# 250 watt grid tie inverter build

#### Thunderchild

##### New Member
I wonder how much you actually get per kWh when you sell power back to the power company. After all when you buy it you also have to pay taxes & delivery charges.
after you have paid for all the equipment particularly their meter to measure what you put back you get the grand sum of 30-50% of what you buy it at if your lucky so unless your house is made of PV panels with giant turbines on each corner, the patio paved with PV tiles and all fence/gate posts replace by turbines you won't make much money from it, I would think that with what it costs to set up you could buy a nice bank of batteries capable of storing 5-10 KW making you indipendant anyhow

#### Thunderchild

##### New Member
What I have been told as of lately is that my local power comany pays equal cost per KWh returned. BUT I have also been told that may not be true all over the united states.

But if it cost $500 to build and tends to break down before its cost avoidance payback is recovered what good does it really do? Even if it was 10% more efficient. And as far as I have ever seen simple, rugged, and reliable lasts! Complicated, dellicate, and fussy does not. I will trade efficiencey for simplicity and durability any day! And for me how heavy it is does not matter. As far as I know once its hooked up you should not need to be moving it. #### tcmtech ##### Banned Most Helpful Member if you can save energy then you will go indipendant faster and with less expence. to say you want to keep your wasteful ways but not pay for them dosen't make entirely sense because most renewable form will take quite a while to pay themselves back so you will be shelling out more money to make enough power to waste. Very true! However I do have an advantage over most others. I have the knowlege, equipment, materials, and location to build a large enough system to keep up with a large personal energy usage. Just by the numbers I should be able to produce around 2000 KWh a month from my local winds. But I do have a honest finacial outlay of around$1500 into the parts right now. And I do expect to have another $1500 more spent before I am finished. Plus factoring in generator and system maintenace costs plus my$30 a month utility connection fee, I dont actualy plan to break even on cost avoidance for this venture for about 3 to 4 years.

I do realize a city dweller with solar panels or a small wind generator unit and less personal knowlege of design would not be able to do what I am doing for anywhere near what I have into it.

But thats why I am sharing this knowlege freely. It will inspire some to try, and thats all I can ask and hope for.

Plus this type of system is not going to be able to be used by everyone. Many have local laws and regulations that will force them to use battery banks and inverters to be able to run off alternate power sources.

But for many like me, getting to legaly use the local power grid as a big alternating current battery is a big cost outlay saver.

If I understood your previous posts you need to run off batteries and an inverter for your alternative power, right?
What did that cost to set up? And if equated to cost per KWh produced over its realistic life span what is the actual number you come up with?

I am just curious. Thats all. Actual numbers help others to find out what will be best for there application.
I fully admit what you are using may very well be more cost efective for some people than what I am doing.

And dont forget that for many just as myself this is also a hobby too!
And most hobbies dont make an honest fincial profit or return. They get measured by fun, learning, and stress reduction, not by dollars and cents!

Last edited:

#### Thunderchild

##### New Member
But for many like me, getting to legaly use the local power grid as a big alternating current battery is a big cost outlay saver.

If I understood your previous posts you need to run off batteries and an inverter for your alternative power, right?
What did that cost to set up? And if equated to cost per KWh produced over its realistic life span what is the actual number you come up with?
yes being grid tied is a huge cost saver as it eliminates batteries and the lost efficiency of charging/discharging that battery. At present I have my old car battery and 40 W of solar panel so I'm quite small scale (cheapo 150 W inverter), the battery is sort of free as it off my old car. however if i wnted to expand I'll be spending a fair but on batteries, the particular set i would like are £ 500 thats the same cost of about 8 20 W solar panels so its quite a burden. I'm not particularly in it for the meney saving either. I just wanted to give it a go and get the hand on experience, infact I have spent more than anticipated after buying tools and other miscelaneous materials and giving a chap a fiva for borrowing his ladder. of course I am also reducing my carbon foot print by a negligeable amount.

in the UK being grid tied costs more than its worth unless you seriously have a house made of PV panels and the patio tiled with PV tile plaus some windmills

Last edited:

#### tcmtech

##### Banned
Since your system is still inthe growing stage this may be some usefull information for you. Maybe.

If you dont mind using fair but used solar panels you may possibly be able to get them cheap by checking with your local highway and street maintenace departments.
Around here it has become standard issue to use the solar powered portable street signs. Those sign carts do get tipped over by wind and dumb drivers fairly often.
When the solar panel glass gets cracked even just a little they replace the whole panel. An associate of mine said he and his neighbor checked in with their local solar sign maintence company and were able to get a pickup load of cracked solar panels for hauling them away!
He did say some were beyond repair but most had large enough sections that they were able to do a little repair work and make a few complete units out of several broken ones.
He said that they spent a good weekend with a glass cutter and were able to rework many of the bigger panel units and got good useable power out of them again. And the price was right!

I dont know what you guys have around your area for portable solar powered street work signs but it could get you a bigger setup for cheap!

