In need of electronics/circuit board knowledge

[brendanh]

ive got a circuit board with 240v in and 25v out, has current overload protection. It for my power feed for my x2 mill however im not happy with the way the speed controlling works, my original plan was to scrap it all together and start fresh with known components that i have tried and tested the problem with that is theirs no current overload protection. reason for current overload protection is if a cutter jams it it will just cut power to the power feed to prevent striping the lead screw nut.
what i want to know is how do i get the raw 25v power with current protection on it so i can wire it into my new PWM controller/potentiometer?

[KBs PensNmore]

Hi Brendan, is that the control board from the X2 or the C2 lathe. I have one (FC350BJ) from the X2 (early) if you want one to play around with or for parts.. Yours for postage cost, or if anyone else wants it, requires repairing though.
Kryn

[brendanh]

No its a control board for the powerfeed i have in it.

[RayG]

You just need to find a 24V DC supply with adjustable current limit. I assume from what you said that the PWM controller just does speed and direction?

[BaronJ]

Hi Brendanh,

Getting a 25 volt linear psu is easy, but you need to specify the maximum current that you expect it to supply before overload fold back kicks in. The psu that you show in your pictures, is a switching one. For the same power output it is much smaller than a linear one but current limiting is much easier to arrange.

Since you have said that you are going to use pwm to control the motor it would be convenient to just use a fuse and let that take care of any overload when using a linear psu. A simple transformer, bridge rectifier and smoothing cap would suffice to provide 25 volts.

[brendanh]

The point was to use this board, as its off my powerfeed and its proven. However i dont like the way it controls the motor speed so i want to use one i have. So i want to use the 25v this board supplys as it has the overload in it alread instead of buying a new transformer.

[RustyArc]

The point was to use this board, as its off my powerfeed and its proven. However i dont like the way it controls the motor speed so i want to use one i have. So i want to use the 25v this board supplys as it has the overload in it alread instead of buying a new transformer.

Probably the simplest way would be to set the existing board to 100%, and run the motor output into your preferred speed controller

[brendanh]

That exactly what i want to do. I want to bypass that boards potentiometer.

[RustyArc]

That exactly what i want to do. I want to bypass that boards potentiometer.

Unfortunately the board's connections aren't shown in the photos - i.e. where the speed pot and other wiring connects to. One could guess based on the terminal labels (P1 etc?), but it might result in smoke.

It'd help if you could show what wires and plugs connect where, and what those wires and plugs go to.

[brendanh]

I beleive p1 p2 p3 where the potentiometer, k1 and k2 was the reset switch for when it overloads and m+ and m- was for the motor, there was a forward and revess switch too. Ill have a look tomorow and confirm what did what.

[RustyArc]

I beleive p1 p2 p3 where the potentiometer, k1 and k2 was the reset switch for when it overloads and m+ and m- was for the motor, there was a forward and revess switch too. Ill have a look tomorow and confirm what did what.

You should test the voltages between P1 P2 and P3. It's most likely P2 is the wiper and P1 and P3 are the rail voltages (0V and probably 5V). If that's the case, shorting from P2 to P1 or P3 will make the board output either max or min duty cycle. Note you need to be sure about the terminals you short out, otherwise you'll blow up the power supply. If you're unsure, a 100 ohm resistor might be a safer option in case you're mistaken, and probably will work just fine, or at least until you confirm which are the correct terminals to short.

I'd put a decent sized electrolytic cap (say 470uf+ rated to more than 25V) as well as a 100nf cap across the motor terminals before your new speed controller to help smooth the voltage just in case it's not quite doing 100% duty cycle at its max setting.

[brendanh]

Thanka for your help. Ill have a go tomorow and let you know what i come up with

[BaronJ]

The point was to use this board, as its off my powerfeed and its proven. However i dont like the way it controls the motor speed so i want to use one i have. So i want to use the 25v this board supplys as it has the overload in it alread instead of buying a new transformer.

Sorry I misunderstood your intentions.

I would go with the suggestion by RustyArc. Just check and make sure that the polarity of the voltage output on the motor terminals is what you expect it to be.

[brendanh]

Please excuse my paint skills, ive done a bit of a drawing as to how it is wired, if it doesnt look right it probably isnt as i had already cut a couple wires off and was peicing it together. however i am confident its wired like this but i cant work out where p2 is wired into the board

[RustyArc]

If you're confident P2 is the wiper connection, then you should be able to short it to P1 or P3 (maybe using a 100 ohm resistor in the first instance to confirm) then measure the voltage on the motor terminals to see which way gives you max volts.