Light Bulb Moment: 3500W DC to AC Inverter - Why can't I build it cheaper?
eiplanner
Posts: 112
I'm just throwing this out here to possibly get some schooling on this subject. If I am way off base or completely in the wrong place that's OK, it's just that I've come to these forums in the past and gotten much good advice and wondered if this could be a project I could take on using the Stamp or Prop as my controller and user interface.
I am dabbling (and I do mean dabbling - know not what I am doing) with the idea of making my travel trailer completely self-sustaining in the middle of nowhere with just wind and solar power. One key element of doing this is being able to operate all of my 120V devices (A/C, Microwave, Television, etc.) In researching all of the components I would need to set up this system, I ran across the need for an inverter to turn my 12V DC into 120V AC. When I started checking on getting one, I discovered the price tags to be outrageously high. I'm no rocket scientist, but I just cannot believe that the components of such a device can possibly be so expensive. 3000W Inverter = $1800 and up. Complete battery bank, inverter, controller systems are in the $13,000 to $20,000 range.
Basic Need: Full Sine Wave DC to AC Inverter to run A/C and other appliance loads
I guess I would just first like to know what it takes to build a 3000 Watt inverter. Can a layman do it with proper schematics and over the counter electronics? I could be wrong but I'm pretty sure there's no materials or technologies involved that would be on the level of nuclear fission or weapons grade plutonium. So, why is it so expensive? Is the price on par with the components involved or is this simply the market capitalizing on the green technologies?
If you have a better than average knowledge of these devices, could you please chime in and let me know what you think and if I'm wrong to believe I could build it for less than 1/4 of that price?
I am dabbling (and I do mean dabbling - know not what I am doing) with the idea of making my travel trailer completely self-sustaining in the middle of nowhere with just wind and solar power. One key element of doing this is being able to operate all of my 120V devices (A/C, Microwave, Television, etc.) In researching all of the components I would need to set up this system, I ran across the need for an inverter to turn my 12V DC into 120V AC. When I started checking on getting one, I discovered the price tags to be outrageously high. I'm no rocket scientist, but I just cannot believe that the components of such a device can possibly be so expensive. 3000W Inverter = $1800 and up. Complete battery bank, inverter, controller systems are in the $13,000 to $20,000 range.
Basic Need: Full Sine Wave DC to AC Inverter to run A/C and other appliance loads
I guess I would just first like to know what it takes to build a 3000 Watt inverter. Can a layman do it with proper schematics and over the counter electronics? I could be wrong but I'm pretty sure there's no materials or technologies involved that would be on the level of nuclear fission or weapons grade plutonium. So, why is it so expensive? Is the price on par with the components involved or is this simply the market capitalizing on the green technologies?
If you have a better than average knowledge of these devices, could you please chime in and let me know what you think and if I'm wrong to believe I could build it for less than 1/4 of that price?
Comments
http://www.ecobusinesslinks.com/inverters_sma.htm
and you can do some simple reality check maths :
3000W at 12V is tough, 24V/36/48V is more sensible.
3000W needs an average of 250A, and a peak of close to 400A.
That's 400mV/milliohm, so just a single milliohm will cost you 3.3% loss.
It's probably smarter to 'divide and conquer', with smaller inverters which also remove a single point of failure.
You slash your 'copper costs' too.
As for building one, if your time is not included, perhaps, but you'll see that's not really over the counter numbers :
You need a DC-DC (12- ~180V) and then a DC-AC (180V to 120Vac) bridge.
Ferrites for 3000W ??
400A switching parts ??
Winding 'wire' for 400A ??
Or you could go older-tech, and use an iron core approach. More kg, but much simpler design, and more likely to be surplus-shop available ?
and simpler, smaller 'camping' inverters may be enough (the Grid-Tie ones cost a lot more)
http://www.voltage-converter-transformers.com/power-inverters.html
These look much more affordable ?
With that said, this may just be a project that is far and above over my head. In searching the internet it is near impossible to find schematics for a working and tested safe Pure Sine Wave Inverter. You can find Modified Sine Inverter schematics everywhere but not working model Pure Sine. Therefore, even if all the components totaled just $100, I still may not be able to accomplish it because there isn't enough free knowledge available on it.
I was just throwing it out here to get a better idea of what I was getting into and how far reaching my thinking was.
Could one use the trailer itself as 'Iron core"? Its right there, can we use it?
That is, wrap wire around sections of the classis to make cores? Or need these be electrically isolated from ... what ever?
-Phil
What about leaf springs, would those count as laminations and reduce eddy currents?
Any estimates of loss of efficiency due to eddy currents and hystersis of structural steel (how much would it cost to use it anyway)?
