Another battery charging quandry

[weeble]

I have a dual alternator system with an external Stirling controller on the domestic bank. 3x 135Ah sealed batteries. Normally, everything works fine with domestics floating around 14.6 - 14.8V. However, for the first time in my life I am now in a marina with mains on tap so I installed a Victron 3-stage charger, which also performs well. 

The problem occurs when I visit the boat after a few weeks (battery fully charged and taking virtually 0 current from the Victron) and  I want to run the engine for an hour to get some hot water. So I turn off the mains charger, wait for the charger leds to extinquish, then fire up the engine. All is well for a minute or so, then the battery charge voltage creeps up to 15.3 volts and higher,  which is too high for comfort! (Starter battery ok at 14.4V).

BTW. If I turn on the fridge and wait for a couple hours before starting the engine everything seems to work normally.

Any ideas as to what's going on?

[WotEver]

I’d guess that it’s possible that the Sterling has decided that an equalisation charge is due. Alternatively the temp sensor could have a fault - what happens if you disconnect it?

[weeble]

I'm not sure that I have a temperature sensor fitted. It's been a long time since I fitted te Sterling but isn't the sensor an 'optional' item that's connected to it's own terminals? If so,then I don't have one.

Not on board atm so can't check

Edited January 6, 2018 by weeble
Clarity

[Tony Brooks]

Does it do this at every visit?  If not and only when cold like today then the Sterling may be temperature compensating and raising the voltage. We had a question about solar doing this a few days ago.  I have no idea if the Sterling has built in temperature compensation like modern solar controllers.

[Sea Dog]

You say the starter alternator is performing as expected, so the first action I'd take us to disconnect the Sterling and have just the domestic alternator feeding the domestic bank.  This would show whether the high voltage was due to the alternator itself or is being raised by the Sterling. 

What are the output ratings of the alternators in amps?  I ask in order to ascertain whether the Sterling unit is actually required. Beta twin alternator engines, for example, often have a 150a or 175a domestic alternator which I would offer is man enough on its own. 

[WotEver]

2 hours ago, Sea Dog said:

I ask in order to ascertain whether the Sterling unit is actually required.

They rarely are on modern engines. Doesn’t seem to stop folk fitting them though. 

[sharpness]

4 hours ago, Tony Brooks said:

 I have no idea if the Sterling has built in temperature compensation like modern solar controllers.

The Sterling I fitted on our 15yrs ago had a temperature sensor fitted to the body of the alternator & one to the domestic batteries but they were external rather than built in.

[Dr Bob]

1 hour ago, WotEver said:

They rarely are on modern engines. Doesn’t seem to stop folk fitting them though. 

Agreed but how old is the OP's boat. Ours is 2002 and needs a Stirling AtoB to get the charge voltage up over 14 volts. Same on our old 2005 boat. Anything over 10-12 years old could require some sort of voltage increase.

I am not sure what the OP refers to in saying "Normally, everything works fine with domestics floating around 14.6 - 14.8V." Is that the absorption voltage from the Sterling unit (and is the sterling controller an AtoB)? We need a bit more info. The 14.6-14.8V sounds high for sealed batteries unless it is temp compensated in which case it maybe spot on. Our sterling AtoB's (one from 2005 and one this year) both had temperature sensors supplied as standard not as an extra although the one we have fitted now does not have the sensor attached - thats a job for later this month.

If it is a Sterling Ato B then there wont be an equalisation charge (at least I cant see that option on ours).

If the sterling is set for open lead acids at 14.8V absorption with a temp compensation operating when very cold, I guess you could see 15.3V for a brief time when starting the engine. It takes a few minutes until the AtoB cuts in. How long does the voltage stay at 15.3V and what are the amps going in? If it is set for lead acids then I would change the settings for sealed. That should drop the voltage by 0.4V IIRC.

[Naughty Cal]

More to the point if the OP has shore power why are they running their engine to get hot water?

Get an immersion heater fitted!

[Dr Bob]

I've just been thinking a bit more about the 15.3V. I had forgotten about our voltage when we went out for a pump out on Friday. We have a new Sterling AtoB so the same might apply to the OP if theirs is an AtoB. When cruising, the AtoB gives us a starting voltage of circa 14.0V which then rises to a max of 14.4V as the batteries charge. As we approach a stable tail current it then goes into float (but I reckon it is not up to 100%) but the voltage is 14.4V. On Friday the boat had been on shore power for a couple of weeks so the batteries should have been fully charged. Disconnected shore power and started the engine. After the 2-3 mins initial lag, the AtoB started its charge and the voltage was 14.7V with a current of around 1A. I didnt check it again after that. I remember asking SWMBO for the reading as we set off and thinking 'thats a bit higher than normal'. I never usually check the battery meter when leaving the marina.

Now, we dont have the temp sensor connected - to be done soon - so interesting that the unit was giving 0.3v more than normally seen under normal running. If the OP has a similar unit, or if it is just a controller acting the same way as an AtoB, then maybe it is set for open lead acids at 14.8V, is temperature compensated - so in the last few weeks could easily be charging 0.3V higher - and with this 0.3V increase I saw, would take it to 15.3V. Even without the temp compensation it could be this high.

Next time we go out I will see how long the high voltage reading stays for and how long it stays in absorption. Cant think it will be very long as this AtoB goes to float far too quickly. For the OP then, without any more info (ie exactly what controller do you have, how long did the voltage stay at 15.3V, what was the current, is the controller set for 14.8v or 14.4v etc?) I would say change the settings for sealed batteries and you should be ok. Yes you may get 15v with temperature compensation but the current should be very low (if it is like ours) and it should switch into float quickly. 15v when the battery temp is 5°C is ok.

