OFF GRID POWER; various thoughts on...

[MountainDon]

Craig,

The inverter has to be sized to be able to operate the microwave. The advertised rating you see, say 600 watts, is the cooking power. A 600 watt cooking power microwave will probably draw about 1100 watts from the inverter. Sometimes you can only find that info on the microwave itself, not in the info or on the box.

The inverter should be a pure sine wave inverter. Personal experience has shown that some microwaves don't work on (cheap) square wave inverters. That may vary.    Even if the microwave works on square wave it will be noisier and fan may run slower. The unit will run hotter; not cooking hotter, but the electronics will waste energy and run hotter with a square wave.

The battery bank and cabling has to be able to supply the current draw. That's one reason why I prefer in 24 VDC systems over 12 VDC battery systems.

[glenn kangiser]

FWIW, I don't even consider modified sine wave for anything but misc. use - say plugged into the truck cigarette lighter or something to charge Ryobi batteries - phone etc. 

For anything serious relating to living, only pure sine wave.

[MountainDon]

Since the subject has come up, I'll get into some pure sine wave vs square wave inverters. I call them square wave, not modified square wave like all the ad talk does. That's because modified or not, if the word square is in there there are disadvantages. Pure sine wave is the only way to go if you are running anything but simple lights.

Advantages of Pure Sine Wave Inverters.

Never any doubt anything you plug in will work if the inverter can supply enough watts.

Items that can have issues are...
Microwvaes as noted above.

Inductive loads like motors (and the microwave) run quieter, cooler and faster. Running cooler means they last longer. This applies to a lot of tools.

Some devices like FL lights, radios, TV's, answering machines, etc might have a hum. Some do and some don't. Some are worse than others. We have a TV that is fine and a couple CFL's that have a slight, usually inaudible, hum.

Laser printer and photocopiers may have problems with output on square wave.

My wife's electronic sewing machine does not work on square wave.

Some variable speed plug in power tools will burn out.

Some microprocessor controlled furnace and pellet stoves may not operate correctly.

Battery chargers that have the little cube that plugs into the outlet may not work or may get very hot and burn out. This may also apply to things like flashlights that you plug directly into an outlet. Not all of them, but I did a number on an AC adapter for a portable radio. Very smelly event. However, most battery chargers that have a regular AC cord and plug that connects a charger to the wall outlet should work fine.

Digital clocks in radios may not work.

As you can see there are a lot of 'may not work'. Electrical devices are not all created equal. In some cases the item works but draws more current putting more load on the batteries. Those items will be running hotter as well and as mentioned above may not last as long due to the heating.

Advantages of Square Wave Inverters, AKA Disadvantages of Pure Sine Wave Inverters.
Pure sine wave are more expensive, much more expensive.

[glenn kangiser]

Some things will burn out -- such as my $600 Bosch rotohammer w/soft start drilling -- Square wave took the speed control out of it.

My water pump  only pumped about 1/2 as much water on the same power on square wave.  I understand there is something else you can add to make it run better but why bother -- get a sine wave and save money elsewhere.

[MountainDon]

As stated, motors run hotter, slower and run longer (not longer in lasting longer, but runs longer as in more time per day). Sort of counter productive making a refrigerator motor run hotter with it located right under the cold box of most refrigerators. And since they are one of the biggest power users that will but much more load on the batteries.

[Okie_Bob]

Don and Glenn, I am really enjoying this topic and would like to see it moved up to the top as one of the regular what ever you call it prime topics. I still believe that the more time goes by the more people are going to be getting off grid. Obviously, not those in town but, those outside the city limits and the further outside the city limits the more people are going to be getting off grid.
Don, you have certainly added some useful notes that I would never have considered had you not posted them and for that I think you.
I may be the only one that is interested in wind power too but, maybe that will change with time? I'd sure like to see more on wind and know Glenn has a wind turbin or two? And I'd really like to hear this same sort of exchange where I can learn from your mistakes!
Okie Bob

[glenn kangiser]

I don't make mistakes, BoB. 

It is called planned obsolescence. Some sooner than others.

For those who don't care to go through the whole Underground Cabin Update looking, here's a link to the start of my Solar Tracker Project, which I might add is a huge success.

http://countryplans.com/smf/index.php?topic=151.msg77051#msg77051

A pix of the tracker and Wind Generator together.



I'll sticky it for a bit and well see how long interest continues.

[NM_Shooter]

Hmmmm... I wonder if you were to use a big isolation transformer on the output of a modified-square wave inverter.  Seems like that should result in a sine at the output of the secondary....

