Alternator voltage levels and windlass batteries

[SimonFa]

I won't be able to look at this for a few days so I'm thinking about where to start when I get chance to do some fault finding.

It looks like my electric windlass and house batteries aren't being charged very quickly, if at all, when I'm running the engine, it seems to be a real problem for the windlass battery which was struggling to haul in the anchor last couple of times I've used it.

Is it possible that the alternator voltage could drop to a level that's low enough not to provide a suitable charging current yet not trigger the alarm? I suppose the alarm could have failed?

I did have the belt off earlier in the season while I changed the coolant and put a new one on while I was at it as the old one as at least 8 years ole that I'm aware off, could that be a problem if not tight enough?

On a related topic, what's the best sort of battery for an electric windlass? A leisure battery was installed when I had the windlass fitted but thinking about the usage I'd have thought a car starter battery would be better as it tends to be short periods of high current drain?

Thanks in advance,

Simon

 

[RichardS]

It's unlikely to be the belt unless it's so loose that it's slipping, in which case you'd probably hear it squealing, although that's easy to check either way.

You need to run the engine at, say 1500 revs, and measure the voltage across the various battery terminals. If the voltage is below 14V and certainly if it's below 13V then there is a problem with the charging circuit, assuming that the batteries are OK. The problem could be the alternator, the diode regulator, the charge splitting device (VSR or whatever), or poor connections somewhere.

Richard

 

[halcyon]

Is it possible that the alternator voltage could drop to a level that's low enough not to provide a suitable charging current yet not trigger the alarm? I suppose the alarm could have failed?

I did have the belt off earlier in the season while I changed the coolant and put a new one on while I was at it as the old one as at least 8 years ole that I'm aware off, could that be a problem if not tight enough?

A new belt always as a habit of stretching, check, the alternator only limits voltage, it does not generate a voltage, the batteries produce the voltage. So as said check voltages, at alternator and batteries, for a volt drop.

Brian

 

[SimonFa]

It's unlikely to be the belt unless it's so loose that it's slipping, in which case you'd probably hear it squealing, although that's easy to check either way.

You need to run the engine at, say 1500 revs, and meazsure the voltage across the various battery terminals. If the voltage is below 14V and certainly if it's below 13V then there is a problem with the charging circuit, assuming that the batteries are OK. The problem could be the alternator, the diode regulator, the charge splitting device (VSR or whatever), or poor connections somewhere.

Richard

Thanks.

I just ran the batteries down to 12.4V. I then ran the engine and measured 13.8V at the alternator connection to the starter motor and one of the other alternator outputs. The 4th output was 6.8V. When I measured at the starter with the engine off it was the battery voltage and the other outputs were 0V.

At the house battery I was reading 12.65V on load and a bit less at the windlass battery off load. The windlass battery didn't have enough power to raise raise the chain from the anchor locker after I'd let it out,

When I connected the battery charger all was well and the windlass had no problem with the chain.

I've checked the wiring diagrams and can't find any diodes.

Any thoughts?

Thanks,

Simon

 

[black mercury]

You will have to trace the cable going from starter battery to the house battery to see if there is a relay fitted. The alternator is working, the 6.8 volts will be the output for a rev counter.

 

[SimonFa]

You will have to trace the cable going from starter battery to the house battery to see if there is a relay fitted. The alternator is working, the 6.8 volts will be the output for a rev counter.

Mine don't work like that, I have to manually switch between the two for output, but their on the same cabling for charging. (Yes, I know I should fit a VSR, just another round tuit)

 

[lw395]

13.8V charging is not very high.
How long had the engine been running?
I think I would watch the 13.8 and see if it was rising.
To fully charge a battery you need to get it over 14.2V for something like 12 hours, or leave it at 13.8V for many hours, a week or more!
Possibly the alternator is current limited and will get to 14+ volts after a period of time.

Can you give everything a full charge on a mains charger? That is the best baseline.
If you can measure the current that would help to see what's going on.

 

[black mercury]

Ok, trying to picture the set up. Can you tell us the way the batteries are wired up? Is it the charging cable you are able to switch between batteries or are you paralleling the batteries when engine is running? What voltage does the house battery read when switched to the charger?

 

[RichardS]

It does sound as if something is wrong with your alternator or there's a poor connection somewhere. Can you remove the alternator and have it checked by an electrical specialist?

Richard

 

[SimonFa]

Thanks for the advice and for the benefit of anyone searching with a similar problem:

A stud had broken off the the earth bus bar in the batter compartment and was hanging loose.

I should have realised something like but as its 30 years since I did any serious electronic/electrics fault finding it never entered my head. More infuriating I'd been poking around in that area and missed it.

 

[RichardS]

A stud had broken off the the earth bus bar in the batter compartment and was hanging loose.

Now that's what I call a poor connection.

Richard

 

[Rocksteadee]

Thanks.

I just ran the batteries down to 12.4V. I then ran the engine and measured 13.8V at the alternator connection to the starter motor and one of the other alternator outputs. The 4th output was 6.8V. When I measured at the starter with the engine off it was the battery voltage and the other outputs were 0V.

At the house battery I was reading 12.65V on load and a bit less at the windlass battery off load. The windlass battery didn't have enough power to raise raise the chain from the anchor locker after I'd let it out,

When I connected the battery charger all was well and the windlass had no problem with the chain.

I've checked the wiring diagrams and can't find any diodes.

Any thoughts?

Thanks,

Simon

At 12.4 v battery is somewhere around 3/4 charge. The alternator would measure this and probably output it’s full rated current, this would drag the output voltage to 13.8 and so is quite normal.
Within 10 min or so of engine running this voltage should rise as the current the battery takes drops as the battery charges
An alternator output of 14.1 or there about would only be once the battery is close to full charge and taking minimal current