Yanmar alternator output dropped from 14.4V to 14.1V

[andrewAB]

My YM30 alternator output seems to have dropped from 14.4V to 14.1V. It's a standard Hitachi 70amp one I think and at most I pull 50 amps for the windlass, or 30 amps fir the inverter and AC freezer.

Also the VSR doesn't seem to function anymore. Maybe coincidence, maybe the lower voltage doesn't activate it. I've disconnected it until I confirm if the alternator us still functional.

Any ideas what the problem may be?
Thanks
Andrew

 

[Boater Sam]

I would look elsewhere before blaming the alternator if it is producing 14.1 volts happily.
Could you have a failing battery? Is one getting warm?

 

[andrewAB]

The start battery is the only battery connected now and it is only a year old and hold voltage when I check in the mornings.

I will check and clean all the connections in the morning.

I'll try and measure the current alternator is producing under load with clamp meter also.

I'm a little worried my alternator will dump me in the middle of a cruise. Not catastrophic as I can rewire one of my solar chargers to the start battery or jumper lead from my house bank.

 

[Porthandbuoy]

Where are you measuring the voltage and what with?
Run the engine at 'fast idle'. ~1,000rpm.
If you measure the voltage on the back of the alternator and then at the battery is there a difference?
When checking the connections don't just make sure they're tight. Undo, clean and remake. Don't forget the negative connections.
I've read that some (all?) Hitachi alternators reduce output when they get too hot.

 

[wonkywinch]

What are you measuring with? The difference is only 2% which would fall well within the tolerance of a cheap multimeter.

 

[andrewAB]

Thanks for the responses.

Yesterday morning the alterator was producing 14.4V and the windlass or freezer running fine and the current flow with clamp meter looked sensible. As the day went on tge vokatage dropped to 14.1V so I suspect could be Thermal reduction. I will research this further and try and understand alternators better. I will do thorough cleaning and redo of the terminals at the end oc the month after haulout. The alternator possibly has always had this drop and I never had reason the check until my VSR stopped working.

I am measuring the start battery voltage with a new Victron smartshunt (auxiliary input) I installed last week. Multimeter across battery agrees.

The VSR is definately not working even with the 14.4V from cold alternator. I've attached a photo of it in case someone recognises the model.

The smartshunt has informed me that my 6 year old dual 6V Trojan T105 bank isn't great capacity. I will try equalising from my Victron Snartsokar controllers tomorrow.

I suspect next season I will go a 280Ah Lithium instal with a Victron DC to DC and live without a VSR for now.

Thanks again,
Andrew

 

[Metalicmike]

I think the charge voltage drops off as the battery voltage gets near to capacity

 

[VicS]

I think the charge voltage drops off as the battery voltage gets near to capacity

If it is the standard (60 amp ) machine sensed alternator the regulator should maintain the output voltage in the specification below.
If would appear that the output voltages which Andrew has measured are within spec.

 

[B27]

+/- 0.3V is a huge difference, from slow charging to madly gassing.

It could be the allowed range of indicated values using a basic voltmeter.

If the alternator has suddenly changed its output, I think that's fair warning to check it out before it fails completely.
It could be something as simple as worn or stuck brushes.

If you have a convenient high current load, it could be worth drawing some amps from the alternator to see if the voltage drops quickly.
I have a couple of headlamp bulbs with test leads, they draw about 10A.

As I have a DC clamp ammeter, I'd also check no great current is being drawn when 14.1V is seen.

Also check the alternator warning light is coming on and going out as it should!

 

[wonkywinch]

+/- 0.3V is a huge difference, from slow charging to madly gassing.

It could be the allowed range of indicated values using a basic voltmeter.

Which is why I asked in post #5 what was being used to measure that voltage. A cheap multimeter would not be anywhere near accurate enough. Just because they have 4 digits, it doesn't mean they are accurate to that degree!

 

[B27]

Which is why I asked in post #5 what was being used to measure that voltage. A cheap multimeter would not be anywhere near accurate enough. Just because they have 4 digits, it doesn't mean they are accurate to that degree!

Most cheap multimeters are 'near enough'.
I've got 3 or 4 of the yellow ones which used to be a fiver in Maplin's.
They agree pretty closely with the expensive Fluke one.
A lot of meters can read rubbish when presented with a 'dirty' DC signal though.
There comes a time to get a scope out.

Also I've seen cheap meters read rubbish if you keep using them for too long when the 'LO Battery' flag comes up.

Even expensive multimeters can lie, I had one for twenty years then one day changed the batteries and it was miles out.
It read an AA cell as 1.6V one way around, but -2.3V the other way.
If in doubt, check the things you thought you could trust!

 

[VicS]

Most cheap multimeters are 'near enough'.
I've got 3 or 4 of the yellow ones which used to be a fiver in Maplin's.
They agree pretty closely with the expensive Fluke one.
A lot of meters can read rubbish when presented with a 'dirty' DC signal though.
There comes a time to get a scope out.

