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Old 2007.01.24, 10:58 PM   #1
shuter
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How To Test FETs ???

I have some 3010 fets that I installed on a board, discovered that the board did not work, removed the fets and reinstalled another pair. I am wondering whether the fets are still good or if I shorted them out. Is there a way to test them with a multi meter to see if they are good or not? Would hate to just throw them away but would hate even more installing them on another board only to find they are no good.
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Old 2007.01.29, 12:48 AM   #2
CrashTestJohnny
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Quote:
Originally Posted by shuter
I have some 3010 fets that I installed on a board, discovered that the board did not work, removed the fets and reinstalled another pair. I am wondering whether the fets are still good or if I shorted them out. Is there a way to test them with a multi meter to see if they are good or not? Would hate to just throw them away but would hate even more installing them on another board only to find they are no good.
Here's how the fets work:

8765
||||
HHH
||||
1234

1 N-channel Source
2 N-channel Gate
3 P-channel Source
4 P-channel Gate
5 P-channel Drain
6 P-channel Drain
7 N-channel Drain
8 N-channel Drain

Usually Pin 1 has a dot near it to identify it.

So there are actually two fets within each chip you want to test, one is an
N-Channel fet (the left half of the chip), which is used as an on/off switch for ground (0 Volts), and one is a P-Channel fet (the left half of the chip) used as an on-off switch for the positive voltage (5 Volts)..

On the chip, pins 1,2,7, and 8 are connected to the N channel fet, and pins
3,4,5, and 6 are connected to the P channel fet.

Basically the way the fet works is that, to make your car go forward, the
N-channel is turned on one chip, and the P-channel on the other chip is turned on, so.. the motor has 5V in one lead and ground in the other.


So what you should do is to test each fet seperately to make sure both are working. Make sure none of the pins on the chip are soldered together.
Get a 5-6 v power source (a couple leads from a set of 4 AAA or 4AA in series is fine). Also get your stock motor, (or a really mild motor).. You'll also need a few alligator clips, to connect things together..

Also before you touch your fets, touch a large metal object to ground yourself, and get rid of any static electricity. (Especially if you are in a carpeted room)

First you'll test the N-channel fet..
-Connect pin 1 to the Ground (negative of the power supply)
-Connect one lead of the motor to pins 7 and 8
-Connect the other lead of the motor to +5V (positive of the power supply)
Pin 2 can be now be used to turn the N-Channel fet on and off.
-Connect +5V to pin 2 to turn the fet on, (the motor should be spinning now!)
-Connect Ground to pin 2 to turn the fet off, (the motor should stop spinning as if disconnected from the battery)

As long as you are able to turn the motor on and off using the Pin 2, your N-channel fet is OK

Now you'll test the P-channel fet
-Disconnect everything you connected to the chip before.
-Connect Pin 3 to +5V
-Connect one lead of the motor to pins 5 and 6
-Connect the other lead of the motor to Ground
Pin 4 can now be used to turn the P-Channel fet on and off.
-Connect Ground to pin 4 to turn the fet on, (the motor should be spinning)
-Connect 5V to pin 4 to turn the fet off, (the motor should stop spinning as if disconnected from the battery)

As long as you are able to turn the motor on and off using Pin 4 now, your P-channel fet is OK

So if both the N-channel and P-channel fets work, you are probably all set.

You can also use the same technique to test out a fet stack you solder together before placing it on the board.


Some other suggestions I have is to use a current limiting lab power supply,
instead of a battery pack, and limit the current to 500mA or so if usign a motor.

Also, if you want to be really safe, you can use an 5 Volt LED (light emitting diode) in place of the motor first, and limit the current on the current limiting power supply to 50-100mA (enough so the LED is not full bright).

Actually, after fetting my car I always use a current limiting power supply in place of batteries to test it out first. Also instead of a motor for testing I connect two leds to the motor terminals on the board (one connected forward, and one connected in reverse.) One LED should light up for forward, and one should light up for reverse. When using the LEDs the current can be limited to 100mA or so, which shouldn't hurt the electronics if something is hooked up wrong since 5V at 100ma is only 0.5 watts, and the fets should be able to dissipate at least 1W of heat continously.












