Digital Volt Meter vs Balmar Smart Gauge

Ward H

.
Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
I recently installed a Blue Sea digital voltmeter with a momentary battery selector toggle switch. My plan is to check the battery voltage when arriving at the boat, prior to turning on any loads, to check battery voltage/SOC. I'll keep in mind the elapsed time since the battery charger was last on or motor last run, to account for surface charge.
(I don't leave the shore power plugged in when not at the boat)

I believe this will give me an idea if I'm slowly discharging the batteries or if the 3/4 to 1 hour of run time the engine gets when I day sail keeps up with my amp draw while sailing.

I've considered the Balmar Smart Gauge, which I believe does the same thing but much more accurately. I just question if I need to spend the money on it considering my use of the boat.
I mostly day sail for 4 to 7 hours, 1 to 3 days a week. Average motoring time per sail is 3/4 to 1 hour. When sailing I use AP, Chartplotter, Depth, Speed, Wind, i70S and usually an iDevice is charging.

I do plan to leave the shore power plugged in overnight once every 2 or 3 weeks to completely charge the batteries to 100%, especially if I spend a night or two on the hook.

With the Balmar Smart Gauge costing about $50 more than my house bank of two GC2 batteries, I question the value added by installing one.

Appreciate your thoughts on this.
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
I think you have a couple of ideas compressed into one which brings confusion.
Firstly, the Balmar Smart Gauge (BSM) and the Blue Sea Volt meter are like apples and oranges. While you may have arrived at a reasonable conclusion "the cost of the BSM is more than the value it serves in my case" it is not supported in the logic you explain in your question.
Some folk just want sensors to tell them everything about their boat systems. State of Charge, Voltage levels, Amp Hours being used, etc. Some folk need all this information.
Your assumption is that your sailing plan is:
  1. Day sailing with return to your dock at the end of each day.
  2. The dock provides an opportunity to recharge your batteries and your plan is to do this every 2-3 weeks.
  3. You will check your battery voltage level - and record it in a boat log so that your not relying on just memory.
  4. You will use your motor and will supply charging to the battery bank
  5. You do not know the Amp Hour usage of your systems used during sailing
  6. Your charting of the voltage levels will tell you the status of your battery bank.
The issue is you will not be monitoring the actual consumption of AmpHrs compared to the AmpHrs supplied in your charging process. So while you can in general understand if the batteries are Alive or Dead you will not have the data to know the State of Charge (SOC) of the battery bank.

You can approximate the SOC if you do hydrometer testing on the battery bank.
You can calculate the approximate SOC if you know the time and AmpHr usage of your systems less the time and AmpHr charging rate of your motor.

Or you can buy hardware to do this for you.

In reality you are not relying heavily on your Battery Bank like a full time cruiser. So your conclusion may be enough to meet your sailing needs and save you a few bucks for beer and cross country adventures.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Ward, I think the value is in accuracy.

When you get done running the engine, the battery voltage will be higher than it will be at a resting state 24 hours later. That will make comparisons difficult.

A slightly less expensive alternative is a Victron Battery Monitor. The monitor shows whether current and how much current is flowing into or out of the battery and has an amp counter. This will be more accurate than simply looking at the volt meter at the end of the day, but not as accurate as the Smart Gauge. MaineSail has written about this on his site.

Installing A Battery Monitor and Making Your Battery Monitor More Accurate
 
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Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
It's amazing how we all survived and enjoyed boating before battery monitors
So true. Some folk still do. It all depends on what you are doing with your boat. And maybe the cost of your batteries. Some folk want to get the maximum service out of their battery bank, and some look at batteries as consumables that will announce when they need changing. At which time the owner just BOAT's.... breaks out another thousand.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
It's amazing how we all survived and enjoyed boating before battery monitors were marketed. We never knew how indispensable they are :banghead:
All depends on what sort of electrical demands you have. On my 30 I only had a VHF, some lights, and an auto helm. Battery SOC was not a big deal and I was only out ~$80 if the group 24 died.

Now I have refrigeration, radar, chart plotter, AP, AIS, the demands are much higher. With a $450 bank of batteries, I want them to last as long as possible. SOC and charging become important.
 
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Oct 29, 2016
1,915
Hunter 41 DS Port Huron
Nah, I went with the SG200 it has prettier lights on it...... but there is an idea I could add the Victron next to it :rolleyes:
 
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Oct 26, 2008
6,044
Catalina 320 Barnegat, NJ
It was the banging head that got a "like" from me. Thanks for the laugh!

@ward, something tells me that you really don't need the monitor. I have one but it probably has been relatively useless because I have yet to calibrate it correctly and I've been killing my batteries anyway. I do routinely read the voltage so I pretty much use it the same way that you would be using the voltmeter.

