What is a shunt, and why would you need or want them in your genverter or off grid power system? Technically, you can make, store and use power from you off grid system without a shunt. Doing so would be like putting on a blindfold and having your friend in the passenger seat give directions as you drive across New York city. Yes, possible, No, not recommended!
A shunt is a resistor
In the electronics world, it is normally called a current shunt. Shunt resistors come in all shapes and sizes, so we’ll just cover the ones used in a remote power system. This is a special calibrated low value resistor does not heat up or change its value, even when large currents are flowing through it. This device is made from one or more parallel strips of metal fastened between two bras blocks with terminals.
what it does
500 Amp Shunt
The shunt is at the heart of your battery bank monitoring system. With the right monitor (like a Trimetric monitor from Bogart Engineering) hooked up to this resistor, you can collect data on how many amp-hours of current go into, or come out of the battery bank. It is the key sensor that will help you get years of service from your battery bank, if you heed its warnings.
where it fits in
Normally it is the last item in series before the main connection to the negative terminal of the battery bank. To connect up your battery monitor, a four wire cable is normally used.
- One wire goes to the positive terminal of the battery bank to power up the battery monitor system, and provide battery bank voltage measurements.
- Another wire connects to the shunt on the side away from the battery bank. This is the sensing voltage plus side.
- Normally a black wire goes to the the negative terminal of the battery bank. It supplies the small power required by the monitor.
- Lastly, there is a wire connected to the shunt terminal nearest the battery bank. It is for the sensing voltage minus side.
Negative side wiring with battery monitor
When this is all together, one might be tempted to ask about why we need two connections to effectively the negative battery terminal. What is the difference between the “minus sensing” wire and the “negative side power” wire??
To gather accurate low voltage readings across the shunt, the “minus sensing” wire is used. There is virtually no current running through this wire (millionths of an amp). The meter power wire does have current flowing through it, a thousand times more. (thousandths of an amp). The voltage at both ends of the negative power wire are not the same, and would affect the measurement. Using the “minus sense” wire has the same voltage at each end, so it is used to make the measurement.
Accuracy in measuring the shunt voltage is critical, as small errors would throw off the system current draw or charge by several amps!
Do you have a shunt in, or planned for your system?
What battery monitor systems do you like?
Join in and tell us what you think, or have found. Comment below!
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