70 and 80 uF 250 VAC Caps

[SolomonMan]

All,
On the work Bench today are two Compressors from my past that have been sitting in corner of the Pole Barn for years.

The Craftsman one turned out to be a Pressure Switch Replacement.

The other one, a Harbor Freight stand up Oil Filled unit, from the Mid to late 2000's(prior to 2010).

Anyways, from memory this unit was having issue starting up. I replaced the oil in the unit back and I also confirmed the pressure switch was ok but I was getting to the point of turning it on and off to get it start/run. Finally it just stopped starting. I threw it in the corner of garage until we moved to consider just utilizing the 30 Gallon Tank for other endeavors. The Oil Filler motor easily turns by hand and still does even today.

So I started digging in to the unit today to find the below (see attached image)

Believe it or not there is no burnt smell in the windings or even coming from the capacitor. There is a slight smell to the white capacitor but its not a burnt smell. I am going to do a ohm reading across the Windings (seen a couple you tube videos describing the process to confirm something else is not awry.

Looks like the white one (70uF) may have been the Starting Capacitor one based on the issue experienced and the mess it is now? The Black (80uF) the running one? But I always thought Running Capacitors were always smaller Farad-wise?

My questions are around the replacement approach. Both will be replaced. The black one actually has a popped plastic top (hard to see). It appears that many of the possible replacements (Farad-wise) are 370 or 440 Volts and the originals were 250 Volts.

I have been told in the past (smaller capacitors) that you can increase a voltage on a Capacitor without much harm assuming the Farads are the same. Is this true on these larger Capacitors?

Are there any brands that are better than others for these larger Capacitors? The originals were AOLEI.

I have looked at EBay, Amazon, and Grainger are there any other suggested locations?

Thanks for the help,
Chris

[redwire]

Re: 70 and 80 uF 250 VAC Caps

There is no penalty using a higher voltage start or run capacitor, other than physical size, getting it to fit. There are industry standard case sizes for them as well. Motor caps fail from either voltage spikes or internal heating of the dielectric, or it dries out if it's the electrolytic type.
250VAC seems low and a bit cheap.

The chinese have taken over manufacturing motor capacitors, so it's good to know the different types they offer. Two common series:
CBB60: Metallized polypropylene film for start and run applications. Lower current rating than oil-filled.
CBB65: Oil-filled metallized polypropylene film, for heavy duty run applications. But bigger size.

The difference between a motor start and run cap is their ripple current rating, the cap's heat dissipation. An oil-filled cap can take high run currents all the time. For starting it's only short-term the cap sees current, so the polypropylene film caps are enough.
I don't use the uF value to see if it's run or start, I use the motor's HP rating.
I think a higher voltage part would last for your compressor.

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

Redwire,
Would the below be a ok replacement (Assuming it fits - The way its arranged is they both sit in a tray))?

https://www.amazon.com/gp/product/B0...D5SSPDPR&psc=1

There is a similar 80uF unit as well.

Thanks,
Chris

[redwire]

Re: 70 and 80 uF 250 VAC Caps

That is a dual capacitor, in one can: 70uF (compressor) plus a 5uF (fan) 440VAC typically for an air-conditioner. You can use just the 70uF terminal and ignore the third 5uF terminal, if you wanted to get it on the cheap as it's only used for a few models, not a generic part.

You can search Amazon "CBB65 80uF" to find an oil-filled run cap, or "CBB60 70uF" for the originals.

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

RedWire,
Again thanks for the response!

I follow on what you are saying on the dual capacitor. Also, to be honest, if I want to make this a quick swap out then those are slightly wider than what should be purchased.

I went looking at this unit a little more and it appears that the Capacitors may have actually had a mounting bolt on the end of the capacitor that fed thru a plastic "case"/base. I have a attached a pic to be clearer. The base is around 4X4 inches square.

As such, something like the below would work for the 70uF. The 80uF is a little harder to locate with a bolt in the end for mounting (fixed mounting).

https://www.amazon.com/250VAC-Capaci...%2C205&sr=8-58

As you said the Oil-filled metallized are heavy duty, I would like to get those type as this is a tool. I have a tendency to depend on my tools and who knows what may be thrown at it in the future. (Constant work - by me doubtful, the other compressor is being given to my brother in law (no compressor) so who knows. Not to mention I have two larger compressors.)

With that said I am trying confirm how the wiring works on this thing and how to test the windings. I would hate to invest $30 to find out its just toast to begin with.

Some Rambling/Questions for this project (My Novice Electronic experience) ,

Also I am trying to understand the reason for the capacitors. I have included a pic I found online. I am not sure if this thing is wired similar but my guess is it is somewhat similar.

It appears looking at the diagram that there are two set of windings. The capacitors - one is in series with the winding and the other in parallel.

I am assuming the capacitors are in the circuit for power conditioning and decoupling but I am kind lost on the whole parallel and series setup (at least with the included diagram). I not sure on the lower wire 100%.

Also how that works in the what I am seeing in this scenario (included image/this compressor). The actual wiring...I probably just need to sit down and study/dissect/draw it out.

I believe, from research, the Capacitors are used for Phase Shifting and as such this allows the motor to start. The degree of Phase Shift is Ideal, I believe, around maybe 90 degrees and the Capacitors/circuit setup are used to "tune" the degree differences for better motor performance.

