Truck frame instead of seperate (-) wire

[cwdtmmrs]

What are the con's of using the vehicle frame for the return path from the camper battery to the truck's charging system? I have talked to EE's and auto mechanic's and get varying opinions. Some say that copper wire back will have less resistance and others say that is true, but the frame is so much larger that it will more than make up for the difference and I will get less voltage drop as long as I have good frame connections. We are talking about 15' one way. The other consideration is that I can go to a #4 single wire instead of #6 duplex wire in the same space I would like to run the wiring.

Thanks,
cwd

www.w8ji.com/negative_lead_to_battery.htm

 

[Boonie]

CWD
For what it's worth, recently while working under my Coachmen class C motor home, I noticed that the house batteries were grounded directly to the frame.

 

[BFH4N]

Do both?

 

[JaSAn]

What are the con's of using the vehicle frame for the return path from the camper battery to the truck's charging system? . . .

. . .as I have good frame connections. We are talking about 15' one way. The other consideration is that I can go to a #4 single wire instead of #6 duplex wire in the same space I would like to run the wiring.

About half of the electrical problems I have had the pleasure of troubleshooting in custom cars have been grounding issues. Usually badly installed connections or corrosion. And they can be frustratingly intermittent.

For my Grandby I ran positive and negative 6 AWG from alternator to house batteries. 6 AWG gives me too much voltage drop to most efficiently charge the house batteries, so this winter I am replacing the 13 foot run with two 4 AWG cables.

So, my advice is that if your choice is two 6 AWG or one 4 AWG, go with the larger wire and chassis ground. Just make sure you have a good chassis ground.

jim

P.S: don't forget to fuse the positive cable at BOTH ends.

 

[rando]

The issue is not the frame itself - it has a massive cross section that would offer far lower resistance than any wire can. The issue is successfully bonding your ground wire to the frame.

 

[Kolockum]

I use my frame for my camper ground and my winch ground. My winch is hitch mounted and has electrical plug ins on both the front and back of the vehicle.

After trial and error I found the best way to connect the ground to the frame is grind off a silver dollar size section of paint around the ground bolt hole and use a stainless bolt with large copper washers smeared with dialectic grease to hold the ground in. The bare metal, copper washer and dialectic grease creates a large area for the electricity to go through. A simple bolt through a hole drilled into a frame won't do much if the paint is still blocking the connection.

 

[Vic Harder]

I use my frame for my camper ground and my winch ground. My winch is hitch mounted and has electrical plug ins on both the front and back of the vehicle.

After trial and error I found the best way to connect the ground to the frame is grind off a silver dollar size section of paint around the ground bolt hole and use a stainless bolt with large copper washers smeared with dialectic grease to hold the ground in. The bare metal, copper washer and dialectic grease creates a large area for the electricity to go through. A simple bolt through a hole drilled into a frame won't do much if the paint is still blocking the connection.

Other considerations to keep in mind:
- are you grounding the house batteries to the camper? If so, then how are you connecting the camper to the truck's frame?
- There will be multiple connection points for this ground, and all should be thoroughly connected as K mentions above, and visible so you can check them

 

[Mark G]

The conduction issue is also maintaining an electrical connection between dissimilar materials. I second using a dedicated wire rather than the chassis.

 

[cwdtmmrs]

Well, I decided to go with grounding to the frame and running #4 power wire (fused both ends) back to the alternator. My house battery is located in the truck bed in front of the wheel well. It is dual post so I am using 2 #1 ga. cables to two different locations on the frame anchored with the bolt/copper washer method. I have replaced the truck battery negative cable with an O ga one as well. I think this will be more than enough for my needs. I do not use much power, probably 12-20 AH's per day tops. I use a 3 Way fridge, LED lights, water pump,a furnace and then switch to a Wave 3 for heat. What I have now is one 9 year old yellow top 55 AH battery fed by the truck's 60 amp alternator through a constant duty 100 amp solenoid triggered off of the ignition's accessory circuit. All with 10 ga wires and I have never run out of power in 9 years, but I do drive some everyday. I am only getting into this because I had to take the camper off for some repairs and everything is exposed. I have started to run the 3 Way on DC while traveling and that sucks 9-11 amps out of the charging system so I am installing a new 120 amp alternator with 4 ga wiring as well. I was told that it will put out 70 amps @idle. I was going to install a 110 AH Powersonic battery, but the old yellow top still is still going strong!

cwd

 

[ntsqd]

An issue with frame grounds that doesn't get much attention or thought are the welds in the frame. It is true that the frame has a large cross-section and should be a good conductor even if it is steel (which isn't an exceptionally conductive metal), and it is also true that we tend to think of frames as being one continuous piece of steel when - particularly in late model trucks - they are not. Each weld that the current must cross presents a resistance to flow and cumulatively they can be quite significant.

Every battery-in-the-trunk hot rod my friends built has hot start problems, even with 3/0 positive cable, until they started running a dedicated ground cable too. Since then I do not use the chassis for a main ground conductor.