Here's some other info too:

http://www.repairfaq.org/sam/semitest.htm#stmos
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Old 2007.01.29, 01:12 PM   #3
shuter
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CrashTestJohnny - Thanks for the very detailed directions for fet testing. Not an easy to set up test for an electronically challenged person like myself but your instructions seem clear enough. It is an interesting project, I'll give it a try.
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Old 2007.02.04, 04:19 AM   #4
henal
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hi i have got 2 n chanel mosfet and 2 p chanel mosfet im not sure if there are blown when i used this methode of tesing them out i got like the source pin was shorted with the drain i test it out with a mulitmeter and i got a hige resistanse on one of them i got about 29 k omhs and the other one i got is like 300 k ohms and it dont metter if i use the gat pin it does do notting



now for the n chanel

theres seem to work but ever time i connet positive to the gate pin it turns on and never stops for a long time

and again there are total brand new bouth form maplin electronics in uk

the p chenal mosfet is bsp250
the n chenal mosfet is irfz24n

need all the help i can im not a noob in electronics i know alot about it i thinks there are blown but there are brand new also i know about the ESD so i did touch an copper pipe there time i was going to solder them and also i know how to soler as i was an ps2 chiper so i dint leave the soldering iron for too long
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Old 2007.02.13, 07:02 AM   #5
henal
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any one some one must know are there blown
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Old 2007.05.09, 08:32 PM   #6
Z_408
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Quote:
Originally Posted by CrashTestJohnny
Here's how the fets work:

8765
||||
HHH
||||
1234

1 N-channel Source
2 N-channel Gate
3 P-channel Source
4 P-channel Gate
5 P-channel Drain
6 P-channel Drain
7 N-channel Drain
8 N-channel Drain

Usually Pin 1 has a dot near it to identify it.

So there are actually two fets within each chip you want to test, one is an
N-Channel fet (the left half of the chip), which is used as an on/off switch for ground (0 Volts), and one is a P-Channel fet (the left half of the chip) used as an on-off switch for the positive voltage (5 Volts)..

On the chip, pins 1,2,7, and 8 are connected to the N channel fet, and pins
3,4,5, and 6 are connected to the P channel fet.

Basically the way the fet works is that, to make your car go forward, the
N-channel is turned on one chip, and the P-channel on the other chip is turned on, so.. the motor has 5V in one lead and ground in the other.


So what you should do is to test each fet seperately to make sure both are working. Make sure none of the pins on the chip are soldered together.
Get a 5-6 v power source (a couple leads from a set of 4 AAA or 4AA in series is fine). Also get your stock motor, (or a really mild motor).. You'll also need a few alligator clips, to connect things together..

Also before you touch your fets, touch a large metal object to ground yourself, and get rid of any static electricity. (Especially if you are in a carpeted room)

First you'll test the N-channel fet..
-Connect pin 1 to the Ground (negative of the power supply)
-Connect one lead of the motor to pins 7 and 8
-Connect the other lead of the motor to +5V (positive of the power supply)
Pin 2 can be now be used to turn the N-Channel fet on and off.
-Connect +5V to pin 2 to turn the fet on, (the motor should be spinning now!)
-Connect Ground to pin 2 to turn the fet off, (the motor should stop spinning as if disconnected from the battery)

As long as you are able to turn the motor on and off using the Pin 2, your N-channel fet is OK

Now you'll test the P-channel fet
-Disconnect everything you connected to the chip before.
-Connect Pin 3 to +5V
-Connect one lead of the motor to pins 5 and 6
-Connect the other lead of the motor to Ground
Pin 4 can now be used to turn the P-Channel fet on and off.
-Connect Ground to pin 4 to turn the fet on, (the motor should be spinning)
-Connect 5V to pin 4 to turn the fet off, (the motor should stop spinning as if disconnected from the battery)

As long as you are able to turn the motor on and off using Pin 4 now, your P-channel fet is OK

So if both the N-channel and P-channel fets work, you are probably all set.

You can also use the same technique to test out a fet stack you solder together before placing it on the board.


Some other suggestions I have is to use a current limiting lab power supply,
instead of a battery pack, and limit the current to 500mA or so if usign a motor.

Also, if you want to be really safe, you can use an 5 Volt LED (light emitting diode) in place of the motor first, and limit the current on the current limiting power supply to 50-100mA (enough so the LED is not full bright).