-f-

[glenn kangiser]

You think it would knock the corners off the squares, Frank?

[glenn kangiser]

Don, or anybody else,  I have some copper plate - maybe about .065 or so.  Stole it from my son, but when I mentioned that fact he gave it to me -- didn't want me to look bad I guess... 

I haven't found much on plate or strip - maybe 1 inch or so wide, ampacity. There must be something on it. hmm

[MountainDon]

Goto Storm Copper  click on ampacity tables.


I'm pondering using copper straps in place of regular battery cables.   

1/16 x 1 would just about cover my needs... 175 amps max more or less.

[glenn kangiser]

That's what I was thinking about.  I think these were parts of metal roofing or for a copper range hood he made for a customer - probably the range hood now that I think about it.  He put a copper roof on in Santa Monica I think it was.

I also want to build my own knife switches so I don't have to leave an Ax nearby to cut the cables in case of emergency.  Shouldn't be any worse than welding though, eh?  'cept for that hydrogen...

Thanks for the link.

[MountainDon]

Ax = the ultimate knife switch     


Storm Copper offers loads of copper goods. They claim they have 1,000,000 pounds of copper stock in inventory.     



FYI, they also sell copper nails and silicon bronze nuts and bolts.

[glenn kangiser]

Cool -- I just picked up my milkbox full of silicon bronze scrap from the valley house.  I think it must have been 150 to 200 lbs.  I use it for casting replica parts though I haven't done it in years.

[glenn kangiser]

Interesting discussion on DC vs AC buss bars.

"  50556
Copper Size for DC low-voltage high-amperage

November 18, 2008

Hello all,

I'm a new plating learner.

Now I have a rectifier which the rating the output rating is 12VDC,4000A. The current size of copper busbar which link from rectifier to chrome tank is 12mm x 100mm. To me, I think it is under size since the the current ampacity of it should be around 2600A (in AC, DC should be less). My question are:

1) What is the actual size of busbar i have to used in this case?
2) How to calculate for DC busbar?
3) Is that the size will be different for DC and AC 50 Hz? In same current, copper which apply to DC circuit should be more larger than AC 50Hz circuit?

Thanks

Khor Patrick
Plating Learner - Malaysia
contact button

November 24, 2008

This link should give you all the info you need.


http://www.stormcopper.com/design/Buss-Bar-Ampacities.htm

Kurt Sammons
- Inman, SC

November 24, 2008

Thanks, Kurt. I think that page should be fine for AC current calculations.

For DC bussing for a rectifier, however, I think the standard number used for decades, 1000 amps/square inch, is an easier and safer approach.

Khor, for an electroplating bussing installation I would consider the ampacity of a 12 mm x 100 mm busbar (slightly under 1/2" x slightly under 4") to be about 1860 Amps, but we could call it 2000 Amps. You need two, not one, 12 mm x 100 mm busbars, although most experienced installers would probably use four 6 mm x 100 mm bars instead. Isn't that what is coming out of the rectifier?

Regards,

   


Ted Mooney, P.E.
finishing.com
Brick, New Jersey

December 5, 2008

Ted
I have never claimed to be an electrical engineer, but have run alot of wire in my day. I never considered that there would be a difference in ampacity for AC vs DC. I reached out to the folks at Storm Copper for validation. My question was very simple:

Is there a significant difference between AC ampacity and DC ampacity?

There response was:

Yes. DC causes greater heating of the bus. I believe de-rate AC values around 30%.

A quick study of their ampacity tables complicates the issue even more. a 1/2"x2" buss is listed at 1000 amps. Fits your number perfectly. A 1/4"x4" buss however is at 1250 amps. Maybe more heat transfer area to keep it cool.

However, Storm is suggesting to derate the AC by 30% for DC current meaning those two bars would be 700 and 875 amps.

Kurt Sammons
- Inman, SC

December 15, 2008

Thanks again, Kurt. I've been sizing bus bar the same way for 40 years and would dearly love to get out of that rut and hear a newer and better way. And I understand that a 1/4 x 4 bar has greater surface area and cooling, and consequently higher current carrying capacity, than a 1/2 by 2 bar.

But the fact is, 1000 Amps/sq. in has proven itself for decades. If these charts indicated higher ampacity than the simple old-fashioned method, I would want to go along with them. But when they suggest that copper can only carry 70 to 87 percent of what we know it has safely and reliably carried in tens of thousands of plating and anodizing installations over 5 or more decades, I think it is they who need to go back to the drawing board :-)

Their figures may be for bus bars enclosed in power distribution boxes or ducts rather than out in the open air though.

