Battery Monitors

[TBOT422]

Does anyone have any experience with the Balmar SmartGauge? I'm thinking about adding a battery monitor, but certainly get differing opinions from the 'experts'. The way I understand it, most conventional battery monitors measure charge and discharge current through a shunt device then 'count' Ah used. They then subtract this from whatever value you put in the system as you battery bank capacity. However the battery bank capacity varies over time and charge and discharge rates, so the accuracy of your state of charge can be woefully inaccurate unless you re-establish your actual battery bank capacity and reset the monitor on a regular basis. Apparently Balmar has developed a new SmartGauge http://www.pbase.com/mainecruising/smart_gauge. This device does not measure or have the ability to display charge or discharge rates, and somehow calculates state of charge magically through some sort of algorithm. Apparently it very accurately calculates state of charge with all sorts of batteries, new or old, and even gets more accurate over time as it's algorithm is 'self-correcting'.

My question is which approach is better, a normal Ah counter that accurately displays charge and discharge current, but is not reliable for actual state of charge due to changing battery bank capacity, or one that seems to magically determine state of charge, but does not provide information as to real time charge and discharge current? What is it more important to know, the state of charge or the charge/discharge rates?

Thanks

[R.B.]

I installed the BMV 600 series from Victron purchased from Jamestown Distributing. It also has an algorithm to calculate state of charge and also gives you Current in/out using a shunt. There is a very good writeup on installs here: http://forums.sbo.sailboatowners.com/sh ... p?t=125606 Also a more detailed version is on his site here: http://www.marinehowto.com/ click to the battery monitor install.

Sorry I don't have any experience with the Smart gauge but I am very satisfied with the Victron.

[TBOT422]

Ralph,

I was familiar with both of those links. The same author, Maine Sail, wrote both articles including the review of the Balmar SmartGauge. He is what raised my question as to what parameter is most important, current charge and discharge rates (Ah), or State of Charge. Typical shunt based battery monitors like the Victron unit calculate charge and discharge current quite well, but then subtract that from a baseline number you enter for the battery bank capacity to arrive at state of charge. Since you probably don't know what the actual battery bank capacity is as it changes as the batteries age and how they are charged and discharged, the state of charge information from this type of battery monitor could be woefully inaccurate. Suppose you had what you think are 600 Ah of capacity in your house bank and you consumed 150 Ah, the battery monitor would show a 75% state of charge. However due to age and other factors what if the actual capacity of your battery bank was only 500 Ah, the battery monitor would show a 75% state of charge, but you would actually be at 70%.

What is interesting about the SmartGauge is that it seems to calculate state of charge accurately regardless of battery age or condition, however it does not calculate charge or discharge current. Which resulted in my question: which parameter is more important to monitor while cruising? Accurately knowing the state of charge so that you know when the batteries need to be charged, or knowing how much net capacity you have used?

[R.B.]

That is interesting regarding the SmartGauge. I will have to look up some info on it. For myself, I leave my gauge on Amps in/out and occasionally check Amp hours consumed, for overnight, and State of Charge during the day since I have solar.