Why do I need a smart shunt?

[Sue&Geo]

Why all the hype about the smart shunt? Doesn't my charge controller tell me the state of charge of the batteries?

The only thing I can see that the smart shunt gives me is the information about what load I am currently pulling. I don't really care about that. If I am using the induction cooktop, I know its pulling about 1800, the microwave, about 1100, etc. And I don't use these for more than a few minutes at a time. So what's so beneficial about the smart shunt? Can't I just rely on the charge controller data for state of charge?

 

[Matt_C]

Sue&Geo,
A smart shunt is part of a Victron battery monitor. While I am not sure what a smart shunt gets you as opposed to an old stupid shunt, I would never again try to live on batteries without a real battery monitor installed.
And, without knowing what your charge controller is, I don't know if you can count on it for true SOC.
Matt

 

[Sue&Geo]

I have not installed my solar system yet (just planning a van conversion) but the charge controller will be either a Renogy Rover 100/40 or a Victron 100/50, both MPPT. I will be installing 400W solar and two Battleborn lithium 100ah batteries. As I understand it, the charge controller shows SOC as part of its readout.

 

[Lou Schneider]

The solar controller only measures what you're putting into the batteries, a shunt in series with the batteries measures both what's going in and what's coming out, giving you an accurate running total of the amount of charge in the batteries at any time.

Voltage based charge indicators are notoriously inaccurate because the voltage level changes with the load on the batteries.

 

[DonTom]

Doesn't my charge controller tell me the state of charge of the batteries?

The Smart Shunt gives you a lot more info. such as how much load there is on the batteries and other such stuff your controller doesn't mention.

It's helpful when there are DC problems anywhere in the system.

I recently purchased one, but I have not yet installed it in my RV.

But I did set it up and watch the current draw of my 12 volt ham radio stuff here in the house so I know it works for when I do install it in my RV.

-Don- Auburn, CA

 

[Sue&Geo]

Thanks all. Very helpful. I have decided to install a lower end monitor that will give me what I need but not go for the BMV712 because of the price.

 

[Isaac-1]

Just be aware some of those lower end units do not perform well in environments where the batteries never get fully charged, which is common in solar only installations.

 

[Sue&Geo]

Thanks. I will also have a dc2dc charger as well and will be driving every couple of days so should be ok.

 

[AStravelers]

It really depends on:
* How often and how long do you dry camp/boondock?
* Which batteries do you have?
* How much battery capacity do you have?
* How many AH do you use in 24 hours.

If your battery capacity and power requirements allow you to only take your batteries down to 75% full by morning. And: 1) you have about as many watts of solar as you have AH of battery. 2) You consistently have good sun for charging, or your run your generator for 1.5 to 2 hours in the morning, or you drive for several hours a day. Then you should be OK. However you really don't know how far down you took your batteries and how well charged you got them w/o a good monitor.

With solar, generator and charging while you are driving, you really don't now how many AH you have put back in and chances are you only get your batteries up to about 70-85% full.

With lead acid batteries and not knowing if your batteries are truly getting back to 100% full:
-- 2 to 4 days and then back on shore power for at least 24 hours with lead acid batteries, you are OK
-- If you go for more than 5-7 days w/o going back to shore power and do this 10-20 times a year then you will likely be replacing your batteries in 1 or 1.5 years because they have sulfated and lost capacity
-- If you only dry camp for a week and do this 2-4 times a year then back to shore power you probably won't notice the reduction in battery capacity for 3-4 years.

The ONLY way you know if you are getting your batteries fully charged is with a good shunt monitor that measures the AH's going out and most importantly going back into the battery.