Replacement for a run capacitor-- recommended specs

[larryq]

I have a 1/2 HP grinder I'd like to replace the run capacitor on. I'm ordering a start capacitor and may as well get a run cap from the same place and save on shipping.

The current run capacitor is oval sized, and has a 370V rating and 6 MFD. This place only carries 5 MFD or 7.5 MFD capacitance in 370v. If I need to choose I assume the 7.5 is the way to go? Or is there a big problem not having exactly 6?

 

[jakemac]

Did you ask if they can order in the matching one from their supplier ?

 

[BMack37]

If you go up in voltage can you get a 5MFD cap? The 7.5MFD should work but it may effect power. Having higher voltage rating is not an issue(other than size/cost). Do they also list size? Make sure it fits!

 

[ovrrdrive]

I'd go same voltage higher capacitance. But I don't know the general rule of thumb for it.

 

[mikebaker1129]

General rule is +or- 10% on capacitance.
I would suggest you try an HVAC/ air conditioning supply ,they keep a good stock of capacitors in stock here in Houston.
You can also parallel 2 caps together, 4+2= 6 and get your desired capacitance.

 

[jallyn]

Either 5 or 7.5 MFD (micro-Farads) are close enough. But like someone else posted, there is no quality penalty for getting a higher voltage-rated capacitor that is 6 MFD as long as it physically fits. Just make sure you don't go to a lower voltage rating (it may burn up). And get as close as possible on MFD since that is what is tuned with your motor winding's impedance to give the best power and running characteristics.

 

[Rookie2]

Both higher uf (lower imp) and lower uf (high imp) will affect performance I suspect but i've never left the wrong one in for any length of time.

http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/

 

[monkeyspanners]

If i had to choose i would go with a lower rated uF one, many motors run for ages with capacitors that have aged and now have a lower rating without apparent harm, but i have seen a motor burn up within a week where a higher uF capacitor had been fitted.

Just get the correct one even if you have to go elsewhere and pay extra postage.

 

[Davefr]

Rule of thumb is to stay + or - 10% but I'd try and match it as close as you can. The reason is if the cap needs to be replaced down the road and it's already deviating from spec by 10%, someone else could deviate another X% and then you have a motor that's too far out of spec.

If you deviate from the OEM spec and least right somewhere on the motor what the original values were.

 

[larryq]

Thanks guys. Think I'll look elsewhere for the run capacitor and stick with 6 MFD to play it safe.