New Power Supply

Repairing a Stepcraft HF Spindle 500W

Last updated on 21st September, 2020

Several months ago I working on my Stepcraft 840 using the HF Spindle 500W. I was cutting some plywood and got a little over confident. I took things a little too deep too fast and ended up stalling the motor. Luckily I was able to get to the kill switch very quickly so everything would be fine right….wrong!

Rookie mistake I know. Given that this is a €530 custom Stepcraft spindle, I expected there to be some protection in the control unit. So I shut everything down, unplugged everything, reconnected everything and started up the system. Nothing. Dead as a door-nail. To say I was a little annoyed was an understatement.

From this point on, things get dangerous! We are dealing with mains voltage, high capacity capacitors, high current, spinning motors and fire risk! Not to mention, you will void all warranty you might have. You’ve been warned…

First things first, check the fuse!

So there was only one thing for it: Repairing a Stepcraft HF Spindle 500W. I started by checking the fuse in the plug. That was my first surprise. The plug had a 13A fuse fitted. As we all know:

    \[ P=VI \]

Where P is Power (watts), V is Voltage (volts) and I is current (amps). Therefore, a 13A fuse is rated for 3kW. This is quite a bit more than my Stepcraft HF Spindle 500W can handle! So I replaced the 13A fuse for a 3A fuse.

Open up the control box

Next it is time to open the control box to see what is going on inside. This is easily done by removing the 4 Torx screws on the 2 sides of the housing. When removing the cover, watch out for the earth cable which is attached by a spade connector. Next came my second surprise.

Inside the control box we have a control board, a interface board, some connections and a cheap power supply!? I fully expected to find an integrated power supply rather than one of the standard off the shelf DC power supplies. It was labelled as a S-500-24 with an output of 24V 20A. Some simple maths tells me that this is rated at 480W. But this is for a Stepcraft HF Spindle 500W right? So that suggests that my power supply will go bang before I reach full power on my spindle?

Whats burning?!

What’s more, I couldn’t see any sign of circuit protection. No fuses, breakers or thermal cut outs. After a little poking around, I found a nice big burn mark on the positive terminal of the power supply. This gave me a strong suspicion that the power supply was dead. A quick check with a multi-meter confirmed my suspicions…the power supply had gone bang.

I wanted to check that the power supply hadn’t damaged any of the electronics when it blew. So I removed the suspect 24v power supply (3 screws on the base) and grabbed an old 19v laptop power supply. The laptop power supply had enough juice to be able to test the electronics and the spindle. Everything looked good and the spindle jumped into life.

Inside the power supply

Now the laptop power supply I had lying around is fine for testing, but it is not powerful enough for long term use. So I opened up the S-500-24 power supply to see if there was anything obvious wrong. The first thing to check is the glass fuse located in the bottom right corner. This was fine. I couldn’t see any other signs of damage on specific components and a quick check with a multi meter proved the same. So at this point I decided to replace the whole unit rather than trying to repair. These units are cheap (around £25) and easy to pick up on eBay or similar. If you do want to push on with a repair, Tom Sanladerer has a great video on repairing this type of DC power supply which is well worth a watch.

Putting it back together

Installing the new power supply was easy. This is because all of the screw holes line up on the new unit to secure it down to the frame. Remember to install the resistor and capacitor across the negative and earth terminals. The cables were also very easy to reinstall but play close attention: don’t mix up your 230v and 24v lines!

Now I wanted to make sure I don’t need to replace the power supply again so I wanted to put in some protection. The easiest way to do this is to install a fuse. I already had an automotive blade fuse holder and a wide selection of fuse sizes. As for which sized fuse, our 500W motor runs on 24volts, so a maximum of around 20.8A.

To air on the side of caution, I went with a 15A fuse. I’ll run this for a while and see how it holds out. The fuse needs to be installed in series on the positive side of the power supply. Check out the photos below.

Wrapping up

When my Stepcraft HF Spindle 500W went bang, to say I was annoyed would be an understatement. It was my own fault. I pushed the motor too hard. However, given the Stepcraft machines are aimed at hobbyists, I thought there would have been some protection designed into the system. Especially since they are charging over €500 for this unit!

The spindle itself is a pretty nice spindle. It has a ER11 collet system and integrates really easily with the Stepcraft machine. The unit can be controlled via software or manually via the control box. This is an air cooled motor and uses an air compressor to pump air directly over the bearings. Because of this, the spindle itself is relatively quiet but the compressor in the background is rather annoying. Especially since this is on all the time and not controlled by the software. JDMusicLabs has a nice little review video here.

“Would I buy a new one? No way.

Although the Stepcraft HF Spindle 500W it is a great little motor, you can get so much more for your money. For almost a tenth of the price you can buy a 500W ER11 air cooled spindle and controller from eBay. Even at Stepcraft, you can pick up a 1000W milling motor for €350. For the full €530, you can buy 2kW+ entry level industrial spindle. So although the HF spindle is great, I would be investing elsewhere.

I hope that this article helps someone out there. If it did, or you have any other questions, stick a comment below or get in touch via the contact page.

September 2020 Update!

Just wanted to share a quick update. The motor coupling on my X-Axis failed causing my spindle to bounce my workpiece. The result was that the tool jammed and stalled my motor. However, instead of burning out the power supply, the fuse blew! Perfect! Therefore I would highly recommend anyone using the HF Spindle 500W to install a 15A DC fuse as I explained above!

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