Amperage draw before and after DC to AC inverter

[Mattycakes802]

So, I've been posting a few stupid questions on here, and I think as I seek to understand how I need my setup to look the biggest conceptual problem I have relates to how I calculate amperage draw. Hoping y'all can help.

I get that Volts x Amps = Watts. I'll be ignoring loss due to inefficiency here.

If I've got 12VDC power (coming from a battery), and I've got 96W device plugged in, it's drawing ~8 Amps.

If I convert that to 110VAC power (via an inverter), the same device is drawing ~0.8 Amps.

If I have a 105Ah battery, it would seem that I'm somehow getting ~10x the runtime on the same wattage device? 105Ah/8Amps = 13.125 hours, 105Ah/0.8Amps = 131.25 hours

If anyone can explain the relationship here I would be so verrrrrrrrrry thankful.

[some seeing eye]

Generally all but the science deniers are OK with conservation of energy. Power is energy times time, so power is conserved too. Watts are power.

The Watts are the same on either side of the inverter, less efficiency which should be well above 85% for modern inverters.

Amps scale when the voltage changes. Watts are still conserved.

Your battery is a 1260 Wh battery.

Actually that was Tesla's argument for transformers in the power grid - thinner gauge wire can carry the same power at higher voltage than thicker wires at low voltage.

By the way if you invent a perpetual motion machine, you will become very wealthy!

[SLOKnightfall]

Your battery is a 1260 Wh battery.

Expanding on what Eye was said, while you converted the device to 110v, you forgot to convert the Ah of the battery to 110v. While it has 105Ah @ 12V, it only has ~11.45Ah @110V

12V * 105Ah = 1260Wh -> 1260Wh / 110v = 11.45 Ah running at 110V

105Ah/8Amps = 13.125 hours - Running the device from 12V
11.45 Ah/0.8Amps = 14.3 hours * 90% efficiency loss due to the inverter = ~12.89hrs - Running the device from 110V
So regardless what voltage you run it at you end up with about the same amount of time

[Mattycakes802]

This is exactly what I needed. Thank you so much.

[2WheelGuy]

Amperage draw is theoretical and based on math equations.....if you use small wires, imperfect terminals and a loose connection, the amperage drop will be significant!!!!

Choose copper compression terminal lugs (bought at commercial electrical supply house), 2/0 or 3/0 copper cable insulated (Lowes). Assemble cable by hiring it done or using propane torch to heat the lug in a vise, dip cable in flux and heat lug and cable, allowing solder to fill spaces and ooze out the bottom. use copper screws and bolts/nuts

Aluminum is inferior to copper because aluminum contacts when compressed in a terminal connection or when a screw or bolt is applied under pressure...in a short amount of time the connection will loosen and capacity will decline. Copper is metallically resilient and does not compress when compared to aluminum

By using as perfectly efficient a connection as possible, you can approach the theoretical amperage

[2WheelGuy]

What brand/type/size of inverter?

Is it a modified sine wave or pure sine wave?

Modified are 20% less efficient than pure sine wave



What is the capacity and peak surge of your inverter?

[Mattycakes802]

I have the following pure-sine inverter (which will be running off a battery charging off a Honda EU2000i to power stuff when the generator isn't on):

As well as this cheaper one to run off a battery that's being charged by a 100W Renology solar panel (to power swamp cooler, tent stuff):

[Captain Goddammit]

Just to throw it out there, the battery charging terminal on an EU2000 won't do nearly as good a job as a decent 120VAC battery charger plugged into the generator while it's running.

In case you didn't feel you'd bought enough goddam gear already... but seriously, if you have one, bring it.

[2WheelGuy]

Specifically, what are the continuous and peak surge requirements of the gear you plan to power?

Have you field tested anything yet?

[some seeing eye]

Of course I always suggest people visit the Alternative Energy Zone Village and the Snow Koan Solar camp to learn more about solar electricity, batteries and inverters. And if you visit the AEZ, of course see the death ray! The Snow Koan organizer is a solar installer in the real world.

[Mattycakes802]

Just to throw it out there, the battery charging terminal on an EU2000 won't do nearly as good a job as a decent 120VAC battery charger plugged into the generator while it's running.

In case you didn't feel you'd bought enough goddam gear already... but seriously, if you have one, bring it.

Luckily I'll be exhausted, wistful, and dusty as hell by the time I get the credit card bill for this one

Any recommendations on a charger? (In light of the following):

Specifically, what are the continuous and peak surge requirements of the gear you plan to power?

Have you field tested anything yet?

Field testing #1 is occurring this weekend - that's why I'm trying to get the whole infrastructure locked down.

Here's the rough sketch of what's being powered:
From Generator/Associated Battery:
-PA System - 300W max (will obviously run lower most of the time)
~100ft of this LED rope lighting:
-100ft of 5050 RGB LED tape
-30W LED floodlight (only on sometimes)
-->Whatever else we have more headroom for? I think the draw of this is wayyyyyyy less than the generator will put out but we're trying to run the generator as little as possible so the 105Ah battery is the bottleneck. It's a quiet generator, but still the less we can add to the background noise the better. You're welcome neighbors

From the 100W Renology solar panel (with 30A charge controller and similar 105Ah battery):
-Swamp cooler (of basically FIGJAM design)
-10W LED floodlight
-Maybe 20ft. of various cool looking LED stuff

Both need to support charging of iPods as sources of music for various things. Backup 60W stereo will run off one of the two sources.

