Up date on Surplus Center Motor

C

copycat

Joined
Jan 2, 2004
Messages
22
For T Blade, Sando, Pendentive,
Today i received a replacement motor, controller, and potentiometer, from Surplus center, with a postage free return label for Ups, gotta love that Surplus Center. Well i first changed the potentiometer, and wired it several different ways, no change. then i changed the controller, i got a little more torque and the motor didn't slow down when i put a piece of steel to it. i changed the motor and it was the same as my old one. I still seems to have 2 problems that i have to solve, the first one is turning the potentiometer from the 12 o'clock postion to the 7 o'clock postion before it starts, and the second problem is when i slow it down too fast, the breaker tripps and i have to wait for it to reset itself. I am going to keep playing with it until one of us gives out. I will keep those interested informed. Tom
 
>> the first one is turning the potentiometer from the 12 o'clock postion to the 7 o'clock postion before it starts,

What happens when you do this?

>> the second problem is when i slow it down too fast, the breaker tripps and i have to wait for it to reset itself.

The breaker on the controller or the one in the house?

When a motor is 'slowing down' what actually happens is the 'juice' is cut off. However the motor is still turning and sending current back into the controller. This is how it knows how fast the motor is running and when to turn power back on. It could be that the circuit board is 'ticked off' because of the amount of current coming back in.

Some questions for you:

Try disconnecting the motor from the grinder and trying it again. Does it still happen or does it happen easier?

Does that unit require a resistor to match the motor size or is there some other way to set it?

It there a POT on the board for requlating the slowdown speed?

Is this the same motor/controller that Pendentive is using?

Steve

PS I'm not a motor guy so I probably can't tell you to 'flip the foobar' and it will all be better. But that is information that will help determine the trouble.
 
Sando,
This is exactly the same setup that Pendentive is using. when i turn the potentiometer from 12 to 7 nothing happens, like is is not connected, then at 7 o'clock it starts to move and as i turn it the grinder goes faster, thats okay, i just don't like the "dead" spot between 12 and 7. Also, yes there is a pot to adjust max and min speed, but when i adjust the pot,i can't get the grinder to completely stop. In other words, when i turn the grinder on it starts to move before i touch the potentiometer and it keeps moving slowly from 12 to 7 and then picks up speed. I tried disconnecting the motor from the grinder as you suggested and yes,it is harder to tripp the controller, which by the way is the circut board from Surplus Center, not the house circut. I hope this answers your questions, thanks for taking the time out to help. Tom
 
I'm coming in late on this conversation so please ignore me if this doesn't apply.

Obviously starting current on a motor is higher than running current. The motor may have "starting" windings that kick under under a certain RPM, this might be what cause the current spike that trips the breaker.

If I read this correctly, you guys want a 0 to whatever max rpm continously variable rpm speed? I'm not an electrician but I don't think you can get that easily with an AC motor, possibly DC but at certain low rpm's the current would be close to stall current.

Where all these compenents sold together as a set? SOunds to me like the compnents are mismatched for what you want to do.

I would guess it's not a "dead spot" in the controller, it's just not send enough power to get the motor going. Substitute a light bulb for the motor and see if it come on at the lower settings.
 
copy cat,

I think I understand a little better.

>> In other words, when i turn the grinder on it starts to move before i touch the potentiometer and it keeps moving slowly from 12 to 7 and then picks up speed.

Oh that's fine. I set my minimum so it is spinning, but the slowest speed that's usable. If you want it to stop you turn it off. The min adjustment isn't for stopping - it's for the minimum speed you want.

The dead spot from 12-7. Adjusting the minimum speed might help. Does the manual give instructions on adjusting those? I'd hate to give you a method that wouldn't work right for you. (Personally I wouldn't sweat it. You don't have to go to zero before turning on and off.)

Do you have a DC volt meter? You can use that to see if you are getting max speed. When it is running full tilt you should get about 90VDC.

Problem 2, sounds like the controller is frustrated with the amount of current coming back at it from the motor. Is there a decelerate adjustment?

Again, does this controller require a resistor to match the motor size? Or does it have an adjustor?

Steve
 
Hello Tom

What kind of controller do you have? Is it a 3-phase type? If it is a 3-phase type, and it was designed properly, you should be able to get the full rated torque of your motor from zero speed all the way to 100% rated speed. The speed of the motor should be continuously and smoothly variable using the pot or keys/buttons on the front of the controller. The motor should not vary in speed as your load is applied up until the controller detects that the current is over the motor's ratings and it trips out.

Check what type of potentiometer you have. It should be something in the range of 10kOhm or so. Make sure that you have a linear potentiometer (50% rotation gives 50% resistance when measured between the middle terminal and any one end terminal). This can be checked with a meter. If you have a logarithmic potentiometer, you may get the effect that you describe when starting. Log-type pots are mainly used in the volume control for your radio, stereo, etc.

Your problem with the motor not starting at zero speed when the pot is at 12 could be due to your having a poor quality pot or a log-type pot. Disconnect the wiring to the pot and check the resistance value of the pot as you rotate it, starting from 12. Your meter should read either 0% or 100% of the pot resistance value at 12.

