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Topic: New Wiring for Coach Batteries (Read 630 times) previous topic - next topic

New Wiring for Coach Batteries

Last year I updated my engine batteries with new 4/0 welding cable and copper busbars. The original thread is here: New Wiring for Coach Batteries

and finished up with this thread: Battery Cable Upgrade and Pricing
 
When upgrading the engine batteries, I created two 1/2" x 2" x 8" copper busbars, one for the positive wires, and one for the negative wires. I made three 4' cables for the positive posts and three 4' cables for the negative posts. They were that long to bring them up to the busbars which I installed in the engine compartment behind the foot of the bed.
 
My coach batteries are three 8D Super Smart Heavy Duty AGM batteries from O'Riellys. They are connected with the OEM 3/0 cables made by Foretravel. They are mounted in the bay with the fuel tank and opposite the propane tank. There are two batteries, "North to South," on the lower level; and one battery on the upper level, oriented "East to West." I will place the busbars in the area above the lower batteries (I think).

I have purchased two 1/2" x 2" x 12" copper bars to use for the busbars. One of the reasons I am doing this is to install the Magnum ME-BMK battery monitor which interfaces with MS2812  inverter/charger. The battery monitor kit includes a heavy duty shunt with 3/8" bolts on each end. I had intended to mount the existing 3/0 cable from the MS2812 onto one end of the shunt and use a short 4/0 cable from the other end to the MS2812.
 
I called Magnum Energy technical support to confirm this was acceptable. They asked what size cables I had and I told them 3/0. They said that it should be at least 4/0 and two 4/0's would be even better! WRT the ME-BMK battery monitor, they said the shunt should be close to the batteries to pick up all of the current leaving/entering the battery. My existing wiring comes from the batteries through the wall in the back, and around the corner to the large electrical panel where it goes to a large stud. There are several wires going from that spot, so I will put the shunt before the black wire stud. Since I was already planning to upgrade the coach wiring to 4/0, I decided to do that in conjunction with the battery monitor installation.
 
Cable Length:

My first question for the brain trust concerns the length of the wires from the battery posts to the busbars. I had used six equal-length cables for the engine batteries, and planned to do the same for the coach batteries. Then I began to think about the design.  :-\  The furthest run is from the black post on the top battery to the wall, about 22". The next longest run us from the red post on the top battery to the wall, about 16". Using the same criteria as before, I would make six 22" cables.  However, what does equal length cables mean? Does it mean they all have to be the same length; or does it mean that all three of the black cables need to be the same length, and all three of the red cables be the same length, but not necessarily the same lengths as each other? Can I make three 22" cables and three 16" cables, or do I need six 22" cables?
 
Shunt Location:

Ignoring for the moment the actual location of the shunt, I want to address its location WRT the busbars. I am thinking that I should cut 4" of the black busbar for the three battery leads. I would then install the shunt between that busbar and the remaining 8" of the black busbar. All the negative/ground leads would attach to the 8" busbar. The red busbar would be one piece, unless I want to install a switch between the battery leads and the rest of the positive leads. But that would put that switch resistance, whatever it is, into the starter cable, which is probably a "no no." Anybody see a problem installing the shunts between two pieces of the black busbar?
 
One More Thing:

Now that I think of it, there was a LARGE fuse on the electrical panel to which the positive cable from the batteries was attached. Maybe I could attach that between a 4" piece and an 8" piece of the red busbar, with the battery leads going to the 4" piece. Appearance wise it would look like the two black busbar pieces separated by the shunt. Hmm . . .
 
More later; thanks,
 
Trent

Trent and Jean Eyler
2000  U295  4003  WTFE  ISC  350
Build#5603 MC#17385

Re: New Wiring for Coach Batteries

Reply #1 –
Quote from: TulsaTrent –
The furthest run is from the black post on the top battery to the wall, about 22". The next longest run us from the red post on the top battery to the wall, about 16". Using the same criteria as before, I would make six 22" cables.  However, what does equal length cables mean? Does it mean they all have to be the same length; or does it mean that all three of the black cables need to be the same length, and all three of the red cables be the same length, but not necessarily the same lengths as each other? Can I make three 22" cables and three 16" cables, or do I need six 22" cables?

I think it's important for the cables to be as short as possible, and for all of the cables of the same "type" to be the same length. Therefore, three black cables of the same length and three red cables of the same length is how I would do it.
David and Carolyn Osborn
1995 U320C SE 40' Build 4726 Feb 1995
FMCA 147762
Motorcade 17186

Re: New Wiring for Coach Batteries

Reply #2 –
Trent, it is always a good thing to think about this stuff. I tend to over think it I think but that is just me. But doing it right one time, neat and tidy and serviceable is the best way.

Resistance in the cable is a function of length, size, the lugs on the ends and the connection of the lugs to the terminals. For the same sized cables (setting aside lugs and connections equal lengths mean equal resistance.  So for each battery to supply the busbar with equal amps equal lengths make sense. The return side is the same. Make sense to make all of those the same length too. In a perfect world both cables to each battery would be the same length and all cables from the busbars to the batteries would be the same length.

