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Forum Index : Electronics : time to build a replacement inverter

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arthur8
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Posted: 10:04pm 20 Jun 2019
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  Warpspeed said   There will always be a huge back EMF kick back from the output choke, or any transformer leakage inductance (or excessively long output wiring) anyway when the mosfets turn off.

That will be effectively clamped by the reverse diodes within the mosfets and by the big low ESR electrolytic that should be placed directly across the dc feed to the bridge.

The rate of voltage rise on the drain will be very fast indeed, and its pretty harmless... Except for capacitive coupling back into the gate.

Your high current gate driver chip, and the very low value series gate resistor must create a very low gate driving impedance. Almost nothing should get back onto the gate from the fast voltage transitions on the drain. Gate drain capacitance is much less than gate source capacitance anyway. If the driver has enough current to really hit the gate hard, its going to be pretty effective at shunting away any capacitive coupling back from the drain. Its mainly a problem with very high drain voltages, which our application does not have.

What can be pretty lethal is any series inductance between the gate driver and gate, or in the mosfet source circuit. All of that can only be due to poor circuit layout, and the more mosfets you are attempting to simultaneously drive, the more difficult it becomes to construct a nice tight physical layout with shortest possible tracks.

The ideal system would be one very sturdy driver chip per mosfet, grounded right at the mosfet source with minimum lead length. A series resistor direct from gate driver to gate, and a bypass capacitor right across the dc supply to the gate driver chip. All with the shortest possible track lengths.

You can then be a bit more adventurous with the logic level pwm signal between your IR2110 galvanic isolator, and the various gate driver chip(s). These track lengths should be kept short too if possible, but there is a lot more freedom away from all the extreme switching violence and extreme high current going on right at the mosfet.

A reasonable compromise might be one gate driver chip placed between each pair of mosfets with the gate resistors splayed in either direction to each mosfet. Connection to both sources can be made pretty direct too with a nice wide low inductance solid copper area. The holy grail is all about absolute minimal lead lengths and minimimum inductances.

Transient suppressors right at the mosfet gate are a band aid solution, and if you are going to do it, use 12v or 15v devices, even if your gate is rated to 20v.

The only practical reason for designing and installing a snubber is to move switching losses away from the switching device and into the snubber.
A snubber only really has application for slow switching devices that operate at higher voltages. Say a slow switching bipolar transistor switching 400v at several amps. If there are switching losses that resulted in ten watts of switching loss, you might design a snubber that dissipated 15 watts into a resistor. That removes some of the direct heat burden from the transistor into the snubber. That is the general idea.

Mosfets and IGBTs are so damned fast these days, and switching losses so low, snubbers are just not necessary.

A snubber that actually does something is going to run hot, and that is just a waste of power unless its actually necessary. Snubber design was a serious design skill at one time, and very necessary back in the dark ages when very slow switching devices were all that there was.
The very early days of switching power supplies were a real challenge for even the very best circuit designers because of the crappy semiconductors that were available compared to today.

Today switching speeds are so incredibly fast, snubbers are no longer required.
Its the high switching speeds now, that are themselves causing new and very different problems to the old days.
The problem now is parasitic inductance and the voltage spikes this creates.
Its now physical layout that is absolutely critical to success.

A good schematic will only take you about 10% towards success.
The the other 90% is all about layout, thermal design, and packaging.
That was not the case in the past, but today, as devices become increasingly faster, layout considerations are becoming increasingly important.


Hi Warpspeed.

I have a very important question. Maybe you (or any other friend) can help me.

If i understood correctly, "excessively long output wiring" will give problems.

My project consists on using two (or three) APC nobreak chassis. One chassis will have the control board + power board and the other will have the transformers.

So, the wiring from Power Board to Transformers will be about 50~80 centimeters.

Do you suggest to try to reduce this wiring?

Thanks
 
Warpspeed
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Posted: 10:58pm 20 Jun 2019
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It should be o/k, but try and put the choke up close to the mosfet bridge on the high frequency side, and run a pair of wires to the transformer primary that are closely bound together.

Those precautions should go a long way to minimizing radiation from the longer than usual wiring.
Cheers,  Tony.
 
arthur8
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Posted: 05:03pm 21 Jun 2019
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Hey Warp.

Thanks for you answer. It helps a lot.

So, this is correct?



To avoid radiation from the transformer wiring, you recommend putting some aluminized tape or copper tape on the wiring?

Thanks.
 
Madness

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Posted: 09:24pm 21 Jun 2019
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This works for me.



