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 > 12V wiring Aluminum Cargo Trailer conversion

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Fisherman

Angus, Ontario, Canada

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Posted: 05/27/20 07:54pm Link  |  Quote  |  Print  |  Notify Moderator

SlideInDad wrote:

Should I bolt a grounding block onto the aluminum frame? I saw comments of no copper against aluminum but what about a steel grounding block on the chassis?


Any dissimilar metal will have galvanic reaction, even steel on aluminum. How about mounting the grounding buss bar somewhere on a spot on wood.

MEXICOWANDERER

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Posted: 05/27/20 10:17pm Link  |  Quote  |  Print  |  Notify Moderator

The NEGATIVE is not a corrosion issue

It is a GALVANIC ISSUE.

Never use any part of a non noble metal as part of an electrical circuit. The circuit must be totally isolated from both AC and DC electricity.

Load negatives back to a distribution block. Distribution blocks to a central bus bar which will connect to the trailer battery AND the wire to the tow vehicle plug. Being mechanically connected to the two vehicle influences nothing. But connect bo grounds to trailer chassis or frame.

SlideInDad

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Posted: 05/30/20 09:23am Link  |  Quote  |  Print  |  Notify Moderator

So I found this article which is quite descriptive of chassis grounding. RV electricity part 1 and
Part 2

It would seem that the ground-plane used for most RVs DC system is for the purpose of serving as a negative return for DC appliances.

The true focus of the ground discussed in these articles is:

"properly “grounded” your RV chassis must have its EGC wire properly “bonded” (connected) to the power company’s service panel “ground/neutral/earth” bonding point. And that bonding must provide an under-1-ohm connection for the neutral of the transformer on the power pole to return any fault currents back to whence they started (in the transformer)"

Since it's become very clear in all my research to date that I should not return any negative DC current via the 100% aluminum chassis of my trailer (will run negative wires from every appliance back to the fuse panel instead) it's starting to sound like the real concern I should have is simply my shore power connection as I will be running zero AC appliances in this trailer beyond the 120 to the converter while at home for charging or connected to my generator while boondocking. I think in the past 20 years I've been to a campground with shore power connections only twice.

Am I on the right track here? Ultimately I'm looking to setup a pure 12V power system on my trailer hopefully 90% of the time charged from my 200W solar setup. My draw should be minimal compared to my old TCs as I will have no inverter and no heavy draw appliances. Really just lights and fans (fantastic fan, propane furnace fan, window DC fan, USB charging station for phones/laptop).

If the IOTA45 converter is simply properly bonded to my house 120V what purpose would the chassis ground serve?


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DrewE

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Posted: 05/30/20 10:50am Link  |  Quote  |  Print  |  Notify Moderator

SlideInDad wrote:


If the IOTA45 converter is simply properly bonded to my house 120V what purpose would the chassis ground serve?


The converter chassis needs to be bonded to the RV chassis (as is detailed in its installation manual), and the 120V ground needs to be bonded to the RV chassis.

The 120V ground to chassis connection is for safety in case there should be an electrical fault in the 120V wiring, causing the hot to short to the chassis. If the chassis were not grounded, it would be hot and pose a shock hazard to anyone entering or exiting the RV (a hot skin). Having it bonded to ground prevents that, and assuming the short is low enough impedance causes the breaker to trip due to overcurrent.

The 12V bond is a bit more subtle. As I understand it, it is practically speaking impossible to totally isolate the chassis from 12V negative ground with typical appliances and lights, and so it's likely that the chassis will be connected to the 12V negative side somehow or another. If there's not a good bond between the battery and the chassis, and the converter output and the chassis, then there's the opportunity for all of the converter current to find its way through e.g. the 120V ground wire or the ground wires for various 12V appliances back to the battery in the case where the main wire from the converter's negative output to the battery is broken or disconnected. This amount of current can easily be a dangerous overload for those wires; hence, as a safety precaution, they must be tied to the chassis with a low impedance wire that will carry the fault current safely.

Assuming you have electric trailer breaks with a breakaway switch, the trailer chassis will have to be grounded for that system to work properly. (I guess that's also assuming you're using the house battery for the emergency braking power, which is standard practice. Having to maintain two separate batteries when one will do just fine on its own seems...well, silly.)





CA Traveler

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Posted: 05/30/20 11:26am Link  |  Quote  |  Print  |  Notify Moderator

Bonding is a basic saftey practice. A very small AC leak to a ungrounded RV can cause a significant shock. Typically these leaks do not trip a CB and can exist even if the CB is tripped - I could be before the CB or it can occur from the negative AC lead.

A little extra wire and connections diverts this current/voltage back to the shore panel via the AC ground wire. This is a basic safety requirement and replaced 2 wire plugs many years ago with 3 wire plugs.


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SlideInDad

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Posted: 05/30/20 12:34pm Link  |  Quote  |  Print  |  Notify Moderator

DrewE wrote:

SlideInDad wrote:


If the IOTA45 converter is simply properly bonded to my house 120V what purpose would the chassis ground serve?


The converter chassis needs to be bonded to the RV chassis (as is detailed in its installation manual), and the 120V ground needs to be bonded to the RV chassis.

