Solonoid to Connect House & Starting Batteries

[Midwilshire]

I know this has been discussed before; I read the search results.  I just want confirmation of my understanding....

About 15 minutes into a trip, I'd like to be able to flip a switch in the dash area and have the big alternator start charging my 24v house battery bank as well.  To do this, I'm planning on running a heavy wire from the positive on the starter bank to the positive on the house bank, and in that line, install a 200amp solonoid from Texas Industrial Electric (Item 15-269).  http://www.texasindustrialelectric.com/relays.asp

I'm good to go with this plan, yes?  I'm not going to blow up my fancy new Magnum inverter or my bus, right?

[Len Silva]

15-269 is only 100 amps, not enough in my book.  I would go with 15-551 which is 200 amp continuous.

Most folks do this automatically by using a fuel pressure switch or other means to make the connection after the engine is running.  Doing it manually as you suggest is just fine as long as you don't forget to turn it off when stopped.  If you get the power to your manual switch from a source that is only hot when running, that should work.  Don't use less than 2/0 cable for this, 4/0 would be better.

[wagwar]

On my MC9, I took a signal from the A/C Blower relay. This 24vdc signal is only hot when the engine is running, the alt. is producing power and the bus is aired up. I don't know the 5C, but there should be something similar.

I tied that signal to a timer that delays the connection of the two banks for 30 seconds, just to be sure. I installed a toggle up front that has an On/Off/Momentary so that if I need to bridge the two banks in an emergency (like the start batts are low). I can use the momentary position and bypass the A/C blower relay and timer.

The On position just allows me to control when the banks are bridged. The nice thing about this setup is the solenoid will be automatically disconnected when the engine is shut down. I also installed a light in the Tell Tale panel whenever the banks are being bridged.

I also used the same signal from the timer to control relays that switch one of my rooftop A/C units to the inverter - only if the banks are bridged. This allows me to run both rooftop units from the inverter while underway.

Sean Welsh was very helpful in suggesting how to do this on the other forum. You might do a search there for more info.

[chev49]

im started redoing mine yesterday.. never thought about a light.... will have to add that to mine.

[Midwilshire]

Great.  Thanks guys!

[Mex-Busnut]

I think you got some very good advice already. However, one important question is how far apart are the two battery banks physically? As Len said, you need to use the thickest cable possible. The farther apart the two banks are, the more important fatter cables will be.