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I've now ACTUALLY got an ignition coil.

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LAN_403

Sun Jan 08 2012, 05:43PM

Registered Member #4146 Joined: Tue Oct 18 2011, 02:01AM
Location: Wisconsin, U.S.A
Posts: 56

Just find and replace which part went bad. ZVS drivers are very simple and easy to fix. if all else fails you have the working circuit in front of you to look at if you wanted to do the extreme and build another one. Either way fixing it should not be that hard

Platinum

Sun Jan 08 2012, 05:47PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

When I turn it on it's short circuit my PSU, and the right MOSFET is warm...

So I can't fix it without buying more MOSFET's?

Sun Jan 08 2012, 05:53PM

Registered Member #4146 Joined: Tue Oct 18 2011, 02:01AM
Location: Wisconsin, U.S.A
Posts: 56

You may have to buy mosfets or parts but they are fairly cheap. In my opinion after all the trouble you had getting a working zvs to begin with it would be well worth fixing it. I can't tell you exactly what may be wrong with it right now but i'm sure the kind people on this forum could easily help you.

Daedronus

Sun Jan 08 2012, 06:06PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

I would recommend trying to find a electronics shop near you, so if you want a mosfet today you don't have to wait one week for shipping + pay shipping.
And, ebay is not always cheaper. I have a shop 1h away from me (not by car) that has rather hard to beat prices. Bad part, is not open on week end days.

For example 1.24euro for a irfp260, eBay or digikey doesn't even come close.

Platinum

Sun Jan 08 2012, 06:18PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I had 2 spark MOSFET's here they are

Removed both 250n's and soldered the 21N50C3's on, and still the right one gets warm?

Marko

Sun Jan 08 2012, 06:21PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Platinum wrote ...

I had 2 spark MOSFET's here they are

Removed both 250n's and soldered the 21N50C3's on, and still the right one gets warm?

Do you understand how to verify whether mosfets are working? Explain how you do it :P

The another common failure is zener getting shorted and causing these symptoms, but that's unlikely to happen unless you really pushed the voltage.

marko

Platinum

Sun Jan 08 2012, 06:24PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Ohh and uh, are zenner diode mean't to conduct both ways?, one measures 900~Ohms, and the other measures about 1Ohm.

Left zenner is 1Ohm, and right one is like 900~, and the right MOSFET gets hot.

Marko

Sun Jan 08 2012, 07:06PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Looks like left zener is a toast. They shouldn't conduct in a reverse direction until voltage is greater than zener voltage! (which I'm pretty sure your ohmmeter doesn't provide. It's possible that it died because the mosfet died first, though.

It'd be probably a very good idea for you to learn how to test mosfets before getting depressed and binning everything, or buying new ones randomly.

I'm going to provide you some advice now - please, listen to it.

Ohmmeter is a pretty bad way of testing components like diodes, zeners and mosfets since it's testing voltage is quite random and often too low to even forward bias a normal diode. "Ohm" readings on diodes mean absolutely nothing since they are nonlinear devices! You probably noticed the result changes if you change the measurement range on your meter. Such measurements mean nothing for you nor us - so better don't bother doing them at all!

Some meters have a diode testing option on them, which actually gives you the forward voltage of a diode and is much more useful. Small signal diodes and zeners should read like 0.5-0.8 V on this in forward direction, and infinite in reverse. If diode shows 0V or inf in both directions, it's a toast!

But let's forget about all this for now - what you truly need is the ultimate "everything tester" :

Connect together a 9V battery, a led, a 1k resistor in series with some convenient alligator clips (for dramatic effect, I like to add a beeper too!).

Testing diodes - in forward bias, the led should light, in reverse, it should not (hopefully that's simple enough!)

Zeners above 7..8V should be the same, under 7V the led might light slightly in a reverse direction (but you'll know zener is a toast if it conducts well in both directions!)

Now, testing mosfets - I don't know why is it so hard to find a single useful tutorial of this, so please listen now:

- hold the mosfet it's printed face up. The pins from left to right are: Gate - Drain - Source

To test the mosfet with your battery and led, hook the - of your tester to the source. Momentarily touch the gate with the + of your tester, and make sure nothing touches it afterwards. Now attach the + alligator to the drain - the led should fully light.

To complete the test, I tend to use my fingers (though you could use another aligator clip as well) - touch the source with one finger, and the gate with another - the led should go out!

Repeat this a few times to get a feeling of it - after a while I'm pretty sure you'll get a great feeling of how a mosfet works. :)

I hope this post will benefit you and not go to waste along with your circuits and mosfets.

Cheers -

marko

Steve Conner

Sun Jan 08 2012, 07:39PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Thanks Marko. I first saw that MOSFET test done by Tim Hunkin in The Secret Life Of Machines, except he used a car battery and headlight bulb.

I trashed lots of components when starting out too, but there weren't any electronics forums where I could bleat for help.

Platinum

Sun Jan 08 2012, 09:00PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Thank you also.

One Zener is fried, so I threw that, and kept the working one, not sure about the MOSFET's, I tried your test, but maybe I did something wrong, I'm searching for other tests too. Checked diodes, they are OK, I presume resistors are OK, so I'm going to buy some Zeners and 250's, what are the part number for the Zener diodes on diki-key?

Also when I was saying Ohm, I was using the diode test, but now I understand that a zener isn't showing a reading of 1100~Ohms, it's it's forward voltage rating? 11v.

I also used this

Nothing though.

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