Solving Motor Braking Circuit Problem in Bowling Industry

[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.

 

[Tom.G]

Here's one more easy attempt. Try connecting a MOV, Metal Oxide Varistor, across the motor Run winding. That would be between SM2 and SM3, or equivalently between SMP-CT and SMP-NIL.

Here is a link to one that seems adequately sized. Its wire leads are only 1 inch long though.
http://www.digikey.com/product-search/en?keywords=v20e130p

 

[jim hardy]

The NO contacts are still arcing.
Is there arcing both at NO and at NC?
If so, is there a difference between the arcs ? Intensity? I wanted to eliminate the old relays. As the contacts being the cause.
Might be one contact needs protection against overcurrent, the other against overvoltage
resistor is to limit current through NC contact
a Quencharc across the motor would try to protect the NO against overvoltage
and protect the NC against arcing during contact bounce interval,

It'd sure help to see it ourselves . Does your cellphone do short videos ?

.....................

I THINK, based on not really on anything solid,
overcurrent transient is what kills the SSR because that circuit board appears to have plenty of capacitors on it and i assume some of them are snubbers.
It'd help to know if a dead SSR shows short between 4-3, 4-7, or/and 6-5

you could risk sacrificing one on a machine that has resistor?

What you think, Tom ?

 

[Tom.G]

It'd help to know if a dead SSR shows short between 4-3, 4-7, or/and 6-5

you could risk sacrificing one on a machine that has resistor?

What you think, Tom ?

I think finding a shorted or an open Triac won't tell us what caused it. Overcurrent causes the active part to melt into an amorphous blob of Silicon with low resistance, if the current is high enough the bond wire from the blob to a package terminal becomes a fuse and opens. An overvoltage can turn the Triac on or trigger avalanche voltage breakdown and you get the same end result.

 

[H012]

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.

Here's one more easy attempt. Try connecting a MOV, Metal Oxide Varistor, across the motor Run winding. That would be between SM2 and SM3, or equivalently between SMP-CT and SMP-NIL.

Here is a link to one that seems adequately sized. Its wire leads are only 1 inch long though.
http://www.digikey.com/product-search/en?keywords=v20e130p

You guys are really trying hard. I know it's frustrating for you given the fact of my limitations. I looked up how to find the inductance of the motor. Forget that for the equations are way over my head! And yes Tom you are correct Both relays NC's fail but by nature of the fact that the sweep has 3 stops in one cycle of the machine vs 1 for the table is why I'm concentrated on the sweep. I will do the MOV simple enough. And many thanks to you guys! I forgot to add the that you are also correct that NO's on some do arc/flash why some contacts arc/flash.only adds to the confusion.

 

[H012]

It'd sure help to see it ourselves . Does your cellphone do short videos ?

.....................

I THINK, based on not really on anything solid,
overcurrent transient is what kills the SSR because that circuit board appears to have plenty of capacitors on it and i assume some of them are snubbers.
It'd help to know if a dead SSR shows short between 4-3, 4-7, or/and 6-5

you could risk sacrificing one on a machine that has resistor?

What you think, Tom ?

I will check one to see.

 

[H012]

You guys are really trying hard. I know it's frustrating for you given the fact of my limitations. I looked up how to find the inductance of the motor. Forget that for the equations are way over my head! And yes Tom you are correct Both relays NC's fail but by nature of the fact that the sweep has 3 stops in one cycle of the machine vs 1 for the table is why I'm concentrated on the sweep. I will do the MOV simple enough. And many thanks to you guys! I forgot to add the that you are also correct that NO's on some do arc/flash why some contacts arc/flash.only adds to the confusion.

Just ordered MOV's. Local electronics store didn't have them.

 

[H012]

I will check one to see.

This is how many I have done since may still have 4 more to do.Next year in May I have change relays again on various chassis. This doesn't count the ones that go bad during the year. So

 

[jim hardy]

why some contacts arc/flash.only adds to the confusion.

arc is somewhat dependent on where in the line cycle the contact opens
if contact happens to open at the instant current is zero it's painless, if it happens to open at instant current is max you'll get a healthy arc

so it's random whether you'll see an arc on opening your NO's, and how big
probably random on closing your NC's too,
statistically a sinewave doesn't spend very much of its time near zero
so you'll get arcing more often than not.

Any help ?

old jim

 

[jim hardy]

This is how many I have done since may

so is this

a NO contact whose center bar moves toward camera to close
or NC contact whose center bar moves away from camera to open ?
Sure looks like melted silver showing...

 

[jim hardy]

found an article that helps understand the MOV datasheet (which i'd say is a pretty good one)

communities.leviton.com/servlet/JiveServlet/downloadBody/2374-102-1-3690/Tech%20Note%20METAL%20OXIDE%20article.pdf

Thanks Tom,G

 

[H012]

so is this

View attachment 104011

a NO contact whose center bar moves toward camera to close
or NC contact whose center bar moves away from camera to open ?
Sure looks like melted silver showing...

The ones you see on pic are NO. All 4 on top are NO. The NC are on the bottom. Very hard to see. I wish I could get a pic.It's not uncommon for me to take one of the enclosed relays apart and one of the NC's to be completely burnt off. Not just the contact surface but the whole base the contact is attached to.

found an article that helps understand the MOV datasheet (which i'd say is a pretty good one)

communities.leviton.com/servlet/JiveServlet/downloadBody/2374-102-1-3690/Tech%20Note%20METAL%20OXIDE%20article.pdf

Thanks Tom,G

Thanks Tom/ Jim I'm getting a lot of good info. I liked how you described line cycle. Me with my lack of in-depth knowledge that it could effect contacts that much. Although I do understand what line cycle I made this drawing maybe it will help to understand the sweep schematic.

 

[jim hardy]

I made this drawing maybe it will help to understand the sweep schematic.

thanks, helps me for it seems to agree with the schematic and that's what I've been working in my head.. It quiets those nagging doubts when two drawings agree.

 

[H012]

thanks, helps me for it seems to agree with the schematic and that's what I've been working in my head.. It quiets those nagging doubts when two drawings agree.

Jim on that drawing. The wire on 44 of relay
That I got noted as going to power the primary on T 1 transformer this draws 8 amps. Is this added load a problem for the contacts considering the load already on the relay.

 

[Tom.G]

Since Jim seems incommunicado at the moment, I'll give it a shot.

Jim on that drawing. The wire on 44 of relay
That I got noted as going to power the primary on T 1 transformer this draws 8 amps. Is this added load a problem for the contacts considering the load already on the relay.

According to your drawing, no, the 8Amp load of T1 does not go thru the relay at all. That current will come from C1-41 HOT to the screw terminal 14, thru the wire that connects screw terminals 14 and 44, then to T1.

 

[H012]

Since Jim seems incommunicado at the moment, I'll give it a shot.

According to your drawing, no, the 8Amp load of T1 does not go thru the relay at all. That current will come from C1-41 HOT to the screw terminal 14, thru the wire that connects screw terminals 14 and 44, then to T1.

OK thanks. Just looking at any possibilities.
I should paid more attention. Kind of goes with common sense. Hopefully MOV's will be here Monday

 

[jim hardy]

The wire on 44 of relay
That I got noted as going to power the primary on T 1 transformer this draws 8 amps. Is this added load a problem for the contacts considering the load already on the relay.

doesn't look like it to me

it just uses the relay for a hopping point, doesn't go through the contacts

what does it power ?

edit i see we crossed in the mail
and we agree !

 

[Tom.G]

I should have pointed out that the MOV I suggested (V20E130P) is for testing purposes. It was chosen for 'just enough' repetitive power capacity and a low price to see if it works. If it solves the problem you should really use the next size up in power handling. The bigger ones are chassis mount, cost around $10 each, and should last for the life of the mechanical stuff. Well worth it if they are indeed a fix.

 

[Tom.G]

Hopefully MOV's will be here Monday

And we continue with Whack-A-Mole on Tue?

 

[jim hardy]

Could one parallel MOV's ? How abrupt is their turn-on ?
Bad practice for Zeners i know, but on these I'm still a tenderfoot.

 

[Tom.G]

Could one parallel MOV's ? How abrupt is their turn-on ?

No, can't parallel 'em. Due to tolerances, one ends up doing most of the work, and fails. (They fail shorted. Then either melt their connections or burn, as in fire.) Don't know their turn-on time off hand but it is fast, will investigate, they are spec'd to clamp ESD impulses of 8us risetime.

 

[jim hardy]

No, can't parallel 'em. Due to tolerances, one ends up doing most of the work, and fails.

gotcha. Same as paralleling zeners or fuses, "Just say No" .

 

[H012]

No, can't parallel 'em. Due to tolerances, one ends up doing most of the work, and fails. (They fail shorted. Then either melt their connections or burn, as in fire.) Don't know their turn-on time off hand but it is fast, will investigate, they are spec'd to clamp ESD impulses of 8us risetime.

Here is properties of MOV see pic.

 

[Tom.G]

How abrupt is their turn-on ?

Under 1nS.

For Engineering and selection details see:
http://www.littelfuse.com/~/media/e...s_terminology_and_theory_application_note.pdf

http://www.littelfuse.com/~/media/e...ng_a_littelfuse_varistor_application_note.pdf

 

[H012]

Under 1nS.

For Engineering and selection details see:
http://www.littelfuse.com/~/media/e...s_terminology_and_theory_application_note.pdf

http://www.littelfuse.com/~/media/e...ng_a_littelfuse_varistor_application_note.pdf

The ones I ordered will work?

 

[jim hardy]

The ones I ordered will work?

I think they will based on what little we know about the motor.

Test will be to feel of it after a few sweep cycles
if it's staying nice and cool i think it'll be fine

if it gets hot we need a bigger one

TomG and i are studying those curves in datasheet
depending on what assumptions we make predicted life comes out between a few hundred cycles and forever.

When it's that close, one test is worth a thousand opinions !old jim