I have a ridiculously cheap and hugely effective system running right now using a single 100W panel, running through a West Marine charge controller ($35.00) into a sealed, deep-cycle marine battery which powers an 800W modified sine inverter (Coleman, via local Job Lots store - $29.99). It runs a 32" flat-screen LCD TV, a stereo w/300 CD carousel, Wii, DVD player and 60W lamp for about 11 hours in darkness. Recharges quickly during sunlight, runs the TV continually during sunny days (150W).
Granted, I paid less for the panel than normal (store went out of business, bought the 100W panel for just under $300) - but my total system price was under $500 including wiring and junction boxes!
I've thought about getting a camper/conversion van and outfitting the same system on it so I can travel with power anywhere... What is different about your requirements that necessitates a pure sine inverter?
Dave
I appreciate the input, that's exactly why I came here. Haven't been on in nearly 2 years but glad to see some familiar people.
In the late 1800s, there was a patent awarded for solar ice making. Now there is a cool idea - use the sun to create your A/C cooling. TV? Are you going to be on cable or satellite dish? Or are you expecting Netflix to deliver DVDs via rural postal service? I suspect that you will find satellite TV both expensive and rather disappointing. We have it in Taiwan, Thailand, and the Philippines and I'd rather have internet than suffer through the kind of programing it offers.
And a microwave? If you need a microwave, you must also need a big freezer for all those frozen dinners. Right? 3500 watts is no where near enough for your choice of appliances and life-style. You might as well start splitting cordwood and build a smoke house to stock in venison jerky instead of using a microwave for popcorn and whatever.
Often a simple swamp cooler can substitute for a real A/C in low humidity environments. If is just a fan and takes quite a bit of water for evaporative cooling, but it does work.
Here are some hints - Get a 12VDC TV, forget the microwave and use a propane or wood stove for cooking, get a solar water heater, and get a propane refrigerator, and make sure the trailer has lots of insulation (you might even have it housed under another roof so there is little heat gain).
Trying to power 'everything found in a house' from an inverter is just plain stupid.
Your laptop and other 'small' electronics can all be powered from 12V(look for chargers meant for use in cars)
After all, an inverter is never better than 80 - 85% efficient, and the laptop PSU is in the same ballpark.
Going through both steps means you end up with an efficiency in the 60 - 70% area. That's a lot of wasted power...
If you absolutely NEED micrwvave oven, fridge or whatever, look for alternative tech, or in a boat supply store.
(Boats comonly have 12V DC, not 120/230V AC)
The biggest inverters I've sen in use is 1000W, and they were mountd in vans(Mercedes Sprinter) where they needed it to power a Laserjet, a Wireless router and a few other bits...
(The router was a Cisco Catalyst 800series, not a 'home model')
You could actually HEAR the inverter when you stood outside the car...
When you get up to the 3000W range, I expect it won't exactly be quiet...
Also, batteries(lead acids as typically used in power systems) is a rather poor energy storage and will require a lot more space than other types of tech like propane. But if you have a large trailer... and don't mind the sagging...
I sold Tripp Light and other brand Iron core and ferrit core inverters .......... the ferrit ones Loved the bulb trick ..
remember VA DOES NOT = WATTS .... ( well unless the PF is 1.0 )
EG right here I have a UPS a TP BCPERS300 its 300 VA but 180W ..
Gadget is right about the Eff of DC to DC . you are WAY better off with a 100$ auto/air boost converter then a inverter running a charger .
Fridge ...... TEC based .........In fact a ton of them are really 12v on the inside .>>I had a 4 CF one and it was just a few TECs and a 12V 8 A PSU ............I kept the PSU but I added a Anderson power pole to it so I can back feed a batt if I needed to ..
Yea they suck in comparison to a nice 40 CF home freezer but for a" cold one" It may just be ok ....Mine was OK but I had no room to move it to my new place..
TV .. or PC .
Some brands of LCD sceens use a external power pack . some are often 12V ....... get plug .. solder and BING you has a 12V Screen ..
and If it has DVI you can get a ada-ter to run it on HDMI .. .. I have a few 12V screens I keep for just such a use ...
Oh Heck most LCDs are 5 V logic or 3.3 .. and 12 - 24 for the back light inverter ( CCFT ) . Ill bet the new LED backlit ones are all on the 5V rail .. have fun hacking a TV ..
PC . I have seen 24V IN readdy to run PC PSUs ....... they are used in server rooms and most are 48V ( old telco stuff )
OR get a mac mini that draws less then Dad's laptop.. Run windows on it ........
BTW the OLD fat case mac minjs were 18 V ........Like a laptop........>>> again a DC - DC for a laptop........
A lot of older 17" Sony screens had the external pack...
