Shunt

System

What is a shunt used for? I have been running my system for sometime with no shunt.

n3qik

Re: Shunt

A shunt is use to measure the current/amps of a system. How it works is a current passes thought the shunt and voltage is developed across the shunt. The voltage, in the mili-volt range is read by a meter. Shunts are rated in two ways. One the max current that can pass though the shunt and how many mili-volts per amp the shunt makes.

BB.

Re: Shunt

As n3qik says--the shunt can take large amounts of current (typically for RE systems ~100-500 amps) and you hook up a voltmeter to read the voltage drop--which then scales to current (i.e., 0.05 v or 50 mV = 100 amps).

The shunts are typically installed between the negative battery terminal and the ground common/bus (all current going into or out of the battery runs through the shunt).

You can see some example of shunts here.

Now, normally a shunt is used to measure high currents and you don't want to wire that current through a Amp Meter (either because the meter is not big enough--or you want to mount the meter some distance from the battery bus).

But, you can also install a battery monitor which will use the shunt to measure the current flow through your battery bank.

Basically a Batter Monitor keeps track of all of the current flowing out of, and back into, your battery bank (Amp*Hours or Watt*Hours)--It basically becomes the gas tank gauge for your battery bank--much more accurate than measuring resting voltage (which you cannot accurately do if you are charging/discharging your battery bank). And much easier than using a hydrometer to measure the specific gravity of your bank (and cannot be done with AGM/Sealed batteries).

A Battery Monitor will give you a very accurate reading of your bank's State of Charge (i.e., 82%)--plus a bunch of other information too. Also very nice if you are not the only person taking care of the RE system... Spouses, kids, visitors, etc.--much easier to tell them to not run your bank under 50% discharge by looking at the meter.

-Bill

System2

Re: Shunt

Thanks for the information.

I have an off grid photovoltaic system on my Mexico beach house. I am installing a new Outback Flexmax 80 because my 60 stopped working, My system uses two Outback FX 2024 inverter/charge controllers, Kyocera panels and six, 4 volt Rolls 1,350 amp hr batteries. I have Mate Controller and a Hub to tie it all together.
I do have a problem making the the mate operate because I had a leak on my Sea Recovery desalinator and sprayed salt water on my Outback system for two days. I have a salt water well in the beach and desalinate my water because we do not have fresh water and I do this using my photovoltaic system.
I was able to save everything during the salt spray episode except the RJ45 connector on one of my FX2024 for the Mate has been corroded so much it does not work. I have not been able to get any information from the mate but can read the array amps and voltage and battery condition using the old 60 controller I was using until it stopped working last week. I have never been able get a usage amp reading from the Flexmax 60 led screen. I do not have a shunt installed and was wanting some help on what I need to do to get a usage display. Does anybody know if anybody repairs FX2024 inverters?

blackswan555

Re: Shunt

You only need a shunt (or up to 3) if your are useing a Flexnet DC
http://outbackpower.com/products/communications/flexnet_dc/ which would be a good idea if you can, You will not get amps reading without,
You can get the individual FX circuit boards, 3 off , FET is about 600, ac and control boards around 300 each, I would think it is your control board, easy to change yourself, There is an outback video on how to do it.
Have a good one
Tim

mike95490

Re: Shunt

Salt water and electronics. As you discovered, a bad combination. You may be able to find a clever tech that can R&R (remove & replace) the bad RJ jack, those are pretty standard drop in parts.

RCinFLA

Re: Shunt

Shunts are just a resistor.

The most two common values used for battery current monitoring are 1 milli-ohm (also known at 100 amp shunt) and 0.1 milli-ohm (also known as 500 amp shunt.

There are two attibutes that a shunt must be designed for. First is metal alloy selection to minimize change in resistance over temperature to keep an accurate reading.

Second is power dissipation. P= I^2 *R, at rated current a 100 amp shunt will produce heating of 10 watts. A 500 amp shunt will produce 25 watts of heating at full current. This is why the 500 amp shunts are much larger then the 100 amp shunt. The maximum current rating is limited to only a few minutes otherwise the shunt gets too hot.

Current is measured by voltage drop across shunt resistor ( V= I*R). Any monitor like Trimetric TM2020 must be programmed to tell it if a 1 milli-ohm or 0.1 milli-ohm shunt is being used. The voltage sensing is taken from two screw terminals on the side of the two main terminal blocks. This separate connection for voltage sense is to avoid any resistance variation at the main high current terminal connections.