arc suppressor for relays

"tm" <No_one_home@white-house.gov> wrote in message 
news:k4ii5p$5hf$1@dont-email.me...
>
> "Jon Elson" <jmelson@wustl.edu> wrote in message 
> news:a_OdnUzCt-COI_HNnZ2dnUVZ_rSdnZ2d@giganews.com...
>> tm wrote:
>>
>>
>>> Can you use a solid state relay? Maybe off the board?
>>
>> There are 8 of these.  If I can find a drop-in SSR that matches the
>> pinout, I sure will do this the next time it needs to be opened up.
>> Off the board won't work, there really is limited space in the "console"
>> that sits above the the washer top/rear.  If it was only one relay,
>> it would have already gotten hacked as you suggest.
>>> Another "designed by monkeys" consumer product.
>> Yeah, they must sell a LOT of these $275 controller boards.
>>
>> Jon
>
> I guess the relay switches 120 volts AC, right? What drives the relay? Is 
> it 5 volts, other?
>
> Is there an optoisolated triac arrangement available that could mount to 
> the solenoids and wire to the board directly?
>
> Can you observe the relay contacts to see if your snubber idea is 
> effective? You might try something like an X rated 0.068 uF and 10 ohms in 
> series across the contacts. You want to suppress the high voltage from the 
> solenoid coil. Almost any amount will help.
>
> What is the make of the washer? I would want to avoid it for sure.

Here is an AC opto coup[led triac that can switch 0.1 A/ 400 volts 
continuos. Google the datasheet from TI for some additional ideas to 
increase the current if needed.

http://www.ebay.com/itm/20PCSMOC3023-RANDOM-PHASE-OPTO-TRIAC-DRIVER-OUTPUT-6PIN-/260793421140?pt=LH_DefaultDomain_0&hash=item3cb87fcd54

tm

"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.


...  Phil

On Wed, 3 Oct 2012 20:22:13 -0400, the renowned "tm"
<No_one_home@white-house.gov> wrote:

>
>"tm" <No_one_home@white-house.gov> wrote in message 
>news:k4ii5p$5hf$1@dont-email.me...
>>
>> "Jon Elson" <jmelson@wustl.edu> wrote in message 
>> news:a_OdnUzCt-COI_HNnZ2dnUVZ_rSdnZ2d@giganews.com...
>>> tm wrote:
>>>
>>>
>>>> Can you use a solid state relay? Maybe off the board?
>>>
>>> There are 8 of these.  If I can find a drop-in SSR that matches the
>>> pinout, I sure will do this the next time it needs to be opened up.
>>> Off the board won't work, there really is limited space in the "console"
>>> that sits above the the washer top/rear.  If it was only one relay,
>>> it would have already gotten hacked as you suggest.
>>>> Another "designed by monkeys" consumer product.
>>> Yeah, they must sell a LOT of these $275 controller boards.
>>>
>>> Jon
>>
>> I guess the relay switches 120 volts AC, right? What drives the relay? Is 
>> it 5 volts, other?
>>
>> Is there an optoisolated triac arrangement available that could mount to 
>> the solenoids and wire to the board directly?
>>
>> Can you observe the relay contacts to see if your snubber idea is 
>> effective? You might try something like an X rated 0.068 uF and 10 ohms in 
>> series across the contacts. You want to suppress the high voltage from the 
>> solenoid coil. Almost any amount will help.
>>
>> What is the make of the washer? I would want to avoid it for sure.
>
>Here is an AC opto coup[led triac that can switch 0.1 A/ 400 volts 
>continuos. Google the datasheet from TI for some additional ideas to 
>increase the current if needed.
>
>http://www.ebay.com/itm/20PCSMOC3023-RANDOM-PHASE-OPTO-TRIAC-DRIVER-OUTPUT-6PIN-/260793421140?pt=LH_DefaultDomain_0&hash=item3cb87fcd54
>
>tm

Keep in mind that SSRs virtually always fail 'on' = flood. Mechanical
relays generally fail off (though I've seen them stick on very, very
rare occasion and a very badly made relay). 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

"tm" <No_one_home@white-house.gov> wrote in message 
news:k4ikis$h50$1@dont-email.me...
> Here is an AC opto coup[led triac that can switch 0.1 A/ 400 volts 
> continuos. Google the datasheet from TI for some additional ideas to 
> increase the current if needed.
>
> http://www.ebay.com/itm/20PCSMOC3023-RANDOM-PHASE-OPTO-TRIAC-DRIVER-OUTPUT-6PIN-/260793421140?pt=LH_DefaultDomain_0&hash=item3cb87fcd54

Not sure about MOC3023 specifically but as I recall the MOCs are made 
specifically for driving real TRIACs, and are rated for that service ONLY.

