Wire Size for trailer batteries?

[cracker39]

I haven't seen any inverters in the 100w to 200w class that were full sine inverters. I don't think anyone makes a true sine wave interter that small. They all seem to be the modified sine wave. I think I read somewhere that they may cause lines on the TV picture.

[GeorgeTelford]

Hi Cracker

Occasionally a modified sine wave invertor will cause rolling line on a CRT TV (its very rare though and usually only with dirt cheap poor quality invertors), I have never seen a problem on any Flatscreen LCD screen.

My favourite manufacturer Sterling power products do a 150W pure sine wave, But I have not found a single item that I want to run thats needed it (yet)

Hi Tom

I can see that your fuse is rated well to protect the cable and to limit the max usage as you intend, I dont think it will present any safety issues at all. It will all work exactly as you intend, what more can you ask for (well hopefully that the regs will see your common sence approach as acceptable)

[cracker39]

Powderburn,

My batteries will be in a box on the tongue, also where the 30 amp circuit breaker for the shore power will probably be located. I was just going to run the wires inside (within the galley cabinet) and up to the fuse distribution panel where the converter will be located, about 7-8 feet of wire. As I understand this, I can either put an inline fuse (30 amps?) where the batteries are located, then on to the fuse distribution panel, or run the wire from the battery through conduit to the area of the fuse distribution panel, and put the inline fuse there where it comes out of the conduit. Does it matter if the conduit is metal or plastic? I like working with the plastic conduit as it is easier to cut (I have a PVC pipe cutter).

[cracker39]

I see no reason not to use electrical PVC conduit. It will not be exposed externally. It will run from my closed battery box, through the front wall into the galley cabinet. It won't even be exposed inside the trailer. I live in Florida, so cold is not a factor. Inside the trailer, heat won't be either as the exterior will be white and I doubt my interior will get up to 122 degrees F. I ran some wire through electrical PVC on the exterior wall of my house between my breaker box and the back porch and it's been there for a couple of years with no deterioration. I don't believe that any of the hazardous conditions listed in that code will exist in my trailer.

[cracker39]

Powderburn:

I think that your statement "If you put the fuse block close to your battery,your runs to your devices will require less wire length.
I think George specified 4 foot lengths? " was referring to a TD where most builders put their fuse blocks in the rear hatch area. My batteries will be in the front, my fuse block close to the front of the cabin (7'-8'), then wire runs up to the ceiling and back to the rear. The only way I can shorten the wire between batteries and fuse block is to put the fuse block in the battery box on the tongue. Then, I'd have to run the wiring from the converter forward to the battery box, then back to the devices, adding to the wire length.

I don't think my electrical setup can be improved by moving any of my components from where I've planned to put them. Using heavier DC wire than I had planned on is probably the answer to more power efficiency.

Here is a very simple diagram of the 12V system. The red lines are the 8ga wire from batteries, through a 30amp fuse, to the Fuse Block located by the converter box. The red line also represents the 12V from the converter charger back to the battery on a separate line. The black lines from battery and converter box represent frame grounding of the battery, converter, and gound terminal block for 12v devices (lights, fans, outlets). The blue lines represent the ground and positive 12 ga. wires going to the 12V devices (separate pairs of wires for each device).

[GeorgeTelford]

Hi

I would remove that fuse from the Battery box, imagine the battery as being a stick of dynomite and the fuse as the detonator and you will not be far from the mark, except a battery is worse than a stick of dynomite because the dynomite doesnt throw lead and acid when it explodes.

Another tip would be avoid using the chassis as the negative lead, it causes electrolytic reaction wherever the joints are and causes many of the arkward tracing faults whenever anything goes wrong. Yes it is a very good conductor (as long as the connections are done well, its the long term rotting effect and the tracing problems that need to be allowed for, your call)

where is the mains coming into the tear? is that aircon hanging out the front? What is the furthest 12v outlet for?

Wire length I always try to plot the shortest runs and overspecify the wire, the wire thickness and amps I specified in the other post are for 3 Meter Max run and will ensure voltage drop remains less than 3% I always aim to do better why waste power as unwanted heat.

[cracker39]

I would remove that fuse from the Battery box, imagine the battery as being a stick of dynomite and the fuse as the detonator and you will not be far from the mark, except a battery is worse than a stick of dynomite because the dynomite doesnt throw lead and acid when it explodes.

I thought a previous post from Powderburn said to have the fuse within 18" of the battery, or am I confused on this issue. Is there really a reason to put a fuse betweent the positive lead on the battery and the fuse distribution panel for the 12V devices? And, if yes, where should it be? At or close to the fuse distribution panel?

Another tip would be avoid using the chassis as the negative lead, it causes electrolytic reaction wherever the joints are and causes many of the arkward tracing faults whenever anything goes wrong. Yes it is a very good conductor (as long as the connections are done well, its the long term rotting effect and the tracing problems that need to be allowed for, your call)

Again, this is confusing. I was told that the 12V system should be grounded to the chassis. Doesn't that mean running a ground wire from the negative post of the battery to the chassis? I am also making a negative wire run (also 8ga) to the ground terminal block. I am not using the chassis as a negative ground. The red lines represent both positive and negative 8ga wirees from the battery to the panels. I failed to show the negative going to the panels, but that is what I intended to do. My drawing is misleading in that regard.

All 12V devices will have two wires to and from the fuse distribution panel and the negative groung block. The blue lines represent pairs of wires, one red and one black.

where is the mains coming into the tear? is that aircon hanging out the front? What is the furthest 12v outlet for?

