Electronics question

[fatelk]

I have a question about capacitors, and my electronics training is rusty.

I have a 15 year old AC unit that gave up the ghost, and I've determined that the problem is the capacitor. The problem is in finding a replacement capacitor. This one is a dual run 50+6 uF. I can find plenty of 50+5 uF, and lots of 50+7.5 uF, but none the same size.

From the little bit of research I did, it appears that it may be important to replace a run cap with the exact same size. Anyone here know if that's true, and where to look for what seems to be a somewhat odd-sized cap?


Added: I just realized that maybe a more appropriate place for this would have been off-topic, if a moderator chooses to move it?

[elmacgyver0]

I have a dehumidifier that the cap went bad, measured 1uf and should have been 15uf. Temporary replaced with a 7.5 and it ran fine, I replaced it with a 15uf after I acquired one from E bay.
I would think either would work but I would go with the 50+7.5uf.
You could go with 2 separate caps a 50uf and a 6uf.
What ever you use make sure it can handle the voltage, you cannot substitute with a lower voltage capacitor.

[osteodoc08]

How bad is the original nomenclature on the capacitor? 50/6 microfarad is not a normal industrial standard. Are you sure it’s not 50/5? Your fan restart capacitors are usually 5 microfard on you smaller (<3 ton units)

[rancher1913]

you need to look at why it failed as well, usually when a fridge cap goes out it is because the compressor is going bad and is struggling to go, we would replace the old capacitor with a hard start one and get another year out of the fridge.

[Hossfly]

50/7 will work. Till something else happens.

[popper]

50+7.5 uF. It will work fine. One is for the compressor, one for the fan. Often a larger start cap will compensate for long lines (& V drop). They go bad due to HEAT and use. They are electrolytic and dry out. Not cheap, mostly made NOT in the US. Check the outside fan also, oil it (even if non-lube type). Often they plug the oil ports, looks like a rivet.

[fatelk]

Here's what happened: I noticed a squeak in the fan motor last year, and this year it was worse and the fan started bogging. I took it apart and replaced the motor bearings (the outside bearing was really bad). I just happened to have the right size bearings sitting on my work bench from when I replaced the bearing in my old Midway 1288 tumbler.

It ran perfect for a couple weeks, until it tripped the breaker in the power strip it was plugged into. I reset it and the fan would not start; it just hummed. I took it apart and found this:

243963243964

Yes, I know; I have a hard time replacing things. I hate spending the money if I don't have to. I've had that old Midway 1288 for a very long time (bought it new). We drive 20+ year old cars with 250,000+ miles on them. A new 10k BTU AC unit isn't very expensive, so I'll scrap this one and buy a new one if I have to, but I like to see if I can fix it if I can. I work on much larger "air conditioning" machines at work, of a little different nature. They get the air so cold we haul it away in tanker trucks. :)

[popper]

Start & run caps on an AC motor. Motor hums, does't turn bad cap.

[skeettx]

Like this one?
https://www.amazon.com/TEMCo-Motor-Capacitor-RC0015-50-Electric/dp/B00FBRWUP0/ref=sr_1_1?gclid=Cj0KCQjwo7foBRD8ARIsAHTy2wlEYL0Sy kQHRFBkRUTJk99R4FYQJns11olQq3YT_B3xRFTdUHv9_XsaAma cEALw_wcB&hvadid=198209184875&hvdev=c&hvlocphy=1026182&hvnetw=g&hvpos=1t1&hvqmt=e&hvrand=2758080921889865205&hvtargid=kwd-324798141069&hydadcr=954_9642223&keywords=capacitor+cbb65a-1&qid=1561238320&s=gateway&sr=8-1

And these are listed on the BAY

Air Conditioner CBB65A-1 50uF 50/60Hz Motor Run Capacitor DT

for $5.50 and free shipping

[fatelk]

Like this one?
https://www.amazon.com/TEMCo-Motor-Capacitor-RC0015-50-Electric/dp/B00FBRWUP0/ref=sr_1_1?gclid=Cj0KCQjwo7foBRD8ARIsAHTy2wlEYL0Sy kQHRFBkRUTJk99R4FYQJns11olQq3YT_B3xRFTdUHv9_XsaAma cEALw_wcB&hvadid=198209184875&hvdev=c&hvlocphy=1026182&hvnetw=g&hvpos=1t1&hvqmt=e&hvrand=2758080921889865205&hvtargid=kwd-324798141069&hydadcr=954_9642223&keywords=capacitor+cbb65a-1&qid=1561238320&s=gateway&sr=8-1

And these are listed on the BAY

Air Conditioner CBB65A-1 50uF 50/60Hz Motor Run Capacitor DT

for $5.50 and free shipping

That’s half of it. The one I need is a dual-run, with three terminals. I could use that one along with a cheap 6uF cap for the fan motor, if need be, but if you all are pretty sure it will be fine I think I’ll just order one of the 50/7.5uF dual run caps.

