Electrical Question

[Byron Kinnaman]

Originally Posted by Spanke

Why Not?

You made the statement and I would like to know your reasoning. But since you why not here's my reasoning.

Here's my reasoning for use either 12 awg or in some cases 14 awg. You can even go all the way to 16 in many cases.

Most 13' fiberglass trailers have a 20 amp 12 volt service. The maximum expected to draw is around 20 amps.
Lets take a look at some common current draws expected.
Standard 12Volt automotive incandescent lamps 1.5 amp each.
LED light replacement bulbs 0.2 amps each.

Furnace fan 3.5 amp (approx.)

Other items like a lap top computer 3 to 7 amps.

The larger gauge wire is more expensive, which is good for the metal thieves.
Larger wire is harder to handle get into small spaces, larger bend radius, and stiffer.

So it just doesn't seem practical to spend the extra money and effort to use the larger gauge wire.

[Jon Vermilye]

The choice of wire size depends on what you expect to pull from (and put back into) the battery. #10 or even smaller would be OK for LED lighting & most loads - using the wire sizing tables at Powerstream shows #10 wire good for as much as 55 amps for chassis wiring.

Unfortunately, it isn't quite that simple because you also need to consider voltage drop. Wire has resistance & some voltage is going to be dropped across the wire in order to push current through it. For some devices even a large amount of voltage drop is OK but for others it will be a problem.

For example, most large inverters shut down when the input voltage drops below a preset amount. If your wire is too small, you may find the wire loss is enough to shut down the inverter before the actual battery voltage is lower than the preset amount.

If you have a 3 stage converter to recharge your battery, too small a wire between the converter & battery may prevent it from going into the "Boost" mode - the fastest charging stage.

For most branch circuits from the fuse panel to most devices the general rule of keeping voltage drop to less than 3% works. There is a calculator at the bottom of the wire size table linked above that lets you enter current, wire size, voltage & wire length to calculate drop. You will find that for most runs over a couple of feet you need to stay well under the maximum current for the specific wire size to keep the voltage drop under 3%.

For example, that 55 amp rating for10' of #10 would result in a voltage drop of 1.13 volts or 10.86 volts at the load (an 9.42% drop). To stay within the recommended 3% the maximum current you could draw would be around 18 amps.

I agree with Byron that you can use wiring smaller than #10 to save money & ease of wiring, however for large loads such as 12V refers, converters & inverters actual calculations will produce better results.

All in all, spending some time planning 12V wiring will save you needing to rewire things in the future. A very useful site for more information is The 12 Volt Side of Life, Part 1 & 2 by Mark S. Nemeth.

[Byron Kinnaman]

Originally Posted by Jon Vermilye

The choice of wire size depends on what you expect to pull from (and put back into) the battery. #10 or even smaller would be OK for LED lighting & most loads - using the wire sizing tables at Powerstream shows #10 wire good for as much as 55 amps for chassis wiring.

Unfortunately, it isn't quite that simple because you also need to consider voltage drop. Wire has resistance & some voltage is going to be dropped across the wire in order to push current through it. For some devices even a large amount of voltage drop is OK but for others it will be a problem.

For example, most large inverters shut down when the input voltage drops below a preset amount. If your wire is too small, you may find the wire loss is enough to shut down the inverter before the actual battery voltage is lower than the preset amount.

If you have a 3 stage converter to recharge your battery, too small a wire between the converter & battery may prevent it from going into the "Boost" mode - the fastest charging stage.

For most branch circuits from the fuse panel to most devices the general rule of keeping voltage drop to less than 3% works. There is a calculator at the bottom of the wire size table linked above that lets you enter current, wire size, voltage & wire length to calculate drop. You will find that for most runs over a couple of feet you need to stay well under the maximum current for the specific wire size to keep the voltage drop under 3%.

For example, that 55 amp rating for10' of #10 would result in a voltage drop of 1.13 volts or 10.86 volts at the load (an 9.42% drop). To stay within the recommended 3% the maximum current you could draw would be around 18 amps.

