Hi Ray,
That sounds about right for a 24 volt transformer with a bridge rectifier and smoothing capacitor with no (Or light ) load 24 x root 2 (1.414) = 33.936 You would then need to subtract about 1.4 volts for the voltage drop in the bridge. So 33.936 – 1.4 = 32.536 As the tansformer is lightly loaded it will probably be giving a little more than 24 volts so this would explain why you get a reading of 35 volts DC. You could drop it to 24 volts using either a linear regulator which would generate a fair ammount of heat. (Depending on the current being drawn.) A switch mode regulator might be a better choice but it is more complex. What current dose the power supply need to provide and what kind of load is it ? (Resistive, a tungsten filiment lamp, or a motor.)

Les.

Hi Ray,

Simple explanation, excuse the appalling diagram.. not to scale

In AC electricity the voltage swings either side of zero volts to give an average swing each side of zero of the quoted value. (A)

The rectifier turns this into a series of swings all one side of zero, and now measuring it will give you the same average voltage. (B)

Add a capacitor and it 'pumps up' to the maximum extent of the swing (which is about 1.414 times the average value) and as it has nowhere for the charge to go, the voltage stays at that higher value. (C)

Put a load on the output and the voltage will drop to the point where the charge 'pumped in' at the peaks will balance that taken out by the load over a complete cycle.

Transformers also usually give more than their rated voltage when the load is light, the %v drop between offload and on load voltage is called the transformers 'regulation', typically 10% for a reasonable one, as high as 25% or more for a very small one.

The role of the capacitor is to smooth out this lumpiness, and this is why it's best for them to be rated at at least twice the AC voltage.

Neil

Hi Ray,
I do not think the voltage is critacal for an EDM machine. If it is one of the two designs on "Mike Cox's" website then I would just add a resistor in series with the 12 volt 50 watt bulb. If it is his Mk3 version you could use an LM7824 to drop the voltage for the motor or add a 24 volt zener diode between the base of the TIP32 and 0 volts. If you do this you may need to put the TIP32 on a heat sink as it would be working as a voltage regulator.

Les.

In view of the nature of this thread. .. can it please be renamed to include EDM..might make searching easier/more productive

Ray..not a criticism. .just as this develops it becomes more Edm and less general..so someone searching for hints etc which might come up here ..would miss out because of title….one of my pet “hates”..nuggets of intrest lost to a search of the thread titles…

Anyway..are you sorted re. Transformer/power supply?

Having now looked at the mike cox erroder…

All above for 35 v is true ..the erroder side would be fine..including the soleniod.coil that jiggles the electrode…maybe when winding it add 30percent extra turns and include the original tap.. ( you now have a 21 – 35 v solenoid. .bonus)
Since the motor control circuit is simply to interface the microswitch current to motor ( TIP 32 acts aa switch..).. the 3k3 resistor at 21V delivers some current to turn on the transistor..well max of say 7mA..but at 35V a max of 12 mA…
Neither will bother the Tip32….
Now ..will the motor mind?..
Not for the tiny intermittent duration of its use…