[fatelk]

At first I did a search using that model number, thought I’d come up with the exact part, but apparently that number doesn’t mean much.

[KenH]

Voltage rating on the capacitor is important also - be sure the rated voltage is equal to or more than listed on original cap. A couple µF extra won't hurt anything.

[WebMonkey]

+1 on 1.5 extra uf won't hurt a thing.

:)
Good luck

[MaryB]

the extra 1.5uf is within tolerance of those cheap caps...

[NyFirefighter357]

+1 on 1.5 extra uf won't hurt a thing.

:)
Good luck

You can always go a little larger even a little smaller but always better to go larger than smaller. As smaller will tax the cap but if will work in an "emergency." If that's the original 14 years is about normal for them to blow.

[jsizemore]

Nothing says you can't use 2 separate caps. I've done it many times in home systems. Use a jumper from the supply to the additional cap. Pipe strap and a couple of self tapping or piercing screws will do the trick.

I'd do this before changing cap values beyond the tolerance range listed on the cap.

[popper]

As my AC went out on Sat, Granger was the only source. ~50$, installed in 15 min. and up and COOL. IIRC a company in Fl bought the tooling from Mallory and is the only US manufacturer.

[AZBronco]

I have to add to the conversation above, you can only trust a made in mexico or made in USA run capacitor,with USA cap 1st choice. I work in the A.C. field and know many other companies that remove the asian capacitors from any new equipment they sell before they power it up !!! I have had these asian capacitors fail in service in less than 15 minutes.

[fatelk]

Nothing says you can't use 2 separate caps. I've done it many times in home systems. Use a jumper from the supply to the additional cap. Pipe strap and a couple of self tapping or piercing screws will do the trick.

I'd do this before changing cap values beyond the tolerance range listed on the cap.

I did a little reading on the subject, on a couple HVAC forums, and found a couple people who said that you shouldn't go over the spec rating for motor run caps or eventually the motor would burn up, then others said there was more of a margin for safety and they'd done it without trouble.

So, I've got a dual run cap in my Amazon cart, a 50+7.5uF (made in Mexico) that fit's in every way except the 7.5uF. It's only $18 and fits right in the same hole the old one came out of, plug and play. Or I could go the other route and put in two separate caps. A correct 50uF is no problem to find, but I'm a little unsure what kind of 6uF cap to get. It looks like there are several types: metal, plastic, round, square.

I'm inclined to just buy the dual-run cap because it's quick, cheap, and easy, but on the other hand it's not that big of a deal to go the other way if need be. Either way, it's just an old AC. If I can get another couple years out of it all the better.

[jsizemore]

A smaller rating will handle less torque at startup and may not have enough umph to get going or stall. When running at near normal speed and under light load shift demands the higher rating will cause a bit of efficiency loss and shorten life. How long that is is anybody's guess. There's a bit of lengthy math that can tell you what those phase shifts are.

This past week I got a call on a 3 ton condensing unit. The start capacitor had blown a hole near the bottom of the phenolic case about half an inch across. Unit still functioned fine except at startup, 5 to 6 times per hour, the cap would discharge through the hole to the units ground wire 3" away. Sounded like a high velocity 22lr going off. The home owner was looking at the unit out a window from just above while his wife started it up the previous night. He said he almost hit his head on the window and he was glad he was in the bathroom. Even in full daylight it was spectacular.

No matter how long your in the business, there's always something to surprise you.

[fatelk]

Thank you.

[MaryB]

Those capacitors are +- 20% tolerance. So 1.2uf on the 6uf meaning it could actually be as low as 4.8uf and as high as 7.2uf...

[fatelk]

On this one it says ±5%

[tinsnips]

I do this for a living so, you can use a bigger one with no problem . Capacitors just get weak with time, an the new ones are not as good as the old ones. Good luck.

[tinsnips]

I forgot to mention the 50 is for the compressor an the 6 is for the condenser fan motor.

[fatelk]

Thanks again everyone. I ordered the easy one. I appreciate everyone's input. I have a degree in electronics but I've never worked in the field. School doesn't mean much compared to actual experience. Not much at all actually. I wasn't meaning to challenge or question anyone, just want to make sure I understand and get it right. I'll let you all know how it runs when I get it back together.

[starbits]

My AC went out Saturday morning. Capacitor for the fan motor needed replacing and after half and hour the fan motor was starting to release that magic smoke. New fan motor and everything is cool.

[NyFirefighter357]

Everything you need to know about caps,

Choosing A New Capacitor For Your Air Conditioner
https://youtu.be/4eQqdxqUKnM

Replacing a Motor Start Capacitor
https://youtu.be/4k4c998kLKc

Start Capacitors & Run Capacitors for Electric Motors
https://youtu.be/OMd9QkinXz4

Start Capacitor Bleed Down Resistors
https://youtu.be/9xzvfsaGKKw

[fatelk]

Just thought I'd let you all know, I put the new cap in and the AC is now working very well!

[osteodoc08]

Excellent! Had to do the same thing a few weeks ago for mine.