Amperage to expect from Alternator

[WotEver]

You should have a nice thick bonding cable from engine to hull, preferably onto or close to the -ve bonding stud.

[jono2.0]

2 minutes ago, WotEver said:

You should have a nice thick bonding cable from engine to hull, preferably onto or close to the -ve bonding stud.

On it, thanks WotEver.  I am getting a nice list of cables to be made up.  I don't have the tools to do such large cable lugs so will need to find a supplier in the Stoke area (where I am at the mo).  Anyone know where I can buy and have made up cables such as 95mm and 50mm etc?

[nicknorman]

From the sound of it, you are currently using part of the hull for the alternator negative circuit. This is a VERY BAD IDEA! Currents through the hull are reputed to cause corrosion.

what you should have is a nice fat cable going from the engine block to the shunt (non-domestic-battery side). There should be a connection between the electrical -ve and the hull at only one point, so there is no possibility of current flowing through the hull.

edited to say I may have misread your post, but anyway my second para stands.

Edited March 6, 2017 by nicknorman

[dixi188]

I hope this is the right place to join in.

My boat has a Barrus Shire engine with  50A and 110A alternators. The previous owner paralleled the outputs and installed a Sterling charge controller.

The batteries charge fine but rarely above 30 amps and, when a high load is turned on, there is always a discharge. e.g. Hair drier that pulls 100 amps via the inverter with engine not running will still cause a 50 amp discharge with the engine running regardless of rpm.

Can someone tell me if I can change the wiring and insert switches to allow each alternator to be turned off in turn to check individual outputs and, should the outputs be fed through diodes to separate them?

Or should I revert the wiring to original.

By the way, the belts are correctly adjusted.

Many thanks in advance.

 

 

[Tony Brooks]

Please specify what you meany by a "Sterling Charge Controller". If its an A to B then it could be faulty. IF its just one of their advanced regulators then it may be fitted to the smaller alternator so the higher voltage causes the large one to shut down after a short time.

I would suggest that it is virtually impossible to safely switch an alternator off when it is being used, you would stand a good chance of destroying it.

IF its and A to D then I think that if you take each pair of thick cables (in and out pos, plus in and out neg - there should be  8 thick cables in all, 4 for ea h alternator) and with then join the in and out pos with a short bolt & insulate. Ditto the neg. Then do the other sets you will have in effect disconnected the A to D.

If you have the ordinary advanced regulator then disconnecting the flying lead that normally just comes out if a slot in the alternator (possibly blue but check on the Sterling instructions) will stop the advanced regulator messing with the alternator so   the  alternator's output will be as set by its sown regulator.

No diodes required but unless both alternator's regulated output voltage is the same one may shut down once the charging voltage rises enough for the regulators start working.

 

See pinned topic on paralleling alternators.

[WotEver]

5 hours ago, dixi188 said:

Hair drier that pulls 100 amps via the inverter with engine not running will still cause a 50 amp discharge with the engine running regardless of rpm

Just to confirm that this demonstrates that something is wrong. It could be your monitoring, it could be the 'controller', it could be that the 110A alternator is dead. With a potential 160A of generation a 100A load should be comfortably covered. 

[nicknorman]

It does suggest that the 110 A alternator is faulty. No need for any diodes, in fact that would be a bad thing. Same for switches.

I suggest that you test for output current from each alternator using a DC clampmeter such as Unit UT-203.

i don't agree with Tony re: the other alternator "shutting down" - if the batteries are discharging under a heavy load the voltage will be way down and the other alternator should be working flat out.

You didn't mention anything about alternator warning lights. Although I'm not familiar with your particular engine, normally with a dual system there are 2 warning lights. They should both come on when you switch on the ignition, and both go out after starting. An alternator relies on the current through the warning bulb to get going so if the light doesn't come on / bulb failed, this can prevent the alternator from producing any current.

Edited March 14, 2017 by nicknorman

[WotEver]

32 minutes ago, nicknorman said:

You didn't mention anything about alternator warning lights. Although I'm not familiar with your particular engine, normally with a dual system there are 2 warning lights. They should both come on when you switch on the ignition, and both go out after starting. An alternator relies on the current through the warning bulb to get going so if the light doesn't come on / bulb failed, this can prevent the alternator from producing any current.

