One for electrical experts

[boatmike]

First a confession. I let my battery electrolyte get very low and had to add more water than I should to top them up so there may be a damaged cell in the bank.
I have a Stirling smart charger fitted which normally charges at 14.8 when on boost. Having run the engine all the way to Cherbourg (boring) I expect the batteries to be fully charged and they show 13.6 volts after a rest period which appears OK. My question is this:
When I start my engine the charge rate goes up to 16 volts when on boost.
When I noticed this I disconnected the Stirling and it dropped to about 14 volts. I know there are various settings on the Stirling but they have not been changed. Does the panel think I have a duff battery or a duff Stirling? I know the Stirling senses battery condition but will a damaged battery cause it to go over voltage?

 

[ex-Gladys]

Batteries are stuffed by the sound of it. 16V is huge overvoltage

 

[halcyon]

A normal lead acid battery on charge will reach 15.5 volt approx, to take a at full charge, so it is probable that the battery is ok, just a lot of gassing and water loss.
Remove the feed to the Stirling, put some lights / load on the battery, and see if the battery voltage falls slowley. Then start engine and see if the alternator regulates , and you have charge amps that slowly falls.
If you have battery is ok, get the booster checked.
If the battery voltage falls rapidly, or charge amps drop within seconds, get the battery checked.

Brian

 

[cliff]

Depends on where the Sterling senses the "battery" voltage, where you measure the system voltage and how the batteries are connected. If the Sterling senses the battery directly and you have diode splitter or other switching between the alternator and the battery and you measure the system voltage between the alternator and the splitter you can read "high" voltages - the Sterling will adjust the alternator output to achieve the necessary voltage at the point of sensing (battery) but the alternator may have to put out a higher voltage to compensate for any loss of voltage between the alternator output and the battery.

Measure the actual voltage across the battery while charging, not upstream of the splitter / switch.

I have a sterling alternator controller and it has for the past 5 years boosted at around 15.8~16.0v across the batteries. The batteries are 5 years old and still seem to do their job despite being drawn down <10v frequently and occasionally down to ~7v before being recharged..

The only problem I have seen over the past 5 years "abuse" of the batteries has been the water consumption - fast charging does consume a lot of water.

Personally I would not worry about it although I am sure some will come on here preaching doom and gloom.
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[boatmike]

Thank you Cliff (and Halcyon) I knew I was missing something. The good old Forum strikes again!
The 16 volts I was seeing was on the engine management panel so it's what the alternator outputs not what the battery gets (doh). The Stirling is sensing the battery direct and there is indeed a diode splitter in the system so I guess I should have been looking at the battery management panel which sees voltage at shunts on the battery side of the diodes which will be less won't it! (that's by the chart table below and I didn't look)
It's just that the 16 volts frightened me so I disconnected the Stirling......
I am surprised though that to get 14.8 at the battery I have to produce 16 volts. Is the voltage drop across diode splitters usually as high as 1.2 volts?
Of course the other thing is that the voltmeter on the panel is only a cheapie analogue dial gauge so may not be that accurate I guess so say 1 volt (?). appprox 7% loss?

 

[savageseadog]

A standard silicon diode forward voltage drop is 0.6V. The best place to measure charge voltage is right across the battery.

 

[Como]

The drop across the diode will normally be about 0.7 volt for standard silicon diodes (less with Shottkey) but on top of that you will also have a drop through the wires from the altenator to the battery which will obey Ohms law i.e. the greater the current the greater the drop which could well account for another 0.3 volt giving a total of 1 volt. The reading you are getting seems about right.

John

 

[halcyon]

Power diodes normally drop 1 volt plus when on load, schottky can be 0.45 to 1 volt depending on spec. Signal diodes are a nominal 0.7 volt, but again not consistant..

Why are you reading alternator volts ?, you should be reading battery volts.

Brian

 

[billskip]

As said by other posts your batteries are possibly ok (you will soon find out if not /forums/images/graemlins/shocked.gif)

However many people just add water when they top up, maybe it would be a good idea to also check the acid as this also evapourates away with the water.

Just a thought

 

[boatmike]

Thanks for that chaps. No mystery there then. Theres my extra volt, no problem. For those who ask why I am measuring alternator volts, read my previous post again. I am measuring both but the gauge on the engine panel as standard will measure the charge rate from the alternator to the diode splitter unless it is rewired to the other side of the diodes won't it? I have not rewired it as I have seperate battery monitoring volts and amps shown down below on a seperate system as I said before. If I had looked at that in the first place I would not have had a panic attack!
Now I have my brain engaged again I will reconnect the sterling and watch my water consumption a bit more often...

 

[Dalliance]

How does acid evaporate with the water? The "acidity" of the battery is determined by the salts (electrolyte) and these may sediment as lead sulphate but they can't evaporate. BTW - lead sulphate does coat the plates over time and can be encouraged to sediment to the bottom of the battery when you refresh the sulphuric acid by adding EDTA (available from good chemists) which chelates the lead and precipitates it (according to my basic understanding of chemistry). One teaspoonful of EDTA to each cell appears to do the trick and has allowed me to resurrect a failed battery in the past.

 

[billskip]

OK Cell bouy Thanks for the info
as said it was just a thought.

It just so happens though, I had a battery that needed an excessive amount of water once,so i topped it up, and it failed. The battery guy empty it all out and said it needed acid and put in acid and water and battery all happy again.