More Alternator problems

[nicknorman]

Just now, Tony Brooks said:

Are you sure?

I think that when this problem cropped up before I said that you could probably just take the relevant alternator and battery cables off the A to B and join them or even put the pair of leads on one terminals, then do the same for the other alternator/bank. The other tong seemed to agree.

The trouble is that voltage on its own is not a good test of alternator output but the best that can be done "in the field" unless you have a dummy load to connect to the batteries.

When alternators are tested properly they go onto a rig with an adjustable load. This allows the maximum output to be checked and then with the load very much reduced the regulated voltage can be checked. Trying to use just voltage taken on a boat with no indication of current can only rely upon informed inference.

To illustrate. Before your D+ to B+ voltage difference test  the date suggested you might have a phase down. That will slightly reduce the maximum voltage but it may still be within figures quoted for a range of alternators but it will make a far larger reduction in maximum current. So if your domestic bank was well charged when RCR tested it the voltage could well have looked OKish despite a fault.

... And of course it’s worth reinforcing that if the alternators are wired in parallel then inevitably the voltage on their respective output terminals must be the same, even if one is completely dead.

[Tony Brooks]

Nick. I am not sure that is true in the case of the A to B because there may or may not be separate "electronic loads" for each alternator before they outputs are combined.

[nicknorman]

9 minutes ago, Tony Brooks said:

Nick. I am not sure that is true in the case of the A to B because there may or may not be separate "electronic loads" for each alternator before they outputs are combined.

I had a look at the A2B manual, multiple alternators are just connected to one input stud.

[Tony Brooks]

So you are correct, That may well explain the hot small alternator.

[nicknorman]

4 minutes ago, Tony Brooks said:

So you are correct, That may well explain the hot small alternator.

Yes. And when that one finally melts it may be discovered that the big one has been dead for a while. Then there will be a crisis!

[WotEver]

8 minutes ago, nicknorman said:

I had a look at the A2B manual, multiple alternators are just connected to one input stud.

And it appears that bypassing it requires nothing more than lifting the input cable and connecting it to the output. 

[Dr Bob]

12 minutes ago, Tony Brooks said:

Are you sure?

........

To illustrate. Before your D+ to B+ voltage difference test  the date suggested you might have a phase down. That will slightly reduce the maximum voltage but it may still be within figures quoted for a range of alternators but it will make a far larger reduction in maximum current. So if your domestic bank was well charged when RCR tested it the voltage could well have looked OKish despite a fault.

Am I sure? Never! You may be right if all the wires come up to the AtoB. The two battery wires come up to the unit and I think the alternator wires do as well - new ones were fitted - but I need to check if the alternator wires were joined before reaching the unit. That however seems unlikely. The wires come in from the engine bay separately and then are 'hidden' until they emerge behind the unit. I need to get in close to check if I can see two alternator wires. Probably not difficult to be able to link them together. It's still a faff to do!

I will check the Amps first. I was going to check it today but there was a load on 'record' on the TV last night so didnt switch over to inverter....so the batteries are still full and the solar is in overdrive charging up any shortfall. I will try it today but I will do a reasonable discharge overnight and check the currents tomorrow.

You're also right,  the batteries would have been on the charger when RCR tested it as at the time, the shore power came in via the victron combi box so the charger was always on (it has been rewired now to allow the shore power to power the boat without going via the combi).

[WotEver]

Disconnect the shoreline.

Cover the solar panels with a blanket. 

Start the engine. 

Turn something on. Toaster would be good. 

Measure current. 

Should take about 5 minutes. 

[Dr Bob]

4 minutes ago, WotEver said:

And it appears that bypassing it requires nothing more than lifting the input cable and connecting it to the output. 

See above post. I'm sure I will be able to bypass it but it is still a faff as access to the unit is not that simple!

Yes both alternators feed into the same stud (as per manual) which is why I want to talk to Sterling about how the load will be distributed between the two alternators - but I wanted to test it first before I called them so I had some facts. You are of course right that the big alternator could be blown and the little one doing all the work but I doubt it. Charging performance has been very consistent for the 6 months before and after fitting the AtoB. Would you like a little wager?

[WotEver]

No need for a wager. Just follow the steps in post 83 and post back here in 5 minutes

[Dr Bob]

3 minutes ago, WotEver said:

Disconnect the shoreline.

Cover the solar panels with a blanket. 

Start the engine. 

Turn something on. Toaster would be good. 

Measure current. 

Should take about 5 minutes. 

Havent got 4 blankets!

Havent got a toaster.

.......I will do something today...once I finish doing all the stuff Mrs Bob has me lined up to do.

1 minute ago, WotEver said:

No need for a wager. Just follow the steps in post 83 and post back here in 5 minutes

Unfortunately the dog needs out and then some 'shopping'. I'll do it this afternoon and report back.

[rusty69]

3 minutes ago, Dr Bob said:

Havent got 4 blankets!

I can lend you four candles if you like. 

[MtB]

6 minutes ago, Dr Bob said:

See above post. I'm sure I will be able to bypass it but it is still a faff as access to the unit is not that simple!

 

If only you’d bought a boat with a proper engine room

[rusty69]

1 hour ago, Dr Bob said:

What's Rusty doin' round your place?

I'm on my boat, eating toast. 

[nicknorman]

9 minutes ago, Dr Bob said:

See above post. I'm sure I will be able to bypass it but it is still a faff as access to the unit is not that simple!

