Lucas A127

[DaveR]

Hi folks,

 

Noticed earlier this week that the voltage from the domestics was going down to the point where two ruptured glow worms would have been better than what the lights were giving out.

 

Next day I checked the voltage which was at 12.0 and when charging from the alternator they went up to 13.2 volts and then slowly to 13.3 volts after an hour on good charge. Charge rate started at 30 amps (at 13.2v) and then settled to 20 amps (at 13.3v) for the rest of the time we were on the move. We were on the move for over 3 hours that day and the battery voltage again was down to 12.0 by 0700 the next day (12 volt fridge running all night).

 

From what I remember the A127 should be giving out 14.2 volts so have the voltage regulators given up or is there something more seriously wrong with the alternator? This alternator has been fitted for just over 1 year but it was in store on the boat for goodness knows how many years before being fitted.

 

Set up on the Bensham is from the alternator to a split charge relay between start battery and 3 x 110Ah domestics. Domestic batteries are less than 18 months old, starter 2 years.

 

Thanks

 

Dave R

[Arnot]

It is probably worth just checking what the output voltage from the alternator is by running the engine for a while and them using meters, check between the case of the alternator and the main output terminal. It goes without saying that you should make sure the fanbelt is tight too!

 

In general standard A127's are about 14.0V to 14.2V but there are a few either way.

 

Regards

 

Arnot

[Sir Nibble]

Suggest you check voltage at the alternator output as Arnot says, then the start battery. If alternator voltage is significantly higher than the start battery, then you probably have a wiring problem, if start battery voltage is significantly higher than the domestic, then you probably have a relay problem. A low charge voltage is extremely unlikely to be a regulator problem, I suggest checking and comparing the voltages from alternator output terminal to earth, and alternator D+ terminal (warning light connection) and earth. Any appreciable difference indicates a diode failure.

 

Hey! Lookit! online from the pub garden, the hamster has a dongle!

[Smelly]

the hamster has a dongle!

 

don't go waving it round, it'll get stuck in something

[DaveR]

Thank you for the ideas, been to the boat and have confirmed that there is 14.2 volts coming out of the alternator (tested between the post and body).

 

From the alternator the wire goes to the ammeter (moving coil) and then to the positive post of one of the domestic batteries. From that post is a take off for the split charge relay.

 

The readings I took yesterday have both domestic and start batteries at 13.6volts but the charge shown on the ammeter is only 15amps.

 

I am stuck again, 14.2 coming off the alternator but only 13.6 at the batteries after only 2m run of wire (8.5mm2) I can not think, other than the ammeter having gone wrong, of where the voltage drop is happening.

 

Thanks

 

Dave

[Gibbo]

Thank you for the ideas, been to the boat and have confirmed that there is 14.2 volts coming out of the alternator (tested between the post and body).

 

From the alternator the wire goes to the ammeter (moving coil) and then to the positive post of one of the domestic batteries. From that post is a take off for the split charge relay.

 

The readings I took yesterday have both domestic and start batteries at 13.6volts but the charge shown on the ammeter is only 15amps.

 

I am stuck again, 14.2 coming off the alternator but only 13.6 at the batteries after only 2m run of wire (8.5mm2) I can not think, other than the ammeter having gone wrong, of where the voltage drop is happening.

 

Thanks

 

Dave

 

The ammeter will be dropping a bit. It's completely the wrong type of ammeter to be using. You want a "shunt" type.

 

Instead of trying to "think" where the voltage drop is. Just measure it! Get you meter out, and stick it at opposite ends of cables and actually find out where it is.

 

It could just as easily be in the negatives. In fact, in my experience of narrowboats it probably is in a negative. For some reason many people put whacking great big cables on the positives but don't realise that the negatives are just as (if not more) important.

 

Gibbo

[Sir Nibble]

It could just as easily be in the negatives. In fact, in my experience of narrowboats it probably is in a negative. For some reason many people put whacking great big cables on the positives but don't realise that the negatives are just as (if not more) important.

 

Gibbo

Quite aqree. It's surprising how often a big volt drop reveals itself as sparking around the loose mounts!

[Smelly]

Isn't 8.5mm a bit small for charge cable?

[Arnot]

Isn't 8.5mm a bit small for charge cable?

Yes I thought that too. I suspect that what we may be dealing with here is an older boat or one wired up like one where the charging system wiring and ammeter were originaly specified for a generator system. If this is the case then probably a lot of the engine wiring will be on the small side including the earth cables.

 

It would undoubtedly charge better it the alternator output were wired directly to the battery and the ammeter ditched completely. Almost any ammeter will give a voltage drop, that's how the shunt types work. The directly wired ones are usually moving iron, hopelessly inaccurate and with all the extra wiring and termination end up with quite large voltage drops.

 

Regards

 

Arnot

[Arnot]

Thank you for the ideas, been to the boat and have confirmed that there is 14.2 volts coming out of the alternator (tested between the post and body).

 

From the alternator the wire goes to the ammeter (moving coil) and then to the positive post of one of the domestic batteries. From that post is a take off for the split charge relay.

 

The readings I took yesterday have both domestic and start batteries at 13.6volts but the charge shown on the ammeter is only 15amps.

 

I am stuck again, 14.2 coming off the alternator but only 13.6 at the batteries after only 2m run of wire (8.5mm2) I can not think, other than the ammeter having gone wrong, of where the voltage drop is happening.

 

Thanks

 

Dave

So...

 

Your alternator is probably OK that's the good news.

 

If you are dropping 0.6 of a volt at 15A then you definitley have a wiring problem.

 

As Gibbo said, the ammeter is completely the wrong type, it is better wired out. If you connect the alternator output directly to the battery the charging system will be a lot better and the ammeter can still be used to measure the drain. You could get a shunt type but they work in a similar way in that they introduce an known resistance and measure the voltage across it. My suggestion would be that unless you are prepared to convert to a battery sensed regulator system (that will compensate for this resistance and a few others to boot) then you should give up on ammeters.

 

Even then, there may still be a problem and that can only really be discovered by measuring the voltage drop across the various parts of the circuit.

 

Is your boat quite an old one? This sounds like the sort of wiring system that used to be used with generators.

 

Regards

 

Arnot

[DaveR]

The Bensham was built in 92 and the cabling used was of minimium dimensions .

 

I am away from the boat for the next 5 weeks, damned w***, but will look at running an earth lead from the alternator mountings to the battery negative which will, or should, take out the "other" side as Gibbo says.

 

The 8.5mm2 has a capacity of 60 amps but I do have replacement cable and it will not hurt to re-wire the alternator to the battery post to solve that side. Will source and purchase a shunt ammeter to take away the old moving coil job.

 

During the refit work I will check the voltages at each stage and identify if there is any voltage drop left over, again following Gibbo's advice.

 

Thanks for the notes so far folks, helped a lot - very logical and has helped me a lot. Somehow when dealing with a problem sometimes the obvious isn't.

 

Dave R