In Part 1 we chose the best type of monitor for each of us (voltage measuring or amp hour counting) and in Part 2 we selected an amp hour counting monitor from Victron for us control-freak nerds.
Now, in Part 3, I’m going to take a deep dive into how to calibrate and use an amp hour counting monitor.
We Got Work To Do
But, wait, these are pretty sophisticated devices. Surely we can just install them and read the state of charge of our battery right off the dial?
Sadly, not. In fact, the biggest bitch I hear about amp hour counting monitors is:
The state of charge is never even close to right.
That’s bad enough, but I’m also betting there are a lot of cruisers out there managing their batteries based on false readings from their battery monitor because they are not even aware that there’s a problem in the first place.
So what can we do about that?
Well, I have good news and better news:
- The good: the monitor isn’t broken.
- The better: we can achieve acceptable accuracy fairly easily.
And, even better yet, in so doing we will often improve the efficiency of our electrical system and extend the life of our batteries, too—talk about a win, win, win.
Let’s dig in:
Hi John,
very useful as usual, thanks. Which values should I use for my 24V system?
Hi Roberto,
Good question, I should have covered that. I have now added a paragraph for 24 volt systems.
Hi John and all,
I have been gearing up to upgrade electrical monitoring recently as my venerable Link 20 has been giving signs that its days working may be coming to an end. For almost 20 years it has been giving me accurate readings of voltage and amps in and out and, early on when I paid attention to it, SOC.
I am pleased that your researches in instrumentation in this area match what I have been leaning toward, and appreciate the added details and the thinking considerations that you include in your reports.
I have gravitated over the years of living aboard to what I think of as a seat-of-the-pants appraisal of SOC. I probably check, takes but a second, the v and amps in/out at least ½ dozen times a day which gives me a picture of the moment as well as a sense of changes over time. For years that was in conjunction with the “amp counter”/SOC capabilities of the Link 20, but gradually I stopped using these capabilities (too fussy and I felt they did not contribute much) and just used v and amps in/out and my multiple checks a day to guide me.
It is my take, subjective as I know it to be, that I my seat-of-the-pants assessment of SOC is not far off while also clear that I have little in the way of base line for this assessment. I will be interested to see, with the new equipment, if they do actually contribute in a substantive way to my battery management.
My best, Dick Stevenson, s/v Alchemy
Hi Dick,
No question that an experienced boat owner can develop a very good “seat or the pants” feel for the state of things, not just batteries. That said, the problem with that approach is that it gives very little real hard data about how batteries and the associated system are doing over time.
So, for example, after getting our monitoring right, in the last couple of seasons I have learned a huge amount about how a batteries charge profile changes over say a week at anchor with no full charges. And that in turn has allowed me to fine tune my alternator voltage regulator to take care of the batteries in a much better way and also means I’m considering adding a small amount of solar for top up. (More on both in future posts.)
This stuff is subtle and only becomes apparent with reasonable accurate measurement.
So I guess what I’m saying is that I think a lot of owners have, in effect, given up on measurement because of the issues I outline above, and gone seat of the pants, but would be better off with accurate measurement. And further, as owners add other charging sources like solar and wind, real SOC information becomes ever more important if they are going to get their money’s worth. I would venture to guess that the vast majority of renewable owners who will tell you that their batteries are charged every day are mistaken due to a seat of the pants approach and the inaccuracies I detail above.
And finally, my recommendation for those who don’t want to get the monitor accurate, is just go with the voltage measurement device I recommend in Part 1. Point being that really getting the best out of charging sources and batteries takes effort and calibration. For those not willing to do that work (nothing wrong with that) we now have a better solution in the form of the Balmar Smartguage.
Hi John,
Agree with the above. I will be curious about what I learn from the new instrumentation and how it changes my patterns.
Thanks, Dick
Hi John,
Great series of articles on monitors. We have the original 702 monitor (non-Bluetooth) connected to a Victron Color Controller, I can’t find where to enter the settings you recommend. I understand the picture you show of your settings is on the app on your phone, but can’t I set ours up the same way, just through the device itself or through the controller?
Hi Bob,
Yes, you can set all of these setting directly on the unit.
Hi John,
First off thank you for the very informative articles. Putting into practice what I learnt here has probably saved me thousands of € and ended up with a much better and reliable boat in the process.
Out of curiosity what made you opt for a “traditional” amp counter vs the Bamar/Merlin Smartgauge ?
Regards
Patrick
Hi Patric,
I cover that in part 1…and I’m a nerd: https://www.morganscloud.com/2018/08/13/battery-monitors-part-1-which-type-is-right-for-you/
In part 1 you made a good case for having both types of monitor – I’d come to same conclusion myself and have BMV-700 and SmartGuage. Very simply I use the SmartGuage to tell me how depleted my batteries are, and the BMV to indicate rate of discharge (or charge).
Can I just rely on the SmartGuage to give confidence that I’m charging to 100%?
Nick
Hi Nick,
I think for day to day monitoring and assessing state of charge and when to recharge the SmartGuage should be just fine. But for doing things like reprogramming a regulator and assessing whether or not a battery is sulphated and needs equalizing (post coming), the Victron will be better, so you definitely have the best of both worlds.
Hi Again Nick,
What would be interesting to know is when charging at full acceptance voltage (about 14.4) what the amps going into the battery are at the moment the SmartGuage clicks over to 100%. If the answer is .5% of battery capacity, then you could totally rely on the SmartGuage to assess 100% charge. But if the amps still going in are higher, the answer would be no. That said, as I said above, even so, the SmartGuage would be good enough for day to day decisions on when to charge.
John – thanks for your thoughts… looks like some careful observations around the 99-100% transition on the SmartGuage are needed!
Nick
Hi Nick,
I would be really interested in hearing the result.
I think something is missing: what if the batteries you are using with the brand new installed monitor are not new ? Chances are that they do not have the announced capacity any more. How can we get a good idea of the remaining total amp/h of our battery bank ? This matters, as we do not want to go below 50% of the real capacity too often ?
Hi Phil,
I had to cut it off somewhere, but you are right if you want to get things really right. By the way, that’s part of why I put in the fudge factor of 55%.
Also, if you follow the instructions in this online book about fully charging and equalizing regularly, your batteries will stay close to full capacity for good long time.
See the Lifeline battery manual for how to do a capacity test: http://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101-Rev-E-Lifeline-Technical-Manual.pdf