The infamous AEG power switch on MiniMax bandsaws (and other machines?)
and how to replace it
History
The story I had understood was that in the past Centauro and MiniMax used a switch from Moeller to control their bandsaws (and perhaps other machines). There was love and peace in the world until Moeller started having all or parts of their switches manufactured in China. Quality plummeted, and reliability problems skyrocketed. The replacement was a switch from AEG. That was the switch on my MM24 bandsaw, and it kept me happy for many years. Until recently when I had to learn more about these switches than I wanted to.
I recently heard that I had history backwards... the once reliable switch was AEG brand, but AEG went bad and the new preferred switch is from Moeller/Eaton. With the exception of the brief section below about Moeller, this web page covers the AEG switch in painful detail.
Moeller/Eaton Switch
This note is courtesy of Erik Loza, formerly of MiniMax.
One thing I have seen with Moeller switches, particularly in machines which see intermittent or seasonal use, is freezing of the starting armature or coil. I do know that on the new Moeller switches I have inspected seem to use some type of lacquer or heavy varnish to (I assume...) protect the switch from moisture. I suspect what happens in a shop environment is that the combination of heating and cooling cycles plus a little sawdust thrown in there creates condensation and gums up that switch in time.
Of course, the switch could be checked with a multimeter but what folks have done in the past as a first troubleshooting step or as preventative maintenance if their machine is going to sit for long periods is to remove the switch from the housing and then lube that armature with some WD40 or electrical contact cleaner. Remember: I am not a certified electrician and you do this at your own risk. (a note from Charlie: Don't use WD40; the solvents can hurt the insulaton.)
Moeller switches can, of course, be obtained from SCM Group (MiniMax) parts at (866)216-2166, or consider the independent dealer, ControlParts.com 717-209-7100, or Google for other lower cost vendors.
In the AEG switch, the "solenoid" that controls the shut down if a door is open, etc., is distinctly an optional part in the AEG switch. In the Moeller/Eaton switch, someone reported that it attaches to the side of the switch (I haven't seen one yet). If that portion of the switch fails, there is no electrical harm if you run without it, but a previous owner may have removed it, leaving no evidence. The part number for the Moeller "solenoid" is U-PKZ0. At least one of the switch models used is Eaton PKZM01-25. The Eaton PKZM01 series has been replaced by the Eaton KPZM0 series of switches, so there might be a slight variation of part numbers on a replacement.
Why Bother?
Why don't we just go to Home Depot or Amazon and buy a two pole toggle switch able to handle the 22-23 amps our 4.8hp motors draw? The price is about $5-$10 or so. Why do we need a $50-$100 switch?
To answer that question, we need geek talk. Somewhat simplified below, but reviewed by at least one electrician working with switching motor power.
A motor is an inductor - an electric coil that creates a magnetic field. When you apply a voltage (turn it on) the current doesn't flow immediately - it lags the voltage (pressure) because the magnetic field has to build up. But when you turn it off, the magnetic field makes the current want to continue until the magnetic field dies down. The mag field builds and collapses 120 times per second in one direction (half of the 60 cycles), and the other direction 120 times per second.
What that means is, if you turn it off while the current is flowing max amount, it will want to keep flowing, and without a place to go (since you just opened the switch) it will create an arc in the switch. In small motors, no big deal - any arc is tiny and probably not enough to weld things. In big motors, worst case, the arc can weld the switch contacts closed... you won't be able to turn it off without unplugging it. Unless, of course, you have some solvent in the shop, then the arc could cause a fire.
The specialized motor switches (rather than the cheap ones from Home Depot) have provision to suppress the arc - to turn off the motor at the right instant and to handle any current that wants to continue when the switch has been off for 1/120 second.
On a small motor, like a drill or vacuum cleaner, the simple switches work fine, but on a 5 hp motor, enough current is involved that things may not be so fine. It may work for the first 100 times before failing. And don't even consider it on a 10 hp motor.
Cover/Stop button
You may have a cover over the switch with a big "mushroom" stop button that you have to twist to reset before you start the machine again. That is required for European safety regulations. It is not required in the United States. You can use that cover if you wish, or remove it and leave it in the collection of MiniMax parts that you never use. Years ago a MiniMax service manager assured me that, in this country, I would not be struck dead if I left it off. I have never used mine. You have to remove this extra stop button before you can even see the switch underneath.