(We have them at the office, hidden away in the IT department, not just because no one wants 17" screens anymore, but also because users tended to unplug the power pack for the LCD and bring that with their laptop... )
*Smacks you with a cod*
The idea is to SAVE power, not waste it. OS X has better drivers for power-management on those machines.
And of course, lots of smaller DC-DC converters is better than one or two large ones.
(It's called redundancy and 'multiple points of failure')
Another thing one should be aware of is that DC-AC inverters have a 'quiescent power draw'...
In other words, they suck a lot of power no matter how little it outputs.
1A or more isn't uncommon even with a small 150W unit.
Maybe nice in the winter as the 'waste' is turned into heat, but in the summer it just means you need to expend more power for cooling...
And again, talk with the boating community. find someone who actually LIVES aboard a boat(not a luxury yacht, but a real boat) and learn how they do it.
Especially the sailboats... Often they only have a couple of smallish solar panels and a small wind turbine, and that's it. Running the engine to recharge the batteries is nearly heresy to them.
(They're real quick to hook up 'land power' when they're in a marina, though. Fuel is expensive. Shore-based electricity is cheaper.)
A friend of mine who lives on a small sailboat used an old HP LX200 pocketcomputer hooked up to his radio to download 'weatherfax' transmissions. The LX200 was programmed to 'wake' at set times and run a script that switched a relay on the radio, started the SW to interpret the sound and stored the fax as a picture, then shut itself off again. I think he was the author of the startup scripting. Using the LX200 instead of the Toshiba laptop meant that he saved a lot of power. Incidentally, the LX200 still fetches a premium on eBay, and it's fair to assume that at least some of those ends up on boats...
The LX200 wasn't powered by the onboard 12V, though, it ran on AA batteries.
(He could have used Ni-mhs but it would have meant an extra charger and that would have taken more space than a couple of sets of AAs for it. And having to recharge it periodically.)
One could use it for cooking, to generate electricity, heat, ventilation, and powering the vehicle. But that's all a tangent.
The the question is NOT whether its a good idea or whether there are other ways, the question is how to get 3500Watt DC to AC, cheaper.
If the answer is "You can't", that's OK, but try to avoid answering the question with "stupid" before the data is collected. Often there is an alternative that comes up that solves the issue.
Calling people stupid just kills the conversation.
IF, on the other hand, everyone says, "That's a GREAT idea! Just change THIS!" the conversation can be a lot more productive.
At one of our seminars we had a contest to to see how big of a string of stupid ideas we could come up with, where the next person had to start the response with "That's a GREAT idea!"
While the total number was eventually large, the sequence was always broken by actual good ideas. We ended up with possible solutions for many of our biggest problems.
I'm just sayin'.
Your point is well taken. Still, you can't solve everything with electricity and be economical.
Peter
Prof; yeah, we know that we should try to help him out as best we can. It's just that in this case some of us believe that he probably didn't look properly at what his problem really is.
The problem isn't 'How to get/build a cheap True sinewave 3500W inverter', it's 'what's the most efficient way to power the equipment'.
I guess we kind of skipped the part where we explained the problem of building such a massively powerful inverter at a reasonable cost while still making it safe. (Not to mention what insurance companies say about it)
The entire reason for coming to this community with this was to first find out if there was any reason whatsoever to pursue building a 3500 Watt Inverter, could I do it safe and far cheaper, what would be involved, and to get pointed in the right direction. If anyone read my original post, you would see that I clearly pointed out that I knew nothing on this subject; never pretended to be highly intelligent about it. "Stupid", in my opinion, would have been for me to start buying materials, plans, schematics, and wasting hours of energy researching and building something that proves in the long run to be a poor application. Hence; throw the idea out here and see if it has merit.
Now, back to the topic: 3500 Watt Inverter
I have found a site that appears to have this device at a reasonable enough price to make building it myself less appealing. If you care to view, it's http://www.dcacpower.com/product/3000ps.html This is listed $1000 cheaper (for pure sine wave) than most other sites I've visited. Major difference.
Other than requiring large supply cables (which are included in their price), I'm not seeing the enormously sized components some have suggested are required for this type of device. It's a relatively compact in design. I'm sure the cooling fan is a bit noisy but other than that, it doesn't seem (on the surface) to be such a big deal. Now, below the surface (as I already knew), it's still going to require a charging circuit, a rather large battery bank, and more solar panels. This is where the decision of practicality really comes to play. The ideas and alternatives posted in this thread are excellent and I will pursue each of them in an attempt to lower the overall demand for power and therefore decreasing the size of the system but I am sure there is still a way for me to invoke the use of a prop chip somewhere in the design. After all, I am still looking to make this a project as well as solve the problem with powering the trailer.
