Engine revs to charge battery whilst operate windlass

[sthurley]

Bit of an odd title but here goes:

I am planning a windlass install and have this query

My chart plotter shows battery voltage therefore when batteries would be getting a charge. At idle revs, 800 rpm, no apparent charging volts, read about 12.4, raise revs in neutral (gear box disengaged) to around 1200 and the voltage lifts. So if operating a windlass the preference is to have engine running to replace power into battery, but if engine on tick over in idle there would not be any power going to batteries, so will the windlass operate? Do I need to always have the engine revs increased by disengaging gear box?

Or do I need to raise the idle running revs?
Or is my alternator not working correctly?

 

[Jim@sea]

I would fit an additional battery.

 

[sailaboutvic]

We always increase the Rev when lifting the anchor .
For a start it works better . Also it replace some of the Amp

 

[nigelmercier]

It is not unusual for an alternator not to charge at tick-over. It depends on several factors, mainly the pulley ratio and the number of poles in the alternator.

 

[MM5AHO]

Change the pulley ratio. I have 14V at idle off my alternator, done by pulley ration change to allow for just this. Means battery charge or windlass operation at idle is not draining battery.

 

[lw395]

Maybe a more modern alternator would help, they deliver a lot more current at low rpm.
But an alternator which doesn't do anything at tickover isn't much good, consider changing pulley ratios.
But bear in mind the maxrpm of the altenator and engine max rpm.
OTOH, if you are otherwise happy, idling the engine at 1500rpm while raising the anchor will do the same thing.

Changing pulley ratios sometimes leads to grief with belt wear, as can fitting an alt that works hard at low rpm.

 

[RichardS]

It is not unusual for an alternator not to charge at tick-over. It depends on several factors, mainly the pulley ratio and the number of poles in the alternator.

+1

And sometimes once the kick in revs has started the alternator charging it will keep charging, albeit at a low rate, even if the revs are dropped back down to idle or slightly above.

Richard

 

[jonjo]

The OP's observations match mine. I have a meter that shows charge amps and have found that 1200 rpm equates to a charge current at rated alternator capacity when the batteries are below 70% charge.

My charging setup is an original factory fitted Volvo design and was configured by engineers far smarter than the typical contributor to a thread like this, hence I suggest the OP does not dabble with pulley ratios.

The OP should also design his windlass electrics so that the system works without any engine input, assistance from the alternator is just a bonus.

 

[Robin B]

Great info about changing the pulley. My twin Perkins operate most of the time at tick-over on the Broads and the batteries are suffering badly. Is there a rule of thumb on what to do? Is it as simple as whipping off the pulley and bunging on a smaller one?

 

[macd]

My charging setup is an original factory fitted Volvo design and was configured by engineers far smarter than the typical contributor to a thread like this, hence I suggest the OP does not dabble with pulley ratios.

Or to put it another way: configured by cost-accountants far meaner than the typical contributor to a thread like this...

But, yes, if the OP does consider changing pulley ratios, he'll need to know the ratings of the alternator in question, and particularly the highest continuous revs it can tolerate. It would be best if he could find a charging curve for the unit. If not, alternators typically begin producing amps at 1200 to 1300 rpm, reaching something approaching peak output by 2000rpm. (That's alternator rpm, of course, not crankshaft.) It would be advisable to have this information before mucking about with pulleys and belts.

On another practical note, most windlass manufacturers warn against pulling the boat to the hook by windless power alone. Trouble is, if you use the engine to drive the boat, it's often too fast, so you end up in a drive-neutral-drive-neutral cycle. In truth my usual approach in benign-ish conditions is to use the windless to reel in much of the catenary; then pause as the weight of the chain drags the boat forwards again, then repeat. All the while the engine's in neutral at about 1000rpm. This seems kind enough on the windlass motor.

 

[[70521]]

My windlass works off its own battery, gives me a spare on the boat and recharges as we are under engine.

 

[prv]

It shouldn't be necessary to run the engine in order to operate the windlass anyway.

Pete

 

[lw395]

It shouldn't be necessary to run the engine in order to operate the windlass anyway.

Pete

Very true, but it can be better for the batteries, particularly if the windlass is running off a domestic bank that's just been used for two days at anchor.
There are a lot of variables, different people use different boats in different ways.
Our club has a committee boat with a windlass, that can get used very heavily, with no long passage afterwards to recharge the battery.
One of the most common ways of damaging a DC motor is to start it under load from too low a voltage.
I normally motor forwards a bit to take the load off the chain anyway.
Windlass or not, I want 14+ V at tickover.

Bearing in mind that some alternators need a few more revs to start charging, as pointed out by RichardS.

 

[TQA]

My Lofrans Tigres is rated at 1200w. That means if working hard it will be be pulling 60 = 90 amps.

I run the engine to save caning the battery bank.

 

[single]

Slight drift but my Tigres 1500w is definitely slower without the engine running. Could this be that my engine start battery simply isn't 'man enough'? I got the smallest battery possible for the engine start but now i'm asking it to run the windlass too.

 

[duncan99210]

FWIW, our windlass is run from the domestic bank. Generally, we tend to run the engine in neutral at about 1200 rpm. There's still a draw on the battery but not as large as when we don't run the engine. I'd always either have a separate, largish battery for the windlass or run it from the domestic bank. Our engine battery is sized for the engine and I'd be concerned about using it to power a windlass.

 

[neil1967]

I think you should be able to use the windlass without having the engine on (although I know some charter boats are configured to prevent you doing this, presumably to protect the batteries, or perhaps to prevent inadvertent operation), but equally, I think it is sensible to run the engine at appropriate revs where/when you can to assist the batteries in what is probably the hardest/highest current job that they do.

 

[prv]

I got the smallest battery possible for the engine start but now i'm asking it to run the windlass too.

Seems an odd combination.

Pete

 

[Heckler]

The OP's observations match mine. I have a meter that shows charge amps and have found that 1200 rpm equates to a charge current at rated alternator capacity when the batteries are below 70% charge.

My charging setup is an original factory fitted Volvo design and was configured by engineers far smarter than the typical contributor to a thread like this, hence I suggest the OP does not dabble with pulley ratios.

The OP should also design his windlass electrics so that the system works without any engine input, assistance from the alternator is just a bonus.

The original engineer designed system in Beneteaus of the age of my boat is that there is a relay attached to the alternator that switches the control circuit on for the windlass. So, no engine running, no windlass!
Stu

 

[single]

Seems an odd combination.

Pete

Which bit? Running windlass from engine start or having a small battery? It recommended that you use a battery that is sufficient to start the engine but no more. I think I might rewire the windlass to the domestics.