Understanding batteries, voltage, amphrs, and etc..

Charles Erwin · Mar 4, 2015

For me anyhow - understanding does not come easy. No commitment => no results.

So here is a worthwhile start. http://www.pbase.com/mainecruising/deep_cycle_battery

Read but don't be satisfied. Let these concepts settle in then comeback and read again.

Charles

JohnShannon · Mar 4, 2015

I think you want a Link or equivalent battery monitor that keeps track of charge (amp-hours) rather than just a voltage monitor.

"bring it up to 12V" is a little odd. Typical charging for a 12V battery is something like C/5 20A for a 100Ahr battery, as the battery charges voltage builds the charger limits the max voltage applied to the battery to something like 14V (sb temp dependent) the charge current tapers off once the voltage limit is reached.

So charging a 12V battery and stopping at 12V is undercharging. Assuming the voltages are correct you should be wait till the voltage gets to 14V.

jlp0217 · Mar 4, 2015

Yes, you are steadily wearing your batteries down. I have a chart before me from emarine systems that says that a battery at 12 Volts is only 25% state of charge. 50% which you should not go below is 12.2 Volts.
I hope you are reading the voltage when the alt is not running, because the alt is trying to produce something around 14.4 volts, but does not get there until the batteries cannot accept as much current as the alt is capable of producing. This is what's called bulk phase .
Once the Alt is able to get the batteries to 14.4 volts, absorption phase begins - the alt maintains 14.4 volts, and the batteries accept less and less current. Their internal resistance climbs as they become charged and since the voltage is constant, ohms law says current must decrease.
There is a lower limit to the current, (an upper limit to resistance) and when it is reached the batteries are fully charged. A smart charger when then go to float voltage.

You probably don't want to run your engine long enough to fully charge your batteries, but you probably should get to at least 75%, or somewhere around 12.4 volts (resting, not charging).

Bill Roosa · Mar 5, 2015

Re: understanding your boat electrical system

You are designing a system: loads, storage, and production.
The charts can be use to determine state of charge if you know amps in or out and the voltage.
I have a spreadsheet that will help you play with the loads and production to see what will work. email me for a copy
Some stuff I've learned:
use it as you produce it and save 20% loss from putting it into and taking it out of storage (10% each direction). So run that reefer during day when the solar panels are working and coast through the night on the holding plate
long time small amp production is better than short high amp production so lean toward solar, wind and hydro.
balance the above with
that nice snug anchorage will probably not have much sun or wind and your hydro will be useless at anchor.

Maine Sail · Mar 5, 2015

Rick Templeton said:
I have a hunter 340 with 2 - 12v and 4- 6v wired thru a Magnum 2012 charger/inverter ( yea I know, big system for someone who doesn't rally understand it ). The motor has a Balmar 100 amp that's set up with its own regulator. When my wife and I go on extended cruises the system works really well for 4 or 5 days with an hour or so of engine time. As the days pass it seems to take more diesel time to recharge.

This is a normal phenomenon under what is called PSOC use of your batteries. PSOC simply means partial state of charge cycling. Each day you don't get back to full leaves more sulfation on the battery plates and thus requires more engine run time to get back to the same SOC you were able to attain the day before.. This usable capacity loss, due to PSOC use, is called walking down.....

Rick Templeton said:
I am assuming that we are steadily wearing the charge down. We have 2 voltage Gage's , one for the house and one for the starters. I always run the engine until I bring them both back to 12 v, I would like to understand the theory behind what is required to recharge the system and keep it up and how long I should expect it to take.

If you are only getting "back to 12 v" running a Balmar 100A alternator you are simply murdering your batteries and taking them down towards 0% SOC. Consider that your average load on a 450Ah bank will be roughly 15-25% of the batteries 20 hour Ah rating so you should not be seeing any battery terminal voltage below 12V before it is time recharge. Charging "up to 12V" and stopping is literally going all Charlie Manson on your batteries.

If you want to treat your batteries in a more healthy manner, during this type of use, set the alternator regulator to 14.7V then hold battery voltage there while charging for at least 30 minutes before shutting off the engine. This will help knock some of the sulfation back off the plates. If you never attain absorption voltage you are simply building up more and more sulfation that becomes permanent and will rapidly degrade your batteries. The effects of sulfation begin happening in as little as 2 PSOC cycles off a 100% SOC charge.

While batteries are referred to as 12V this is the nominal voltage. A healthy fully charged golf cart battery will have a rested (24 + hours at 77F no loads, no charging) open circuit voltage reading in excess of 12.72V. In order to attain a full battery it will take 10+ hours of engine run time, at a minimum, once any sulfation has set in. With golf cart batteries that are sulfated your Coulombic or charge efficiency is in the realm of 120-130% +. This means if you take out 100Ah's you need to return 120-130Ah's in order to get the batteries full. 100% charge efficient lead acid batteries simply don't exist. Charge efficiency gets worse with age..

Most installed DC volt meters are also incorrectly installed which leads to horribly erroneous readings. A volt meter needs to have the positive and negative leads running straight to the house banks physical battery terminals. Pulling the voltage readings from the DC panel means you are reading the voltage drop in the wires feeding the DC panel not the actual battery terminal voltage. Also, every 10% SOC in a lead acid battery is represented by an approx 0.1V change in battery terminal voltage so to use a volt meter it needs to be accurate. They can not be accurate if they don't physically connect directly to the battery terminals and do so independently of any other wires. If I had to guess nearly 90% of all boats I set foot on have incorrectly wired volt meters.

