I would guess the change from 1/2 HP to 1 HP would extend the life of the motors.. Easier startup..

I also have bought AFTERMARKET start capacitors over the years. I normally do not go back to the "motor manufacturer"... they didnt build the capacitors, they bought them... Capacitor should have a RATING stamped on the side of it.. You need to be in the right VOLTAGE rating .... the CAPACITANCE does not need to be exact, but it helps to be close.. That determines the TIME it takes for the motor to windup to full speed.. You dont want to take too long, but you dont want instant MAX RPM either..

Finding start caps is easy ,once you KNOW the values...

Typically it'll say xxx MFD / yyy VAC where xxx is the value of capacitance and yyy is the voltage. Voltage will generally be 350-450 AC volts,allows for 120 or 240 volt operation.
Capacitance value could be stamped as a 'range', say 80-120 MFD. The value varies according to the motor,but whatever WAS on the motor, THAT is the value you want. You can't swap in a 230 MFD for a 100 MFD !!

Welcome to the World of CONS.

yes, old skool motors ran for decades. the 35 year old ,1/2HP furnace fan  motor  I pulled from my 96% eff furnace still runs (only downgraded to a 93% eff fce for insurance ).

While the 'new tech' DC motors have better control,they are cheaper to build,cost more and need a 'computer' to run them.

I had a look, I can buy 1/2HP TEFC motor for $240, or 1HP for $300,both made in China,of course. neighbour had a well pump 'go'( indoor.cistern use), it looked brand new...krapped out, no parts available( starter ),sigh....

Ask about replacement parts ! friend has $2000 exercise bike,asked me to fix it, needs a $5 part.If under warranty,it's replaced. it's NOT  ,so now LANDFILL !!

BTW caps don't like the heat ! They 'dry up' internally and fail. If you can source 'industrial duty' caps buy them. They have a better 'temperature range' unlike the 'residential' ones.

Leeson are industrial grade.  Grizzly are asian imports, and while better than something coming out of Harbor Freight, they're certainly not in the realm of Baldor, Dayton, or Century.

If you went from a 10 year lifespan to a 2 year, there's something else seriously wrong.  Start and run capacitors DO fail, but usually they fail because they've been either overloaded, overheated, or under-rated.  Don't go below 330v for a 240v circuit, lest it WILL have a much shorter service life.

Get a reflective tachometer, and put a piece of tape or dab of white paint on the motor sheave and take a measurement of the running RPM, and compare that to the NAMEPLATE RPM on the motor.  While a 60-cycle motor's synchronous speed (unloaded) will be either 3600, 1800, or (in the case of a 6 pole motor) 1200rpm, the LOADED speed will be shown as something like 3450 or 1725rpm.  These are the FULLY LOADED speeds, and the DIFFERENCE between loaded speed and synchronous speed is called "SLIP".  If the loaded motor's RPM falls BELOW that point, you'll have excessive motor heating going on.

Usually, in big ventilators, the bearings in the blower get draggy, and the drum or flights (blades) accumulate a fine layer of dust, and when this happens, the motor load comes up considerably.  There's two things I'd check before dismissing the motor as a problem:

First is a visit from a pressure washer- that cuts off the dust layer and cleans up the airflow pathway.

Second, is a check of the bearings, and a full loading of fresh and proper grease.

These two things are the most likely problems that would cause a whole bunch of fans to start exhibiting problems after years of service... and the latter (grease) would be a most likely cause of a simultanious loss of performance... specifically, the TYPE of grease used.  What often happens, is a guy comes through with good intentions, and gives all the bearings a couple pumps of grease...   and the bearings run great.

One year, a guy comes through, gives 'em all grease, and again, they run great.

Six months later, the motors start to run warm... and by the end of the second year, they're all having difficulty.

The element that started it wasn't that they got greased on regular basis, but that the guy coming through had a DIFFERENT KIND of grease in his gun.

The grease that you normally have in your grease gun of 1970 would've been a silicon or sodium-based wheel bearing grease... because that would've been the most commonly used grease in farm machinery...  but nowdays, the most common is an NGLI-2 Lithium based grease.

If you take a bearing that's been running on one base of grease for 40 years, and you shoot in a DIFFERENT type, a chemical reaction occurs... Saponification... where the two greases' base metals electrolytically react, and become basically stone.

After that, you can try to add as much grease as you want... the bearings will NOT spin freely... they'll drag.

I don't think your motor problem is a motor problem, I think it's a motor load problem- the loading has changed... and you'll probably find that the running RPM is wrong, thus, your motors are overheating.

I would NOT remove all the ventilation motors and replace them with DC drives or AC VFDs... that's a significant increase in technology that, in the event of serious electrical excursion (like a utility line problem, or a lightning strike) could take out ALL your ventilators at once.  The simplicity of a synchronous AC induction motor makes it much more robust against such things.  A simultanious loss of all ventilators on a hot day could result in the loss of your whole flock.

Yeah, the ammonia is a very quick killer... we had a strange weather day about 8 years back, and lost ventilation in our brooder bin, and it took out two dozen chicks.

