Please review my wiring diagram.

[richard5933]

I'd be using much heavier gauge wire for the battery parallel connections and the connections between the battery bank and the bus bars. Probably at least 4 ga. There's no point in cutting corners on a few feet of cable considering all the effort you're going through to get this done correctly. This will leave you open to making additions to the system later on without having to swap the cables. The converter putting out 45 amps means that the smallest gauge you can use on the connections to/from the batteries and from the converter is 6 ga.

The wire size for your 12v devices will depend on two things...1) The draw of the device, and 2) the distance.

Here's a great chart for calculating the wire size minimums: https://www.bluesea.com/resources/1437

My hunch is that you'll find that 16 ga wire is too small for most 12v circuits.

[gator.bigfoot]

Just for proper terminology, you don't use ground as a name for the negative in a dc circuit. There is positive and negative. In a AC circuit there is hot and neutral. All ac circuits have ground wires.

There can be a ground wire in both ac and dc circuits. But commonly we don't refer to the negative as a ground. I know people wire DC circuits in automotive and trailer applications with the chassis being the negative and ground, but technically it is wrong. Always better to have 2 wires to your loads. One of the most common failures in these circuits is that the ground connection corrodes.

[Serf27]

Richard, I had originally wanted to run 4 gauge wire but was told it was overkill.
If 4 gauge is recommended for all heavy power items, I will use that.

This brings up another question I had, the 7 pin trailer harnesses I’ve seen all have a 10gauge 12+ wire which charges the battery from the truck.
This wire is going to the circuit breaker in my diagram and then to the batteries. Is the wire thick enough to charge the batteries? Or do I need to run a separate power/negative wire from my truck to the batteries?

I was also told to use 12/3 SOOW CORD from my breaker box to any receptacles I add and that this would be good for 20amp breakers and would handle a small ac unit or heater/microwave.
Is this correct?

The only wiring now left in the trailer is the interior lights. It looks to be 16 gauge and also looked to be hard to replace without removing panels.
Would it be ok if I left this wire here?

It is basically powering 6 led lights, which I don’t think they will be all one at once.
Bathroom light, kitchen light, above bed light, center living area light and porch light.
I wanted to add a second bed light for the other bed and a second porch light, making it 8 led lights in total.

I was looking at these lights for above bed
3 watt/12v each.
Leisure LED 2 Pack 12V Led RV Ceiling Dome Light RV Interior Lighting for Trailer Camper with Switch, Single Dome 300LM https://a.co/d/cAohKX4

And these for the other interior lights.
6watt/12v
Kohree 12V Led RV Ceiling Double Dome Light 640 Lumens RV Interior Lighting for Trailer Camper with ON/OFF Switch, Natural White 4000-4500K, 48X5050SMD (Pack of 5) https://a.co/d/99alzlt

If 8 lights is too many, I could run separate wires to the bed lights and porch light.

I am still trying to figure out how to use the calculator to determine gauge thickness.

All other wires besides the int lights (if allowed, will be new and can be any type of thickness.


Gator, I will stick to negative and positive and neutral.
Even I was getting confused at times.
Each accessory will have its own power wire. I should run the ground wire from the accessory back to the ground block too then?

I was looking at this converter.
Powermax 110 Volt AC to 12 Volt DC Power Supply Converter Charger for Rv Pm3-45 (45 Amp) https://a.co/d/5W5zS90


But just found these other 2 that are half the price.


VEVOR 35 Amp RV Power Converter Charger, 110 Volt AC to 12 Volt DC, Power Supply Battery Converter Charger 600W with 13-16V DC Adjustable Operating Range, Three-Stage Inverter, for RV Trailer Camper https://a.co/d/7njAFWk

DC 12V 50A Power Supply 600W Switch 110V/220V AC to DC 12V PSU SMPS Converter Power Adjustable Transformer for LED Strip, LCD Monitor CCTV, Radio/Car Stereos, 3D Printer-Includ 2 Clamp Wire https://a.co/d/g5Y9lD5


Thanks for the help guys.

