Solving Motor Braking Circuit Problem in Bowling Industry

[H012]

I am positive the reason the SSR fail so soon on these machine is the repetitive cycling of the machines when we are busy average is about 15 seconds and the lack of adequate heat sinking on the MOSFETs is the problem.

 

[H012]

If you zoom in on this photo from Post #7, you will note at the left contact that the substrate metal is discolored from overheating. That would indicate either low contact pressure (faulty relay), contanimints (oil or particulate matter) or significant overcurrent. For arcing to cause that, there would have to be sustained arcing or highly repetitive arcing.

Side comment:
Many years ago I was on a project for electric trains, not the toys, the big ones like subways and rapid transit. At one point we had a batch of relays that would quite literally explode on contact closure. Close them into an 1200A load and there was a fireball and shrapnel everywhere. These were typical open frame construction with a return spring to open the contacts upon removing coil power and the movable contacts spring loaded on the armature. I finally tracked down the difference between the 'good ' and 'bad' batches to the spring that mounted the movable contacts on the armature. The bad batch had a weaker spring, hence lower contact pressure. Of course the relay mfg. was "informed." After a few days the mfg. reported back to us that it was an inventory problem on their part. Somebody and put the the wrong springs in the parts bin for that assembly line. I always wondered how many pieces were in that batch!

I have on many occasions taken one of these enclosed relays apart to see the nature of the NO failure. The spring on any brand relay contact of the class that are used in these machines are very light. The contact just pivots on the one spring. Would definitely be better if there was a spring on each end of contact, but that's my opinion
I'm electrical engineer. I can understand more how contact bounce can occur. Or just not able to be firmly mated to the other contact.

 

[jim hardy]

guys some speculation here, followed by a question...

i've been obsessed by the thought the contacts are being eroded by current from the motor
and have tried to operate the braking sequence millisecond by millisecond in my head..
loooking for a relay race between the NO contacts opening and the NC contacts closing
it is necessary for the NO's in upper left to clear before the NC's below close , else we have a near dead short across the supply as shown in post #43

what if... entertain this thought experiment for a moment ... HO12 answered this long ago when he said

H012 said: ↑
The only fact I know is that the NC arcing occurs when they open, only because I can see it.

when what opens ? The NC's or the NO's ? We established by test that there's no current through the NC's when they open by measuring voltage at junction of the two capacitors if i understood. It drops to zero after motor starts and remains so until braking.

So if the arcing is observed at braking time when the NO's in upper left open, that's not surprising because they are interrupting motor current and it's an induction motor.

Anybody who's arc-welded knows an arc can persist surprisingly long

so in the thought experiment, think millisecond by millisecont from the instant the S relay plunger starts to travel to de-enegrgized position
1. NO contact opens a ten-thousandth of an inch establishing an arc
2. NO contact continues its travel, arc gets longer
3. NC contact makes initial contact , connecting motor to capacitors which are nearly a dead short
4. Current through NC contact consists of current from motor plus any leftovers from the arc - at this instant NC does not yet have full contact pressure so some melting might occur
5. NC that's NO contact continues widening its airgap, quenching the arc (sorry for the mistake )
6. NC contact establishes full contact pressure and commences to cool whatever metal was melted in 4.

Now here's the speculation
Which comes first ? 4 or 5 ? If NC makes before NO has extinguished its arc, we have a short across supply through a not quite extinguished arc and a not well seated NC contact that's still bouncing... see post #87

Is that scenario plausible?

so the relay race i was looking for isn't contact vs contact mechanical travel overlap but contact travel vs arc quenching time overlap.

How does energy deposition between two arcs in series divide?
Is this plausible, guys?
If so, a snubber across motor as in post #89 might help NC NO quench the arc before NC makes.('nother durn mistake )

That old saying, before you figure out what it is you'll figure out a lot of things it ain't.

I am positive the reason the SSR fail so soon on these machine is the repetitive cycling of the machines when we are busy average is about 15 seconds and the lack of adequate heat sinking on the MOSFETs is the problem.

If the SSR is SCR based and can't turn off the NO contact until a current zero crossing happens,
then there's an interval where it connects 1000 uf right across the line which could be a bodacious surge.

Looking for holes in that line of thinking
and any thoughts on how to test for it.

old jim

 

[jim hardy]

I'm electrical engineer. I can understand more how contact bounce can occur. Or just not able to be firmly mated to the other contact.

okay i apologize if i seemed to be talking down, that was not my intent
i think in simple steps and it's the only way i know to communicatedo you guys have an oscilloscope?