That said, I'd guess that you would get frustrated if you didn't know what was going on behind those voltmeter readings, especially if you got a variety of readings at various times that you couldn't explain. Perhaps, you would simply find the same voltage readout every time you came back to the boat after leaving her for a few day, so there would be little need to monitor amp usage. There is probably no harm in adding a monitor in the future if you find that you need more data just to satisfy your curiosity. I image that the thought is in your head that you want to know the history of your batteries by starting when they are new.

BTW, are you considering Balmar because it doesn't require a shunt? If you got the Xantrex LinkPro, you could show me how to properly calibrate it! (always thinking of my own self-interest) :cool:
 

TomY

Alden Forum Moderator
Jun 22, 2004
2,758
Alden 38' Challenger yawl Rockport Harbor
So true. Some folk still do. It all depends on what you are doing with your boat. And maybe the cost of your batteries. Some folk want to get the maximum service out of their battery bank, and some look at batteries as consumables that will announce when they need changing. At which time the owner just BOAT's.... breaks out another thousand.
I'm one of those, our boat uses minimal storage (no refrigeration). Our house bank batteries are still about $100 a piece (grp 27). I get an average of 5 years over the last 20-30 years and two boats. Many people would use these batteries for another season or two but we've been at our maximum needs of the small bank so I change them once I think they're failing.

As to failing; we've usually left our boat for a week or more on a mooring between uses and everything is turned off at the battery switches.

I'm confident of that resting period so that's the only time I check the voltage of each battery. I'm using the same digital voltage meter I bought 30 +- years ago, from an electrical supply (meaning I thought it was a decent one).

Testing on a 100th's setting, I get a good feeling of their state of charge and age, in relation to engine charging.

I don't think my digital gauge gives me a reading that would be of much use - by itself. What it gives me is a floating number that I can compare to previous numbers (I'll jot them down), that tell me, my battery is giving notice.

Last time I replaced the starting battery (separate), I went with one of the dual purpose (which I've read is a lot of bunk?). Anyway, that one is lasting longer that previous typical cheap grp 27 deep cycle. May get 10 years.

Too much information, in the wrong hands (which could be me), could be a worse method. :)
 
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Sep 25, 2008
7,075
Alden 50 Sarasota, Florida
So true. Some folk still do. It all depends on what you are doing with your boat. And maybe the cost of your batteries. Some folk want to get the maximum service out of their battery bank, and some look at batteries as consumables that will announce when they need changing. At which time the owner just BOAT's.... breaks out another thousand.
I often wonder if there is any correlation between service life and the machinations some go through to maximize it. I read the advertising too but wonder how much effort, time and money is spent vs. the benefit derived - for my case, it's likely the difference between replacing batteries this year or next year.
 

Ward H

.
Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
What started me off on this project creep was changing from a battery management practice of using house for starting and house loads and keeping the other bank as an emergency reserve, to isolated banks for house and starting by installing a DCP switch. I did this because despite having a 220Ah house bank and 14 awg wiring to the AP and chart plotter, I would get instrument drop out when starting the engine while sailing.

I had the digital voltmeter already so I installed it so I could do a quick check of battery voltage in both banks when arriving at the boat in the morning. Basically a "Yep, neither battery died since the last time I was here" type of thing. If one looked unusually low I'd pull off that battery's negative cable and put the battery switch in combine for the day.
I figured I could compare it to this chart that Maine Sail has posted in the past.
Battery SOC at Resting Voltage and 80f (Source Trojan Battery)
100% = 12.73
90% = 12.62
80% = 12.50
70% = 12.37
60% = 12.24
50% = 12.10
40% = 11.96
30% = 11.81
20% = 11.66
10% = 11.51


I thought about an Ah counter like the Victron monitor but a device that requires Maine Sail to write two articles on how to program it to make it accurate is really more complicated than I need to get into. And to keep it accurate you need to adjust the settings yearly depending on the age of your battery bank. A little too complex for me.
The simplicity of the Smart Gauge install and programing is what made me think about it.

I hadn't considered the SG200. If that is simpler to set up and maintain, I'll consider it.
 
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Ward H

.
Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
That said, I'd guess that you would get frustrated if you didn't know what was going on behind those voltmeter readings, especially if you got a variety of readings at various times that you couldn't explain.
There is that.
 
Apr 22, 2011
865
Hunter 27 Pecan Grove, Oriental, NC
Balmar came out with their first battery monitor in the early 90's when I was equipping our boat for, as it turned out, a six year cruise of the Caribbean. Being a gizmo loving kind of guy, I bought the monitor and shunt and also a 100amp Balmar alternator. They both performed perfectly, but I found myself after a year or so making charging decisions based solely on battery voltage. The lowest voltage would occur first thing in the morning because of the frig running all night and lack of solar input. If it was 12.2 or higher, there was no reason to run the engine for charging as the solar would top it off during the day. 12.1 run engine for 30',, 12.0,, run a little longer. After many cycles I got to know the batteries and it didn't seem necessary to refer to the monitor.