Is Your Battery Monitor is Accurate..?

dparilla · Feb 23, 2015

Great write up, as usual. Thanks for sharing!

Solstice · Feb 23, 2015

Excellent write up MS. It's great that you put everything related to this topic in one place. Unless you followed this topic over the years through the various threads, you can see why there are so many myths and misinformation that gets repeated over time. Had a similar conversation with the President of Rolls Battery over the weekend and he said he can only roll his eyes when he hears some of the stuff that comes from customers regarding monitoring batteries....

Well done!

Bad Obsession · Feb 23, 2015

That is some complicated stuff! I had a link 10 on my Catalina 30 and I would imagine that it was never right!

After reading that I may just hold off for a while and buy a smart gauge. That seems like a better set-up for me.

Good article....I bet Mainesail has nightmares about battery banks, battery monitors, and Perk's exponent. LOL

CYQK · Feb 24, 2015

Thanks Maine smart article!!!!

weinie · Feb 24, 2015

Wow! It almost seems that the way people have been using these battery monitors that they might have been just as well off if they never even used one (and a few dollars richer to boot)!

Prime Time · Feb 24, 2015

It seems that doing a capacity test is a real pain in the butt. I have 5 batteries wired in parallel and it would be a lot of work! Great article and I enjoyed reading about the smart gauge too. Maine Sail, Can the traditional link monitor when also used with the smart gauge give you an insight into true battery capacity? Start with full charged batteries. Start with an assumption of the bank capacity. Add a DC load at the assumed 20 hr amp hr rate. Do it for 1 hr. See what the smart gauge says the SOC is. If your actual capacity is less than assumed, then the SOC as a percent will be lower than predicted. You now have the ability to calculate a new assumed capacity which won't be exactly accurate because it was computed at a higher than the 20 amp hr discharge rate. Repeat the test using the new assumed capacity. Keep repeating and the assumed will approach the actual minus the amps pulled during the testing. Or one can recharge between tests.

gettinthere · Feb 24, 2015

Thanks RC. I will definitely overide the auto feature.

I was surprised at how little specific gravity played into this dissertation. I was expecting or hoping that sg could be used to cross check soc or something similar.

Don Lucas · Feb 24, 2015

I'm positive that my BM is programmed correctly except for the real AH of the batteries. I just am not going to be constantly testing the batteries to find the true AH capacity. So far as I'm concerned the BM is only good to tell you the AH out of it, the voltage, and the current. After that you have to guess at the SOC based on those three.

But I think that is probably enough as long as you understand.

Otherwise it is time to add a SmartGage to your system.

Stu Jackson · Feb 24, 2015

Don Lucas said:
1. After that you have to guess at the SOC based on those three.

2. But I think that is probably enough as long as you understand.

3. Otherwise it is time to add a SmartGage to your system.

1. Most algorithms on BMs have a choice to readout SOC, usually in %s. RTFM (Bruce, F stands for Funny!

).

2. Yes, and see #1, too.

3. If you don't want a counter, then get one.

In another recent thread, one of our skippers made up an app for an energy budget. Since the amp draw of most of the stuff we have on our boats hasn't changed in decades, there's no reason to either not use his app or do your own energy budget on a spreadsheet, like this one:

The All-Important Energy Budget:

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

What comes OUT is sooooo easy. It's what goes back IN when charging that is harder and where a Smart Gauge or BM really comes in handy.

Battery Acceptance by Stu http://c34.org/bbs/index.php/topic,4787.0.html

And here's another discussion on why overriding the auto reset feature is important. It reflects, in a somewhat different and much longer way, what Maine Sail wrote in his writeup.

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

http://c34.org/bbs/index.php/topic,4922.0.html

DEFAULTS are factory settings that are made to be modified to suit your setup.

All U Get · Feb 24, 2015

My brain can handle The Rube Goldberg SOC test. Do I just need the voltage at the battery posts? Now I just have to get the boat back to 75-80 degrees.

All U Get

dparilla · Feb 24, 2015

Battery Budget

Here is an old spreadsheet posted on the forums once upon a time. It is a great battery management starting point, and easy to adapt to your use.Battery Budget Spreadsheet

weinie · Feb 24, 2015

Maine,
Is there any advantage, other than price of course, to choosing one of these "Ah counters" versus the Balmar Smart gauge for basic, no frills SOC measurement? It would seem that the Balmar easily wins in terms of accuracy, ease of installation, ease of configuration, and ease of use.

weinie · Feb 25, 2015

Maine Sail said:
The benefits of an Ah counter are:

Lots of information, Amperage, Ah's consumed, Voltage and SOC (if programmed well), historical data, and a host of other nice to have items. They start at about $170.00 for a decent one though there are pretty crappy models for even less.

The benefits of the Smart Gauge:

Accuracy, simplicity, never having to re-program and ease of installation....

A lot of folks worry and ask about

"With the Smart Gauge I won't know how much I have left?"

and my response to most is;

"The programming on your current Ah counter is so bad you still have no clue how much you have left and may get to a point where you begin to over discharge your bank."

If you use a SG like the fuel gauge in your car you get used to it. "Oh gee I only have 1/8" tank, I know I can make it home."

Most times the car owner has no clue what 1/8 of a tank means, in gallons, (read Ah capacity) nor do they even know how many MPG their vehicle gets (read age fade) but they develop a feel for how long they can go........

There is no perfect battery fuel gauge. The Smart Gauge is the most lifetime accurate but it is simple so owners will have to choose which path they want to go down if they want a battery fuel gauge beyond a typical volt meter.

Thanks Maine.
I see a SG for me in the near future.

gettinthere · Feb 26, 2015

RC
Please clarify for my spinning head...

To disable auto synch I set VC, voltage charged to 14.6v. Is that all I need to change to disable auto synch?

Thanx much

E

walt · Feb 26, 2015

I have had a battery monitor for a bunch of years and it is still all I need. However, I never use that "capacity" function.. One reason is that I don’t trust it for all the reasons given in Maine Sails link but I also really never get my battery down below about 20% (which might be off by 50% but that still has a lot of margin).

The one function I wish the battery monitor did was to find the battery impedance (which the balmar gauge likely does). The main thing I would use this for is to just look at battery health when its fully charged. I usually can tell when the battery is getting worn out by noting an unusually high voltage drop when you put on a load or also the battery goes into acceptance limiting "too early" (based on your past experience) when trying to charge the battery. Both of these are the result of increased battery impedance. You can however manually use the battery monitor to get impedance and it’s simply R = delta V / delta I.. You can do this for any state the battery is in. Write down the V and I before you turn on some load and then the V and I after the load. Battery impedance is just delta V / delta I. Next time I get fresh batteries, I’m going to do this for the fully charged battery at rest, keep track of the number and maybe just re-do that test once per year. Unfortanetly I wont know what the results completely mean until I have done this over the life of a battery.

I like knowing the amp hours used by individual loads on the boat – which is what the monitor gives. The Balmar gauges doesn’t give this so I would still rather have the BM with its limitation on capacity accuracy. What would really be ideal is an instrument that both measured current (and integrated current) plus all the stuff the Balmar gauge does.

I am barely organized enough to add water to my batteries twice a year.. doing all of the below in addition for that percent capacity reading.. seriously??? And it will likely be inaccurate one year later..

Must Do Bare Minimum Programming Steps:

-Program Accurate Ah Capacity Of Your Bank (obtain through testing)

-Program Your Banks Peukert’s Constant (obtain from battery manufacturer or calculate)

-Program Your Banks Charge Efficiency (obtain from battery manufacturer)

-Program Your Battery Temp (Should be done at least monthly if temps change or use model with temp sensor)