battery monitoring

[john]

I followed a very useful and informative discussion about battery maintenance a few weeks ago but am still puzzled over how to monitor my battery's condition. I have a Ty and the only electrics/electronics are the radio, running lights, and (currently not functioning) analog knotmeter. My outboard has a charging circuit, which I will hook up this year, though I think its output is very low, as the local Mercury dealer says it poses no danger of overcharging the battery without a regulator.

Do I need some guages to check on the battery from time to time or do I just go by whether or not the lights go on as an indicator of when its time to haul it ashore and put it on the charger (automotive type 6/2 amp)?

Thanks for your expertise.
John



john.hoft-march@appleton.org

[Don Carr]

John; First my CD25 has a battery test meter on the power distribution panel. If you don't have one, get a cheap multimeter from Radio Shack and measure the voltage. A fully charged battery should show 13.1-13.8 volts. If it reads less than 10.5 volts it's dead.

IMHO you should check the battery once a every couple of weeks during the season, more frequently if you know you've used some capacity.
It's probably a good idea to charge it once every couple of weeks at any rate as a discharged battery (liquid cell at any rate) will tend to reduce ultimate capacity quicker.
Different schools of thought on charging depends on battery category(gell, liquid, deep cycle, combo deepcycle/starting) but a 'smart' multistage charger seems to be the preferred way to go.

As far as your o/b charger is concerned, take the aforementioned multimeter and measure output at various engine RPM's just to verify
what the dealer said. Too many times I've heard from the experts 'no-problem' only to find that in fact there can be a problem

IMHO/FWIW



carrds@us.ibm.com

[D. Stump, Hanalei]

John,

About a year ago, I purchased a Sears Craftsman multimeter for $20.00. Its' readout is digital, and LARGE, so old eyes can read it easily. I'm not too impressed with Radio Shack, but that's just my opinion.......fwiw

D. Stump, Hanalei

[Will W.]

Hi John
I didn't follow the previous discussion so I may repeat a few things but here goes. Assuming you have a wet cell deep cycle which is typical.
First of all to prolong the useful life of the battery you should avoid letting it go below 50% full charge. Full charge being 12.6 volts and up, 50% depleted is at 12.2 volts. As you can see you need a digital voltmeter or preferably a digital multimeter. Make sure the battery has been unused for at least an hour to allow equalization of the cells for an accurate reading. Letting the battery get to where the lights dim is too long.
If you leave the battery unused for long periods, like winter, it will loose its charge slowly. So it is a good idea to check it occasionally. Again for ideal storing it should be kept at full charge . A battery's life is measured in cycles so the fewer charging cycles ( from 50% to full for example )you put a battery through the better.
I read all this in Nigel Calders book "Boatowner's Mechanical and Electrical Manual" 2nd edition. It is expensive but vastly informative. It thoughroly detials the whys and whatfors of what I have passed on to you( basically the tip of the iceberg ).
Before I read anything I cruised last summer mostly day sailing. I don't have much more electronics than you and I would go for weeks without recharging. I was probably depleting the battery beyond 50% but it does not seem to be harmed yet. Calder's book also explains how to ckeck on the battery's overall condition ie. usefull life remaining.
You can also figure out what your power needs are and size your battery appropriatly. Or, since you already have a battery and it is in good condition or new, you can get the number of amp hours AH available from the battery. It should say somewhere on there what the AH is. Given that you do not want to go below 50%, if the AH at full charge is 100 then you have 50 AH to work with. Now figure out your power consumtion. A 10 watt bulb draws .83 amps per hour( the formula is: Watts/volts=Amps, you have a 12 volt battery so that is 10/12=.8333). If each running light is 10 watt and you have four on(rear white,bow and red and green), then you are using 3.33 Amps for each hour you keep these four lights on. A vhf only draws about .5 amps when recieving, 5 amps when transmitting. I don't transmit enough to even figure it in the equasion. So at .5 amps, if you have the radio on for ten hours, you will use 5 amps. So for the day you have 5 amps from the radio and say 2 hours with the nav lights on at 3.33 an hour. Thats 11.66 AH used of an available 50 AH. At this rate you can cruise for 4 days without a charge.
Hope this helps.

Will Wheatley
Suzi Q
CD25

I followed a very useful and informative discussion about battery maintenance a few weeks ago but am still puzzled over how to monitor my battery's condition. I have a Ty and the only electrics/electronics are the radio, running lights, and (currently not functioning) analog knotmeter. My outboard has a charging circuit, which I will hook up this year, though I think its output is very low, as the local Mercury dealer says it poses no danger of overcharging the battery without a regulator.

Do I need some guages to check on the battery from time to time or do I just go by whether or not the lights go on as an indicator of when its time to haul it ashore and put it on the charger (automotive type 6/2 amp)?

Thanks for your expertise.
John

willwheatley@starpower.net

[Steve Alarcon]

Hi Will,

I think you had a typo that is worth noting. Everything I have seen indicates that a battery is fully charged at 12.7 volts, and it incrementally looses charge of 10% per .1 volt depletion. Thus, 50% depletion is at 12.2 volts as you correctly stated.

Cheers

Steve Alarcon
CD36 Tenacity
Seattle



alarcon3@prodigy.net

[Bob Loewenstein]

A fully charged battery should show 13.1-13.8 volts.

You want to make sure the battery voltage is measured several, if not many, hours after charging. A fully charged 12 volt wet battery should show 12.7 volts.

[Will W.]

