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Messages - Twospoons

Pages: [1] 2 3 ... 6
1
Transformer (Iron Core) / Re: Increase frequency of NST
« on: September 03, 2021, 11:13:52 PM »
The laminated iron core will limit how much you can increase the frequency before core losses ( heating) become unsustainable.

2
I'm glad you found FEMM to be useful. Numerical simulation (done with the appropriate caveats in mind) is great for getting answers where analytical solutions are prohibitively difficult. Analysing magnetic systems is definitely one of those situations.  I've been fortunate enough to have access in the past to Ansys Maxwell, a full 3D electromagnetic FEA software package. Very capable, very slow on complex problems (days to run some of my simulations), and of course very expensive (NZ$30k per CPU core!).  I was using it to simulate PCB coils for wireless charging, so the geometry was very complex, hence the long simulation times.

3
Electronic Circuits / Re: IGBT Desaturation Detector
« on: August 08, 2021, 11:12:35 PM »
That SOA curve looks a bit wrong. Usually they're shown in datasheets like this:


As you can see the SOA is also a factor of time.

4
Printed Circuit Board / Re: Toslink eagle library (FCR6842031R)
« on: July 30, 2021, 12:08:11 AM »
Eagle? Eww! Just spent 6 months forced to use that POS. And the paid version too. Never again.

5
Electronic Circuits / Re: repair of Panasonic microwave inverter
« on: July 28, 2021, 01:39:46 AM »
Oh yes I'm, aware of the bathtub curve. But the cynic in me thinks the bathtub is rather smaller than it used to be as makers of consumer goods engage in a 'race to the bottom' -trying to be the cheapest on the market in order to boost sales.
I worked for an appliance maker 25 years ago, and as I recall the design life was 10 years. I doubt that is true now, based on the dishwasher I bought recently.

Maybe inverter MWs are just more delicate - the old style with a tfr, two diodes and a fat cap seem to go forever.  But I much prefer the defrost performance from the inverter type, so I guess Ill be replacing it every 3-4 years.

6
Electronic Circuits / Re: repair of Panasonic microwave inverter
« on: July 24, 2021, 10:41:38 PM »
Are these drivers a single IGBT quasi-resonant topology like induction stoves?

It would seem that way based on the schematics I've seen. The only power devices in this inverter are the one IGBT and the diode bridge.  With a single switch pushing 1kW I can't see how else it could be done - the way the transformer is built would lead to considerable leakage inductance, and the only sensible way to handle that, at that power level, would be a quasi-resonant topology.

So far everything is still running, after cooking dinner last night. And I still have a set of spares if it dies again.

And like most appliances these days I guess its designed to outlast the warranty, and not much more.  So they can sell you another one.
https://en.wikipedia.org/wiki/Phoebus_cartel <- this is why consumers get screwed over, and the world has a waste problem.

7
Electronic Circuits / Re: repair of Panasonic microwave inverter
« on: July 24, 2021, 03:16:27 AM »
Having replaced both the diode bridge and IGBT the microwave appears to be working again.
It bothers me that there is no obvious reason for the IGBT to blow, so we'll see how long it lasts.

Certainly cheaper than replacing the microwave!

8

Odd.  Is Q2N3904 really a PNP?  2N3904 is very common NPN.  Can't find any data on Q2N3904.

try 2n2904   :D

9
More likely its taking time to turn the transistor off after the CB junction gets forward biased - bjts perform pretty badly in that mode as I recall.  I ran a sim without the transformer and got the same turn on delay step.   It can be fixed with a Schottky diode in series with the collector to prevent the CB junction from getting forward biased.

10
Yes thats what 2.5D means. Also know as "axisymmetric ".  Good for any "solenoidal" type of problem.

11

  I don't have experience with any finite-element software (except for viewing results others generated).  Is there a free or cheap application that is reasonably easy to learn?
https://www.femm.info/wiki/HomePage
Free 2D and 2.5D finite element simulator for magnetics, electrostatics, current  flow and heat flow.  Surprisingly useful, as many problems can be reduced to a 2d slice and still yield good results.
I think the hardest thing to get to grips with is setting up the boundaries around the problem - I usually use periodic boundaries to simulate the rest of the universe. There's a pretty good manual, included with the software, that describes all this.

