21 volts out of battery

[revertmastec]

Guys,<br /><br /> Went out in the driveway today to clen boat. Turn the ignition key and my volt gauge pegged out at 16 volts. Checked the battery directly and my volt meter showed 21 volts. Whats up? How can a 12 volt battery put out 21 volts? Is there a short in the battery? Thanks for all replys

 

[petryshyn]

Re: 21 volts out of battery

Was the battery on charge?<br />How many batteries on board?<br />Did you check from post to post?<br />Is the electrolyte low in level?<br /><br />A sulphated battery can read that high after charging, but the voltage will quickly drop when a load is placed on it.....<br />

 

[revertmastec]

Re: 21 volts out of battery

Thanks schematic,<br /><br /> Yes the battery was on charge and after cranking the motor volts dropped back down. Thanks for the help

 

[petryshyn]

Re: 21 volts out of battery

You're not "out of the woods" yet. A battery that will allow this kind of open circuit voltage has issues. This also shows why one should never charge a battery while still connected to the boat, vehicle etc. 21 Volts will damage various electronics on a 12v system. Keep an eye on that battery. I think she'll fail soon, as it sounds sulphated.

 

[mnmfors]

Re: 21 volts out of battery

just curious, sulfated?

 

[petryshyn]

Re: 21 volts out of battery

A condition in where the sulphuric acid from the electrolyte combines with the lead compound plates and forms lead sulphate. This occurs naturally each time you discharge a battery either from a load or extended shelf life. This condition can be reversed if the battery is charged up in short order, but becomes permanent if the battery is left in this condition for a extended period of time. If this occurs, the battery will aquire a high internal resistance (allowing high charge voltages and high surface charge) but will not be able to deliver its rated current. Thus comes the term "Permanently Sulphated" (junk).<br />Marine batteries fall prey to this quite often because the less than adequate charging systems cannot replenish a low battery in a short operating time. This issue is compounded if you have several accessories pulling the battery down as well.<br />Thats why I always maintain to buy a battery with GOOD warranty.........cause you'll likely need it!

 

[mnmfors]

Re: 21 volts out of battery

thank you, good advice on warranty..

 

[revertmastec]

Re: 21 volts out of battery

Think I will get a new one to be on the safe side. Thanks for the help