Bleeder Resistors

[Alan Bienlein]

Yes they have mentioned something about the advantages of 3 phase but for right now a resistor that I had in my electronics parts bin that didn't cost me a thing is slightly cheaper than converting to three phase.

[Jeff Bratt]

Electronic discussions sure can stir up passions. Plus, there was ambiguity in some of the posts, and that never helps. But I'm certainly open to the idea that a bleeder resistor across the start cap could have the effects described. But learning something new usually brings up more questions...

There are lots of medium HP induction motors with start capacitors/windings -
Is this phenomena common to all of them?
Are there actually resistors installed on many motors, and it's just not apparent?
If not, do some motors exhibit this behavior more than others? Why?
Do some motors or applications "need" this resistor more than others?

I wonder - would Baldor or Leeson (or others) respond to questions like this?

[John P. Smith]

Well I think I benefited from this thread as I went out to my ts3650 tablesaw and put a 7,000 ohm 3 watt resister across the terminals of the start cap and noticed a difference right away. Before when I turned the saw off the whole tablesaw would shudder just as the centrifical switch for the start cap would close and now with the resistor when that same switch closes after I turn the saw off it smoothly comes to a stop. No more shudder or vibration. The 7,000 ohm resistor is all I could find in my electronics parts at the time but I'm going to try a 15 k just to see if there is any difference.

There has to be a reason for this little add on to smooth out the motor on shut down so instead of saying it has no use why not take another look at this and maybe post something useful as to why it works like this.

This is the real answer, you gotta try it to find out. It just proves the knowledge of a baseball player: "In theory there is no difference between theory and practice. In practice there is. " Yogi Berra

Ken, please leave this thread up, some good is gonna come of it after all. Now that we have all the theory's out of the way, and some guys start putting it into practice, we can find out what works, or doesn't. Anyway, they didn't really get ugly, just each sticking up for what they believe.

My question for Alan, if 7K works, why do you want to try a 15K? I know very little about electronics, so have no idea why you would want to go up or down with the resistance. It is a serious question, although I don't have any motors that shudder on shutdown, but I might someday.

[Anthony Whitesell]

Why 15K? Because 7K 3W is underrated. 220V over 7K requires 7W. Even 15K 3W will be underrated. One point that is fact, when the capacitor is in the circuit the resistor is across the 220V supply. The 97% discharge time for the capacitor is Capacitor * Resistance * 3. Although the time requirement could start a new thread in of itself, my thought would be to set the time value around the shortest amount of time one would expect the machine to be one.

[Callan Campbell]

The lack of agreement among people who actually know something about electricity makes me feel much better about my own complete ignorance on the subject.

Perhaps the best post in this whole thread................

[Aaron Rowland]

Many thanks to my supporters on this thread I hope some of you file this info in you head and pass it along some day to some who asks. The mags pay money for tips like this. You have my permission to use any of my ideas for free and make a buck. I'm not interested in the mag bit and never read them.

After all the arrows and slings hurled at me I was about to call it quits. Just one guy turned the tide and I thank you from the bottom of my heart. I also thank the others who joined in and Ken who did not pull the thread.

The wattage on the 7K resistor is marginal but ok since this resistor is only use for a very short period of time. 2-3 seconds at most. If its the shudder you are after I suggest that you run the 7K with another 7K one in parallel. That drops the total resistance value to 3.5K and may work a bit better. The wattage per resistor remains the same and should be ok if that's the only wattage available to you. Bigger in wattage is always better of course.
"
I mentioned in another post on" how many starts per hour can you make on a cyclone". I'll fall back on the old IT DEPENDS answer. Some motors have a built in thermal switch that shuts down the motor if overheated. Heat will wreck almost any electrical item and is to be avoided even with the thermal switch. The question is how come it overheated? Application specific motors should not over heat ever! My cyclones motors don't and I use two of them together. Why don't they over heat you ask? They are 5HP each running at a draw of 4 HP each. Totally under rated. I'm familiar with PF so don't go there please. On top of this the motors weigh over 90 lbs each and have a lot of mass. You can buy a 5 HP Motor that weights a 100 lbs or one cheaper one that weighs 50 lbs. No free lunch and the 50 lb one will over heat for this app if started to many times per hour.

During set up of your new cyclone run a amp draw test . A meter from HF is cheap insurance. Check the motor label for amps and deduct 10%. If you pull more then this during running talk to your supplier. I also know why this may not be 100% correct but don't go there.Please. Also check the impeller diameter to see if it matches the motor HP. Some suppliers, one in particular, hides the impeller diameter. Why I ask? I think I know and it's not pretty.

Allan, the thingey on the cord is an anti-theft device with a built in Cookie. It has a big memory and keeps track of how many times the saw was used. start up and amp record. Then once a month it hijacks your computer and emails the mfg with this info and your address. I read this on the net and of course then it must be true.( Wink).

[Halgeir Wold]

Hi Guys....
Been a member here for some time now - great forum -I'm a fairly regular lurker, but don't post or answer all that often, as many of the topics are rather "US related", and not always very relevant to a european way up north...
I really envy you your lumber yards - the most I can find of wood around here is construction grade pine.....

Now to this thread - there's a good mix-up of facts, heresay and urban myths in here....and yes- I'm a BScEE with 35 years of practice, mainly in electronics, but also in regular electrical engineering.

Motor capacitors are rated in two different categories - start and run capacitors. Start cap's are as indicated used just to start a motor, and are usually not as rugged as a run capacitor. Typical rating is 1.5-2%, indicating the expected percentage that cap is supposed to stay in-circuit. Run capacitor are usually of a more rugged design, as they are intended to stay in the circuit for continous operation.

