Alternator low voltage output

[rogerowen]

My boat batteries failed to start my Yanmar 1GM10. We had motored all the way up the channel from our mooring at Lymington to the open Solent, kept the motor ticking over whist sorting out the sails - after about an hour and a half of finding no decent wind, we motored back to our mooring and shut down the motor. I always run some fresh water through the seawater engine cooling system - but the engine would not restart, just a clicking noise from the starter. I replaced the starter - but still no starting. I checked the volts coming out of the alternator and only got a reading of 1.7 volts, so I replaced the alternator. The new alternator puts out even less volts - about 0.7 volts.this is at tick-over, at slightly higher revs I get 1.5 volts. We have a solar panel that trickle charges the batteries, and we have not had a problem over the last 2 and a half years. Batteries are connected via a splitter diode and are currently delivering around 12.7 volts each. Is it usual for an alternator to deliver such a low output at low revs?

 

[roaringgirl]

The voltage reading at the alternator output should be the same as the voltage reading across the battery, as they are in the same circuit, are you sure you're measuring it correctly? Is the alternator internally or externally regulated? Given that you have a diode pack in the system, where does the alternator regulator read the circuit voltage from? What is the voltage here when you measure it? What happens to the output voltage if you remove the field wire? Is the alternator earth good?

 

[rogerowen]

The voltage reading at the alternator output should be the same as the voltage reading across the battery, as they are in the same circuit, are you sure you're measuring it correctly? Is the alternator internally or externally regulated? Given that you have a diode pack in the system, where does the alternator regulator read the circuit voltage from? What is the voltage here when you measure it? What happens to the output voltage if you remove the field wire? Is the alternator earth good?

Thank you. I'm taking the reading off the back of the alternator at the point where the + and - leads attached with multimeter set to 20 volt DC range. I've tried with the cables connected as well as disconnected - no difference. I'm not sure about regulation, in addition to the + and - connections at the alternator there is 2 prong plug - not sure what that is or where it goes to, there's an ammeter in the cockpit - maybe going there. Most of the wiring on my boat is a little curious - but I'm mostly concerned that I'm not getting a better voltage output directly from the brand new alternator - which as you say may be a regulator issue or I'm not reading correctly.

 

[Pye_End]

If your batteries have 12.7v (presume this is a voltage taken when not being charged by solar at the time) and not starting the engine it would be worth checking to see if you have a poor joint - and I would start with the -ve onto the block. Look at the battery voltage when you try to turn it over - should show a healthy drop, though if it drops too much then it could be a battery issue. Not dropping probably wiring.

Perhaps the alternator is not being energised?

 

[rogerowen]

If your batteries have 12.7v (presume this is a voltage taken when not being charged by solar at the time) and not starting the engine it would be worth checking to see if you have a poor joint - and I would start with the -ve onto the block. Look at the battery voltage when you try to turn it over - should show a healthy drop, though if it drops too much then it could be a battery issue. Not dropping probably wiring.

Perhaps the alternator is not being energised?

Thank you, I'll give all the contacts a good clean. Actually, my battery voltage test was with the panel connected - Doh! But my main concern is that the alternator is not putting out a decent enough charge at the alternator end with nothing connected - I could be reading it wrong. I would have hoped to see reasonable voltage coming out even at low revs.

 

[mikegunn]

Thank you, I'll give all the contacts a good clean. Actually, my battery voltage test was with the panel connected - Doh! But my main concern is that the alternator is not putting out a decent enough charge at the alternator end with nothing connected - I could be reading it wrong. I would have hoped to see reasonable voltage coming out even at low revs.

The alternator needs to be connected to a battery before it will produce a charge. Initially the alternator’s field draws current from the battery. Once the alternator starts to produce a current it weans itself from dependence on the battery and becomes self sustaining. That initial starting supply of electricity required by the field comes from the battery via the engine’s ignition switch and ignition light. When the alternator is generating sufficient electricity to become self sustaining the ignition light will extinguish. Make sure that the field wire is receiving a voltage when the ignition switch is turned on and before attempting to start the engine. You won’t see 12V because of the resistance of the ignition light. I can’t remember what it should be but guess somewhere around 8V. Someone more expert than me will be along in a minute with a more realistic figure.

Mike

 

[roaringgirl]

The big black wire should be connected via some route to -ve of the battery and the big red wire should be connected to +ve which is why the voltage at the alternator should match that of the battery, are you able to continuity test them both? What is the voltage across the red and black of the alternator when it's not running?

 

[Pye_End]

But my main concern is that the alternator is not putting out a decent enough charge at the alternator end with nothing connected

As post 6. Quite likely the two problems are connected.

