Super cheap battery monitor

[Bill Roosa]

More specifics

In my model I track:
a running total of AH into the bank
a running total of AH out of the bank
voltage history
current voltage
the current current flow
battery temperature

I'd use basic math and some sophistocated programing to evaluate the banks history in basicly the same way my brain does currently to come up with a state of charge.

I believe that the state of charge of a bank can be deternined once you start measureing stuff and paying attention to the charge discharge cycle. Basicly I intend to replace my anal monitoring of volts - amps - loads - charging with a program that does just that and accounts for the bulk - absorption - float isues of charging, the varance in capacity with battery temp, the varance in capacity with changing discharge rates, the battery internal resistance - AKA bat impedance and some other technical stuff. Knowing all the above and accounting for it as mentioned all i really want then is:
a) is the bank charging (i.e. solar - load = charge? or discharge?)
b) what is the current state of charge (so I know how far, based on past experience of looking at the thing, I can go.

If a fault (i.e. lots of AH in after float volts is achieved indicating a shorted cell as one simple example, or a loss of bank capacity based on AH out not being what i previously measured when the voltage got to some triger level being another) is found the an alarm is set and the user can "pull the codes" to see what the unit found. Perhaps an upgraded version would have some switching to stop the user from doing dumb stuff or keep dumb stuff from happening like my Cadillac turning off any thing left running 10 minutes after I get out of the car but that is down the road a piece.

I'd really like to keep the user interface simple as the cost of buttons and LCD screens and the problems with keeping them working and dry ...... really drive up the cost. I think I can build one for around $25 and sell them for $50

 

[Quoddy]

Battery Bug

Does it look like the Argus Battery Bug analyzer is a gimmick or could it actually tell you what it says it will? www.argusanalyzers.com

 

[Bill Roosa]

Battery bug

Well in theory if you record the voltage over time you can tell lots of stuff about a battery provided you know how it is being used. I suspect that batteries in cars see a pretty standard usage regiment. Start - recharge - alternator supports all loads while battery sits there - stop - battery stores power till needed.
just measuring the voltage over time could tell you a lot given that setup. It is a bit more involved when you try to run on batt power as part of the regime. I note that the cable does not have sensors on it and is not big enough to be a shunt so I'm thinking that this is an automotive only type solution. Course THEY would be my competition so take what I say with a grain of salt.

 

[Quoddy]

Deep cycle

I should add I was looking at the deep cycle version of the Bug.

 

[Bill Roosa]

battery bug

Looks the same to me. I'd have to conclude that it is a voltage monitoring type unit. You could tell lots of stuff about deep cycle batteries provided you understand how they are used. If this is an RV/ambulance type vehicle then that is a regieme that is understood. Cruisers don't operate there batt banks that way though. An RV/ambulance will bring it's batts up to full charge every time they drive it. Same with a power boat. Sailboats typically don't motor enough to do that when cruising.
FWIW

 

[Deadhead]

I wouldn't skimp on a Battery Monitor

Of all the upgrades to my last boat I believe the Victron Battery Monitor was the most useful. At less than $300 and about 4 hours to install it was a bargain.

I had made a spreadsheet that estimated my energy budget first. I calculated just under 150 amp-hrs/day. Not wanting to discharge more than 50% of the total charge a 300 amp-hr battery was dictated.

I simultaneously installed a 325 amp-hr wet cell battery with the monitor. Calibration was straight forward and the monitor gave a snapshot of the state of my battery at any time. This made time spent at anchor much more relaxing than when I had 2 Deka dual purpose group 27's as a house bank and a single dual purpose group 27 as a cranking battery and no battery monitor. As far as cranking & deep cycle vs. dual purpose I always felt that the dual purpose battery had the benefits of neither and the drawbacks of both.

The new boat has an incredible 800 amp-hrs of AGM battery for the house bank (the PO didn't skimp on anything!) with single AGM group 31's for cranking & the bowthruster. And my first upgrade will be to install a monitor.

Regards.
DH

 

[walt]

In fairness to the battery bug.. I will defend it a little bit..

It is doing something very different than just monitoring voltage (it is of course also monitoring voltage).

http://www.argusanalyzers.com/battery-monitors/technology/large-pulse-resistance.html

It periodically puts a very short duration load on the battery and in the short time frame is looking at the voltage..

Ie, it is measuring battery impedance. This of course is a key feature for motor starting in a car, but it is also an indicator of battery acceptance and when my batteries were getting worn out, I could definitely tell that the battery impedance had gone up. I don't know if this is true or not but argus would tend to indicate that battery impedance is also an indicator of how well a battery is charged.

