Battery charging problem

[rgriffiths]

I am not sure but I think I have a problem with my battery set up as they regularly need the engine on to bring them back up. I have three brand new 110 batteries and a single alternator. I also have one of these Sterling advanced alternator boxes. There is also a small solar panel. I have had the alternator checked and that is working fine.

 

The odd thing is when I put the meter across the alternator when the engine is running I get 14.2 volts but when I test at the battery it is never more than 13.2. That does not seem right to me but then I am not sure how the Sterling box works. Does anyone have any ideas of what I can check?

Edited June 24, 2016 by rgriffiths

[Alan de Enfield]

Bullet Points :

 

1) When charging 14.2 volts is OK (14.5 / 14.6 better)

2) ONLY test the actual battery after couple of hours of NOTHING IN & NOTHING OUT, Fully charged will show 12.8/12.9 Volts

3) 13.2 volts is just showing the surface charge on the battery plates - not the 'deep' voltage.

4) Do you have a split charge system ? (what type ?, you can loose1 volt between alternator & battery if you have the 'wrong' type)

If the batteries are needing recharging regularly, then you are maybe taking too much out.

 

You need to do a full electrical audit looking a total usage, and total electrical charging (eg running the engine 2 hours per day may - possibly - not enough to replace your usage)

Edited June 24, 2016 by Alan de Enfield

[rusty69]

Check for bad connections

[Chewbacka]

If during engine running the alternator is putting out 14.2V but the battery has only 13.2V then either the charge controller is faulty or you have some diodes after the charge controller. Maybe a split charge diode box between the engine start battery and the leisure battery.

What is your layout?

 

Added

Also try checking across each connection and switch contact with a volt meter to see where the volts are being lost.

Edited June 24, 2016 by Chewbacka

[gazza]

Loses thru old undersized battery cabling the most likely culprit.

 

I've just replaced all our cables and have seen a huge improvement in charging performance.

 

Red key isolators can also be a cause of high resistance connections resulting in a drop in voltage.

[mickp]

Possible split charge diode stealing your volt,but the sterling box thingy should solve that by raising the alt volts?so im no help sorry

[ditchcrawler]

Did you check that battery voltage with the engine running, also check the volts entering and leaving the Stirling thing

[ditchcrawler]

I don't know the Stirling thing but would it drop the voltage if it had decided to go into Float? It calls its self a 4 stage charger

[valrene9600]

Are the correct lights showing on the sterling. Should be a guide on cover as to what each light means.

How small is that solar panel. Has this just become an issue or have you changed anything lately.

[valrene9600]

Two posts running here.

[Tony Brooks]

That Sterling thing is only an external alternator regulator so apart from the possibility of the battery sense wire being on the wrong battery I can not see how measuring the voltages there will help - its not an A to B thing.

 

As long as all the voltage checks were done with the engine revving I agree with those who suggested volt drop on either the pos or neg side of the circuit. We need to be told what type of charge splitter is in use if any.

 

For the OP. the Sterling box overrides the alternator's own regulator when it thinks fit so the alternator delivers a higher voltage. You seem to have lost voltage between the alternator and battery so look start looking for lose/dirty connections, undersized cables and also put both big leads on the battery isolator on just one terminal. If the problem goes away its a faulty switch - remember to put the leads back though.

[wrigglefingers]

Hang on to your hats, there's two threads running on this one so I'm going to try to merge them ... Could be bumpy ...

Two posts running here.

Sort of resolved ... Posts might be a bit disordered, but it is all interesting information, so as you were ...

[Tony Brooks]

If the Sterling goes faulty one of two things happen

 

1. It shorts so it no longer controls the rotor current so the alternator voltage will get ever higher as the charging progresses (not the case here). Sterling.

 

2. It stops working but in that case the alternator's own controller will still work. That 14.2 (but dependant on the charging current) suggests this is a possibility.

 

The difference in voltage between alternator and batteries has nothing to do with the Sterling.

I don't know the Stirling thing but would it drop the voltage if it had decided to go into Float? It calls its self a 4 stage charger

 

No, it can't Brian. If it tried the alternator's own regulator would override it. If it was an A to B it may well.

[ditchcrawler]

 

 

No, it can't Brian. If it tried the alternator's own regulator would override it. If it was an A to B it may well.

Ta, I just saw the pretty graph on the photo with the volts (guessing) going up and down

[rgriffiths]

Thanks all for the advice. I have been away from the boat all day but will have a good look on Sunday.

 

Yes it has a split charge relay and I did notice the other day that it was extremely hot having run the engine for an hour or so. The cables are not that meaty which could well be the issue. The lights on the Sterling box all appear to be lighting correctly according to the info on the box.

 

As far as what I have plugged in I am not using much other than lights and the fridge. That said the fridge is pretty old so could be quite a drain.

 

Will report back after further investigation.

 

Apologies for the double thread. I couldn't seem to delete it once posted.

Edited June 25, 2016 by rgriffiths

[Tony Brooks]

The relay may well need replacing but more to the point the charging circuit is probably wired in a manner that shortens the relay's life. The relay coil will get warm but not hot. The heat suggests resistance somewhere like in the contacts or the big terminals.

 

Make sure the main charging lead goes to the DOMESTIC battery bank. I think that you will find it goes the the engine bank.

[rgriffiths]

I have been having a good look at the electrics. This is the layout of the system:

 

 

Are the corrections the correct way around to the relay?