My drawing has the front of the trailer on the right. The AirCon is on the left, hanging out of the rear near the top of the cabin. The main (shore power) will enter the battery box on the tongue at the right of the picture., go into the cabin with the 12V wiring, and then to the converter in the galley cabinet. I could also have the mains enter the cabin where the converter is, but space in the cabinet is restrictive and there is no room for my main 30 amp breaker. That's why I decided to use the battery box to enter the main power and have the main breaker there, then run the 115VAC on to the converter inside the cabin.

Wire length I always try to plot the shortest runs and overspecify the wire, the wire thickness and amps I specified in the other post are for 3 Meter Max run and will ensure voltage drop remains less than 3% I always aim to do better why waste power as unwanted heat.

I will have one 12V outlet in the rear in case I need it for a fan or other 12V device, but it probably won't be used much. Another will be at the galley for any 12V appliances I may decide to get later. The converter could be placed further to the rear. Not shown in my picture is a low cabinet for the porti-potti. It spans the area from the galley cabinet to the left side of the doorway, opposite the door. The converter and fuse distribution panel could be placed in the left end of that cabinet, shortening the wire run to the rear by nearly 5 feet.

[cracker39]

Your "MAIN" fuse has to go within 18 inches of the wire AFTER it has left the conduit inside the trailor.

If your using a fuse block,you must also have a main fuse thats rated according to the size of your service wire

Ok...I am running conduit to the panel location. It seems if I have a main fuse where the wire comes out of the conduit near the panel, I have met these two conditions above.

I think its a good idea to put the fuse where its at,if you can protect the fuse from fumes and acid.There is no restriction to having it there but,there is a restriction on how far your wire can traven after its entered the camper.

If I put a main fuse near the battery, I'll have to vent the battery box, which might be a good idea anyway. A small vent on each side. But, then, according to the first two statements, I'd need two main fuses. One near the battery and another near the panels. Or does the 2nd statement mean that the main fuse whereever it is must be "rated according to the size of your service wire"?

The ground wire is "required" to be grounded to the frame but,its still better to carry a ground wire to your devices too.

I am doing both.

[cracker39]

Your answers help, and common sense does come in to this. I'm sure that most TDs built don't adhere to all those rules, but I'll try to follow them as closely as possible. I'll find a place inside for the 115VAC main breaker and keep both breakers and fuses out of the battery compartment, unless I divide it into two separate compartments and vent the battery side. It is all a lot of information to digest, but I think I have the gist of it down pretty well. I'll work it all out as I put it together.

[GeorgeTelford]

Hi

when a battery is under the hood having a fuse close by is not usually a problem the airflow under a bonnet (hood in usa) is so great, that explosive fumes rarely build up, only once ever heard of a battery going off under the hood and that was a rare old set of circumstances. Also the engine generator (alternator) does not really produce enough power to rapidly produce gas like a real charger again this doesnt allow a great build up.

In a battery box its a whole different ball game, say your on shore power and the battery is bubbling away making explosive gas and then your unsealed fuse blows, the resulting explosion is the same power as a stick of dynomite with lead and acid shrapnel thrown in for good measure.

In the uk we vent fumes away with a tube and all caps are sealed on the battery. seems USA still use vented filler caps, BTW beware of sealed batteries these still have emergency vents so its still not agood idea to have sparks (fuses breakers etc) near them

Seperate compartments could be made to work.

Any unprotected length can short and cause fire so as soon as main wire leaves the battery box area get that inline fuse in position, for complete piece of mind fuse positive and negative then even a weird set of circumstances could not cause fire inducing short.

The requirement to ground is a throwback to an automotive vehicle, its pretty pointless on a tear though, If you ground only to battery (At a single point only) it will lower the electro reaction, it will now only be the interaction of disimilar metals.

Powderburn, I am mightily impressed with the American codes, they seem to match real world not dogma and are adaptable too amazing.

[GeorgeTelford]

Hi Powder

Bear in mind that I have already said that if code requires it, ground it in one place, we both agree on that and the reasoning.

But now you have intrigued me with this next bit and I quote If the frame werent grounded,a short could possably damage the tow vehicles circuitry

If the frame was not grounded, ie it were totally isolated, how could it possibly have any effect on the tow vehicle in the event of a short?

[cracker39]

I wondered about that, but I've asked so many questions, I just thought I'd wait to see if anyone else did too.

[GeorgeTelford]

Hi Powder

I still cannot follow that through, If the frame is isolated in the tear nothing could be transmitted via the hitch, which probably means the computer would be safer.

[cracker39]

Hi Powder

I still cannot follow that through, If the frame is isolated in the tear nothing could be transmitted via the hitch, which probably means the computer would be safer.

George, Powderburn,

That statement is quite related to a question earlier in this thread. I cannot see that any of my wires can possibly short against my frame due to the construction of my trailer. I will have no wires touching metal anywhere in my trailer that can come into contact with the frame. It will all be attached to wood. I only agreed to ground the battery to the frame after much reading of the codes that state that the battery should be grounded to the frame, and I still plan to follow that rule, as well as grounding the converter and the incoming 115VAC shore power to the frame.

[GeorgeTelford]

Hi Cracker

Yes we all agree that following the codes is best. (but only a single ground wire to chassis each from 12vdc and 120vac) The question we are now discussing is more theoretical in nature.