Using a Battery Monitor

[Matlock]

I was fortunate when dipping my toes into the ice water of house batteries to take the advice and understand and buy a good informative battery monitor. I chose the Trimetric 2030R.


The other option was the Victron BMV 700 series, if I remember right.


They are priced about the same @+ - $150.00
And I know the Trimetric requires a Shunt and I believe the Victron needs the same.

(Can't inset another pic, I'll add to this page.... )
This is a 500A DC shunt, another $35-$40. Battery neg in and out of shunt, small wires included to wire to the monitor and to your battery + terminal.
I've never set up the Battery % Full setting in the Trimetric, I use the at rest Voltage reading and the in - out amps when charging or consuming power.

With all the confusion around power I'd highly recommend adding one of these into your budget.

If anyone has another option with a read-out, please feel free to add to the thread.

my disclaimer... no affiliation with product etc, etc. just a user.

 

[Matlock]

Shunt


This is a 500A DC shunt, another $35-$40. Battery neg in and out of shunt, small wires included to wire to the monitor and to your battery + terminal.

 

[B and C]

I have the Trimetric 2030-RV with a 500 amp shunt. It has a little smaller footprint.

When you tell the monitor how big your bank is, it will give you a percent full reading. This is one of its' biggest features and one I use all the time. This will tell you when the batteries are full. This is how I know to start charging other stuff. Reading voltage is a very poor indicator of charge. It also has the nice feature of connecting to your engine/starting battery to display its' voltage too. I step through all the displays several times a day. The engine battery monitor is nice so when you try to leave you don't discover your starter battery is dead.

I also have the shunt connected to my solar charge controller (CC) so CC knows what is going on and doesn't use a timer. I use end amps to tell the CC when the battery is full.

 

[WalkaboutTed]

My BMV-700 came with the shunt.
Ted

 

[jonyjoe303]

those who don't plan on using 500 amps and don't want to spend 150, there is the tk15 you can find on amazon for 28 dollars. It comes with a shunt only rated for 50 amps. I use it on my lifepo4 for the past year. Any battery monitor that can count amps in/out is better then no monitor especially on a battery like lifepo4 where the voltage is same for the majority of the time. But any battery well benefit. If you know you used 20 amps the night before, then the following day you know you need to at least put those 20 amps back, with these meters (coulombmeters) it makes it very easy.
Before I was using the dc wattmeter (12 dollars) when ever I needed to track amps, but they only measure amps in one direction. I had to reverse it whenever I wanted to measure in opposite direction. It works but not convenient.

tk15 50 amp coulombmeter


Here its on my lifepo4, Its next to a dc wattmeter to compare accuracy

 

[Weight]

Rod Collins has a full instruction for installing and keeping the monitor accurate. Here; https://marinehowto.com/programming-a-battery-monitor/
Rod uses the Victron in his explanation, but the information will apply to any shunt-based monitor. One advantage of the Trimetric Monitor is it can be linked to a charge controller from Trimetric.

 

[B and C]

If you know you used 20 amps the night before, then the following day you know you need to at least put those 20 amps back, with these meters (coulombmeters) it makes it very easy.

You have to remember that you have to put more back in than you took out, always.  Chronic under charging shortens battery life a lot on lead acid batteries.

 

[frater secessus]

...there is the tk15 you can find on amazon for 28 dollars. It comes with a shunt only rated for 50 amps. I use it on my lifepo4 for the past year.

I picked up one of those earlier in the year and it works fine like yours.  My only complaint is the backlight stays on, unless I am missing a setting to turn it off.
50A might seem like a tiny limit but I don't hit it in practice.  My usual max from the alternator is <40A , and once saw 43A which is right at C/5 for my flooded batts.  Folks with AGM could probably exceed 50A pretty easily.
There's also a 350A version for $60 but it has no reviews and I haven't used it.

 

[Seminole Wind]

dont put too much faith in this style battery monitor. to begin with they are only as accurate as they are programed/set up. and that accuracy is just for the start. as the battery capacity dwindles the accuracy can drift significantly. also all of the meters i am familiar with up to the last year or so use a fix value for dealing with the Peukert Law issues. unfortunately the real value varies based on state of charge. the companies just have to guess as to what the average amount of time in bulk vs absorb vs float will be and pick a number. if you never discharge below 80% or always go down well below 50% the charge efficiency will very greatly and due to The Peukert Law a battery monitor can easily get off. also if you run your batteries in a partial state of charge situation a lot, your capacity will degrade and your monitor will think you have more capacity left in the battery than is really there. last ly, most, including the trimetric for sure have a 100% reset to try and make up for drift. only problem is it can be fooled on a cloudy day and reset to read 100% when you might be closer to 80% or less

i have seen these problems come to play on a system using the bogart trimetric in conjuction with matching charge controller. i have sen the 100% reset get things way off. and as the batteries aged and lost capacity then it was a crap shoot to try and guess the new/current capacity to reprogram the monitor since i dont have a means of doing a 20 hour test on location

yes battery monitors can HELP you keep track of your batteries. but count on them to be your only means.

 

[Jedi Clampette]

it is not possible to know battery state by measuring voltage in use. We keep thinking the battery monitors are like a fuel gage that can measure in an instant the voltage capacity. Battery monitors are a little sneaky, to give us aprox amp hour capacity. You charge the battery pack and then let them sit without having any load for 24hrs. If after 24 hrs of no load, it measures 13v+ volts we can make the assumption that the battery bank is full, then when we put the battery monitor on it, it measures amp hours going in and out based on that imaginary full load condition. So altho it cannot know what the real status of the battery bank charge, for our practical purposes we can monitor volts in and out and assume battery status.

 

[Spaceman Spiff]

dont put too much faith in this style battery monitor. to begin with they are only as accurate as they are programed/set up. and that accuracy is just for the start . . .

yes battery monitors can HELP you keep track of your batteries. but count on them to be your only means.

That is true of any measurement system: they are only as good as their calibration and the user must understand the limits of the device.  An old saw in engineering: an idiot proof system gives results only an idiot will believe.

I am not familiar with any reasonably priced equipment that can give a highly accurate state of the battery.  C/20 tests (SAE J537) have been shown to vary by as much as ±15% under lab conditions.  The Cadix Spectro system requires expensive equipment.

Amp counters (Trimetric, et.al) give a good 3rd order approximation of state of charge for a reasonable cost.  But you (since you are your own power company) have to understand what it is telling you and its limitations.

What do you use to monitor your batteries state of charge?

 

[Weight]

Peukert formula is not that important for general monitoring. Making a good guess of the AH capacity is. (Or better having it measured.) I use a Victron and when I can plug into the grid I reset the battery % to 100. The Trimetric doesn't have a setting for Peukert.
Rod Collins has a good description of how to calibrate a Victron monitor. Find him at Marine How To dot Com/

 

[Weight]

What Spiff said ^^

 

[B and C]

Here is a link to what Bogart Engineering (Trimetric) has to say about peukert compensation:

http://www.bogartengineering.com/wp-content/uploads/docs/PeukertsComments.pdf

 

[rollinghaus]

Here is a link to what Bogart Engineering (Trimetric) has to say about peukert compensation:

http://www.bogartengineering.com/wp-content/uploads/docs/PeukertsComments.pdf

There we go. There is a reason I went Trimetric.

 

[wayne49]

Interesting pdf. Thanks.
I have a Trimetric as well. Just works as it should for over three years.

 

[Weight]

That is one man's opinion of peukert. There are many more engineers that think it has importance. Especially for high amperes, such as mine. The only thing better about trimetric is the ability to synchronize the charge controller with the monitor.