4-0 welding cable has a resistance of 0.0668 ohms/1000'  Voltage drop difference for a 16" cable compared to a 22" cable is less than 0.01 volts.  V=ohms/ft x ft x amps.  Some cables may be different.

So, for short cables make them the length that makes them easy to work with and gives you some future flexibility.  Two lugs are going to cost more than a foot of cable so that shouldn't be a big influence.  You can get much more resistance in a poor lug to cable connection.  Use the right tool or have them made.  Make sure your posts are clean, coated with corrosion resistance stuff ot electrical grease (not dielectric) and that the huts are tight.  Check the nuts periodically.

Shunts are very low resistance devices. Voltage drop across them gets you amps.  Mine are mounted to the wall near the batteries where you are thinking.  One neg cable from the batteries goes to the shunt. The cable from the other end goes to the big negative post.  All of your batteries to one side of the busbar, the shunt bridging to the other end of the busbar and then all of your neg cables connected to that end should work fine.  Make it neat and tidy, easy to connect cables to and tighten nuts and connect wires to the shunt.

I would leave the BIG fuse (350 amps as I recall) where it is. 

I hope my opinion helps.



Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: New Wiring for Coach Batteries

Reply #3 –
Are your batteries on slides? Mine are on full extension slides, and so I found the shortest length that would allow the battery slides to be able to fully extend, and made all of them the same length. This required several mock ups to insure that none of the connections would be under excessive strain from the bends (4-0 tinned marine cable is very flexible, but it is so thick that the radius of any bend is limited as the outer strand bundles will have farther to go on any given bend). It would of course be possible to only extend the slides far enough to loosen the connectors and that would save some length of the cable run. It was also a challenge (especially with four batteries as opposed to three) to route and manage the cabling to allow for the slides to move without binding the cables. I posted about my project with quite a few pictures here;
Installing 4 batteries and a busbar setup in a 99' 36 foot U270
Don
The selected media item is not currently available.
Don & Tys
1999 U270 3602 WTFE #5402
Xtreme Stage 1 w/Headlight, Step Conversion, etc.
2009 Honda Fit Sport with Navi
Freedom is NOT "just another word for nothing left to lose"... with apologies to Kris Kristofferson

Re: New Wiring for Coach Batteries

Reply #5 –
 Trent, as I had revamped my battery cables etc to Bus Bars a few years ago I tried to make all cables the same length and the shunt is right behind the batteries using a cable coming off the end of Neg bar. So very close to "action".
One thing I will stress is the importance of somehow making a cover for these Bus Bars to protect from accidentally touching them or?
with anything that is conductible as there are a lot of Amps on them from the 3 or more Batteries and this will cause a bad burn or worse still a fire. I have a thin plywood panel that is fastened to frame of bay that does just that.
JohnH
Coachless, now use aircraft. 2003 Ford Travelair TC280 class C. Super shape. Just for 1 yr .
1994 Ford E350 ClassC,total renovation inside and out. Now sold.
2000 U295  36' Cummins 350 c/w Banks Stinger, Resonator upgrade,Solar, LED lites.Residential fridge with slide out pantry. Build 5674. Sold
ex 92 GV 022C ored Cummins. Sold
ex 95 GV240 cat 3116. Sold
2017 Mini cooper s & 2016 land Rover LR2 HSE  LUX.
jhaygarth@aol.com    SKP #130098
treat everyone as you would like to be.

Re: New Wiring for Coach Batteries

Reply #6 –
Quote from: Roger & Susan in Home2 –
I would leave the BIG fuse (350 amps as I recall) where it is. 

Roger,

I intend to replace a lot of the wires on that electrical panel with 4/0 wiring. By moving that fuse to the single combined positive lead from the battery bank, I am protecting all of the power runs from the battery bank. By moving it off that panel, I am preserving more real estate for the bigger wires that will replace the smaller ones. Or am I overlooking something else that prompted your suggestion?

I see this as comparable situation to having the shunt on the negative line from the battery bank. As I understand it, by locating the shunt on the single combined negative lead from the battery bank, I am measuring all of the amps into and out of the battery bank. That is what the Magnum ME-BMK battery monitor uses to track the state of charge for the coach battery bank.

The busbars for the engine battery were an obvious improvement, partly because most of chassis wiring was already located back there (ignoring things like headlight wiring runs). On the coach battery side, not so much, because a large electrical panel already exists. It is still important to use a small "busbar" to combine the three equal length wires from the coach battery posts. From there, a single (combined) cable will route the battery bank power on its merry way.

Guess I am going to have to spend some time with that big white fiberglass cover off the electrical panel and the Foretravel wiring diagrams to determine what is really happening with the coach battery distribution. Between my electrical engineering background and input from my buddies on this forum, I have a chance to not just git-r-dun, but, hopefully, get it done right. Will attempt to document my journey so the next person who wants to improve their Foretravel will have a better knowledge base from which to proceed.