I gather that you are slowing down the motor by turning the pot. When you slow down the motor using the controller, the motor is made to act as a generator. The motor converts the kinetic energy (momentum) built up in the rotating parts of the motor, and all the connected moving parts, into electrical energy. The energy energy is transfered from the motor to the controller. Unless you have a really sophisticated controller that can put that energy back into the mains supply, the energy has nowhere to go and it accumulates in the capacitors across the DC bus of the controller. This pumps up the DC bus voltage. At some point, the DC bus voltage will get too high and the controller will trip out to protect itself. The motor will no longer be controlled by the controller and just free-wheel to a stop. Depending on how the controller was designed, you may or may not get some indication of why the controller tripped. If you do, it should be something along the lines of "DC bus over-voltage". There are two ways to prevent the controller from tripping when slowing down the motor. The first is to decrease the rate at which you slow down the motor. You will have to find out what rate is useable by trial and error. The second way is to add a dynamic brake resistor to your controller, if it allows this. If it does, the controller will automatically connect the resistor across it's DC bus when the voltage reaches some threshold. The resistor will absorb some of the energy coming in from the motor, keeping the DC bus voltage within the design limits. By using a big enough resistor (low resistance, high power), the motor can be made to stop almost instantaneously. The resistor will get really hot so it will have to be mounted where there is cooling air and you will not be able to be burnt by it.

When starting a typical 3-phase motor by connecting it directly to the mains power, it will draw up to 6-8 times the rated running current for a second or two. This is due to the physics related to the coils in the motor and the speed of the motor (zero) at that time. Reducing the rate of speed increase of the motor will reduce this current surge. Your motor controller should have the ability to do this for you.

Sorry for the long post. My last job was in the R&D department of a company that makes 3-phase motor controllers.

Phil
 
Phil, I believe he is using a DC treadmill motor, and a solid state controller for it, possibly open type.:eek:
 
Hmm, sounds to me like you have an overload condition on your motor, does your grinder turn freely? it should!, the 12 to 7 deal sounds like the controller has to pump a lot of current in order to get things moving. it could be that you have too much inertia for the motor/controller to handle.(Inertia is an important factor when sizing a motor to an application). also double check your wiring to make sure that you dont have the armature and field wires reversed. I don't know exactly what would happen if you did but I'm sure it wouldn't run properly. also check to see if there is a pot labled "BOOST" this is an adjustment for adding current to help with inertia. If everything runs ok with your grinder disconnected, then your motor controller are probaly ok! if not triple check your wiring
these kinds of problems are usually operator error, even with people experienced in these matters.

good luck, Jerry

P.S. If you don't go crazy you will learn a lot about motor/controllers.
 
Thank you to everyone who took the time to answer some of the problems i'm having. The controller does have a brake built in,its not hooked up at this time maybe i have to look into that. The controller is a Minarik, and they have a website with the manual listed, ( I did't get one with the unit) the website is www.minarik.com-PDFs, (sorry, i don't know how to link it). Thanks again to all, Tom
 
I reread the posts again, and feel i didn't answer all the questions, Phil, its not a 3 phase, Mike yes its a threadmill 1 1/2 to 2 hp motor with a solid state motor, Sando, i don't know if it requires a resistor. To anyone who wants to see a pictures of this, so a search for kmg on a shoestring budget by Pendentive, I have exactly the same setup except for the reversing switch. Tom
 
Tom

Sorry about the off-target stuff regarding the 3-phase controllers. I should have waited for the answer to my first two questions.

I do think that my comments about the pot could still be valid. I have not designed DC controllers but they will have the same type of circuit to sense the position of the pot as in an AC controller.

I suspect that my comments about the controller tripping when slowing the motor may apply also. The output stage of your controller will look like one-third of the output stage of a 3-phase controller and DC motors will also regenerate in that situation. The energy from the motor will have the same sort of effect on your DC controller as it would in an AC controller. Connecting the dynamic brake resistor should take care of this problem. Check the manual to see if the controller has an internal brake resistor. If it only has a "brake chopper transistor", or something like that, you will have to add an external brake resistor.

Phil
 
Hi Phil,
You're right about the braking, according to the manual, it says i need a 40ohm resistor with a minimum power rating of 448 watts, is says something like the motor current flows one way and when you slow it down the current flows the other way and that might overload the system. I hope that makes sense, electronics is not one of my strong points. I will try the resistor when i get a chance to go to the store and buy one, right now i'm snowed in, and the wife is snowed in at work, i have nothing to do but play with my toys, ahhh life is good. Thanks,Tom :D
 
Copycat,

>> 40ohm resistor with a minimum power rating of 448 watts

From what the manual says, sounds like that's exactly the problem. BTW finding that resistor is tricky. Once, upon a day Radio Shack had a nice selection and you could count on getting what you needed. But now they are full of cell phones.

Better use the phone or the internet to hunt one down. BTW there isn't any problem going over 448 watts. You could use a 10,000 watt resistor if it would fit. The important number is 40 ohms.

