[rcheli]

I have a KL-4820 unregulated toroidal power supply running on 240v. How do I calculate the proper fuse size?

https://www.automationtechnologiesin...l-psu-kl-4820/

Originally I had calculated 960w / 240v = 4 amps. Not sure how to account for in-rush current. So I put a 5amp fuse on the primary side. This worked but occasionally blew the fast acting fuse so I switch to a slo-blow 5amp. Again, worked for a while and now it is blowing the 5 amp slo-blow with nothing attached to the secondary side. Tech support said to try a 10amp due to the in-rush but it sounded more like an arbitrary value rather than a calculated one. I get the reasoning with regard to the in-run current but why would the fast acting 5amp fuses work originally and now it blows the slo-blow with nothing attached? I have turned the machine on and of a lot of times while testing my HAL programming in LinuxCNC and made a couple of parts with these fuses but now as soon as I turn on the power it blows the fuses.

Also, what would be the expected resistance across the primary windings wired in series for 240 volt use be?

Thanks
John

[Jim Dawson]

It depends on where the AC is in it's cycle when you turn it on as to whether it blows the fuse or not. The instantaneous in rush is highest at the peak and lowest at zero crossing. If you want to almost never blow a small fuse, install a zero-crossing turn on relay. For that power supply I would probably use a 15 amp, D curve dual breaker.

If it is now constantly blowing fuses with no load, then I would start looking at the bridge diode or filter caps, it may have failed. It would not be the first time I have seen one of those fail.

[rcheli]

Thanks Jim,

I'll check the brides diodes and caps tonight.


I found these.

https://www.automationdirect.com/adc...)/FAZ-D15-2-NA

They have a 10 & 30 amp version. Would I use the 10A since it is zero crossing? Or, just go the extra $20 and use the 30A?

https://www.automationdirect.com/adc...-SSR210-22-DCZ

Thank you
John

- - - Updated - - -

Thanks Jim,

I'll check the brides diodes and caps tonight.


I found these.

https://www.automationdirect.com/adc...)/FAZ-D15-2-NA

They have a 10 & 30 amp version. Would I use the 10A since it is zero crossing? Or, just go the extra $20 and use the 30A?

https://www.automationdirect.com/adc...-SSR210-22-DCZ

Thank you
John

[Jim Dawson]

The breaker is fine, but I would use this relay, less money and higher switching current capacity. 2 required to switch 240V, you need to switch both lines, this is true for either relay. https://www.automationdirect.com/adc...SSR625-DC-280A

[rcheli]

Thanks Jim. I am going to order the items you recommended.

I tested the rectifier and it is bad. Diodes are shorted. The bare transformer can be powered up using the 5 amp fuses and puts out 34.68 volts AC.

Thanks again
John

[rcheli]

Two more questions about my 48volt power. I believe the rectifier failed because the wire I have going to my stepper motors is crap. The black conductor will just not allow a good solder joint and therefore the conductor became disconnected on more than one occasion and shorted out. Should I have fuses on the DC side? I have Gecko G203V's and they survived.

Any recommendations on good wire for the steppers? I was looking for 18 gauge shielded that is real flexible. I got some wire from Automation Technologies but it is pretty stiff.

Thanks
John

[Jim Dawson]

I had one of those power supplies fail right out of the box with no load on it, they sent me a new board.

I normally put fuses on the DC side. I don't think those power supplies current limit when overloaded.

This looks like a good option. Should have combined it with the breaker to get free 2 day shipping

https://www.automationdirect.com/adc...8_AWG_Shielded

[rcheli]

I put a new rectifier in the power supply and installed the breakers on the input, fuses on the outputs and the SSRs. What a difference. Previously there was the clicking of the relay and the clunking of the steppers locking up when the power came on. Now, just silence. I had to look at the lights on t he SSRs and feel that the stepper was locked to know the power was on.

It may be overkill but I also put heatsinks on the DIN rail mount I made for the SSRs.

Attachment 400136

Attachment 400138

John

[Jim Dawson]

Nice Job ! :cheers: