Alternator Problems

[Kraken]

The alternator is a Cav AC5. Notes from the previous owner said the warning light would remain on while the engine was running and flash when the batteries were fully charged. Why would this be? After many years the alternator stopped working, which turned out to be a burned out warning light. I replaced that and it burned out again after a couple of years. This time I couldn’t find a 2 watt bulb and used a 5 watt bulb instead. This burned out in about an hour melting the light lens. I carried on for a while by removing the bulb after the alternator was excited. Then the alternator started to self excite and there was an unexplained 3 amp current with all the electrics off. Eventually it stopped working all at all. I took the alternator in to be checked and they said it was burned out and needed a rebuild. They had to remake some of the internals due to lack of available parts. On reinstallation the starter battery was initially charging at 1 ½ amps and about 15 volts, the domestics not at all. There is a lead from the alternator IND terminal to the warning light and the split charge contactor. You can see that the contactor is not being activated. It’s like there is nothing coming from the IND terminal. Why would this be? After turning the engine on and off a couple of times to check things there was no output at all. Took it back to the rebuilder who says it’s fine on his test bench. Any ideas? Could it be that something in the rebuild (rewinding?) has caused a need for more current to excite?

[Tony Brooks]

I am not sure that I can help but I would like to know what regulator you have. I am just wondering if its an ex MOD FFR one in large (for a regulator) sheet metal box rather than the much smaller cast aluminium unit with the charge voltage wander lead.

 

I hope Sir N chips in but as it is, as far as I know a standard 9 diode unit and the symptoms do not immediately make much sense to me.

[Kraken]

I am not sure that I can help but I would like to know what regulator you have. I am just wondering if its an ex MOD FFR one in large (for a regulator) sheet metal box rather than the much smaller cast aluminium unit with the charge voltage wander lead.

 

I hope Sir N chips in but as it is, as far as I know a standard 9 diode unit and the symptoms do not immediately make much sense to me.

It's the small trapezoidal shaped one mounted on the end of the alternator, but it's turned off by an Adverc (I think that's the way it works)

[Tony Brooks]

Thanks for the quick response.

 

I do not like the sound of a contactor being fed from the Ind terminal. Contactors tend to demand more current than relays so it may have overloaded and damaged the field diodes.

 

The Adverc only comes into play when the output voltage reaches the regulated voltage otherwise it just sits there waiting.

 

The whole thing sounds like an alternator fault that may have been there for years.

 

What happens if you disconnect the contactor and rev the engine. It may be that the contactor is "robbing" the warning lmp current so nothing is left to energise the alternator.

[Kraken]

I'll try that next time I'm at the boat, maybe Wednesday. The contactor (the one recommended on Gibbo's site) is a relatively recent change, in the last couple of years, and doesn't necessarily coincide with the current problems. It was a preventative measure to replace the tiny one that is supposed to be a potential problem, but hadn't been for the previous 14 years.

[Tony Brooks]

By and large split charge relays are only a problem if the main charging lead runs to the engine battery as long as they are adequately rate and from a quality supplier.

 

I think there is something odd going on and still suspect the alternator/regulator.

[MtB]

Contactors tend to demand more current than relays so it may have overloaded and damaged the field diodes.

 

 

May I raise peripheral question please?

 

What's the difference between a contactor and a relay? I thought they where two names for exactly the same thing, i.e.a high current switch operated by a low current solenoid.

 

Many thanks.

[Tony Brooks]

Contactors are normally rated for much higher currents often with a copper bar moved by an armature that connects two contact pads rather than a single lightish contact like a relay. Being heavier and needing to make two points of contact (one at each end of the bar) they often require more current to operate them. I do not have the data for the Albright contactor that I think the OP has but I have seen one where the coil had overheated, swelled and jammed the armature.

 

Low current - yes, but probably not as low as a split charge relay.

Edited November 8, 2016 by Tony Brooks

[WotEver]

Yes, think of a contactor as a high-current relay. Like 200A instead of 5A for instance. It's a relay that's been to the gym.

A relay will often have contacts that are on the end of bendy springy arms whereas a contactor is more likely to have a bar moving against a coil spring.

[MtB]

Fanx chaps.

 

So it does the same thing then, as I thought. It's mainly a difference in size and robustness, and a different arrangement inside.