In my opinion, I like what this device is measuring. As mentioned before, it has to be near the batteries - which I don't like only because the display is also at the batteries. But the display could be at the end of a long cable with with power and serial com (.. like a USB cable)

 

[Witzend]

Why not use a modified version of a specific gravity meter where the float is connected to a position sensor integrated to one of these devices:
http://www.allegromicro.com/en/Products/Categories/Sensors/currentsensor.asp
After all, we're really just interested in is the level of ions in the electrolyte anyway. The higher the level the denser the electrolyte the greater the state of charge.

 

[Quoddy]

Load test

Do all battery monitors work on load testing in some way to determine power available or do you think this is just a cheap shortcut?
It seems Argus uses this method. The following is a quote.
“Argus LPR technology draws a large load current pulse from the battery for a very short period of time and simultaneously measures the voltage of the battery. Using Ohm?s law (V = I*R), the tester directly measures the DC internal resistance of the battery.
The internal resistance is correlated to a cold cranking amp (CCA) value for a particular battery and state of charge. As internal resistance increases, the battery's CCA decreases.”

 

[druid]

Voltmeter, Ammeter, and Turkey-baster hydrometer. All you'll ever need. My GPS (Garmin 420S) displays voltage: useful to see if your alternator is charging (voltage goes up when I start the engine).

druid

 

[Stu Jackson]

Ie, it is measuring battery impedance. This of course is a key feature for motor starting in a car, but it is also an indicator of battery acceptance and when my batteries were getting worn out, I could definitely tell that the battery impedance had gone up. I don't know if this is true or not but argus would tend to indicate that battery impedance is also an indicator of how well a battery is charged.

In my opinion, I like what this device is measuring.

Walt,

Impedance, schimpdance.

The very best way to know your batteries are becoming toast is by YOU putting a REAL load on them, like a few lights or a fridge, and seeing what happens to your voltage. In fact, Rich Stidger did just that with his batteries until he understood and I summarized and distributed "The GOTCHA Algorithm" to avoid undercharging his batteries. What he saw was a rapid drop off of voltage when a real load was applied.

Now, you might say that turning on loads is exactly what the Battery Bug does.

So, why spend one penny of your hard earned $$ to have a volt meter with pulses do exactly what you could do for free?

OTOH, a battery monitor, measuring amps in and out over time is something you CAN"T do in your head (amps out maybe, I am quite good at that, but amps in with battery acceptance is downright impossible for any human on a recreational boat).

Deadhead got the idea right: do an energy budget, size the house bank properly, monitor it.

I'm not sure about how specific the bug can get for that all-important last 10 to 15% of charge to bring the bank up to 100%, that last hard part to get charged if it's only giving % readings itself.

I still don't understand folks' reservations about something that actually does work: the battery monitor. I'm not saying everyone ought to have one. But they have been proven to be really helpful to sailors who may be somewhat less knowledgeable about electrical systems. They aren't a "battery fuel gauge" as some used to think, and require some understanding of how they work. But what's so wrong with that? Increased knowledge is always helpful.

The Battery Bug is simply a gimmick being peddled to sailors.

 

[walt]

The very best way to know your batteries are becoming toast is by YOU putting a REAL load on them, like a few lights or a fridge, and seeing what happens to your voltage.

I don't know if the battery monitor does a better job at measuring impedance or not than putting on real load - please explain how you arrived at your conclusion. Do you keep a calculator handy so that you know the real battery impedance and so that you can compare values when the batteries were new vs old? What if I don't have a fridge (and probably never will)?

Note also that the battery bug is only consuming about an average of something like 1 ma to continually measure the impedance (the big pulse averaged over time is about 1 ma). Another thing I like about this method.

Note - Im not arguing that battery impedance is better than knowing amp hours (in case you wanted to argue that). It is something that I would like - but Im not sure how much I would spend to get this measurement.

 

[walt]

Argus LPR technology draws a large load current pulse from the battery for a very short period of time and simultaneously measures the voltage of the battery. Using Ohm?s law (V = I*R), the tester directly measures the DC internal resistance of the battery.
The internal resistance is correlated to a cold cranking amp (CCA) value for a particular battery and state of charge. As internal resistance increases, the battery's CCA decreases.”

Quoddy, I think your assessment is correct above.

I could be wrong about battery impedance but I think it is possibly is a more valuable parameter regarding battery state than simply watching amp hours. When batteries are new, you can tell what reserve you have based on amp hours. But as the batteries age, amp hours used tells you less and less about actual capacity - as I personally found out.

