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Old 21-10-2008, 11:00   #1
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Battery Shunt ? ? ?

What the #$%@ is a battery shunt? & Why do I have/need one?

Ok, I have this french built boat, and it has 2 starting/house banks of batteries, 2 T-105s on each side as both house and starting banks. They are split in to 2 seperate banks. I am instaling a starting bank of group 27s, 1 at each engine and going with the T-105s as a single house bank of 4 T-105s in series/paralle (spl?).

The battery switches are a Positive switch for each side (total of 2), 1 negitave switch for both sides and then a postive "SHUNT" switch. Why ?
Dan
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Old 21-10-2008, 18:19   #2
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Quote:
Originally Posted by S/V Mother Ocean View Post
What the #$%@ is a battery shunt? & Why do I have/need one?

Ok, I have this french built boat, and it has 2 starting/house banks of batteries, 2 T-105s on each side as both house and starting banks. They are split in to 2 seperate banks. I am instaling a starting bank of group 27s, 1 at each engine and going with the T-105s as a single house bank of 4 T-105s in series/paralle (spl?).

The battery switches are a Positive switch for each side (total of 2), 1 negitave switch for both sides and then a postive "SHUNT" switch. Why ?
Dan
In the most basic terms. A shunt is a resistor in the circuit to control current. (Think Voltage regulator in your car.)

You have to have a means of measuring/regulating both the power coming from your batteries, as well as the power going into them. Without knowing both, you could never get an accurate measurement of the state of charge and would be prone to over-charge or over-discharge. All the shunt is doing is measuring/regulating the current going in and out of the battery so it can assess & manage battery charge levels. It's a bit curious that yours says "positive" at your switch unless they are trying to imply that "Positive" simply means "On" (ie opening the circuit for measurement/regulation?) Still kinda odd imo
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Old 21-10-2008, 18:39   #3
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Areyor sure this is a shunt or perhaps a high amp fuse bar?
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Old 21-10-2008, 19:22   #4
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It is very common to measure the amount of current flowing into or out of a battery. This may be the purpose of your battery shunt.

Besides what was mentioned above, shunts can also be used for determinng current. The voltage difference across a shunt is directly proportional to current flow through the shunt. Analog ammeters that use shunts are actually volt meters with the scale in ampres. There are also digital ammeters that use shunts. Shunts are typically 500mV shunts which means a current of 500 amps flowing through it creates a voltage difference of 500mV or 0.5 volts. 50mV shunts are also common.

They typically look like this:


Is this what you have? If there are two smaller wires that lead from each side your shunt to an ammeter, then there is your answer.
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