Connections to the AEG switch
Please read this section very carefully. After corresponding with several people who were having trouble, they wrote back, apologetically saying that they reread it more carefully, and it solved their problem.
This is the infamous AEG switch number Mbs 25. But look at the fine print at the bottom of the front plate... it is for 20 to 25 amps but the specs go on and on and on. There are many variants of this switch and far more specifications for each. For example, with a 1 phase motor, it can control up to 2 hp at 115 volts, but up to 7.5 hp at 460 volts. As a 3 phase switch it can control up to 7.5 hp at 230 volts, and other specs for higher voltages. We will face the 1 vs. 3 phase question later, but for now note that the FULL part number for this AEG switch is Mbs25-O (letter Oh) or you can use the suffix Mbs25 910-201-212 for a 20-25 amp switch.
If you have an older machine with a smaller motor, the numeric number may be 910-201-211 (16-20 amps, MBS25-N) or 910-201-210 (10-16 amps, MBS25-M)
The switch posing for this photo is obviously my new switch, not the used switch from my machine, since the white adjustment to the left of the stop button should be set to about 22-23 amps for the usual 4.8 hp motor used by MiniMax, not the 25 amps shown here.
Apology to those who previously used this web page. I had the definition of the T and L terminals reversed (I remembered L as Load rather than Line from my EE course in the early 1960s). If you just put in a new switch and wired it as before, you are in good shape. If you followed my instructions precisely, it would have been more difficult to install since the old wires would be going to the wrong place, and you will have wired the switch backwards. It will work, but it will not last as long... the protection to suppress the arcs (see the geek part above, under "Why Bother") will not be right. The instructions below have been corrected. Thanks to Phil Soper of Inner-Tech, Inc. for discovering my error early 2020.
Note on the picture above, the terminals 2, 4, and 6 are labeled T1, T2, and T3. These are the switched Terminals where the motor is connected. Don't panic about three phase yet, if you have a single phase machine.
Note in this picture, at the right, the terminals 1, 3, and 5 are labeled L1, L2, and L3. This is where the three phase Line power is connected - brought into the machine.
If you have single phase power, here is where we can play a trick. The switch expects to have power going through three "internal magnets" and "heaters" to provide protection, but we can trick the three phase switch into working with single phase. Put one side of the 240 volt connection into L1 and connect the first side of the motor/load to T1. Think of it as the neutral if you wish (but don't touch it). This activates the first set of internal protection.
See the heavy wire from T2 to L3? We will put the other side of the single phase 240 volt power into L2. It will make one trip through the switch (a second activation of the protection) and come out of T2, but we will give it a third trip through the switch, out of T2 through that heavy wire into L3, and then we will connect the load, the second wire to the single phase motor, to T3. With this trick we can use the 3 phase switch which handles up to 7.5 hp, while the simple single phase connection only handles 2 hp.
If you are using a phase converter on your single phase power supply to operate a three phase machine
If it is a simple (cheap) phase converter, the three phase power is not equal on all three legs, so you must wire the switch for single phase power as above, and put the phase converter after this switch and before the machine motor. Without full current through each leg of the switch it will probably not work correctly.
If you have a sophisticated phase converter (e.g. Phase Perfect or most rotary converters) where equal power is provided on each "leg" you can skip the trick with the jumper from T2 to L3, and use this switch with the three phase power from the converter coming into L1, L2, and L3, and your three phase motor load connected to T1, T2, and T3
The cream colored plastic cover on the switch comes off with lots of wiggling and pulling but there are no fasteners or latches - just a very tight fit with alignment tabs. You may have to send young children and impressionable ladies from the room as you do it - the amount of wiggling and pulling is likely to invoke unpleasant language.
Once the cover slides off you can see the three magnets/heaters that provide protection for the three phases. This picture was taken of the switch outside of the machine, but you should be able to take the cover off while it is still in the machine.
On the other side of the switch is a black device with two wires (that don't seem to have a home - they thread out the side of the switch cover). This is the infamous solenoid that keeps the machine off (or turns it off) if the brake is pressed or any doors are open.
