Table Saw On/Off Switch Burnt Contacts

[xroad]

I repaired the power switch to my table saw. It was a mechanical toggle problem. While I had the switch opened up, I found the electrical contacts burnt. The switch still works. Power still turns on. What cause the burnt contacts?

 

[Kevin C]

Ryobi saw? All switches will arc and burn to some extent. Contact grease will help. On mine, since I didnt have any electrical contact grease, I used some Mobil 1 synthetic grease that I had handy. I put a dab on each contact.

Its been six months and its still working great.

 

[tcianci]

The contacts in any switch tend to arc upon opening and closing and even the best switch in the world has a limited service life. Good switch designs employ a "wiping" action of the contacts in order for them to function repeatedly with extremely low resistance. You mention that you had to do a mechanical repair on the switch and at that time you found the burnt contacts. It could be that the mechanical malfunction caused the snap action and positive contact pressure provided by the switch mechanism to be compromised causing excessive arcing and the resultant burnt contacts. Your best bet is to replace the switch with one rated for the application. If you continue to use the switch, the burnt contacts may cause an excessive voltage drop across the switch contacts which will ultimately cause the switch to overheat and fail.

 

[xroad]

Yes, Ryobi table saw. I ordered a switch through the Ryobi web site. Was happy to find it $11.65. Not too happy to find the shipping and handling $12.45! Almost $25 for a switch

I suppose I can bypass the OEM switch and wire in a $2 toggle switch from Radio Shack but the saw is still in great condition and I don't want to start kludging it up yet.

What concerns me is that I have not use the saw all that much. I have about 1 or 2 small projects each year. If the life span of the switch is so short, I am looking at a new $25 switch every 3 years. Maybe that kludge plan is not that bad ...

 

[Kevin C]

Mine would get stuck on. Seems like a safety issue , it also seems to happen to a lot of Ryobi table saws. I tried the grease after filing the contacts on mine a couple of times, seems to help a lot. Not sure what the factory lube was but it did not hold up.

Switch Lube:

http://www.nyelubricants.com/lubenotes/LubeNotes-Elec Switches-09-7.pdf

 

[xroad]

Yes, it is a safety issue. My switch as stuck ON and I had to rush to unplug the power cord. I don't recall if I register the warranty card when I first purchased the saw. If I did, and there was a recall on the switch, they would inform me, I hope.

I'll use the new replacement switch. If it still craps out, then I will kludge up a more robust switch.

 

[rlitman]

If it is a safety issue, you should report it to the CPSC. Enough people need to do that, before you'll see a recall.

 

[Kevin C]

Good call on letting the CPSC know.

My saw is a BTS15. I will file a report with the CPSC. I did find a number of similar reports with differant Ryobi saws.

http://www.saferproducts.gov/Search/Result.aspx?dm=0&q=ryobi+saw&srt=0

 

[Kevin C]

Just filed my CPSC report...

 

[ForceFed70]

Like already mentioned, contact arcing is common with applications such as this.

However, the problem can be worsened by excessive voltage drop. If you are using an extension cord, or a shared circuit, or something else that would result in excessive voltage drop the switch will fail sooner.

Had a contractor buddy of mine with this problem. His fancy tile saw was constantly burning up switches at $30 a pop because he was always using long extension cords.

 

[Kevin C]

However, the problem can be worsened by excessive voltage drop. If you are using an extension cord, or a shared circuit, or something else that would result in excessive voltage drop the switch will fail sooner.

Strange, I figured that contact welding would be reduced with extension cords, since when the switch is flipped the peak inrush current would be reduced. Peak inrush would/ should be controlled by the resistance of the circuit and the voltage. My mental model says that since the motor has not started to rotate, back EMF wont be a factor.

BTW All contacts arc when you make of break the power. That includes my stereo and my 3 hp 220 volt compressor. The compressor has lasted 20 years on its original power control switch.

I think this is a matter of how well designed the switch is for the application and about how it fails. Perhaps they stopped using cadmium in the contacts? I'm sure TTI used that same switch in a lot of other tools. I know of a couple of other people with Ryobi saws that had the exact same issue.

