best I can remember, the reason for putting back to front diodes across electromechanical components is because when they are switched off you can get a reverse voltage coming out of them, which can then destroy other components, particularly if you have something driven by a transistor. In this...
jateau, your diodes across the motor and relay are back to front for protection diodes. As you have drawn them they short out motor and relay. Likely result immediate diode burnout, I would guess.
Some of the pictures Ive seen show a diode pack with six pressed in diodes rather than four. I'm guessing that would be three diodes in parallel twice, so the current is shared by three diodes 1/3 each whereas this one has 1/2 each. So Iam guessing they do a higher power rated version. But it...
Im still bugged by the transformer arrangement having two secondary coils. I'm sure it would be more efficient to use the same weight of metal in just one coil instead of two, because the resistance would be less. There would be additional power loss because of the extra voltage drop because two...
I think its more correct to say it is two half wave rectifiers connected in parallel. I have one of these and I think all four diodes are pressed into the heavy metal plate the same way round. The diodes are arranged in two pairs of diodes in parallel. Best I could make it out, the diodes are...
Dont know the layout of your sip, but they seem to be very similar. here is a photo of an old one and I have added two arrows showing where the black wires to power the motor were attached to the weld supply. One to the bolt hanging in the middle and one to the thick wire on the rectifier...
If there is now a wire hanging around broken off, that sounds a likely source of your problem. I am not sure from your description whether the wire feed runs or not. I think the black wire going into the green connector should connect back to the weld supply somehow and complete the circuit to...
Does anyone know what the rating of the MOV on the controller board is? (usually a round yellow thing in the bottom left corner on the pics I have seen)
Id say thats a vote for making a separate very steady supply to the motor. The relay brake is necessary if you introduce smoothing capacitors into the supply. I think possibly the original circuit might have given a bit of an extra boost of power when the motor starts up, but certainly some of...
Thanks for the replies. There might be a danger that what you are saying is that on an expensive machine the current will also be very well controlled so naturally it would want a very steady motor too.
In this case I dont think there is much prospect of improving the current stability, but...
I have read several mods on here and dont know which is best. There seem to be two fundamentally different approaches to powering the wire feed motor, either getting the power from the big weld transformer, or providing a separate dedicated supply.
Sip seem to favour getting it from the weld...
I have found another controller circuit here http://www.wizardanswers.com/hfwelder.html which is supposedly for a harbour freight 90A welder. It is similar to the one you posted except it does not derive the power for the transistor base from that going into the motor, rather from a steady +ve...
Im afraid I dont understand what you are doing (see request above for pictures). Which mod are you doing? Wiring varies a bit from model to model. The Black wire originally went to the +ve output from the big diodes fed by the weld transformer (big one). The white wire went to drive the...
I dont think i could solve this from what you have said, which I agree doesnt make sense. R Kraft posted a link to voltage multiplier circuits. I dont know whether if the terminals in a bridge get mixed up it is possible to make a voltage multiplier by accident? (anyone?) You need capacitors to...
I dont understand quite what is happening but can make a few observations.
What sort of meter have you got? If it is an electronic one with very high input impedance, it is possible this may affect the result as compared to a cheap dial one which puts a bit more load on the circuit. Just a...
To get back to the original board and trying to mod it without having to build a giant new circuit. I think one of the things wrong with it is that there is no stabilisation of the voltage applied to the transistor base. The + supply comes from the weld voltage, but the - is all connected to...
thanks for the id on the yellow blob. In this case Id guess it isnt to suppress spikes but to act like a zener and limit the maximum voltage which can be dropped across the transistor. Either to protect it from over voltage, or to make sure that at least some voltage is always across the motor...
Right thanks, I had misremembered which way round the gate on the scr works and was thinking it had to go down wrt anode to fire, rather than go up wrt cathode. Lets try again. Let me know what you think of this one.
So from cold start, voltage from P2 gets to the scr gate via a resistor and...
The manual is at http://www.sip-group.com/acatalog/04796.pdf
It is not the same as the one you have posted. In the sip one the motor is connected directly to weld voltage through the thyristor when it has fired. On the face of it that seems a bit odd, but hey. When the thyristor is off, I am...
I dont have a board but I am interested in the question of designing a better one. Are you willing to say what you have in mind?
I had a look at the sip website where there is a rather blurry online version of the manual for the newer migmate T155/T135. The control board is significantly...