Nigel recommends 24 hours before measuring if you can wait but also says to wait at least an hour. I guess when at sea it is more important to fix the problems than to wait for an exact reading. On a chart in Calder's Manual ,page 44 2nd edition, It says that a fully charged reading is 12.6 and up. However it also says that 75% to 100% is 12.4 to 12.6 figuring that it makes sense to take a step up from the 75 to 100% that lands you at 12.7
BTW I took a reading today to check my battery and it reads 13.15 It has been a month since I charged it. Does this mean I overcharged it? Or does overcharge and damage related to overcharging only occur while being charged? The chart saying that 12.6 and up was fully charged led me to believe that low 13 readings were ok. A few posts seem to agree. Any thoughts?

Will Wheatley
Suzi Q
CD25

A fully charged battery should show 13.1-13.8 volts.

You want to make sure the battery voltage is measured several, if not many, hours after charging. A fully charged 12 volt wet battery should show 12.7 volts.

willwheatley@starpower.net

[Larry DeMers]

Your voltmeter is a tad high I expect. Ordinarily, you do develope a "surface charge" on the bank while it is in the float mode. But internal resistance (leakage) will deplete this in short order. I would think that anything over 12.6v is indicating a full battery. But the truth is devined by checking the specific gravity (SPG) at temp. This will tell you the state of charge accurately. For the exact numbers to look for, consult Nigels book, or let me know and i will look it up for you. This would be a good check in your case, as there are conditions in wet cells that can result in a higher open circuit voltage like you report, but usually it has to do with a low cell (electrolyte level) or two.

Larry DeMers
s/v DeLaMer
Cape Dory 30

Nigel recommends 24 hours before measuring if you can wait but also says to wait at least an hour. I guess when at sea it is more important to fix the problems than to wait for an exact reading. On a chart in Calder's Manual ,page 44 2nd edition, It says that a fully charged reading is 12.6 and up. However it also says that 75% to 100% is 12.4 to 12.6 figuring that it makes sense to take a step up from the 75 to 100% that lands you at 12.7
BTW I took a reading today to check my battery and it reads 13.15 It has been a month since I charged it. Does this mean I overcharged it? Or does overcharge and damage related to overcharging only occur while being charged? The chart saying that 12.6 and up was fully charged led me to believe that low 13 readings were ok. A few posts seem to agree. Any thoughts?

Will Wheatley
Suzi Q
CD25

A fully charged battery should show 13.1-13.8 volts.

You want to make sure the battery voltage is measured several, if not many, hours after charging. A fully charged 12 volt wet battery should show 12.7 volts.

demers@sgi.com

[john]

Your voltmeter is a tad high I expect. Ordinarily, you do develope a "surface charge" on the bank while it is in the float mode. But internal resistance (leakage) will deplete this in short order. I would think that anything over 12.6v is indicating a full battery. But the truth is devined by checking the specific gravity (SPG) at temp. This will tell you the state of charge accurately. For the exact numbers to look for, consult Nigels book, or let me know and i will look it up for you. This would be a good check in your case, as there are conditions in wet cells that can result in a higher open circuit voltage like you report, but usually it has to do with a low cell (electrolyte level) or two.

Larry DeMers
s/v DeLaMer
Cape Dory 30

How do I go about checking specific gravity and what do I look for?
Thanks.
John



john.hoft-marchNOSPAM@appleton.org

[Mark Yashinsky]

The 13.x is typically the charging voltage from the alternator. Has to be higher than the battery for the battery to be "force fed". This is the surface charge that has to dissipate before measuring the battery. Dont go for an expensive multimeter, if you plan on keeping it on the boat (marine environment and unsealed electronics dont mix).

[Mark Yashinsky]

Go look at your local automotive shoppe. Looks like a big kitchen baster (glass though). Read the instructions. Are not applicable for "truly" sealed batteries (Optima) and not sure about the gel cells. Basicily measuring the chemical compostion of the acid water mix.

[Don Carr]

Larry, et.al.;
I run gell cell technology where most if not all the rules change. Fresh out of the box it measured 13.2 volts (Prevailer spec). Float charge is 13.8 volts absorbtion charge is 14.3 (warm) 14.6 (cold).
Gells do not have nearly the capacity loss during storage that traditional technology has. I find that one week after float charge Iam down to 13.1 volts; after a month down to roughly 12.8.

FWIW



carrds@us.ibm.com

[Larry DeMers]

SPG testers come in at least two flavors; A floating ball type where one ball floating says you toasted the battery to a flat state and 4 balls floating says ya gots a good charge matey! The second flavor is a SPG tester that actually tells the Specific Gravity of the liguid tested via a pointer needle that floats int he water, but points at a scale on the case of the tester. The actual number you consider as fully charged depends on the ambient temperature, with the nominal reading as indicated on the tester, without correction, is equal to 70 deg. F.Nigel Calder goes into this in his book..be sure to get this puppy, it's a keeper.

Cheerio,

Larry DeMers
s/v DelaMer
Cape Dory 30

Your voltmeter is a tad high I expect. Ordinarily, you do develope a "surface charge" on the bank while it is in the float mode. But internal resistance (leakage) will deplete this in short order. I would think that anything over 12.6v is indicating a full battery. But the truth is devined by checking the specific gravity (SPG) at temp. This will tell you the state of charge accurately. For the exact numbers to look for, consult Nigels book, or let me know and i will look it up for you. This would be a good check in your case, as there are conditions in wet cells that can result in a higher open circuit voltage like you report, but usually it has to do with a low cell (electrolyte level) or two.

Larry DeMers
s/v DeLaMer
Cape Dory 30

How do I go about checking specific gravity and what do I look for?
Thanks.
John

demers@sgi.com

[Bob Loewenstein]

Go to

http://www.rollsbattery.com/

Look at the FAQ, and somewhee they have nice info sheets on charging wet cell batteries, specific gravity measurements and adjustment for temperature, etc.