[Richard10002]

With my Sterling inverter charger, the initial voltage is generally a bit higher than absorption charge voltage I have set.

e.g. If I set it for an absorption charge of say, 14.8V, it starts charging at about 15.3V for a while, before dropping back to 14.8V.

Id guess the algorithms are similar to the alternator/Battery gizmo?

[weeble]

Thanks to all for the replies. Sorry I couldn't reply earlier but I'll answer your questions as best I can.

I don't think it's relevant to the 'problem' but the boat is 17 years old, three cyclinder Beta, and domestic generator was changed a couple years ago to [I think] 90A or 120A.

The external controller is a Pro Reg D (the one with a fan on the top) and looking at the picture on the Sterling website I can confirm there are no temperature sensors connected.

The battery charger is a Victron Blue Power IP22 12V/30A Three outputs.

New batteries and battery charger were installed last May.

Low load demand. Shorepower 12V fridge, Avtex low power tv, LED lights + usual pumps.

I take on board that I might need to drop the voltage from 14.8V to 14.4V. I'll take a look at the battery manufacturer's spec when I next visit the boat.

As the batteries are as fully charged as they're likely to get, the current drawn at the 15.3V is negligible.

-----------------------------------------

I don't think the situation is temperature related because I first noticed it last June on the first trip out after the batteries/charger were installed. It was certainly not a cold day and I arrived at the marina, loaded up, disconnected the mains, then immediately set sail. I noticed the high voltage about 10 minutes later while waiting at our first lock. The trip was 18 days (Calcutt to Oxford return) and the high voltage didn't appear again throughout the trip.

Second trip was the same, (21 days September, Calcutt-Stratford return), high voltage on the first day after disconnecting the mains then everything OK thereafter.

Third trip was the same (late October 7 days locally).

I don't know how long the high voltage existed but on the second trip we'd been cruising for nearly half an hour before I picked it up, so it appears not to be a short-lived event. But once the controller drops back into float mode the voltage seems to correct itself.

We don't normally spend nights in the marina but last week we decided to go up for 3 nights, relaxing to get over the effects of having the house full of grand-kids over Xmas. That's where I noticed the high voltage situation again, a couple minutes after turning on the engine for the first time to get some hot water (note that the controller has a 2 minute soft start feature).
So, this is when I turned off the engine and ran on batteries for a couple hours to take the edge off the battery voltage before starting up again, whereupon everything went back to normal. I spent the three days running from battery with the charger turned off and, once again, the situation didn't reappear. 

So I don't think there's much doubt that temperature is not a factor, but the mains charger is! Perhaps there is reservoir capacitor or something similar on the charger's output that remains charged for a period after the charger is turned off which somehow affects the controller.

On reflection, what I should have done was to have turned the charger back on for a short period, say 5, 10, 20, 30 minutes.... between engine starts, to see when the problem returned, but I was too 'relaxed' to bother about it by then :)!

-------------------------------------------

Dr Bob: I'd be interested to hear if you experience the same results on your next trip to the pump-out. I wonder if anyone else has noticed similar symtoms.

Cheers....

[Tony Brooks]

Right.

 There is a thin wire running from the controller to what is normally a thin wire coming from the back of the alternator, not from a terminal. This is the wire the controller uses to mess with the alternator's own regulator. I am not sure of the colour that Sterling uses for this. Disconnect this wire and insulate the ends. This returns control to the alternator's own regulator.

If the high voltage goes away the the Sterling device may be faulty but before condemning it make sure ALL the battery connections and alternator main lead connections are clean and tight. this includes cleaning the battery terminal posts and clamps.  If the problem restarts once everything, including the Sterling) is reconnected the Sterling devise is suspect.

If the voltage stays high then suspect an alternator fault, potentially a blown diode, possible a field/auxiliary diode. Put a voltmeter between the alternator main output terminal (B+) and the alternator warning lamp terminal (D+) and rev the engine. The voltmeter should read less than 1 volt. If more you have a blown diode.

[ditchcrawler]

2 hours ago, Tony Brooks said:

Right.

 There is a thin wire running from the controller to what is normally a thin wire coming from the back of the alternator, not from a terminal. This is the wire the controller uses to mess with the alternator's own regulator. I am not sure of the colour that Sterling uses for this. Disconnect this wire and insulate the ends. This returns control to the alternator's own regulator.

If the high voltage goes away the the Sterling device may be faulty but before condemning it make sure ALL the battery connections and alternator main lead connections are clean and tight. this includes cleaning the battery terminal posts and clamps.  If the problem restarts once everything, including the Sterling) is reconnected the Sterling devise is suspect.

If the voltage stays high then suspect an alternator fault, potentially a blown diode, possible a field/auxiliary diode. Put a voltmeter between the alternator main output terminal (B+) and the alternator warning lamp terminal (D+) and rev the engine. The voltmeter should read less than 1 volt. If more you have a blown diode.

I was just wondering exactly where the voltage was being read, if its from somewhere other than the battery terminals then when on charge the voltage at the terminals could easily be lower than what the volt meter is indicating due to volt drop. I would measure the voltage on the battery terminals while charging first. NOTE terminals not cable clamps, or lugs.

[weeble]

1 hour ago, ditchcrawler said:

I was just wondering exactly where the voltage was being read, if its from somewhere other than the battery terminals then when on charge the voltage at the terminals could easily be lower than what the volt meter is indicating due to volt drop. I would measure the voltage on the battery terminals while charging first. NOTE terminals not cable clamps, or lugs.

Voltage sensing is definitely direct from the battery.