Yes both alternators feed into the same stud (as per manual) which is why I want to talk to Sterling about how the load will be distributed between the two alternators - but I wanted to test it first before I called them so I had some facts. You are of course right that the big alternator could be blown and the little one doing all the work but I doubt it. Charging performance has been very consistent for the 6 months before and after fitting the AtoB. Would you like a little wager?

There’s no need to or point in talking to Sterling. The alternators will (should - if they are both working properly) share the load roughly in proportion to their respective max outputs. That presumes they have similar regulated output voltages and similar regulation curves, which they probably do. With the regulation curves being pretty soft, there will be a wide range of current demands where both alternators are contributing roughly in accordance with their sizes. If one alternator is doing all the work over a reasonable range of current demands, the other alternator is faulty.

[Dr Bob]

2 hours ago, rusty69 said:

I can lend you four candles if you like. 

We're Ok, all our forks have handles.

[Dr Bob]

Right, all set to start looking at this alternator. First I need to work out how the clamp meter works. Next -cover the solar panels. I have thrown some bread on them to see if I can get a flock of ducks to land on them. It's not working. I've sent Donald up to be a decoy while I finish my cup of coffee. I'll report back as soon as some ducks arrive and I get a reading.

[rusty69]

29 minutes ago, Dr Bob said:

I've sent Donald up to be a decoy while I finish my cup of coffee.

Your still here aren't you?Thats a big cup of coffee, Get on with it..............................

[Dr Bob]

Right major update.

Four ducks landed on the second to front panel and started eating the bread. The dog (the one we are babysitting for a few weeks) took exception to said birds and because our duck keeps chasing him, decided to chase the ducks off the boat. He's on one of those extending leads, and as he jumped onto the roof he took the TV mast down when Mrs Bob was watching something really important. All hell let loose. The ducks taking off, the dog overshooting and ending up in the water on the other side of the boat and Mrs Bob shouting about loosing the TV signal and loosing a few stiches on the thingy she was knitting. Took at least half an hour to recover the TV aerial and get the telly working again. The dog is soaked through and sat in front of the stove and eco fan and stinking the boat out. Mrs Bob has not calmed down yet.

.....the alternators. Damn! Damn! Damn! Wotever was right (as usual)....see you should have taken that bet! 33A going up from the 55A alternator and 1A from the 90A. Looks like the 90A one is shot hence the little one overheating. Phone call to RCR. They can come and replace it.

Looks like buying that infrequent red thermometer was a good buy. I wouldnt have noticed until the small 55A burnt out if I hadnt measured the engine temperatures. The clamp meter is pretty cool too.

Thanks for the help from all of you. I couldnt have got this far without you

[Tony Brooks]

Be aware they may not and if they do they may well charge you a call out plus cost of the alternator. I fear they will say its the domestic one, does not stop the boat moving, so is not covered. Hope they don't.

I am still rather mystified why the D= to B+ voltage did not show a problem. I wonder if you have an appallingly poor crimp on the wirirng for the large alternator. I would say at least feel all the crimps on the large leads just in case one is warm.

Edited March 29, 2018 by Tony Brooks

[nicknorman]

10 minutes ago, Tony Brooks said:

Be aware they may not and if they do they may well charge you a call out plus cost of the alternator. I fear they will say its the domestic one, does not stop the boat moving, so is not covered. Hope they don't.

I am still rather mystified why the D= to B+ voltage did not show a problem. I wonder if you have an appallingly poor crimp on the wirirng for the large alternator. I would say at least feel all the crimps on the large leads just in case one is warm.

I dont know the exact design of that particular alternator, but with a normal 9 diode version, is it not possible to have the field diodes still intact but the main output diodes blown?

[WotEver]

Now wire the engine alternator direct to the engine battery and leave the domestic wired via the A2B, feeding just the domestic batteries. Repeat the test. 

It’s exceedingly unlikely but nevertheless possible that the domestic alternator had simply shut down. The above test will prove or disprove that. 

[Sea Dog]

2 minutes ago, WotEver said:

Now wire the engine alternator direct to the engine battery and leave the domestic wired via the A2B, feeding just the domestic batteries. Repeat the test. 

Yes. And then wire the domestic alternator directly to the domestic batteries and see what it does without the gizmo in the circuit. Then you'll have a full picture.

[WotEver]

1 minute ago, Sea Dog said:

Yes. And then wire the domestic alternator directly to the domestic batteries and see what it does without the gizmo in the circuit. Then you'll have a full picture.

Best place for said gizmo is bottom of the cut anyway. 

[Tony Brooks]

15 minutes ago, nicknorman said:

I dont know the exact design of that particular alternator, but with a normal 9 diode version, is it not possible to have the field diodes still intact but the main output diodes blown?

Yes but that would give a lower voltage on the B+as long as one phase is working.

However if the thing has an open circuit rotor/brushes I suspect you will get battery voltage on both B+ and D+ terminals and as the A to D is still charging the batteries it will look like the thing is charging with no voltage difference.

Maybe RCR were measuring the small alternator output voltage on the large alternator's B+ but had not twigged that is what an A to B would cause.

These gizmos seem to offer very little that a decent regulated voltage, decent alternator wiring that a VSR will not, they just serve to make fault finding more difficult and hide faults.

Edited March 29, 2018 by Tony Brooks