But amp hours is still the best for understanding what the loads in your boat are doing over time.

 

[lehighsail]

Wow, my head is spinning like an electric meter. Could someone suggest a link that would explanin volts, amps ah etc and their relationship to each other and why I need to know each and the value of each? Thanks so much. I have a monitor on the boat but really don't know how to read it.

 

[Bill Roosa]

My point (and audience) exactly!!!

There are lots of folks that even if they have a battery monitor don't really know what they are looking at. Not very useful to know AH into the battery if you don't even know about bulk-absorption-float stuff. I think most just want to sail and not have to deal with engaging their brain in that fashion. I know I only do it because I have to.

I'm proposing a computer chip that does all that stuff for you and converts it to a "fuel gage" type output AND monitors the bank for faults like over-under charging, shorted cells, battery life left ......

Now if we could get back to the initial purpose of the thread??!!

How big (AH) is your battery bank?
How many house banks do you have? (assume one start battery)
How far is it from your house bank to the nav station? (wire is very expensive I'd like to reduce the length to a minimum.)
What is the max current flow into and out of the bank?

Thanks Mainsail for your input

 

[Bill Roosa]

Answers to questions in the thread

How could you not know if the batteries are discharging if you have an amp meter?
I know most inverters and electric winches/windlasses connect directly to the batteries. Most ammeters only show panel (load) amps and they do not tell you anything about production amps. So the situation arrises where my solar panels are putting current into the batteries but not through my panel ammeter while my inverter is taking them out also not through the panel meter. Is my battery charging or not? The only way I can guess at it is to monitor my battery volts. You do get proficient at it but I'd rather be sailing!

Battery impedance is just internal battery resistance. It is a very good measure (if taking in a historical context) of how much life the battery has left in it. An increasing impedance over time (a number of mesaurments all taken at full charge) means the batts are on their way out. Plot those data point against time (sort of it gets technical, Use would be a better term) and you get a graph that will develop over time an inflection point (a knee) where the rate of change of impedance dramaticaly increses. That point is when you start loosing capacity fast enough to think about having a spair or replacement. Don't try using a ohm meter to measure your batteries it don't work that way. You have to supply a known, largish load for a known length of time and measure the voltage drop. As some will remember a voltage drop is due to resistance, battery internal resiatance akd impedance in this case. If you wanted to you could turn on a load when the batteries are fully charged and then measure the voltage drop as seen from the panel amp and volt meters. You are looking for the initial drop to a stable voltage.
Course you don't HAVE to do it at full charge but the math gets pretty complicated and who would want to write all the data elements (some of which you don't even know but could guess at) down then compile them every so often..... Lets go sailing instead and buy a device that does this for me.

 

[arghhh]

Walt,

Impedance, schimpdance.

The very best way to know your batteries are becoming toast is by YOU putting a REAL load on them, like a few lights or a fridge, and seeing what happens to your voltage. In fact, Rich Stidger did just that with his batteries until he understood and I summarized and distributed "The GOTCHA Algorithm" to avoid undercharging his batteries. What he saw was a rapid drop off of voltage when a real load was applied....

...The Battery Bug is simply a gimmick being peddled to sailors.

Battery impedance (or ohmic value) is the de facto standard to detect and trend failing and bad batteries. Low voltage can lead you to a battery but a good battery tester can tell you exactly how bad it is. Combine this with impedance trending and you can predict a failure before it happens. A cheaply made gadget may not really work better than YOU paying attention.

Most good quality testers like an Alber Cellcorder or Midtronics are thousands of dollars. I doubt the Battery Bug is something I would bet my life on. Since the quality testers are really out of the range of most of us, Stu gives good advice. Like Stu suggests I would load them up with a static load and observe the voltage.

If you really want to monitor your batteries real time, invest in a cellwatch system. Although just running the system will probably blow your energy useage out the window

 

[Stu Jackson]

Boat Electrical Simplified Links

Wow, my head is spinning like an electric meter. Could someone suggest a link that would explanin volts, amps ah etc and their relationship to each other and why I need to know each and the value of each? Thanks so much. I have a monitor on the boat but really don't know how to read it.

Try the West Marine Advisors: http://www.westmarine.com/webapp/wc...51&catalogId=10001&page=West-Advisor-Articles Read the DIY articles, too.

BoatUS has a bunch of Don Casey articles that are good.

An since you have a monitor, read the Gotcha article Rich & I wrote: http://c34.org/bbs/index.php/topic,4922.0.html