[richard5933]

First, the converter...

I'd definitely stick with a name brand with well-known quality. The converter is a key piece of equipment, and I wouldn't want to put something in there that could be unreliable or fail unexpectedly just to save a few bucks. Go with the name brands like Progressive Dynamics another well-known brand. I have no experience with Powermax myself, but they do seem to be used by quite a few people in travel trailers. I'd also suggest not getting the converter from Amazon and getting it from a place like bestconverter.com where you'll have customer service after you buy it.

Wire size...

The key to choosing the correct wire size is knowing how many amps you plan to carry over the wire. This involves a bit of math, so first a formula.

Watts = volts x amp

...and a few variants...

Volts = watts/amps
Amps = watts/volts

If you know how many watts a device is, you can divide by the voltage to find the amps.

To find the number of amps being carried on a circuit, you simply total up the amp rating for all the devices on a circuit. If they are telling you the watts, then divide by the voltage to find how many amps they pull.

One of the LED lamps you mentioned show that they are 3-watt lights, so 3 watts/12 volts = 0.25 amps, and the 6-watt lights are 6 watts/12 volts = 0.50 amps.

Just add up the number of these lights you plan to put on a circuit. For instance, if you have two of the 3-watt lamps and six of the 6-watt, then you'll have about 3.5 amps on the circuit. Of course, I've got no way of knowing if the lamps actually pull more or less than their stated rating, so I'd figure this at 5 amps to be sure.

Just continue doing the math and add up any other lights on this circuit, and once you know the total amps for the circuit you go to the Blue Sea chart I linked to. The way that works is simple...find the total amps you need to carry on the wire in the headings above each of the colored columns. Then you find the length of the circuit in the left-hand column. Remember that the total length of a circuit includes the length of the positive wire + the length of the negative wire.

You'll see two distance columns, each representing a percentage of voltage drop. The longer a circuit is, the more resistance there is in the wiring. This causes the voltage to drop between the source and the load. Some devices are more sensitive, and therefor a lower level of voltage drop is recommended. For these devices use the 3% column. For things where it's not as critical you can use the higher 10% column.

Once you know the amps and the distance, you follow the distance across to the right and the amps down the column, and where they meet is the minimum wire size you need. In this lighting circuit with up to 5 amps, you'd use the first colored column. Let's say that the furthest lamp was 10 feet away you'd calculate as a 20-ft circuit length and then choose between either the 3% or 10% from the left column, which would give you either 16 ga or 14 ga. Since these lights have a workable voltage range of 11-18v, you could go with the non-critical 10% and use 16 ga wire.

You'll find that for things like roof vents, the refrigerator, water pump, etc. you'll need heavier gauge wire. The math works the same.

The same basic process has to be done on every circuit - you need to know the total load you'll put on the circuit and the total length of the circuit. Then you can use the chart to determine the wire size.

For your 120v circuits, I should not suggest using SOOW cord. Airstream uses Romex, but some don't recommend it. The gold-standard option is using marine-grade triplex wire like this: https://www.wireandcableyourway.com/marine-wire-cable

It's more expensive, and I'm not convinced it's necessary if you properly secure the Romex to prevent it from moving around as the trailer goes down the road.

[Serf27]

Thanks for the detailed explanation.
I think I understand it.

What if all lights are on at the same time? Does the watts and amps increase?

For example, the exterior led lights I’m looking at are rated at. 2.7 watts each.
Running 4 of them gives me 2.7x4= 10.8 watts.
Divided by 12= .9amp

These are defined as non critical correct?
I would be looking at the 10amp area of the top chart and if the distance of the + wire at the fuse box to the last light and the negative back to the ground block = 20 ft, then the recommended gauge is 16g?

Or is that wrong and I am only to do that math for 1 of the 4 lights even if all may be on at the same time? 2.7watts divided by 12v= .2 amps, still results in the same 16gauge wire, but unsure if to account for all or just 1.

