Warning light

[Tony Brooks]

What I think you have is a work around for a problem which is still there and could get worse. So in answer to your original question, no, I don't think it is ideal.

 

I suggest you get all of the wiring checked out by a good engineer and have the alternator tested. As mentioned, it should give you over 14 volts if it's working properly and testing will show whether the DC output is smooth and correctly rectified.

 

Also as mentioned, a bigger pulley on the crankcase end would help but I assume everything was fine up until the fault.

 

Once the fault has been rectified (so to speak) it might be best to remove the work around to simplify the circuit and prevent that causing a future problem. I hope you get it sorted.

 

 

I agree that it should but in probably the majority of cases I doubt it will. I don't think I can recall a test bench with an oscilloscope sat next to it. Most just seem to check the current and voltage. I know engine testing scopes will measure the ripples but they are usually in a different part of the workshop - if they have one.

[Mikexx]

Once I start the engine I switch the exciter off.

And yes it stays off.

 

 

With the boat sitting out the water just now on blocks

I am not going to be giving it full throttle

 

Thanks, I'm not proposing full throttle, just set in a position to provide what could be described as high cruising revs.

 

The fact the light stays out, and presumably only comes on when the engine is topped, implies the alternator is working fine.

 

Can you measure the voltage at the alternator terminal when running and report back?

 

It is possible that the wiring between the alternator and battery is suspect.

[rowland al]

 

 

I agree that it should but in probably the majority of cases I doubt it will. I don't think I can recall a test bench with an oscilloscope sat next to it. Most just seem to check the current and voltage. I know engine testing scopes will measure the ripples but they are usually in a different part of the workshop - if they have one.

I'm eluding to a dodgy rectifier. You'd see that on a scope or as excessive AC. Either way a good engineer will be able to find the real fault.

[Tony Brooks]

I'm eluding to a dodgy rectifier. You'd see that on a scope or as excessive AC. Either way a good engineer will be able to find the real fault.

 

I know you are but you use the word "good" rather than "typical". I would never assume an alternator I had put in for testing had anything more than the charging current and regulated voltage tested unless I had specifically asked for the ripple to be measured - even then I suspect it would confuse many who do alternator testing. I think to assume the ripple had been checked is not to face reality.

[Sir Nibble]

I've not put a scope on an alternator since I was an apprentice. The fact no one does it is a good indication of what it's worth. It could for instance show up a phase imbalance which would otherwise go unnoticed.

[Mikexx]

I'm eluding to a dodgy rectifier. You'd see that on a scope or as excessive AC. Either way a good engineer will be able to find the real fault.

 

Most fitters would observe the corresponding lower voltage output and recommend a new alternator.

 

I bought one recently on eBay for less that £50 for 75A lookalike, such I wasn't going to start investigating my problems any further although brushes are just a few ££.

 

If Roxylass confirms that the output at the alternator sits at 13.6V when running, whilst all else looks good then it does point to a diode. By the time an expert dismantles it and changed the diode pack it would cost more than a new alternator.

[Sir Nibble]

Most fitters would observe the corresponding lower voltage output and recommend a new alternator.

 

I bought one recently on eBay for less that £50 for 75A lookalike, such I wasn't going to start investigating my problems any further although brushes are just a few ££.

 

If Roxylass confirms that the output at the alternator sits at 13.6V when running, whilst all else looks good then it does point to a diode. By the time an expert dismantles it and changed the diode pack it would cost more than a new alternator.

Seconded. There is no point looking too closely for a symptomless "fault". If it doesn't show up without a scope, it's not a problem. Ultrasound crack testing is good too and if anyone really wants an alternator built and tested to aviation standard I can do that, so long as it carries an aircraft standard price.

[rowland al]

 

Most fitters would observe the corresponding lower voltage output and recommend a new alternator.

 

I bought one recently on eBay for less that £50 for 75A lookalike, such I wasn't going to start investigating my problems any further although brushes are just a few ££.

 

If Roxylass confirms that the output at the alternator sits at 13.6V when running, whilst all else looks good then it does point to a diode. By the time an expert dismantles it and changed the diode pack it would cost more than a new alternator.

I agree too. A new alternator could be much cheaper than the damage caused by someone fiddling about.

[ditchcrawler]

I asked the question has it always been like it and you replied only since the started and belt were attended to. In that case something has changed and you really need to find out what that is.

[Sir Nibble]

Exactly.

[Tony Brooks]

 

Most fitters would observe the corresponding lower voltage output and recommend a new alternator.

 

I bought one recently on eBay for less that £50 for 75A lookalike, such I wasn't going to start investigating my problems any further although brushes are just a few ££.

 

If Roxylass confirms that the output at the alternator sits at 13.6V when running, whilst all else looks good then it does point to a diode. By the time an expert dismantles it and changed the diode pack it would cost more than a new alternator.

