Bigger is Better - 2/OT vs 4/OT - Case study

[gpounder]

12 Volt power systems have little margin for error when dealing with high current levels. I have a Class A with a classic 2000 Watt inverter and I had always noticed a significant voltage difference between the Magnum power panel and my Victron battery Monitor and here is why.

Case study
Test load - 1500 watt portable heater
Magnum Inverter/charger
Factory installed 2/OT battery cable

3 lengths @2/OT with the following inline:
1 300 Amp Fuse
1 200 Amp battery disconnect switch

6 GC2 Batteries Total 690 Amp Hour

Digital volt meter and DC clamp tester

Other factory lengths 3/OT


After applying the load I made the following measurement and discoveries.
Inverter voltage 11.2
inverter amps at the connector 156
Watts consuming 1747

Battery voltage 12.17
Volt drop Battery to Inverter .97
Wattage loss in wiring 151

Result: hot to the touch (not burning) all the 2/OT wires.
Basically I was operating a 151 watt heater from the 2/OT wires.
That is a lot of power being wasted.

The Fix and results
Replaced the 3 - 2/OT wires with 4/OT
Volt drop from the battery to the inverter lowered to .22
Now only 34 watts are lost in wiring and now none of the wires get so hot.

There was nothing dangerous about using the 2/OT wire but the losses could have caused the inverter to shut down prematurely as the battery cutoff voltage got reached.

Under high load it made me think the batteries were getting low when in fact they were almost 1 volt higher than I though.

These losses are bi-direction and will slow the batter charging process as you waste power.

This test will expose any loose connection or bad, undersized wire as that sport will get warm.

This was a great opportunity to clean up all connections and tighten everything.

[36PFT]

You are 100% correct. The size of the cable is also very important to the cranking motor (starter). An under sized cable will cause the starter to work harder and have a shorter life. Stan

[757driver]

Keep in mind also that the Magnum remote panel will give a voltage difference (compared to what the actual battery voltage is) when charging or under a high load due to the fact that Magnum does not use a dedicated voltage sense line for the remote.