 

[rogerowen]

The alternator needs to be connected to a battery before it will produce a charge. Initially the alternator’s field draws current from the battery. Once the alternator starts to produce a current it weans itself from dependence on the battery and becomes self sustaining. That initial starting supply of electricity required by the field comes from the battery via the engine’s ignition switch and ignition light. When the alternator is generating sufficient electricity to become self sustaining the ignition light will extinguish. Make sure that the field wire is receiving a voltage when the ignition switch is turned on and before attempting to start the engine. You won’t see 12V because of the resistance of the ignition light. I can’t remember what it should be but guess somewhere around 8V. Someone more expert than me will be along in a minute with a more realistic figure.

Mike

Thanks Mike, The batteries have enough charge to start the engine - probably thanks to the solar panel (although I have just discovered that the negative lead from the solar controller has parted company from the battery) - not sure if this is related, but would mean that the solar panel was not charging the batteries after all. I now need some confidence that the alternator is actually charging the batteries as well. I also need several pairs of hands as boat currently on the driveway and I'm finding it a bit tricky controlling water flow to the intake whilst attempting to hold the multimeter leads on the alternator output while the engine rocks around like a mad thing. The ammeter is not registering anything as far as I can see.

 

[rogerowen]

The big black wire should be connected via some route to -ve of the battery and the big red wire should be connected to +ve which is why the voltage at the alternator should match that of the battery, are you able to continuity test them both? What is the voltage across the red and black of the alternator when it's not running?

Zero voltage reading across the alternator both with ignition on or off. Only about .3 of a volt when running.

 

[roaringgirl]

Zero voltage reading across the alternator both with ignition on or off. Only about .3 of a volt when running.

The alternator is not connected to the battery. Fix that first!

 

[Tranona]

The starting problem is probably not connected to the alternator issue if you have 12.7V at the starter battery. 1GMs are notorious for poor connections in the starter circuit at the panel the fuse in the loom, the connector in the loom and poor connections to the engine block and starter. solenoid click is a good indicator of poor connections.

 

[roaringgirl]

The starting problem is probably not connected to the alternator issue if you have 12.7V at the starter battery. 1GMs are notorious for poor connections in the starter circuit at the panel the fuse in the loom, the connector in the loom and poor connections to the engine block and starter. solenoid click is a good indicator of poor connections.

Solenoid click is an indicator that there's some, but not enough power getting from the battery to the starter, it says nothing about why.

 

[Tranona]

Solenoid click is an indicator that there's some, but not enough power getting from the battery to the starter, it says nothing about why.

Given the battery is well charged then connections between the two are the obvious place to look - and plenty of possibilities as I outlined, as changing the starter did not make any difference.

 

[roaringgirl]

Agreed, I just didn't want people to take away from this thread that a solenoid click *alone* was an indicator of poor connections.

 

[mikegunn]

Thanks Mike, The batteries have enough charge to start the engine - probably thanks to the solar panel (although I have just discovered that the negative lead from the solar controller has parted company from the battery) - not sure if this is related, but would mean that the solar panel was not charging the batteries after all. I now need some confidence that the alternator is actually charging the batteries as well. I also need several pairs of hands as boat currently on the driveway and I'm finding it a bit tricky controlling water flow to the intake whilst attempting to hold the multimeter leads on the alternator output while the engine rocks around like a mad thing. The ammeter is not registering anything as far as I can see.

Can you please clarify the situation? You’re saying that “the engine rocks around”.
Does that mean that you are able to start the engine?

Mike

 

[jamie N]

As others have stated, I'd be busy looking at the connectors at each end, and actually pulling the wire. With many cables like them, they'll corrode to a verdigris oblivion. This will allow a VDM to record continuity maybe, but no current to be drawn.

 

[rogerowen]

Can you please clarify the situation? You’re saying that “the engine rocks around”.
Does that mean that you are able to start the engine?

Mike

Yes, it only didn't start once, then I changed the starter motor and it didn't start again, Then the boat came out of the water and I recharged the batteries and now it's starting - but I'm not convinced that the batteries are getting a charge from the alternator. As many have indicated - it's looking like a connection or a fuse problem somewhere.

 

[Daverw]

I had a similar problem a few years ago, the battery neg terminal on the engine had cracked and was not full connected. Had charging issues and slow starting. Remade this and problem solved.

 

[rogerowen]

I had a similar problem a few years ago, the battery neg terminal on the engine had cracked and was not full connected. Had charging issues and slow starting. Remade this and problem solved.
[/QUOTE
Thank you, Yes, it's looking more and more like a simple connection issue - which I hope to track down soon. Just wish I hadn't rushed to fit new starter motor and alternator. Hallo Ebay.