My guess is that my switch failed in less than 1000 cycles.

 

[nehog]

Ryobi saw? All switches will arc and burn to some extent. Contact grease will help. On mine, since I didnt have any electrical contact grease, I used some Mobil 1 synthetic grease that I had handy. I put a dab on each contact.

Its been six months and its still working great.

for the record: do not grease, oil or other substances to power contacts. It will cause premature failure as the substance will breakdown under the arc conditions found on make and break.

I suspect the Ryobi units may have under sized contacts from what you and others are saying.

 

[Kevin C]

for the record: do not grease, oil or other substances to power contacts. It will cause premature failure as the substance will breakdown under the arc conditions found on make and break.

May want to reconsider that statement, contact lubricants are a common method of improving service life of all types of switches.

From a manf of switch lubes:

Contact lubricants increase the reliability and lifetime of all current carrying metal interfaces Contact Lubricants Contact lubricants increase the reliability and lifetime of all current carrying metal interfaces. These include switches, connectors and busbars. .

http://www.echeloninc.com/contactlubrication.htm

Greases for sliding electric switch contacts must meet the same demands of any mechanical sliding: film strength, appropriate low and high temperature fluid range, and stay-in-place capability. In particular, a switch grease’s ability to prevent wear is critical.

Wear debris creates two problems. It can inhibit current flow when the contact is closed, increasing millivolt (mV) drop. When the contact is open, conductive wear debris can cause open circuit resistance (OCR) problems. In either case, switch performance is compromised.

When selecting a switch grease, also note that the viscosity of the base oil should
complement the contact force of the switch. Low current/low contact force applications require lighter base oils. High current/high contact force applications benefit from more viscous base oils.

Lubricants for arcing contacts. Because the temperatures reached in an electric arc are
sufficiently high to degrade any organic molecule, a lubricant’s tendency to “burn cleanly” is a definite advantage. Greases for arcing contacts should be formulated with fluids and thickeners that degrade with fewer by-products than traditional greases. A recent innovation is the addition of an additive that scavenges surface oxides to reduce contact resistance.

New non-burning switch lubricant technology. Greases that oxidize under arcing
conditions pose a special problem for low load/low current applications. Traditionally, cleaner burning glycols were used to minimize carbon build-up. A new approach to eliminating problems associated with oxidation is to use UniFlor™, non-burning perfluoropolyether-based greases. Dispersed in a non-flammable, ozone-safe, fluorinated solvent, these greases leave a thin film of lubricant, ideal for low load/low current
applications. An additional benefit, this thin film does not attract dust and debris.
Lubricants for distribution switchgear.

Lubricants for distribution switchgear, which may remain unactuated for long periods, serve a protective as well as a lubricating role. They should be oxidatively stable over time, water-resistant, and non-migrating. Because high temperatures may be induced by high current flow or high-temperature industrial conditions, wide temperature capability can be important.

http://www.nyelubricants.com/lubenotes/LubeNotes-Elec Switches-09-7.pdf

 

[rlitman]

for the record: do not grease, oil or other substances to power contacts. It will cause premature failure as the substance will breakdown under the arc conditions found on make and break.

Well, yes and no. Yes, you shouldn't just add any grease you have on hand to a switch. It may breakdown in an arc, and add carbon to the contact surface. BUT, a proper lubricant is something that most switches require.

Strange, I figured that contact welding would be reduced with extension cords, since when the switch is flipped the peak inrush current would be reduced.

Arcing happens when the switch is opened, not closed. Inrush current has nothing to do with it. The impedance of the circuit does, and the "RL" filter circuit formed by the motor and extension cord, will create a higher voltage spark when you have a higher resistance cord.

 

[Kevin C]

Well, yes and no. Yes, you shouldn't just add any grease you have on hand to a switch. It may breakdown in an arc, and add carbon to the contact surface. BUT, a proper lubricant is something that most switches require.

Good, you agree that some types of grease can be used. Again, the correct lube is preferred. That said, when I was only taking the switch apart and re burnishing the contacts they would re weld themselves pretty quickly.

I did that three times... Each time the switch lasted a few weeks. I was in the middle of a project and just wanted to get the saw up and running.

