Shopsmith Forums

drmcroberts

From one EE to another; Didja ever hear of switch 'bounce' on make? If it occurs late enough after initial make with a large(>> steady state rating) motor START current, arcing can occur on 'make' with a larger energy arc than a 'normal' break.

I hope your second pole is more reliable/durable than the pole you WERE using.

BTW EVERYONE His efforts to minimize voltage drop from source to SS is laudable, but MAY have caused the switches early demise. The energy being provided by 'low loss' wiring etc COULD accelerate the failure caused by whatever arcing was occuring(IMHO).

ALSO When did SS start closing at 17:00 EST?????:(

P.S. When you get the 'new' switch and connect it up, wire the two poles in series. This would spread the fireworks around and if it tends to misbehave like the first one, you will have eliminated the need to re terminate when 1 pole sticks closed!!!:D

73's

drmcroberts wrote:Well, my problem is fixed and I'm a very happy SS camper!

Here's what I did. The power switch used in the newer models is still double-pole, single-throw (DPST) BUT, they only switch the hot-lead to the motor. That means you have an "extra" backup switch built-in to every newer model SS! So, all I did was reach in and move the two wires from one side of the switch to the other. I now have a "new" switch that should last me for who knows how long. I also have a replacement coming (some day) that I can then use two more times, if necessary.

It is good that you once again have an operational Mark V. Your observation, however, creates a question.

In times past, I believe the DPST switch was wired so as to switch both the hot and the return sides. Some time back (not all that long ago), Shopsmith began switching only the hot side.

I suppose I should blindly accept that this production change was based on sound technical advise but I can't help but wonder.

Why not switch both sides?

A question for jpg or anyone else with an explanation: You have made the recommendation to wire the DPST switch with the poles in series to reduce premature switch failure. In a series circuit does the same current level not flow through all components in that circuit. Why not wire the poles in parallel causing the currents through each switch to be halved thus reducing the propensity for arcing.

Arcing is most effectively reduced by what - reducing voltage drop across the contacts by 1/2 OR reducing the current flow through the contats by 1/2?????

Do we want to decrease damage to each pole, or avoid a rewiring? Which is best????????????? Only the PHANTOM knows.

If they tend to fail by becoming stuck on, series is better(both poles must fail on). If they tend to fail by failing to make, parallel is better(only one required to turn on).

Either way the arcing (over time) is distributed between both poles thus reducing the damage to each.

[quote="jpg40504"]drmcroberts

From one EE to another]

Hmmm, contact bounce. Yup, you are correct "if" there is some contact bounce late enough in the startup cycle. Without a complete analysis of the timing of that particular switch, there is no way to say whether contact bounce is actually occuring and whether it is late enough in the startup cycle to effect the surface of the contacts themselves. Connecting the two sets of contacts in series would mitigate a portion of the risk but without knowing what is actually happening it is only a stab in the dark. A parallel arrangement would also result in a similar potential reduction of risk.

Of course, in my case, where I have reduced the circuit losses by using heavier gauge wiring, perhaps I have introduced something the SS wasn't counting on in their designs. Oh my, this could go on forever.

Me thinks I'm getting too old for all of this risk analysis and theory so, I'm not going to worry about it and just hope that I've at least found a way around the current problem of not being able to shut down my SS.

Thanks for all of the inputs though - they were great!

drmcroberts wrote:
Of course, in my case, where I have reduced the circuit losses by using heavier gauge wiring, perhaps I have introduced something the SS wasn't counting on in their designs. Oh my, this could go on forever.

Indeed it could. I think WE have given it more thought/guessing/analysis than SS! Shall we move on...........

jpg40504 wrote:Indeed it could. I think WE have given it more thought/guessing/analysis than SS! Shall we move on...........

Agreed - let's move on to more interesting things!

I'm still going to call SS tomorrow morning to see what they have to say about the issue. I'll post here once I make that call

After an almost 20-minute wait on hold, I finally got through to a SS rep.
I inquired about my back-ordered power switch. It is supposed to be in Jan 25th and then will ship to me the following day. I also asked if the switch was a known problem and he said they do go out occassionally and need to be replaced. I asked him about why it was on back-order. His reply bothered me in that he said they no longer keep them in-stock and only order them when needed due to their desire to keep down costs. That really bothers me from the standpoint that this is an item that seems to be problematic on a regular basis and they are making the customer wait for them to get a replacement in stock.

He also asked if my Mark V was not usable so I told him I had moved the wiring to the unused set of connections on the switch. He said another way would be to use a power strip with a switch on it.

I also received an email from SS this morning saying they were sorry for the parts delay and offered me a 50% discount on their plans CD's. Too bad that wasn't for a planer - I would have jumped on that one in a split-second

Wonder how long the switch in the Power Strip would last?:D

beeg wrote:JUST in time inventory or so has been the life at SS for about 6 months or more. B.O's seem to be almost common for them. But it's a way to weather this economic environment. None of ua are happy about it, but live with it.

Well, that's not my definition of JIT inventory. They should have received the replacement switch the same day I placed my order

Yes, you are right, we have to live with it. Anyway, how many companies design a spare set of switch contacts in their switches? Now, that is pretty ingenious if you think about it!