Simple Battery Management

Hermit Scott · Feb 16, 2009

12.7- 100%
12.64-95%
12.58-90%
12.52-85%
12.46-80%
12.40-75%
12.36-70%
12.32-65%
12.28-60%
12.24-55%
12.20-50%
12.16-45%
12.1 volts is somewhere around 37.5%, and probably dangerous for damaging the batteries. 11.9 V is discharged. And yes deep cycles should be kept above 50% for maximum battery life.

Bob V · Feb 16, 2009

One thing to remember about voltmeters

is that you do not get a true reading unless there is a long wait time (like 6 hours) from the time that there is a load on the batteries to the time you read the meter. It works the same way with a charge. If you check you voltmeter right after you stop the engine it will give you an inflated reading probably close to 100% in most cases. Shut everything off and come back in 6 hours and you will get a reading that is more realistic. The same with waking up in the morning and turning off your anchor light and other loads. When you check the voltmeter it will read much lower than what it would 6 hours later with no load drawing off the batteries. A battery monitor that reads amps or amp hours used or remaining would be more accurate.

Stu Jackson · Feb 16, 2009

The book is NOT vague

read the section on specific gravity. It is VERY specific!

The voltage-only tables are beginning to sound like old wives tales.

Given the now low cost of battery monitors and amp hour management, those simple-minded-table-thingies should be relegated to the dustbin.

Hermit Scott · Feb 16, 2009

But it's not real practical to always be pulling out electrolite. What is a good battery monitor for a cheapskate?

Steve_Catalina · Feb 17, 2009

Neil McDonald said:
I am about to replace my house batteries (2 Trojan 6V wet cell golf cart batteries wired in parallel)

Neil,

I assume you actual have your two 6v trojan's were wired in series for
a 12 volt system

Steve M.:dance:

sailingdog · Feb 17, 2009

This might do the job for you...but I'd personally spend the extra money and get something like a Xantrex Battery LinkPro.

Hermit Scott said:
But it's not real practical to always be pulling out electrolite. What is a good battery monitor for a cheapskate?

Don S/V ILLusion · Feb 17, 2009

I think the thing Sailingdog refers to above is actually a gross voltage meter which wouldn't provide anywhere near the info Neil's Link20 would once he calibrated it.

Neil - the Link20 you have is excellent at providing state-of-charge info once you get a chance to play with it and if not available, the instruction manual is readily available on the internet.

Neil - two things shorten battery life - discharge below 50% and incomplete re-charge, the latter being difficult to mitigate while cruising which is why many folks have gensets, solar panels, more complex engine charging systems or a larger battery bank, any of which can adequately address your issue.

Stu Jackson · Feb 17, 2009

Hermit, in answer to your #5

Read reply #19 here: http://c34.org/bbs/index.php/topic,4623.15.html

I think I'd linked this from a different thread about 1-2-B switches and the dual circuit switch sometime in the past.

...and it should BECOME very practical to get the specific gravity meter out and USE IT. It's like checking your engine oil every time before you start your engine. And you don't "pull out electrolyte" you just test it and the specific gravity meter squishes it right back into the cells.

And you should equalize your house bank regularly.

Download the Ample Power Primer, www.amplepower.com, technical documents.

Your boat, your batteries, your pocketbook, you self-named "cheapskate!"

:naughty:

Don's absolutely correct in his recommendations.

and don't parallel your two 6 V batteries, series them for 12 V. A helpful parallel universe resource I found on the C25 website from NautiDuck from the RV world is this which shows how to wire two six V batteries into a 12 V bank: http://www.ccis.com/home/mnemeth/12volt/12volt.htm

RichH · Feb 17, 2009

Hermit's listed values are good .... However, these values are for a 'resting battery', not one that is supplying power to a circuit.
With these values and a good calibrated digital voltmeter I can do better than a Link 2000, etc. IMHO.