A regular 3-phase moter can be run with singel phase and cap - the norm value is usally aorund 70-80 uF pr kW. A run cap for a single phase motor - being a bit of a misnomer as it usually requires a support phase with a cap - value is usually around 30-50 uF pr kW. From my experience, they are usually in the lower rated range for motor around 2-3 HP, or roughly 1-2 kW.
An extra start cap is often used in parallell to increase the starting torque, and swithed out of the circuit by a start relay or PTC resistors - typical for smaller motors, like refridgerators and the likes.
Motor capacitors are also film type caps- polypropylene mostly - not electrolytic. Electrolytics are polarized caps - used for DC circuits ( or sometimes for lov voltage AC, like audio signals...) Voltage should usually be 1,41 x line voltage + 15-20% for safety margin.

During my years, I've fixed, changed, repaired quite few motor "thingies", like table saws, planers, pumps, dish washers, washing machines - etc. I've never seen a bleeding resistor, though, and quite frankly never experienced this "thump" like behaviour. As described, a capacitor that is suddenly switched out of an AC circuit, like a start cap, will hold the momentary voltage it was left with, when the switch opened. If that switch is arching, it's just introducing a small timedelay, leaving that cap with another voltage along the sine curve. A good motor cap will hold this charge for hours and days......

While I've never seen a resistor used like this in a motor circuit, and never experienced the mentioned problem, I see no problems as such in using that resistor, but the comment on power rating is indeed very appropriate - 220V over 7kohms gives 7W of power, so that resistor better have some good rating and proper mounting, in case of a switch failure.....
7W for a few seconds is noe problem, though......

Best regards

[Alan Bienlein]

I guess I should have mentioned that my ts3650 is wired for 120 volt operation. The reason I was considering trying the 15k resistor was to see what difference it made. I also have some 7.5 watt resistors but can't remember there resistance right off hand.

Theories are good but until you actually try it it's only just a theory. Now can some explain to me why my motor comes to a smooth stop now that I have installed this particular value resistor accross the terminals of the start cap? Is it because all the voltage is bled off where as before there was still some voltage on the cap that momentarily energized the start windings when the centrifical switch closed again on shut down?

[Halgeir Wold]

Just read through that DC start/stop thread......while there certainly may be bad motors out there, the reason for the limited start/stop rating is probably the use of lower quality capacitors, with a limited service time as compared to regular run capacitors.
A 2% start cap is intended to stay in-circuit less than 2% of service time. If one estimates a 5-10 sec start up cycle, this ends up with a max of 72 sec pr hour, or appx 7-12 startups pr hour... A 1,5% service cap gives 5-10.....
- Guess I'd change that to a full service cap........

[Dan Hintz]

Some motors have a built in thermal switch that shuts down the motor if overheated.

If the starter winding is the weak link, does the thermal switch pay the majority of its attention to that section of the winding? Unlikely, so I can't say that's a safe thing to trust in...

[Dave MacArthur]

Based on the title of the thread, I thought this thread was going to be about people who get kidnapped in a bar, then wake up in a bath-tub full of ice and a cell phone taped to their hand with a note-- "you're missing your kidney now, call 911!", and that some people survived better than others because they were bleeder resistors...

I see now it isn't about some urban myth at all though!

[Aaron Rowland]

Urban Myths seem to be alive and well in some of the early comments posted here. I sure would like to know if any of these posters with an anti bleeder stance but with an electrical background have Cyclones and if they do did they use metal or PVC for the duct work. And if they used PVC did they attempt to ground it.

No looking for for trouble but there could be some valuable information passed on here by people who have an advanced knowledge of things electrical.

[Anthony Whitesell]

I don't know if I am anti bleeder or not. I don't have a cyclone and PVC duct, but a bagged DC with ABS duct. I can tell you that the shocks I got from the ductwork made my hand or arm numb (depending on where I got hit) for several minutes until I added a bare copper wire to dissipate the built-up static charge. There have been plenty of threads on this and I don't think this is the place to expand on this topic further.

[Dan Hintz]

And if they used PVC did they attempt to ground it.

Trying to ground PVC is akin to nailing a puddle of water to the wall.

[Aaron Rowland]

Thanks for posting Anthony. While there has been a lot of posts on this there may not be a consensus. If you live in a cold or dry climate the PVC can really build up a charge that makes you hurt.. I remember as a kid shuffling my feet on the carpet and getting shocks. That really fascinated me and I would do it over and over. As a 5- 6 year old I liked to unscrew the light bulbs and touch the sides or center of the socket and wonder why I got a shock from the center pin but not the out side edge. Was years latter in school I found out why. Our kids were the same way. The first grade teacher told the class not to ever stick a hair pin in a wall socket. Use your imagination here.

While a perfect insulator will not conduct electricity PVC pipe is far from perfect and when covered by a bit of dust readily conduct static. The out side of the pipe acts like a dust magnet because of the charge. That's good and helps cut down on the super fine dust particles in the air. To bleed off the static charge all one has to do is spiral wrap the out side of the pipe with wire, insulated or not. Makes no difference.Don't use anything inside because that could snag chips and stuff. I've seen posts about using sheet metals screws in both PVC and metal for assembly. NG, don't do that.

The best and cheapest wire is door bell wire. It's insulated but static does not care whether the wire it's insulated or not. Use only one strand with about a 6"-12" spiral. Ground one end and that's the end of getting shocks.

I have mine set up as a trick demo. I ran a sheet metal screw inside the pipe just a bit with door bell wire attached. Then I made a spark gap of about 1/8"-3/16" to ground near the cyclone entrance. Sawdust moving inside the pipe is what builds the charge. This puppy will really put on a show for visitors who know nothing about electricity and it terrifies them because they think its going to l blow up. I was going to build a more elaborate display like lighting a florescent light tube but never got to it. I should move on that idea. Spark throwing is more fun however.