# 1000W power inverter transformer

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Tausen, Apr 14, 2012.

1. ### TausenNew Member

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Hi everyone!

New at these forums, please bear with me - I've searched around and couldn't find a post that covered my subject.

I'm working on a 1000W power inverter, inspired by the circuit from here. I'm a bit confused with the transformer, though - can I buy a transformer like this, and what should I look for? Can anyone explain to me what "24 volts, center tapped to 110 or 220 volts" actually means?

I understand that the voltage ratio depends on the ratio between the number of turns in the primary and secondary coils - but that pretty much covers my transformer knowledge. Could anyone please point me in the right direction?

Thank you very much in advance!
-Tausen.

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Attached are a few images of a 24 volt center tapped transformer, ironically I just posted them in another thread. Transformers like this are very common. Unfortunately the author does not give a part number. I do see a small problem. The transformer is actually a step down power transformer. Transformers don't care so a step down can really be used as a step up. The pulsed voltage is applied to the secondary and the output taken off the primary side. Transformers like this come in many sizes as to their current rating. You are building a 1,000 watt inverter which will make for a pretty large transformer. More on that later. You do not mention if you are looking for example a 220 volt output or 120 volt output? That is important to know. That determines if you want a 120 or 220 volt transformer primary. There are also dual primary transformers that can be used.

Running a 1 KW inverter is quite the load on a battery, I hope you have a large battery in mind with a preference for a deep cycle type.

Roughly put 1,000 watts at 120 VAC is about 1000 / 120 = 8.33 amps. Keeping it simple that is a 1,000 VA transformer. It will carry a hefty price tag.

Ron

Last edited: Apr 14, 2012
3. ### TausenNew Member

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Sorry for not specifying, but I'm planning to use the 220V output. I'm planning to have a truck battery (or multiple truck batteries) on the battery end - I'm not much of a battery expert either, but the project calls for ~1kW, so I'm hoping it'll work. I'm very happy that you say these transformers are very common - and the physical size of the unit is not a problem (as long as its not house- or shedsized, it's all good ).

When you say "hefty price tag", in what range are we talking? Hundreds of \$, or...?

Thank you very much for your help!

4. ### DaveNew Member

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Before I forget and this may be important. Inverters like this output a modified sine wave or actually a square wave. While this is fine for many applications the output waveform is not good for all applications. If your planned load requires a nice clean 220 VAC sine wave (like from a wall outlet) using this type inverter design will not work. No, not hundreds of dollars likely well below \$100 USD. I have several UPS (Uninteruptable Power Supplies) around here that are 1500 VA and they are not all that large so while not gigantic they just aren't small.

Let me do some looking and get back to you.

Ron

6. ### TausenNew Member

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Thank you very much for the warning - I'm only trying to run standard home appliances such as a TV, fridge, light bulbs etc., and as far as my googling has brought me, it seems the square wave signal will do OK. Do correct me if I'm mistaken, but it seems that only sensitive audio equipment and such will have issues.

Would I be better of with, for instance, a couple of 300W inverters instead of one 1kW? I'm trying to bring prices down to a minimum.

Again, thanks for the help - I'm looking forward to hearing what you find out

7. ### tcmtechWell-Known MemberMost Helpful Member

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That seems like an overly complicated circuit to run a simple unregulated 50 - 60 Hz iron core transformer based inverter circuit. A common LM3525 or one of its newer equivalents working as the driver for the inverter would greatly simplify your whole inverter driver down to one IC plus you have the capacity to add a simple feedback circuit to keep the output voltage more regulated.

As far as the transformer selection goes I would recommend something considerably lower than a 24 VAC center tapped one being you have to produce a peak voltage on your output along with the RMS voltage as well. 24 VAC has a peak voltage of 34 volts so you would need a 16+ volt input just to break even on the 24 VAC peak levels before any losses are factored in. I ideally I would recommend a 14 - 16 VAC center tapped transformer if you are going to be working with a 12 volt base input.

FWIW I would just spend the money and buy a off the shelf 1000+ watt unit and be done with it. You will never build one that will equal even the cheapest store bought units performance for the same money.

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I would also be remiss if I did not mention what tcmtech points out. Generally when this subject comes up the suggestion is buy over build for a number of reasons. You generally will not save money building as many good reliable units can be bought for less that they can be built for. I also agree as to using a transformer with a lower secondary voltage than 24 volts. Something in the 14 to 16 volt range as mentioned would be a good choice. All things considered buy is a better choice. For example I can buy a nice 1,000 VA UPS here in the US for about \$150 USD which includes a display telling me everything going on with the power. I can go 1,500 VA for about \$189 USD. That includes basic batteries installed and many have the option to connect an external battery. They also maintain a charge on the batteries. I have several APC make 1,500 VA units I use around the house.

Ron

9. ### BoncukNew Member

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pure sine wave inverters are pretty cheap to have by chinese manufacterers.