I agree with Byron that you can use wiring smaller than #10 to save money & ease of wiring, however for large loads such as 12V refers, converters & inverters actual calculations will produce better results.

All in all, spending some time planning 12V wiring will save you needing to rewire things in the future. A very useful site for more information is The 12 Volt Side of Life, Part 1 & 2 by Mark S. Nemeth.

Voltage drop in most cases is insignificant, that's why I didn't mention it. What in your trailer is going to draw 55 amps?????

Larger loads, refers = 9.5 amp.
converter ???? Wrong direction
Inverter... Maybe if you have a big one. But you won't use it very long before the battery is dead.
Think Practical....

[Jon Vermilye]

Originally Posted by Byron Kinnaman

Voltage drop in most cases is insignificant, that's why I didn't mention it. What in your trailer is going to draw 55 amps?????

Larger loads, refers = 9.5 amp.
converter ???? Wrong direction
Inverter... Maybe if you have a big one. But you won't use it very long before the battery is dead.
Think Practical....

I'm not sure what you mean by the wrong direction for the converter - when charging the battery the DC is going over the same wires to get from the converter to the battery. Many converters can charge at 40 amps or better in the boost mode.

As to the inverter, many individuals use a large inverter for short periods of time without problems. I have a 900 watt inverter that lets me make a pot of coffee. It does draw 600 watts for around 5 minutes - that works out to around 4.2 amp hours which my solar system puts back in the batteries in an hour or so.

Again, I'm agreeing with you in most cases, but there are times large wires are useful.

[Laura & Rick]

Originally Posted by Byron Kinnaman

You made the statement and I would like to know your reasoning. But since you why not here's my reasoning.

Here's my reasoning for use either 12 awg or in some cases 14 awg. You can even go all the way to 16 in many cases.

Most 13' fiberglass trailers have a 20 amp 12 volt service. The maximum expected to draw is around 20 amps.
Lets take a look at some common current draws expected.
Standard 12Volt automotive incandescent lamps 1.5 amp each.
LED light replacement bulbs 0.2 amps each.

Furnace fan 3.5 amp (approx.)

Other items like a lap top computer 3 to 7 amps.

The larger gauge wire is more expensive, which is good for the metal thieves.
Larger wire is harder to handle get into small spaces, larger bend radius, and stiffer.

So it just doesn't seem practical to spend the extra money and effort to use the larger gauge wire.

Referring to the picture of wire sizes, in my area for house wiring 14 gauge is rated for 15 amps and 12 gauge for 20 amps.

[Jon Vermilye]

Automotive chassis wiring is generally rated at higher currents than NEC uses for household wiring.

[Byron Kinnaman]

Originally Posted by Laura & Rick

Referring to the picture of wire sizes, in my area for house wiring 14 gauge is rated for 15 amps and 12 gauge for 20 amps.

That's pretty much "electrical code" for breaker sizes as associated with wire size. Code is developed by a bunch of people deciding what would they would make legal and what they would make not legal.
Then there's the physics. I'm not sure what criteria was used for the picture but, my guess is that has to do with heat rise.
I'm probably getting way too technical for most people, so I'll drop out this subject at this time.

[floyd]

Originally Posted by Byron Kinnaman

That's pretty much "electrical code" for breaker sizes as associated with wire size. Code is developed by a bunch of people deciding what would they would make legal and what they would make not legal.
Then there's the physics. I'm not sure what criteria was used for the picture but, my guess is that has to do with heat rise.
I'm probably getting way too technical for most people, so I'll drop out this subject at this time.

The question was about the wire from the battery to the converter.That wire would feed all the 12V circuits in the trailer.
Before answering the question correctly, other questions must be answered...
1] how far from the battery to the converter?
2] how many 12V cicuits do you use coming off the converter?
3] what loads are supported on those circuits
4] How much power is supplied from the converter to charge the Battery?

Of course if you could answer all those questions you would not need to ask the first one!

Answer... 12ga.

[Spanke]

I stand by my original recommendation of 10 Ga wire. The original question that I answered asked what size the wire from the battery to the fuse block should be used.

