Start Capacitor #of Starts

[Silverbullet]

Hey brave65' have a question ,how long is an [ ever] , ha just funnin , but ya never know right an ever could be a lifetime.

 

[cdhknives]

Motors can also be rated in starts per hour. The big boys I work with (4160 nominal Volts) generally get 2 start/restart tries before a mandated 20+ minute cooling period. For your lathes 5-10 starts over a 10 minute time is probably okay if you unload your spindle every time and let it run 10 minutes or so after. Running pumps cooling air through or over it. This is why you always start your lathe with the spindle disengaged...the extra time to spin up the extra mass is all going to greater heat in the starting circuit and motor windings. A 1.15 service factor motor helps, as does a larger Hp motor. Most of this is beyond the scope of out little 1/3-1 Hp motors on our Atlas lathes, but some of the big boys y'all may also work with will want to consider this.

Heat is the #1 enemy of electrical parts. Bar none. Electrolytic caps dry out faster with use as they are warmer. The reason for the myth of the 'dry out in storage' is time...some time during storage it dried out that last bit to fail, in use it would have died even sooner, but it wasn't being used so no one noticed. In other words, it may have died in 1 year from last use if still in weekly service, it did die in year 3, but wasn't turned on until year 5 so 'that electrolytic cap dried up from non-use'!

 

[silence dogood]

These capacitors do have a life span and that includes the shelf life. I realize that the specs say the cap can take -40 to 65 degrees C. Still, I would not let them freeze or sit in the hot Texas sun.. There is a paste inside of them. And while you are replacing the start cap, check the contacts on the centrifugal switch. If the contacts are dirty with carbon, the motor may not get up to speed. If the contacts don't open, you will be blowing caps. One final note, a guy gave me a old Rockwell 9" table saw. Aside from some cleaning and adjusting. I replace the start cap, it was in a box separate from the motor. It also had a start relay instead of a centrifugal switch. It was a little rectangular black box that said Klixon 4CR on it. Unfortunately, these things aren't available anymore. An electrician told me to wire in a 20 amp momentary on switch in series with start cap to the start winding( red wire in this case). So now when I turn on the saw, I press both switches at the same time and hold approx. a sec. for the motor to build up speed. I must say even though this saw was a cheapy in it's day, it's still a lot better than this $200 or less crap that one buys in the store now a days. Mark

 

[John Hasler]

Motors can also be rated in starts per hour. The big boys I work with (4160 nominal Volts) generally get 2 start/restart tries before a mandated 20+ minute cooling period. For your lathes 5-10 starts over a 10 minute time is probably okay if you unload your spindle every time and let it run 10 minutes or so after. Running pumps cooling air through or over it. This is why you always start your lathe with the spindle disengaged...the extra time to spin up the extra mass is all going to greater heat in the starting circuit and motor windings. A 1.15 service factor motor helps, as does a larger Hp motor. Most of this is beyond the scope of out little 1/3-1 Hp motors on our Atlas lathes, but some of the big boys y'all may also work with will want to consider this.

Heat is the #1 enemy of electrical parts. Bar none. Electrolytic caps dry out faster with use as they are warmer. The reason for the myth of the 'dry out in storage' is time...some time during storage it dried out that last bit to fail, in use it would have died even sooner, but it wasn't being used so no one noticed. In other words, it may have died in 1 year from last use if still in weekly service, it did die in year 3, but wasn't turned on until year 5 so 'that electrolytic cap dried up from non-use'!

*Old* electrolytic capacitors, as in pre-WWII, did dry out in storage (they dried out even faster in use). However, I have electrolytics from the 1970s in my junk collection upstairs that are as good as new. The start cap in the static converter on my mill came out of a thirty year old air conditioner that had sat in my machine shed for at least a decade.

