Tale of two start capacitors. Why is the US-made one so much smaller?

[Banjorear]

The start capacitor went out on one of my AC units. Thankfully, I had a spare in my stash. Capacitor is 45+5 mfd and rated for 440/370 vac.

The one in my stash was made by Titan Pro in China. I picked up another one to replace the one I used in case I need it later on. The new replacement is a Titan HD and made in the USA. Same rating as the Chinese unit, but it's overall much smaller.

Can anyone shed some light on why there is such a difference in size between the two capacitors? Thanks,

 

[Jack_K]

Capacitors do vary in size depending on the manufacturer and exact model number.

They may or may not have different current ratings.

 

[john.k]

Rare earth capacitors can be tiny with big capacity

 

[rlitman]

Manufacturers usually have a smaller inventory of cases than they have of cap values. It's entirely possible that it just happened to be the largest value cap in the USA made case, but the smallest value cap in the China made case, but without the rest of the lineup to compare, and without ripping them apart, it's difficult to draw a solid conclusion.

 

[Dagny]

Actually those are run capacitors. However they do play the role of starting an air conditioner and are left in the circuit all the time.

 

[mm08822]

I've always seen the higher voltage rated caps having bigger cans. Not the case here!

I'm going with @rlitman 's thinking.

 

[cgrutt]

Same spec made in different facilities could just be how tooling in facility was configured. Film windings may be short and wide in one but long and narrow in the other. Could have different oil contents. One is made in China the other is made in USA. Either one will work if it fits in your bracket

 

[Lassen Forge]

All about Technology... old school took more size to do what modern tech. materials can do in a mush smaller package.

 

[mike93lx]

I bet it's just the can sizes available for each manufacturing site and the best balance of cost.

 

[Banjorear]

Thanks, all. The difference was significant enough to make me do a double take and question the specs/labeling.

 

[fitter30]

Shape and size of the same uf or voltage doesn't make one better than the other. Manufacturers use smaller caps to fit in a tight electrical space so you have to go back to them for a replacement. A 440 vac one can be used on a lower voltage . Lower voltage can't be used for a higher voltage. Having a spare caps for compressor / condenser fan, furnace fan and condenser contact. Put them by your furnace so you know where they are.

 

[mm08822]

Shape and size of the same uf or voltage doesn't make one better than the other. Manufacturers use smaller caps to fit in a tight electrical space so you have to go back to them for a replacement. A 440 vac one can be used on a lower voltage . Lower voltage can't be used for a higher voltage. Having a spare caps for compressor / condenser fan, furnace fan and condenser contact. Put them by your furnace so you know where they are.

Biggest PIA is when the original mounting hardware can't accommodate the replacement due to size differences.......a few cable ties fix that.

Even 2 single caps (each of the correct value) is a reasonable repair when parts are otherwise scarce and getting back online is the priority.

 

[mike93lx]

Even 2 single caps (each of the correct value) is a reasonable repair

What do you mean by this? Two 20's in place of a 40?

What happens if you use a bigger one?

 

[mm08822]

What do you mean by this? Two 20's in place of a 40?

What happens if you use a bigger one?

I meant using a 45mfd and a 5mfd....2 separate caps.

Another possibility is
Two caps in parallel could also be used in a pinch....20 paralled with 25mfd to make the 45. Would still need the separate 5mfd.

A bigger cap than required would increase the current within the motor, possibly overheat, shorten life.

 

[mike93lx]

I meant using a 45mfd and a 5mfd....2 separate caps.

Another possibility is
Two caps in parallel could also be used in a pinch....20 paralled with 25mfd to make the 45. Would still need the separate 5mfd.

A bigger cap than required would increase the current within the motor, possibly overheat, shorten life.

Got it, thanks

 

[Dagny]

The capacitor I have sold the most of in my life is a 590 to 708 mfd in 125 volt almost all were on larger 240v motors. They are wired 2 in series then parallel 4 total. I have done some very interesting combinations over the years to get something going. Farmers like that.

 

[bonneyman]

Not to sound old but I remember run capacitors for compressors that were rated at 45mf/440v - yet were the size of 1 pound coffee cans! Of course, caps failing in those days were rare.

 

[rharman]

Just went through this last week with a run capacitor for my A/C. Amazon had the right electrical specs but the physical size was wrong - too small diameter. It was noted in several comments/reviews. So, I asked Amazon AI "Do you have the same thing in 1-3/4" diameter?" It came back and said "Why, yes! Here's one that meets that spec exactly. It's an exact replacement for Rheem **-xxxxxx-** and <some others>."

The Rheem # is just what I was looking for. Fit perfectly but didn't fix my problem. New control board on order. Ugh!

 

[Banjorear]

Interesting comments, fellas. The more I think about it, the smaller diameter could be an issue. I do like that the new, smaller one is made in the USA though

 

[dscheidt]

Interesting comments, fellas. The more I think about it, the smaller diameter could be an issue. I do like that the new, smaller one is made in the USA though

Too small is a lot easier to deal with than too big. Caps have gotten smaller as technology improves.

