Why are my terminals not marked on my capacitor?

[dana198]

TL;DR

I recently purchased a capacitor for my air compressor but the terminals are not marked by any means , i have never seen that before can anyone tell me what i should do ? Does it matter ?

 

[tech99]

I think is is a bi-polar type intended for AC, so polarity does not matter.

 

[AZFIREBALL]

The marking of capacitor terminals is an antiquated practice that is no longer necessary.

Capacitor terminals at various times in the past were designated with terms such as: In and Out, Up and Down, Plus and Minus, + and -, Charge and Discharge, etc. These terms where ambiguous to the neophyte to say the least.

As you know, today’s electric bolts consist mainly of poles and holes and are much more sophisticated than they once were. They therefore, are able to decipher which terminal is which, without the need for overt designations. And due to the fact the frequency of DC is much lower today than it once was; along with today’s environmental need to always be politically correct, the terminals must be capable of being used without prejudices or discrimination.
Then again, I might be wrong.

[Humorous post deprecated by the Mentors]

 

[Baluncore]

It is a 250 VAC capacitor. It is 100 uF. It has symmetrical construction because it is for use in an AC circuit. It is not polarised and can be connected either way.

It could be the start or run capacitor for a single phase AC induction motor.
Is that the original or a replacement capacitor ?
What was the voltage rating and capacitance of the original capacitor ?
What is your supply voltage closest to; 115 VAC or 230 VAC ?
What is the HP or kW rating of the motor ?
Is there another capacitor on the motor, what specs ?

 

[Borek]

The marking of capacitor terminals is an antiquated practice that is no longer necessary.

Nope. Especially in the case of electrolytic caps it is crucial to connect them following polarity:

 

[phinds]

The marking of capacitor terminals is an antiquated practice that is no longer necessary.

Capacitor terminals at various times in the past were designated with terms such as: In and Out, Up and Down, Plus and Minus, + and -, Charge and Discharge, etc. These terms where ambiguous to the neophyte to say the least.

As you know, today’s electric bolts consist mainly of poles and holes and are much more sophisticated than they once were. They therefore, are able to decipher which terminal is which, without the need for overt designations. And due to the fact the frequency of DC is much lower today than it once was; along with today’s environmental need to always be politically correct, the terminals must be capable of being used without prejudices or discrimination.
Then again, I might be wrong.

Is this whole post supposed to be a joke?

 

[Baluncore]

Is this whole post supposed to be a joke?

Probably. Maybe written with excessive Christmas lubrication.

 

[hutchphd]

Is this whole post supposed to be a joke?

If a joke it is in the same classification as the "inject chlorox for COVID" variety. Hopefully fueled by lubrication and not dementia.
But to reiterate:

The marking of capacitor terminals is an antiquated practice that is no longer necessary.

This is completely and totally incorrect. Many modern capacitors are polarized and failure to recognize this can be disastrous.

/

 

[jrmichler]

To the OP: Your capacitor is clearly marked 250 VAC. That is the correct rating for a capacitor intended for use in a 120 volt AC application, such as a motor start or motor run capacitor. Posts #2 and #4 are correct.

To everybody who wants to be helpful: This thread is about motor capacitors. It is not a general thread on electrolytic capacitors. Please stay on topic. Also realize that the OP is clearly not an electrical engineer, so this is not an appropriate thread for EE jokes such as Post #3.

 

[Baluncore]

Your capacitor is clearly marked 250 VAC. That is the correct rating for a capacitor intended for use in a 120 volt AC application, such as a motor start or motor run capacitor.

A motor START capacitor will be rated at close to the motor voltage. A motor RUN capacitor needs to be rated for about 1.8 times the motor voltage.

 

[sysprog]

A motor START capacitor will be rated at close to the motor voltage. A motor RUN capacitor needs to be rated for about 1.8 times the motor voltage.

Why wouldn't that be the other way around?

 

[AZFIREBALL]

To the OP: Your capacitor is clearly marked 250 VAC. That is the correct rating for a capacitor intended for use in a 120 volt AC application, such as a motor start or motor run capacitor. Posts #2 and #4 are correct.

To everybody who wants to be helpful: This thread is about motor capacitors. It is not a general thread on electrolytic capacitors. Please stay on topic. Also realize that the OP is clearly not an electrical engineer, so this is not an appropriate thread for EE jokes such as Post #3.

Sorry for the injudiciousness. Too much Christmas Eggnog!

 

[Baluncore]

Why wouldn't that be the other way around?

Maybe you can explain why you think I put it backwards.

The quick way to identify a run cap is from the higher voltage rating. I believe it is because with varying loads, the run capacitor can react with the winding inductance to generate higher voltages in the series circuit.

 

[sysprog]

Maybe you can explain why you think I put it backwards.

The quick way to identify a run cap is from the higher voltage rating. I believe it is because with varying loads, the run capacitor can react with the winding inductance to generate higher voltages in the series circuit.

That makes sense to me $-$ I was thinking of initial current draw being greater on start $-$

 

[berkeman]

Is this whole post supposed to be a joke?

Yes, it has been deprecated...

 

[berkeman]

Sorry for the injudiciousness. Too much Christmas Eggnog!

You should have included the [ humor ] [ /humor ] tags...