 

What I have checked:

I have been running the engine has been running for about two hours and all devices in the boat turned off. I measured the voltage across the starter battery when the engine was running I get around 13.5. If I then turn the domestic swtich to off then this jumps up to 14.3 which I assume is what it should be. Turn the switch to on and it drops down again.

 

The voltage across the domestic batteries is never higher than 13.3.Tracing back the voltage goes up:

 

between domestic swtich and earth 13.4

between relay and earth 13.5

between engine switch and earth 13.6

 

Any further thoughts?

[Robbo]

It would be better if you moved the alternator feed from the engine switch to the house switch for better charging of the house batteries and reduced amps going via the relay. BUT Always remember that the house batteries must be turned on with the engine running (a relay to stop you accidentally starting can be added if wished)

 

Also give all connections a good clean. What size are the cables?

Edited June 27, 2016 by Robbo

[rgriffiths]

I have changed the alternator cable around so that is goes to the domestic switch. There has been an improvement to 13.7. Here is a pic of the setup (I suspect everyone will say it is a little archaic!!)

 

 

As things are, still 14.2 if I test at the alternator to earth, but now 13.7 from the other end of the alternator cable to earth. I am going to change this cable now and see if that improves things further. By the way the alternator is a 50 amp alternator.

Edited June 27, 2016 by rgriffiths

[Tony Brooks]

If your alternator is much more than about a 55amp job then my feeling is the cables are a bit undersized but remember I am only going by the photo. You also have DIY type crimped charging terminals on the relay. IF the same are on the alternator and connections to the master switches they may well be causing voltdrop.

 

Stick a voltmeter across the master switch terminal at first start up and rev the engine at about 1500 rpm or more. If the meter reads much more that 0.2 to 0.3 volt I would suggest cleaning the contacts in the switch. Such switches are normally the RR type using but I have found the contact faces can corrode over the winter.

[rgriffiths]

Thanks Tony. Across the master switch terminal? Sorry but I am not sure what that means. Do you mean from the domestic swtich +ve in and +ve out?

[Tony Brooks]

Yes, exactly that.

 

Ignore any readings until you have it at maximum charge.

 

You can do the same thing across the relay contacts although now the alternator feed is going straight to the domestic battery there is not much point for domestic charging.

 

Also at both ends of a run of wire, preferably on the studs/nuts/screws/blades so it is measuring the voltdrop along the wire, in the terminal crimps, and in the actual connection.

[rgriffiths]

I have put the alternator output back to the engine swtich. I have been advised that were the relay to fail then the engine battery would not get charged if connected to the domestic side - makes sense.

 

I have a new alternator output lead which is 16mm² (it said 110 amp) with decent connections at both ends. I still get 14.2 at the alternator and now I am up to 13.8 or so at the switch end and across the batteries. The engine has been running most of the day as I try to get to the bottom of this but I am still a little confused why there could be a 0.4 drop from the alternator to the switch, especially as the Sterling box is meant to increase the voltage. Unhooking the regulator lead to the Sterling box (the white lead in the pic) makes no difference at all.

 

Tony - there is no drop across either of the switches anymore after a good clean. There is a 0.02 drop across the relay.

Thanks again all - any more thoughts?

Edited June 27, 2016 by rgriffiths

[Robbo]

I have put the alternator output back to the engine swtich. I have been advised that were the relay to fail then the engine battery would not get charged if connected to the domestic side - makes sense.

You have been advised incorrectly, more amps will go via the relay if the alternator goes to the starter battery which will help it fail more likely! Starter batteries require little amps to get fullly charged again after starting the engine so it makes better sense to connect the alternator to the house batteries so you have less voltage drop.

 

If the relay fails your volts on your engine panel will highlight the issue.

Edited June 27, 2016 by Robbo

[Tony Brooks]

 

I have put the alternator output back to the engine swtich. I have been advised that were the relay to fail then the engine battery would not get charged if connected to the domestic side - makes sense.

 

I have a new alternator output lead which is 16mm² (it said 110 amp) with decent connections at both ends. I still get 14.2 at the alternator and now I am up to 13.8 or so at the switch end and across the batteries. The engine has been running most of the day as I try to get to the bottom of this but I am still a little confused why there could be a 0.4 drop from the alternator to the switch, especially as the Sterling box is meant to increase the voltage. Unhooking the regulator lead to the Sterling box (the white lead in the pic) makes no difference at all.

 

Tony - there is no drop across either of the switches anymore after a good clean. There is a 0.02 drop across the relay.

Thanks again all - any more thoughts?

 

 

 

Edited to add:-

 

 

So you rewire it in a manner that is likely to cause premature failure - nice one. I, and others, might just as well save our efforts of trying to help.

 

Although the starter draws a high current while starting on a good engine it does it for such a short time it only takes a few amp hours and that is normally replaced within an hour of running. Hence engine batteries normally last years.

 

As, even after starting, the engine battery is all but fully charged the current flowing into the battery will be low so wired the way I instructed the current flowing through the relay will be, low causing minimum stress on the contacts.

 

The way you have now re-wired it ensures that the much more discharged domestic battery draws the maximum alternator output through the relay PLUS an unknown but likely significant amount of charge from the engine battery. This can easily be in excess of the relays rating and even if not leads to overheating the contacts and premature failure.

 

So take your pick as to who's advice you follow, you now know why I gave you the advice I did.

Edited June 27, 2016 by Tony Brooks