with Stuarts - Vire - Dolphin - Lister .... with dynamos .... what a luxury to then have an alternator !! No longer thrashing the engine to get useful charge out of it ...
TBH - in those days - people avoided adding battery banks to boats not only because it was early days for mass electronics - but also the problem of getting them charged in the short engine run times ..

Alternators can shred belts at low RPM, when you've just fired up the engine with the battery a bit low.
Give it a few more RPM and avoid having to clean up black rubber dust.

Of course if you have some solar float charging over the winter, the current may be pretty low anyway.

I like to run my engine a few times over the winter, as I don't 'winterise' it. I run it in gear against the incoming tide, it warms up quickly.

 

[Robih]

Deleted, it upset refueler.

 

[ean_p]

Why is it the point ... the discussion was about people charging at tick-over .. a post basically suggested that tick-over would not charge and was pointless. My reply was to say that it does charge.
The mention of dynamos was based on what appears to be some thinking that alternator at tick-over is not delivering - which was the dynamo problem.

The point is that yes there is an output at or around tickover, but it is little more than a trickle....and that an insignificant increase in revs ie 30% will give a 400% increase in output based on the info from Balmar. Therefore people running their engines solely for charging would be better off generally ( assuming they have a system that can utilise the output) increasing the engine revs a small degree and not as you state in #48, leaving it at tick over when responding to #45.
Look at the Balmar chart and the difference is blinding for just a very small increase as per #49.

 

[Refueler]

Alternators can shred belts at low RPM, when you've just fired up the engine with the battery a bit low.
Give it a few more RPM and avoid having to clean up black rubber dust.

Of course if you have some solar float charging over the winter, the current may be pretty low anyway.

I like to run my engine a few times over the winter, as I don't 'winterise' it. I run it in gear against the incoming tide, it warms up quickly.

Awww C'mon DB .... think about it ....

Lets say for arguments sake we compare alternator output at different RPM ... lets take that Balmar table - that'll do nicely as they say ...

Alternator Output Curves - Balmar

Power out is based on two factors : energy IN and demand OUT.

Energy IN - is based on the RPM of the engine and in turn the alternator itself. Lets take the 750rpm ... line shows 15A to 20A out at 13.5V.
Whether battery is flat or part discharged - it is not going to get anymore than that. So demand is actually not met most likely.

Now lets crank her up to high RPM .. lets say 2500RPM .... line shows 66A to 76A out at 13.5V. Battery will now be able to meet demand until voltage rises in opposition to the alternator output ... which in fact will cause alternator to work harder until regulator cuts in.

Would you like to tell me where the torque required at low RPM can be higher than at high RPM ? Given the hugely different WATTS output ??

The drive belts suffer wear at start up - initial act of getting reluctant alternator to spin up ... and any rough / uneven / corrossion / misalignment of pulleys ....
Another factor is when someone decides to install a higher output alternator than designed for the single pulleys / belts. Seen it too often ... alls' well at low RPM ... it appears all good - until throttle is opened up to high .. alternator is now too much for belt and it starts to slip .... soon it lets go and now zero !

 

[Refueler]

The point is that yes there is an output at or around tickover, but it is little more than a trickle....and that an insignificant increase in revs ie 30% will give a 400% increase in output based on the info from Balmar. Therefore people running their engines solely for charging would be better off generally ( assuming they have a system that can utilise the output) increasing the engine revs a small degree and not as you state in #48, leaving it at tick over when responding to #45.
Look at the Balmar chart and the difference is blinding for just a very small increase as per #49.

Why are you labouring this point ?? Did I say it charges at high rate at tick-over ? Funny - I thought I agreed that tick-over is a low rate ..

Regardless of my agreeing that a small increase in RPM is better - the fact is I was replying to a post that suggested tick-over has zero charge rate...

I see Balmar say 500rpm is zero ... given that most diesels I use / see actually idle at 600 - 650 ... they do actually put that light out and charge .. albeit at low rate.