Stu Jackson · Feb 17, 2009

Rich, oh NO you can't! That's because ya just don't know what's been put BACK into the banks when charging. I thought the same way you did for years until I installed our Link 2000. I was WAY off on knowing what went back in because the battery acceptance reduces the amount of input dramatically as the banks get full. And leaving a battery undercharged reduces it's life. It may have "nice" voltage (do you wait for 6 hours until the banks are at rest after you sail into your slip?), but not have the amp hours returned to be fully charged.

The voltage tables are only part of the answer, and shouldn't be depended on to give the whole picture. 1970s technology is so way old...

As to Sailing Dog's reference link, it's made by ProMariner, the guys who gave us the FlyBack chargers that burned up batteries and boats in the 80s and 90s!!! I wouldn't trust those guys as far as I could throw them. Hard to tell for sure but it does look like voltage only. See, told ya!

Bill Roosa · Feb 17, 2009

Poor mans battery monitor

I'm a self confessing cheapskate. As such, I already had a laptop the boss bought me and it had Excel installed. Now I know it is hard to believe but most of us use power on the boat in a fairly predictable fashion. We turn the nav lights on at dusk and off at dawn, use the microwave just before dinner and to make popcorn at night, etc.
An enterprising young cheapskate would be able to make a spreadsheet that had all the loads in one column and 24 columns for each hour of the day. You could even have 72 columns for those weekend cruises.
Then you could enter how you use each piece of equipment and when the alternator/wind/solar are producing and add and subtract that (taking into account bulk-absorption-float charging rates) from the AH stored in the batteries.
this would give you a pretty good idea of how the batteries are being used and how much you discharged them on the trip. If you are exceptionally annal you could enter the amounts "on the fly" and have an even more accurate measure of the battery state of charge.
And since you don't want to worry about this stuff when sailing anyway you could develop (back at home) a "sail power usage plan." Once you established how you want to cruise you could size your generation and storage to accommodate it and NEVER have to worry about it again!!!!!!
I have done this and found it to be very accurate at predicting my battery state of charge.

Be happy,
get a copy of the spreadsheet
and
don't worry while sailing again.
and
save yourself the bucks and hassle of installing a battery monitor.

Additionally, if you load a battery with a known load of say 10 amps (macerator for instance) and watch the voltage drop you can get a VERY accurate estimation of the state of charge of the batteries. But you have to know where you started and do it numerous times to "get the feel" of how the speed of voltage drop relates to the state of battery charge.
If you where REALLY annal you could develop a spreadsheet that tells you the AH in the battery based on the voltage drop during the 20 seconds you run the device. Or just get out to the boat more often and it will become pretty obvious what is going on for every device you have.
william-roosa@us.army.mil

Don S/V ILLusion · Feb 17, 2009

Bill
As he already has a Link20 to tell him what's going on, this is kind of academic but, for those who do not, how do you know what acceptance rate to use in your calculation of state of charger, particularly as it can change over time? Also, how do you know what the alternator is doing as this varies with both engine speed and temperature?

Also, I'm curious if you ever verified your numbers against empirical data.

Stu Jackson · Feb 17, 2009

Don, Bill's spreadsheet is pretty good

and I understand from one of his more recent posts that he's updated it to include "time to recharge" which, I admit, I haven't investigated in detail. So, I don't know how he did it. Perhaps I'll get to reviewing it.

That said, I fully agree with both you and Bill. One, the battery acceptance drops off the ability to recharge, as we've both said, to an incredibly low rate of charge as the bank gets fuller and nearest to full. Many times, now based on my Link 2000 experiences, it takes almost overnight to fully recharge a bank.

For Bill, as I've said many times, what goes OUT becomes easy to learn and just as you've stated in your last post here. It's what goes back IN that most people are missing, and relates to the state of charge in a very direct manner.