 

 

However 13.6 into a well discharged battery may well be perfectly satisfactory. The important parts in the above is "sits at". If the batteries are well discharged over an hour or so the voltage should have started to rise (depending upon degree of discharge, alternator output and bank size).

Edited February 3, 2017 by Tony Brooks

[Mikexx]

 

 

However 13.6 into a well discharged battery may well be perfectly satisfactory. The important parts in the above is "sits at". If the batteries are well discharged over an hour or so the voltage should have started to rise (depending upon degree of discharge, alternator output and bank size).

 

Except Roxylass said "The battery shows 13 volts before starting"

and

"Engine running not even half throttle it's showing 13-50 13-60"

 

That possibly implies the battery wasn't flat but equally wasn't taking a charge.

 

I agree we might get a more accurate picture knowing the battery voltage after 1/4 or 1/2 hour or so of running.

 

I would still like to know the terminal voltage at the alternator!

[Roxylass]

How would I check the terminal voltage at the alternator

I am neither a mechanic or auto electrician

Going to the boat tomorrow so I will put the voltmeter on the battery before i start the engine

And take a reading after 20 minutes i will take another reading and write them down

Also I will take a closer picture of the alternator

Thank you very much for bearing with me

And I will run the engine at a good cruising speed

[MtB]

 

Mechanics that don't know these engines often think the camshaft IS the crankshaft, because its thick and beefy.

 

 

A bit like most (but not all) of the mechanics I've encountered over the years...!

[Mikexx]

How would I check the terminal voltage at the alternator

I am neither a mechanic or auto electrician

Going to the boat tomorrow so I will put the voltmeter on the battery before i start the engine

And take a reading after 20 minutes i will take another reading and write them down

Also I will take a closer picture of the alternator

Thank you very much for bearing with me

And I will run the engine at a good cruising speed

 

The fat wire leading from the alternator is the one of interest. There should be a terminal at the alternator with a approx a10mm nut on a stud. Can you measure the voltage here? And with the black voltmeter wire on the alternator body? It goes without saying, make sure your fingers stay away from the belt.

 

I'm now wondering with your refurbished starter if this is an isolated starter and you've lost an earth somewhere.

[ditchcrawler]

 

 

 

I'm now wondering with your refurbished starter if this is an isolated starter and you've lost an earth somewhere.

As I said, somethings changed and that is what we need to fined, it worked before and now it doesn't.

[Sir Nibble]

If you are measuring at the back of the alternator then check the voltage at the warning light terminal too. It's ok to disconnect the wire whilst you do this if need be.

[Roxylass]

Down the boat this morning.

The battery 12v 140ah reading 13-65 let it run for 20 minutes tested again reading 14-60.

Including a pic of volt meter is this at the correct setting for testing the alternator.

[Tony Brooks]

Sorry but that is set to measure AC voltage - the wavy line is the AC symbol. You need to point the dial at the white 20 above the orange characters. The parallel solid and broken lines signify DC that the engine electrics use (apart from rev counter drives).

[Roxylass]

This the correct one

[bizzard]

This the correct one

Yes it is. That thin grey wire I think is the warning light wire coming from the alternator. It looks like its under stress.

[Mikexx]

If you are measuring at the back of the alternator then check the voltage at the warning light terminal too. It's ok to disconnect the wire whilst you do this if need be.

 

I'm not sure if much is gained by this??

 

What might be more relevant is the difference between the warning light terminal and the alternator output terminal. That might indicate if a diode is U/S.

 

In spite of the earlier measurements being made on an AC setting, it does indicate all is well, at least somewhere.

 

Its also not clear where the black and red multimeter leads were making contact and what was being measured.

Edited February 4, 2017 by Mikexx

[Roxylass]

The readings were done on the battery terminals

And the volt meter was at the setting in the last picture

I will take an alternator reading this afternoon.

[Tony Brooks]

 

I'm not sure if much is gained by this??

 

What might be more relevant is the difference between the warning light terminal and the alternator output terminal. That might indicate if a diode is U/S.

 

In spite of the earlier measurements being made on an AC setting, it does indicate all is well, at least somewhere.

 

Its also not clear where the black and red multimeter leads were making contact and what was being measured.

 

I think that if a field diode had failed then the main output volts would be fine or a bit high but the alternator would need more revs to self energise. The warning lamp may also glow.

 

A blown field diode could explain the warning lamp symptoms.

 

 

 

[Roxylass]

Started the engine thick cable wasn't bolted on to the alternator spade connection

Got it off without touching anything red probe onto it black probe onto the alternator casing

Got a reading of 15/81

Smaller wire for the warning light is just above it

Forgot to take the iPad

Get a couple of close up pics tomorrow