 

[cdhknives]

I have to disagree. There is no such thing as a perfectly sealed electrolytic capacitor. Well made modern electrolytic caps may have a lifespan of 50+ years, but the slightest manufacturing defect in the case or seals on the leads going into the can and that lifespan is greatly shortened. Most electronics won't even survive long enough to know the difference. Motor caps, with the heat and torture they endure, can and do fail from simply drying out. BTW, there are 'dry' electrolytic capacitors, we're only talking about so called 'wet' electrolytic capacitors as the dry type are significantly more expensive. Bottom line is no electrolytic cap case is absolutely perfectly sealed against all permeability, and well made units are probably going to be killed by misuse (power surge, for example) long before they dry out.

Also, most people see a cracked capacitor case and assume the crack caused it to fail. The case rupture is usually from internal overpressure as it overheats. Metal can caps have a blowout tab, usually on top. Plastic cases just crack. When I taught a second year college electronics lab we had a tradition of signing the ding when you blew a cap and it hit the wall...usually from polarity reversal but a couple of times the only explanation I could find was infant mortality.

 

[wa5cab]

Knives,

Although you are correct that there are (or were) both "wet" and "dry" electrolytics, I don't think that any "wet" ones have been made since the 1930's. At least I I routinely work on vintage US military radios made mid 1930's and later and don't think that I have ever actually seen a "wet" one.

However, as applied to "dry" electrolytics, "dry out" is misleading. The dielectric layer in dry electrolytics is created during manufacture. Unfortunately, the process is reversible by time and temperature. The degradation process has for decades been commonly referred to as "drying out". But it is actually electrochemical in nature. And is itself sometimes reversible. At least with single polarity capacitors. The repair process is commonly referred to as "reforming", and involves applying a current limited voltage across the capacitor and monitoring either the voltage or the current during reforming. But I don't think that you can reform a non-polarized capacitor. So the obvious repair procedure for AC motor start or run capacitors is replacement.

 

[Alan Douglas]

There is, or was, an online video from a large capacitor manufacturer in the US, showing the etching and forming process. It involves large rolls of aluminum foil and heated tanks of electrolyte. The formed foil is then wound into capacitors.

I presume the improved lifetime of modern electrolytics is due to increased purity of the aluminum, rather than "drying out." Certainly modern electrolytics show far less leakage current than older ones. Electrical leakage is from defects in the dielectric layer.

There may have been some liquid-filled electrolytics made post-war but if so, they weren't common. Military gear never used them at all, I presume because they wouldn't work at Arctic temperatures and in all positions. Their advantage was mainly in home radios where they would absorb the voltage surge at turn-on.

 

[coolidge]

Then there is the issue of counterfeit capacitors...outwardly the cap looks like a higher priced capacitor and you peel off the outer cover and find a cheapo China capacitor inside. (face palm)

 

[RJSakowski]

There is, or was, an online video from a large capacitor manufacturer in the US, showing the etching and forming process. It involves large rolls of aluminum foil and heated tanks of electrolyte. The formed foil is then wound into capacitors.

I presume the improved lifetime of modern electrolytics is due to increased purity of the aluminum, rather than "drying out." Certainly modern electrolytics show far less leakage current than older ones. Electrical leakage is from defects in the dielectric layer.

There may have been some liquid-filled electrolytics made post-war but if so, they weren't common. Military gear never used them at all, I presume because they wouldn't work at Arctic temperatures and in all positions. Their advantage was mainly in home radios where they would absorb the voltage surge at turn-on.

In doing some reading on the subject, I discovered that apparently the Japanese company, Rubicon, reintroduced wet electrolytics in the 1990's in an attempt to reduce ESR. Because they didn't get the formula right, it led to a rash of exploding capacitors in the early 2000's. My electronics experience goes back several decades and I, like you, thought that wet electrolytics went out before WW II.

 

[John Hasler]

In doing some reading on the subject, I discovered that apparently the Japanese company, Rubicon, reintroduced wet electrolytics in the 1990's in an attempt to reduce ESR. Because they didn't get the formula right, it led to a rash of exploding capacitors in the early 2000's. My electronics experience goes back several decades and I, like you, thought that wet electrolytics went out before WW II.

The Rubicon caps worked fine. The ones that popped were made by Chinese companies that tried to copy them but bungled the formula.