If you get a chance , see how much current we get on coastdown (volts at resistor or capacitor centertap?)

and a sanity check on my previous post ? we crossed in the mail.

old jim

 

[H012]

guys some speculation here, followed by a question...

i've been obsessed by the thought the contacts are being eroded by current from the motor
and have tried to operate the braking sequence millisecond by millisecond in my head..
loooking for a relay race between the NO contacts opening and the NC contacts closing
it is necessary for the NO's in upper left to clear before the NC's below close , else we have a near dead short across the supply as shown in post #43

what if... entertain this thought experiment for a moment ... HO12 answered this long ago when he said
when what opens ? The NC's or the NO's ? We established by test that there's no current through the NC's when they open by measuring voltage at junction of the two capacitors if i understood. It drops to zero after motor starts and remains so until braking.

So if the arcing is observed at braking time when the NO's in upper left open, that's not surprising because they are interrupting motor current and it's an induction motor.

Anybody who's arc-welded knows an arc can persist surprisingly long

so in the thought experiment, think millisecond by millisecont from the instant the S relay plunger starts to travel to de-enegrgized position
1. NO contact opens a ten-thousandth of an inch establishing an arc
2. NO contact continues its travel, arc gets longer
3. NC contact makes initial contact , connecting motor to capacitors which are nearly a dead short
4. Current through NC contact consists of current from motor plus any leftovers from the arc - at this instant NC does not yet have full contact pressure so some melting might occur
5. NC contact continues widening its airgap, quenching the arc
6. NC contact establishes full contact pressure and commences to cool whatever metal was melted in 4.

Now here's the speculation
Which comes first ? 4 or 5 ? If NC makes before NO has extinguished its arc, we have a short across supply through a not quite extinguished arc and a not well seated NC contact that's still bouncing... see post #87

Is that scenario plausible?

View attachment 103718

so the relay race i was looking for isn't contact vs contact mechanical travel overlap but contact travel vs arc quenching time overlap.

How does energy deposition between two arcs in series divide?
Is this plausible, guys?
If so, snubber across motor as in post #89 might help NC quench the arc.

That old saying, before you figure out what it is you'll figure out a lot of things it ain't.
If the SSR is SCR based and can't turn off the NO contact until a current zero crossing happens,
then there's an interval where it connects 1000 uf right across the line which could be a bodacious surge.

Looking for holes in that line of thinking
and any thoughts on how to test for it.

old jim

Here is a pic. of a SS relay (bad)

 

[jim hardy]

oops step 5 above should say "NO contact continues widening.." instead of NC.. believe me it's frustrating to be so awkward...
will fix now
then look at ss relay picture thanks !

 

[H012]

oops step 5 above should say "NO contact continues widening.." instead of NC.. believe me it's frustrating to be so awkward...
will fix now
then look at ss relay picture thanks !

Jim I found this doesn't match schematic.Iook at pic. I tried to upload pic site won't let me Do you have Gmail?

 

[H012]

Jim I found this doesn't match schematic.Iook at pic. I tried to upload pic site won't let me Do you have Gmail?

I got it to upload. Jim the black and blue wire are both coming from same hot at all times terminal strip in wire duct? Am I dumb!

 

[jim hardy]

I am positive the reason the SSR fail so soon on these machine is the repetitive cycling of the machines when we are busy average is about 15 seconds and the lack of adequate heat sinking on the MOSFETs is the problem.

still trying to figure out that SSR

Mosfets. Hmmm

the little white MOC3012's are optocouplers ,
http://www.ti.com/lit/ds/symlink/moc3009.pdf
probably they make gate drive for whatever are those big power semiconductors ?
Do those have a part number ?

I'm a little behind you HO12...

Do you have Gmail?

check your "Inbox" button at top...

 

[H012]

still trying to figure out that SSR
View attachment 103732

Mosfets. Hmmm
View attachment 103726

the little white MOC3012's are optocouplers ,
http://www.ti.com/lit/ds/symlink/moc3009.pdf
probably they make gate drive for whatever are those big power semiconductors ?
Do those have a part number ?

I'm a little behind you HO12...

check your "Inbox" button at top...

I will look at PN# at home can't see it without magnification. Thanks

 

[jim hardy]

gotcha. Can you tell any difference in arcing ?

I got it to upload. Jim the black and blue wire are both coming from same hot at all times terminal strip in wire duct? Am I dumb!

not at all, just learning the details of your machine.
Machieavelli says a good prince knows not just every hill of his princedom , he knows every rock and every shrub on every hill of it. See my avatar...

 

[H012]

gotcha.Can you tell any difference in arcing ?

not at all, just learning the details of your machine.
Machieavelli says a good prince knows not just every hill of his princedom , he knows every rock and every shrub on every hill of it. See my avatar...

View attachment 103736

View attachment 103739

I don't think so because wouldn't run anyway. I went just for the heck of it and took out the black wire. As I thought runs and breaks fine. I did this on a different machine. Not the one with the resistor as someone is bowling on it. The arcing is still there but it's not blueish white it's white. I have a chassis I'm finishing up with new relays. Going to put resistor on that machine
I put the new relays in.

 

[jim hardy]

Is your dead SSR shorted
3 to 4
4 to 7
5 to 6

all or none of the above?

 

[H012]

Is your dead SSR shorted
3 to 4
4 to 7
5 to 6

all or none of the above?

Jim I don't check them. Same as always sweep doesn't work when bowler bowls. The sweep really is tough on relays. Thing is it's not heavy. Just has to run 3 times for every one time of the table.like tonight these machines have been running more or less since 9 am

 

[Tom.G]

ref Post #132

I don't think so because wouldn't run anyway. I went just for the heck of it and took out the black wire. As I thought runs and breaks fine.[/color] I did this on a different machine. Not the one with the resistor as someone is bowling on it. The arcing is still there but it's not blueish white it's white. I have a chassis I'm finishing up with new relays. Going to put resistor on that machine
I put the new relays in.

I lost track of something here. If the removed Black wire refers to the sketch showing Black and Blue duplicate feed to the S and T relays, that shouldn't make any difference if the schematic matches the real world.[/color]

HEY GUYS, THAT REDUCED THE ARC TEMPERATURE BY 1000 TO 2000 DEGREES C. On the right track!

ref post #129
@jim hardy

Mosfets. Hmmm

TRIACs.

 

[H012]

ref Post #132I lost track of something here. If the removed Black wire refers to the sketch showing Black and Blue duplicate feed to the S and T relays, that shouldn't make any difference if the schematic matches the real world.

HEY GUYS, THAT REDUCED THE ARC TEMPERATURE BY 1000 TO 2000 DEGREES C. On the right track!

ref post #129
@jim hardy

TRIACs.

Exactly my thoughts. That's why I took it out.
Because it didn't match. When I leave here I want whomever not to have guess. To what it's supposed to be.

 

[Tom.G]

Exactly my thoughts. That's why I took it out.
Because it didn't match.

At least we agree that as a wire just in parallel with another wire, it shouldn't make any difference. Sounds like it wasn't just in parallel. Tracking down where things are really connected may find other anomalies or the root cause of the relay arcing problem.

Unfortunately in the real world, we sometimes have to go with what works and move on.

 

[H012]

At least we agree that as a wire just in parallel with another wire, it shouldn't make any difference. Sounds like it wasn't just in parallel. Tracking down where things are really connected may find other anomalies or the root cause of the relay arcing problem.

Unfortunately in the real world, we sometimes have to go with what works and move on.

Common sense I say. Good way to put it. Can't go around trying to understand why people do what they do. Thanks Tom!

 

[jim hardy]

Im still not clear, pardon me but I'm always a day behind in any conversation

Did the arc get less intense? White and small vs blue and big? Resistor ought to do that.

I never did get it real clear whether you can see arc on NC's or NO's or both...

If you have that motor run capacitor, tack it across motor main winding and see if arc changes. Dont leave it there without some resistance in series,

but if it makes arc smaller take a look at this product

http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

http://www.cde.com/resources/catalogs/Q-QRL.pdf

getting behind again

great working with all you guys
and i hope @Svein is still here - he told us so !

I like to understand a machine before i tinker with its design , that's all...

 

[H012]

Im still not clear, pardon me but I'm always a day behind in any conversation

Did the arc get less intense? White and small vs blue and big? Resistor ought to do that.

I never did get it real clear whether you can see arc on NC's or NO's or both...

If you have that motor run capacitor, tack it across motor main winding and see if arc changes. Dont leave it there without some resistance in series,

but if it makes arc smaller take a look at this product

http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

http://www.cde.com/resources/catalogs/Q-QRL.pdf
View attachment 103743

getting behind again

great working with all you guys
and i hope @Svein is still here - he told us so !

I like to understand a machine before i tinker with its design , that's all...

 

[H012]

As I stated the arcing at NC was a blueish white now it,s just white as far as intense
I can't really tell the arc happens so fast. There is a few relays that the NO do arc but these relays have some age one them. Jim I had looked into the QuechArc but the formulas are over my head. I,m still going to get the run cap and try it. Thanks I will let you know.

 

[jim hardy]

As I stated the arcing at NC was a blueish white now it,s just white as far as intense

Ahhh it's at the NC - Thanks !
Since we don't have a peak capture ammeter or o'scope your observed intensity is our measure. Those Quencharc equations do look scary
Had you needed instead to protect the NO contacts from arcing when they open, the approach i use is this simpler one
...objective is to give the load current a path into a capacitor ( instead of through the contacts) for those first few microseconds while the contacts separate those first few thousandths of an inch
that way the inductive kick charges the capacitor instead raising the voltage enough to strike an arc
just like points in a car ignition are protected by the condenser

the car ignition uses around 0.22 uf for coil current of maybe two amps, ~ 0.1 uf per amp

what rate of voltage rise does that give ?
i = c X ΔV/ΔT
2 = .22 X^10-6 X ΔV/ΔT

ΔV/ΔT = 2/.22 X^10-6 = around 9 volts per microsecond
.1uf per amp would be 10 volts per microsecond
and that seems to protect the contacts in automobile points, which cycle a few hundred times per second
your six amp motor by that criteria, 0.1uf per amp, would get about 0.6 uf

so i just picked a Quencharc with a little more capacitance than that
and lowest resistance they offer
because the voltage across that resistor appears across the contacts and 6 amps X 22 ohms is 132 volts at instant of contact opening,
a lot less than the full inductive kick would make.

Hope that helps in your next relay adventure ...

old jim

 

[H012]

Ahhh it's at the NC - Thanks !
Since we don't have a peak capture ammeter or o'scope your observed intensity is our measure.Those Quencharc equations do look scary
Had you needed instead to protect the NO contacts from arcing when they open, the approach i use is this simpler one
...objective is to give the load current a path into a capacitor ( instead of through the contacts) for those first few microseconds while the contacts separate those first few thousandths of an inch
that way the inductive kick charges the capacitor instead raising the voltage enough to strike an arc
just like points in a car ignition are protected by the condenser

the car ignition uses around 0.22 uf for coil current of maybe two amps, ~ 0.1 uf per amp

what rate of voltage rise does that give ?
i = c X ΔV/ΔT
2 = .22 X^10-6 X ΔV/ΔT

ΔV/ΔT = 2/.22 X^10-6 = around 9 volts per microsecond
.1uf per amp would be 10 volts per microsecond
and that seems to protect the contacts in automobile points, which cycle a few hundred times per second
your six amp motor by that criteria, 0.1uf per amp, would get about 0.6 uf

so i just picked a Quencharc with a little more capacitance than that
and lowest resistance they offer
because the voltage across that resistor appears across the contacts and 6 amps X 22 ohms is 132 volts at instant of contact opening,
a lot less than the full inductive kick would make.

Hope that helps in your next relay adventure ...

old jim

Thanks Jim

 

[Tom.G]

Just measured a car ignition coil primary. 0.5 Ohm, 4.9mH.

 

[jim hardy]

Just measured a car ignition coil primary. 0.5 Ohm, 4.9mH.

Old battery and points coil? Must use external "Ballast" resistor..
half the inductance of the motor you measured.

found an old Quencharc datasheet that includes the "how to" attachment i remember reading years ago
http://www.panconcorp.com/PDFs/capacitors/QRL-Quencharc.pdf

 

[Tom.G]

Old battery and points coil? Must use external "Ballast" resistor..

From a '97 Ford Crown Victoria (Taxi Cab/Police Interceptor). Computer driven, V8 engine, 2 coil assemblies, each having 2 center-tapped coils so that each coil connects to 2 spark plugs. That means the coil fires when the associated pistons are at TDC, once per engine revolution. No ballast resistors or caps visible or shown in the shop manual, but the Engine Control Computer is shown as a black box.

 

[jim hardy]

Probably CD ignition on one that new


Battery and coil is sized i as best i recall for 2 amps running, twice that during cranking by bypassing the ballast resistor with an aux contact on starter solenoid,
on the premise you need all the spark you can get
because engine is cold and battery voltage is probably sagging as starter huffs and puffs pushing that piston up to TDC on compression stroke, right when you need voltage most...

 

[Tom.G]

Entirely possible. Even likely.

 

[H012]

Old battery and points coil? Must use external "Ballast" resistor..
half the inductance of the motor you measured.

found an old Quencharc datasheet that includes the "how to" attachment i remember reading years ago
http://www.panconcorp.com/PDFs/capacitors/QRL-Quencharc.pdf

Thanks Tom. Well today before I saw this post I put a chassis in the lane Jim had me put the resistor in with 2 new Table and Sweep relays The NO contacts are still arcing. I wanted to eliminate the old relays. As the contacts being the cause.

 

[Tom.G]

Okaayy... We seem to be switching back and forth on whether it's the NO or NC contacts that are arcing. I suspect they are both arcing under different conditions/faults on different machines, but so far it is very confusing. Getting this settled is important because appropriate fixes depend on the timing and specific conditions that the arcs occur. It would be extremely useful if you could post a video of a Sweep relay for a whole sweep cycle showing arcing. Ideally using one of the old style open frame relays so we can see the contact movements and where the arcing occurs, and infer where in the operating cycle it all happens.