Tear drop trailer electrical best practices

[saltydawg]

Okay, we have lots of threads I reply in that are electrical in nature. I was asked by someone if I would do a basic wiring diagram for the simple electrical system. I basically said no for various reasons. He understood, but he is correct about "differentiate between the nice to have, the essential and the actually detrimental." type info. So I will give my ideas here on what should be done, and I will even explain why for each item. Remember this is a simple smaller teardrop.

First we start at the battery. I say lifepo4, why no need to keep 100% charged, they self protect for too low of voltage or too high of voltage. They are also a lot lighter, and smaller for the capacity they have. The draw backs or no charging below freezing, cant just hook to the tow vehicle to charge. Lead acid, while it works and is cheap one time of over discharge can do serious damage to the battery. They off gas so they should be in a vented compartment. Capacity, 100 amp if lead, 30 to 60 if lifepo4 depending on use of teardrop.

Next, and this one I feel pretty strongly about and its two parts. The wire connection to the battery. First the connections on our batteries are not designed to connected and disconnected alot. It would be easy strip out screws if you did. So I say use a short run of #8 wire to an anderson connector, say about a foot long. The two parts of this is why a connector and why number 8 for a small trailer. First is the connector can be used as the disconnecting means, two it saves wear and tear on the battery terminals, three #8 wire is rated for 50 amps ( in the real electric world ). We know we would not have much voltage drop over a 1 foot piece of wire. But remember that the battery at this point is unfused, and it can put out hundreds of amps of power on a short. ( another reason for lifepo4, they can put that out but will shut themselves off ) Better for spend 2 bucks more and not melt a wire if something goes wrong.

Now we get into the wiring attached to the trailer. We are starting out at the anderson connector. Again a short piece of # 8 wire to out main fuse block, which for a simple trailer I would do a 40 amp fuse. Why a 40, its realistic that we may never blow it, and its sized smaller than what the wire can handle. So if we do have a short, we simply replace the fuse, instead of a melted/burnt wire.

After the fuse block, another piece of wire I would go with #8 to a distribution fuse block. It might be a short run, it might be the other end of the trailer, make sure its big enough to handle what the fuse will protect. Again, we dont want a short to burn the wire, Let the fuse take the damage and do its job.

Now we get to the distro fuse block. I think we should have at least a 4 fuse block, they are cheap enough. Why 4, well a fuse for lights/fans, a fuse for power points, a fuse for water pump if you have one, and a fuse for any charging input. If you need more just get a larger fuse block. Now why do I put the charging input on the fuse block, not at the battery. Its simple if your charging and using power why would you run the power from the battery thru the other wiring to the fuse block, tie it in where its being used at. And if not using any power we have a nice big #8 wire to get the power back to the battery ( see the bottom on solar ) Now we are talking about a simple power system. Inverters and such are a different story.

Personally at this point I would mount a simple 4 switch bank feed from each fuse. Why you ask? because its a simple shut down of the trailer or a simple isolation. Someone pointed out in another thread they found usb power points drew a fair amount of power even when not being used. So why not have the ability to just have on what you need, when you need it. With the 4 switches, you want lights turn the switch on, you want the power points to work turn them on. You get ready to travel or put the teardrop away for a few weeks, 4 switches and everything is shut off no going opps I left the usb or 12 volt power points on and my phone charger just killed my battery. Which if a lifepo4 would be okay just charge it, but if LA its time for a new battery if you have done this a few times.

Next wire and fuse size thru out the teardrop.
Lights at this point better be led, and a fans does not draw much either. Runs to the lights, if under a few feet and led 18 gauge should be fine, if its anything more than 3 or 4 feet 16 gauge, if you looping it all the way around the trailer to all the lights start with 14 gauge, as you get closer to the end of the loop you can drop to 16, and between the last 2 if they are close enough. With the leds lights have even if you run 14 gauge you should still fuse it for the smallest wire, so if you have 16 gauge wire any where in the circuit even it it starts out with 14 gauge, use a 10 amp fuse. That way a short again blows the fuse, not the wire. I would do my best to have 14 gauge to the fan, not looped in with the lights

Power points, if they are lighter plug style, I would run 12 gauge, unless it will never have anything larger than a cell phone charger than 14 gauge is fine. Other wise 14 gauge to all power points. Fuse them at 15 amps, unless a large use 12v lighter jack fuse at 20 amps and 12 gauge.

Water pumps, most draw around 4 to 6 amps, run 14 gauge, unless its a short run under a few feet. Fuse at 10 or 15 amps.

Chargers, you want them fused accurately, if its a 20 amp charger, 20 amps of fuse, 12 gauge wire. 15 amp, 14 gauge, 15 amp fuse. Thats the same as above, power in where its being used, if not you have a nice big wire back to the battery to let it charge right.

Now some will say but what about voltage drop, screw voltage drop. we are not sizing to be at a max voltage drop. We are sizing for what will work the best, not compromise on using some sort of math that says this is allowable. We are doing what maybe way past whats needed. But its safe esp sense things like the wire may cook if there is a short we want the fuse to blow instead. Its easier to replace a fuse than to try to replace a wire sized for voltage drop, but not sized for the fuse.

Now we do need to make sure we account for long runs, which as a general rule all the above will pass with flying colors. This is all based on a simple teardrop, nothing with large loads, no inverters etc. Even a 15 foot run at 2 amps using 14 gauge wire will have 1.3 % or .16 volts of drop. Bump it to 4 amps for say a water pump we are at 2.6% or .3 volts of drop.

The only thing we really need to seriously oversize is solar. You want the charge controller close to the fuse block, or battery. The nice briefcase style put the charger at the panel, but if its 20 feet from the trailer the charge is not seeing the proper battery voltage. If you cant put the charge controller at the battery, I would run 10 gauge at a min for a 100 watt panel, even for a short 20 foot run. If the panel is putting out 100 watts ( it wont ) thats only 8.3 amps, but .25 volts of drop. Enough that the battery will not charge right.

Remember one thing, esp for stuff like motors and leds drivers. Voltage drops, amps go up. So a light that says it draws .1 amp at 13 volts, when the voltage drop to say 11 it might now draw .15 amps. Thats why we use watts for this stuff, it is not voltage dependent. Watts equals volts divided by amps. As I used to say, Watts is watts voltage does not matter, its still a watt.

[saltydawg]

Going from a basic system, to using the info I posted would as a 100 bucks the cost of wiring, 100 bucks gets you bigger wire, a real fuse block, and an anderson connector.

Oh lastly do not use solder connections except at things like battery lugs. On smaller stranded wires it makes the wire brittle, the solder wicks up the wire and makes it solid for a 1/4 inch or so. Use good quality crimps with heat shrink and the proper crimping tool. Then give then a tug before you heat shrink to make sure its secure.

https://www.amazon.com/BUNKER-INDUST-Ba ... 163&sr=8-5

https://www.amazon.com/dp/B07GBV2MHN/re ... =UTF8&th=1

https://www.amazon.com/Acouto-12-24V-Ro ... 64&sr=8-15

[tony.latham]

a real fuse block...

I vote for one with a neutral bus bar instead of what your link shows. It makes wiring-life so-much-easier.



https://www.amazon.com/gp/product/B000THQ0CQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1



Tony

[saltydawg]

That was more of just an example of a fuse block. I have the same exact one for mine that you do.

edit I just changed it to one with a neg bar, just in case people buy the exact thing I linked

[saltydawg]

Next installment

Battery monitors vs voltage meters.

When we talk about how much battery you have, we mean how many amps you have that you can use. When you use a lead acid battery, voltage is a decent indicator of how discharged the battery is. The issue is the battery needs to be rested for it to be correct, that means a few hours of no discharge or charge. When it comes to lifepo4 batteries the voltage is so flat over their discharge curve you cant really use it as a base line.

In comes the battery monitor there is a decent little monitor that costs 40 bucks or so. Once this is programmed it measures how much is discharged out of the battery or charged back in. What this means is no matter the type of battery you set it to what you want, if your running a 100 amp hour lead acid, and you want to set it to show you the safe discharge amount of 50 amps, you simply tell it you have 50 amp hours. It then displays how much of that you have used, if you get on charge, be it solar or what ever, it sees what goes back into the battery and tells you what you have available at that exact moment. You can also set it for the full 100% of the batteries amp hours for if you need to go past the safe discharge amount so you can see how far you have gone.

This brings up where to connect your charging sources, the need to have the monitor between the battery and the charger. That way it sees everything going in or out of the battery. In the case of my OP, you want it directly after the anderson connector.

it works with any battery type be it lead acid, lifepo4, heck even nicad.

https://www.amazon.com/gp/product/B07CT ... UTF8&psc=1

The only draw back of this monitor it is slowly flashes anytime there is charging going on. so have a cover for it if you charging at night while trying to sleep.

[saltydawg]

Time for solar.

Okay I wont get in to types of panels, be it hard panels, flex, mono or poly. Its more about the charge controller and wiring size and series vs parallel

Firs there are 2 types of controllers, pwm and MPPT. But before we get in to them we need to discuss a little about the panels. First a 12v lot panel actually will put about 18 volts on an open circuit in full sun, you ask why a 12 volt panel puts out 18 volts. Well first batteries normally need 14.4 to charge, so they are not truely 12 volts. Secondly thats under perfect sun, and it has to do with warranties. The panel manufactures would rather say a panel is good for 12 volts, have it put out 18 volts in full sun and say 16 volts on a cloudy day. Than to have it put out 14.4 in full sun and 12 on a cloudy day and have people trying to return the panels. Or if the panel is supposed to put out 18 but its not perfect and it puts out 16, its still over the rated 12 volt design.

Now where this becomes a problem is the rated wattage is at the 18 volts. Say a panel is 100 watts at 18 volts, thats 5.5 amps going to your battery. NOPE, remember your battery only wants 14.4 volts at charging. So you actually only get 79 watts, 14.4v x 5.5 amps.

This is where a pwm vs a mppt charger comes in. The pwm controller basically has a little circuit that turns on and off only allowing the 14.4 to go the battery, the other 3 or so volts is lost to heat and other losses in the controller. A mppt charger will take that extra 3 volts turn it into usable power. So you may be getting 6.6 amps at 14.4 volts or 93 watts.

When to use a mppt over a pwm. Well there are a few times you really need to spend the extra on the mppt. Shading ie if you live in a cloudy area, and partial tree cover where the panel is only putting out 12 volts, the pwm will say there is not enough voltage to charge the 14.4 battery so I wont even bother trying. Long runs of wire to the panels, say the panels are putting out 16 volts, but they are a long way away, or the wire is too small and there is lots of voltage drop. The mppt can adapt and give you charging when the pwm wont.

This does not mean dont use pwm, it just means there is reasons why mppt is the way to go. But if you use your teardrop in full arizona sun, go pwm.

The next reason for mppt, as we know the mppt can take larger voltage and use it to charge a lower voltage battery. This means you can use a 24 volt panel, or 2 ( or 3 ) 12 volt panels in series. This means less amps on the wire, longer runs with less loss etc. once again this does have draw back, if you have 3 panels in series putting out say 45 volts and then the sun moves and one panel gets shaded by a tree, all 3 panels stop providing power.

more on wiring them series, as we touched on it above, being able to run 3 or 4 panels, or a higher voltage panel in series gives us longer runs with less voltage drop. It does cost us if one panel is not performing right due to age, shadows etc. So if your in utah dessert run series and an mppt charger, but if you in the woods run parallel. The other reason for parallel is its easy to have a 100 panel on the roof, and another 100 briefcase style you put out in the sun when you can, with parallel you just hook it right in, no issues and it will add to the charge.

[MickinOz]

This should be a sticky at the top of the electrical section.
I think I pretty much have the basics.
I used exactly the same fuseblock.
At $22 Australian with fuses and labels, why not?

[ricky herbold]

a real fuse block...

I vote for one with a neutral bus bar instead of what your link shows. It makes wiring-life so-much-easier.



https://www.amazon.com/gp/product/B000THQ0CQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1



Tony

Yup, I second this


Sent from my iPhone using Tapatalk