Wearite/Ferrograph capstan motor capacitor value? - UK Vintage Radio Repair and Restoration Discussion Forum

pentoad · 14th Jul 2020, 12:04 pm

0.75uf - Is the value critical as I am finding it difficult to source - would 0.45uf do the job? (or two in parallel 0.94uf) as I have those at 650vdc

barrymagrec · 14th Jul 2020, 2:23 pm

The value is not super critical but if it is much under the torque will be affected and if it is too high or low flutter will be increased, though this probably won`t be noticeable with the idler drive system. I would want it closer than you examples. I would go to .68 or .82 if pushed.

pentoad · 14th Jul 2020, 3:15 pm

If I can't find 0.75 I will go for 0.68 then - thanks

DMcMahon · 14th Jul 2020, 4:30 pm

If this is the Run capacitor for the Capstan motor then make sure the replacement is a proper motor run capacitor which will be AC voltage rated and rated for continuous usage, modern ones will be Polypropylene.

pentoad · 14th Jul 2020, 5:09 pm

Quote:

Originally Posted by DMcMahon

If this is the Run capacitor for the Capstan motor then make sure the replacement is a proper motor run capacitor which will be AC voltage rated and rated for continuous usage, modern ones will be Polypropylene.

I was considering this:

CBB61 motor fan start running capacitor

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Not sure if it is designed for continuous or just for starting

There are old secondhand Hunts type as original on fleabay but I would rather use new.

Other alternative 0.68uf:
https://www.ebay.co.uk/itm/I150V468K...EAAOSwtCNeFiK0

barrymagrec · 14th Jul 2020, 5:22 pm

+1 on using a proper motor capacitor - the AC voltage across them can be significantly more than the incoming mains.

DMcMahon · 14th Jul 2020, 10:54 pm

I have successfully used the CBB61 type for R2R Motor Run use, they are described as suitable for Motor Start and Motor Run so should be OK but do not appear to actually state continuous running.

Lucien Nunes · 15th Jul 2020, 9:06 am

The intermittently-rated motor capacitors are specifically AC electrolytics typically 50μF or greater, rated for starting duty only. All other types are continuously rated. I would always try to get a close match for a run cap, 5% is standard, and as mentioned be prepared for the AC terminal voltage to significantly exceed the motor supply voltage.

DMcMahon · 15th Jul 2020, 3:30 pm

Quote:

Originally Posted by Lucien Nunes

The intermittently-rated motor capacitors are specifically AC electrolytics typically 50μF or greater, rated for starting duty only. All other types are continuously rated.

That is good to know.

David

14th Jul 2020, 12:04 pm	#1
pentoad Hexode Join Date: Feb 2011 Location: Newcastle upon Tyne, Tyne and Wear, UK. Posts: 280	Wearite/Ferrograph capstan motor capacitor value? 0.75uf - Is the value critical as I am finding it difficult to source - would 0.45uf do the job? (or two in parallel 0.94uf) as I have those at 650vdc

14th Jul 2020, 2:23 pm	#2
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,557	Re: Wearite/Ferrograph capstan motor capacitor value? The value is not super critical but if it is much under the torque will be affected and if it is too high or low flutter will be increased, though this probably won`t be noticeable with the idler drive system. I would want it closer than you examples. I would go to .68 or .82 if pushed.

14th Jul 2020, 3:15 pm	#3
pentoad Hexode Join Date: Feb 2011 Location: Newcastle upon Tyne, Tyne and Wear, UK. Posts: 280	Re: Wearite/Ferrograph capstan motor capacitor value? If I can't find 0.75 I will go for 0.68 then - thanks

14th Jul 2020, 4:30 pm	#4
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Wearite/Ferrograph capstan motor capacitor value? If this is the Run capacitor for the Capstan motor then make sure the replacement is a proper motor run capacitor which will be AC voltage rated and rated for continuous usage, modern ones will be Polypropylene.

14th Jul 2020, 5:22 pm	#6
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,557	Re: Wearite/Ferrograph capstan motor capacitor value? +1 on using a proper motor capacitor - the AC voltage across them can be significantly more than the incoming mains.

14th Jul 2020, 10:54 pm	#7
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Wearite/Ferrograph capstan motor capacitor value? I have successfully used the CBB61 type for R2R Motor Run use, they are described as suitable for Motor Start and Motor Run so should be OK but do not appear to actually state continuous running.

15th Jul 2020, 9:06 am	#8
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Wearite/Ferrograph capstan motor capacitor value? The intermittently-rated motor capacitors are specifically AC electrolytics typically 50μF or greater, rated for starting duty only. All other types are continuously rated. I would always try to get a close match for a run cap, 5% is standard, and as mentioned be prepared for the AC terminal voltage to significantly exceed the motor supply voltage.