The heavily inductive load (if this is indeed the failure mode --  
remember, _it's EDMing right through entire blob-O'-metal contacts_) might 
not even allow the TRIAC to turn off, ever.  The solution in either case 
(thrysitor SSD or mechanical) is an arc suppressor or snubber, as 
mentioned elsewhere.

The reason MOS SSDs were suggested is because they turn off so slowly, 
absorbing switching energy and damping transients.  They have to be rated 
for enough peak thermal dissipation, which unfortunately isn't normally 
part of the datasheet.  One would suppose the manufacturer rates them 
appropriately for the load current, both continuous, turning on, and 
turning off.

RC snubbers may work better than TVSs or MOVs because the latter allow any 
voltage up to breakdown.  A spark will start on the (mechanical) contacts 
as soon as they open, growing in voltage roughly proportional to gap 
length.  If the arc voltage never hits TVS/MOV breakdown, it simply won't 
do anything.  MOVs may have some advantage because they have fairly high 
capacitance.

Now, a capacitor helps greatly because it limits turn-off slew rate; 
unfortunately, a cap across the contacts is a similarly bad idea at 
turn-on.  A series resistor yields an acceptable compromise between 
turn-off peak voltage and turn-on peak current.  For the solenoids in a 
washer I'd be very surprised if 0.1uF / 100 ohm didn't fix things 
completely.  (A sudden transient would have to carry 2A to reach the same 
peak voltage of 200V that a TVS might begin conducting at -- more than 
enough, since solenoids can't carry more peak current than the steady 
state peak current, which is fractional ampere.)

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message 
news:fopp6856rs18f4nuat0agrpjp90gtqotis@4ax.com...
> Keep in mind that SSRs virtually always fail 'on' = flood. Mechanical
> relays generally fail off (though I've seen them stick on very, very
> rare occasion and a very badly made relay).

I once welded a 60A contactor.  I guess they don't like switching into 
fault current on a residential 50A, 240V circuit (probably ~2kA peak). 
;o)

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

Jon Elson wrote:

> Jamie wrote:
> 
> 
>>Jon Elson 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.
>>>
>>>Also, would it be better to put the suppressor across the relay contacts
>>>or across the valve solenoid?  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
>>
>>  Get some DC controlled SSR's (solid state relays), that can operate
>>from 120 DC Or AC, diode them from the coils supply, place a cap on the
>>control terminal of the SSR. The M1, M2 terminals will go across the
>>contacts.
>>   What this does is the SSR first comes on before the contacts close,
>>there by removing the load. when the contacts close, the SSR will not
>>conduct and thus it won't be doing any work.
>>
>>   The cap on the control terminal allows for a slight time off delay,
>>this allows for the relay to open and the SSR will be conducting for a
>>very short time afterwards..
>>
>>  Actually, I think there are add on products that already do this.. Not
>>sure.
> 
> No room for double relays.  I'm not sure your double relay scheme will
> fix the problem, anyway, it occurs on shut-off!  The SSR would shut off
> first, then the mechanical relay would drop out later, and still arc
> (although the off SSR might have an internal snubber or avalanche mode
> that would reduce the arc.)  First, there are EIGHT of these in a tiny
> space, so adding 8 more relays will never work.  But, why use TWO
> relays when one good one will do it?
> 
> A cap big enough to delay the turnoff of the SSR could damage the relay
> driver chip, and would also keep the magnetic relay on.
> 
> Jon
  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

