Renewable Energy Questions/Discussion > Wiring and Code discussion

The Basics of using Wire, Volts-Amps-Insulation

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ChrisOlson:
Hey, this is a good thread and I'm following it with interest.  Not much to contribute because I don't know anything about it.  But there's not very many places where you can find these things explained very well.

Carry On.
--
Chris

oztules:
"Skin effect is one of the very reasons many Modified Sine Wave inverters work using much lighter hardware."

I don't believe this is the case.

Skin effect is a negative problem for high speed switching, and is simply overcome by selecting wire diameters as per Woof tables. We need to negate or nullify any skin effect . If we don't, we have wasted copper that does not conduct anything.

Thats why we developed Litz wire.... specifically to overcome the skin effects by having independently insulated fine wire to make up the diameter we need to carry the current. You will see this in modern microwave ovens where they have replaced the heavy transformers with a PWM and small transformer.........

We get to use small ferrite transformers instead of heavy iron cored stuff for completly different reasons than efficiency and skin effects.

When we design a transformer, we need to calculate the magnetising current so we don't saturate the core at that frequency (whatever we choose).

At 50-60 hz ranges, we need about 4 -6 square inches of iron  core to get 1volt per turn. So to wind a powerful transformer, we will need 240 turns of wire at 50hz on a big iron core for the primary. Secondary will be whatever ratio to this we want... for 24v use 24 turns for the secondary and so on.......

If we double the frequency, we can use either the same turns and smaller core, or the same core and less turns. If we take this further, we can see where it's going. If we go to 50000hz,  (thousand times faster than 50 hz) we can use a much much smaller core, and very much fewer turns to achieve the same result..... so we do.

So now we can use heavy wire (split up into multi insulated turns in hand) and few turns on a tiny core to achieve the results of a big "welding" transformer". The heavy wire gives us the very low resistance we want, and the high frequency gives us much less turns.

In some of the 1kw ones I have wound, I use 2 in hand 13 gauge wire for 18 turns for the primary (320vDC) to 6 in hand 13 gauge 5 turns for the  secondary. The skin effect can be used to help cool the transformer. ie in this case at 20khz, there is a small skin effect where some of the copper is not utilised for current transfer (the pipe woof refers to), but the mass gives some thermal advantages if you have a winding window to accommodate it.

MSW does the same thing for the same reasons. We use a push pull PWM to drive the small transformer/s you see in there to generate the 320 volts (or 160 or more USA) at 30-40000 hz. So we need a small transformer for the 12v or 24v input, with many" turns in hand"  to cater for the for the high currents with small core few turns but still heavy current capacity..... we have a tiny transformer compared to our low frequency equivalent.

The secondary is rectified to DC. They then  chop this DC into the MSW 50 or 60 hz. This is generally done at low frequency, by a h- bridge output stage. Varying the frequency is not necessary, and messy. We keep the oscillator fixed, and vary the pulse width to vary the loading.

A different application of those same principals is in aeroplanes where they use 400hz instead of 50 or 60 hz. This allows for much smaller cores and windings for the same power supplies.... lighter to carry into the air.

So at higher frequencies, a given transformer can deliver more power without reaching saturation..... etc


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

Wolvenar:
Oz I think that I was attempting to say the same thing you are, but I failed miserably ..

I will get my wording correct, and verify what I am trying to say IS in fact corrected with a number of the IRC guys, and repost a corrected explanation.

Thank you for pointing out that I was not getting this across in the right way.

oztules:
I look forward to the new explanation wolf. The IRC guys are likely to give us the correct explanation. (some smarter guy than me there)


...........oztules
Edit.... I really shouldn't post with half a cask of wine and a half bottle of scotch in me... hic.... (friday night on an island is hell) :D :D

Bryan1:

--- Quote from: oztules on January 20, 2012, 05:56:15 am ---
 I really shouldn't post with half a cask of wine and a half bottle of scotch in me... hic.... (friday night on an island is hell) :D :D


--- End quote ---

Sheesh only 1/2 of each...................... cutting down on the grog are we   ;D ;D ;D ;D ;D

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