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Posted: Thu Jul 25, 2013 2:14 pm
by BuckeyeDennis
JPG40504 wrote:I would not attempt to connect an induction motor to a typical 'power strip' since the common practice of using printed circuitry when line surge protection(and worse all connectons to sockets) is present does indeed act as a fuse. The SS motor surge is above 25A and even higher if starting under load. The printed circuit foil can take overload current but only for a very short duration. Also the use of solder makes for a problem if overheating occurs.
As for the switch making, the start up current is delayed due to the inductive load presented by the motor coils. That same inductance causes potential arcing when the switch is opened. That arcing is what wears switches out. IIUC the hp rating of a switch is directly related to contact size. Switches can arc when making, but that is caused by contact 'bounce'(brief period of make/break/make/break/. . .sequence) and would occur while the current to a motor is still ramping up.
The typical 'power strip' came about with the advent of personal computers and serves that function reasonably well. There are great differences in their construction. The less 'robust' designs will perform poorly under with higher current 'appliances'.
Yes, the "typical" power strip clearly is not up to the job. Out of curiosity, I checked to see if you can buy a 20A strip that
is up to the job. It appears that you can, like this one that mentions power tools as an application:
http://www.tripplite.com/en/products/mo ... delID=3462. The downside is the price, roughly $60 from Amazon, and twice that through industrial electronics distributors. I'll probably keep using my cheap one for hand tools and such, and plug the SS directly into a 20A outlet.
You undoubtedly know this already, but for the non-EE's edification, printed circuit boards
can be designed to carry heavy currents. I personally designed a 600V, 80A servomotor drive that we use for machine-tool spindle drives. It is 100% printed circuitry, but uses heavy (i.e. thick) copper and wide traces (or even entire regions of a circuit-board plane) for the high-current stuff. Full rated current will cause a copper temperature rise of no more than 10C. But a $10 garden-variety power strip is unlikely use more copper than is necessary for the typical PC and lighting applications.
BTW, I hadn't thought about the motor inductance protecting the switch contacts while making, but that makes perfect sense.
Posted: Thu Jul 25, 2013 2:36 pm
by JPG
BuckeyeDennis wrote:Yes, the "typical" power strip clearly is not up to the job. Out of curiosity, I checked to see if you can buy a 20A strip that
is up to the job. It appears that you can, like this one that mentions power tools as an application:
http://www.tripplite.com/en/products/model.cfm?txtModelID=3462. The downside is the price, roughly $60 from Amazon, and twice that through industrial electronics distributors. I'll probably keep using my cheap one for hand tools and such, and plug the SS directly into a 20A outlet.
You undoubtedly know this already, but for the non-EE's edification, printed circuit boards
can be designed to carry heavy currents. I personally designed a 600V, 80A servomotor drive that we use for machine-tool spindle drives. It is 100% printed circuitry, but uses heavy (i.e. thick) copper and wide traces (or even entire regions of a circuit-board plane) for the high-current stuff. Full rated current will cause a copper temperature rise of no more than 10C. But a $10 garden-variety power strip is unlikely use more copper than is necessary for the typical PC and lighting applications.
BTW, I hadn't thought about the motor inductance protecting the switch contacts while making, but that makes perfect sense.
Another PC 'trick' is soldering a piece of wire in high current areas.
I prefer the ones with real duplex receptacles and a metal box. For shop use I would likely make one from electrical boxes(surface mount). Ganged if needed.
Dusty's video clearly shows the lag in current buildup at startup(IIRC).
The power pro
might benefit from line surge suppression. An induction motor will not be susceptible to damage from 'power "surges"'. Brown out on the other hand!
Posted: Thu Jul 25, 2013 3:13 pm
by BuckeyeDennis
dusty wrote:The start up current for a 510 is higher than the run current but it is very short duration and should have no ill effect given that the supplied power (115 vac) is adequate and applied through proper wiring (12 or 14 gauge wire with either a 15 or 20 amp breaker).
I have posted a uTube video showing the currents being drawn during startup.
I'd like to see the video, but couldn't find it on YouTube. Do you have a link (or a search term)?
Posted: Thu Jul 25, 2013 3:18 pm
by dusty
BuckeyeDennis wrote:I'd like to see the video, but couldn't find it on YouTube. Do you have a link (or a search term)?
I believe
this is what you are looking for.
I hope it works and that it helps. YouTube says my channel has been updated so I don't know what to expect.
Posted: Thu Jul 25, 2013 3:19 pm
by JPG
dusty wrote:I believe
this is what you are looking for.
I hope it works and that it helps. YouTube says my channel has been updated so I don't know what to expect.
You can expect it to tell us it is 'private'.
Posted: Fri Jul 26, 2013 12:33 am
by skou
JPG40504 wrote:Another PC 'trick' is soldering a piece of wire in high current areas.
This reminds me of my old hobby, overclocking PCs.
On a motherboard designed for overclocking, the manufacturers would apply solder to the entire trace, providing the power, not just at the connections. Some of them would just run a bunch of non-conducting traces, under the CPU, to help dissipate heat. The mobo maker I used (Abit) did both. (And had some of the best OCing boards around.)
Back to (almost) the subject, the ER with a "Skip" DC motor can be turned to low speed while stopped, and you don't have these issues.
Oh, if you have an ER with the speedchanger, you can SEE what happens, if you change speed with no power. I wouldn't advise it.
steve
Posted: Fri Jul 26, 2013 2:30 am
by JPG
skou wrote:This reminds me of my old hobby, overclocking PCs.
On a motherboard designed for overclocking, the manufacturers would apply solder to the entire trace, providing the power, not just at the connections. Some of them would just run a bunch of non-conducting traces, under the CPU, to help dissipate heat. The mobo maker I used (Abit) did both. (And had some of the best OCing boards around.)
Back to (almost) the subject, the ER with a "Skip" DC motor can be turned to low speed while stopped, and you don't have these issues.
Oh, if you have an ER with the speedchanger, you can SEE what happens, if you change speed with no power. I wouldn't advise it.
steve
When adjusting the '10' speed changer one should never let the springs on the control arm fully compress. This can happen moving either direction.
Posted: Thu Jan 09, 2014 9:11 pm
by jere
I have been powering mine all the way down lately. I have found that if I don't especially in cold weather, the motor doesn't want to spin up, and bogs or trips the breaker. I do use the SS in temperatures much lower than what the motor lists it's operating temps at.
Opps sorry this is an old post sorry to bring in back from the dead.
Posted: Thu Jan 09, 2014 10:27 pm
by charlese
jere wrote:
Opps sorry this is an old post sorry to bring in back from the dead.
That's O.K.
Reminders like this are a good thing!
Posted: Fri Jan 10, 2014 5:52 am
by robinson46176
I almost never turn any of mine all of the way down when shutting them off. I do however often slow them down part way if I am done and I have had any of them cranked up pretty high. Just dropping a letter or two makes a big difference in start-up if I am in the upper ranges.
I have never really had any starting issues.
On a somewhat related side note, While all wiring in my basement shop is #12 I do find a need from time to time to use an extension cord. Usually about 6' is plenty and I found long ago that the best way to deal with it is to buy extra-heavy-duty Air conditioner extension cords...
I've not had any SS power cords need to be replaced on the ones I use and most of the time the cord is long enough by itself but when I do replace them I will use #12 cords and make them about 4 feet longer.
.