Some electronics help please?

[Quinten]

Last year at Stoneleigh I bought one of these and although it worked fine for the past year, today I discovered it no longer switched my fan on/off.  Upon investigating I came upon this mess

The white wire is soldered to a piece of metal which was connected to the component that had completely come away from the PCB.  The middle pin appears to be cut short, although it may also have been connected to the same metal piece.  This is where I need some help from the likes of @Kit Car Electronics.  I'm not scared of doing a little soldering, but I'm not sure what the connections should be.  The white wire would carry 12V if the temperature of the sensor (connected to those 4 wires on the left hand side of the PCB) reads between the lower and upper limit set on the display (not shown).  The red and black wires are the 12V in and GND to power the controller.

[Quinten]

Found out the component is a MOSFET and the top bit and middle pin are effectively the same, so if I can find the model, I should be able to replace it.

[Blatman]

Dumb question (I'm only good at dumb questions...) but would replacing it with the same part run the same risk, IE failure in 12 months? Is there an underlying cause that should be addressed?

[Quinten]

No idea.  It appears to be heat related, so I imagine with it being made in Russia, it is used to lower temperatures  

At the moment it looks like a £1.99 fix.  If it is not fixed, then I'll look at replacing it and confirming the warranty conditions with CBS.

[Ian Kinder (Bagpuss) - Joint Peak District AO]

I'd be mounting the replacement MOSFET on a heat sink remotely to prevent recurence. You'll probably need an isolating pad under the body of the device as it will probably be at 12V. The ones below are for my indicators, rear fog and indicator still on buzzer. The pad is the brown coloured item under each MOSFET.  These are P channel MOSFET's part number IRF9Z34NPBF.(https://uk.farnell.com/infineon/irf9z34npbf/mosfet-p-55v-17a-to-220/dp/8648689?scope=partnumberlookahead&ost=IRF9Z34NPBF&searchref=searchlookahead&exaMfpn=true&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fw%2Fsearch)

 

 

you could try this heatsink: https://uk.farnell.com/aavid-thermalloy/tv1500/heat-sink-to-220-218-14-c-w/dp/179934?ost=179934&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fsearch

Isolator pad: https://uk.farnell.com/multicomp/mk3306-s/insulating-kit-to-220/dp/522636?MER=sy-me-pd-mi-acce

 

Mounting bolt: https://uk.farnell.com/multicomp/mk3311/fixing-kit-nutbolt/dp/520160?MER=bn_level5_5NP_EngagementRecSingleItem_2

[Wobblyprop]

Mounting such a device w/o heatsink is naughty as it's clearly been getting hot for a while judging by the PCB, and soldering direct to the tab is very, very naughty indeed!  Definitely one for the rogues' gallery.  If I were you, I'd be investigating alternative suppliers.

[Kit Car Electronics]

The spec says it can switch 4A, which isn't enough for any fan or pump that I can think of - did you have it triggering a relay for the main load, Q? I can't tell where the damaged trace on the right hand side was headed, or if that has survived, either...

[Quinten]

You've confirmed my suspicion Mike, I think I have to conclude that this fault is of my own doing 

My fan is ground switched, so when I installed this last year, I used the switched 12V on a relay to switch to ground.  In other words, it wasn't connected to the fan.  But a couple of weeks ago, when I was tidying up the wiring, I put the 12V directly on the fan, bypassing the fan relay.  Surprisingly it managed to last the odd hundred mile I've done so far.  And if it wasn't for re-doing the original relay wiring again today, the first time I would have noticed is my car overheating in traffic!

Doh!  I've ordered a new MOSFET now, so I'll give it a go at least... but I dont think I can hold the Russians responsible now  

[Ian Kinder (Bagpuss) - Joint Peak District AO]

Oops own goal- good spot Mike

[Lyonspride]

 

That PCB isn't really suitable for automotive use, starting with the obvious fact that it's not conformally coated and has suffered corrosion to the soldered joints.

It's functionality is similar to a W1209 thermal controller, which you can get for a few £, but W1209 can handle higher current due to relay output, I actually have one in the Westfield (inside an enclosure) to bypass the coolant stat and use the rad fan to keep the engine bay cool in traffic.

[Quinten]

After the seller shipped me the wrong part and an additional delay in getting the replacement MOSFET, I've just attempted to repair the PCB.  Alas, it didn't work, so I've ordered one of those W1209 boards with an acrylic case.  Thanks for the headsup on that one @Lyonspride.  Where have you got the sensor itself mounted?  I currently have it on the metal 'hockeystick' close to the thermostat housing, which with a little experimenting, had a temperature reading of approx 30C lower than the gauge would indicate.

[Lyonspride]

On 27/04/2019 at 12:11, Quinten said:

After the seller shipped me the wrong part and an additional delay in getting the replacement MOSFET, I've just attempted to repair the PCB.  Alas, it didn't work, so I've ordered one of those W1209 boards with an acrylic case.  Thanks for the headsup on that one @Lyonspride.  Where have you got the sensor itself mounted?  I currently have it on the metal 'hockeystick' close to the thermostat housing, which with a little experimenting, had a temperature reading of approx 30C lower than the gauge would indicate.

 

I'm using mine to keep under bonnet temps in check, and not for coolant temp, so mine is clipped to one of the breather hoses high up in the engine bay.

The analogues gauges are never right, but you'll also be getting an error from having the sensor in open air. In your case I'd either try to get a sensor that's plumbed into the cooling system, any 10k thermistor should work, or failing that i'd bond the sensor to the radiator so that it's getting as accurate a reading as possible.

 

Seeing as you've got a W1209 on my recommendation, here's a little advice/help.

Be really careful with the min/max setting, it's supposed to be the min/max temp setting that it will allow you to enter, but on some W1209 (probably copies) it triggers the high temp alarm and actually stops the whole thing working. Also P5, this is a delay time between operations, and probably a bad idea in this application.
Hysteresis probably wants to be 5 degrees or more, else it'll keep switching on/off every few seconds.

 

[Quinten]

Cheers @Lyonspride!  I've just installed it and had to extend the temperature sensor cable first as it was ridiculously short.  But that was quickly sorted and with the build in relay I had it up and running in no time.  Should have opted for one of these last year!