Author Topic: DC Wiring - Best Practices  (Read 2009 times)

Offline Seangie

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DC Wiring - Best Practices
« on: November 19, 2012, 07:16:43 PM »
Hey all.  Happy Early Turkey Day if i don't get back to you by Thursday. 
Hope you all have a spectacular week planned.

I have been putting off electrical for a while.  Partly because it was the most complete system when I bought the bus and needed the least amount of attention and partly because I love electrical work more than any other and was saving the best for last.  (Really I needed to get Sean's advice before he sails off into the sunset :))

Well, the time has finally come to start planning out the electrical for the coach.  First I am going to deal with the DC and I will move onto the AC later.  Both systems are up and running it is just a matter of taking what is in place and organizing, simplifying, updating, cleaning up and putting it back together.

For the DC circuits - Overall plan is to keep it simple & safe.

1. A single battery bank for house and starting.  I am planning on (4) L-16 AGM Batteries
2. An isolated bus bar for distribution to positive side of the DC Circuit
3. A grounded bus bar (grounded to bus frame) for the negative side of the DC circuit
4. Fuses where needed - Primarily large fuses for the Battery Bank and Alternator circuits - Most of the other circuits have individual fuses for each run
5. There will be one long run of 4/0 cable to the front of the bus (Front DC) to a separate DC panel.  This will help with voltage drop to circuits on that side of the bus.
6. The battery bank and inverter will be close within 5 feet.
7. Oversized cable for most runs.  For the sake of the board - Not mentioning cable type
8. The leveling system is the "Big Foot" style RV levelers that are each individually fused.

This is my initial layout - Looking for some good feedback and concerns about what I have planned.  I am sure I have missed a few things -

My questions are -

1. Do I need to add a voltage regulator - maybe on the battery circuit as that is the only "non" regulated device adding voltage?
2. Should any of these circuits have protection against the amps that the starter is going to throw on the wire?  I've seen some devices that "protect" house batteries against the starter but if the starts and house batts are the same - does it make a difference? 
3.  Is there any other advice or parts/pieces that I should take into consideration?

I have a bunch more questions but wanted to get these simple electrical questions but I'll keep this short and focused for now.

I am sure you will all answer the unasked in replies anyways.

Thanks again.

'Cause you know we,
we live in a van (Eagle 10 Suburban)
Driving through the night
To that old promised land'

Offline Oonrahnjay

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Re: DC Wiring - Best Practices
« Reply #1 on: November 20, 2012, 06:54:18 AM »
    Sean, have you run the use of the AGM L-16's as start batteries past the manufacturer's tech guys?  I'm guessing it's probably OK but I'd want to be sure that those batteries are suitable for starting.
Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long

(New Email -- brucebearnc@ (theGoogle gmail place) .com)

Offline bevans6

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Re: DC Wiring - Best Practices
« Reply #2 on: November 20, 2012, 07:53:10 AM »
The way you have it, the alternator output is fused twice and the starter is fused, because the battery negative is fused.  I would not fuse either one.  They are never, in my experience, fused in automotive applications, including buses.  My MCI stock wiring does not have fuses for those devices.  Using one bus bar each for hot and ground, and running the high current load of the starter through it is, in my opinion, also a bad idea.  I would run a 4/0 wire from the batteries directly to the starter through a disconnect switch.  The alternator is quite close to the starter, so I would run a 2/0 from the alternator to the starter.  That would give me start current from the battery and alternator current to the battery, over one wire (what I described is in fact the stock MCI wiring setup).  I would then run a cable sized to support the house loads from the disconnect switch to a bus bar and distribute from there, and run a cable to the bus load distribution that already exists.

The problem with this setup is that if you throw the disconnect switch while the engine is running, the alternator can run away while it's still connected to bus and house loads.  This again is a problem with the stock setup as well, I don't know a way around that.
« Last Edit: November 20, 2012, 07:54:52 AM by bevans6 »
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia

Offline TomC

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Re: DC Wiring - Best Practices
« Reply #3 on: November 20, 2012, 08:15:05 AM »
Using the 4-L16 AGM batteries is a great idea for your house system-these are the batteries I'll be using.

Nix the combined system of starting and house in the same battery pack. If you run down the batteries (which is possible even with them being so large) you'll be dead in the water.  Instead use just two size 31 starting batteries and have a jumper solenoid (300amp to handle the alternator) so if you're having a hard time starting, you can kick in the L16's.  Then you can also charge the L16's going down the road. I do not have a separate battery for my genset-just use the starting batteries. Believe me, I have used the jumper solenoid many times-whether it be for jump starting myself, or kick starting the deep cycle batteries when I left something on, etc. Using the same battery bank for all is just not a good idea.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.