What I've seen, for example is this, from our Link 2000:

--- Return from a day sail, bank is down 15 amp hours, plug into shore power with our 75 amp charger, batteries will only ACCEPT 15 amps (360 AH house bank, they're pretty fully charged if only 15 ah down)

--- Most people will then assume that it will take an hour to replace the 15 amp hours at 15 amps of charge

--- NOT!

--- As the batteries absorb that 15 amp charge, they get fuller

--- The charge RATE goes down to 10 amps after 15 or 20 minutes and the bank is now down to 10 amp hours down

--- Now, it should only take another hour to charge those minus 10 amp hours at 10 amps -- assumption again; we're now up to an hour and twenty minutes to fully charge, right?

--- NOT again, because this keeps recurring

That's why a full charge takes a LOT longer that most people expect.

What goes OUT is easy, what goes BACK takes longer.

Please believe me, guys, because I see this all the time now that I have the Link 200 installed and working.

This is why people say the BEST investment for un-knowledgeable and knowledgeable skippers alike is to buy a battery monitor FIRST. Wish I did, because I'd been chronically UNDERCHARGING my house bank, even after all the spouting I do here and on other forums!

Believe it!

Stu Jackson · Feb 17, 2009

Neil McDonald said:
The key is my new understanding that it does not work by taking an instantaneous reading of battery state of charge, but instead keeps track of total amp hours in and out of the battery. I did not know that it was quite so clever...

Neil,

Please be careful about definitions. The Link will give you a number of things. It can read instantaneous amp draw.

It can also average amp draw over a period of time to calculate time remaining on your individual banks based on the amp draw (instantaneous, 4 minutes, 8 minutes, 16 minutes or 32 minutes). YOU set how that works. I find that the longest is the best, but if I want to know what any particular time remaining based on what any given load is I can switch to instantaneous.

It's NOT an "instead" thing, it does a lot of things.

The state of your battery charge is determined by the MINUS amount of AMP HOURS. Once that gets to zero, you're fully charged. The Link calculates this by first knowing what your bank capacity is, and subtracting your loads. It does all the math for you!

It does NOT use voltage, which is why I keep saying that voltage tables are old school technology and battery condition theories.

Our Link 2000 can also be programmed to show on the screen the % of charge instead of the MINUS amp hours. Some people like that instead of MINUS amp hours. I know our bank size in my head, so I can do the math based on the amp hours down shown on the display, so I don't use the % display. Maybe your Link 20 can do that, too, I haven't checked the manual for your unit.

You're right, read the manual and learn how to use the Link. It took me a few times to figure it out, but start using it and you'll get real good at it.

Bill Roosa · Feb 18, 2009

Sailing vs watching my link tell me stuff

Don, you are of course correct in pointing out that many things, alternator temp, engine speed, battery charge...... are all changing during the charging of the batteries.
I use the little known law of statistics to simplify my sailing lifestyle. I always run the motor at about the same speed, I always run it for about the same amount of time just before anchoring as we cruise around the gunk-hole "finding the right spot", etc. So while my regulator may be adjusting things to charge the battery, on average, it acts like a battery charger and the batteries control the amount of AH that go into them.

The one important assumption I use throughout my spreadsheet is that there is a pattern to my use and production of electricity. Once I establish how my sailing lifestyle uses electricity I can factor in various generation schemes and size my production and storage components to fit my lifestyle. So my components don't drive my lifestyle, my lifestyle is in harmony with my use, production, and storage of electricity.

To answer your question on how did I come up with the numbers for bulk, absorption, and float charge rates I did the following;
I assumed that the only variable is the state of battery charge.
I assumed the following charge schedule based on the state of battery charge:
Battery state of charge % of total production used
0-80% 100%
81-84% 50%
85-88% 25%
89-92% 12%
93-96% 6%
97-100% 0.5%

All the production means get summed together in an hour by hour fashion and the % of total production numbers can be tweaked if you think they need it. You can develop an even more detailed schedule if you wanted using this same methodology but I thought 5 steps was sufficient.