The stove is propane, the heater is propane (except for 12 volt blower), the fridge will operate on propane (except for 12 volt solenoid gas valve), I can use percolator for coffee pot, as stated here the TV can be converted to 12 volt, the radio is already 12 volt, I can live without the microwave
I am still very interested in these alternatives and suggestions and would like as many as I can get. I appreciate those taking time to offer something positive and productive. Anything I can build or convert myself to save money would be great. I think the term "going green" was coined because of the cash involved. Jury still out on practicality.
For the batteries, any welding shop can provide good heavy copper cables of large dimension and in long lengths if required.
I can understand not wanting to use a swamp cooler as high humidity causes it to not work well. And living in Taiwan, I generally sit in an A/C environment most of the year.
(Assuming a 80% efficiency)
So yeah, expect the fans to blow... And even when they don't blow, this thing will be noisy.
I sugget putting it somewhere on the outside of the RV.
2000W input on the AC?
Exactly how large a room is it designed for?
That thing draws twice the juice of the the air-to-air heat pump(think AC running in reverse) I use to heat my apartment in the winter...
OK, kidding aside, what do I need to do to make this work? Currently, I operate my trailer on a 3500 watt generator. With the A/C running in summer, I use about 14 gallons of gas each 24 hours. Yes, I know I could lower this by shutting it down at times throughout the day or turning up my thermostat, but frankly, I do not want to babysit the generator nor give up my nice cool air. Sue me for being spoiled. I want to be able to use anything and everything my trailer is equipped with whenever I get the fancy. If a 3500 watt inverter isn't the answer, then what else may be possible? Would it be a significant help if I were to put more batteries in series; maybe raise it to 48 volts or 60 volts? Does this really change anything or increase the efficiency of an inverter? Would making my battery bank 120VDC be better? Is there other alternatives to inverters that would be able to run air-conditioners off a DC battery bank? I mean, truly, 14 gal = $48 per day to operate the generator and it's far noisier than an inverter would be. I can get decent deep cycle batteries for $68.00 each. With only a months worth of the fuel cost I could have a large battery bank. Am I cutting off my nose to spite my face with this way of thinking?
All opinions and hilarious comments are welcome.........
1. Electricity is the most efficient means of transmission over distances. And, it does have the ability to localize and greatly control pollution emissions.
That doesn't mean that electricity is the best energy source when you are 'off the grid'. If you have coal bearing geology on your own private land, it would seem wiser to burn coal for most of what you require. If you have an ice cave, use that for cold storage and tap into for cooling. Of course, if you are traveling with a trailer, much of your concern is about what energy sources you can carry with you or easily find everywhere.
2. Any energy conversion has a significant loss. So if you go from chemical to electrical to mechanical power, you have significant losses at each step along the way. If you deal with cooling as entirely a thermodynamic process, you have far less wasted energy - if that is possible.
3. Simple transfers of energy usually have losses in the range of 10-30% due to friction, heat loss, and so forth.
In sum, when you rely solely on electricity, some things are quite efficient and other things are not. To get the utmost efficiency, each task may require a different source of energy. But if that high efficiency source is more expensive, you are still wasting money. And then there are the issues of pollution.
What you begin to see is that there is always something that is changing the balance point and major energy consumers are always looking for a better balance as a means to reduce costs and enhance their profit.
~~~~
Regarding that 14 gallons of gasoline per day, I'd calculate the R-factor (insulation) of your trailer as they are usually far less than a modern home. I'd try to bring the R-factor up to R-19 for the walls and R-30 or more for the roof. Triple pane windows might be worthwhile too. Suddenly you might find yourself using half as much gasoline, but there is an issue to providing healthy amounts of fresh air into the trailer as well. Many trailers that are stationary have a second roof put over them to reduce heat gain from direct solar.
Only after you get as much insulation as possible into place, should you consider changing to another electrical source. You might find that switching from gasoline to natural gas for your generator to be a better economical solution. After all, natural gas is a fraction of the cost of gasoline. Even diesel would be better.
Note that hydro-power and wind turbines can(Depending on generator and so on) generate AC and may not suffer the same 'horrible' losses when being converted.
When out sailing, using a solar panel to power the radio, lanterns and whatever means that they won't need to run the engine to produce electricity.
Thee trick when using solar is to pick a suitable voltage on the system, then make certain that as many as possible of the devices you have can use that efficiently.
(You won't believe how many electronics hobbyists lives on sailboats. Well... if you consider 'capable of putting together a DC-DC Step-up/down regulator' as an 'electronics hobbyist', that is. )
I've seen radios, monitors and lots of different electronics that was once 'AC-powered' with a decidedly 'non factory-issued' wire coming out of the back...