I have a SmartGauge AND a good BEP battery monitor. I bought the SmartGauge because the BEP was becoming more and more inaccurate, up to 50%!!!! SmartGauge is not "snake oil", it does work, and it works much better than than the BEP now that my 10 years old Lifeline AGMs are losing some capacity.
If you search this forum there are lots of posts on SmartGauge, but lets try and make this a SmartGauge only post!
Why and how does SmartGauge work?
But the SmartGuage doesn't use a shunt - it monitors the battery voltage 1100 times a second - if you were doing that you would get a pretty good idea what you batteries were doing! It learns you battery status and becomes more accurate the more it "learns". You only have to tell it what type your batteries are, not their capacity, and it uses complicated algorithms to determine the State of Charge.
Why shunt Battery Monitors aren't accurate"
As useful as shunt battery monitors are, keeping the displayed Ah capacity and the actual capacity synchronised is one major problem with them.
There are many complicated reasons for this The battery parameters have to be correctly input to the software
. The capacity of the bank has to be entered. Peukerts constant for the batteries being used has to be entered. Also an accurate charging
Ah count is affected by the “efficiency” of the battery at accepting charge. Wet cells may be only 75% efficient whereas AGMs may be 98%. If all these values are not input correctly it will upset the Ah count accuracy. Batteries also have a self-discharge up to about 10% per month which the battery monitor cannot detect.
All of these values change as the batteries age. This can introduce large errors.
To increase their accuracy the Ah count must be reset to 100% when the bank is 100% charged.
The manufacturers Auto Re-sync default value may be set for example at a charging
current below 5 amps for 5 minutes at a voltage above 13.5 volts. These values are usually much too conservative, but they do want the battery monitor to reset earlier rather than never.
Ideally the proper values should be set so that the current is about 0.5 % of the battery capacity C at the battery absorption voltage of about 14.4 volts. This voltage/current is impossible to achieve as all regulators will have reset to a float voltage much lower than this long before the current has reduced to 0.5% of C.
There is also a problem with solar panels
that sometimes may not deliver a high enough current but may meet the Auto Re-sync voltage values. This will prematurely re-set the battery to 100%. This feature can be disabled completely by setting the reset voltage at something like 16 volts – which it should never reach. Then the Battery Monitor can be reset manually when the batteries are known to be fully charged.
Battery Monitor Installation Problems
Another big problem with battery monitors is that the shunt needed to measure the current is often installed incorrectly. It must be as close to the battery as possibly – usually on the negative post – and a new bus bar must be installed immediately after the shunt to take all the negative cables
. All other battery negative cables
MUST go via this bus bar. Often extra equipment
is added at a later date and the installer may well have followed the installations instructions to the letter and installed the new equipment
“directly to the battery”, but not to the shunt bus bar.
The starter battery negative must also be connected to the bus bar, not to a service
battery negative terminal. This error is probably one of the major causes of battery monitors not reading the charging amps.
With all these problems the military finally demanded more accurate battery monitors - so enter the SmartGuage. Nobody believed it could work, including the man who finally bought the company, MD at Merlin Equipment UK. Tests by Enersys who make Optima batteries found it to be unbelievably accurate.
It is so simple to install. Its downside is that it doesn't measure current so a separate cheap
digital ammeter/Ah counter should also be installed, just to keep an eye on all the systems.
The only problem I have found with it is that it shows 100% a bit too early - well before the a current of 0.5% of Capacity at >14.2 volts. As soon as it goes "off charge" it will correct itself. You'll see it drop from say 100% to 96%.