With this theory, I assume that over time Capacitors start to fail (heat, time, resistance, etc) which throws this degree of Phase Shift off and makes it harder to start/spin the motor? My original problem?

My worry is burnt windings. I figure that is the ender of this project. As there is a heat protection mechanism involved in this compressor. I would think it would be difficult to burn the windings. At least that is my hope

Thanks for the help,
Chris

[Per Hansson]

Re: 70 and 80 uF 250 VAC Caps

Also I am trying to understand the reason for the capacitors. I have included a pic I found online. I am not sure if this thing is wired similar but my guess is it is somewhat similar.

It appears looking at the diagram that there are two set of windings. The capacitors - one is in series with the winding and the other in parallel.

I am assuming the capacitors are in the circuit for power conditioning and decoupling but I am kind lost on the whole parallel and series setup (at least with the included diagram). I not sure on the lower wire 100%.

In general you can consider most induction motors (asynchronous motors) as being 3-phase.
The reason is you need a rotating magnetic field to turn the motor around, and this will not exist with a single phase system.
To get around that you use a capacitor to create a virtual third phase that is out of phase with the others in a single phase system.
The start capacitor, if it exists is taken out of circuit by a centrifugal switch inside the motor that disconnects when it comes up to speed.
However it does not make sense that it would have the same rating as the run capacitor: normally it would need to be 2 to 3 times larger...
So please verify your circuit, perhaps the capacitors are really in parallel and used only as a run capacitor with a total rating of 150uF?

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

In general you can consider most induction motors (asynchronous motors) as being 3-phase.
The reason is you need a rotating magnetic field to turn the motor around, and this will not exist with a single phase system.
To get around that you use a capacitor to create a virtual third phase that is out of phase with the others.
The start capacitor, if it exists is taken out of circuit by a centrifugal switch inside the motor that disconnects when it comes up to speed.
However it does not make sense that it would have the same rating as the run capacitor: normally it would need to be 2 to 3 times larger...
So please verify your circuit, perhaps the capacitors are really in parallel and used only as a run capacitor with a total rating of 150uF?

Thanks for the reply!

Agreed, on the need for verification of circuit. Unfortunately my time lately has been between large projects. 10 or 15 minute windows. Hopefully today (weekend) I will get some sit down time on it.

Also I need to locate the Model of Compressor and see if I can locate a wiring schematic. The wiring for this seems to be hidden somewhat in the electric Motor. Meaning the Wires seem to come out of the motor only. For example the overload circuit wires just come out the top of the motor. Likewise for the Capacitor wiring (Bottom).

Another thing it appears Harbor Freight may carry parts for some of there compressors. My feeling this thing is to old for that approach but who knows.

Lets say its in parallel (150uF). From what I can gather online the Phase Shifting is still involved (Capacitor). Its probably simpler to buy the Capacitors as two components (for wiring it up). Could I also buy it in a single Capacitor? Would there be any advantage to the single capacitor Approach?

I guess the question, curiosity, also floating around in my head, Why are there all these different types of Electric Motors. Why are there ones with a Single Capacitor versus a Start/Run Capacitor(2 capacitor) setup? I assume there are advantages and disadvantages for each...but in these two scenarios can anyone elaborate on what they may be?

Thanks again for the help!
Chris

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

All,
Update of Sorts...
Awaiting the Order on the Caps to Arrive from Amazon they say this week possibly by Wednesday.

Ended up with two Sydien Cylindrical CBB65 Caps. They are aluminum housed and of the proper Farad and dimensional size.

With a little luck maybe this weekend to reassemble.

Thanks everyone I will let everyone know the outcome.
Chris

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

All,
The Harbor Freight unit is up and running. I believe the Capacitors were in Parallel but honestly the capacitors came quickly and I got "put" on another family chore (Car issue - Fuel and brake line rot). So I really did not get much chance to verify the circuit how I wanted. I may get under the "hood" again as I have to add a 15 amp thermal protector yet.

I say it was probably in parallel as I ended up working on the Craftsman initially as it ended up not being the pressure switch but actually the Starting Capacitor. The Craftsman had a 480uF Starting and 40uF Running capacitor arrangement. The unit also had a bad leak at the regulator which did not allow the pressure switch to disengage. So the pressure regulator was involved just it did not need replacing. I have since corrected the leak.

The Craftsman unit also had a centrifugal switch. I did not see a switch in the Harbor Freight unit. This Craftsman switch as mentioned before in fact was also of issue as it was not "aligned" correctly to the shaft mechanism. the screws to the "capacitor and Switch "Cage" had cracked (previous owners attempt to fix). A couple of Tie Straps (good measure) and screws (now with washers) corrected the alignment issue. I have filled, drained, and refilled it at least a half a dozen times and it no longer blows fuses etc.

I still need to get a few odds and ends for each unit but both will be very useful once again as they once were previously.

All thanks for the help/consideration!
Chris

[SolomonMan]

Re: 70 and 80 uF 250 VAC Caps

All,
Almost 2 months later everything has ran as it should on both compressors.

I would like to thank everyone who helped with these projects!

Again Thanks,
Chris