mystery battery cable

[boohoo222]

there is a red battery cable near the motors batt in front of the radiator it is not connected and runs under the drivers seat and seems to disappear, anyone have any ideas what its for

[Rickf1985]

Hydraulic jacks? Generator starter? They are two of the high amp draw things I can think of back there.

[boohoo222]

thanks but I checked those, its not eather one of those, I'm wondering if it goes to the house battery bank?

[Rickf1985]

There will be a cable from the house batteries to the chassis battery but it should go through a solenoid. I am not really sure about your year but on the newer ones it would go through a momentary relay and could also go through a latching relay. It should not go directly to the chassis battery from the house batteries though.

[boohoo222]

rick, what would it be for if it does go as you said

[Bnova]

The set up on mine will allow me to flip a switch and connect the chassis alternator/battry to the coach battery for charging it while driving.

Additionally, the momentary flip of another switch will allow for connecting the coach battery to the chassis battery for additional starting power, should I inadvertently run my chassis battery down by using the stereo or what ever. 

[boohoo222]

that sounds great ill check that thanks

[Rickf1985]

Yea, What he said. :)rotflmao

[HandyDan]

It might go to the inverter.  I have a large red and a black cable from the coach batteries that go to it.

[HamRad Mobile]

Good morning, BooHoo and Dan; 

     The mystery red battery cable.  You did not say what size that red cable is.  The only other thing I can think of different from what others have said, is maybe a cable going to a trailer lighting and power connector by a trailer hitch on the motor home back to go to the towed vehicle for keeping a car battery charged or to keep charged a battery on the trailer to operate the trailer electrical brakes if there is a trailer hitch break-away failure. 

     However, for any accessory wiring I put in, I also put a fuse in that red cable somewhere near the battery for any accessory system powered off either of the two battery systems.  Automotive parts stores have Pico brand Type 0969C fuse holders with 8 AWG Copper wire for use with the large Bussmann Type MAX fuses with 3/8 inch wide blades.  I use the blue 60 Ampere rated fuses in mine.  The fuses are available up to 80 Amperes, but the 8 AWG Copper wire is only rated at about 55 Amperes.  Smaller ones are also available. but I run fused power to a separate terminal strip for the smaller branch circuits.  It simplifies the wiring on the battery terminals.  The Blue Sea brand 12 VDC marine wiring products at boating supply stores, such as West Marine and others, have the terminal strips.  There are lots of things available for making a reliable and good looking wiring system on a motor home.   

     Running a 120 VAC inverter off the vehicle engine starting battery.  Dan, you said that your large Red and Black cables going to your inverter are wired to the RV coach batteries.  That is correct.  I do not think that very many people will suggest wiring an inverter to an engine starting battery, if that can be avoided, and it can be avoided in the average motor home RV. 

     The main reason for that is the amount of power required to operate the inverter for such a load as a microwave oven.  Most of the motor home microwave ovens seem to be about 800 to 1,000 Watts.  That will be from about 7 Amperes to almost 9 Amperes at 120 VAC to run the microwave.  Allowing for the conversion inefficiency, that will require just about a around figure of 80 to 100 Amperes from the battery to have the inverter provide that 120 VAC power. 

     When you start the engine of your motor home, you will normally use about 3 to 5 seconds of cranking the starter with 150 to 250 Amperes of current.  With the microwave oven, it will be on for a minimum of about 1 minute, and often for more than 5 minutes.   5 seconds of a 150 Ampere load on the battery, or 5 minutes of an 80 Ampere load on the battery; which is the harder load on the battery?  Especially when that battery is designed just for short term, high amperage, engine starting service, and it is not a long term load "deep cycle" battery. 

     There are some real reasons why an inverter is not connected to the engine starting battery when there are the coach auxiliary batteries available. 

     And, I have also transferred the power wires from the vehicle AM-FM radio over from the original engine 12 VDC power system and onto the coach RV 12 VDC power system.  If I spend too much time enjoying the music on the Sirius-XM "Fortys on Four" channel, I do not need to worry about an inability to start the engine, and I can hit the switch and use the engine driven 105 Ampere rated alternator to recharge the RV coach batteries after my indulgence. 

          Enjoy; 

          Ralph 
          Latte Land, Washington