Also I've seen cheap meters read rubbish if you keep using them for too long when the 'LO Battery' flag comes up.

Even expensive multimeters can lie, I had one for twenty years then one day changed the batteries and it was miles out.
It read an AA cell as 1.6V one way around, but -2.3V the other way.
If in doubt, check the things you thought you could trust!

I have a couple of those ( 2 for £5 at one point)

According to the operator's instruction manual the accuracy on the DC voltage ranges is ±0.5% of the reading..

Wonkywinch must have found some really cheap junk if the accuracy is only 2% or worse

 

[andrewAB]

Thanks for the suggestions.

I'm almost certain now that the alternator is as it always was and it was the VSR being non functional and new SmartShunt that made me investigate further.

The alternator appears to output the correct current. I see 60A output from alternator with anchor raise/lower at 2000 rpm (in neutral).

I neasure 40A from alternator with raise/lower anchor at idle 1000 rpm. The other 10 - 25A needed I have seen coming from start battery.

I've measured 50A used to lower anchor from house battery.

All the alternator connections look corrosion free so I haven't touched any of them (yet).

I measue 22A from alternator for the freezer and zero from start battery. Even at this low load and 2500 rpm fast cruising the voltage still drops to 14.1V so I will have little look further at this and check alternator temperature curves. I have a IR temp sensor gun, DC Clamp meter and voltmeter so should be able to work out if something is wrong.

And for £135/150 euro I can get a genuibe replacement alternator which I might just do bext season as the original is getting close to 20 years old.

Thanks again
Andrew

PS I've had a great week sailing the 200 miles from Zakynthos downto the southern Peloponese and back up to the south Ionion islands. Hardly motored at all.

 

[Porthandbuoy]

Here's a tip. Select a low voltage range on your multimeter (assuming it's not auto-ranging) and see if there is a volt drop between the battery post and the cable crimp. A few connections dropping just a few millivolts soon add up.

 

[B27]

Thanks for the suggestions.

I'm almost certain now that the alternator is as it always was and it was the VSR being non functional and new SmartShunt that made me investigate further.

The alternator appears to output the correct current. I see 60A output from alternator with anchor raise/lower at 2000 rpm (in neutral).

I neasure 40A from alternator with raise/lower anchor at idle 1000 rpm. The other 10 - 25A needed I have seen coming from start battery.

I've measured 50A used to lower anchor from house battery.

All the alternator connections look corrosion free so I haven't touched any of them (yet).

I measue 22A from alternator for the freezer and zero from start battery. Even at this low load and 2500 rpm fast cruising the voltage still drops to 14.1V so I will have little look further at this and check alternator temperature curves. I have a IR temp sensor gun, DC Clamp meter and voltmeter so should be able to work out if something is wrong.

And for £135/150 euro I can get a genuibe replacement alternator which I might just do bext season as the original is getting close to 20 years old.

Thanks again
Andrew

PS I've had a great week sailing the 200 miles from Zakynthos downto the southern Peloponese and back up to the south Ionion islands. Hardly motored at all.

It would be more informative if you could measure voltages and currents from the alternator simultaneously.
Ideally at a few different RPM.
An alternator giving 14.4V into a fully charged battery with negligible current might give for example 14.3 with 20A drawn at the same RPM. At its full rated load it might be down to 13.5 or less.
A more modern alternator will likely give a high % of its rated output at a lower RPM.

A 20 year old alternator may or may not have been regulated lower than 14.4V. If you said 30 or 40 years old, I'd say it was extremely likely, it was the norm for alternators supplied with high-duty engines like generators and tractors, whereas cars typically were nearer 14.4V to suit being used lower hours daily. As boat electrics evolved, people upped the volts on yacht alternators to suit the increased domestic loads and lower engine hours than commercial boats.

Back in the day, you could often make a big improvement simply by swapping to an alternator from a car.
It can be a bit of a moot point when you have great sailing and don't motor very much, and solar does the business!

 

[PaulRainbow]

It would be more informative if you could measure voltages and currents from the alternator simultaneously.
Ideally at a few different RPM.
An alternator giving 14.4V into a fully charged battery with negligible current might give for example 14.3 with 20A drawn at the same RPM. At its full rated load it might be down to 13.5 or less.

Where do you get these bizarre figures from ?

A more modern alternator will likely give a high % of its rated output at a lower RPM.

A 20 year old alternator may or may not have been regulated lower than 14.4V. If you said 30 or 40 years old, I'd say it was extremely likely, it was the norm for alternators supplied with high-duty engines like generators and tractors, whereas cars typically were nearer 14.4V to suit being used lower hours daily. As boat electrics evolved, people upped the volts on yacht alternators to suit the increased domestic loads and lower engine hours than commercial boats.

This is just total nonsense, why do you continue to post such misinformation ?

Back in the day, you could often make a big improvement simply by swapping to an alternator from a car.
It can be a bit of a moot point when you have great sailing and don't motor very much, and solar does the business!

Swapping what to a car alternator ?