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Capacitor mF vs. uF confusion when replacing

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GTEK

Nov 24, 2022
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I'm working on a 3/4 Hp water pump. It runs, but won't get to speed, so I suspect the capacitor is bad.

The manual says replacement capacitor is 45mF, 250V, 45 x 71 mm. However, the original installed one is a 60uF, 250V.

So, which should I purchase? Is one better than the other?

Thanks.
 

Minder

Apr 24, 2015
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The mF is misused due to the originator not using Mu .
It is the same thing.
The 60µf may have been replaced previously due to unavailability of a 45µf version.
If in doubt, maybe go with the manual, ensure you get a Motor Start rated cap.
 

GTEK

Nov 24, 2022
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I purchased the pump new, no doubt it, (the 60uF) is the original factory installed cap.

Here is a pic of the original installed one, showing it's a 60uF, however, as I mentioned previously, the manual says (when replacing), to install a 45mF. I'm wondering if the manf. determined later that 45mF would be more robust and/or reliable?

Can someone explain the difference between the two and if one would be better than the other?
 

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Minder

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The whole idea of the start cap is to give the optimum phase (~90°) shift to the start winding.
There may not be a great deal of difference, only a current check of the winding would tell.
 

Bluejets

Oct 5, 2014
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Have you had the cap tested to determine if it is at fault or not....???

Before being undecided on which may or may not be more suited, it would be the obvious place to start rather than just "assume" it is faulty
 

davenn

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Can someone explain the difference between the two and if one would be better than the other?

Minder gave you that answer earlier :)

the only difference is that one is a lower value ... 45uF rather than 60uF

It would be wise to get the 60uF one which is what was in the motor when built
 

GTEK

Nov 24, 2022
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Original installed is 60uF, which equals 0.06mF
Recommended replacement by manual is 45mF, which equals 45,000uF

From an online converter:
60 microfarad = 0.06 millifarad
• 45 millifarad = 45000 microfarad

Would seem that 45mF has much more capacitance????

Reply to Bluejets: Would love to test original cap. I have a digital multimeter, but only have basic knowledge of it's usage. (Voltage and continuity) I looked at several YT videos, but remain a bit unsure of what to set it on. (I may give it a try later). Here is a pic of my multimeter, if someone could give me a pointer or two on what to set it on to test the 60uF cap, I'd appreciate it.
 

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Minder

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At 60µf I would suspect that is a bi-polar dry electrolytic version, if so, it is a start cap only and requires a start switch in the motor or motor circuit in order to switch it out when up to speed.
They cannot be left in circuit for more than a few seconds.
If it is a non-electrolytic, the best types are oil filled-paper.
Either way, they should be replaced with motor start rated versions.
It is difficult to obtain a positive reading/value of a cap with a normal VOM, unless the cap happens to be shorted condition etc.
 

bertus

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Nov 8, 2019
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Hello,

Some old manuals use the m for micro, wich can be confusing, as nowerdays µ (mu sign) is used.

Bertus
 

GTEK

Nov 24, 2022
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Here is a picture of the wiring. If it's a "Start" cap, I don't know where the start switch would be. As mentioned, the pump motor always seems to spin up, but when the impeller is immersed in water, it seems like it doesn't get up to speed. However, having said that, occasionally it does and pumps vigorously.

It's looking like I'll have to ignore what's in the manual as I don't find one rated at 45mF that fits the space, so I'll look for something that's identical to what's currently installed. (60 uF)

I need to get this right, as it's actually a sewage pump and as you can imagine, not the most pleasant job to remove for service! I don't mind paying a bit more for a "good" one, however on Amazon there seems to be an abundance of Chinese made units. It may be that some of those are ok, but don't know how to tell.
 

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Minder

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I suggest taking the cap into a local motor rewind shop and asking them to identify it, they should also have a replacement.
Or a local electrical supplier.
For motor applications< I would steer clear of Chinese origin, these are the main cause of Chinese supplied motor failures.
 

