Voltage reading

[Mickey_Fx]

A few days ago I looked at the voltage at the battery while the engine was running and measured 14.8V. This is .5V higher than I like to see on a 12V nom system.

Can anyone else report what voltage they are seeing?

 

[mark777]

Mickey,

Everything I have with an alternator reads between 14.2 - 14.6. Is 14.8 too much?

 

[BobRip]

Some systems (automotive anyway) when cold have a higher voltage than when warm. 14.8 seems high. 14 is about right on a system that is warmedup. Check the manufacturers spec. is the best advice that I can give you.

Bob Rip

 

[Mickey_Fx]

</font><font color="blue" class="small">( Mickey,

Everything I have with an alternator reads between 14.2 - 14.6. Is 14.8 too much? )</font>
Mark, let me say this to begin with, when I was a working man, an ME for HP, one of my assignments was to learn a lot about the care and feeding of lead acid batteries, so I have some knowledge.

Now to your question. For cyclic use like one finds in an automotive like application, a 12 volt charging system should be no more 14.25V. The longer a battery is being "charged" the lower the voltage needed to prevent overcharging. For float charge situations 13.25 is about right. When charging for shorter periods of time the voltage can be increased. A 12V LA battery can rise to about 13.8 volts and hold there without problems but higher voltages that permit quicker charging needs to be limited in time to prevent overcharging and "boiling". The engineering aplication books I've read say to charge between 2.1 and 2.4 volts per cell with decreasing charge times as the charge voltage rises.

In single stage/voltage charge systems, one has to compromise between fast charging and minimizing over charging. For systems like this I would like to see the voltage setting between 14 and 14.25 volts.

For me the 14.8 volts I measured is too high if operating the equipment for several hrs or more at a time. At these higher levels one needs to keep a close eye on battery water level. IMO you will compromise battery life if they are charged at the higher voltages and done so for extended periods of time.

Oh, by the way, a fully charged 12v battery that has been at rest for 4-6 hrs should read very close to 12.7 volts.

 

[California]

What does the manual say it should be?

 

[paulBurns]

Could this be a function of the voltage regulator to determine the voltahe output of the alternator/generator. Also can the spific gravity of the individual cell be read during charge and with charge off as a trouble shooting aid??

 

[kayssupply]

If Yanmar has a weakness it is their "current limiter". They are solid state and external. They stop charging on 3 out of 10 tractors I have had. I would assume they could overcharge also. The good news is, they are easy to get and easy to replace. Two screws and a plug, your back in business.

 

[reb]

There are some other variables to consider in this application. What is the accuracy of the meter being used? 5% accuracy yields about .7v of error. I wouldn't expect better than 5% with the common aftermarket gauges. If the voltage is measured somewhere except directly at the battery, such as with a dash-mounted gauge, the voltage drop of the wiring, switches, connectors, etc. in the harness will contribute some error.

With mine I monitor the performance of the circuit and watch for variations from normal. Then meter accuracy and wiring harness-induced errors are not a concern.

 

[Mickey_Fx]

</font><font color="blue" class="small">( What does the manual say it should be?

)</font>
Don't see any reference to this in my owner's/operator manual.

 

[Mickey_Fx]

</font><font color="blue" class="small">( Could this be a function of the voltage regulator to determine the voltahe output of the alternator/generator. Also can the spific gravity of the individual cell be read during charge and with charge off as a trouble shooting aid?? )</font>
Regulating the output voltage is the very purpose of a VR. In Yanmar's case the VR also contains the bridge rectifiers for the conversion from AC to DC and circuitry to control the battery idiot light.

IMO you can't get an accurate reading on state of charge until the battery has been at rest for several hrs. I also prefer voltage measurements over specific gravity. Voltage Vs capacity (as a % of rated capacity) curves are well established. I personally never use specific gravity and on some LA batteries it is not possible.