Tip the solenoid away and lift it out, and you have a switch that is wired in and ready, and can control your machine, but you don't have the protection of interlocks, and the foot brake will not stop the motor. If you are not sure if the problem is the switch or the solenoid, take the solenoid away from the switch and try running the machine. If it starts and stops normally with the buttons, you can use the machine without the solenoid, and without the safety protection it provides. Your saw will be no more dangerous than all the other bandsaws I have used.
Note the small copper/brass spring loaded lever coming out of the switch. If the solenoid holds this down, everything stops. If the solenoid releases this, the switch operates normally. Applying 240 volts to the solenoid makes it release.
if you find the solenoid is the bad part, and you want to run without the solenoid (permanently or temporarily), you have to disconnect and remove it. The plastic dust/safety cover will not go back on with the solenoid loose.
This is the back of the solenoid by itself. The number stamped on it, 400363, didn't give me any useful information, but I later found the part number was MBS25-100-C.
The two small black legs on the bottom are where it connects/aligns with the switch. The top of the solenoid is then tipped against the switch and held in place by the plastic cover.
This is the front of the solenoid - no useful part numbers (MBS25-100-C) but it does say it will "trip" if the 60 Hz voltage drops below 240 volts. I know it doesn't trip if the voltage is slightly below 240 volts, but it does trip if the voltage in interrupted by a safety interlock or foot brake. Thus the "undervoltage" device is actually used as the means to turn off the machine if one of the doors or brake pedal are used.
The switch itself mounts in an AEG mounting box (separately installed in the machine.) Along one side of the box is a bus (fancy word for a wire) between two screw connections, so that you can connect the green wire or yellow/green wire safety ground entering the machine to the safety ground system within the machine.
At the top you can see the alignment pin and clip, repeated at the bottom, that hold the actual switch in place.
The switch itself (with or without the solenoid) snaps into the mounting box, with an alignment pin and a plastic latch on the top and bottom.
You can see the heavy wire coming around from L3 to T2. The other wires are not yet connected in this picture.
The manufacturer indicates that the mounting box plus a front cover plate are part number Mbs25-S4F (see page 94 of their catalog) with a list price of $16. You certainly do not need to replace this part if you have a failed AEG switch, but probably will need it if you are moving from a different type switch.
Wiring in the Solenoid
The solenoid is a 240 volt single phase device; in a three phase system it can operate off any phase. The L1 and L2 suggested for single phase works for three phase as well. The whole trick here is to take the 240 volt supply (as it comes to the machine, before it is switched), from Terminals L1 and L2, and run it through all three safety/stop switches in series, and the solenoid, in any order. One end of this loop is connected to L1 and the other end is connected to L2. This provides 240 volts through all the switches - only a small amount of current will flow (to operate the magnet in the solenoid), but that flow can be interrupted by the foot brake or either door switch.
Each of the switches has a pair of wires coming into the column behind the switch. Since it doesn't matter the order the power goes to each switch, you do not have to identify which pair of wires goes to each safety switch. Yes, the full 240 volts goes to each switch in the machine, but the amount of current is just enough to operate the solenoid - it is not the power to run the motor. To summarize, the connections start with the one side of the 240 volt power coming in, and end with the other side of the 240 volt power (L1 and L2) and through the following, connected in series (A to B to C to D), in any order
The microswitch from the upper door
The microswitch from the lower door
The microswitch from the brake pedal
The solenoid
Some people are concerned about the power being on the solenoid when the shop is "closed" or not in use. A simple trick is to leave one of the doors cracked open, which removes power from the solenoid. If you remove tension from the blade when it is not in use (virtuous), I recommend opening one of the doors as a reminder to re-tension the blade before using the saw.
Sources
I am sure MiniMax parts department will be glad to sell you a new AEG switch complete with solenoid. Call 1-866-975-9663 or (866)216-2166. Discussion on the forums suggest it is worth checking elsewhere since this is a standard motor starter, not a part unique to MiniMax.
