wgriswold wrote:
One thing that puzzles me is the worry about the gauge of the wire that connects two 6V batteries in series. The length would be 1 to 1 1/2 feet and the load about 30 amp. Charts tell me that 12 or 10 gauge would be sufficient.
But people are talking about fabricating 1/0 gauge connectors. I may be not understanding something or perhaps my memory of a 30 amp fuse on my positive lead to the battery bank is wrong.
What is wrong with just getting a short 4 or 6 gauge connector from the auto store?
Something called RESISTANCE.
RESISTANCE IS THE ENEMY OF LOW VOLTAGE APPLICATIONS.
You CANNOT USE VOLTAGE CHARTS FOR 12V HIGH AMPERAGE DRAWS, those are designed for 120V and higher.
5% at 120V is 6V of loss which IS a acceptable 114V.
5% of nominal 12.8V DC is .64V DC loss which puts you at 12.16V DC, most inverters will go into low voltage alarm at 10.5-11.0. This gives you VERY LITTLE headroom to work with.
Keeping in mind as you draw the 12V battery down (discharge), its NO LOAD VOLTAGE ALSO DROPS. This narrows just how long or how much you can run something at 12V and running a high amperage load now becomes impossible to maintain for but a few minutes before the inverter alarms and shuts off..
If you are using nothing more than the 12V furnace and a few lights you have nothing to worry about using a min of 8 ga interconnects.
Why 8 ga?
Simply put, your battery IS fused or has a auto reset breaker attached within 18 inches of the battery. That breaker or fuse IS there to protect YOU AND YOUR TRAILER from a SHORT CIRCUIT OR OVERLOAD of the battery to converter wiring.
Typically this is a 40A fuse or breaker, you fuse to the WIRE SIZE, 40A will require a min of 8ga wire for an interconnect. In other words your interconnect cables MUST BE NO LIGHTER GA THAN THE WIRES CONNECTED FROM THE RV TO BATTERY!
The Interconnect cables however CAN BE HEAVIER GA THAN THE RV TO BATTERY WIRING.
You can ALWAYS upsize the wire with no fear..
12V wiring is no place to cheap out, 12 GA, 10 GA interconnects are undersized for the fusing and creates extra unwanted voltage loss.
As you mention, 2 GA and 4 GA interconnects are easily available but when you are after high amperage things like 1,000W - 3,000W inverters it leaves a lot to be desired as far as voltage loss..
