help with general electrical question/inverter

Airvet · 09-30-2021, 02:39 PM

Hello fellow Winnie owners!

I have a Minnie Winnie TT with solar....
Now, I took 3 quarters of Physics waaayyyy back when, and I did pretty well until the 3rd quarter that covered electrical circuits...

I have solar. I know it recharges the batteries. The battery then allows me to use the lights in my trailer because they are 6v? I want to be able to power the microwave for a few minutes to warm coffee, zap something quickly and/or charge my phone. I have a generator which I can hook my trailer up to and get all the above powered. But....

Is there an inverter (yes I know I need one to go from DC to AC power--didn't fail physics, just had problems with it

) that I can plug into the outlets in my tt and then plug the micro, phone, or coffee maker in it? I know I can probably attach one to the outside battery, but is there any way to make it simpler? I also know that they can drain the battery faster, but my solar recharges it quickly.

I don't think I have an inverter, per se, wired into my tt, and I'd rather not go through a rewiring of my trailer.

Anyone have any ideas? My trailer is a 2013 1801FB and I can't find an electrical wiring diagram.

Thanks in advance,
Stephanie

Morich · 09-30-2021, 03:42 PM

Some points are okay but need more study!
One is that it is likely your Rv is 12 volt unless somebody has done it different.
But from there what you want to do depends on how much power (watts) you want to use and for how long.
You can get a small inverter that puts out 300 watts for around $30, plug it iin to an outlet that is fused for the amount of power it requires to run and that is quick and easy to get you the somewhat limited amount to run a few things like chargers, laptops, etc.

https://www.lowes.com/pd/BESTEK-300-Watt/1002762586

Or you can go as large as you want to spend and the amount of wiring changes and improvements to go higher power to run more items.
Example:
https://www.lowes.com/pd/Schumacher-...att/1001008522

But with each step up the dollars and the wiring both get much more expensive and difficult as it requires lots more available battery storage as well as much larger wires to support the added input and output.

Some consider it worthwhile but it doesn't sound like that fits what you want. Phone charger, yes, microwave or coffee pot are likely way out of the question for low price as they require in the 1200 watt range and lots of battery supply.

BobC · 09-30-2021, 04:02 PM

Quote:

Originally Posted by Morich

Some consider it worthwhile but it doesn't sound like that fits what you want. Phone charger, yes, microwave or coffee pot are likely way out of the question for low price as they require in the 1200 watt range and lots of battery supply.

I'm with Morich, my propane stove works just fine if I don't have shore power.

Airvet · 09-30-2021, 04:32 PM

My stove works also, just wanted to see if I could get the others working with an inverter.

Morich · 09-30-2021, 04:56 PM

It's a decsion to make as electrical stuff is all over and we are used to it, so some looking may be needed to see how it fits what you want. Not something to let me talk you out of it as it is good for , not for others.

Some of the points to look at is the rating in watts on what you want to use and that is often stated on the nameplate, etc. of things when we shop. That total fo all the things you might want to use at one time will give you a baseline figure of what size inverter it would take. A 300 watt inverter is somewhat close to running 5 sixty watt bulbs. But a microwave or heating items are often way high, like a toaster that takes lots more than light bulbs.

A second part is how much power the inverter choose may take out of the batteries that feed it and that is a combo of how much per hours and how many hours but for lots of stuff the load drains the batteries really quick if we don't do major additions.

Once figuring in the out and in loads, the wiring has to be big enough to carry that amount of current and that gets pretty hard to figure as we go higher.

So good stuff to think and consider before jumping in to say it works for each of us.
No reason to not consider it but it does get high priced as we go bigger.
Just like everything else I want to do!

Airvet · 09-30-2021, 05:21 PM

Thanks again!

That’s a lot of things to think about. I didn’t even figure in the wiring and how much it could handle.

Guess I really need to figure out if I really need it.

bigb · 09-30-2021, 06:10 PM

One thing to help understand is when a 1,200 watt appliance is running on 120 volts it uses 10 amps which can be safely carried by #14 wire. The same appliance running on an inverter from 12 volts will take 10 times the amps from the 12 volt source (not counting losses) so the cables from the battery bank would have to be at least 1/0 just to support the 1,200 watts. The wiring would generally be sized to support the maximum amount the inverter can supply plus voltage drop compensations so for a 2,000 watt inverter the wire now needs to be at least 2/0.

