Overcharging Batteries

[Thepipdoc]

My boat has twin engines with 3 batteries. Off load a handheld meter shows all 3 batteries to be holding around 13.5 volts. When both engines are started both volt meters on the dash show 16volts - in fact they hit the stop inside the meter so perhaps they could read even higher. When the ignition is turned off both meters read 12.5 volts.
All electricals i.e. lights, water system, fridge etc seem to be working fine. Is this something to be concerned about? What's the potential damage?

 

[Wiggo]

16v is too high. I'd be worried of I saw 15V - although the max does depend on the type of batteries I think 14.5 is about the safe limit. Having said that, the panel meters can be very inaccurate.

Fully charged, they should show 12.8V (or thereabouts) once the charging source has been removed and they've rested with no load for a half hour or so.

 

[halcyon]

What boat is it ? you could have one alternator regulater failed, and running over voltage, so both engines are showing over voltage when on charge.

If charging at that voltage, 13.5 volt is not impossible.

Brian

 

[Bilgediver]

This could be many things and it would help if you made it easier by just giving the hand held meter readings for everything and not referring to two disjointed meters. The dash meter may well be a volt or two out so before diving in and getting over excited lets see what the true situation really is...Can you beg borrow or steal a digital meter?

Using a reliable meter check the battery voltages when you return to the boat and all is off load and the engines stopped.
I would hope for at least 12.8

Check the voltages by prodding the actual battery lead posts and nothing else.

start the engines and then check the voltages again in the same place.

This should be above 14.4 volts but not more than 15.5 volts

Take swimbo for a trip across the bay to do some sunbathing and with the engines still at fast idle check the voltages again.

This could still be 15.5 but may have reduced to 14.4 or 13.8 depending on the battery state.

Stop the engines and enjoy the surroundings and whatever else SWIMBO allows and and check the readings after an hour or so of normal use ie ice maker, AC, washing showering etc.

This could be anything from 12.6 down but if too far down you will be rowing home unless you have a separate engine battery. Keep an eye on it as you visit the ice box as it will give an idea as to how fast the battery is discharging and when it gets to below 12 volts switch everything off and it should recover a bit however this is you with not much left for the hair drier. If the battery is around 12.2 at rest IE nothing switched on then thats it needing a re charge.

It is possible your boat is fitted with a 3 stage Gizmo for boosting the charge and these can go to 15.5 volts if the batteries are down but then reduce the charge in stages as the battery charges up. If you also have a diode charging unit then the charge voltage at the alternator will go to 16 plus volts to get over the diode voltage drop. This is why you should be measuring at the battery posts.

It is possible that in fact you have nothing wrong as the voltage you see would be quite normal if measured at the alternator on a boat fitted with a 3 stage charger and having low batteries.

Maybe Vic will be along soon and you ll understand his english accent more easily Boyo /forums/images/graemlins/smile.gif But thats my twopenneth

 

[SwedishLass]

I would be inclined to get the regulator(s) checked as a matter of urgency. Most are designed to chuck out about 14.2 volts on charging. A smart regulator can up this but most of them trip out at 15v.

In terms of problems boiling batteries, exploding batteries are both strong possibilities apart from some of the more sensitive elctronic kit having a hissy fit.

 

[Thepipdoc]

Thanks for the very comprehensive answers so far. I never cease to be amazed at the response level on this forum - excellent stuff.

I can confirm that I've checked the batteries with a digital meter and off load they are producing 13.5 volts. What I haven't checked is what they are producing whilst under load i.e. with the water system pumping and perhaps the fridge running. i'll check that as soon as I can get back on to the mooring. By the way, my boat is a Sea Ray 270 1998.