want to attempt some powerjack mods and could use some help. oztules?

[oztules]

As you seem to want high power for long periods, three should do fine, but you will have room for 4 I suspect, so more never hurts... you only get to do it once.

How does that smaller single stack one perform now?

The pics are good, some text to explain them would help in their interpretation too.

The CT bypass is simply that... or neater and easier, is to change the resistor value on the output. You will see that under the board, and it generally looks like they have added it later on... they have... I think they make the same board and change the resistor for the expected wattage they want.... reduce that resistor, and it wlll damp the ct signal,... so more power.

Nice looking core there too... well done.

............oztules

[Dr_Zogg]

thanks for the compliments, without your help none of this would have been possible.

i am hoping to do some better testing on the smaller one tomorrow when i bring some of my better batteries here from my block where we are building.
i will report on that tomorrow night.

do you have any suggestions on a good value to start with for the current shunt? or is it more of a trial and error thing,
would you think that 70mm2 would be  adequate for the primary?

here are a few pics of the 15kw boards i have. i bought a complete 15kw inverter about a year ago and stripped it down for this project as the sellers at the time were refusing to ship me boards by themselves, but i figured compered to the price of other inverters that don't even seem to do half of what these can it was still cheap buying.
plus i now have the 3 transformers from it to play with. i am going to use one of them to experiment with the oil cooling idea. and am thinking of driving it with one of the control cards you are working on and one of the driver boards clockman and you are doing, could make for an interesting project.

anyway thanks again for sharing your knowledge with the world.


Cheers,
            Sam

[Dr_Zogg]

oops forgot the pics.

[Dr_Zogg]

i just pulled the control board off, flipped it over and removed the tape, but i can't seem to find the resistor for the current bypass. what area of the board should i be looking in? i presumed it would be across the ct but i may be wrong.

Cheers,
           Sam

[oztules]

Look to the front of the board for R109.... second in from the edge. If you think you have it, check for continuity from it to the CT output leads... then thats it.

70mmsq primary will be more than good

current shunt.... trial and error.. I suspect if you halve the resistance you have doubled the current needed to trigger.



................oztules

[Dr_Zogg]

thanks for the quick reply. i will sus it out now.

Cheers,
            Sam

[Dr_Zogg]

that was the one. thanks for that.
do you think it would work if i removed that resistor, soldered 2 wires onto the pads then soldered them to a socket glued to the top of the board,
so that i can easily change the resistors without pulling too much apart?

Cheers,
           Sam

[rossw]

do you think it would work if i removed that resistor, soldered 2 wires onto the pads then soldered them to a socket glued to the top of the board, so that i can easily change the resistors without pulling too much apart?

If you think about the way a CT works, you can deduce it will be fine, within reason.

A CT has a primary (usually a single turn), and a secondary - of some number of turns. Lets say it's 1000 turns.
For 10 amps through the primary, there will be 10/1000 amps in the secondary.
With no current, the voltage across the output will skyrocket (which is why you NEVER open-circuit the secondary of a CT!)

The burden resistor (load, or shunt, if you like) across the output of the CT determines the voltage across it, for a given current. So in the example above, 10A in a 1000:1 CT, means 10/1000 = 1/100A = 10mA
With a 1K resistor, you should see 10V. With a 100R resistor, you should see 1V

If the load resistor is very low value, then connection resistance will be an issue, but for any "sane" value of R, the connection resistance from your connector will be negligible.

[oztules]

... and if your lazy and can be bothered with the maths, a trim pot of 1000r will give you infinite control... but use cautiously.
 I use the big welder, and trim down until I don't see the led flash...... and thats it.


...............oztules

[Dr_Zogg]

thanks for the explanation rossw i had a rough idea of how the ct worked, but i did't know how the shunt fitted into the equation but it is clear to me now thanks to your excellent explanation. and thanks again oz for yet another great idea.


Cheers,
           Sam

[Dr_Zogg]

hi oz i saw on some of yours it look like pvc insulation tape instead of mylar. is it ok to use that instead?

[oztules]

It probably has the same melting point as your primary will.... but only as an outer wrap ( cosmetics), not for wrapping the secondaries... use the proper tape ....although if you don't have any.....better then nothing I guess.

Mine was cosmetic on the first ones I think.

...............oztules

[Dr_Zogg]

hi guys,
i just did some testing on the small inverter and i'm not sure if all is well.
it powers normal loads ok. but if i try to start my compressor 3Hp belt drive it won't start output voltage drops to 109v and no alarm.
i fire up my bandsaw, oldschool .33hp belt drive alarm light flashes once and off she goes. so i decided to plug in my inverter ac dc tig welder so that i can vary the load with the foot controller, so i ramped it up slowly and the voltage holds stable at 238v right up until i am pulling 9.5a from the inverter then it drops instantly to 108v and the welder starts spluttering. i also tried my 2000w makita chop saw and on startup the voltage dips to 108v for a second then it plugs away fine.
from what i have read about this setup i thought it should have been a bit beefier than this, or i could just be wrong?
any ideas?

Cheers,
           Sam

[Dr_Zogg]

i swapped out the control card for the one on the 15kw board and it fired everything up fine and worked how i thought it should and here comes the BUT.
but when i fired up my compressor for the second time i heard a crack and got that distinct burnt semi smell i can't see any burnt fet's but i am going through it now
it didn't go off with a big bang, no smoke but no output now

cheers,
           Sam

[Dr_Zogg]

there is no physical damage to the FET's but is there any way to do a rough check on them while they are still in the board? i have had a quick check and some of them are short between all 3 pins and others are open between all, not sure where to go from here?

thanks,
           Sam