To keep it simple make sure that with each charging cycle you are attaining a bare minimum of 14.4V at the battery terminals. With golf cart batteries preferably 14.6V - 14.7V for at least 20-30 minutes, before shutting down. Get to shore power as often as you can to get a full charge or add solar and allow it the time to fully recharge the batteries...

Your Balmar regulator is also likely improperly installed in relation to voltage sensing. For short duration fast charging this is fairly critical if you want to get the most current back into the battery in the shortest time..

Regulator Voltage Sensing, Why Is It Important?

Stu Jackson · Mar 5, 2015

"Walking down" can also be thought of as a "steadily diminishing law of returnA" where what you remove (use) is more than what you replace (charge), coupled with a woefully low charging voltage.

Have you done an energy budget?

The All-Important Energy Budget:

http://c34.org/bbs/index.php/topic,3976.0.html

Do you have the regulator manual? If not, download it from www.balmar.net It includes a very good description of the voltages used and how three stage charging works, with voltages and currents explained.

Anoother good battery info source is

The Ample Power Primer http://www.amplepower.com/primer/primer.pdf

There is a great deal of boat electrical system info here:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

Seems you have some homework to do.

Good luck, when you've read up, c'mon back with any ?s.

PS - we've all been there, none of us were born electricians.

rardiH36 · Mar 5, 2015

Maine Sail said:
Most installed DC volt meters are also incorrectly installed which leads to horribly erroneous readings. A volt meter needs to have the positive and negative leads running straight to the house banks physical battery terminals.

Hello Maine Sail:

Is connecting volt meter leads at the A/B/Both switch acceptable? I would have thought the large diameter battery cable between the battery terminals and A/B/Both switch would make voltage drop negligible?

Thanks

Maine Sail · Mar 5, 2015

rardiH36 said:
Hello Maine Sail:

Is connecting volt meter leads at the A/B/Both switch acceptable? I would have thought the large diameter battery cable between the battery terminals and A/B/Both switch would make voltage drop negligible?

Thanks

This is the same battery switch & wires we may be passing 100A of charge current through.....?

Unless you have 0.0V drop, under all loads where you would find the volt meter useful, at your battery switch, the best location for any volt sensing is at the battery terminals....

Bill Roosa · Mar 5, 2015

Voltage drop through a resistance is a very handy concept to understand. you normally think of the total voltage drop from + terminal through the load and back to the - terminal but each little wire and connection and the load itself all have their own voltage drops. you can only measure these when there is current flowing BTW.

Benny17441 · Mar 6, 2015

OK, here is a layman's version. A few things you need to know, figure out the setup what batteries compose your starting bank and what batteries make up your house bank. Once you have segregated your house batteries figure out the size in amps for that bank. Conduct a power survey to find out on the average how many amps you use in a 24 hour period (day). An appliance that draws 1 amp per hour if operated for three hours will have consumed 3 amps and an appliance that draws 6 amps if operated for 1/2 hour will also have consumed 3 amps. Tally up all your electrical fixtures, their rated draw and for how long you use them and you will have an approximation of total of amps used during a day. Now you can introduce re-charging. The science of battery chemistry with the variables of temperature and age makes it a hard target to determine how long will they take to recharge. I always use my rule of thumb that it takes at least 5 hours to recharge a battery that has been drawn down to around 50% of its capacity. The time it takes to recharge a battery is more dependent on its acceptance rate than the size of the charging device. That acceptance rate also diminishes as a battery gains charge. It may take 3 hours to return a battery to 90% and 2 additional ones to get it to 100%. This why a lot of cruisers only return their batteries to 90%. You have probably been running a deficit as 1 hour a day of charging will not likely do much. To be able to determine a battery's state of charge by reading a volt meter the batteries need to be at rest with no loads or charge for at least 2 hours. A volt meter can be useful but you need to learn how to read it. Learning to read it is about observing the changes and how they relate to the electrical system rather than just what the gauge indicates. Just know that a battery which has been subjected to a load will give a lower voltage reading than what it actually has and one that has been subjected to a charge will give a higher reading than actuality. Hence the incorporation of a rest period to get a better reading. I use a voltmeter and can estimate pretty fairly the estate of charge of my batteries based on the experience of past readings. Recharging time can also be estimated based on past experience of the time to return the gauge to a particular reading. I mean the margin of error can be large so I would not recommend to try and push the limits of your batteries but it has served me well over the years to adequately provide the power to fit my needs. Now there are conservation practices that may need to be followed and that is why the survey and power budget need to be performed. Every outing may have different requirements and a plan for each may need to be developed. When we go on a long trip we just use brute force and pack a generator. If there is one thing that I have learned in sailing it is that there are very few absolutes and usually more than one way to skin a cat.

mitiempo · Mar 7, 2015

Benny17441 said:
The time it takes to recharge a battery is more dependent on its acceptance rate than the size of the charging device. That acceptance rate also diminishes as a battery gains charge. It may take 3 hours to return a battery to 90% and 2 additional ones to get it to 100%. This why a lot of cruisers only return their batteries to 90%.

80 to 85% is more like it. The last 15 to 20% takes more than 3 hours - closer to 6 to 8 hours to full as the battery accepts less and less.

You are confusing amps and amp hours. If a device uses 1 amp it still uses only 1 amp in 10 hours - but it consumes 10 amp hours in 10 hours.

Understanding batteries, voltage, amphrs, and etc..

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