Furthermore, you may find that under 'normal' circumstances when the batteries are well charged, one of those warning lights will come on (this isn't always the case though). If that happens and then you switch on a heavy load the light will extinguish as that alternator switches back on. 

However none of this is relevant to your current problem, I offer it simply as a bit of information for the future. 

Edited March 14, 2017 by WotEver
Light comes on, d'oh!

[nicknorman]

8 minutes ago, WotEver said:

Furthermore, you may find that under 'normal' circumstances when the batteries are well charged, one of those warning lights will go out (this isn't always the case though). If that happens and then you switch on a heavy load the light will extinguish as that alternator switches back on. 

However none of this is relevant to your current problem, I offer it simply as a bit of information for the future. 

"Come on" rather than "go out"?

[WotEver]

Just now, nicknorman said:

"Come on" rather than "go out"?

Oh yeah, I'll go edit it. Thanks

[dixi188]

Thanks for your replies.

Not sure which Sterling controller it is. I think the data plate must be on the back. There is a series of LEDs visible through a slot that show the charging mode.

There is only one Alt warning light and looking at the wiring diagram it is for the 50 amp alternator. The diagram shows a warning light for the 110 A one in the voltmeter but I've never noticed it. I wonder if it has been disconnected.

The wiring changes, as far as I can see,  the B+ cable is removed from the 50 A alternator and a 25 mm jumper linked to the B+ of the 110 A alternator. 

The more I think about it , it seems as though the 110 A alternator is not working. Under high load the voltage drops to about 11.3 ish volts with a 50-60 A discharge.

I am going to get a clamp meter and do as nicknorman says.

As for switching on/off, would a switch in the field line do the job. I used to work on light aircraft and the twins had a switch for each alternator so you could check each one in turn under load.

I'm not back at the boat for a few weeks so I'll report back later.

Many thanks guys.

Many thanks guys.

 

[rusty69]

Is it one of these 

 

https://sterling-power.com/products/universal-advanced-digital-alternator-regulator-pro-reg-d-pdar

[Tony Brooks]

Quote

 

If you can gain access to the field line (either the pos or neg side) than it is true that you can turn the alternator on and off but on most/many modern alternators this would involve partial stripping and a varying degree of butchery with fly leads out of the back.

If you can identify the warning lamp terminal on the 100 amp alternator (D+) then while its running dab a short length of cable between the main positive terminal and the warning lamp terminal. If the alternator suddenly energises you have a problem with that alternator's warning lamp or circuit. Potentially a problem in any large mulitway connector on the main harness or a blown bulb. If it is the bulb I think I would be fitting a proper warning lamp but make sure its at least 1.5 watts, 2.2 is better still. Grain of wheat bulbs and LEDs will not provide enough energisation current.

Edited March 14, 2017 by Tony Brooks

[nicknorman]

11 minutes ago, dixi188 said:

Thanks for your replies.

Not sure which Sterling controller it is. I think the data plate must be on the back. There is a series of LEDs visible through a slot that show the charging mode.

There is only one Alt warning light and looking at the wiring diagram it is for the 50 amp alternator. The diagram shows a warning light for the 110 A one in the voltmeter but I've never noticed it. I wonder if it has been disconnected.

The wiring changes, as far as I can see,  the B+ cable is removed from the 50 A alternator and a 25 mm jumper linked to the B+ of the 110 A alternator. 

The more I think about it , it seems as though the 110 A alternator is not working. Under high load the voltage drops to about 11.3 ish volts with a 50-60 A discharge.

I am going to get a clamp meter and do as nicknorman says.

As for switching on/off, would a switch in the field line do the job. I used to work on light aircraft and the twins had a switch for each alternator so you could check each one in turn under load.

I'm not back at the boat for a few weeks so I'll report back later.

Many thanks guys.

Many thanks guys.

 

I'd look into the 110A warning light circuit. It is possible that a resistor has been used to replace it, but ablown or disconnected bulb fits the symptoms.

light aircraft alternators often have remote regulators making interruption of the field current easy, but boat alternators normally have an integral regulator making surgery required. Interrupting the circuit to the warning lamp will probably stop the alternator from starting, but won't turn off one that is already charging.

[dixi188]

Rusty 69.

Those pics don't look like the one I have. Unfortunately I am over 100 miles away at the moment so can't take a photo.