GTEK

Nov 24, 2022
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I'm in a bit of a rural area, not too sure I can find someone locally to help, but I'll look.

Most frustrating is the fact that when trying to determine whether it's a Start or Run cap, is that looking at the specs, it says it's a Run, but then they say that most Run caps are Alum, and this one's plastic.

Also, Start caps have a MFD "range", but this one just says 60 uF, etc. I'm find contradictory info where ever I look online!

You'd also think that just searching for the exact same thing that's installed would either reveal a site that has it, or a reference to it, or something that would replace it, but so far, hours of searching got me nowhere!

Even inputting what appears to be a brand (NR) and then CBB60A 60 uF, +/-5%, 250V, 50/60 doesn't get me much.

Actually, I DO have something in my Amazon cart; it's the right specs and physical size, but it looks so cheap, I'm not sure I want to take a chance on it! Like I said, it's a sewage pump, was no fun taking it out of the sump! Don't want to have to do it again anytime soon!

It's starting to look like I'm buying a new pump! I hate to do that, as while this one is 8 years old, it really had very minimal usage, and was way overkill (All Stainless Steel, 3/4 Hp, etc.) for the anticipated usage (rarely used guest bathroom).
 

Minder

Apr 24, 2015
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For a start, the µf , mf, MFD is all the same in this context.
If the cap is in circuit all the time and connected to the start winding without any kind of disconnection means, either internal or external to the motor, then it cannot be a electrolytic, as I already stated, the most durable types for RUN caps are oil filled paper such as made by CDE Co etc.
Mouser has them, https://www.mouser.ca/c/passive-com...l Dubilier - CDE&product=Motor Run Capacitors
 

GTEK

Nov 24, 2022
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Huh? What are you talking about?????
You're not being helpful!

I see that you're a moderator. I'm surprised that you would berate someone who's struggling to understand something.

I came here seeking help; I don't expect to be "chided" for posting and discussing something that I have limited knowledge about.

That's not very "moderator" like and makes me feel like I'm not welcome at this forum. If I posted something that's incorrect, then the other participants of this thread will, I expect, patiently take the time to share their expertise and if needed, correct me.

Kindly step aside and allow the more understanding responders to guide me and help me arrive at the proper solution.

Thank you.
 

Bluejets

Oct 5, 2014
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Huh? What are you talking about?????
You're not being helpful!

I see that you're a moderator. I'm surprised that you would berate someone who's struggling to understand something.

I came here seeking help; I don't expect to be "chided" for posting and discussing something that I have limited knowledge about.

That's not very "moderator" like and makes me feel like I'm not welcome at this forum. If I posted something that's incorrect, then the other participants of this thread will, I expect, patiently take the time to share their expertise and if needed, correct me.

Kindly step aside and allow the more understanding responders to guide me and help me arrive at the proper solution.

Thank you.
It has already been explained to you on several occasions, then you go away, half read facts and come back with crazy claims.
I'd suggest you quitely retract and re read all the information above a couple of times and see if it sinks in.
 

GTEK

Nov 24, 2022
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I suggest you're mistaken. I haven't "HALF read" any facts (how do you you know how much I read????) And how is it helpful to bizarrely accuse me of making "CRAZY" claims????? That's a very strange thing to say to someone that's asking for help, not to mention very condescending!

If I posted something incorrect, show a little patience and understanding and correct me! Jeeez, what's wrong with you guys? I thought this was a HELP forum! I guess that's something else that I thought that apparently is "CRAZY"!
 

davenn

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Sep 5, 2009
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OK since you wont listen to the good info people are giving you
a number of us have tried several times to help you
Not sure as to why you will not listen to that info ??
I came here seeking help; I don't expect to be "chided" for posting and discussing something that I have limited knowledge about.

you were given the answers a number of times but you still went off with your own thoughts and
as I previously said, you continue to confuse yourself with your wrong ideas
Please review what you have been told :)

thread is closed
 
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