Capacitor testing

Reply

  #1  
Old 11-30-19, 09:10 AM
Member
Thread Starter
Join Date: Nov 2019
Posts: 29
Received 0 Votes on 0 Posts
Capacitor testing

Hi everyone. I pulled 2 200v 1,000mfd capacitors from an ecm control module for a furnace blower.
the blower would only spin slowly back and forth before the system cut it off for not getting to 250rpm. I replaced the module entirely and the blower works therefore I know the module I had was bad. So now I want to isolate the issue and hopefully have it as a backup

the replaced the icl (thermistor) which is known to go bad on theses units with no luck. So now I am focussing on the capacitors. Visually tge board has no burns and capacitors are not bulging. I do not have a capacitance tester but a ran a test with applying ohms to the leads and not capacities counted to infinity. I also tested voltage at that point and the showed voltage

my question is can they pass these tests and still be bad? Is it possible they may not have the 1000mfd? I could pick up a tester but donít want to spend the money if the capacitors are ok

 
Sponsored Links
  #2  
Old 11-30-19, 11:33 AM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 6,877
Received 96 Votes on 88 Posts
With a analog mater you can measure across the capacitor see the needle slowly go down as the cap charges. Reverse the leads watch the action again. Do the same test on the working unit and see if the reactions are the same.
 
  #3  
Old 11-30-19, 11:40 AM
Member
Join Date: Oct 2005
Location: USA
Posts: 1,391
Received 12 Votes on 12 Posts
Out of the circuit RC time constant should work. All u need is a resistor of about 1000 ohms and a dc voltmeter and a stopwatch.
 
  #4  
Old 11-30-19, 01:44 PM
Member
Thread Starter
Join Date: Nov 2019
Posts: 29
Received 0 Votes on 0 Posts
Thanks for the suggestions

I am not sure I completely understand. So I would set the
multimeter to ohms and connect the leads to see if the ohm go up to Io infinite .... do I discharge the capacitor and do the same again with the leads reversed ?

 
  #5  
Old 11-30-19, 01:55 PM
Member
Join Date: Sep 2019
Location: Canada
Posts: 487
Received 45 Votes on 43 Posts
Yes capacitors can be bad even though they pass a meter test because you are not applying the working voltage to them.
 
  #6  
Old 11-30-19, 02:11 PM
Member
Thread Starter
Join Date: Nov 2019
Posts: 29
Received 0 Votes on 0 Posts
What if it passes a capacitance test ? Ie reads close to 1000mcf?

I just do t want to go through the hassle of ordering capacitors if I donít need them
 
  #7  
Old 11-30-19, 02:26 PM
Member
Join Date: Sep 2019
Location: Canada
Posts: 487
Received 45 Votes on 43 Posts
I understand but you cannot be sure that they are 100% OK.

Odds are high that they are OK.

Caps are just foil with an dielectic (insulator) between the layers and a charge builds up between the foil layers.
If the dielectric fails then charge can jump the layers.
So you may be able to put 10 volts on it with no problem but it may fail when lets say 100 volts is applied.
 
  #8  
Old 11-30-19, 02:43 PM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 6,877
Received 96 Votes on 88 Posts
do I discharge the capacitor and do the same again with the leads reversed ?
No just reverse the leads. The bit of charge from the first test move the needle and it will slowly go down as it discharges. If you do it with the cap still on the board, you can do it to the working and non working broads and compare the results. If the results appear the same likely not a cap issue.
 
  #9  
Old 11-30-19, 03:05 PM
Member
Thread Starter
Join Date: Nov 2019
Posts: 29
Received 0 Votes on 0 Posts
Thanks everybody

I will try the test of reversing the leads

I will also try to borrow a capacitance tester to test the 1000mcf

the capacitors look Pristine but when I removed one I noticed a burn mark under the solder on the board contact? Perhaps I burned it my during the de soldered process ?

i also do understand that the capacitor may perform differently when 110 volts are applied. Not sure how I would ever know that though?
 
  #10  
Old 12-01-19, 06:44 AM
Member
Thread Starter
Join Date: Nov 2019
Posts: 29
Received 0 Votes on 0 Posts
I tried it using the ohms setting with a multimeter. It slowly went up to 199 the 1 and then I reversed the leads and it counted up from -40 . It tested the same way on both capacitors out of circuit

given the both tested this way and both look ok I am assuming they are both good? What are the odds of both being bad?

after this I canít really do anything with the module as the rest of the unit is encased in a silicone material

like I said I changed out the thermistor and it still didnít work and the old thermistor tested fine out of circuit. Not sure what else is not working on the board. It sends power to the blower windings but not enough to fire it up to speed...just sputters
 
  #11  
Old 12-01-19, 08:43 PM
Member
Join Date: Apr 2014
Location: us
Posts: 643
Received 9 Votes on 9 Posts
The old way to test electrolytic capacitors was with analog meter set at resistance scale of 100,000 ohms or more.

Attach negative meter lead to cap negative. While watching meter, connect meter positive probe to cap positive. Meter needle should swing nearly fill scale to toward zero ohms, then slowly climb back to a 10,000 ohms or more.

If needle stops at some value before 10,000 ohms it is probably going bad.

I just did this with 560 mfd 250 volt cap and Micronta meter. Needle took nearly 30 seconds to reach 10,000 ohms. Caps of 1,000 mfd or more can take much longer.
 
  #12  
Old 12-02-19, 02:28 PM
Sn3akyP3t3's Avatar
Member
Join Date: Aug 2019
Location: United States
Posts: 14
Received 0 Votes on 0 Posts
I've found the Blue ESR as an invaluable tool for debugging bad circuit components including capacitors as well as batteries. Not cheap, but worth it if there is a constant need to fix electronics otherwise destined for the landfill! https://anatekinstruments.com/produc...esr-meter-besr
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: