Battery Shunt ? ? ?

[S/V Mother Ocean]

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

[Lancerbye]

A SHUNT is a low resistive bar or wire that has a very specific accurate low resistance used to develop a voltage that a meter will use to measure current. The meter is matched to the shunt resistance for a specific current range. E.g 200 amp shunt would provide a 200 amp full scale reading on a meter by developing a small millivolt drop which is translated as amps.

Having explained all that, considering it is a european boat where meanings are sometimes different it could also be a switch that connects the two batteries together. Having to deal with European wiring, I find daily challenges since my training, experience and qualifications are North American.

[GordMay]

Originally Posted by Lancerbye

... it could also be a switch that connects the two batteries together...

As Lancerbye indicates, in this case, it's almost certainly an emergency parallel switch.

[S/V Mother Ocean]

So I should keep it? I was going to trash it. I do have a volt meter on the panel but not an amp meter.

Dan

[cal40john]

Originally Posted by S/V Mother Ocean

So I should keep it? I was going to trash it. I do have a volt meter on the panel but not an amp meter.

Dan

As Gord said, and as Lancerbye gave in his second guess, it is unlikely to be a (shunt) resistor for an ammeter as in this case it is actually a switch. It is much more likely a way to connect the two battery banks together in an emergency. You can also disconnect a bad battery bank using its main switch and use the shunt switch to connect the other bank to the circuits normally supplied by the bank with the bad battery. You can use it to start your engine with your house bank if your starting battery is dead for some reason.

John

[btrayfors]

In electrical circuits, the term, "shunt", has two very different meanings which should not be confused:

1. a low-resistance path between two parts of an electrical circuit; sometimes known as a "bypass"; and

2. a conductor connected in parallel in one part of an electrical circuit, and designed to pass a known fraction of the current.

In the first case -- which is almost certainly the meaning on your boat -- it is a means of directly connecting two battery banks together (or "BOTH" in the common U.S. marine switch usage).

In the second case, it is a device used to reduce current/voltage levels in a circuit to a level compatible with metering. Example: in high amperage circuits you don't connect an ammeter directly in the circuit, because the meter isn't designed to handle huge amperage loads. Rather, you employ a "shunt", which passes the high amperage load just fine, but bleeds off a tiny portion to feed the ammeter, which is calibrated to read the total amperage passing through the circuit.

RE: your on-off switches, if you're going to have a single house bank consisting of T-105s in series/parallel, you only need one load switch, and that on the positive side.

You need another on-off switch for the dedicated engine battery.

You need appropriate fusing as well on the house battery circuit and, optionally but recommended, on the starting battery circuit. High-amperage ANL fuses and holders are one good way to go.

Don't know how you plan to set up your charging, but the preferred way these days is to run ALL charging sources (alternator, wind generator, solar panels, battery charger, etc.) to the HOUSE batteries, and then to use a small device such as an EchoCharge or a DuoCharge to maintain the starting battery (which requires very little charging).

Bill