Low battery charge from alternator?

[ITH]

Having only limited knowledge of electrickery, would be grateful for advice:

On a recent passage (280Nm) from Sicily to Greece, we had the engine on for 28hours, including two nights. On arrival we connected up to shore power and I was surprised to see that the domestic batteries (2 x 180Ah, sealed lead acid, 1year-old) were discharged down to 60% - according to my Clipper - and took nearly 15 hours of 'smart' shore charging (Victron 12V40A charger) to restore them.

The engine alternator is rated 90A and has a 'smart' regulator fitted. On night passage we ran the auto-pilot, nav and instrument lights, fridge, water pump: so I guess some 12A to 15A draw? Engine instruments indicated 12/14V and 4/6A charging during the night.

Am I missing something obvious (wouldn't be the first time!), are there simple checks I can carry out - or do I need to clutch my wallet and send for an electrician. (Boat is currently in Greece, I'm back in Blighty)

Any suggestions gratefully received.

 

[kyleview]

I suggest your Smart regulator is not working, maybe even interfering with "normal" alternator charging. With the amount of engine running I would still expect the batteries to be up around 75/80% using the alternator in a non regulated way - but that does depend on what % you started out with.

 

[VicS]

I think the first step is to check the output from your alternator.

Volts are easy to measure so check the volts output after discharging the battery somewhat and/or putting a good load on the system. Does it get up to the 14.4 or whatever you expect for the smart regulator.

If you have a clip on ammeter check that the alternator is delivering the current you expect.

Any suspected problems with the alternator then get it checked, and repaired if necessary, by an automobile electrician.

Quite possible that the shorepower charger is set to deliver a higher voltage that the alternator regulator .. Check the specs

 

[pvb]

I suggest your Smart regulator is not working, maybe even interfering with "normal" alternator charging.

Most add-on "smart" regulators work in parallel with the alternator's own regulator and, should the smart regulator fail, the alternator simply continues to operate as if it didn't have a smart regulator. Consequently, as VicS has suggested, the first step should be to check that the alternator is functioning properly.

 

[ITH]

Thanks for that Kyleview: I think the batteries were 100% prior to leaving Sicily - since they had been on shorepower for several days. From the suggestions by VicS and pvb, I guess that it's call for an electrical engineer. I have checked alternator output with a multimeter and it shows circa 14V, but haven't got any way of checking Amp output. I did see at the time the engine was running that the instruments showed 12/14v output and 4A output?

Grateful for your input.

 

[halcyon]

On a recent passage (280Nm) from Sicily to Greece, we had the engine on for 28hours, including two nights. On arrival we connected up to shore power and I was surprised to see that the domestic batteries (2 x 180Ah, sealed lead acid, 1year-old) were discharged down to 60% - according to my Clipper - and took nearly 15 hours of 'smart' shore charging (Victron 12V40A charger) to restore them.

Assuming you are under sail, and without full knowledge of when engine was running, 60% capacity on arrival is not bad.

!5 hours to put around 130 amp hr into the batteries from mains looks bad, would have thought 7 hours max.

Problem with the alternator output is the type of load applied, i.e. lights, fridge, etc. can result in lower charge voltage, thus lower charge current.

Before returning buy a cheap (£25-30 ) DC clamp multimeter, allows you clamp it around the main DC power cables and measure the amps, though if you have a battery monitor this should give the same result.

But run the batteries down a bit, then start engine, no loads on ( fridge etc ) and check alternator output. If volts or amps are very low, then splash out on a leccy.

Do the same for the mains charger, that looks odder for output than the alternator.

But I would monitor the levels for a bit, see how they go as they don't look that bad.

Brian

Brian

 

[pvb]

I did see at the time the engine was running that the instruments showed 12/14v output and 4A output?

There's a big difference between 12v and 14v when the engine's running! It should be close to 14v (or higher with a smart regulator).

 

[halcyon]

There's a big difference between 12v and 14v when the engine's running! It should be close to 14v (or higher with a smart regulator).

Never believe voltages given to me from engine voltmeters, at 12 volt he would have had flat batteries on arrival. He did a long passage, arrived with 60% battery capacity, that is not bad.

Which is why, before spending money on a leccy, I said monitor, and check the system, rather than saaume a problem.

Brian

 

[mawm]

Simple things first - check the tension on the alternator belt.

 

[mikegunn]

I'm with Halcyon on this one. I don't think that you necessarily have a problem. Whilst under engine its alternator would have kept the batteries topped up, but I notice that you were only running the engine for 24 hours, out of what I assume would have been a 40-48 hour passage. When you were not running the engine (presumably during daylight hours) you would have been consuming the contents of the battery bank at a rate of, say 10 amps/hr. So approximately 14 hrs sailing without engine during the latter part of the passage would have left you with about 60% capacity.
Regarding the length of time to recharge the battery from shorepower, again, you may not have a problem. The battery charger will "bulk" fill the battery at whatever the maximum charge rate of your charger may be. 30 A/hr is typical, but it won't continue at that rate. Once it gets to its "absorption" level the rate drops significantly until a "float" level is reached. If your were to monitor charging amps against a timebase the characterisitics of the charger would become apparant. Provided of course that you are not discharging the battery at that time.
Again, like Halcyon, I would suggest that you don't panic, but just carry out a few fairly simple checks to first determine whether or not you really have a problem.
Hope this is some help.

Mike

 

[ITH]

Low battery charge from alternator

Thanks Halcyon and Mike Gunn; I'll invest in a DC clamp multimeter before going back to the boat, and doing some checking of the system. (MAWM - I did have a look at the belt tension, which is fine).

I'll be more careful about recording times/outputs etc more accurately in future. On night passages in particular I have only ever given a cursory glance at engine instrument readings. Must also get the 12V Bible off the shelf and resolve to learn more about electrics to decide what is or isn't a 'problem'.

Your inputs much appreciated.