Regards,


Ted Mooney, P.E.
finishing.com
Brick, New Jersey"

http://www.finishing.com/505/56.shtml

[glenn kangiser]

I put my new bank of batteries in last night using copper buss bars.  Boy is that easier than cables.  I cut my bars off sheet copper with a power hacksaw (band saw) as it was raining and I did not want to start my shear - had to move a welder/generator - two trucks and a trailer  for power. 

I drilled holes low near the ends so they would fit the terminal bolts easily.  I would have spent hours making cables.  The buss bars took less than an hour for all 8 of them and are much neater in appearance.  I may split hose to slip over them for insulation - lots of bare copper there.  I'd hate to drop a wrench across them.

Reading the charts over I decided that 1/6 x 1" was big enough but I went about 1 1/4" on the buss tying the two banks together and attaching to the inverters.  I drilled 2 extra holes in the center of that buss for future connections.  Possibly I'll get a pix today.

[soomb]

Please post the pics when you get them.  I am still learning and I think I have a visual on what you are discussing but the photos will be of great help.

Thanks

[MountainDon]

Like these. These are lead coated or silver plated copper.

[soomb]

thank you sir.

Based on the discussion of using hose to jacket them, do they get all that hot?

[MountainDon]

No. But sheathing them will give more protection against accidental short circuiting.

[glenn kangiser]

Those are the commercial version of what I did - I wonder if they will go sideways like mine as there is only about 5/16 clearance from the bolt to the lead of the terminal.  I guess a tin snips could take care of that though. 

Here's mine - love that old wiring on the original set.



I wonder if the lead or tin coat makes a significant difference?  There is something called skin effect - seems more to do with a/c but it is effected by the coating such as copper over steel works pretty good.

[glenn kangiser]

thank you sir.

Based on the discussion of using hose to jacket them, do they get all that hot?

soomb, there is no heating involved especially with the amount of batteries I have using several different supply paths.  I sized the strips I cut assuming maybe near 200 amps max current so the 187 was close enough for me for the 1/16 x 1" copper and like the old engoineers comments above - I am not worried about derating it.  I will never reach near that load.

Assuming 4000 watts per inverter - I have 2, so 4000 watts / 24 volts = 166 amps  - round up to 180 amps for inefficiencies - so running 240 volts with both inverters I could pull max 360 amps or so.  180 amps each - the bars I used would do that at 30 degrees C according to the chart or 86f temp. rise. I would not hit that often as my biggest load is the pump at 10 amps per inverter - or possibly some of my machines may be more.  Also though - that would be on 2 banks of batteries only - I now have 5 banks of 4 batteries so each would only get about 70 amps at maximum current draw of both inverters. 

Even the 1/16 x 1/2 is good for 103 amps under the following conditions.

"* Applicable to typical in-service conditions (indoors, 40C ambient temperature), horizontal run on edge, and free from external magnetic influences." So I have used twice as big a buss as necessary for my purposes.  I myself would not like to see the temperature rise they allow as that is just power being wasted to create heat -- so I went for the larger buss bars.

I do find heating under heavy charge or heavy use if a terminal is corroded increasing it's resistance.  When heavy charging with the welder I often take the non-contact thermometer and take temp readings at all of the terminal connections cleaning any that get a temperature rise.

[MountainDon]

I wonder if the lead or tin coat makes a significant difference?  There is something called skin effect - seems more to do with a/c but it is effected by the coating such as copper over steel works pretty good.

Something to do with removing the oxidation of Cu from the battery bank I would imagine; though that is conjecture. From the Storm Copper website on battery interconnects...

Generally, Battery Connectors are plated in Tin for sealed battery applications and Lead or a Tin/Lead Alloy for Flooded Battery Connector applications.

I figure one could cheat and simply apply solder to the ends of the straps once the holes are drilled/punched.

[MountainDon]

Glenn, I got to tell you I would not have believed those were your batteries with the nice neat battery strap connectors if I had not seen the familiar rats nest wiring job behind it.      I am impressed to no end. 

My GC2's have vertical threaded stud mounts so I could run the straps flat. I think that is what I will do between batteries.

[glenn kangiser]

  I couldn't even believe the difference. 

I think I will coat the ends with protectant of some sort - petroleum jelly ? Grease - guess I'll google it.  The NAPA battery protector stuff doesn't seem to last.

I see from the quote above they are rated standing on edge, but with the smaller batteries cooling should not be a problem.