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Thread: Why relays are being replaced by SSRs

  1. #1
    Super Moderator Javaphile's Avatar
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    Why relays are being replaced by SSRs

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Ever wonder what the inside of a 20 year old relay looks like? This is what happens over the years as the contacts close and open hundreds of thousands of times.



    The point circled in blue was completely unused with no wires even being connected to it. The blackening on it is some of the burned off metal from the other contacts that was deposited on it. The 2 circled in yellow are all burned away and havent been making any contact at all since turning the machine on this fall. The point circled in red was the only one making any contact at all this fall and only a small fraction of it was actually touching and completing the circuit. The actual point is all burned away and just a small portion of the underlying copper (Brass?) bar was touching to complete the circuit. Until it too failed last night.


    Java "Sensing an SSR in his future" phile

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    Senior Member trentski's Avatar
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    Re: Why relays are being replaced by SSRs

    Only 20 years aye?

    Dont make them like they used to ;D

  3. #3
    KJM
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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 5A7166716078797C75100 link=1320313933/0#0 date=1320313933
    Java "Sensing an SSR in his future" phile
    Just dont forget to heatsink the SSRs if youre powering something beefy (which judging by the contacts, you are). Thatd be the one advantage of a good relay against comodity SSRs - the relays dont dissipate much energy!

    /Kevin

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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 525354190 link=1320313933/2#2 date=1320573108
    Just dont forget to heatsink the SSRs if youre powering something beefy (which judging by the contacts, you are). Thatd be the one advantage of a good relay against comodity SSRs - the relays dont dissipate much energy!
    Indeed! This contactor is what turns the power to the heating elements on and off in my 2 group M28 Cimbali. Most of the SSRs Ive been seeing look to generate 1.2-1.4 watts of heat per amp passing through them. IN this case that would mean roughly 60 watts of heat to get rid of on a ~20% power on duty cycle. If you dont get rid of that heat the SSR will very quickly fail and typically fail in the power on position.

    A SSR was not my first choice to replace the contactor with. But with a new contactor running $200 from any of several espresso service centers I contacted it was something I was having to seriously consider as the SSR would only run me about $40 and I have plenty of heatsinks sitting around here that I could use with it as well as appropriately sized fans should it come to that. Fortunately it appears Ive managed to source an appropriate contactor for the princely sum of $5 off of fleabay. Ill know in a couple of days once it arrives. Until then I removed the shunts from the 3 fried legs in the contactor, cleaned the whole assembly up, and wired in one of the 3 heating elements into the remaining good (Never used.) circuit. A bit slower recovery but as its a home unit I can live with that.
    :)


    Java "Enjoying his cuppas once again!" phile

  5. #5
    KJM
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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 68435443524A4B4E47220 link=1320313933/3#3 date=1320580226
    A SSR was not my first choice to replace the contactor with. But with a new contactor running $200 from any of several espresso service centers I contacted it was something I was having to seriously consider as the SSR would only run me about $40 and I have plenty of heatsinks sitting around here that I could use with it as well as appropriately sized fans should it come to that. Fortunately it appears Ive managed to source an appropriate contactor for the princely sum of $5 off of fleabay. Ill know in a couple of days once it arrives. Until then I removed the shunts from the 3 fried legs in the contactor, cleaned the whole assembly up, and wired in one of the 3 heating elements into the remaining good (Never used.) circuit. A bit slower recovery but as its a home unit I can live with that.
    OK - your average relay (contactor) has lots of different shapes and sizes. I would have thought theyd be plenty of space inside the machine, so any old relay would do (to a first engineering approximation ;)). $200 seems crazy high (although it is from a coffee place ::)).

    The heat dissipation in SSRs comes from the fact that they have a couple of semiconductor junctions in there, and they run to (about) 0.6V each. So about 1.2W per ampere is a good rule of thumb. Here in Oz given our 240V supply, we usually have half the amps, which works out handy for SSR adoption - much smaller heatsinking requirements!