The 120V ground to chassis connection is for safety in case there should be an electrical fault in the 120V wiring, causing the hot to short to the chassis. If the chassis were not grounded, it would be hot and pose a shock hazard to anyone entering or exiting the RV (a hot skin). Having it bonded to ground prevents that, and assuming the short is low enough impedance causes the breaker to trip due to overcurrent.

The 12V bond is a bit more subtle. As I understand it, it is practically speaking impossible to totally isolate the chassis from 12V negative ground with typical appliances and lights, and so it's likely that the chassis will be connected to the 12V negative side somehow or another. If there's not a good bond between the battery and the chassis, and the converter output and the chassis, then there's the opportunity for all of the converter current to find its way through e.g. the 120V ground wire or the ground wires for various 12V appliances back to the battery in the case where the main wire from the converter's negative output to the battery is broken or disconnected. This amount of current can easily be a dangerous overload for those wires; hence, as a safety precaution, they must be tied to the chassis with a low impedance wire that will carry the fault current safely.

Assuming you have electric trailer breaks with a breakaway switch, the trailer chassis will have to be grounded for that system to work properly. (I guess that's also assuming you're using the house battery for the emergency braking power, which is standard practice. Having to maintain two separate batteries when one will do just fine on its own seems...well, silly.)


I do have a breakaway system with an old dead battery, was figuring on wiring it to the new 12V house battery system. I haven't looked yet but assumed it was grounded back to the Tow Vehicle?

DrewE

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Posted: 05/30/20 02:26pm Link  |  Quote  |  Print  |  Notify Moderator

SlideInDad wrote:

DrewE wrote:


Assuming you have electric trailer breaks with a breakaway switch, the trailer chassis will have to be grounded for that system to work properly. (I guess that's also assuming you're using the house battery for the emergency braking power, which is standard practice. Having to maintain two separate batteries when one will do just fine on its own seems...well, silly.)


I do have a breakaway system with an old dead battery, was figuring on wiring it to the new 12V house battery system. I haven't looked yet but assumed it was grounded back to the Tow Vehicle?


The ground for the trailer brakes (and hence also the ground for the brake lights and whatnot) needs to be connected to the negative of the battery, and the positive from the battery goes to the breakaway switch, and the other side of the breakaway switch to the brake coils in parallel with the brake wire from the tow vehicle connection. The ground connection can't go back all the way through the tow vehicle, of course, since the whole point is to activate the trailer brakes should the trailer and tow vehicle become separated from each other. It is shared with whatever ground is there from the tow vehicle connection, which I think might be what you meant.

I did a tiny bit of research, and apparently the accepted best practice for aluminum trailers is to run ground wires to the brakes and lights and still bond the frame to the ground connection from the tow vehicle. The bonding among other things helps prevent static buildup (I assume mainly from the tires rolling down the road). Apparently sometimes the brakes and lights are both grounded to the frame themselves and also grounded via a ground wire; for many trailer lights, they'd be grounded to the frame simply by being installed unless special care was taken to electrically isolate them. I had been under the impression that brakes were at times similarly grounded via their mounting to the axle, but it seems that was a false impression--they have wires for both sides of the coil to be connected up.

djglover7

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Posted: 07/07/20 02:56pm Link  |  Quote  |  Print  |  Notify Moderator

All,

I am slightly comforted seeing others have questions on grounding. This thread has been very informative.

I am utilizing 3 voltage systems, 12VDC chassis, 12VDC coach, 120VAC shore. There is a coach battery that supports various chassis and coach power.

My one unresolved issue is:

*IF* I bond/connect 12VDC negative to chassis *AND 120VAC ground to chassis, is there *ANY* issue with voltage surges/spikes/daemons going from AC to DC?

The big concern is surges/spikes/daemons going from AC to the tow vehicle (DC).

Please advise.


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wa8yxm

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Posted: 07/07/20 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

IF you want 'Best results' there is a special connector to connect copper to aluminum. beyond that I have no knowledge as I've never actually seen one

I'm guessing a ring terminal with an aluminum screw to the chassis (or bolt) is the order of the day but the ring terminal is crimped onto the copper and it is a SPECIAL type of terminal made for that job.


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BFL13

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Posted: 07/07/20 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

Yes, the 120v and 12v share the same RV frame for ground (120)/neg (12). Typical RV power centre has the 120v incoming to the 30a Main breaker with the bare ground wire going to the RV frame. Meanwhile the converter in that power centre uses the same RV frame for much of its several neg paths to the various 12v items such as slide motor, jacks, etc. The metal skin of RVs that have that is the negative path for the clearance lights too.

The metal casing of the power centre is grounded to the frame as is the "lower portion" 's metal casing (chassis) so that is the "chassis ground" for the converter. If you have a deck mount converter it will have its own chassis ground from a lug on its metal casing. Same with a bigger inverter.

Warning--do not bring the chassis ground of an inverter back around to its own neg input terminal. That does get to the frame via the battery's neg ground to frame, but you are supposed to run the inverter chassis ground direct to the frame.

Those inverter chassis grounds are to reduce radio interference.


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