Jobo Resistor

[Nicholas Lindan]

Sparky should get replaced - if not the relay contacts will pit and you will have to replace the relay. It isn't an extremely urgent repair. When the resistor doesn't spark that is because the relay contacts are sparking to save the resistor.

The little blue capacitor next to sparky should have some numbers on it - 0.01 would be 0.01 uF 10,000 pF, 10nF or 10KpF; 0.1 would be 0.1uF, 100nF, 100KpF and so forth.

Capacitors marked "250VAC" are for connection to the AC wiring. They are actually 1,500V or 3,000V capacitors so they don't fail if there is a lightning strike to the power lines or some such. These capacitors are big, say 2 cm long.

If you can't read the markings on the capacitor on the board then a use a 100kpF capacitor and everything should be OK. Expect the capacitor to be larger than the one that failed. Get a capacitor rated for 400VDC.

The resistor and capacitor you will be replacing are not direction sensitive, though some other components are.

In the last picture of the motor you can see the two brown/orange capacitors used for suppressing EMI (radio interference) from the motor brushes - the capacitors work with the coils on either side of the brushes. Capacitors and resistors across the relay contacts are there to suppress the inductive voltage surge that happens when the relay opens to reverse direction - they also suppress the 'click' you would hear on the radio when the motor reverses.

 

[Steve Smith]

Nicholas is right, if you have a choice between a 250 volt and 400 volt capacitor, get the 400 volt one.

I don't know if this will help you understand the function of the resistor and capacitor but it's like the capacitor (usually called a condenser) in the distributor of a car with a set of points and coil (rather than a more modern electronic ignition system). If you run the engine without the capacitor you will get large sparks when the points open which will quickly wear out their contact surfaces. The capacitor/condenser absorbs most of this energy so the points last longer.


Steve.

 

[polyglot]

100K does not mean "100kPF", it means 10pF with tolerance K (10%); if you buy one marked 100K, it is 10000x too small. The marking XYZ means XY * 10^Z pF so if you want 10nF, it needs to be marked 103. If the markings on the old one aren't obliterated, get one with the same markings though the K doesn't really matter, it's just the default cheap grade. If the markings are obliterated, I would suggest 100nF (104) instead.

Some (typically monolithic) capacitors come marked in nF anyway, e.g. "100nJ" (100nF, 5%), which is what you want. Note that that must be a lowercase n; "100N" would mean 10pF with 30% tolerance.

The Jobo motor runs only at about 24V (so your mains voltage is pretty irrelevant); the reason for the high voltage rating on the capacitor is because it's part of a snubber network that needs to absorb all of the inductive energy from the motor when the relay contacts disconnect. That means that the capacitor will charge up to quite a high voltage and you should get the 400V one if you can, if it will physically fit and only if it is of the same type (probably ceramic).

You want either a ceramic or monolithic capacitor. Polyester is acceptable but not great, tantalum and electrolytic are unacceptable.

The resistor and capacitor are both non-polarised, so direction is electrically irrelevant. And because this is a bidirectional motor circuit, the snubber will be operated in both polarities anyway. People tend to try and have all the components facing the same way on the board so that they can be easily read without flipping the thing back and forth.

 

[Nicholas Lindan]

I've never seen the "KpF" designation used in the States - but 100KpF would be read as 100,000 pF / 100nF / 0.1uF with a scratch of the head.

Capacitors are marked 104K in the US for a 100,000 pF 20% capacitor but there is no trailing pF on the part. One marked "100K" would indeed be a 10pF capacitor. nF are common on EU parts and rare on US made. The use of uF for marking small capacitors is fading in the States - though still used in the imaginations of the older generation...

In this Spanish distributor's web site, though, it seems that KpF does mean thousands of pF:
http://www.cetronic.es/sqlcommerce/disenos/plantilla1/seccion/Catalogo.jsp?idIdioma=1&idTienda=93&cPath=962&expand=0
To allay the sort of confusion arising here the distributor also shows the values in uF.

Where a picture is shown the part itself shows 100nF for a capacitor listed as 100KpF
http://www.cetronic.es/sqlcommerce/disenos/plantilla1/seccion/producto/DetalleProducto.jsp?idIdioma=1&idTienda=93&codProducto=215004016&cPath=962

Different countries have different designations for the same part. The use of K here can certainly cause confusion in the ROW.

 

[Moskva4]

hello
I rencently bought a Jobo CPE2 down, with the hope of repair.
the previous owner changed the relay, but I'm not sure that the installation is good. have you the pinout of the genuine relay , thank you

 

[polyglot]

I haven't a CPE2, but looking at your photo, pins 4-5 are clearly the coil. 1, 2 and 3 will be the contacts and it will be single-pole double-throw (SPDT).

Looking near the hole near the middle, there's a 4-pin device that looks like a WO4 bridge to me, with the top-left and bottom-right pins being the rectified outputs. Note that they go to relay contacts 1 and 2 (and a big capacitor on the left acting as filter/snubber), so I would assume that they are the NO and NC contacts. That leaves 3 as being the C (common) contact.

That's my guess, anyway.

 

[Moskva4]

Thank you, someone gave me the reference of the relay http://www.datasheetcatalog.org/datasheets2/61/61740_1.pdf
The coil on 3,5 common 4 end contacts 1,2.
On my board, I found the original failure, it is the thermistor PTC975 it break down at too low intensity (1,5 A for 3A nominal)