12
I would have thought fat litz > foil for the transformer.  Looking at the transformer in the Panasonic microwave oven inverter on my desk they've used multifilar (not true litz wire) wire on both primary and secondary.  The primary looks to be at least 50 strands of 0.2mm enameled wire. This is only a 1kW inverter.

If you have a gap in your core you might find some odd current distributions turning up in the foil.  Easy to run a sim with FEMM as a sanity check.

I'm interested to see what you come up with as I'm toying with the idea of a more modest 2kW induction heater, also offline.  But I really need to finish a lot of other projects first  :-[

13
If the batteries are all the same capacity you should be OK.  But you should definitely keep a close eye on the electrolyte levels and terminal voltage of each battery because it is likely there will be a weak one in the group that will get overcharged / overdischarged.  As I recall lead acid batteries are reasonably tolerant over overcharge - they just boil off electrolyte - but over discharge will lead to sulfation and further loss of capacity.

I would be inclined to connect them like a ladder -  connecting two batteries in parallel, then connecting the three pairs in series. Helps average out the capacity at each level.

14
Yeah, that was not meant as a suggested part - its just the default PNP that Simetrix sticks in. I should have deleted the part number.

15
You can also try this arrangement:



You get damping of the GDT with the 20 ohms, and faster turnoff thanks to the current gain of the transistor. It wont give you negative gate drive though, which can be useful sometimes.

16
In Denmark that is Post Nord and they charge 20€ for handling taxation,

 :o Ouch!

Used to be that anything less than NZD400 didn't get taxed, probably because the cost of collection was more than the tax.
As I understand it, the taxes are now collected directly from most of the larger offshore companies such as Alliexpress.  Maybe that's harder to arrange in the EU, with so many countries involved.

17
Same thing happened here in New Zealand, mostly because local retailers were complaining they couldn't compete. They still can't compete, but the govt gets to collect more tax.
No matter - I use my company to buy stuff, and claim the tax back.

18
General Chat / Re: How Much Propellant ...
« on: June 27, 2021, 04:37:33 AM »
Last time I looked civilian GPS chipsets were velocity limited, precisely so that civilians can't easily make guided missiles.

https://en.wikipedia.org/wiki/Comparison_of_solid-fuelled_orbital_launch_systems is a list of solid fueled orbital lifters - and provides an idea of the scale required. The smallest payload to LEO in that list is 4kg, and the launch vehicle weighs 2600kg.

So you are probably looking in the region of  1000-2000 kg to chuck a kg into LEO.

19
Electronic Circuits / repair of Panasonic microwave inverter
« on: June 27, 2021, 02:31:58 AM »
Has anyone here any experience with repairing the Panasonic microwave inverters?  Mine has a blown diode bridge and IGBT, but without a schematic its a bit hard to work our what else might be dead.  No point replacing those parts if they're heading straight to silicon heaven.
My particular board is F66459X92AP.  The only reference sch I could find  must be wrong as it doesn't show a diode / zener /zener string connected to the IGBT that I can see on my board.

Would be nice to repair the microwave, rather than sending it to the trash heap.

20
General Chat / Re: How Much Propellant ...
« on: June 26, 2021, 10:52:57 AM »
Composite casing and primitive guidance I don't think are the limiting factors,

No, getting permission to launch is going to be the biggest issue.

AFAIK any kind of active guidance on a rocket will bring you all sorts of unwelcome attention.  Governments don't like amateurs building missiles.

As for the weight of propellant - you have to choose your propellant first.  Obviously you'd want the highest ISP you can get.

How many stages? 2, 3, 4 ? Necessary because you want to shed dead weight as soo as possible, and  also  because you want to change nozzle as the altitude and pressure change.

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