I found several sources on the internet for the switch itself - it is apparently often used to control the motors of large ventilation fans. Some vendors use the 20-25 amp rating rather than the latter part of the part number. Be careful, some vendors are apparently planning on ordering from the factory when you place an order with them, and will ship to you when it arrives, but you may need to wait until they meet the minimum order requirement from the factory. One vendor had an obvious typo in the part number (I think it was M6S rather than Mbs), but a very low price. Another vendor offered the same part (with the typo) but would not respond when I asked how quickly it would be available - they were apparently planning on ordering it from the first vendor. One friend found a deal where he could buy three switches for less than the usual price for one switch, and sold one to me.
The box my new switch came in has a GE label for a manual motor starter, Catalog number SFKOL Ref number 120012. UPC code 8 425095 200128. I could not find it on any GE parts site, and a Google search of the UPC led me to a fill hose for a Whirlpool appliance. Apparently it is sold in some other countries by GE.
The part number (MBS25-O) for the switch is just for the switch, without the solenoid. The intimate way the solenoid connects to the switch, it clearly has to be an AEG part, number MBS25-100-C.
EEControls
Through this process I thought AEG was the manufacturer. Wrong. AEG is a line of controls manufactured by EEControls in Brewster New York, 845-278-5777 or 800-963-4400. It is not an end-user friendly web site - the site says clearly that they sell to high volume manufacturers or through stocking dealers. You can see the AEG MBS catalog as pages 94-97 of their overall catalog (merely 4 pages of EEC's 240 page catalog). The switch MBS25-O is on the second page of that file (catalog page 95, $90), and the solenoid MBS25-100-C is on the third page of the file (catalog page 96, $48) from their web site.
Forum member David Lauffenburger kindly pointed me to EEControls, and apparently bought from them a couple years ago. The contact he recommended is no longer there. In the process of exploring EEControls, I somehow got tied to Wolf Automation, one of their dealers, below.
CalCentron
Forum member Rick McGill kindly pointed me to Cal Centron in Stockton California, 800-252-2094 or sales@calcentron.com.
This switch is in their AEG catalog as part number MBS25-O (letter oh) available for $90. The same switch is available today on eBay for $40.
Their AEG accessory catalog suggests that the 240 volt undervoltage trip solenoid is part number MBS25-100-C for $48
CalCentron terms and shipping are reasonable - minimum order $20, accepts major credit cards. Shipping is carrier charges plus $2.99 handling, except $3.99 handling for postal shipments. One or several switches should fit in a flat rate priority mail post office box for $5.95 (plus $3.99 handling for a total of $9.94)
Wolf Automation
As I was exploring EE Controls, recommended by forum member David Lauffenburger, I somehow linked to a major distributor for EE Controls, Marshall Wolf Automation in Algonquin, Illinois, 800-325-9653 or sales@wolfautomation.com
Wolf Automation has rebuilt their web site, so none of my previous links worked. However their previous info was attractive, so I would consider them as a vendor.
I called Wolf Automation and spoke to salesman Jim Frazzetto, since I could not find the solenoid. He referenced the EEControls spec page, and quoted a price of $39.80 each, with one week delivery.
Wolf Automation accepts major credit cards plus PayPal, and has a flat rate shipping for small orders like this, of $8.95,
IMS Distribution
Now that I found I should be searching for EEControls rather than AEG as the manufacturer, I found IMS Distribution (http://www.imsdist.com/) - search for Mbs25 910 201 212 ($90-) with the switch MBS25-O for $72 and the Solenoid MBS25-100-C for $48, and when I talked to a salesman I was quoted lower prices. I did not check on shipping and other terms.
Scibetta Distributors
Another search found Scibetta Distributors (www.scibettadist.com) in Baldwinsville NY, 315-622-3993, or sales@scibettadist.com
David Scibetta assured me that the current price for the MBS25-O from them is $69.00 each and the price for the MBS-100-C solenoid is $35 each. They accept credit cards through PayPal, and charge actual freight using either UPS or Priority Mail, your choice.
West Side Electrical and Industrial
Dan, one of the forum readers, bought the solenoid from West Side for $33.74 plus $15.53 shipping and handling - total just under $50 - he was looking for someone who had it in stock. He felt the shipping was a little steep, but they delivered as promised from Illinois in February 2015.
I need your help. I am a happy MiniMax user, but not a MiniMax employee, and have not used all the different equipment. I do not have special access to official information. If you have additions or corrections to this information on MiniMax products and usage, please share it. Please email your MiniMax info to me.
