Jamie wrote:> > THe scheme does work because we do it.. It has increased the life > contacts driving heavy loads greatly. >Sure, for heavier loads this makes sense. But, this is probably a 100 mA or less solenoid, but massively inductive. A small SSR can handle this load and produce minimal heating. I'm also trying to do this with minimal hacking of the PCB, and I don't have space to add extra relays. Jon
arc suppressor for relays
Started by ●October 3, 2012
Reply by ●October 4, 20122012-10-04
Reply by ●October 4, 20122012-10-04
On 2012-10-04, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:> You didn't absorb the post.. The diode prevents the other side from > back draining. SSR have very little current at the control terminals, > they are so low infact, that we have to put burden resistors on them in > many cases to prevent cross talk from other control lines in the race > way from triggering them on. > > THe scheme does work because we do it.. It has increased the life > contacts driving heavy loads greatly. > > We use lots of 24 volt logic and in area's where we have a potential > of this happening, we place a small SSR across the contacts with a diode > and cap on the control brick, sometimes we need to have a drain R there > because it stays on too long. Which you do not want to happen, i'll burn > out the SSR if it can't handle the full load for prolong periods. > > btw, they make softstart contactors with this topology in them. > > Jamiedo you do this with inductive loads? -- ⚂⚃ 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply by ●October 4, 20122012-10-04
"Jon Elson"> Phil Allison wrote: > >> >> "Jon Elson" >> >>> We have one of those $1K high efficiency washing machines. It does work, >>> and >>> clearly reduced our water and gas bill, so I'm not complaining. >>> >>> Lately, it has been getting "slow fill" errors, and I tried a bunch >>> of typical stuff before finding the REAL problem. They have a bank >>> of electromechanical relays to operate a bank of solenoid water valves. >>> There is no arc suppression on these relays, and the cold water valve >>> relay is totally shot. I have replacement relays on order, but want to >>> add arc suppression to prolong the life of the relays. >>> >>> The coils are 120 V AC, the relays are TINY things. I ordered some >>> Zener-type transient suppressors which indicate a 193 V trip voltage, >>> bipolar. >> >> >> ** The relays are arcing because of the back emf from the solenoid coils >> at the instant of opening. >> >> The time honoured fix is a "snubber " across the relay contacts. >> >> 100nF ( class X2) and 100 ohms in series is a good start. > > The problem here is I have practically no space to put a classic > snubber.** That is the ** LAMEST ** excuse I ever heard of !!! YOU have a whole FUCKING washing machine available !!!! The leads do not have to be very short - use your brain fool. .... Phil
Reply by ●October 4, 20122012-10-04
Phil Allison wrote:> Jon Elson wrote: > The problem here is I have practically no space to put a classic > snubber.> > ** That is the ** LAMEST ** excuse I ever heard of !!! > > YOU have a whole FUCKING washing machine available !!!! > > The leads do not have to be very short - use your brain fool.Thanks, as usual, flying off the handle. There is a HELL of a lot of wire in there already, some low-level for sensors, some 400 V for VFDs to the motors. I don't want to cause an EMC problem while fixing this. There are 12 relays on two boards all packed in a nice plastic ventilated housing with a dozen connectors to the rest of the machine. There are a few reasons it would be very good to keep all the mods inside this housing. All the electronics, valves, etc. fit in a little "console" above and behind the top-loading lid to the washer basket. This console also has the operators panel, with a big encoder knob, buttons, and dozens of LEDs. There really is NOT a lot of room left in there to add additional parts. I did add one Opto-22 style SSR with R/C snubber to replace the failed relay, as it was getting worse each washer load, and either sizzling, not making contact or working correctly at about even chances. This works, but isn't really a permanent solution. I found a Sharp SSR that looks like it might be able fit the existing space, but it will be tight. So, I might be able to fit SSRs and snubbers in fairly cleanly. Or, I might just use the electromechanical relays with TVS devices and be done with it for the next 15 years. Without the snubber, the relays last about 4 years. I opened up the bad relay and was surprised at how little damage was visible. The contact plating was gone, exposing blitzed base metal and some dust all over, but it really wasn't as bad as I thought it would be. Jon
Reply by ●October 4, 20122012-10-04
On Wednesday, October 3, 2012 12:23:31 PM UTC-7, Jon Elson wrote:> We have one of those $1K high efficiency washing machines.> Lately, it has been getting "slow fill" errors.... They have a bank > of electromechanical relays to operate a bank of solenoid water valves. > There is no arc suppression on these relays, and the cold water valve > relay is totally shot.I'd try the manufacturer's replacement part first; it could just have been a weak spring or some stuck-half-on that caused arcing. If the relay ratings can be read, you might consider the gas-filled sealed relays (like, around here, used to be surplused from the aircraft manufactory...). They're very reliable, and it's hard to find one that isn't an improvement to the civilian washing machine parts I've autopsied. Pressurized gas suppresses arcs quite effectively.