Tony Brooks and Nicknorman.

I'll look into the W/L wiring.

Many thanks for your help.

 

 

[WotEver]

2 hours ago, dixi188 said:

As for switching on/off, would a switch in the field line do the job.

As others have said it might, if you could access it, but most modern alternators will self-excite and won't shut down once running and generating. If you only want to shut one down to check that it's operating then you're far better off using the clamp meter anyway. 

[Chewbacka]

If you want to stop the alternator generating power without any risk, the easiest way is to simply slacken the mounting bolt and remove the drive belt, though thinking about it, if it is like my beta engine, removal may be a bit fiddly as the belts are behind each other, in which case ignore my idea.

[MtB]

4 minutes ago, Chewbacka said:

If you want to stop the alternator generating power without any risk, the easiest way is to simply slacken the mounting bolt and remove the drive belt, though thinking about it, if it is like my beta engine, removal may be a bit fiddly as the belts are behind each other, in which case ignore my idea.

 

A better way would be to stop the engine, disconnect the output wires then start it again.

Alternators only self-destruct if disconnected whilst running, AIUI.

[Chewbacka]

15 minutes ago, Mike the Boilerman said:

 

A better way would be to stop the engine, disconnect the output wires then start it again.

Alternators only self-destruct if disconnected whilst running, AIUI.

Some alternators have enough residual magnetism to self excite so I would not chance it, though you might be ok...............

[MtB]

58 minutes ago, Chewbacka said:

Some alternators have enough residual magnetism to self excite so I would not chance it, though you might be ok...............

 

I was still under the impression failure is caused by the sudden change in current if disconnected whist running. The fatal collapse in the current will not occur even in a self exciting alternator if it isn't connected to anything in the first place.

Others may know otherwise...

[WotEver]

1 hour ago, Mike the Boilerman said:

I was still under the impression failure is caused by the sudden change in current if disconnected whist running. The fatal collapse in the current will not occur even in a self exciting alternator if it isn't connected to anything in the first place.

Others may know otherwise...

I agree. It's the sudden lack of load when an alternator is running at full chat that can allow the output to suddenly and briefly rise to a very high voltage, blowing the diodes. 

At least, that's how I've always understood the risk. 

[nicknorman]

23 minutes ago, WotEver said:

I agree. It's the sudden lack of load when an alternator is running at full chat that can allow the output to suddenly and briefly rise to a very high voltage, blowing the diodes. 

At least, that's how I've always understood the risk. 

I think it is, primarily. But what happens if the residual magnetism creates enough oomph to take the open-circuit voltage beyond the diodes' voltage rating? I'm not saying this is an issue - I don't know. But it could be in theory.

[BEngo]

With an internal regulator, it can't. As the main coil voltage rises so the regulator power  supply /field diodes swing into action and the regulator controls the field easily.  The rate of rise of o/p volts is mainly dependent on mechanical factors like the acceleration of the rotor and that is all dead slow to electronics.

For an extetnal regulator it would depend on where the field current and the regulator power come ftom but a decent design should control the voltage into an open circuit from rest.

N

[nicknorman]

44 minutes ago, BEngo said:

With an internal regulator, it can't. As the main coil voltage rises so the regulator power  supply /field diodes swing into action and the regulator controls the field easily.  The rate of rise of o/p volts is mainly dependent on mechanical factors like the acceleration of the rotor and that is all dead slow to electronics.

For an extetnal regulator it would depend on where the field current and the regulator power come ftom but a decent design should control the voltage into an open circuit from rest.

N

I disagree. You are presuming that all the magnetism comes from the field current. But in reality the iron rotor has some residual magnetism, even when the field current is zero. Regulators don't take the field current into negative territory to eliminate the residual magnetism. So depending on the magnitude of the residual magnetism and the rotor speed, there will be an output voltage into an open circuit of some sort. The only question is how much.

[BEngo]

Yes there will be some voltage ftom residual magnetism, but it cannot exceed the regulated voltage because  it must be there all the time since  it arises solely from the unvarying iron magnetism not the (regulator varied)  field. It would be there regardless of whether the  machine was or was not open circuit.

How would one control an (nominal 12V) alternator with a minimum o/p voltage of, say, even 20 V due to residual magnetism?

 

N