There are only 10 types of people in the world: those who understand binary, and those who don't.
 
arthur8
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Posted: 10:06pm 21 Jun 2019
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  Madness said   This works for me.





Looks like ~20cm each wire.

Here i will be running about 80cm. Maybe this is a problem? I can try to reduce this size.
 
Madness

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Posted: 10:38pm 21 Jun 2019
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The way I built it was to take advantage of natural convection. There are 140mm fans top and bottom on both sides as you can see. Most of the time the fans do not run but the top of the case is noticeably warm. Doing this way also allowed me to keep the Toroid as close as possible to the power board. The cables between them though is still close to 300MM when straightened out.

BTW that was the first homemade prototype of the TOTEM pole power board.



Edited by Madness 2019-06-23
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
arthur8
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Posted: 12:02am 22 Jun 2019
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  Madness said   The way I built it was to take advantage of natural convection. There are 140mm fans top and bottom on both sides as you can see. Most of the time the fans do not run but the top of the case is noticeably warm. Doing this way also allowed me to keep the Toroid as close as possible to the power board. The cables between them though is still close to 300MM when straightened out.

BTW that was the first homemade prototype of the TOTEM pole power board.




I've tried to make your power board at home some months ago using silk transfer but it really went bad. Much better to have the original Mad power boards.

To keep the EI transformers cool i will be using some old server fans. My cooling design is not good as yours, but is the only chassis i have at the moment.

So, the better is to keep this wiring small as possible?

30CM doesn't sounds impossible here, but it will be very difficult. But i will be studing a way to keep the wiring small as possible.
 
Madness

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Posted: 01:38am 22 Jun 2019
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If you were told the wires have to be less than 200MM you would find a way.

It is not worth trying to make the PCBs when I have them for $30AUD each, It cost nearly that much for the materials then a lot of time to etch and drill plus failures and you can never make anything anywhere near as good as the professional boards.


I have few left at that price, if I get more made I won't be selling them that cheap as costs have increased.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
Warpspeed
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Posted: 02:20am 22 Jun 2019
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  arthur8 said   Hey Warp.

Thanks for you answer. It helps a lot.

So, this is correct?



To avoid radiation from the transformer wiring, you recommend putting some aluminized tape or copper tape on the wiring?

Thanks.

Yes that is how to do it.
Its mainly about keeping the wires very close together to prevent noise possibly radiating into the control system. With close spacing, the electrical and magnetic fields tend to cancel at a distance.
Cheers,  Tony.
 
BenandAmber
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Posted: 05:46am 22 Jun 2019
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I like that two box design for a inverter

Really neat craftsmanship also

I have motor controller boxes this would probably work well with

I have all the big relays capacitors and surge arresters and stuff too if anybody needs themEdited by BenandAmber 2019-06-23
be warned i am good parrot but Dumber than a box of rocks
 
Madness

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Posted: 06:11am 22 Jun 2019
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  arthur8 said  
  Madness said   This works for me.





Looks like ~20cm each wire.

Here i will be running about 80cm. Maybe this is a problem? I can try to reduce this size.


To get some scale the long side of the main PCB is 300mm long. If you take a piece of wire and bend it to the shape of the white wires going to the toroid on your screen and then straighten it and compare to the PCB it is very close to the same length. This does not take into account bends towards the front or back that are flattened out in a 2D photo.

If you look at this Video of Clockmans the Toroid primary wires are quite long. So don't worry about what I have been saying about length.

Edited by Madness 2019-06-23
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
poida

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Posted: 07:55am 24 Jun 2019
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hmm, time for an update on running the Chinese inverter boards.
All was well until the wfe chose to run the bar heater on the inverter.
Ka-pow!
Replaced 1.2 the bridge MOSFETS, in April.
Yesterday I chose to run the board with the frypan, doing a nice boneless roast lamb.
1/2 hour into it. Ka-pow!
I can't seem to build the modifications into a board (such as this one here My Dog, the board is $200 each now. That seems a lot of fun tickets. Am I on drugs? I recall paying $120 AU or something.)
so that it can provide 2500W

Not to worry, I am building a Madness power board now, driven by the nanoverter or Madness control board (not a lot of difference between the 2, maybe lower idle power)
I will be including some ferrite beads on the Drains of all high and low side MOSFETS.
This is for lowering the emitted electro-magnetic interference (EMI) and so providing
a good situation for the control boards to work in.

(no need to pictures of the gory explosions. We have all seen enough of this..)