Reply by ●October 4, 20122012-10-04
Jasen Betts wrote:> On 2012-10-04, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: > >> You didn't absorb the post.. The diode prevents the other side from >>back draining. SSR have very little current at the control terminals, >>they are so low infact, that we have to put burden resistors on them in >>many cases to prevent cross talk from other control lines in the race >>way from triggering them on. >> >> THe scheme does work because we do it.. It has increased the life >>contacts driving heavy loads greatly. >> >> We use lots of 24 volt logic and in area's where we have a potential >>of this happening, we place a small SSR across the contacts with a diode >>and cap on the control brick, sometimes we need to have a drain R there >>because it stays on too long. Which you do not want to happen, i'll burn >>out the SSR if it can't handle the full load for prolong periods. >> >> btw, they make softstart contactors with this topology in them. >> >>Jamie > > > do you do this with inductive loads? >Yes. At one time you used to be able to get add on soft start SSR's where you connect the relay coil to a terminal dedicated for it. This was to insure the SSR was on (zero crossing) before the coil itself got energized. The turn off did the opposite.. The control off voltage would turn off the relay coil and wait for the contacts to open before it was turned off. We used to burn up relays every 6 months on a pick of equipment due to the large inductive response the contacts were wire too. This got cycled a lot and a modification was done to stop the arcing. Due to the amp load that is there, the relay still needs to be replaced but it now last at least 5 years or so. Jamie
Reply by ●October 5, 20122012-10-05
whit3rd wrote:> I'd try the manufacturer's replacement part first; it could just have been > a weak spring or some stuck-half-on that caused arcing. > > If the relay ratings can be read, you might consider the gas-filled > sealed relays (like, around here, used to be surplused from the aircraft > manufactory...). They're very reliable, and it's hard to find one that > isn't an improvement to the civilian washing machine parts I've autopsied.Very unlikely to find a 12 V 16 mA coil aircraft relay that will also fit the spot available. I may have found a really small SSR that will fit, but require some fooling around with the leads to fit the board. Jon
Reply by ●October 5, 20122012-10-05
"Jon Elson"> Phil Allison wrote: >> Jon Elson wrote: >> The problem here is I have practically no space to put a classic >> snubber. > >> >> ** That is the ** LAMEST ** excuse I ever heard of !!! >> >> YOU have a whole FUCKING washing machine available !!!! >> >> The leads do not have to be very short - use your brain fool. > > Thanks, as usual, flying off the handle.** As usual, when confronted by a obvious nut case & damn LIAR.> There is a HELL of a lot > of wire in there already, some low-level for sensors, some > 400 V for VFDs to the motors. I don't want to cause an EMC > problem while fixing this.** That is an even LAMER excuse !! You re so full of BULLSHIT. PISS OFF !!!
Reply by ●October 6, 20122012-10-06
On Wed, 03 Oct 2012 16:05:28 -0400, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:>On Wed, 03 Oct 2012 14:32:02 -0500, Jon Elson <jmelson@wustl.edu> >wrote: > >>We have one of those $1K high efficiency washing machines. It does =work, and>>clearly reduced our water and gas bill, so I'm not complaining. >> >>Lately, it has been getting "slow fill" errors, and I tried a bunch >>of typical stuff before finding the REAL problem. They have a bank >>of electromechanical relays to operate a bank of solenoid water valves. >>There is no arc suppression on these relays, and the cold water valve >>relay is totally shot. I have replacement relays on order, but want to >>add arc suppression to prolong the life of the relays. >> >>The coils are 120 V AC, the relays are TINY things. I ordered some >>Zener-type transient suppressors which indicate a 193 V trip voltage, >>bipolar. >>I'm not clear about whether this is the level at which all units will >>start to conduct or the level at which none will conduct. > >You ordered parts without looking at the data sheets? Or do you need >help in interpreting the data?=20 > >Here's a typical TVS data sheet:=20 > >http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/=DATASHEET/CD00000720.pdf> > >Take, for example, the P6KE220CA.=20 > >No more than 500nA at 188V >At 1mA nominally 220V, but no less than 209V or more than 231V > >At 1.85A (surely beyond your required clamping current) no more than >328V. At 10.3A, no more than 388V.=20 > >It's a bipolar device, so the ratings apply for either polarity of >applied voltage.=20 >> >>Also, would it be better to put the suppressor across the relay =contacts>>or across the valve solenoid? =20 > >I'd put it across the solenoid coil.=20 > >You could also try one of these, which you may have parts for in your >junk box:=20 >http://www.digikey.ca/product-detail/en/104M06QC100/338-2581-ND/2503688 > >Those built-up ones are stupid expensive, you can just try a 630V >0.1uF film cap series with a 1/2W 100R resistor for < 1/10 the cost.=20 >Oh yeah. Proper snubbers work great.>>If the device fails to short when across the >>contacts, it will just turn the valve on all the time, causing a flood. >>If across the valve coil, it will blow something, hopefully not circuit >>traces off the board. >> >>So, I'm looking for practical suggestions on how to choose the =supressor>>type (Zener or MOV) style, trigger voltage and where to put it in the >>circuit. >> >>Thanks, >> >>Jon
Reply by ●October 6, 20122012-10-06
On Wednesday, October 3, 2012 3:23:31 PM UTC-4, Jon Elson wrote:> We have one of those $1K high efficiency washing machines. It does work, =and>=20 > clearly reduced our water and gas bill, so I'm not complaining. >=20 >=20 >=20 > Lately, it has been getting "slow fill" errors, and I tried a bunch >=20 > of typical stuff before finding the REAL problem. They have a bank >=20 > of electromechanical relays to operate a bank of solenoid water valves. >=20 > There is no arc suppression on these relays, and the cold water valve >=20 > relay is totally shot. I have replacement relays on order, but want to >=20 > add arc suppression to prolong the life of the relays. >=20A "bank" of valves and relays? Usually there are just two, one for cold wat= er and one for hot water, not anything complex. You may actually reduce con= tact life with the addition of arc suppression. The relay contact materials= and operating characteristics such as contact pressure, overtravel, and re= lease geometry have been optimized for the weakly inductive solenoid valve = type of loading and any modification will most likely reduce contact life. = The solenoid loading should only be a few milliamps.