Steve
 
All right, the new/used in good condition motor arrived 2 days ago. I hooked it up and before starting I’ve been turning the pot to 0. Turn on the motor, turn up the pot and away she goes, no problem with speed control. Turn the pot back to 0, the motor winds down to 0 RPM, shut off the motor, turn the DPDT switch to reverse direction, pot on 0, turn the motor on, turn up the pot and away she goes, no problem with speed control, from full speed to 0 RPM.
I did this for several cycles, and then all of a sudden the motor would not operate. As the temp in my garage was in the single digits, I didn’t hang around to see if it was the internal breaker on the controller (by waiting for it to reset itself). Heck, I didn’t even know that there was a breaker on the system. That was the day it arrived in the mail, when I got home from work. yesterday I didn't go out in the garage as it is colder than the day before.
As the grinder is not complete, all testing is done while the motor is lightly clamped in my bench vise.
Reading the threads here, I can adjust the controller pots later for a minimum RPM other that 0.
Also, these tests are repetitive on and off, which when in real use would not be happening, so I would think that it wouldn’t trip the breaker, I hope.
Like copycat, this is the same setup that Pendentive is using, same part #’s from the same sources.
Also, being the procrastinator that I am, who knows when it will be finished, I still haven’t gotten the bearings for the grinder, which still needs to be welded together. Soon, one of these days, oh yeah. :rolleyes:
This Saturday, I may end up at Indian George’s and work on the grinder that HammerFall wants to put together, I got the steel for the grinder, I got enough for 2 units, and HammerFall is getting one.
I wonder if pendentive is having the breaker problem.
Also, what size pulley is being used on the grinder drive shaft, as I was thinking that 4800RPM is awfully fast, using a larger pulley at the grinder will slow the machine down and increase torque, how much, I don't know the math on that, but I know that's the way it works.
If this thread doesn't make sense in areas, that's because I don't make sense all the time either. :D :D :cool:
 
Sando, T Blade,
Again you're right Sando, i went to Radio Shack and asked for a 40 ohm resistor and the guy looked at me like a had 2 heads, i'll do some research and call a few friends to see if i can find one. T Blade, I'm glad you received your motor and everything seems to be working, but you might have to use the resistor, you'll see what i mean when you put a load on the motor, its annoying that everytime you slow the motor down it tripps and you have to wait cause theirs no reset button. Keep us informed of your progress. Tom
 
Grab a chunk of a dead heating element, measure it and wind it on a piece of pyrex or ceramic . Or else there's a suitable power resistor at Surplus parts look for
RWF-HLA100-200 200 ohm 100w, Adj. WW Restr 9.00 five of them in parallel will do the deed

HTH
Jorge
 
Tom

I would not expect that you could buy your braking resistor at Radio Shack. The guy in motor drives sales, here at work, suggested looking up companies that sell motors or motor controlers/drives in your local yellow pages. Those companies should have access to appropriate suppliers. He also suggested checking e-Bay.

Your cheapest source would be any surplus electronics stores in your area. You may be able to find some suitable ones that you can connect together to get the rating that you want. The most common type you will find there will be in the form of a brown ceramic tube, about 6-12 inches long and about 1-2 inches in diameter (see example at www.ohmite.com/cgi-bin/showpage.cgi?product=270_series). You can also pull them out of some junk equipment. It is obvious if the resistors are bad - they look burnt.

The values of 40 Ohm, 448 Watts is probably not that critical. Just do not go under them. 47 Ohms is a common value and would probably work. A value of less than 40 Ohms may blow out your brake chopper transistor. A resistor with a rating of less than 448W may burn up. It is acceptable to make the resistor up using a number of separate resistors connected in series and/or parallel. Get some help if you don't know how to do the calculations or make the connections. Check the final assembly with a meter to make sure that you got it right. Make sure that you mount them where there will be good air flow to cool them. If possible, put some kind of wire mesh cover over them so that you wil not get burnt or touch the electrical connections (high voltages present!).

One last suggestion the sales guy made was to use a bank of light bulbs. It would take some experimentation to get this right though since the current drawn by the light bulbs would not be constant.

Hope this helps.

Phil
 
For a good price on your resistor try surplussales . They offer their part number RWF-J81-0373-20 (20 ohm, 225W 10% Tubular) for $6.95/each.

Two of these wired in series will yield a resistance of 40 ohm and a power rating of 450W.

A new 40 ohm, 440+ watt resistor will cost about $60 to $100.
 
Seeing as most of this drive equipment that copycat and I purchased is from SurplusCenter, I went back there and plugged "resistor" in their search engine and this is what I came up with http://www.surpluscenter.com/item.asp?UID=2003082613345366&item=11-2102-R43&catname=electric I don't know if this would work, it seems to be for a lesser HP motor, but it's the highest HP rating that they have. I guess I could call the technician at Surplus Ctr. and ask them.
 
That's about a 3-5 watt resistor , It'll make a nice light show though!

N Hamilto40:The reason I spec'd the other resistors is with a parallel connection , if one fails you'll still be partially functional. With two parts in series , either one opening causes a failure.
my 2c Jorge
 
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