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48V 5000W Oil cooled inverter build
#51
The filters are to stop higher frequency (well above 23kHz) harmonics and noise leaving the wires and transmitting to the world as noise or causing issues with other items plugged in.

With the switch on rise and too much inductance you end up with oscillations as shown (as a more extreme example - and a slow switch on event due to no load as the inductance is slowing the voltage rise more)


This is the voltage switch on event for the FET's with too much inductance, under load and shows an additional distortion in the ramp up of the voltage.



The filters will then these higher frequencies from going down the wire to the house and also block any noisy applicances back feeding into the inverter and potentially causing issues.

The E70 cores (ferrite) take out a lot of the high frequency noise but you can still end up with residual noise/harmonics after the E70's.

Filters are only dampening or reducing the extent of the signal as they can't take out 100% of any unwanted component, unless you are dealing with a digital system.... so with analog you end up with a compromise.

The 5uF is there to do two jobs, one to smooth out the 23kHz and also to create an out of phase resonance with the toroid (75Hz) to help stop the 50Hz wave from being distorted and creating harmonics. If you use one 5uF or 5 x 1uF caps they do the same thing. Caps are the same as batteries in that regard, parallel or series they give the same way. I still need to measure and test for the exact value for 75Hz resonance with the transformer and have a bunch of smaller caps to add or combine in different ways to get any value I need.

So far after I set it up to test live I have not powered it down (now at 773kWh through) but need to do this soon, or in about a month under my deffinition of soon, lol.
Korishan likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#52
Yeah I'm aware of how caps parallel :-)
I was thinking of how some caps differ internally (some better @ HF than others, internal inductance, etc, etc) & given that 5uF cap is getting the full brunt of the transformer's output! Must be under some serious stress!

Re the filters, was wondering about this position in the cct:
FETs > E70 inductors > main transformer > 5uF cap > {insert new filters here} > CW4L2-20A-T.

Re the waveforms, the second one with the wrinkle half way up the leading edge, that wrinkle is FET switching point oscillation, gate drive resistance also affects this.
Agree the second trace has too much ring at the top.
Some of that ring might be from inter-winding capacitance.
Great to see the traces there :-)
completelycharged likes this post
Running off solar, DIY & electronics fan :-)
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#53
Teaching to suck eggs... :-)

The capacitor is polymer X2 self healing. Has to be self healing so there is no sudden cap failure and the inverter suddenly exposing everything to a 24kHz PWM. Under load the for a ripple of 15V (235V to 220V) stores 15.9 milli Joules and at 24kHz, 50% duty the load would then be 762W (reduce the duty for lower loads...). Suppose this is a bit simplistic as it's not really taking into account the larger phase offset at lower loading (at idle the apparent load is near 100% capacitance, the 5uF).

Increasing to 90% duty, maintaining a maximum 15V ripple the load tops out at 3.8kW, that is if all of the PWM smoothing were to be handled by the cap on it's own..... 4V ripple and 98% on duty the cap can handle 5568W.... This is partly why i am suging the board at maximum 6kW, even though it is 'rated' (chinese deffinition) for 10kW as I don't want a high ripple on the output under high loads as I think this would lead to failure quite quickly.


Adding a separate filter in I had looked into that, specifically something around a 8kHz low pass rather than the higher frequency units I have ended up with. For a 8kHz low pass you then need something like an inductance of 850uH and a 0.47uF cap.
The 850uH would then need to remain unsaturated for currents upto say 25A (minimum) for a 6kW load at 235V, which can then make for a rather large choke. Using a single T-400-26D core (AL262) you then need 57 turns on a single T400 and that saturates at 21A so....

Stack two T400's and 41 turns then saturation is raised to 29A. I only have one T400 and did try it on the output with 56 turns but the wire I used for the test was 0.75mm2 (5A) and did not go back to re-winding it.

I may end up ordering another T400 and wind them, ideally I was initially hoping to source all the parts for the build off the shelf at a sensible price so that they could then be used as a nice easy standard kit.. a plug and play alternative to the way over $1k inverters for 5kW.

I'm not an electronics engineer by proffession so this has all been an interesting learning curve... (this is the disclaimer that I'm not sure I am 100% right in all or any of what I have said !) Still a lot to learn, test and implement...
Korishan likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#54
(06-08-2019, 08:29 AM)completelycharged Wrote: Teaching to suck eggs... :-)
Definitely learning from reading your progress path here! :-)

(06-08-2019, 08:29 AM)completelycharged Wrote: The capacitor is polymer X2 self healing. Has to be self healing so there is no sudden cap failure and the inverter suddenly exposing everything to a 24kHz PWM.
Good point.
(06-08-2019, 08:29 AM)completelycharged Wrote: Under load the for a ripple of 15V (235V to 220V) stores 15.9 milli Joules and at 24kHz, 50% duty the load would then be 762W (reduce the duty for lower loads...). Suppose this is a bit simplistic as it's not really taking into account the larger phase offset at lower loading (at idle the apparent load is near 100% capacitance, the 5uF).

Increasing to 90% duty, maintaining a maximum 15V ripple the load tops out at 3.8kW, that is if all of the PWM smoothing were to be handled by the cap on it's own..... 4V ripple and 98% on duty the cap can handle 5568W.... This is partly why i am suging the board at maximum 6kW, even though it is 'rated' (chinese deffinition) for 10kW as I don't want a high ripple on the output under high loads as I think this would lead to failure quite quickly.

Adding a separate filter in I had looked into that, specifically something around a 8kHz low pass rather than the higher frequency units I have ended up with. For a 8kHz low pass you then need something like an inductance of 850uH and a 0.47uF cap.
The 850uH would then need to remain unsaturated for currents upto say 25A (minimum) for a 6kW load at 235V, which can then make for a rather large choke. Using a single T-400-26D core (AL262) you then need 57 turns on a single T400 and that saturates at 21A so....

Stack two T400's and 41 turns then saturation is raised to 29A. I only have one T400 and did try it on the output with 56 turns but the wire I used for the test was 0.75mm2 (5A) and did not go back to re-winding it.
Some serious currents there....
I'm thinking such a filter might be best with two inductors (one each leg) to reduce the RF noise?

(06-08-2019, 08:29 AM)completelycharged Wrote: I'm not an electronics engineer by profession
You've had us fooled the whole time :-)
completelycharged and Korishan like this post
Running off solar, DIY & electronics fan :-)
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