Actually, after fetting my car I always use a current limiting power supply in place of batteries to test it out first. Also instead of a motor for testing I connect two leds to the motor terminals on the board (one connected forward, and one connected in reverse.) One LED should light up for forward, and one should light up for reverse. When using the LEDs the current can be limited to 100mA or so, which shouldn't hurt the electronics if something is hooked up wrong since 5V at 100ma is only 0.5 watts, and the fets should be able to dissipate at least 1W of heat continously.












Here's some other info too:

http://www.repairfaq.org/sam/semitest.htm#stmos
CrashTest,

When are you going to drop by the store to race?

Z_408
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Old 2007.06.08, 12:24 PM   #7
HammerZ
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I lost forward on one of my cars. I pulled these off and put on a pair of 4562 fets that I had on hand. Usually you would see some type of damage to the fets in a burned place. These look a little too clean.
Attached Images
File Type: jpg Fets 01.jpg (90.8 KB, 128 views)
File Type: jpg Fets 02.jpg (103.8 KB, 92 views)
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Old 2007.12.18, 01:14 AM   #8
BryceVR
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Typically the gates of an IC are burned with 40-60v. A short or spike can drop one of the gates without manifesting external symptoms. (They don't all blow the top off) It's only the typical failures (too much current) which will "POP" the FET, other damage can be done with little indication.
shuter. Why go to all the headfork of putting in what are essentially stock FETs. Surely just go with some hot FETs and swap out a stock late model board if you want to go stock racing.
CrashTestJohnny Great synopsis. Probably one of the most succinct I've seen.
Can I use this for a tech article (pm me with credit info).

Last edited by BryceVR; 2007.12.18 at 01:17 AM.
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Old 2007.12.18, 10:42 PM   #9
shuter
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BryceVR - Thanks for the information about how fets fail and clairification of their visual condition. I have had a fet stop working and could see no visual irregularities. I have not yet tried Crash Test Johnnys test procedure but may do soon soon. I bought the mini alagator clips needed to make the test connectors but am not very motivated to test as we lost our track location. One of the guys here has set up my track and lap counter in his basement but nobody is interested in racing much. Very small town. His basement is not quite big enough to run HFAY track layouts and there is little interest to continue racing here. Headfork?

I was interested in replacing everyone's 3004 fets with 3010 fets because 3010's had become the new HFAY Stock standard and are a clear a performance increase. When coupled with an MA-010 motor there is a substantial performance improvement over a MR-02 stock motor and 3004 fets. I have cars with higher capacity fets and more powerful motors but do not have the driving skills to make use of them.

New boards are roughly $100.00. Replacing fets is inexpensive.

You may not have noticed but this is an old thread. You have, however, advanced the ball and I appreciate the information.
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Old 2008.09.07, 01:35 PM   #10
marc
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It would be cool if somebody could invent snap-on FETS for those none-soldering kind of people.
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Old 2015.02.25, 09:15 AM   #11
Jshwaa
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Quote:
Originally Posted by shuter View Post
I have some 3010 fets that I installed on a board, discovered that the board did not work, removed the fets and reinstalled another pair. I am wondering whether the fets are still good or if I shorted them out. Is there a way to test them with a multi meter to see if they are good or not? Would hate to just throw them away but would hate even more installing them on another board only to find they are no good.
*Disclaimer - This method is for experienced users of electrical equipment such as a power supply and knowledge of measurement techniques such as current measurements with a multimeter, do not do this is you have little or no experience in either, or of course, do no have the proper equipment. You could possibly make your FET situation worse or destroy perfectly good FETs.*

A proper test for the installation of FET's or integrity of existing FET's, is to set up a little circuit such as the one below. Of course you can just throw cells in your car and see if the motor runs in forward or reverse, but if not properly tested first, a bad FET installation could unnecessarily destroy the FETs and/or your mini-z elecs, so if done right this procedure can save you that outcome.



1) Set the power supply to 4.8V and 0.1A max current.

2) Power up, and while monitoring current, throttle 'half-way' in forward and reverse. Do not full throttle, as you will draw max current and the voltage will drop and the elecs will shut off. Only throttle as long as it takes you to verify a current reading. If you get a current reading that is near the power supply current setting, then so far so good.

3) Feel FETs for heat. If you feel heat, wait for it to dissipate before continuing. If you feel abnormal heat or the FET's start to blister, then obviously stop as you've reached your answer...the FET's are in failure mode.