I am not a solar panel person so do not know exactly what is involved in reworking one though.

#### Thunderchild

##### New Member
not sure we have that sort of thing around here. there is the odd fixed flashing signal that has a solar panel and tiny wind turbine but as they never move they don't get brocken and are far and few between anyhow. my main issue is the battery cost, as the battery's serve little purpose overall but are needed to temporarily store the power

Last edited:

#### electronrancher

##### New Member
Definitely!
I would be happpy to do a bigger more complex GTI build with you.
Awesome! Give me a few days to finalize some work stuff and I will ping you with my first thoughts on the topology. Then, we can decide to start a thread for that device, or just to take it off-line until it becomes a little more concrete.

Last edited:

#### welshmx

##### New Member
H Bridges

I hate to show how green I am to this, but I find all the components readily available except the H Bridges. I guess I don't know the correct search descriptors or likely places to scrounge these.

##### Banned
Look for bipolar stepper drivers, those are usually dual H-bridges.
I've had the same trouble finding h-bridges on Digikey searching for h-bridge or it's variants

#### electronrancher

##### New Member
The H-bridge is actually made of 4 mosfets, say IRF540. But now you need a way to drive them. You can either buy an off-the-shelf H-bridge driver or build one up yourself out of discrete npn/pnp's.

One good source is to look up the schematics for UPS converters (of which there are many on the web) and look at how they drive their H-bridges.

Here's another resource for you:
H-Bridge Electronic Circuits

#### tcmtech

##### Banned
The H-bridge is just a configuration term. It can be a four single devices or any combination of devices. A half bridge is a pair of devices configured in series. Two of them make a whole H-Bridge.

Here is three examples of what they look like in actual schematical and in real life terms.
These are just for reference. However you can buy these or ones like them on surplus electronics sites and eBay rather cheap.
(However you probably dont nees 600 amp 1200V units though!)

#### Attachments

• 64.4 KB Views: 706
• 58 KB Views: 589
• 77 KB Views: 646
Last edited:

#### tcmtech

##### Banned
Control system Component Function Basics I.

This GTI build up Thread is intended for residants of the united states only! Should you decide to build and use such a device as this you may be breaking laws and can face possible fines, and or jail and prison time for it. Should you chose to build such a device as this and intend to use it for saving energy in your home or dwelling you are still breaking the law. Beware you are considerd a pirate Grid tie operation, which is considered illegal in many countries!

For the control system to work properly you will need to be able to monitor several different AC line signals and the simplest way to do it is with a good old fashion voltage comparators. These circuits may seem a bit crude and simple but have proven that when built right they are reliable and efficient for the purpose.

HIGH – LOW WINDOW COMPARITOR

This circuit uses two comparators set up the same as the dead band window comparator circuit but instead it monitors a voltage signal and the output only goes high if the signal is between the minimum and maximum limits.

If the input signal is below the minimum input reverence voltage X1 and X2 are both in a low output state and the LED in the opto-coupler is off. When the input signal rises above the minimum set level determined by X2 its output goes high and sends a voltage output to the opto-coupler and then is retuned back to X1 with has its output low. Thus turning on the opto-coupler LED.
This give you a high output state until the input signal raises above the reference voltage of X1. When the input signal goes above the X1 reference signal its output goes high also. This blocks the returning signal coming back from the LED in the opto-coupler and effectively turns it off.
Once the input signal drops below X1’s voltage reference its output drops back to low state and turns the opto-coupler on again. As the input voltage continues to drop and passes below the reference voltage of X2 then it too changes its output state back to low and turns off the opto-coupler.

This allows you to have a minimum and maximum limit for whatever source you are using. This circuit is primarily used for the line voltage and frequency monitoring functions being they need to stay within an upper and lower limit window during normal operation.

ON – OFF DELAY TIMER

This is a simple time delay circuit used on most of the control circuits to act as a glitch filter. That is it’s primary purpose is to simply keep the control circuit from false triggering due to odd interference and false state changes from momentary dips or spikes that naturally occur during normal operation.

It uses a simple 555 timer IC setup to give a delay between its input state and output state change. R1 and C1 determine the time delay for both the delay on and delay off functions.
If the input state is high and a changes to low the 555 IC output will not change to low until the time delay has passed. If the input state were to change back to high before the time delay has been reached the output will not change states. It will remain in the high level.
If the input state is low and changes to high the 555 IC output will not change to high until the time delay has passed. If the input state were to change back to low before the time delay has been reached the output will not change states. It will remain in the low level.

Depending on the function it is being used for the time delay can be set for any where from 1 to10 seconds. Personal choice is up to the user. I prefer a 5 second delay in order to ride out line voltage dips and peaks from higher powered devices around my home turning on and off.

Basic circuit diagrams are below.

#### Attachments

• 55.5 KB Views: 1,141
• 30.5 KB Views: 1,748
Last edited: