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Thread: Ulka 24V AC EX5 needs a diode or not?

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    Ulka 24V AC EX5 needs a diode or not?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi folks

    Just replaced my old Ulka NH26 in the faema E98 Compact A1 with a new EX5 ulka. Now, the old pump had an external diode. Does the new pump also require it? (seems to be running fine with it connected already...)


    Ta
    Matt

  2. #2
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    well yes it seems to need one. Diode checker shows no voltage changes in either direction with the bare coil and with no diode hums very quietly (still pumps water!) and gets hot. Takes a while to build up pressure without the diode. Unfortunately the new pump is much much noisier than the old one (with the diode)!
    With the diode it sorta goes ditttttrrrrrrrrrrr which was like the old one, but noisier.
    Last edited by floatingkiwi; 7th September 2016 at 02:27 PM.

  3. #3
    Mal Dimal's Avatar
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    Yep...

    Definitely requires the Diode.
    This causes the pump piston to achieve a full travel Stroke in the cylinder as it is only receiving a "pulse" each half-wave with the diode in circuit. With full-wave AC applied, the piston is only able to travel a fraction of the normal stroke within the cylinder...

    Mal.

  4. #4
    Senior Member artman's Avatar
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    Some have the diode built in don't they? I recall seeing a diode symbol on them, or is that just telling you to install one?

    Cheers

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    Mal Dimal's Avatar
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    All of the Ulka units I've seen or worked on have a moulded receptacle on the coil encapsulate that is intended to 'house' the Diode. This allows for simple and speedy replacement of the Diode rather than having to replace the entire Pump or the Coil...

    Mal.
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    Senior Member brettreaby's Avatar
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    so with a bridge rectifier it would pulse at 100HZ and deliver more power with perhaps less noise?

    Quote Originally Posted by Dimal View Post
    Yep...

    Definitely requires the Diode.
    This causes the pump piston to achieve a full travel Stroke in the cylinder as it is only receiving a "pulse" each half-wave with the diode in circuit. With full-wave AC applied, the piston is only able to travel a fraction of the normal stroke within the cylinder...

    Mal.

  7. #7
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    A bridge rectifier would give insufficient off cycle.

    Pretty sure the later Ulkas, including the EX5 have an internal diode rather than external. It'd be worth checking.
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  8. #8
    Mal Dimal's Avatar
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    Quote Originally Posted by simonko View Post
    Pretty sure the later Ulkas, including the EX5 have an internal diode rather than external.
    Bit of a bugger if they're doing that...
    Sell more pumps/coil assemblies that way I s'pose...

    Mal.

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    Senior Member sprezzatura's Avatar
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    Quote Originally Posted by floatingkiwi View Post
    Hi folks

    Just replaced my old Ulka NH26 in the faema E98 Compact A1 with a new EX5 ulka. Now, the old pump had an external diode. Does the new pump also require it? (seems to be running fine with it connected already...)


    Ta
    Matt
    The new pumps have a forward-biased diode inside. Some may come (the machine harness) with a thermal diode which cuts off power to the coil so it doesn't get a hot spot and melt.

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    Quote Originally Posted by Dimal View Post
    All of the Ulka units I've seen or worked on have a moulded receptacle on the coil encapsulate that is intended to 'house' the Diode. This allows for simple and speedy replacement of the Diode rather than having to replace the entire Pump or the Coil...

    Mal.
    That receptacle is for the thernal cutout to sit.
    Pretty much all vibe pumps are manufactured with internal diodes now.

  11. #11
    Mal Dimal's Avatar
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    Quote Originally Posted by noidle22 View Post
    That receptacle is for the thernal cutout to sit.
    Pretty much all vibe pumps are manufactured with internal diodes now.
    Not on the units I've worked on over the years....
    There's always been a Diode sitting in there.

    Mal.

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    Quote Originally Posted by Dimal View Post
    Not on the units I've worked on over the years....
    There's always been a Diode sitting in there.

    Mal.
    Strange. 100% of domestic machines I've worked on have all had a Klixon thermal cutout there and I've seen pretty much every machine ever made for the domestic market.

    Perhaps Italian and other higher end machines have a diode there instead. Were the machines old that had the diode there?

  13. #13
    Mal Dimal's Avatar
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    Yes mate...

    They were all old-ish Italian machines and none of them had any kind of thermal protection fitted.
    My new-ish BFC machine on the other hand looks as though it does have an internal diode since there is nothing observable on the outside of the coil encapsulate... I can only hope that if the diode ever fails, it does so and remains in a shorted state. I could then use a replacement external diode as per the older machines...

    Learn something new every day...

    Mal.

  14. #14
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    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by artman View Post
    Some have the diode built in don't they? I recall seeing a diode symbol on them, or is that just telling you to install one?

    Cheers
    Yes, this one also has that symbol on the side, leading one to assume that it has an internal diode (as, in actual fact, it states on every sales website!), but, when checked with a diode checker, appears to have nothing inside.
    Plus the fact that you can connect the external diode to either end of the coil and it works means there is no diode. If you altered the polarity there would be one configuration where no AC would get to the coil at all.

    The small pocket on the side is for a heat cutoff that some machines utilize - or at least that is what all the Ulka sales sites say!!



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