Ever since I put the "wrong" grease in the switch (Mobil 1) it has been working perfectly (about four months). Probably a coincidence.

Arcing happens when the switch is opened, not closed. Inrush current has nothing to do with it. The impedance of the circuit does, and the "RL" filter circuit formed by the motor and extension cord, will create a higher voltage spark when you have a higher resistance cord.

Great point (well kind of). But our switches are sticking closed. Google the term contact bounce. Might be something to that inrush current theory?

BTW I have had to deal with these issues when design test equipment. I included a link to an app note that addresses this problem.

http://www.maxim-ic.com/app-notes/index.mvp/id/764

The ideal switch operation depicted in most textbooks—a single transition that occurs instantly on actuation, followed by zero on-resistance—has never existed! Real switches exhibit a finite resistance called "contact resistance," that increases over time with the number of switch actuations. Contact resistance for a new switch ranges from less than 50mΩ to 100mΩ, depending on the contact material, power loading, environmental conditions, and switch usage.

As a switch changes state, its contacts travel through several open-close cycles called "contact bounce" before coming to rest in the final state. In some cases, this rapid contact bounce produces a changing resistance as the moving contact wipes across the stationary contact. In Figure 1, a pushbutton switch supplies 24V (a typical industrial-control voltage) to the resistor. Notice that at least four major switching transitions occur before the output comes to rest at 24V. To a digital control system, these transitions could be interpreted as four separate contact closures.

http://www.physicsforums.com/showthread.php?t=489034

Inductance from a lighter gauge cable is a problem? I would love to see some info to back that up. This is not a tiny speaker being driven on your home audio system by a set of Monster Cables. The inductance of the motor dwarfs that of the cord a factor of at least 1500 to 1. Worst case, the inductance across the switch would change by .008% if you went from a 12 gages to a 16 gage cord.

Perhaps the real problem is from having a coiled extension cords or running long cables out in the open when there is sunspot activity.


Regards,

Kevin

 

[Kevin C]

Update on this.... I filed a claim with the CPSC and an inspector came by and looked at the saw.

http://www.saferproducts.gov/ViewIncident/1242485

Report Link.

Today I got a call from the manufacture. I was told that yes the switch was defective and it was recalled in 2006. My bad, I should have registered my saw. They are sending me a new switch, free of charge.

This is the first I have heard of a recall and I never found one on the CPSC site or from Ryobi. Seems that calling is the only sure way to find out.

Short story: Call Ryobi and filing with the CPSC works!

 

[Ben Secor]

I had the same problem with my Ryobi BTS15 back in 2009. I fixed the switch twice myself, since then I have been using the extension cord as the switch. After reading your thread, I registered my product online and waited a couple of months. During that time, I received NO warnings about faulty switches related to my BTS15 table saw. I decided to call Ryobi and find out if I was due a replacement. The person who answered the phone knew of no such recall. I mentioned that this was a safety hazard, and I could be hurt. She said my complaint will be sent to safety dept, and someone will look over my complaint and call at a later date.
Three days later I received a new switch in the mail, no charge! I hope this helps someone with their situation. Potential liability cases are great motivators for free replacements.

 

[LS6 Tommy]

Ryobi saw? All switches will arc and burn to some extent. Contact grease will help. On mine, since I didnt have any electrical contact grease, I used some Mobil 1 synthetic grease that I had handy. I put a dab on each contact.

Its been six months and its still working great.

Good way to start a fire or give yourself a shock. Never use any lube that isn't dielectric or rated for switching purposes. It can cause a direct short to the nearest conductive material.


Tommy

 

[theoldwizard1]

Ryobi saw? All switches will arc and burn to some extent. Contact grease will help.

The contacts in any switch tend to arc upon opening and closing and even the best switch in the world has a limited service life. Good switch designs employ a "wiping" action of the contacts in order for them to function repeatedly with extremely low resistance.

The best grease for this application is silicon dielectric grease.

Because it is high voltage (120v) and high starting current (>5A) other types of grease will also work. Lower voltage and/or current, stick with the dielectric grease.