A 1,000W inverter includes frequency control and voltage output stabilization circuits for 50Hz at at 220V (230V)

1,000W inverters are in the price range of US\$60.

They normally use a toroidal transformer which can be kept smaller than normal EI-core iron transformers and have a higher efficiency ratio.

At an output power of 1,000W the current of 1,000W/220V~4.55A the input current yields for 1,000W/12V~83.33A without losses.

Maximum possible efficiency ratio is estimated to be 80%, increasing input current considerably at full load output.

I abandoned the idea to build my design of an inverter after receiving offers from China.

Boncuk

10. ### chemelecWell-Known Member

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Inverter is a Stolen Circuit.

This Circuit has been taken fro mY Website witout Permission.

The Only Consulation is: He kept my Name and Copyright on it!

http://inverter-circuit.com/1000w-power-inverter-circuit.html/1000w-power-inverter-circuit-diagram

Here is MY Origional Article:
http://chemelec.com/Projects/Inverter-2/Mosfet-Inverter.htm

And trying to get 1000 Watts from a battery is prtty difficult.
It would require a LARGE Custom Made Transformer and Multiple, Parallel Mosfets to handle that amount of power.

11. ### JimBSuper ModeratorMost Helpful Member

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Cheeky little tinker isnt he?

At least he is not claiming it as his own work, he does mention somewhere that this is a collection of circuits from the web.

Still, I can appreciate that it is a bit galling for you.

JimB

12. ### chemelecWell-Known Member

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If it is a Collection, He should than put Links to the Origional Articles.

This is a Good, BUT Older Inverter design.
Newer Designs use High Speed Switching and Much Smaller Ferrite core Transformers.

And today it is much easer and cheaper to just Buy the Inverters.

13. ### audioguruWell-Known MemberMost Helpful Member

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Many electronic products do not work from a square-wave inverter because its peak voltage is much lower than the peak voltage of the sine-wave from the electricity mains. Some TVs, radios, compact fluorescent light bulbs and motor speed controllers do not work properly when fed a square-wave.

A square-wave is good for electric heaters (without electronics) and incandescent light bulbs (which are also heaters).

14. ### TausenNew Member

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Thanks everyone for the feedback, very much appreciated!
I will try to find a cheap Chinese version somewhere and see how that works out - thanks for saving me from wasting too much money and time on this

I am still interested in how one would go around making one - at least to satisfy my curiosity or in case I one day will have to make one.

So, a center tapped transformer means one coil is split up in two - so 14 VAC center tapped means there's 2x7V coils on one side and (for instance) a 230V coil on the other?
I'm still not sure I understand why the 24 VAC would be too high, though - but I reckon that's a longer explanation I should save for my books.

The LM3525 shows up as a "Single Port USB Power Switch and Over-Current Protection" when I search for it - is this the IC you mean? I haven't thought much of how the circuit actually works - but I guess if all it does is switch the voltage back and forth, I can picture how it could be designed simpler.

So if I ever was to make an inverter myself, I'd go for a toroidal transformer?

I'm sorry, I never claimed to have invented this circuit, but only to have used it for inspiration - I figured my noobish questions were a dead giveaway I googled my way to it, if you believe your copyright has been broken you should contact whoever is in charge of the website linked in my initial post.

Thanks - I'll keep this in mind and make sure to get an inverter that at least resembles a sine wave.

Again, thank you all very much for your feedback, I'm very surprised to get this many replies in such short time.

15. ### tcmtechWell-Known MemberMost Helpful Member

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16. ### audioguruWell-Known MemberMost Helpful Member

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My electricity is reliable and I do not go camping to get eaten by bugs so I have never needed and never used an inverter.
Do you think a cheap Chinese inverter will last longer than one week if it doesn't catch on fire sooner? I would stay away from one.

17. ### unclejed613Well-Known Member

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i wrote a blog entry on this subject a while back http://www.electro-tech-online.com/blogs/unclejed613/81-1kw-inverters-free.html

going for the 1kW jugular is a bit ambitious. as some have mentioned, this is the realm of big and heavy. all of your primary (battery side) wiring will need to be heavy gauge copper (4 AWG, (or 126/0.4 for metric wire gauge)). with the currents you will have on the primary side, every milliohm will count. your transistors will require a very large heat sink.

if you are using this for continuous power, also be aware that you will need more than one set of batteries, and some type of selector switch to switch to a fresh set of batteries while recharging another. switches rated at high currents in excess of 50A are not cheap.

18. ### TausenNew Member

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Thank you very much for the advice. I'm going to re-think the whole 1kW thing, will see if a lower wattage can do the trick
Thanks everyone!

19. ### audioguruWell-Known MemberMost Helpful Member

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Deleted Off Topic.

Moderation. E

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20. ### TausenNew Member

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While that is great advice, I want the inverter for my allotment garden No bugs out there, but there's water and solar panels.

21. ### gary350Well-Known Member

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I bought a 12 VDC to 120 VAC inverter 1500 watts on ebay for \$76.