Economical Battery Monitor

[Bill Roosa]

Well FourPoints, I keep my plugged in and floating all the time. The batts where pretty old (at least 2 years when I bought the boat) and they now have 4 more on them so I think I can safely say that floating the batts for extended time does not harm them. This assumes that your charger is doing that correctly of course.

Stu
How many systems do you have that cycle on and off? Reefer, freezer (5 amps effective at 90 deg F), fresh water pump (<2 amps for <15 minutes a day ---> <<< 1AH so ignorable), ....thinking,.... thinking... Autopilot? Not really a cyclic load but close enough. Assume worst case of rough seas and high response rate and the manual gives 4.5 amps effective draw.
A casual examination of the situation is while there may be "lots" of cyclic loads they are not very big so you don't have to manually calculate them. The reefer and freezer are far and away MUCH larger loads.
My engineer sense tells me that you can ignore the small stuff and focus on only the top few and get sufficiently accurate results. So if the batts get low turn the reefer off. WOW! That is complicated.

I certainly do not agree that you should cycle batteries to 50% to extend their life. There is plenty of data that proves there are a limited number of cycles on any battery and more cycling for no reason only sucks the life out of them needlessly.

 

[Tim R.]

Bill, this is Tim , not Stu.

The problem is that my batteries never cycle. My solar keeps them up all the time in the summer and they stay on float throughout the winter. This recommendation is direct from Lifeline for their AGM batteries.

If I shut down my reefer, I lose a lot of food. Not an option if I cannot get ice. I also have quite a bit of food in the freezer that would thaw. Thawed ice cream upsets the admiral. Warm beer upsets the admiral and captain.

My AP uses a hydraulic pump that cycles quite a bit. Even straight line sailing has constant small corrections.

On any given day while sailing I will have these systems running.

AP(2 stations), Chartplotter(2 stations), Radar, AIS, VHF(2 stations), instruments, frige, water pump, wash down pump if anchoring, lights(mostly cfl but some incandescent), any number of 12v chargers for portable radios, laptop, cell phones, mifi, bilge pump.

I will also have charging sources from my solar, wind generator and engine.

I have much better things to do then sit down and calculate the loads and feeds. That is why I spent a very nominal amount on a decent battery monitor.

Would you use one if it were free?

 

[FourPoints]

This assumes that your charger is doing that correctly of course.

It's the one Maine Sail reccomended for my small panel, Genasun GV-4, so I assume if he is suggesting it (and I beleive using the larger model on his boat too), it works correctly.

 

[mitiempo]

I don't see anything wrong with leaving the shorepower charger on 24/7 as long as it is a proper 3 stage charger. I do not know of any batteries damaged by this. Or any other 3 stage controller as with solar panels.
With some shorepower chargers, Xantrex for one, you are able to set it to 2 stage charging. In this mode after bulk and absorption it goes to sleep, only coming on when the lowest battery drops to 12.5 volts.

 

[Stu Jackson]

Some answers

In answer to a number of questions on this thread. Source is the "Ample Power Primer."

1. Voltmeters as source of understanding state of charge. They simply can't be used as a reliable source of information when the battery is being used. When there's a load on the bank, the voltage dips.

[FONT=&quot]During discharge, battery terminal voltage is not a valid indicator[/FONT]
[FONT=&quot]of remaining capacity. This fact rules out the voltmeter as an[/FONT]
[FONT=&quot]accurate gauge that tells you when to stop discharging and start[/FONT]
[FONT=&quot]charging. Only when a battery has not been charged or discharged[/FONT]
[FONT=&quot]in the last 24 hours, can voltage be related to state of charge. A[/FONT]
[FONT=&quot]fully charged battery will show a voltage of about 12.8 after being[/FONT]
[FONT=&quot]rested for 24 hours. A battery with a 50% state of charge will exhibit[/FONT]
[FONT=&quot]a voltage of about 12.2. These values are general and do vary[/FONT]
[FONT=&quot]somewhat from manufacturer to manufacturer.[/FONT]
[FONT=&quot]With only 0.6 Volts between a fully charged battery and one 50%[/FONT]
[FONT=&quot]discharged, it should be apparent that inexpensive analog voltmeters[/FONT]
[FONT=&quot]are not accurate enough to be meaningful.

[/FONT]
2. Amp Hour meter advantages: Most folks simply don't know. Meters help inexperienced users. It extends battery life by adding knowledge. Maybe a bunch of us here know how to do this, but the folks asking the questions may not yet be up to speed. Bill's an example of someone who knows. His boat, his choice. It's not for everyone. We're simply trying to help with what now are relatively inexpensive battery monitors. I paid a LOT more for my Link 2000 13 years ago than a Victron costs now (2X as much!). I have also posted many times before about how I should have installed it earlier than i did. It should be among the very first things folks install, after they get as big a house bank as they can (unless they're marina hoppers). The cost of one Victron is maybe two batteries. Extend the life of your batteries and you get an instant payback.