Sometimes I think I know what I am doing, other times it's clear I have idea at all.

wronger than a phone book full of wrong phone numbers
 
Madness

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Posted: 08:16am 24 Jun 2019
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I haven't seen a blown board for long time, a picture won't hurt. :)

My experience is that if you have a small enough breaker there is no bang, just a tripped breaker that won't stay on.

Not trying to brag but it's been a few years now since I have seen a MOSFET with craters or a PCB with black on it.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
arthur8
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Posted: 08:20am 24 Jun 2019
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  Madness said  
  arthur8 said  
  Madness said   This works for me.





Looks like ~20cm each wire.

Here i will be running about 80cm. Maybe this is a problem? I can try to reduce this size.


To get some scale the long side of the main PCB is 300mm long. If you take a piece of wire and bend it to the shape of the white wires going to the toroid on your screen and then straighten it and compare to the PCB it is very close to the same length. This does not take into account bends towards the front or back that are flattened out in a 2D photo.

If you look at this Video of Clockmans the Toroid primary wires are quite long. So don't worry about what I have been saying about length.



Hey Mad.

Thanks for answering. This is good to know. Was a bit afraid because of that.

Thanks again for all help.
 
arthur8
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Posted: 08:22am 24 Jun 2019
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  poida said   hmm, time for an update on running the Chinese inverter boards.
All was well until the wfe chose to run the bar heater on the inverter.
Ka-pow!
Replaced 1.2 the bridge MOSFETS, in April.
Yesterday I chose to run the board with the frypan, doing a nice boneless roast lamb.
1/2 hour into it. Ka-pow!
I can't seem to build the modifications into a board (such as this one here My Dog, the board is $200 each now. That seems a lot of fun tickets. Am I on drugs? I recall paying $120 AU or something.)
so that it can provide 2500W

Not to worry, I am building a Madness power board now, driven by the nanoverter or Madness control board (not a lot of difference between the 2, maybe lower idle power)
I will be including some ferrite beads on the Drains of all high and low side MOSFETS.
This is for lowering the emitted electro-magnetic interference (EMI) and so providing
a good situation for the control boards to work in.

(no need to pictures of the gory explosions. We have all seen enough of this..)

Sometimes I think I know what I am doing, other times it's clear I have idea at all.



Poida,

I would like to thank you for the boards. I will never forget this.

And i owe you a beer.

You guys are fantastic!
 
BenandAmber
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Posted: 05:40pm 24 Jun 2019
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Is there anything that's not recommended to run on the madness board

Or does Madness just give it hell on anything and everything as long as it has a good breaker for Kicking It Off

I am ready to get started on my madness board just as soon as it comes in

So any tips you post will be greatly appreciated
be warned i am good parrot but Dumber than a box of rocks
 
Madness

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Posted: 08:15pm 24 Jun 2019
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The only thing I would try to avoid is short circuits.

Seriously just use like it is mains power, however, I have all 24 MOSFETs installed if you want to use less for some reason I don't know the answer to your question.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
BenandAmber
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Posted: 02:11am 25 Jun 2019
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Madness I'm going to do exactly what other people tell me to do

I have a hundred h hy4008 mosfets if you guys tell me to put them all in there I will

I'm hoping to copycat poida the greats build

He has been so good to me in the past

not wanting anything in return just wanted to be a good guy

I deeply appreciate him

I don't have enough knowledge and don't have a lifetime to get enough knowledge

to be anywhere close to all you guys on here

So I'm trying to keep my foot out of my mouth and not be a pain

( maybe trying too hard)

Even though you guys are the brains behind it I'm still have a lot of fun putting them together

And I do learn a little bit along the way
( mainly that I don't know as much as what I think I know)

This board it's pretty awesome pictures don't do it justice by the wayEdited by BenandAmber 2019-06-26
be warned i am good parrot but Dumber than a box of rocks
 
Madness

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Posted: 02:22am 25 Jun 2019
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One other caveat I will put on my previous statement.


I am using my own control board, not Poidas, I am sure Poida's control board is perfectly fine but as yet I have not used it.

I have tested my Inverter 8KW for 30 minutes, the Toroid was getting up around 90 degrees at the end but it did that test without any problem. Since I have started using grid tie inverters with my system I don't draw more than around 5KW at the most at night. The inverter actually works harder during the day running backwards to charge the battery.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
BenandAmber
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Posts: 961
Posted: 02:30am 25 Jun 2019
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I guess I will be using poidas control boards unless poida decides to use your control board

I do appreciate you selling me a board it is really nice board

Do you use a nano style or 8010 styleEdited by BenandAmber 2019-06-26
be warned i am good parrot but Dumber than a box of rocks
 
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