BobC · 09-30-2021, 06:25 PM

And this makes wonderful coffee and espresso, no electricity needed.

https://www.amazon.com/AeroPress-Cof...s%2C240&sr=8-3

Airvet · 09-30-2021, 06:45 PM

Thanks! I will check it out!

Marine359 · 10-01-2021, 05:34 AM

This makes 6 cups and will stay warm for 1/2 hour or more. But there are a bunch of ways to make coffee without ac.

https://www.amazon.com/dp/B07L6LQHB4...DFS9MFSFH62QXS

Marine359 · 10-01-2021, 06:21 AM

Quote:

Originally Posted by bigb

One thing to help understand is when a 1,200 watt appliance is running on 120 volts it uses 10 amps which can be safely carried by #14 wire. The same appliance running on an inverter from 12 volts will take 10 times the amps from the 12 volt source (not counting losses) so the cables from the battery bank would have to be at least 1/0 just to support the 1,200 watts. The wiring would generally be sized to support the maximum amount the inverter can supply plus voltage drop compensations so for a 2,000 watt inverter the wire now needs to be at least 2/0.

Hey Brian,
I wired my 2000w inverter/charger with 1/0, so I’m wondering if I went big enough. Most inverter makers recommend 1/0. I must have misread the charts which show 1/0 (0awg) for short distance between inverter and batt. Since 1/0 is good to 150Adc, should wire be sized to normal load or max surge load? Plus 2/0 (00awg) is really difficult to bend in small spaces.

I thought this video helpful for a subject that can be a bit confusing:
https://youtu.be/aKs3oZnBOPM

Would appreciate some clarity on this.

bigb · 10-01-2021, 07:44 AM

Quote:

Originally Posted by Marine359

Hey Brian,
I wired my 2000w inverter/charger with 1/0, so I’m wondering if I went big enough. Most inverter makers recommend 1/0. I must have misread the charts which show 1/0 (0awg) for short distance between inverter and batt. Since 1/0 is good to 150Adc, should wire be sized to normal load or max surge load? Plus 2/0 (00awg) is really difficult to bend in small spaces.

I thought this video helpful for a subject that can be a bit confusing:
https://youtu.be/aKs3oZnBOPM

Would appreciate some clarity on this.

I think you will be ok, I was going off memory for AC current which would require 2/0 but if you look on this chart
https://www.powerstream.com/Wire_Size.htm
it shows you have plenty of room to spare on chassis wiring with your 1/0. Sorry for the confusion.
As far as load, we size to max load but not surge or inrush, at least in AC. Surge or inrush is used in selection of short circuit and overload protection of motors but not conductor size.

DavidM · 10-01-2021, 07:52 AM

Here are two things that you can do to achieve what you want, in a progressive list starting with the easiest and cheapest and then moving to the most expensive:

1. If you don't have a cigarette lighter outlet, which you can plug in a $5 USB charger adapter for your phone, etc., you can easily wire a USB panel to your DC electrical system.

2. Then buy a 1,500+ watt inverter with built in transfer switch to power your AC loads. Wire the AC input directly to your TTs shorepower inlet and then wire the AC outlet to the place where your shorepower connects with your converter's AC panel. This way when plugged into shorepower, everything works, but when shorepower in unavailable the inverter will power everything up to its wattage limit. This means that you can't use the coffee pot and the microwave at the same time (or ever use the air conditioner) on inverter power.

Then wire the DC input directly to your batteries. Use #2 wire if you can install it within 5' of the batteries, 1/0 if 10'.

Using an inverter with a transfer switch avoids doing a lot of AC rewiring to power these appliances. Also I would make sure I had at least two G27 house batteries, preferably two G31 batteries and even better two golf cart batteries wired in series to supply the heavy current to the inverter.

David

BobC · 10-01-2021, 08:04 AM

Quote:

Originally Posted by bigb

I think you will be ok, I was going off memory for AC current which would require 2/0 but if you look on this chart
https://www.powerstream.com/Wire_Size.htm
it shows you have plenty of room to spare on chassis wiring with your 1/0. Sorry for the confusion.
As far as load, we size to max load but not surge or inrush, at least in AC. Surge or inrush is used in selection of short circuit and overload protection of motors but not conductor size.

Shouldn't length factor into this, or does the table make an assumption regarding maximum length in "chassis wiring"?

bigb · 10-01-2021, 08:27 AM

Quote:

Originally Posted by BobC

Shouldn't length factor into this, or does the table make an assumption regarding maximum length in "chassis wiring"?

Length is always factored in but it is a separate calculation. You choose your conductor size by using the ampacity tables then do a voltage drop calculation using actual connected load amps (not total circuit ampacity) and length of circuit, then upsize if necessary. Circuit length in a 12 volt DC circuit has a much bigger impact in a shorter distance than on a 120/240 volt AC circuit. On an AC circuit we generally don't have to worry about voltage drop till we get to around 100 feet.

BobC · 10-01-2021, 09:18 AM

One thing that can be confusing when it comes to the larger wire gauges. It's obvious after you know it but not so much if you don't:

The format x/0 as in 4/0 or 3/0, etc. refers to the number of zeros in the AWG (American Wire Gauge) size. Therefore 4/0 is equivalent to 0000, 3/0 to 000, 2/0 to 00 and 1/0 to 0 (in the order of larger to smaller).

From there the AWG wire gauges, again larger to smaller, proceed to the more familiar: 1, 2, 3, 4, 5......10, 11, 12, etc.

Note that 4/0 AWG wire aka 0000 is much larger, at 0.4600", than 4 AWG wire at 0.2043" in diameter.

If you want to know all the details, you can find them here:

https://en.wikipedia.org/wiki/American_wire_gauge

DavidM · 10-01-2021, 09:19 AM

Quote:

Originally Posted by BobC

Shouldn't length factor into this, or does the table make an assumption regarding maximum length in "chassis wiring"?

I partially answered this question in my post above: "Use #2 wire if you can install it within 5' of the batteries, 1/0 if 10'"

This answer assumes that:

1. The maximum current drawn will be 150 amps, which is good for a microwave or a coffee pot.

2. The most voltage drop you can stand at that current is 0.25 amps.

Neither are hard and fast criteria, particularly the second one. Most RV microwaves are at the lower end of the power scale and might very well draw only 100 amps DC into the inverter.

The voltage drop is rather arbitrary. Inverters can operate down to 11 volts or so, below which they shut down. But the batteries can be drawn down near that particularly if they are well discharged. A 1/4 volt maximum drop gives some lagniappe there, but nothing says you can't work with 1/2 volt maximum drop.

Look at a voltage drop calculator table or program and put your own parameters in.

David

Marine359 · 10-01-2021, 11:02 AM

Thanks Brian,
I thought I was reading the charts correctly, and I would be good on the dc side up to 150 amp max of the 1/0. With only 3ft total cable, voltage drop was negligible. But just to be sure, after install, I ran my microwave for a minute off battery, and put my hand on the wire afterward. The wire had not heated at all, so I thought I was fine. Guess that’s kind of a stupid yeoman test, but I felt better after that. I suppose if I tried to load to the 150 amp max of the wire, it would have heated a bit, no?

bigb · 10-01-2021, 12:32 PM

Quote:

Originally Posted by Marine359

Thanks Brian,
I thought I was reading the charts correctly, and I would be good on the dc side up to 150 amp max of the 1/0. With only 3ft total cable, voltage drop was negligible. But just to be sure, after install, I ran my microwave for a minute off battery, and put my hand on the wire afterward. The wire had not heated at all, so I thought I was fine. Guess that’s kind of a stupid yeoman test, but I felt better after that. I suppose if I tried to load to the 150 amp max of the wire, it would have heated a bit, no?

The chart I linked actually shows 245 amps for chassis wiring. Since every part of a circuit has some resistance, including the wire, it will get warm relative to current flow and time. That is the reason we size circuits at 125% when the load is continuous (3 hours or more) and the same reason why some circuits are allowed to be undersized, for instance welding machine circuits, due to the duty cycle of the welding machine there is no danger of the smaller conductors overheating. Circuit conductors that are loaded to near max for extended periods will get hot which is evident in 30 amp RV cords when running AC or heat pumps for long periods and why the plug melting is not uncommon.

Morich · 10-01-2021, 12:37 PM

And it is always good to remember that most of the specs are based on a specific idea of conditions and that doesn't always come out to be what we do in an RV. Temperature and how the insulation holds up is one that makes a difference. If we run the wire in a space where it gets little cooling from air or in a bundle of wires, we get a different problem than if we have lots of space and air!

If you look at the lines bringing power to the house, they are not all that big and they load them with lots of current but they are also out and get lots of cooling.

What type of insulation makes a difference also but those careful calculations are what I felt was not what the OP was wanting to get into as they do involve lots more questions!