[Tony Brooks]

Fanx chaps.

 

So it does the same thing then, as I thought. It's mainly a difference in size and robustness, and a different arrangement inside.

 

And operating current.

[MtB]

 

And operating current.

 

 

Yes that's what I meant! Larger currents need bigger and more robust devices to switch them.

[Arthur Brown]

Draw out the charging circuit that you actually have, check what wires really go where, follow wires carefully through bulkheads etc, follow wire colours. Once you know what you really have it's probable that the fault will be blindingly obvious -something wired in the wrong place.

[WotEver]

 

 

Yes that's what I meant! Larger currents need bigger and more robust devices to switch them.

TonyB meant the operating current for the coil. A contactor, because it's beefy, has a larger coil consuming more current.

[Tony Brooks]

An idea to test the alternator.

 

Disconnect the warning lamp wire form the alternator and connect a voltmeter (DC) between the alternator terminal and battery or alternator negative.

 

Clip a length of cable to the battery positive taking care not to short the free end to any metal. (If you do let go of the cable PDQ!)

 

Start the engine and rev to (say) 1500 rpm.

 

Touch the free end of the cable to the warning lamp terminal for a split second and observe the meter.

 

The meter should jump to battery voltage as you touch the terminal and then almost immediately rise to the charging voltage and it should stay there when you move the cable away. (I suspect it will not, I think it will drop).

 

If the voltage stays at charging voltage the problem is probably in the boat's wiring.

 

If the voltage drops then change the meter to AC and repeat.

 

If the meter then keeps showing a voltage the field diodes are faulty. That 15 volts you mention might point to failing field diodes.

 

If it still drops to zero I suspect the regulator, brushes or slip rings are faulty.

 

I think that the CAV AC series of alternators use proper radial sip rings, not the idiot face slip rings that Lucas like, so the re builders may have introduced a short where the rotor wiring passes under one slip ring.

[Kraken]

OK, thanks Tony, I'll try that.

[Sir Nibble]

Firstly, re making knackered parts is something I do all the time on elderly units but I can't think of anything inside an ac5 I can't buy new. Field diodes are big half inch jobs and rarely fail. Let me have a think.

[Sir Nibble]

Had a think. I don't know what caused the warning light on when charging performance but it whiffs of field diode. The sudden 11/2A draw is almost certainly a main pos diode short. Current symptoms strongly suggests field diode. Sounds like failed diodes have been individually changed and maybe one got missed. What's the voltage at ind?

[Kraken]

Thanks for that, I'll check later today.

[Kraken]

 

Hello Tony, I tried the tests you suggest. With the engine running the meter already showed battery voltage minus a couple of tenths. When I touched the lead from the battery to IND, it didn’t jump to battery voltage since it was already there, but did jump from battery voltage to charge voltage immediately. Charge voltage was 17.7 volts and 30 amps. This was starter battery only since the contactor was not activating. I switched the engine off and connected starter and leisure batteries together, because the leisure batteries were quit discharged as the contactor hadn’t been working and I needed some power. Over a few hours the voltage varied between 13.5 and 14.4 volts and current between 22 and 30 amps for the leisure batteries and between 5 and 8 amps for the starter depending on time and revs. So fairly normal I guess once the alternator is excited. So from your comments this would point to a fault in the boat wiring, but why nothing from the IND terminal. This points to some fault in the alternator.

Regarding your other suggestion, disconnecting the contactor made no difference.

Other things I have discovered. Testing the contactor independently, it doesn’t work. Also the ignition switch is faulty. There is power to the momentary on position for the starter but nothing to on position. So everything connected to it (alternator warning light, Adverc warning light, engine hours meter) doesn’t work, but of course the alternator warning light comes on when the alternator is excited and stays on. It also glows dimly when the IND terminal is disconnected.

So what would cause all these components (alternator, ignition switch, and contactor) to fail? And why the initial 17.7 charge voltage?

[Kraken]

Had a think. I don't know what caused the warning light on when charging performance but it whiffs of field diode. The sudden 11/2A draw is almost certainly a main pos diode short. Current symptoms strongly suggests field diode. Sounds like failed diodes have been individually changed and maybe one got missed. What's the voltage at ind?

