Trouble with Rod Coleman DHT reg

[cowneko]

Hmm I thought the 9 volt windings were each rated at 2 amps? A10% drop with a 1 amp load doesn't sound right and a +30% drop with a 1.4 amp load is not good. Is the primary voltage solid and does not go down at all, no load to 4 ohm load.

Well no drop of the primary voltage in any situation, it's steady at 230V

However I took measurements across the resistors not on the secondaries. If I take measurement right at PT secondaries with the two 8ohms res connected, I get my 9,5V

 

[pchw]

Can you draw a diagram with the voltage at your measuring points? Keep it simple, use only one secondary and leave the other open (tape it so that it will not be shorted accidentally). We are going to trouble shoot this as a 9VAC 2.22A transformer.

 

[Hearinspace]

Well no drop of the primary voltage in any situation, it's steady at 230V

However I took measurements across the resistors not on the secondaries. If I take measurement right at PT secondaries with the two 8ohms res connected, I get my 9,5V

So on the sagging measurement what was between the transformer secondaries and the resistor?

 

[cowneko]

Here we go!

An externally hosted image should be here but it was not working when we last tested it.

all measurement done with a TRMS Dmm

 

[Bigun]

Sorry ! but that drawing makes no sense at all - a schematic assumes zero resistance for 'wires' and so the voltage drops must all be the same. If not, these aren't 'wires' they are resistors and you should draw them as such. Could the physical wires be part of the problem ?

 

[Hearinspace]

So the 7.06V is measured with only the one resistor in place and the 5.692 was measured after that second resistor was added?

 

[MelB]

Bigun you may have solved it. Resistor wire!

 

[cowneko]

i'm using 40cm connection wire with crocodile clips, that may be the source of the problem

 

[cowneko]

Well the cables where the cause of all that, i've redone the connections using short single core wire and now, no more voltage drop even at 4 ohm (maybe only 50mV).
You nailed it Bigun but I feel a little stupid now

 

[avinunca]

Mmm. That few cm of straight line on the diagram. I wondered where that volt drop was. Must have been very skinny cable! Don't feel foolish. It's a learning experience.
I was puzzled by the comparison of bridge rectifier input ac volts rms and dc output V. I believe it should be
1.41 x VRMS - (2 x 0.7) with your circuit. You measured the dc voltage as lower than ac rms. Maybe you weren't measuring rms.

 

[cowneko]

All is fine now, the regboard is delivering a steady 5V after tweaking RV1. So much troubles because of such a trivial thing as wire resistance.......I learnt a new thing here, thanks to all of you

 

[Rod Coleman]

I am back from travels now - sorry to be absent while you needed help! But I am ready, if you have questions about getting the best from the regulator.

 

[cowneko]

I am back from travels now - sorry to be absent while you needed help! But I am ready, if you have questions about getting the best from the regulator.

Please don't be sorry , I wasn't expecting you to be at my disposal, people here where kind enough to help me with my problem (witch was, in the end, the dumbest possible).

Now that the PSU is feeding the regboard correctly, I'm in the process of etching a Pcb for it, then I'll pursue the tweaking o fthe reg, maybe I'll need your enlightements then.

Thanks a lot Rod