Deltec KM500 Kalkwasser Stirrer Repair

[Origami]

This Deltec KM500 kalkwasser stirrer has seen over a decade of use. In recent years, the stirrer bar would sometimes stall or stop. A drop of light machine oil on the bearing that was visible on the back side of the motor often helped get it going again. If that didn't work, I could often turn up the variable power supply that it came with to get it started. However, after it stalled a while back, I stopped using it and replenished calcium and alkalinity solely with my calcium reactor.

 

Yesterday, I decided to look into the stirrer and get it going again. After reverse engineering the stepper motor circuit card and determining that it and the power supply were functioning correctly, I disassembled the stepper motor

 

 

removing the armature.

 

 

Notice that there are two bearings on either end of the armature. Over the years, I've often put a drop of light machine oil on the back end of the armature (shown below).

 

 

I found this bearing a little "sticky," so I applied couple of drops of light machine oil on the bearing (in the slot that forms the first circle around the center) and worked it smooth. Noticing a little rust-colored oil coming out, I worked a little oil in and wiped the excess off until I no longer had discolored oil surfacing.

 

I never thought about it, but there's a bearing on the shaft-side, too.This bearing was frozen - that is, it wasn't turning at all but felt stuck. This frozen bearing is why the stirrer was not working.

 

 

I put some oil on the bearing and let it soak in then worked the bearing for several minutes as it gradually freed up. 

 

With both bearings operating smoothly again. I put the armature back in the motor and closed everything back up.

 

The end result was a stirrer operating just like new.

 

By the way, in my reverse engineering, I managed to diagram the stepper motor driver circuit. Reach out to me should you need information about it. It uses two integrated circuits, one of which is an MC3479 stepper motor driver. The second, 8-pin chip was a bit of a mystery as it looked like the markings were either deliberately washed off or had faded. It's hard finding any information about this mystery chip on the KM500. Under the right lighting and on a dissecting stage, I managed to determine that it's an ICM7242 fixed timer/divider chip. It's set up to generate a 12.5 KHz reference signal that, divided down, generates a 50 Hz square wave to drive the clock input on the MC3479. The rest of the components on the board pretty much just set up and filter the supply voltage, and set the timing for the ICM7242.

[Bruleyii]

so beings you turned up the variable power supply, did it go warp speed after you freed up the barrings? Also, with the barrings you could always just switch them out with ceramic and be done with it.

[Origami]

so beings you turned up the variable power supply, did it go warp speed after you freed up the barrings? Also, with the barrings you could always just switch them out with ceramic and be done with it.

No. Speed does not vary much with the voltage (because the speed of the motor is regulated mostly by a time constant set by a resistor and a capacitor) but torque seemed to be affected. Ceramic bearings. Interesting idea. The bearings are press-fit, though. I'd need a small gear-puller and a light press to remove and replace. I'd also be afraid that I might damage the armature without the right equipment. 

[Bruleyii]

I see. yeah. Replacing them might be a pain.

[Rayman]

I found this post really useful as I am havimg similar issues. Unfortunately, mine doesn't seem to be a bearing problem. The armature just becomes difficult to turn after running for a few hours and I think my motor is trashed.

 

I am led to believe this is a Moons stepper motor type 16HY0405-08. They only seem to be sold in MOQ's of 10 for around 20 bucks each. I looked on their website but couldn't find a datasheet for it.

 

If anyome can point me in the right direction or has a circuit diagram I would be grateful.

[Origami]

Did you pull the motor apart to check the bearings? There are two. I got both to spin freely and the stirrer is still working. I wound up ordering spare bearings as a backup and found ideas for how to build a small DIY bearing puller for just this sort of job.

 

The idea that "the armature becomes difficult to turn after running for a few hours" is exactly what I was seeing when I initially did an incomplete repair job. That's why I ordered the backup bearings. Keep flushing the bearings with oil and you may get it cleaned out and working again.

 

I diagrammed the circuit but don't have it with me. I'll look for it this evening. I had a similar problem finding more detail on the motor. However, the drive chip tells you a little bit about how it works.

[Origami]

Found it. I found the base schematic at this link. However, I discovered that the pinout on the driver chip was backward, so I renumbered it on the schematic below.

 

 

I took a few notes while examining and probing the circuit. The notes are somewhat cryptic, but I'll include them in case they prove useful.

 

 

There are two IC's on the board. One's a 16-pin stepper motor driver, MC3479P. The other is an 8-pin timer chip, an ICM7242. A snapshot of the first page of each data sheet is shown below:

 

 

 

Finally, here are some pages/notes on the motor itself, including a decoder for the part number, 16HY0405-08:

 

 

 

 

 

 

Hope this helps. I have a larger pack of information at home that I can email to you (if you want). Most of the other pages relate to the forum thread where I found the schematic and the rest of the pages of the IC datasheets.

[Rayman]

Hi Tom

 

Thanks for all your help and input on this, it really has helped.  I found this particular motor available here http://spwindustrial.com/moons-stepping-motor-type-16hy0405-08-10-each/?setCurrencyId=1but with an MOQ of 10 it isn't worthwhile given the original motor is about 12 years in the running.

 

I have removed the armature and the bearings seem good but I have oiled them anyhow. The datasheets and your notes have been especially helpful as I hadn't been able to obtain one for the motor at all. I have also found a German reef store selling the motor's individually for around 50 Euro + postage but this is too expensive given a replacement stepper of similar characteristics will be around $15 or $20.

 

In the event I source a good replacement NEMA 16 type motor I will update the thread. Thanks for all your input, help and advice.

 

Duanne

[Origami]

Duanne, did you try checking the DC voltage going in? I recall initially turning mine up to 7.5 volts or so and overcoming the resistance from the corrosion in the bearings. Then, later on, when I tried to turn the voltage up even higher (9 volts, maybe?), the motor would not turn very efficiently at all. There does seem to be a sweet spot where it operates best and, if your DC converter has begun to fail, it could be that. The circuit card itself has a fairly large operating voltage range. Also, it does have electrolytic capacitors which, over time, might dry out and begin to fail. That would be another area where you could try replacing a few cheap components and see if it makes a difference.

 

Finally, if you've got access to an oscilloscope, check the clock input on the driver chip. I think that it's also pin 3 out of the timer chip. It should be a 50 Hz square wave (or somewhat close to that). If it's out of spec, it may not be very effective turning the motor. Timing on that is probably controlled by a nearby resistor and capacitor.

[Rayman]

Following the bearing check my next step was to check voltage in and I initially suspected that based on my findings, this was possibly part of the problem. However I fooled around with different supply voltage and it made little or no difference. I will try your suggestion of the capacitors next. I don't have a 'scope but know someone who may be able to help me with this aspect.