Understanding Shore Power

[Ikigai]

So I’m trying to understand shore power, I think I’ve got it figured out, but was hoping someone can confirm if I’m right or not. 

If I plug into a 15 Amp 115 VAC plug (the “normal” house plug) I only need to make sure I don’t exceed the wattage, so 15 Amps X 115 V = 1800 W.

So when looking at battery chargers I can use up to the 50A that my battery can take as that would be only 12 V * 50 A = 600 W. 

So the 12V/25Amp charger would be fine as it doesn’t exceed the Watts.  The fact that the charger is 25 Amps which is greater than the 115VAC 15Amps doesn’t matter since they have different voltages?

Could I then also wire a few “house style” receptacles for charging laptop, small heater, water heater, etc, as long as my total voltage use at any one time doesn’t exceed 1800W? (or 3450W for 30A)

Even simpler, could I run an outdoor extension cord with surge protector, and plug in up to 1800 Watts of stuff (the battery charger plus appliances), no wiring required?
 
The charger I am looking at is the Victron Energy Blue Smart IP67 12/24-Volt 5-25 amp Battery Charger (Bluetooth) (link to amazon site).

I don’t plan on having an invertor in my system as I don’t have a huge use for AC, but would want to take advantage when at a campground.

Thanks all!

 

[highdesertranger]

You're assuming 100% efficiently. No conversion is 100%, Plus every at every conversion you are losing power. 1500 watt is about the max you want to run off of a 15amp outlet. and then everything better be right, as in wire gauge and connectors must be tight. Extension cords are another loss. the smaller the gauge the more the loss. Highdesertranger

 

[bullfrog]

Most campgrounds have a hookup for an RV plug-in for 50 amp, 30amp and 15 amp. You can get adaptors and heavy duty cords at most any RV dealer/repair place. Be sure to get one of the cheap testers to insure the circuit integrity before plugging into an unknown power source. Lots of times one or more of the plugins may be bad or wired improperly.

 

[MrAlvinDude]

You have got the principles right.

Energy is measured in Watt. And so long as the Watts, stay under the fuse limits, then you are - in principle - correct.

However, as what has been mentioned, then some practical details, can mess with you, especially if things are used at (or very close to) their design / specification limits.

Both in principle and practice, you can indeed pull up to about 1800W via a 15A 115VAC socket/wire/splitter.
It is however highly advised, that you use as beefy components, as you can lay your hands on, if you push anything to the limits of their design specifications.

When used at (or close to) the design limits, then any weakness is much more likely to cause overheating. You especially want to look out for poor connections at the socket-plug points. You also want to limit the pinching of wires. 

Any level of damage to your wires and/or connectors, will cause the theoretical limit of 1800W to be lower in actual and practical use.
The indication that the 1800W theoretical limit should not be used, is if any part of your wiring (or sockets/plugs) start to heart up.
So if you one day, do use over 1000W, then do feel the wires and the connectors, to make sure that they do not feel too warm.




Yes, it is possible to run an extension cord to the vehicle, and connect several things, so they may charge at the same time.

One reason why people add a special socket in the wall of their vehicle, is to avoid the pinching of the extension cord, in the door (or window) where the extension cord is brought into the vehicle.

Here is an example of a very simple extension cord, that can safely bring 115VAC through the metal wall of a vehicle.
https://www.amazon.com/Journeyman-Pro-Integrated-Extension-Waterproof-5278GCP1/dp/B07F6HVFH4/



Now that you have got the basic understanding of Watt limits fairly well lined up. then you need to look at the idea and concept of fuses.

Fuses protects the wires and connectors from being overloaded (and overheating). 

As in, a 15A wire (or connector), used in a 20A or 30A socket, WILL overheat, if more than 15A is accidently (or purposefully) being pulled through the wire/connector.


So when you move into the area of 30A options, then you need to look into how traditions are set up, so there will still (and always) be a 15A fuse, in front of any 15A wires, sockets, splitters etc.

 

[MrAlvinDude]

The mentioned through-vehichle-metal-wall extension cord,
( https://www.amazon.com/Journeyman-Pro-In...07F6HVFH4/ )
uses 14AWG wires. This awg size is appropriate for any 115VAC wire that is going to be in a fixed placement (or tightly enclosed space, as inside a dry wall, or similar).

If you can get your extension cords (and splitters) to also be 14awg, then you have a good solution for 115VAC wiring.



For your longer extension cords (longer then 50 feet), you will want to look at 12awg wires.



Some math about long 115VAC extension cords

With a 100 ft, 14 awg extension cord, at 15A, you will loose about 3.75V in the wire.
At 15A this is 57W lost in the wire.

With a 100 ft, 12 awg extension cord, at 15A, you will loose about 2.38V in the wire.
At 15A this is 35W lost in the wire.


If you will however only draw 10A in the same long extension cord, these are the numbers:

With a 100 ft, 14 awg extension cord, at 10A, you will loose about 2.53V in the wire.
At 10A this is 25W lost in the wire.

With a 100 ft, 12 awg extension cord, at 10A, you will loose about 1.59V in the wire.
At 10A this is 15W lost in the wire.


I hope this gives you an idea about the value of a good and beefy (long) extension cord

 

[user 37446]

Great replies, that should help the OP out. Thanks forum!

 

[Ikigai]

Yes, great replies, thank you! Sounds like I just need to use a safety buffer and I should be good to go. I've already got a few beefy and not too long extension cords, I'll have to take a look, hopefully the rating is stamped somewhere. That will probably be good enough for version 1.0. I'm planning on growing my build over time as I figure out how van life works.

I have also been pouring over the internet trying to figure out fuses and wire sizes, and I think I've got it mostly figured out. Although I can't figure out how to size the one from the battery to the positive bus, everyone uses a big one there, but no one says why!

 

[MrAlvinDude]

In order to avoid blowing the fuse at the battery plus, you want a big fuse.  But still no bigger that your wires can easily accommodate the amps.

The size wanted for the fuse, should accommodate your biggest load.
For most people, the inverter will be the biggest load. 

If you do not have an inverter, then you can make due with a much smaller fuse, at the plus of the battery.
You will however still want it to accommodate your biggest load.  But hardly any other 12V loads will come close to the 12V load of an inverter.


Some numbers:

a 1000W inverter, will draw 1000W / 12V =  83 amp (drawn from the battery).
a 2000W inverter, will draw 2000W / 12V =  166 amp (drawn from the battery).

Your highest 12V amperage, might however be your 25A charger.

So in order to limit the size of the wire, going from the battery, to your 12V fuse-block, you might opt for a 30A fuse, for all of your other 12V things. And then in the Fuse-block use even smaller fuses, so the wires going to your 12V outlets, can be even thinner.

 

[bullfrog]

Direct Current (DC) needs thicker wire (less resistance) as it does not travel longer distances well, not nearly as well as Alternating Current (AC). Voltage is basically electrical pressure and most DC circuits are lower voltage like 12 volts. In the USA most AC circuits are 120 volts. The lower the voltage the less electrical pressure, the more difficult it is to get it to travel through the wire. Thicker wire allows the electrical pressure to flow easier.

 

[Ikigai]

Thanks for the help! I think I almost got it!