Sword repair

[Rory535i]

I've taken the sword out of my car and I'm about to buy the MOSFET transistors to replace the old ones but I can only find 14A 50V ones. All the repair procedures i've read say to replace them with 16A 60V transistors. Is it crucial to use the correct type or will the lower rated ones work? As i'm in Australia, the cost of getting the parts shipped from mouser.com is about 5 times the price of the parts where as I can get the 14A's down the road for a couple of bucks! What should i do? .

[shogun]

If you want to repair it, you have to replace the 4 (four) MOSFET's TO220, housing BUZ 71 can be used.

http://www.bimmerboard.com/forums/posts/136145
Another comment on a German board says (I translate this as good as I can):

"I would not use BUZ 71, because they only have 45 Watt, the BUZ 100 would be better, it has 250W and 60A. The fan max. pulls 30A, that are at 12V 360W, at 14V 420W. Based on this 2 x BUZ 100 are better than BUZ 71,
4*45= 180 Watt.
However, at low fan speed the MOSFETs become warmer then at highest speed. Or better use BUZ10 / 11."

Now it is the turns for the electric experts.

[Bellicose Right Winger]

This procedure says use the 13A 50V MOSFETS.
http://www.bmwe34.net/E34main/Mainte...ical/Sword.htm
I think you're good to go.

I'd remove and check the fan motor also. Relube it at a minimum and consider changing the brushes. Motors draw more current as they age, due to bearing issues, loss of brush pressure due to wear can contribute and this is hard on the MOSFETs.

Paul Shovestul

[Bellicose Right Winger]

The guy on the German board has misread the datasheet. The BUZ71 can deliver 14A at 50V, which is 700watt. The 45 watt rating (actaully only 40 watt according to attached datasheet) is the amount of heat that must be dissipated thru the heat sink when the BUZ71 is operating at rated current and rated voltage.

http://www.jaycar.com.au/images_uploaded/BUZ71.PDF

Paul Shovestul

........
http://www.bimmerboard.com/forums/posts/136145
Another comment on a German board says (I translate this as good as I can):

"I would not use BUZ 71, because they only have 45 Watt, the BUZ 100 would be better, it has 250W and 60A. The fan max. pulls 30A, that are at 12V 360W, at 14V 420W. Based on this 2 x BUZ 100 are better than BUZ 71,
4*45= 180 Watt.
However, at low fan speed the MOSFETs become wormer than at highest speed. Or better use BUZ10 / 11."

Now it is the turns for the electric experts.

[misfortune]

The guy on the German board has misread the datasheet. The BUZ71 can deliver 14A at 50V, which is 700watt. The 45 watt rating (actaully only 40 watt according to attached datasheet) is the amount of heat that must be dissipated thru the heat sink when the BUZ71 is operating at rated current and rated voltage.

http://www.jaycar.com.au/images_uploaded/BUZ71.PDF

Paul Shovestul

http://www.bimmerboard.com/forums/posts/91956

Try that. Thats all I did. It works great now.

Just resolder the part near the arrow.

[kev535i]

http://www.bimmerboard.com/forums/posts/91956

Try that. Thats all I did. It works great now.

Just resolder the part near the arrow.

this was the same repair to fix mine -thanks pundit

[pundit]

http://www.bimmerboard.com/forums/posts/91956

Try that. Thats all I did. It works great now.

Just resolder the part near the arrow.

Yes, it would be worthwhile try the 'flex' test with the sword removed (but still plugged in and powered up) to see if the variable fan speed control is intermittant. Any intermittant operation will indicate a faulty connection rather than a failed component. If that is the case then it's unlikely the mosfets are the cause. My fan controller has been working fine ever since I resoldered the bad joint about 10 months ago.

[pundit]

this was the same repair to fix mine -thanks pundit

That's interesting. It seems this particular fault maybe not that uncommon. If that's the case, I wonder how many people have uneccessarily replaced mosfets?

From what I could tell the leads on the capacitor seemed to have been cut too short with the tip of the lead barely poking through the PCB. This probably accounted for the poor solder joint as the lead may not have 'tinned' properly resulting in a dry joint. As the component leads are cut automatically during the production process an incorrectly adjusted machine could have cut many thousands of leads too short.

[Rory535i]

Thanks for all the suggestions. Problem is that my car is in a million pieces at the moment with the alternator in bits and no battery in the car so i can't test the sword till it's all back together again. Never thought about checking the wreckers...good idea. how much do they usually go for on ebay?

[Javier]

they are in parallel, so four of them are 56 amps, blower can not be that much.

Also doubt the mosfets are fried, would check soldering points as suggested. The must probable status a blown mosfet will end in a circuit like this one is short-circuited, so blower symptom for burnt mosfets would be running at max speed allowed by the progressive control (not max stage).

Javier