    Happy hacking
    /Kevin

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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 727374390 link=1320313933/4#4 date=1320740902
    OK - your average relay (contactor) has lots of different shapes and sizes. I would have thought theyd be plenty of space inside the machine, so any old relay would do
    There is surprisingly little empty space in the electronics box/area on my machine. It is pretty well filled up with big clunky electro-mechanical components. I have an old Cimbali M28 Start which has no micro-electronics in it at all. The most modern/complex thing in it would be a relay.
    :)

    As far as a replacement contactor goes I needed one with 3 (The existing one had 4 but only 3 were used.) isolated power legs/circuits each of which needed to be rated at a minimum of 2kw capacity and the triggering coil needed to be 12vdc.

    As you might imagine coming from a 20 year old machine the part is obsolete. A new design/series contactor direct replacement is made by the manufacturer. While the repair shops wanted $200 for the part I could get one direct from a manufacturer rep for $100 and from a 3rd party source I found an open box one for $68. All of these prices did not include shipping.

    In my digging looking for a better price I discovered that the Allen Bradley contactors are made in the same factory as the Sprecher & Schuh one I was looking for. Plus they looked outwardly identical other than the label and had identical specs. It was an Allen Bradley contactor I found on fleabay that while not identical was close enough in the circuits/shunts it had.

    The original S&S had 4 normally open main power circuits rated at 2kw each and the AB one I found had 3 normally open main power circuits rated at 2kw each and an aux circuit (Typically used as an indicator circuit.) with a lower rating. The only question was whether it had a 12vdc coil in it. The seller was clueless in re that and with only an hour left on the auction when I found it and with no bidders with an opening bid of a single penny and S/H running $4.99 it was worth taking a chance on. If, as was most likely, it did not have a 12vdc coil the new model was close enough in design that I felt I could swap parts between the two and get a fully function contactor out of it.

    Upon receiving the new unit this morning I found that the coil was a 110vac module and it was not a direct swap between the two. That was the bad news. The good news was the upper assembly which contained all the contact points and shunts was a direct swap between the two. Fifteen minutes after receiving the new unit I had a brand new fully functional contactor in my machine and Simba was back up to full heating power and working perfectly. No need to mod anything and no need to go the SSR route and no need to spend $200.
    :) :) :)


    Java "Twas a good day to be a tech!" phile

  7. #7
    Senior Member trentski's Avatar
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    Re: Why relays are being replaced by SSRs

    The downside is you are going to have to do it all again in 20 years ;D

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    Re: Why relays are being replaced by SSRs

    Funny you should say that. Someone else said pretty much the same thing to me earlier.

    Andy Freeman wrote:
    ...and you have scheduled the next contactor change for 2030?

    And my response:

    Actually I put it on the calendar for 2026. :P I figure no downtime that way! ;D ;D ;D

  9. #9
    KJM
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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 696F7873696E76741D0 link=1320313933/6#6 date=1320749850
    The downside is you are going to have to do it all again in 20 years*
    While Ive only used big (as in high power - 2kW is high power for me) contactors for my three phase pump on the dam, Im pretty sure the documentation claimed 100k operation cycles under inductive load. The espresso machine would be purely resistive, so the lifecycle would be higher. Maybe 250+k. The heating is probably 1:3 duty cycle or something similar. So maybe 20 years is technically a bit past the expected service life ;)

    Javas burnt contacts looked a fair way past end of life!!

    Glad its all back and working!

    Cheers
    /Kevin

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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 7D7C7B360 link=1320313933/8#8 date=1320757581
    The espresso machine would be purely resistive, so the lifecycle would be higher.* Maybe 250+k.
    Per the manufacturer the life duty cycle for the contacts on this model is 700k.