Talking to an EE at work the other day was illuminating. It is not the easily calculated cable lug contact area that matters in current conduction thru a bolted joint, but rather the force with which the lug and it's mating surface are held together. Essentially the bolt's applied torque completely dominates the conductivity. That is immensely counter-intuitive I know, but it why all high end high current electrical/electronics components have a fastener torque spec. I had a hard time wrapping my head around it, but he assured me that many studies have been done on the topic and they all agree.
Here's where it gets tricky, what happens is that the higher the force, the more aspirates are crushed. The more aspirates crushed, the more metal in close-tight contact. So it really is a contact area that is important, but due to deflection and surface roughness you can not easily calculate it or even approximate it. It is not simply the area of the flat of the lug minus any over-hangs.

 

[cwdtmmrs]

Wow...I am going to attach the ground cables to the same side of the frame which is I piece and hope for the best. I know it is much shorter run, but a normal vehicle starter doesn't have a dedicated ground wire and they tend to pull a lot of amps. My truck always starts when I turn the key.

cwd

FWIW, The shop next to mine is full of EE'S...(they tend to be a strange lot, but I digress.)...and have been watching my project. They did not like the frame grounding at first either, but after all the pros and cons and seeing how the installation is going to be done, they thought it would be ok.

 

[ntsqd]

They are a strange, but very necessary group. I'm sure they think the same of my fellow Mechanicals & MFG's.

Never seen a OEM installation starting battery not grounded to the engine block (if not the actual starter) with a large-ish cable as the primary grounding. Some 70's era GM's had their primary ground on the alternator tensioning bracket, and though I doubt it's directly connected those vehicles tended to have hot-start problems. I always moved those to a block ground.

 

[cwdtmmrs]

I agree about the starting battery grounded to the engine block, that is why I am ground the camper battery to the frame with a 1/0 cable from the top post and a #4 cable from the side post. I know I will get less voltage drop this way.

cwd

 

[DavidGraves]

I was crushing some aspirates just the other day...its the only way I can deal with my bursitis.

DavidGraves

 

[mib]

A lot of very true stuff has been said. I had painful issues with incomplete ground connections as well. Do it properly!

BUT:
You're worried about losing fractions of a volt doing it one way or the other. This is because you want to keep your camper battery fully charged. Your alternator, however, does not do a good job in charging a yellow-top. It's doing a sufficiently good job in charging the starter batteries under the hood, but it never reaches a perfect charging voltage for a camper battery. After those feets and feets of cable, you will always have some voltage drop, and even without such you'd never have an adequate charging program that truly fills the battery to 100%. Your generator doesn't care about the temperature in your truck bed either, making things worse. In hot summer, it may cook your camper battery, while in cold winter it only charges to 80% or so.
My advice: get a B2B-Booster, which converts your generator-voltage (14.xV) to a voltage that is adequate for the charging state (such as IUoU line) and the temperature of the battery. It may sound complicated, but your best bet would be the CTEK Dual 250. It's pretty plug and play - if you can route a AWG4 cable to the truck bed, you can install the Dual.
With such, it wouldn't really matter whether you have an AWG4 or 12 running from the front. All you need is a thick enough cable to carry about 250W = 20A. Any voltage drop (be it through your thin + wire or through your chassis connection) would be compensated by the charger.
Nice side effect: a 20A MPPT solar charger is in there as well. Just hook up whatever panel you have.


I had them in multiple camper and love the simplicity and that fulfill ALL the needs for a camper battery (solar+generator, good charging, temp compensation, reasonable amperes).
Best,
Michael

 

[cwdtmmrs]

The CTEK Dual 250 looks very interesting, but like I posted earlier, my system has worked well for almost 10 years without a glitch and I have never had a dead battery and only charging off of the 60 amp truck alternator. I will keep the CTEK in mind.

cwd

 

[mib]

I agree, I'm not saying your setup wouldn't be sufficient. Especially since you said you drive almost every day. A mere solenoid on ignition will easily top up your battery, since there will be quite some current flowing (50A?). You're probably talking about fractions of a volt of more voltage drop with your chassis ground (unless some ground strip to the engine block or transmission rips).
When it comes to getting the maximum Ah out of your battery (think of 3 days of standing on a beach with your 55Ah), the CTEK will play its cards. For daily driving, it won't - mostly because it only charges with 20A. You can get the SmartPass addon, but then you're talking about 400$ to "repair" something that works perfectly for you as it is.

So, if I were you, I'd keep it exactly like it is, just taking extra measure to make sure your bolts don't rattle lose. I like Loctite for this.

 

[cwdtmmrs]

Thanks for the input and info on the CTEC stuff. I bet I get less voltage drop using the frame. I will measure when I am done. I have see several videos ( on You Tube, so it has to be true... ) that show more voltage drop, albeit fractions, with a 1/0 cable back then using the frame. We will see. with the addition of a 120 amp alternator, I am hoping to charge the battery with very minimal engine usage or idling each day.

cwd