Two fans one capacitor...

[monkey spanners]

Say you have a unit with two 120w condensers fan motors run off a common supply, they both need 5uf capacitors to run correctly.

Could you run them both off one 10uf capacitor by linking the two start windings together?


Jon

[install monkey]

cant u spin the 1 without a capacitor and keep it permantly running

[install monkey]

you could fit the 10uf cap on the other fan as your allowed 10%

[monkey spanners]

I mean you've got 240w worth of motor so link both the lives, neutrals and starts together and just chuck a 10uf on instead of two 5ufs...

It don't sound right but can't see why it wouldn't work?

[install monkey]

it should work, but why did the original capacitor fail-is the motor running hot?

I mean you've got 240w worth of motor so link both the lives, neutrals and starts together and just chuck a 10uf on instead of two 5ufs...

It don't sound right but can't see why it wouldn't work?

[stufus]

Try it and let us know
Cheers
Stu

[mikeref]

5 uf caps are only a few bucks. Guess you ran out of them and it is too far to grab new ones or parts supplier won't let you in the shop with muddy feet. Interested on the outcome Jon

[monkey spanners]

Theres one make of equipment i service where they link the motors together so they can reverse the rotation during cleaning, so i was more curious about any electrical theories as to why you can't or can do it rather than an actual system i have run out of parts for. (i have about 30 5uf caps after a slight rs components ordering issue...)

They also do the same thing on the agitator motors on another make tank and with these i have seen one motor and get hot due to previous company wiring up the two motors differently and the replacement being a pattern part with different spec motor.

Jon

[chilliwilly]

If one either of the start windings doesn't disconnect at the same time, you will have one start winding with twice the size cap than specified. For the short time the start winding is in circuit could cause premature failure, and unecessary recalls £££!


If you were to short out the centrifugal switches and configure the motors so they were connected like a pot with a current relay. That in turn disconnected both start windings you might get away with it. But if the cap fails then neither motor will run and you will get certain condensor problems. Maybe a mod that you should stay away from.

[install monkey]

psc motors dont have a centrifugal switch
the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).^[6] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,^[6] and what correspond to the start windings (second windings) are permanently connected to the power source (through a capacitor), along with the run windings.^[6] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where a variable speed is desired.
A capacitor ranging from 3 to 25 microfarads is connected in series with the "start" windings and remains in the circuit during the run cycle.^[6] The "start" windings and run windings are identical in this motor,^[6] and reverse motion can be achieved by reversing the wiring of the 2 windings,^[6] with the capacitor connected to the other windings as "start" windings. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also, provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding

[stufus]

Monkey has this copy and paste lark licked.

Cheers
Stu

[install monkey]

ive searched for 2 fans 1 cap and i think it must have been banned!! i even tried google aus and no joy there too!

Monkey has this copy and paste lark licked.

Cheers
Stu

[chilliwilly]

psc motors dont have a centrifugal switch
the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).^[6] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,^[6] and what correspond to the start windings (second windings) are permanently connected to the power source (through a capacitor), along with the run windings.^[6] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where a variable speed is desired.
A capacitor ranging from 3 to 25 microfarads is connected in series with the "start" windings and remains in the circuit during the run cycle.^[6] The "start" windings and run windings are identical in this motor,^[6] and reverse motion can be achieved by reversing the wiring of the 2 windings,^[6] with the capacitor connected to the other windings as "start" windings. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also, provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding

I didn't know that he was refering to a psc motor. So I assumed that he was refering to a traditional cap start motor as most of the old equipment that I work on still have them. In which case he will still have the same problem if the cap fails, and maybe one or two odd grunting noises if both sets of windings in the two motors aren't symetrical, and either of the bearings start to wear at different rates.


The method of connecting a three phase motor to a single phase supply and interconnecting a cap between two of the windings only works on a constant torque load machine. Indoors or where sheltered from the elements its fine, but can cause problems on equipment outside facing an ever changing wind.

[SeanB]

Monkey spanners, you must have ordered 6, and did not realise the SSM was 5 then. I also have a lot of extras from RS that way, but you will eventually use them. Nice is the real time stock check, though most of the stuff I order is always 4-7 days...........

[monkey spanners]

Thanks for the replies, i will take some measurements next time i get the chance and see what is going on with the linked motors, i have taken amp readings before and they've been over what the should on the lives but ok on the neutral, now i think about it i expect this is due to all the lives and start connections being linked. Think i will disconnect one and see if its getting a feed back on the start winding connection.

Monkey spanners, you must have ordered 6, and did not realise the SSM was 5 then. I also have a lot of extras from RS that way, but you will eventually use them. Nice is the real time stock check, though most of the stuff I order is always 4-7 days...........

I was getting a bit low on caps and got a special offer through for 20% discount if i spent over £200, when they turned up i went to put the spare ones in the stores and found the rest of the last order in the safe place i had put them....

Cheers Jon