As in the previous post, the first time I started the engine, voltage at IND was 17 volts and the second time 15 volts, so both times, similar to charge voltage. This was after exciting the alternator from the battery.

Edited November 12, 2016 by Kraken

[Tony Brooks]

Hello Tony, I tried the tests you suggest. With the engine running the meter already showed battery voltage minus a couple of tenths. When I touched the lead from the battery to IND, it didn’t jump to battery voltage since it was already there, but did jump from battery voltage to charge voltage immediately. Charge voltage was 17.7 volts and 30 amps. This was starter battery only since the contactor was not activating. I switched the engine off and connected starter and leisure batteries together, because the leisure batteries were quit discharged as the contactor hadn’t been working and I needed some power. Over a few hours the voltage varied between 13.5 and 14.4 volts and current between 22 and 30 amps for the leisure batteries and between 5 and 8 amps for the starter depending on time and revs. So fairly normal I guess once the alternator is excited. So from your comments this would point to a fault in the boat wiring, but why nothing from the IND terminal. This points to some fault in the alternator.

Regarding your other suggestion, disconnecting the contactor made no difference.

Other things I have discovered. Testing the contactor independently, it doesn’t work. Also the ignition switch is faulty. There is power to the momentary on position for the starter but nothing to on position. So everything connected to it (alternator warning light, Adverc warning light, engine hours meter) doesn’t work, but of course the alternator warning light comes on when the alternator is excited and stays on. It also glows dimly when the IND terminal is disconnected.

So what would cause all these components (alternator, ignition switch, and contactor) to fail? And why the initial 17.7 charge voltage?

 

 

Red - this indicates an open circuit to the rotor in my view but if that is the case how the devil did it energise.

 

Blue = it should not be a monetary connection. It should be permanent as long as the switch is held in the start position - faulty ignition switch?

 

The symptoms of high charging voltage and glowing warning lamp sounds like a field diode problem. Try putting the voltmeter between D+ (W/l) and b+ (main pos. output) terminals of the alternator and revving the engine. Unless the meter reads well under 1 volt you probably have a field diode problem.

 

I think you now need a reliable and knowledgeable alternator rebuilder. It would be well worth a drive down south in my view so why not PM Sir N with a view to [paying him to sort it out.

 

[Kraken]

Blue = it should not be a monetary connection. It should be permanent as long as the switch is held in the start position - faulty ignition switch?

By momentary, I meant when held against the spring for the starter. This seems to work normally but the on position seems to be dead, so it looks like this part of the switch is faulty.

[Tony Brooks]

 

 

Red - this indicates an open circuit to the rotor in my view but if that is the case how the devil did it energise.

 

Blue = it should not be a monetary connection. It should be permanent as long as the switch is held in the start position - faulty ignition switch?

 

The symptoms of high charging voltage and glowing warning lamp sounds like a field diode problem. Try putting the voltmeter between D+ (W/l) and b+ (main pos. output) terminals of the alternator and revving the engine. Unless the meter reads well under 1 volt you probably have a field diode problem.

 

I think you now need a reliable and knowledgeable alternator rebuilder. It would be well worth a drive down south in my view so why not PM Sir N with a view to [paying him to sort it out.

 

 

I think the switch may be wired incorrectly, see if you can make head or tail of this:

 

http://www.tb-training.co.uk/MarineE06.html#The%20ignition%20switch

 

before you discard the switch.

 

Typically one of the 9mm blades will be for the main input and one for glowplugs. Paired 6mm blades are usually the ignition on aux. connection and a single 6m blade the start connection. It is correct that the start will be energise all the time you hold the key in the start position but usually the aux. is a swell. Otherwise the warning lamps go out when you turn to start.

[Sir Nibble]

What a downright can of worms! All sorts of things can happen, like a rotor winding earthing and providing anything from a shut down to full blast. This need to be looked at by someone who knows what they are doing. Really it would be futile to try and sort this at a distance. For instance, it seems that the warning light may well be energised by means of the starter solenoid! so that the lamp earths through the solenoid and glows when it's charging, but why no split charge relay operation? Is it maybe on the wrong side of the lamp and bashing in when the starter's cranked? When you go to a job like this your head is full of questions and as data from eyes, ears and instruments comes in you get less questions and more answers but it's so difficult at a distance.