Tony Williams said:
I breadboarded it.............
Low--------------------------------------+
/|\ |
230Vrms | /
Vout 590\ Load
120V 120V | /
+ - + - \|/ |
High-----//////---------//////-----------+
====== ======
+---//////---------//////---+
| + - - + |
| 18V, 0.4R 18V, 0.4R |
| 5R |
+-----------/\/\------------+
| + |
+------------||-------------+
Idc /|\ 10000uF |
| 11R |
+--/\/\--- + DC - ----------+
0-28V variable.
2x 50VA transformers, wired for 120V primaries and
18V secondaries. Total secondary resistance is 0.8R
and the max rated secondary current is 2.77Arms.
230Vrms supply and a 590R load.
I ignored Ken's nagging and just put the 5R in
first of all, to see what the circulating current
was....... it's large and there is a reason for
that. So Ken's cap is a neccessity. By using a
huge capacitor the AC peak-peak voltage is always
lower than Idc*0.8R, so a polarised electrolytic
can be used safely.
Quick first measurements, to be refined later.
Idc(amps) Vout(rms) dVout/dIdc
0.0 3.9 ______ 162.5 Volts/Amp
0.2 36.4 ______ 146
0.4 65 ______ 130
0.6 91 ______ 115
0.8 114 ______ 95
1.0 133 ______ 85
1.2 150 ______ 75
1.4 165 ______ 70
1.6 179 ______ 65
1.8 (187) 192 ______ 55
2.0 (203) 203 ______ 50
2.2 (212) 213 ______ 5
2.4 (209) 214 ______ 5
2.6 (210) 215 ______ 0
2.8 (215) 215
Those figures in brackets. Up in the 1.8 to 2A
dc control region there seems to be a control
hysteresis. If you casually fiddle the DC supply
up and down to get it spot on then the AC results
can be all over the place. The figures not in
brackets were taken by creeping the supply upwards
only.
You can see from the table that with a 230V supply
then the Load should be rated for about 200V max.
The control power increases unreasonably above
that figure.
Note that the sec windings are rated for 2.77Arms
maximum and at 2.8Adc they are carrying the dc,
plus whatever the circulating current is that point.
Note for Win..... I put a large low pass filter
across Vout and confirmed that there is Zero net
DC voltage there. This allowed a signal transformer
across Vout to allow for a scope to look at the
output waveform.
And why is there a large circulating current between
the two secs, that requires Ken's cap?
It's obvious when you look at the scope and see that
the circulating current is mainly peaks and at 100Hz.
The DC signal drives the two cores in opposite
directions, so one core handles +AC peaks and the
other -AC peaks. So the AC voltages across each
are mirror images, and that's where the circulating
current comes from when the secs are connected together.
More later when domestics permits........