Charging at 15.2V

[JackFrobisher]

Help! Have I got a problem?

Got on board yesterday to do a few bits ready for the Easter weekend and found the batteries at 12.9V. After a week since the last use/charge, good, I thought.

Started the engine as I usually do, so I can run the heating to keep the boat as dry as poss inside. At 2,000 rpm or so it was charging at 14.7. Again, that's OK, I thought.

Did what I had to do, shut down the heating and knocked the revs down to idle for a few minutes to equalise the engine temperature (whatever that means), like it says to in the Volvo handbook (it's a 2003). Looked at the volt meter and it was reading 15.2V. Panic! Raised the revs to 1,500 rpm and it dropped back to 14.7V. Raised to 2,500 rpm and it was still steady at 14.7V. Back to idle (800 rpm) and it went back to 15.2V.

Have I got a problem and how should I proceed?

 

[Powersalt]

Im no expert on this but I had a similar problem last year and when the electrician came all he did was to fill the batteries with distilled water. They took 4 ltres, aparantley this can occur when the batteries are dry.
Dont know if its relevent but for what its worth....

 

[jackho]

Not an expert but suggest you don't have a problem - I believe at low revs. your not charging and you are reading the "open circuit" voltage off load.

 

[andy01842]

12.9 volts is a bit high for a rested battery, you need to turn a few light on to pull a few amps from the battery for 10 minuets then rest the battery for 10 minuets. This will give a more accurate reading. 14.7 volts could also be a bit high depending on the type of regulator you have. 15.2 volts is OTT. I have seen volt meters that are 1.5 volts inaccurate i.e. as much good as an ashtray on a motor bike! Many meters do not like RF so if some one was using a radio or radar close to you expect 50 volts plus! A hydrometer will always give a better indication of the state of a battery as you can check each cell. A dead cell can give a high voltage with no load. My old battery had 16.5 volts no load put a small load across it for a few minuets and it when down to 10.5 volt.

 

[pheran]

I don't think you've necessarily got a problem either. Immediately after charging (as you were doing via the altenator) the battery will register a 'surface voltage' which is invariably higher than normal. You need to allow the battery to settle for at least an hour before taking voltage readings.

 

[pheran]

[ QUOTE ]
12.9 volts is a bit high for a rested battery

[/ QUOTE ] Really? I have always been told the a fully charged battery at rest should read 12.8v and given the other imponderables, an extra 0.1v is neither here nor there.

 

[VicS]

[ QUOTE ]
Im no expert

[/ QUOTE ] [ QUOTE ]
Not an expert

[/ QUOTE ] Without meaning to be too disrespectful to two posters offering advice in good faith I think the above might be the most relevant parts of first two replies.

Check the electrolyte levels by all means but if that cures the problem I hope someone can explain it.

15.2volts is way too high and even 14.7 is as well. 14.4 is the absolute maximum if you are not going to boil the batteries. Even 12.9volt on a rested battery should have set the alarm bells ringing.

The most likely cause is a faulty regulator but poor connections to the regulator could be the cause. I cannot expain, however, why it sould fall when the revs are increased and rise again when they are reduced, worn/ dirty brushes/slip rings maybe.

I think they way forward may be to get the alternator checked. You don't have any fancy regulator installed do you that may be playing up?

 

[sailorman]

dont know whwt the prob is but alternators normally charge @ 14.2v

 

[duncan]

anything over 12.8v and somehing is wrong somewhere is the message - you seem to be both confirming this and questioning it at the same time!

/forums/images/graemlins/wink.gif

 

[Talbot]

agree 14.4 volts is the max for lead acid. If you have a fancy stepped charge regulator in the system, and have hi-tech batteries, this can be raised, but even then I seem to remember that 15.2v was the absolute max for those , and that this voltage would be death for a standard lead acid.

However, I would also check the voltmeter first!

 

[Tisme]

Before you do anything else it may be an idea to check the readings with a multimeter. If your panel meter is faulty.........

Edited: Damn it. Talbot beat me to it! /forums/images/graemlins/smile.gif

 

[pheran]

You should read my post again!

 

[duncan]

suppose it depends on your definition of imponderables then but at the end of the day a battery reading 12.9 after a week of rest would have me looking for an issue somewhere rather than pondering.......digital voltmeter that normally reads correctly doesn't just decide to add 0.1v for the hell of it.

 

[andy_wilson]

\"equalise the engine temperature\"

After a period of very hard running at full or high throttle, I can see the point, this is normally accomplished by the time you have manouvered around the marina or moorings, and the mooring warps are secured.

After a period of charging the batteries at 2000 rpm, the engine will be cool enough to switch straight off.

 

[JackFrobisher]

Thanks everyone.

I'll check the voltage with a DVM, the water levels and get a hydrometer.

I was thinking of getting an intelligent charging controller... At the moment have a Vetus split-charging diode and the alternator that came with the engine.

 

[rhumlady]

If you have split charge diodes and ONLY the onboard altenator regulator then yes I think you have a problem as these regulators are mostly machine sensed, that is they see the voltage produced at their output and regulat to this. This does not allow for the 0.7 volt drop across the diodes which should restrict the battery voltage by that amount. An Ardvec or Stirling regulator will sense the voltage at the battery an thus give a higher output from the altenator to overcome the problems of the diodes and allow the batteries to fully charge. There is more to it than that but I do think you need to check things out.

 

[rhumlady]

By the way the Stirling and probobly the Ardvec(but I'm not sure) will bulk charge till the battery is at 14.7V at which point it drops to about 14.2 and continues to float charge the batteries.

 

[VicS]

[ QUOTE ]
This does not allow for the 0.7 volt drop across the diodes

[/ QUOTE ]
The curently available Vetus split diode assembly only drops the volts by 0.2v according to the website so a normal machine sensed alternator should beOK with it.

However it would be a good idea, now that we know a split charge diode system is fitted, to check out the sensing.

If it is an older type of diode assembly that does drop 0.7v then a battery sensed alternator may be fitted with the sensing from one of the batteries. A poor connection in the sensing could give rise to the problems encountered.

Some diode assemblies have an additional diode to which the the sensing connection is made (but I don't know if that applies to any past Vetus ones). Again a poor connection here could cause the problems.

Another possibility is that an additional external diode has been fitted in the sensing circuit. Again another possible source of the trouble.

 

[LeonF]

I am no authority on most things mechanical or electrical but...On my last boat I bought some AGM batteries to accompany my new Adverc. When fully charged off the mains, the voltmeter would read up 16V at times at low revs. See my previous posts for the entire saga. Never got to the bottom of it, either with Adverc or the battery supplier, so I returned the batteries and with a little gentle persuasion got a full refund. The interesting discovery I made with a more technical friend was to test a cars voltage at low revs...it was very unstable, tested with a voltmeter via the cig lighter socket.