[FONT=&quot]Amp–hour instruments are available in a wide range of capability[/FONT]
[FONT=&quot]and price. Not everyone needs the same level of capability, but[/FONT]
[FONT=&quot]many people select a less expensive unit because they don’t understand[/FONT]
[FONT=&quot]battery capacity, and think that a simple meter may suit their[/FONT]
[FONT=&quot]needs.[/FONT]
[FONT=&quot]The opposite is true. A true battery expert can usually manage a[/FONT]
[FONT=&quot]system quite well with just a voltmeter and ammeter. Adding a[/FONT]
[FONT=&quot]simple Amp–hour meter to such a system may seem like a luxury[/FONT]
[FONT=&quot]to the expert. On the other hand, a user not intimately familiar with[/FONT]
[FONT=&quot]battery characteristics needs an Amp–hour meter that not only displays[/FONT]
[FONT=&quot]linear Amp–hours consumed, but also Amp–hours remaining,[/FONT]
[FONT=&quot]which compensates for the rate of discharge.[/FONT]
[FONT=&quot]The more expensive meters often include regulation and[/FONT]
[FONT=&quot]control options, alarms, and other features that makes their higher[/FONT]
[FONT=&quot]price warranted by the value they offer.[/FONT]

3. Why not keep on float?: Because most folks do not equalize their banks, and many do not know it even exists!

[FONT=&quot]Liquid electrolyte batteries that have been floated at a low voltage for[/FONT]
[FONT=&quot]long periods need to be periodically equalized. Equalization is the[/FONT]
[FONT=&quot]process that equalizes the specific gravity in all the cells. Basically,[/FONT]
[FONT=&quot]equalization amounts to a controlled overcharge.[/FONT]

 

[Bill Roosa]

Hey Stu
read the document, it explains all the voltage drop due to load/charging.

I would have to agree with para 2, I'm always trying to help folks be less amacherish amd more of an expert, it's safer that way.

 

[Stu Jackson]

Stu
How many systems do you have that cycle on and off? Reefer, freezer (5 amps effective at 90 deg F), fresh water pump (<2 amps for <15 minutes a day ---> <<< 1AH so ignorable), ....thinking,.... thinking... Autopilot? Not really a cyclic load but close enough. Assume worst case of rough seas and high response rate and the manual gives 4.5 amps effective draw.
A casual examination of the situation is while there may be "lots" of cyclic loads they are not very big so you don't have to manually calculate them. The reefer and freezer are far and away MUCH larger loads.
My engineer sense tells me that you can ignore the small stuff and focus on only the top few and get sufficiently accurate results. So if the batts get low turn the reefer off. WOW! That is complicated.

Bill,

It's not that complicated, and I assure you, I can handle it. You and I have been proponents of energy budgets for as long as I can remember on this forum, and have shared our experiences many, many times. You offer your spreadsheet, and I link to mine quite a lot (http://c34.org/bbs/index.php/topic,3976.0.html). I've also shared this experience: http://c34.org/bbs/index.php/topic,6353.msg41471.html#msg41471

I KNOW, and you know, it's easy to figure what comes out. It's what goes back in that's harder, way harder, as Maine Sail's excellent Battery Acceptance topic clearly shows: http://forums.catalina.sailboatowners.com/showthread.php?t=114054

I've summarized a lot of this in my Electrical 101 Topic: http://c34.org/bbs/index.php/topic,5977.0.html

Most people use their boats on weekends and plug in all the time when they leave their boats. I see that as a possibility of a fire waiting to happen and don't find it safe. And being plugged in all the time without equalizing their batteries is simply KILLING their expensive investments!!!

While I have a very nice slip with all amenities, I work my boat as if it was on a mooring, like others who contribute here. I fill up my batteries when I return (my Link tells me when), and I unplug and let the solar do the rest when I'm away.

Tim has a different use for his boat. And does things differently.

But all have the same goal: a reliable, consistently trustworthy SYSTEM that works for us.

I'm not saying you're wrong in how you do what you do. All I'm sayin' is that most folks do NOT have your experiences and that there are instruments on the market that are cheap compared to the cost of replacing batteries simply because of lack of knowledge.

We can't make people even buy voltmeters and ammeters, or even begin to make them learn how to use them.

We can, however, offer them INFORMATION to allow them to make their own choices.

That's all.

 

[Bill Roosa]

Hey Tim
I cought that after I posted, sorry for the confusion.
I would note that the guys that sold you the batteries sell batteries for a living. They probably have kids to put through college and would like you to help with that endever. Another way of saying that is they don't want your batteries to last forever.

 

[Bill Roosa]

I'm hip Stu
I don't care one nit if folks want to buy a monitor.
However, it is my belief that most of us want to become the best sailors we can and be proficient in the basics at the very least. Keeping the bats charged up is one of those basics and I would be remiss if I didn't offer the simple solution presented.

For the record if you are going to have an argument (discussion type not mean type) you HAVE to have someone taking up the counter argument. I find myself arguing a lot of stuff that I personally don't even agree with just to support the discussion and tease out the real topics. Sometimes this comes off as, well argumentative. I assure you I have a very thick hide and don't take any of it personally, pretty sure you don't either.

 

[Stu Jackson]

Thanks, Bill, I understand, and it brought out some more good links for everyone.

 

[Tim R.]

Hey Tim
I would note that the guys that sold you the batteries sell batteries for a living. They probably have kids to put through college and would like you to help with that endever. Another way of saying that is they don't want your batteries to last forever.

Hmm, that sounds a little like an insult. I think I can tell the difference between marketing hype and good support.

Companies with good products and excellent support do not need to lie about how to destroy their product. What do you think is better? I kill my Lifelines in 3 years and buy someone else's batteries or they last 5-6 years and I buy more Lifelines. Lifeline has been around for a while.

You never answered my question. Would you use a battery monitor if it were free?

 

[Maine Sail]

Worked on a boat yesterday with no battery monitor and an owner who swears he "knows" how to read his "volt meter". Bank is less than two years old and ready for the lead recycling bin....

Measured it with resting OCV, a load test and capacitance tester. Alternator putting out 8 amps and is a 55 amp. Alternator wiring and sulfation issues that will get corrected. A $158.00 monitor would have alerted this owner to these issues two years ago before ruining nearly $450.00 in batteries, the "volt meter" did not..

He swore they were full because he ran the motor for two hours last weekend. Bank 1 at 11.7V (resting OCV) and bank 2 at 11.9V (resting OCV). Neither bank could support voltage under load test and both banks came it at less than 30% of CA using a capacitance tester.