750w Inverter. How much Draw?

[Danno]

I have a Black and Decker 750W inverter that I bought a few years ago. It's the same one pictured here:

http://www.amazon.com/Black-Decker-750W ... B000NRZIMA

Now, on the back it has input specs. I have a two part question, since I'm new to this and I am considering using this in my pending TD build.

1. Should I assume that the draw is variable dependent on the output that is required?

2. If the answer to 1 is yes, then how do i calculate my draw so I can have a better idea of how much battery I need to run certain things when not on shore power?

Basically, I'm wondering if I can run a fridge off of the thing and draw as little power as if I had a small 100-200w inverter.

[Shadow Catcher]

1. Should I assume that the draw is variable dependent on the output that is required?

Yes BUT an inverter has a certain level of inefficiency of something like 80% and unless it has a sleep mode it draws power even when it is not supplying any. see http://www.fieldlines.com/board/index.p ... 27523.html for a test.

Your load is not something that can be calculated with out some numbers, how big is the actual load in amp hours, how big is your battery...

My suggestion would be to go to http://www.wind-sun.com/ForumVB/index.php Lots of info

[Danno]

I'm even more confused now. I assumed that LOAD is exactly the same as OUTPUT. You can't take more than you can get.

anyway, now that you are asking for amps and all of that, i think that maybe I wasn't clear. I'm planning on loading on devices after I know what my capabilities are.

Right now all I can tell you is that I have a fridge that has a sticker on it that says 1.1amps at 110-120v. When I left it plugged into my Kill-A-Watt for "164hours" it said it used "4.56Kwh" When it was running, it said it was at ".87amps". I saw a spike on startup, but was never able to pin it down, think it was 189watts at one point. This isn't the fridge I'd use in the TD, though. I was thinking that some day it might go in a TTT.


I think maybe I'd like to plug a TV into it, but I'm not sure, as I have 12v options there, same with cell phone chargers and lights. Maybe a 200w heater on occasion, maybe wife's blow dryer at it's lowest setting (500ish watts). I found a coffee pot that's 300 watts. haven't decided on a venting option yet, but again there are 12v options there, too.

[eamarquardt]

Running items designed for household use off a battery and inverter while camping for extended periods is the "height of optomism". You can't get 100 amp hours from a 100 amp hour battery. Depending on the design maybe 50 to 80 percent of the 100 amp/hour rating. In addition you shouldn't draw or charge at more than 10 percent of the battery's capacity at a time. So for a 100 amp/hour battery that's 10 amps or maybe (factoring in the efficiency of the inverter) 100 watts or so.

Running a 1500 watt hair dryer, a 500 watt heater, microwave, refrigerator, or similar unit is simply not practical without a huge battery bank. In addition, once you use the "juice" you have to put it back into the battery before you do it again. How do you plan on recharging your battery?

If you need that kind of power a generator makes sense but they are expensive, noisy, and you don't want to run all the time for a refrigerator.

Look through my posts or do some searches for more on this topic.

Cheers,

Gus

[Shadow Catcher]

calculators
http://www.bdbatteries.com/acdcrv.php
http://www.mrsolar.com/content/off-grid-calculator.php
http://www.planet.orconhosting.net.nz/i ... ttries.htm

[2bits]

When I was considering this, it became obvious that I could only power low power devices. I then found that pretty much all of these devices had DC versions available, i.e. cell phone charger. and coffee makers so you could just power them directly. (Buying these versions means having all your teardrop stuff stay in the teardrop which is nice too). Things that had a compressor or otherwise high draw, were pretty much out except when parked at a state park. Then after all that thinking, I realized after the first year of camping that I only camped in parks with AC power anyway. Finding rural camping here is actually extremely hard if you don't have a friend with land, but that is here.

You might take a step back and look at it conceptually for what camping you will be doing. I mean if you are at a car show, tailgating at NASCAR, or boondock camping, or in a friends backyard, would you need a hair dryer? The fridge could be a case, but a couple of coolers with ice have always done nicely especially when you carry a spare cooler that you never use except to carry spare ice. The only thing I might "need" when camping is AC and heat and both of these are high draw items so during the seasons where temps are not pleasant, I camp at parks, not like I have done otherwise, but a couple of backyard parties have been around.

I am only saying this because I went through the same questions and found it was something not worth thinking about. I bought a fuse box with a 110 to 12v converter and still haven't installed it because I just plug in the power strip at the park. I am still looking to boondock for the first time.