Also, I haven't bought the batteries yet, so if there's something else I should be doing there then by all means let me know.

Thanks all!

EDIT: Obviously most of this is lighting and only need be run at night. Even then, probably 4 hours at most. I'd like to have a small subset of the lighting as always on, with the rest on-demand in the event people are trying to chill at camp.

[Mattycakes802]

Side note to Captain Goddammit - I began figuring this out about three weeks ago with absolutely no idea how electricity worked and your posts on various other threads have been way more useful than anything else on the internet. Hats off to you sir.

[2WheelGuy]

Be sure to use a strong surge protector between your generator and all your power loads.

Not only is the cost of a excellent surge protector cheap insurance, it's much cheaper than replacing the equipment damaged.... And once on the playa you'll have no recourse.

Search Graybar and Grainger for a strong surge protector

We'll look forward to hearing back from your field testing event

[Mattycakes802]

You think this surge protector will do the trick?

And yes, I'll definitely report back after the weekend. Really appreciate the help everyone.

[Captain Goddammit]

It's very highly unlikely you'll ever get any damaging voltage surge from an EU2000.
The surge protector won't hurt but if budget is tight, I'd sooner put that money toward the highest-amperage battery charger you can get. That will reduce the hours of generator running time for battery charging. The generator itself makes plenty of power to charge your batteries at a fast, high rate but most inexpensive home battery chargers are only putting out 10 amps or so. At 12 volts that's around 100 watts, plus or minus depending, which means you run the generator for many hours. So go after the most powerful charger you can.
Disregard the ridiculously high so-called "starting" or "cranking" power claims. They never really make that much and the higher rate on that setting is only good for very short bursts, then the unit overheats and shuts off until it cools.

[some seeing eye]

I think we might be getting a little off track here.

The wire gauge to carry power, AWG (gauge), is determined by the Amps. Having 2x the amp capacity in gauge is not a bad idea. Having insulation in the sun that is a dark color is a not a good idea. 10 Amps would be #14 or #12 with a >2x safety margin. That's a standard extension cord or single THHN or THWN insulated one conductor wire by the foot at a home despot store. Smaller number is a bigger and more expensive conductor.

Surge protectors are three terminal devices which protect against noise and voltage spikes. Agree with Mr Goddammit. "Surge protectors" depend on the earth ground-third prong for much of their effectiveness. Although Tripp Lite is the best in the industry, they will be much less effective in a playa portable generator application which almost never has an earth ground. Most electronic equipment will have rudimentary power filtering built in. Of course the playa destroys electronics on its own.

[Captain Goddammit]

Minor addition to all that good info, wire gauge is also affected by the length of the wire. Longer needs heavier wire.

[gyre]

Voltage and length are the main factors determining wire thickness required.
As voltage goes up, the amperage for the same total power goes down.
So 12 volts requires thicker wire for the same total power = wattage.
It's the same way mass and speed can result in the same foot/pounds with different size firearms.

You can build your own protection out of the raw parts pretty easy.
Movs, etc.

[gyre]

A sealed inverter like the morning star will survive better than one with a fan.

I've seen connections doped with silicone dielectric that looked like new after decades in place.
That quality of equipment always had heat sink compound between the transformers and the aluminum case too.
All like new.
Westinghouse.

[mozburrn]

Voltage and length are the main factors determining wire thickness required.
As voltage goes up, the amperage for the same total power goes down.
So 12 volts requires thicker wire for the same total power = wattage.
It's the same way mass and speed can result in the same foot/pounds with different size firearms.

You can build your own protection out of the raw parts pretty easy.
Movs, etc.

As far as cable sizing goes, it's actually the other way around. Current determines the thickness of cable required. Because of this, the cables required for running anything at 12V will generally need to be thicker than those required for their household equivalents.

ref: https://en.wikipedia.org/wiki/Ampacity

[Captain Goddammit]

You could say it either way assuming the wattage was to remain constant.
But it's more clear and a little more accurate to talk in terms of current (amps) and length when determining proper wire gauge.

[gyre]

Yes, I was just trying to make it clearer for people that find it so baffling.
It's all the same thing.
Amperage matters when the voltage is lowered.
It's simply an amperage comparison as long as voltage doesn't change.
Important thing is to realize that sizes for 120 volt will not work for the same power at 12 volts.
That's why I think people get in trouble.

http://www.powerstream.com/Wire_Size.htm

[rufus13]

Wire: copper is not a superconductor. More like a heater.

Previous post: yes, the limits of wire is not Watts, but Amps. Reasonable (not heating much, 2% voltage drop) current is limited by the circular area of copper, and voltage drop is a combination of area and length. A 100' 12 ga cord will drop twice as much voltage as a 50' 12ga cord. Real-world example can be found in a 100' 16ga cord that I believe contributed to the early end of a weed whacker. Too much voltage drop led to me overworking until smoke came out.

The best inverters are about 93% efficient, worse ones drop into high-70's % efficient.
Rule of thumb: up to 1000W 12v okay. 2000W: really outstanding 12v may be okay, 24v will work fine. 3000W inverter: you NEED 24v dc and a 250# battery bank to really use it. 3000W and 48v battery is great. Good safe portable power is expensive.