 

[CityguyUSA]

I know the theme here has been going back and forth from lighthearted comedy to some truth. For now I'd like to focus on the truth.

I have an A/C capacitor that has no markings regarding poles and that makes sense to me. What doesn't make sense is when I reverse my multimeter test leads and get a different capacitance result.

I did notice a very light coating of oil on the exterior so I'm going to replace it although I don't see any evidence of protrusion or obvious leaking locations but am I right about getting the same result regardless of which lead is on which pole?

 

[DaveE]

I know the theme here has been going back and forth from lighthearted comedy to some truth. For now I'd like to focus on the truth.

I have an A/C capacitor that has no markings regarding poles and that makes sense to me. What doesn't make sense is when I reverse my multimeter test leads and get a different capacitance result.

I did notice a very light coating of oil on the exterior so I'm going to replace it although I don't see any evidence of protrusion or obvious leaking locations but am I right about getting the same result regardless of which lead is on which pole?

Tell us about your multimeter. I assume it has a capacitance measuring function? How much difference? What kind of capacitor?

The truth is out there... but it often requires some investigation. We aren't clairvoyant here.

But yes, theoretically there should be no polarity involved. I'm having a hard time imagining a failure mode that's polar.

There are circuits where you put two electrolytic caps back to back and pretend it's an AC cap. Which could have different values based on polarity. But I'm guessing you have a HV cap, like for a motor, where they wouldn't do that.

 

[CityguyUSA]

Of course now it's doing something different. lol This morning when I shorted the terms it read 504mfd which is what it should read. Then when I reversed the leads it was bouncing around at .9**. I wonder if I had the leads reversed initially if it would have read the same only with the reversed leads?

The cap is from a single-phase 1hp Delta (Marathon) motor. It's a York cap in an aluminum can with 2 terms incredibly hard to read. It's stamped maybe printed in black ink. SFS2450A14 0208 50 MFD 240VAC 50-60hz A-102060-3:1000AFC is what I think I read. It's a 115 volt setup so is this even the right cap or is that an upper limit on the voltage? The motor can be wired to 230v.

I just re-checked the reading the first time I got .9** and up and down and up and down but overtime dropping lower. I watched it drop to .79. When I switched the leads similarly .8** bouncing around but ultimately going lower I watched it drop into the .6**. My guess is going to 0? I switched the leads multiple times each time it seems to start lower at the lower end of the last reading.

This is the multimeter I used. Yes, it has capacitance and it's auto sensing. I haven't used it a whole lot so I don't know how accurate it is in reality but I have no reason to mistrust it anymore than anything else coming from Asia.

 

[Baluncore]

Maybe your AC capacitor is effectively built out of two DC capacitors in series. One has aged faster than the other, or become leaky, so the total capacitance has become asymmetric.

When a functional electrolytic capacitor is biased with DC, it "learns" to become a better capacitor. One of the two series capacitors becoming leaky, would explain the asymmetry.

 

[CityguyUSA]

Maybe your AC capacitor is effectively built out of two DC capacitors in series. One has aged faster than the other, or become leaky, so the total capacitance has become asymmetric.

When a functional electrolytic capacitor is biased with DC, it "learns" to become a better capacitor. One of the two series capacitors becoming leaky, would explain the asymmetry.

So it needs replaced but is this the right one for 115v/230v currrently wired for 115v?

 

[Baluncore]

So it needs replaced but is this the right one for 115v/230v currrently wired for 115v?

50μF is about the right value for a "motor start capacitor" on a single phase 1 HP motor. I guess your motor has a centrifugal switch that disconnects the start cap once running. Some motors also have a run capacitor.

Replace it with a 50μF, 230 VAC capacitor if you can find one. Otherwise, a lower voltage rating would also be OK for 115 VAC.

 

[hutchphd]

I know the theme here has been going back and forth from lighthearted comedy to some truth. For now I'd like to focus on the truth.

I have one more interesting tidbit of orienting axial foil capacitors. The outer electrode is marked. Not directly relevant here: more a high end tube amp issue.

 

[CityguyUSA]

50μF is about the right value for a "motor start capacitor" on a single phase 1 HP motor. I guess your motor has a centrifugal switch that disconnects the start cap once running. Some motors also have a run capacitor.

Replace it with a 50μF, 230 VAC capacitor if you can find one. Otherwise, a lower voltage rating would also be OK for 115 VAC.

I have 2 capacitors. I assumed this was the run capacitor because it was dogging while cutting but it seems to start ok. The other capacitor is 340-408 mfd 115v.

 

[Baluncore]

I have 2 capacitors. I assumed this was the run capacitor because it was dogging while cutting but it seems to start ok. The other capacitor is 340-408 mfd 115v.

You are probably right, the big one is the starter. The higher voltage is usually a run capacitor.
Replace the faulty capacitor.
If that does not fix it, trace out the wiring diagram, including the motor windings and centrifugal switch. Then we can analyse the problem more deeply.

 

[CityguyUSA]

You are probably right, the big one is the starter. The higher voltage is usually a run capacitor.
Replace the faulty capacitor.
If that does not fix it, trace out the wiring diagram, including the motor windings and centrifugal switch. Then we can analyse the problem more deeply.

Thanks