Does this also determine the fuse size needed in the fuse box for these circuits? That is another question that I have not asked.
If a circuit is .2 amps, the fuse would be a 5 amp fuse. If it is .9 it would be a 10amp fuse?

Is the same calculation done for the 120v circuit?
I will go with the Romex cable. I plan to have everything secure as to not cause any damage.
If the romex cable travels 6 ft or less from the breaker box to the receptacles, and I am using 20 amp breakers, the required wire gauge would be 12gauge?

Good idea on ordering from a website rather than Amazon so I can have customer service.
They have a lot on their website and it’s a bit overwhelming, I will try to email them.

Do I need a 45 amp converter if my breakers are only 25 amp?

[richard5933]

I calculate my DC circuits assuming max load - the wiring should be able to handle all the devices on the circuit being used at the same time. If you have 6 lamps on a circuit, calculate the wire size as if all are turned on simultaneously. If it's close to the max for a wire size, I usually go up to the next size.

Critical vs. non-critical...

This typically refers to the sensitivity of the device to voltage drops, not how important the device is to you or your comfort. As in, how critical is it that the device has the correct voltage.

The BlueSea chart show two columns - a 10% voltage drop and a 3% voltage drop. For example, if you're out dry camping and have system voltage of 12.5v a 10% voltage drop would mean your device is only getting 11.25v and you need to be sure that the device won't be damaged by a voltage that low. A 3% drop would provide 12.13v, which is much less likely to cause damage to sensitive devices.

Things like LED lights tend to have a wide range of allowable input voltages, but some things do not. Some electronics have a narrow input range, and some things like fan motors will run on the lower voltage but will get hot, ultimately causing damage to the windings in the motor.

Converter size...

This relates to how quickly your batteries will be able to be charged up. It is typical for it to be larger than any individual circuit on your 12v panel. But, the fuses and the wiring between the converter and the batteries should be large enough to handle the charging current of 45 amps.

[Serf27]

I got a bit lost.

So when you calculate all your devices one 1 circuit, you add all devices up together as if they will all be in use at one time? Is my example from above correct?

If I have 4 led lights at 2.7 watts.
2.7 x4 is 10.8 watts.
So I’d divide 10.8 by 12?
Giving me .9 Amps, which is round up to 10 Amps?

When you say fan motors, are you referring to any size fan?
I wanted to install a vent with fan in the restroom and run it off the led light wires, but maybe not if the motor will go bad.

I do not have any fuses in my digram between the converter and batteries, I’ve only accounted for the thick wire gauge. Is there normally a fuse between these 2? And is it the fuses that usually come on the converter? Or a separate inline fuse?

Thanks.

[richard5933]

Originally Posted by Serf27

I got a bit lost.

So when you calculate all your devices one 1 circuit, you add all devices up together as if they will all be in use at one time? Is my example from above correct?

If I have 4 led lights at 2.7 watts.
2.7 x4 is 10.8 watts.
So I’d divide 10.8 by 12?
Giving me .9 Amps, which is round up to 10 Amps?

Seems like you missed your decimal point on this one - should be 1.0 amps, not 10. Otherwise correct.

Originally Posted by Serf27

When you say fan motors, are you referring to any size fan?
I wanted to install a vent with fan in the restroom and run it off the led light wires, but maybe not if the motor will go bad.

What I had in mind was mentioning fan motors was to be aware that some are sensitive to voltage drops - the result may be slower speed and/or more heat buildup in the motor. What this means is for this type of device use the column marked "critical" in the BlueSea wire size chart. This is because accurate voltage is more critical for these devices than some other devices.

You can always use the heavier wire size shown shown for critical devices on non-critical ones, but you can't go the other way and go to a smaller size.

In your example you could combine the fan with LED lights. Add up the amps and use the wire size based on the amps - if anything on the circuit is sensitive to voltage drop, use the "critical" column.

Originally Posted by Serf27

I do not have any fuses in my digram between the converter and batteries, I’ve only accounted for the thick wire gauge. Is there normally a fuse between these 2? And is it the fuses that usually come on the converter? Or a separate inline fuse?

Thanks.

Many newer converters have built in fuses, some do not. Check the manual for the converter you'll be installing and if it calls for fuses install them.

[Serf27]

Ok I think I got it.
So I’ve added up 7 lights in total for the exterior and interior.

Three 7 watt lights
Two 3.6 watt lights
Two 6.2 watt lights

This puts me at 3.3 Amps an under non critical, so the existing wires in the ceiling should be fine for these lights. The fuse for these lights would be a 5 amp fuse since that’s the smallest one I can use?

This how I determine fuse amp sizes?
Calculate amps being used by a set of wires and round up to the next fuse size?

I also ordered this vent for the bathroom.
https://www.ebay.com/itm/18387650793...mis&media=COPY

It has a small fan and I was going to tap into the lighting wires, but a similar fan I found was rated at 2.2amps, which converts to 26 watts.
Is that correct, that small fan needs 2.2 amps to function correctly?!

[richard5933]

Originally Posted by Serf27

Ok I think I got it.
So I’ve added up 7 lights in total for the exterior and interior.

Three 7 watt lights
Two 3.6 watt lights
Two 6.2 watt lights

This puts me at 3.3 Amps an under non critical, so the existing wires in the ceiling should be fine for these lights. The fuse for these lights would be a 5 amp fuse since that’s the smallest one I can use?

This how I determine fuse amp sizes?
Calculate amps being used by a set of wires and round up to the next fuse size?

I also ordered this vent for the bathroom.
https://www.ebay.com/itm/18387650793...mis&media=COPY

It has a small fan and I was going to tap into the lighting wires, but a similar fan I found was rated at 2.2amps, which converts to 26 watts.
Is that correct, that small fan needs 2.2 amps to function correctly?!

Generally speaking, fuses are sized to protect the wiring, so you would choose the appropriate fuse for whatever wiring you have. If you have some sensitive equipment like a radio you can add a smaller inline fuse to protect it.

[gator.bigfoot]

Originally Posted by Serf27

What posts make it easier to make it easier and what wires are you talking about?
So you’re running a thicker wire after each connection?

I was planning on using 8 gauge wire for all battery connections/converter and 16 gauge for any 12v accessories leaving the fuse box.
Led lights, radio.
Should I use 10 gauge for the water pump?

Do the batteries need thicker wire or this is fine?

.

The posts I'm talking about are labeled as single stud junction terminal or block. You can search for them. The thicker wire makes it easier to connect to them when connecting multiple heavy gauge wires to one location.

6 gauge is minimum for battery cables. I would go 4 if you can.

10 is fine for the water pump.

16 gauge for the other circuits will work, but I'd go larger to 14 as minimum. Make sure your wire has a temp rating. Don't buy the cheap stuff. Also make sure you have some insulators when running your wires through metal holes. You don't want the vibrations to wear through the insulation on the wires.

One thing that almost all online calculators don't give you is the voltage losses with increased temperature. I wrote my own calculator to figure this out.

[Serf27]

Finally time to start running wires.
So, I am getting:
10 gauge wire for the water pump
16 gauge for ceiling LED lights
14 gauge for the radio and exterior lights.

Aside from the 10 gauge water pump and 4 gauge battery wires, all other 12v accessories will be find on 14 gauge?

[Serf27]

I am also looking at this fuse box.
WUPP Boat Fuse Block, Marine Fuse Panel with LED Warning Indicator Damp-Proof Cover - 12 Circuits with Negative Bus Fuse Box Holder for Car Marine RV Truck DC 12-24V, Fuses Included https://a.co/d/8UL0UHW

Based off my diagram and a video I saw,
The battery 12v+ Goes to the fuse box and so does the + AC to DC converter.
The fuse box linked only has 1 + post.
Would I just put both the battery + and conger + on that single post?