This is an invitation and request for information, suggestions, recommendations, advice and observations for this part of my project to upgrade my coach battery wiring. Please don't take my follow-on questions as a form of criticism, but merely my attempt to stuff more understanding into my 72-year old excuse for a working brain. (When I finally get around to posting a picture of myself, you will see how obvious it is that Roger and I are really twins.)

Thanks,

Trent

Trent and Jean Eyler
2000  U295  4003  WTFE  ISC  350
Build#5603 MC#17385

Re: New Wiring for Coach Batteries

Reply #7 –

Did you get one of those crimping tools from Bay Marine Supply?  I had one of the hammer types which works OK on smaller cables but the 4/0 lugs are big and tough. I got some cables made at the local ag equipment place.  For what they charge, the big crimper (which does all of the bigger sizes, #6 and up) has earned it keep long ago.  And I get to make the cables the length I want, when I want.  Best of all if you want one end lug to be turned 90° left or right from the other end, you can do that.  Bay Marine has high quality lugs as well and cheaper in bags of 10 and a fixed shipping cost. 

FTZ Heavy Duty Lug Crimp Tool

Moving the big fuse into the battery bay between the two halves of the plus busbar works but it changes the existing protection.
The + cable from my batteries runs 3 ft or so to a common post, then to the 350 amp fuse and then to the inverter. The 350 amp fuse is more to protect the inverter perhaps?  A cable goes from the common post to a 120 amp breaker and then to the master battery disconnect switch.  On my coach another cable runs from the common post to a 150 amp breaker and then to th HWH hydraulic pump.

I guess if I were replacing the cables I might consider moving it but it is in a protected place now.  And it is doing a slightly different job.  There is a big 3/0 cable coming from the house battery side of the boost solenoid up to that same common post as well and then to the batteries.  Looking at the wiring diagram I do not see where that line is fused.  In general I don't like to alter the general idea that exists unless there us a really well thought out reason. If I am adding new stuff, how it was done makes a pretty safe guide.

Think this one through. Look at the wiring diagram for your coach (B-2126).  If you don't have one I can send you a copy. Lots of experience here on the Forum so I am hoping you get some additional thoughts from those who have worked through this. 

I have used these for common terminations or junctions...

Amazon.com: Pico 0810PT Military Style Top Post Battery Terminal 1 Set...

For new Battery terminals I have used these...

Amazon.com: Positive Insulated Battery Power Junction Post Block 3/8 Lug X...

Let me know if I can help.

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: New Wiring for Coach Batteries

Reply #8 –
Roger,

Quote from: Roger & Susan in Home2 –
Did you get one of those crimping tools from Bay Marine Supply? . . . I get to make the cables the length I want, when I want.  Best of all if you want one end lug to be turned 90° left or right from the other end, you can do that.
No, I got the 16 ton unit from Harbor Freight. So far it has worked flawlessly. the only difficulty is determining which size dies to use. For my 4/0 connections, I use 120 mm dies for the normal heavy duty lugs, and 150 mm for the even heavier battery lugs.

Quote from: Roger & Susan in Home2 –
The + cable from my batteries runs 3 ft or so to a common post, then to the 350 amp fuse and then to the inverter. The 350 amp fuse is more to protect the inverter perhaps?  A cable goes from the common post to a 120 amp breaker and then to the master battery disconnect switch.  On my coach another cable runs from the common post to a 150 amp breaker and then to th HWH hydraulic pump.
What Foretravel used as a "common post" is what I envision for the longer part of the positive busbar. The cables that now go from the common post to another location would be replaced by 4/0 cable going from the busbar to that location. If that wire goes to a breaker or fuse at the far end, it would be a straight forward replacement. If it goes to a fuse, then to a far away place (inverter), I would like to mount one end of that fuse on the busbar and go from the other end to the (inverter) connection.

Quote from: Roger & Susan in Home2 –
In general I don't like to alter the general idea that exists unless there us a really well thought out reason. If I am adding new stuff, how it was done makes a pretty safe guide.
Think this one through. Look at the wiring diagram for your coach (B-2126).
Lots of experience here on the Forum so I am hoping you get some additional thoughts from those who have worked through this. 
That's why I keep asking questions. I have spent a lot of time with the wiring diagrams and a large magnifying glass. I have thought of making a larger copy, but think it might be better to scan it and then I can enlarge it on the screen, add colors, etc..
I keep hoping we can get more members interested in our dialog; maybe it's just the weekend.

Quote from: Roger & Susan in Home2 –
I have used these for common terminations or junctions...
For new Battery terminals I have used these...
Let me know if I can help.
I used those standoffs and then wound up mounting them onto framing parts from my vinyl fence. Think I will try mounting the busbars to the vinyl framing instead; it should accomplish the same ends without spending the extra money.

You have already been helpful with all of your previous posts and ongoing interaction.

Thank you,

Trent
Trent and Jean Eyler
2000  U295  4003  WTFE  ISC  350
Build#5603 MC#17385