    Quote Originally Posted by 7D7C7B360 link=1320313933/8#8 date=1320757581
    The heating is probably 1:3 duty cycle or something similar.
    The measured cycle is 22 seconds on and 224 seconds off so a 9% duty cycle. That would mean theres about 350 cycles of the contactor per day. With the unit left on 24/7 for approximately 8 months of the year that would give the contactor a life expectancy of roughly 8 and a third years.

    Quote Originally Posted by 7D7C7B360 link=1320313933/8#8 date=1320757581
    So maybe 20 years is technically a bit past the expected service life Wink

    Javas burnt contacts looked a fair way past end of life!!
    So yeah, just a bit past their expected EOL! ::)

    Looks like I should maybe move up that calendar date a bit! ;D ;D ;D


    Java "Math? We dont need no stinking math!!!" phile

  11. #11
    KJM
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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 042F382F3E2627222B4E0 link=1320313933/9#9 date=1320790236
    The measured cycle is 22 seconds on and 224 seconds off so a 9% duty cycle. That would mean theres about 350 cycles of the contactor per day. With the unit left on 24/7 for approximately 8 months of the year that would give the contactor a life expectancy of roughly 8 and a third years.
    Im impressed. Thats a pretty low duty cycle (just judging on how often the machine in our tea room cycles on/off). 9%! I guess the boiler is insulated?

    /Kevin

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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 0B0A0D400 link=1320313933/10#10 date=1320811071
    I guess the boiler is insulated?
    Nope! No insulation on it at all! Its an (em)bareassed boiler! ::) ;D

    Ive debated insulating it but while it costs more to operate running bare, and doesnt get used in the summer due to the heat it generates, it actually saves me a good chunk of change in the colder/heating months of the year. It is on the first floor in the kitchen which is on the opposite side of the wall from the thermostat that controls the houses furnace. With the massive bare metal 12l boiler putting out gobs of heat it is providing a good chunk of the heat necessary to maintain the temperature on the first floor. Which means the furnaces isnt turning on anywhere near as often as it would otherwise. Which would cost me significantly more money as I have a two story plus basement house. The furnace heats all three levels while the espresso machine heats only the first floor. By running the espresso machine in the cold months my total energy bill is lower than if I didnt run it. Enjoying my cuppa, having instant access to hot water for tea and cooking, and having a perfect plate warmer actually puts money in my pocket!
    :) :) :)


    Java "Gotta love that!" phile

  13. #13
    KJM
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    Re: Why relays are being replaced by SSRs

    Quote Originally Posted by 1D362136273F3E3B32570 link=1320313933/11#11 date=1320812275
    Nope! No insulation on it at all! Its an (em)bareassed boiler!
    Oh dear - I get a good sense of the humor of the Javad one ::) ::)

    The engineer in me rails against using a resistance heater for space heating!! It is just so inefficient!!

    Still, if it works economically - it works! I guess youre paying a lot less for electricity than we are >:(

    I cant imagine keeping a machine going here - especially in Summer - probably even worse than for you!

    Interesting marketing angle though - buy a space heater and get an espresso machine for free :o

    /Kevin

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    Re: Why relays are being replaced by SSRs

    Behmor Brazen - $249 - Free Freight
    Electricity here is at about 15 cents a kwh. The total bill to run the espresso machine 24/7 is roughly $35-$40 a month. The reduction in my heating bill is at least $60 and in the depths of winter well over $100 a month. It gets quite cold here in the winter (The record low in Minnesota is -51C!) and by not keeping 2/3rds of the house at the 20C it is on the 1st floor (The basement and 2nd floor are typically running about 10C give or take a few degrees in the winter.) it dramatically reduces the heating bill. Plus some of that electricity bill I would be paying anyways running the stove to make my soups and hot teas in the winter.
    :)

    Running the espresso machine in the summer would kill me with the electricity cost as for every dollar it cost me to run I would be paying out another buck 20 or more to my AC to remove all the heat the espresso machine puts into the house! So I happily survive on CP in the warm months of the year here.
    :)


    Java "As Andy says, Its not my espresso machine. Its Javas Heater! ;D" phile



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