Same story for the negative side of both the battery and converter on the single - post on the fuse box?

Thanks.

[Serf27]

I am also looking at this fuse box.
WUPP Boat Fuse Block, Marine Fuse Panel with LED Warning Indicator Damp-Proof Cover - 12 Circuits with Negative Bus Fuse Box Holder for Car Marine RV Truck DC 12-24V, Fuses Included https://a.co/d/8UL0UHW

Based off my diagram and a video I saw,
The battery 12v+ Goes to the fuse box and so does the + AC to DC converter.
The fuse box linked only has 1 + post.
Would I just put both the battery + and conger + on that single post?

Same story for the negative side of both the battery and converter on the single - post on the fuse box?

Thanks.

[richard5933]

It's much easier to use a bus bar for both the positive and negative side of your 12v system. These will give you a central point to gather all the different cables needing to be tied together.

On my trailer I used bus bars to connect the battery cables (on the positive side), feed from converter/charger, feed from solar controller, feed to inverter, power feed to fuse box, etc.

I've got a red and black version of this: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

There are others out there with different capacities and different screw/lug sizes. You need the bus bar to be able to handle more than your max possible total current draw.

A pair of bus bars will make things much more simple and avoid having to double/triple connections at your batteries or fuse box.

[Serf27]

Originally Posted by richard5933

It's much easier to use a bus bar for both the positive and negative side of your 12v system. These will give you a central point to gather all the different cables needing to be tied together.

On my trailer I used bus bars to connect the battery cables (on the positive side), feed from converter/charger, feed from solar controller, feed to inverter, power feed to fuse box, etc.

I've got a red and black version of this: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

There are others out there with different capacities and different screw/lug sizes. You need the bus bar to be able to handle more than your max possible total current draw.

A pair of bus bars will make things much more simple and avoid having to double/triple connections at your batteries or fuse box.

Thanks for the reply, I like those bus bars you linked.
Are they $40 because they can handle the current draw or for other reasons?

And the fuse box? I only find the ones with a + and -.
I could order one and try it, but the fuse box should still send power through the fuses with only the positive wire on it?

[richard5933]

Originally Posted by Serf27

Thanks for the reply, I like those bus bars you linked.
Are they $40 because they can handle the current draw or for other reasons?

And the fuse box? I only find the ones with a + and -.
I could order one and try it, but the fuse box should still send power through the fuses with only the positive wire on it?

They're probably priced at $35.99 because they are well made. They are also covered, which is a big plus in avoiding accidental contact.

You can certainly find cheaper bus bars with a lower capacity but then you limit your system. Remember that a system is only as robust as the weakest component.

Fuse blocks will often include a negative side as well as a positive, and this is to provide a convenient place to connect each circuit's negative side. You can also find fuse blocks with just positive sides.

If you're using a fuse block rather than self-resetting breakers be sure to place it somewhere you can easily get to when a fuse blows. They will.

[waninae39]

+1 from gator.bigfoot points out that -ve and ground are not always the same

the VW bettle had a +ve ground system

All telecom phone systems around the world use +ve ground. (This was selected in the 1930's as the best means to minimize corrosion of wires in underground lines. Still in place )

[richard5933]

Originally Posted by waninae39

+1 from gator.bigfoot points out that -ve and ground are not always the same

the VW bettle had a +ve ground system

All telecom phone systems around the world use +ve ground. (This was selected in the 1930's as the best means to minimize corrosion of wires in underground lines. Still in place )

Pretty sure that most all systems being discussed here are negative ground.

[Wazbro]

With the industry going to 120v/12v compressor fridges instead of 120v/propane absorption fridges, running 12 gauge maybe even 10 gauge wires to the fridge now could be a good idea.

If you have a 3-way fridge (120v/12v/propane) you would need wire at least 10 gauge for the 12v line.