 

[cgrutt]

Just went through this last week with a run capacitor for my A/C. Amazon had the right electrical specs but the physical size was wrong - too small diameter. It was noted in several comments/reviews. So, I asked Amazon AI "Do you have the same thing in 1-3/4" diameter?" It came back and said "Why, yes! Here's one that meets that spec exactly. It's an exact replacement for Rheem **-xxxxxx-** and <some others>."

The Rheem # is just what I was looking for. Fit perfectly but didn't fix my problem. New control board on order. Ugh!

Are you saying the replacement cap caused your control board to fail or that the run cap was not the issue?

I recently went through this with a garage door opener. Thought problem might have been the cap but tested it and it was in spec. Control board was the problem. It was actually another bad cap that I replaced and repaired control board.

In OP's case the two caps should be electrically identical and interchangeable so long as it fits physically. But it won't resolve problem if original cap is still good and issue is elsewhere.

 

[mike93lx]

Interesting comments, fellas. The more I think about it, the smaller diameter could be an issue. I do like that the new, smaller one is made in the USA though

All of my a/c's have straps with a bunch of holes for the hold downs. Smaller wouldn't be an issue with those

 

[rlitman]

All of my a/c's have straps with a bunch of holes for the hold downs. Smaller wouldn't be an issue with those

There's also those hold downs that go ZIP when you pull on them.

 

[rharman]

Interesting comments, fellas. The more I think about it, the smaller diameter could be an issue. I do like that the new, smaller one is made in the USA though

Are you saying the replacement cap caused your control board to fail or that the run cap was not the issue?

I recently went through this with a garage door opener. Thought problem might have been the cap but tested it and it was in spec. Control board was the problem. It was actually another bad cap that I replaced and repaired control board.

In OP's case the two caps should be electrically identical and interchangeable so long as it fits physically. But it won't resolve problem if original cap is still good and issue is elsewhere.

All of my a/c's have straps with a bunch of holes for the hold downs. Smaller wouldn't be an issue with those

There's also those hold downs that go ZIP when you pull on them.

@cgrutt - Funny you mentioned door opener. Not all that long ago, I replaced two cpas on my Liftmaster control. Posted about it here: https://www.garagejournal.com/forum...-do-in-your-garage-today.126997/post-11453133

And, just to be clear, in my case I'm talking about a run capacitor for the blower - not a start capacitor for the compressor.

As to the A/C cap issue....

The cap on mine slips into a hole on a sheet metal bracket with a screw that just catches the rim to hold it in place. The smaller one would have just passed through the hole.

The cap I took out was a 15µ. It measured 13.3µ when I tested it. Didn't sound low to me but that's below the ±10% tolerance. Google said that 13.3µ was low enough to possibly be problematic. New one tested at 15.5µ. Put it in but blower motor still wouldn't run.

Appears to be a bad motor relay on the control board. Wiggling it made the motor run but it also threw a couple of sparks. There's an upgraded control board/modification kit for it so that's on order. Hard to complain as it's 33 years old.

You can see the cap and the hold-down screw at the bottom here...

 

[rlitman]

...You can see the cap and the hold-down screw at the bottom here...

I don't think I'd be comfortable with it hanging like that. Ideally, you want to mount an AC run cap with the seal and terminals facing up, and with the case grounded. If it doesn't fit in the factory metal strap, I did suggest zip-tying it in the same location (which is far from ideal), but do at least try to have the metal case in contact with something grounded.

 

[cgrutt]

@cgrutt - Funny you mentioned door opener. Not all that long ago, I replaced two cpas on my Liftmaster control. Posted about it here: https://www.garagejournal.com/forum...-do-in-your-garage-today.126997/post-11453133

And, just to be clear, in my case I'm talking about a run capacitor for the blower - not a start cpacitor for the compressor.

As to the A/C cap issue....

The cap on mine slips into a hole on a sheet metal bracket with a screw that just catches the rim to hold it in place. The smaller one would have just passed through the hole.

The cap I took out was a 15µ. It measured 13.3µ when I tested it. Didn't sound low to me but that's below the ±10% tolerance. Google said that 13.3µ was low enough to possibly be problematic. New one tested at 15.5µ. Put it in but blower motor still wouldn't run.

Appears to be a bad motor relay on the control board. Wiggling it made the motor run but it also threw a couple of sparks. There's an upgraded control board/modification kit for it so that's on order. Hard to complain as it's 33 years old.

You can see the cap and the hold-down screw at the bottom here...

Funny the garage door opener that I repaired was an Access Master but believe its made by Lift Master. Different control board though. Similar issue.

As far as OP is concerned I don't believe physical size differences will matter the two caps should be identical from an electrical standpoint.

 

[rharman]

I don't think I'd be comfortable with it hanging like that. Ideally, you want to mount an AC run cap with the seal and terminals facing up, and with the case grounded. If it doesn't fit in the factory metal strap, I did suggest zip-tying it in the same location (which is far from ideal), but do at least try to have the metal case in contact with something grounded.

That is the factory mounting. It's not hanging. That metal bracket is part of the furnace/blower structure so it's grounded. The rim of the cap stops it from passing all the way through the hole when you insert it and the sheet metal screw overlaps the rim to anchor and bond it to the structure. I'm assuming Rheem knew what they were doing when they designed it.

Lasted 33 years and is likely still functional. I'm just leaving the new one in and keeping the original as a spare.