3) Increase current by 0.1A.

4) Repeat 2 through 4 until you reach 2A.

If your elecs responded by drawing current through each step, then they should be good. For those of you that would like to push them to the max, then keep repeating the current increments as far as you feel your FETs should handle, while maintaining the 4.8V. Most power supplies can't do what good cells can do in this regard, so don't feel bad if your 'bench' power supply doesn't fit the bill for this procedure, AND DON'T DO THIS WITH CELLS AS THEY ARE UNFORGIVING IN SHORT CIRCUIT SITUATIONS.

Last edited by Jshwaa; 2015.02.25 at 07:17 PM.
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Old 2015.02.25, 10:17 AM   #12
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For less than a dollar a pop on some electronics sites... better just to buy new fets than to bother testing anything or re-using possible faulty ones.

JMO

Just ordered 25 for around 82 cents each.
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Last edited by imxlr8ed; 2015.02.25 at 10:50 AM.
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Old 2015.02.25, 10:35 AM   #13
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Quote:
Originally Posted by Jshwaa View Post
*Disclaimer - This method is for experienced users of electrical equipment such as a power supply and knowledge of measurement techniques such as current measurements with a multimeter, do not do this is you have little or no experience in either, or of course, do no have the proper equipment. You could possibly make your FET situation worse or destroy perfectly good FETs.*

A proper test for the installation of FET's or integrity of existing FET's, is to set up a little circuit such as the one below. Of course you can just throw cells in your car and see if the motor runs in forward or reverse, but if not properly tested first, a bad FET installation could unnecessarily destroy the FETs and/or your mini-z elecs, so if done right this procedure can save you that outcome.



1) Set the power supply to 4.8V and 0.1A max current.

2) Power up, and while monitoring current, throttle 'half-way' in forward and reverse. Do not full throttle, as you will draw max current and the voltage will drop and the elecs will shut off. Only throttle as long as it takes you to verify a current reading. If you get a current reading that is near the power supply current setting, then so far so good.

3) Feel FETs for heat. If you feel heat, wait for it to dissipate before continuing. If you feel abnormal heat or the FET's start to blister, then obviously stop as you've reached your answer...the FET's are in failure mode.

3) Increase current by 0.1A.

4) Repeat 2 through 4 until you reach 2A.

If your elecs responded by drawing current through each step, then they should be good. For those of you that would like to push them to the max, then keep repeating the current increments as far as your power supply will take you, while maintaining the 4.8V. Most power supplies can't do what good cells can do in this regard, so don't feel bad if your 'bench' power supply doesn't fit the bill for this procedure, AND DON'T DO THIS WITH CELLS AS THEY ARE UNFORGIVING IN SHORT CIRCUIT SITUATIONS.
I'm sorry but this must be the DUMBEST commentary I have ever read.
First off, nobody except the real electronics geeks have an adjustable power supply.
Secondly, suggesting to make a deliberate shortage is like saying get a lighter to see if you still have gas in your car...
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Old 2015.02.25, 10:44 AM   #14
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Quote:
Originally Posted by LED View Post
I'm sorry but this must be the DUMBEST commentary I have ever read.
First off, nobody except the real electronics geeks have an adjustable power supply.
Secondly, suggesting to make a deliberate shortage is like saying get a lighter to see if you still have gas in your car...
Whoa, take it easy. Adjustable power supplies aren't rare by any means, and that is the reason for the adjustability, so you set a max current. No matter what, your elecs will only draw up to that setting. Nothing to worry about. The dumb part would be to not heed the disclaimer, and especially to attempt a FET surgery and test by way of roulette.

So, there are no electronics geeks that are into RC cars? I beg to differ, but I'm not here to argue or trash other people's input either, so...

Put a lighter to your car all you want, but doing so would suggest a lack of sanity on your own part or taking what was posted completely wrong on purpose. If you have a better way of testing FETs in the mini-z application I'm all ears, sir.
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Old 2015.02.25, 10:58 AM   #15
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I like your posts Jshwaa... very in depth and you're pushing things in your own way. But yes, for most of us it is a bit too much to set up a whole test rig for testing fets.

Keep pushing it though! It was nice to see an ocilliscope plot the output signal from a fet... that was a first in my book!
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