I have been using it to predict my usage and it sure seems to work. The only empirical data I have is watching the battery charger after a longish cruise. It agrees well with the numbers in the spreadsheet.

Buck420 · Feb 19, 2009

Uh, Stu,

Stu Jackson said:
Read reply #19 here: http://c34.org/bbs/index.php/topic,4623.15.html

I think I'd linked this from a different thread about 1-2-B switches and the dual circuit switch sometime in the past.

...and it should BECOME very practical to get the specific gravity meter out and USE IT. It's like checking your engine oil every time before you start your engine. And you don't "pull out electrolyte" you just test it and the specific gravity meter squishes it right back into the cells.

And you should equalize your house bank regularly.

Download the Ample Power Primer, www.amplepower.com, technical documents.

Your boat, your batteries, your pocketbook, you self-named "cheapskate!" :naughty:

Don's absolutely correct in his recommendations.

and don't parallel your two 6 V batteries, series them for 12 V. A helpful parallel universe resource I found on the C25 website from NautiDuck from the RV world is this which shows how to wire two six V batteries into a 12 V bank: http://www.ccis.com/home/mnemeth/12volt/12volt.htm

How do I get the specific gravity of my AGM (or Jel) batteries? ...

Just jerking your chain; I agree w/ all of your "rantings"

;
I have totally depended on my Link 2000(R) ever since I got my current boat. It's another one of those "don't leave home w/o it' .. s".

Stu Jackson · Feb 19, 2009

Not evryone has a pattern to sailing

Bill, I understand your concept, but we use our boat very differently everytime we go out. Sometimes it's a daysail. Sometimes I use the fridge, others, not. We motor out to anchor out sometimes. Sometimes we sail to the anchorage. We often do two or three nights out, and using the motor depends on the winds. We're sometimes gone for a week or more, anchoring or traveling as winds, currents and desires allow. So, while I can pretty well guesstimate our power OUT, what goes back IN varies tremendously. I applaud your concern for details and your spreadsheet, but continue to recommend that a battery monitor, for especially un-knowledgeable electrical folks, is the way to go. From a guy who never uses a diesel fuel gauge, I believe a battery fuel gauge is a must for most sailors to maintain and extend battery life. Bill, you & I can almost do this stuff in our heads. Most recreational weekend warriors simply can't, or can't be bothered with it. If they get a monitor, it's one less thing to worry about and the days of bad electrical systems that don't work could well be over.

Bill Roosa · Feb 19, 2009

Scenarios

Hi Stu
I'm hip man. Some folks can't even spell Ohm. The way I have the spreadsheet set up you can play with all that stuff. I'm not sure I buy the "I can do it in my head" comment cause I learned a few things that are not blindly obvious to the casual observer. I certainly would not have been able to figure out how many amps a wind generator would need to be producing to keep my batteries fully charged as I played with the loads. And I guess that is why I built the thing in the first place. The problem was simple but had lots of moving parts which made it hard to get my head around.

I made several "tabs" for different scenarios because even I have several patterns in my usage of the boat. But there are still patterns. The nav lights come on at dusk the reefer runs all the time..... I broke it down to "at sea with no engine", at anchor, weekend cruise and another one that escapes me right now. By messing with each I found that at sea without an engine is by far the hardest to do and why. It gave me some insight as to where to cut usage to save the batteries in an emergency (or just in general) and still have the food not go bad. Some kinda silly things like running the engine twice a day for 1/2 hour is better then once for a full hour and that when you run the engine can have a dramatic effect on the state of charge.

I guess some would rather pay the money and trust the instruments. And that is fine, I'm not looking down my nose at them. I'm of the opinion that monitors are not that accurate. Especially when you do a lot of cruising and don't get the batteries fully charged for long periods of time. They never auto reset due to a full charge being on the batteries and so get out of sync with reality. I'd be interested in finding out how folks with monitors use their boats.

I do think it is a great resource to size components and learn how things interact. FWIW