The longer start time can be a couple of things, but foremost, the starting capacitor and it's centrifugal switch (they CAN get sticky and worn).

Another thing you CAN do, at the cost of a little full-flow volume, is reduce the drive ratio (increase the reduction) so that startup and full running load is slightly lower, hence quicker... and your peak (startup) and running power consumption will be reduced.  Since you're running it on a timed cycle, the full-flow performance is not critical in maintaining the habitat.

curious about the '5 minute ' timers...

Are you saying the fans 'cycle' is on for 5 minutes, then off for 5 minutes, 24 /7  ?

Trying to figure out how many starts and often you have ? The start switch wasn't made for a zillion cycles.Well water pump switches  fail this way.

Just curious if another solution might be more reliable ?

My gut is telling me the the fans have too much CFM. Running a motor or 30 seconds is really hard on them,especially if driving a fan through a belt. They probably don't get up to speed before beiing shut down.

In your case having DC motors whose speed is controlled by ammonia concentration makes sense and is an easy system to design and configure. I'd have each fan on it's own PLC and sensor NOT an 'all-in-one' design. That way when a sensor fails,the others can take up the slack.

I dont know how big your fans are.. But you might consider a SMALLER fan, or change belt drive on 1-2 fans toward the middle of the building so they pull fresh air from each end.. and run constant...

Start  cap will have one wire going to the centrifugal start switch.

There 'should' be a wiring diagram inside the cover where the power wires go into the motor.

 All else fails ,google the make/model of the motor or post that info here...

as for source of caps... post the 'numbers' here, or picture... DIGIKEY is the largest electronic supplier in USA/CDA.... most stuff overnight for me......

sad you 'hands are tied'...as it'd be an easy swap over to more efficient/better air for the birds...... sigh....

I feel for you man.....

Tyler, the resistor across the terminals is called a 'bleeder resistor'.  it's function is to slowly discharge any energy that remains IN the capacitor, so that it won't be storing a whallop that'd blow your fingertips off if you touched it. 

Since it's a chemical device, one can charge a capacitor fully, then discharge it fully, then open up it's leads, and it will actually start to rebuild a partial charge, because the discharge process may dump a whole lotta current, it cannot dump it ALL, because it's a chemical device... some of that chemistry takes time to fully equalize.  The bleeder is there to drain off any charge that'd build up as a result of finishing equalization.

Most motor START capacitors are paper electrolytic type.  Most motor RUN capacitors are oil-filled types.  The former have considerable capacity, but cannot tolerate extended cycle times before overheating and erupting.  The latter are much, much more electrically robust under continuous cycling duty, albeit at a lower capacity than the electrolytic start type.

try http://www.grainger.com" rel="nofollow - www.grainger.com ! I did a quik chek...

They have several 'run capacitors', check the specs.

A higher voltage is better as well as higher 'max operating temperature' ( 85*C is typical).

 It's what will PHYSICALLY fit is kinda important.

Also buy more than ONE !! Shipping is same and always have a spare,that you won't need is way better than needing one Saturday night at 2AM...

https://www.grainger.ca/en/product/CAPACITOR-189-227MFD/p/WWG2MDR5

is a 'run one, 200MFD'.....

dang 36 fans ! See where the 'qty discount' point is ! I used to buy computer parts in Quebec cheaper than here in Ontario and that's after shipping / taxes were added.

Also keep track WHICH fans are failing. Is it random or always 'the four on the south west wall' ?If the former..probably life of the parts, if latter, an 'environmental' issue ?

The run capacitor operates at a higher applied voltage, for a longer period of time, than a start capacitor.

For the RUN capacitor, Johnstone Supply catalog pg 138 shows thier G35-270 as Titan part POCV15A  Motor Run Capacitor, oval shape, 15MFD, 440v, height 2.75" width 2.75, depth 1.75" for $11.00

They list the same capacity 15MFD 440vac diam 1.75 height 3.25" in round form factor pg 140, G35-383, part PCRF15A, also $11.00

If your motor's failed capacitor is a Motor START cap, then replacing it wht a Motor Run will be death knell for it- they can NOT be interchanged of purpose.

life of motors..quality of air...

been thinking about the 'hen house hell' and have a suggestion

Instead of running 2 fans for 30 seconds each, run ONE fan for a minute. The combined volume of air moved is the same BUT each motor doesn't get 'short cycled' and destroyed.

You said 36 fans, so if in one loooooog building, wire them up 'odds and evens'. #s 1,3,5,7,35 come on together then 2,4,6,36. That would be a better air moving pattern and distribute the 'wear and tear' on the motors and fan units evenly. I know you'll have to adjust for ammonia,but the idea is to have fewer fans on longer. It'll meet the guv regs(CFM/pound/hr ? ) and should save on repairs.

I did a similar setup for a bank with all electric heat and AC. Only two HVAC came on for 5 minutes. The pattern was 1,2 then 2,3 then 3,4 then 5,6 then 6,1. Loop repeats. was my first PLC program. Saved the bank 10K a month,so they were happy.