[Danno]

I hear what you are all saying, but I want to build something that will be fairly simple and isn't expected to be running anything major at one time, BUT, if I want to run something like a blowdryer, then I can. If I want to run AC for a few minutes at a car show off of batteries, in order to impress some guys, or maybe to take a siesta in 100 degree temps, then I want a system that can do it.

I really intend to run as much as possible through straight 12v, but I've been researching the fridge for a while on this forum and others, and have concluded that for simplicity and cost I'm going with an AC option with an inverter. What I need to really determine is whether or not I should use the 750 (or bigger) inverter or whether I should have two, a dedicated smaller inverter for the fridge, AND one larger one that can be switched on to run other junk if I absolutely need to.

I am most concerned about being able to tow for 8 hours and have the fridge run off of the battery for that length of time WITHOUT a charge system from the TV. More than likely the TV will be able to charge the TDs battery/batteries, but if one of my siblings wants to borrow it, or I want to tow it with a different vehicle, I want to make sure it's going to work without TV charging.

[mj1angier]

Well I can't give a way to know what you can run, but I can tell you what I can not run. I have a 1500 (2000 surge) inverter and 2 group 31 (?) deep cell batteries. It will not run a window a/c, well it will run the fan but when the compressor kick in it shuts down the inverter. It will run a 800 watt heater for 45-65 min. before the low charge alarm sounds. It will run LED lights all night and hardly use any power. So for it to run an a/c unit your inverter will need to be close to 2000 watts and a pure sine wave is best. For heat you need something that draws 250 watts or less or have a bunch of battery power. For a fridge you will be better off getting a pure 12v model.

you can get batteries that will have more amp hours than what I got, but plan to spend 200-400 per battery.

[Danno]

Geesh, the Window ACs draw that much on startup? My window AC is rated on it's sticker at 515watts. I didn't figure it could be much more than double on startup!

I looked for 12v fridges and all I could find was thermoelectric junk. I didn't think that the ratings on the AC Fridges was that high, so I figured inverting them might not be too crazy of an idea. Am I missing some good 12V fridges that are reasonable?

I have this 200w heater from wal-mart, and I think it would only need to be run very rarely. I don't plan on doing much cold weather camping, and if I do, I probably will have shore power.

[Shadow Catcher]

The question is not can you run what ever, it is how long your battery(s) will last and the answer is dependent on the load and that is the point behind the calculators. Do the math
There are refrigerators Waeco and Engel which do not come cheap that will run on 12V efficiently and having the advantage of a top load (cold air does not spill out when you open the door) but even they suck amps. AC figure for a 5000 BTU window shaker at 515W 4.8 amps this works out to 57.6 amp hours about the entire capacity of a 100 amp hour battery for one hour.

[Danno]

Yep, been playing with those calcs a little. Forgot to give you a thanks for the links a couple of posts back.

[2bits]

Aside from the power concerns, I can say that my little $15 heater from Wal store kicks on just every so often when I am camping in weather that is around freezing. These Teardrops really do good for keeping in body heat. too bad it is not the case for summertime.

[Danno]

Aside from the power concerns, I can say that my little $15 heater from Wal store kicks on just every so often when I am camping in weather that is around freezing. These Teardrops really do good for keeping in body heat. too bad it is not the case for summertime.

will the same be true for a build that has solid walls? I'm doing this cheaply and it's pretty small, so I'm using 1/2-3/4 for the floor, and 1/4 for the walls, and then 5mm on the roof.

Anyway, I have a handful of those walmart heaters that run about 1500w on a thermostat and they would be major overkill for a TD unless it's like negative 30 degrees F out, lol! The one that i bought is underkill for just about any application in the world except to do what they say they do. You are supposed to put it under your desk by your feet or on your desk just a few inches away in order for it to do any good! It seems to work pretty well as a doghouse heater, too. That's where I put mine. The 200watts is pretty useless anywhere else.

I estimate that it will be about 79360in^3 or 46 cubic feet. My BTU calculators say that I should be able to heat the joint with two bodies and 200watts as long as It doesn't get too much below freezing.

[2bits]

I couldn't say what you would get, don't get me tryin to calculate all that stuff. I just think in this kind of enclosed space body heat goes along way. I have 3/4" plywood walls and 1/8" Headliner with insulation then 1/8" Masonite on top of that with the aluminum capping it off.

[Shadow Catcher]

One danger is keeping things too tight, one individual in this forum had an experience of waking up gasping for air. I used computer case fans in the vent.