10 gauge chassis wiring can handle 55 amps of power. If the user has a 50 amp converter, (as several people I know have) the load to the battery could be 50 amps for short periods of time. When you're putting new wire in you might as well design for a worse case scenario.

10 Ga stranded wire is not that much more expensive that 12 or 14 Ga., nor more prone to theft. It's not like I recommended 4 Ga. To me, it is easy to work with and the little bit of insurance from a larger wire size is worth it for my peace of mind. Just sayin"!

Spanke

[Byron Kinnaman]

Originally Posted by Spanke

I stand by my original recommendation of 10 Ga wire. The original question that I answered asked what size the wire from the battery to the fuse block should be used.

10 gauge chassis wiring can handle 55 amps of power. If the user has a 50 amp converter, (as several people I know have) the load to the battery could be 50 amps for short periods of time. When you're putting new wire in you might as well design for a worse case scenario.

10 Ga stranded wire is not that much more expensive that 12 or 14 Ga., nor more prone to theft. It's not like I recommended 4 Ga. To me, it is easy to work with and the little bit of insurance from a larger wire size is worth it for my peace of mind. Just sayin"!

Spanke

If charging the battery with 50 amps is the reason you want 10 awg wire, I think I'd rather have a much smaller wire that will limit the current for a bit. I really don't like loud noises.

[Ralefan46]

WOW,,thanks all for the discussion and responses. I will say that my plan for right now as far as the 12v system is to run wire from the battery to a fuse block. From that I plan only to run wires to operate lights inside. To keep the battery charged I was going to hook up a battery tender to it. Figured it could charge the battery while we slept. I do plan on putting the battery on the tongue so we wont have to worry about any fumes from charging. We usually only camp where there are hook-ups (wife preferred). Now in the future I may add a converter to the system but right now I don't see any reason for it.

[Spanke]

Originally Posted by Byron Kinnaman

If charging the battery with 50 amps is the reason you want 10 awg wire, I think I'd rather have a much smaller wire that will limit the current for a bit. I really don't like loud noises.

If you want smaller wire, I have a bunch of partial boxes of cat5 I'll give you to use! That ought to limit your current.

[Raz]

If I were to replace the wires from my battery to the distribution box in my trailer I would use 12ga stranded wire with a 20 amp fuse in an inline holder located about a foot from the positive terminal. Here is why. First I have a single group 24 battery. If everything in my trailer were on at the same time, let's say I have 4 lights that were still incandescent (6A), a fantastic fan on high speed(3A), a furnace fan (4A), and a water pump (2A), I have a total load of 15 A. If one wants to add a danfoss fridge or charge their computer there is still capacity to do so with a 20A. service. Next, the resistance of 10 ft. of 12 ga. wire calculates to 0.016 ohms. At 20A. a voltage drop of about 1/3 volt would occur. If I were to use 14 ga. wire the resistance would be 0.025 ohms and a voltage drop of about 1/2 volt would occur. I agree with Byron, both are insignificant. I would choose 12 ga. wire over 14 ga. wire for mechanical reasons. It will handle the vibrations and wear and tear longer. Can I use 10ga? Sure. But it would be like using a grade 8 bolt where a grade 5 would work.

Now if one wishes to run their microwave, big screen TV, food processor, air conditioner etc. while off grid they will need an inverter to produce a 120Vac 60hz. voltage. The only way to equate AC to DC is through power, i.e. Pac = Pdc. Since power = voltage x current, a lower DC voltage means high DC current and thus a larger gauge wire, more and larger batteries,etc. And with such high currents I would be inclined to continually check all my connections for fear of one loosening and overheating. It just isn't worth the hassle to me but as Donna likes to say YMMV. Raz

[GeorgeR]

There are other points which could be considered in sizing wire gauge between battery and converter for potential future upgrades.
- Solar panels - if solar panels are connected at a converter than 12AWG should be OK; (13AWG at 10’ at 10A losses would be low at 3%).
- Inverter – 200W would need at 10’ 14AWG wire but for 500W 8AWG would be required. For me the 1500W inverter drove the gauge of my cables.
George.