"Tim Williams" <tmoranwms@charter.net> wrote in message 
news:k4ipko$8ef$1@dont-email.me...
> "tm" <No_one_home@white-house.gov> wrote in message 
> news:k4ikis$h50$1@dont-email.me...
>> Here is an AC opto coup[led triac that can switch 0.1 A/ 400 volts 
>> continuos. Google the datasheet from TI for some additional ideas to 
>> increase the current if needed.
>>
>> http://www.ebay.com/itm/20PCSMOC3023-RANDOM-PHASE-OPTO-TRIAC-DRIVER-OUTPUT-6PIN-/260793421140?pt=LH_DefaultDomain_0&hash=item3cb87fcd54
>
> Not sure about MOC3023 specifically but as I recall the MOCs are made 
> specifically for driving real TRIACs, and are rated for that service ONLY.
>
> The heavily inductive load (if this is indeed the failure mode --  
> remember, _it's EDMing right through entire blob-O'-metal contacts_) might 
> not even allow the TRIAC to turn off, ever.  The solution in either case 
> (thrysitor SSD or mechanical) is an arc suppressor or snubber, as 
> mentioned elsewhere.
>
> The reason MOS SSDs were suggested is because they turn off so slowly, 
> absorbing switching energy and damping transients.  They have to be rated 
> for enough peak thermal dissipation, which unfortunately isn't normally 
> part of the datasheet.  One would suppose the manufacturer rates them 
> appropriately for the load current, both continuous, turning on, and 
> turning off.
>
> RC snubbers may work better than TVSs or MOVs because the latter allow any 
> voltage up to breakdown.  A spark will start on the (mechanical) contacts 
> as soon as they open, growing in voltage roughly proportional to gap 
> length.  If the arc voltage never hits TVS/MOV breakdown, it simply won't 
> do anything.  MOVs may have some advantage because they have fairly high 
> capacitance.
>
> Now, a capacitor helps greatly because it limits turn-off slew rate; 
> unfortunately, a cap across the contacts is a similarly bad idea at 
> turn-on.  A series resistor yields an acceptable compromise between 
> turn-off peak voltage and turn-on peak current.  For the solenoids in a 
> washer I'd be very surprised if 0.1uF / 100 ohm didn't fix things 
> completely.  (A sudden transient would have to carry 2A to reach the same 
> peak voltage of 200V that a TVS might begin conducting at -- more than 
> enough, since solenoids can't carry more peak current than the steady 
> state peak current, which is fractional ampere.)
>
> Tim
>

In another response I suggested a snubber and I think the OP asked about 
that originally. We do not know any details about the solenoid current, etc. 
so yes, reviewing the datasheet for the MOC is in order. It does have 
example designs for controlling a secondary triac. For fail safe, maybe put 
two in series, who knows? It appears space limitations are forcing the use 
of too small a relay. Using a 0.1uf with a fuseable resistor would be my 
first choice plus an annual relay inspection :).

"tm" <No_one_home@white-house.gov> wrote in message 
news:k4iuld$ush$1@dont-email.me...
> It appears space limitations are forcing the use of too small a relay. 
> Using a 0.1uf with a fuseable resistor would be my first choice plus an 
> annual relay inspection :).

The real crime is they didn't even reserve the space for basic protection 
like this.  I put at least some effort into ESD / overvoltage / 
overcurrent protections on all connections entering and leaving my PCBs.

If nothing else, one could hack into the solenoid wires and place the 
snubber there.  It's low frequency energy, so it's not as big a deal if 
it's *at* the switch or not.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

tm wrote:


> What is the make of the washer? I would want to avoid it for sure.
Sears kenmore Oasis or Whirlpool Cabrio or Calypso.  Probably a
dozen more brands using the same control.  All of these have a big
knob in the center of the panel to select the cycle.  The later ones
have LEDs around the knob to verify the cycle selection, I think the old
ones just had a pointer on the knob.

Jon

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.  The R is small, but the cap will be fairly big.  A
TVS device will fit for sure.  I think I'm going to have to retrofit
one SSR for the failed relay just to keep washing clothes until
the replacement relays come in.  That will give me some time to
research the situation, and do some experiments with some
spare solenoid valves to determine the best snubber R/C if
I can find components that fit, or work with the TVS devices
to be sure they will work reliably.

Thanks,

Jon