Jump to content

12 volts?


Recommended Posts

So you're sailing along on the Tillerpilot and you see the voltmeter reading 'X' amount of volts and you think that is getting down, time to start motor charging.

Qestion is what amount of volts do you consider you should start recharging?

Its about 12-4 volts

Link to post
Share on other sites

Depends on the current draw, wire length, gauge and where you are measuring the voltage from.    The best solution is Invest in a battery monitor that can count amp or amp/h consumption. These types have a shunt or better still a hall effect sensor.

Link to post
Share on other sites

12.4 while running a tillerpilot for some time is likely still quite good. As erice said, a 12v (wet lead acid) battery will sit at about 12.7 fully charged at rest. The 'at rest' part is why voltage is a bad reference, if you have just charged it might read high, if you have just had / do have a draw it will read lower than it's resting voltage. You need to stop all current draws and let the battery sit, for a length of time depending on the size of recent current draws, for the voltage to stabilise through the battery, then take a reading. Not so easy while sailing on AP. Get a battery monitor (properly installed and calibrated) if you actually want to know. Or do it like BP says, and likely over discharge your battery often and shorten its life.....

Link to post
Share on other sites

The above. (minus BP bat killer)

 

For a US batteries FLA battery, 12.35V =  approx. 50% of capacity. Which should be max DOD.

But needs to be measured in unloaded state, ie everything off plus a few minutes to stabilize.

12.4V may get to 12.45V with TP off & rested = approx. 65% so still good for a bit.

Th odd deeper discharge happens, but best to get back to 100% asap.

 

My rule of thumb anyway.

 

Plenty of charts of SOC vs V,   temp  compensated, on net.

Link to post
Share on other sites

Agreed, but "a few minutes" is not sufficient to let a battery stabilise its voltage properly. 10 HOURS or more is not unusual on a large bank. The only way to really know is a meter. Even then, it's only a guide - garbage in, garbage out - proper programming is essential. BP will be destroying the life expectancy of his batts.

Link to post
Share on other sites

Yep as IT said. All battery Voltage checks should be carried out under no load, after a 10hr (at least) rest.
Plus the more discharged a battery becomes, the greater the "sag" in it's ability to maintain a Voltage as a load is applied. So a fully charged battery will read 12.6V after the rest/test period and then, under a load, drop a few points of voltage. But a Battery at 50% charge may read 12.1V at rest/test, but under load, could well drop to 10.5V. 
  So just because a Voltmeter says the bank is down to 12V(while it is under load) is not telling you the correct discharge level. Remove the load and the Voltage will climb again and after the rest period, the voltage will be back to whatever it's actual discharge Voltage is. A Volt meter is not very useful except for giving you a very ruff and quick reference that things are OK or not. A proper monitor (set up correctly) will give you the only true story.
      Yes a monitor is expensive. But so is a Battery Bank and we need to ensure several things with a House bank. We use the rule if thumb of 50% depth of discharge. This is based on the fact that a Battery starts to die (even at full charge) the day the Acid is poured in. In otherwords, leave the battery trickled charged and come back an measure it in say 1000yrs and it is likely to be flat and never accept a charge. (I say 1000 because I don't know how long it would actually last). When we start cycling a Battery, if we allow it to discharge to say just 10% and then recharge, it may last 100yrs perhaps. At 20%, it may last 25yrs. At 50%, it hopefully will last 10yrs (likely much longer). Then you have to make a sizable investment on a new Batt Bank again. So the 50% discharge rule is based on how often you have to replace it and the cost. Draw these out on a graph and you could say that this is the point at where the two lines cross. The most economical between getting power over Cost, or "cents per watts".

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...