Well my home brew metal cutting 20" three wheel bandsaw has finally semi died. it has been used hard and worked great for over 2 years now. The other day I was using it and it just died. Checking it out, I found the fuse in the DC controller blown. Replaced the fuse with a standard 10 amp fuse and it blew right away when i turned it on. However I can put a 10amp plug in type CB i it and it will work fine.......original fuse was one of those slow blow types...
Anyhow the motor runs fine, but I have no speed control. The saw runs full speed all the time. I have no clue what to look for in tesitng the speed pot, so is there any guidance on that process? I even turned down the internal trim pots to minimum and the motor was not affected, and still runs full speed. So if the speed pot itself was bad would not the internal trim pots still be capable of regulating the speed? I have a hunch its not the speed control pot used to control speed, but something internally in the controller that went south. But I am open to all suggestions.
The control is a Dart 250G. Any suggestions appreciated.
DC motor controller........no control........help
Re: DC motor controller........no control........help
There are several methods of speed control: scr or triacs using phase control in conjunction with bridge rectifiers or as part of the bridge, high power FET or
less efficiently a high power junction transistor(s) with pulse width modulation. As power semiconductors tend to fail shorted, it is likely that the power handling end of your controller has failed and is delivering the output of the power supply to the motor. The design of the controller will determine if the rest of the controller is toast as well. Some designs will leave the rest of the controller intact, others will take out most of the active circuitry. There may be an internal fuse but that is not likely to be the problem. SCR, triacs and FETS are easily replaced but other semiconductors need to be checked for downstream domino effect failures. A simple DC motor controll can be built with a dual 555 PWM controller, a power supply (15VDC and whatever the motor needs) and a enough 8-10amp 250-400v
FETs paralleled to handle the load. FETs are very efficient and don't get hot when pulsed at 10-20khz. either as series controllers or in an H bridge.
Steve
less efficiently a high power junction transistor(s) with pulse width modulation. As power semiconductors tend to fail shorted, it is likely that the power handling end of your controller has failed and is delivering the output of the power supply to the motor. The design of the controller will determine if the rest of the controller is toast as well. Some designs will leave the rest of the controller intact, others will take out most of the active circuitry. There may be an internal fuse but that is not likely to be the problem. SCR, triacs and FETS are easily replaced but other semiconductors need to be checked for downstream domino effect failures. A simple DC motor controll can be built with a dual 555 PWM controller, a power supply (15VDC and whatever the motor needs) and a enough 8-10amp 250-400v
FETs paralleled to handle the load. FETs are very efficient and don't get hot when pulsed at 10-20khz. either as series controllers or in an H bridge.
Steve
Re: DC motor controller........no control........help
Yo Roy,
First, Steve is correct in everything he says. I will try to be more specific. I googled <Dart 250G> and the second link is the full manual in PDF. Excellent [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
From your description you most likely have one or both shorted SCRs (Q3 - Q4) Use an ohmmeter, preferably an analog type like a Simpson or Triplett, or a digital model with a diode position to measure Q2 & Q3 for a short circuit condition between the cathode and anode. You should also check diac Q2-2, D10 & D9 which is your downstream path. A visual check of the circuit board for burnt traces is also a good idea. Q2-2 may be the only other thing damaged.
These power (SCR) parts are the most common failure mode as they are the most stressed. If you have the manual, it should help with ordering parts. If you don't, the link is below. Good luck.
http://www.dartcontrols.com/InternetCon ... Manual.pdf
Also make sure D7 across the motor in not open. This is your back emf protection diode.
After reading the manual a little more, the SCR package may be a sealed proprietary item. Manufactures do this to make it difficult for someone else to repair it. Making you buy their inflated pricier parts. If they will even sell it to you. (SOBs!)
First, Steve is correct in everything he says. I will try to be more specific. I googled <Dart 250G> and the second link is the full manual in PDF. Excellent [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
From your description you most likely have one or both shorted SCRs (Q3 - Q4) Use an ohmmeter, preferably an analog type like a Simpson or Triplett, or a digital model with a diode position to measure Q2 & Q3 for a short circuit condition between the cathode and anode. You should also check diac Q2-2, D10 & D9 which is your downstream path. A visual check of the circuit board for burnt traces is also a good idea. Q2-2 may be the only other thing damaged.
These power (SCR) parts are the most common failure mode as they are the most stressed. If you have the manual, it should help with ordering parts. If you don't, the link is below. Good luck.
http://www.dartcontrols.com/InternetCon ... Manual.pdf
Also make sure D7 across the motor in not open. This is your back emf protection diode.
After reading the manual a little more, the SCR package may be a sealed proprietary item. Manufactures do this to make it difficult for someone else to repair it. Making you buy their inflated pricier parts. If they will even sell it to you. (SOBs!)
"The machines are gaining ground upon us; day by day we are becoming more subservient to them" ~ Samuel Butler (1863)
Re: DC motor controller........no control........h
Thanks guys..y'all confirmed my thoughts. I guess its toast then as I am not electronics smart by any means......a few simle things yes, dut I could not tell the anode from a cathode if it had big letters on it....Just looking up some prices however there probably is not $15.00 worth of parts in it if I was to replace all the items that were listed as "suspect" or to check...........I found quite a few of those items thayt equated to part numbers of actual electronic components, but none of the Q-"X" were listed but they still are cheap from just a handfull of ones I looked at.........The board is able to be removed but most items are pretty well encapsulated in clear epoxy, but I think they could still be replaced.....
So any suggestions on a replacement unit..........that would work with my Leeson 1.5 hp, 107 VDC, 15 amp treadmill type motor.......or owuld I be better off ditching the motor and go with something else with a new controller? I wa initialy told I oculd get by with this controller on the 107 VDC motor and it did work fine for 2 years or so, and the controller was bought used.
I have some other DC motors but most are also typical treadmill types of 90 or 180 VDC and in the 2+ hp range.......and I prefer to keep it on 115 VAC input if possiible.
Thanks again for the insight on my problem........at least it not dead dead, and I can still cut some wood and plastics but its metal cutting days are over for now..........at least temporarily.
So any suggestions on a replacement unit..........that would work with my Leeson 1.5 hp, 107 VDC, 15 amp treadmill type motor.......or owuld I be better off ditching the motor and go with something else with a new controller? I wa initialy told I oculd get by with this controller on the 107 VDC motor and it did work fine for 2 years or so, and the controller was bought used.
I have some other DC motors but most are also typical treadmill types of 90 or 180 VDC and in the 2+ hp range.......and I prefer to keep it on 115 VAC input if possiible.
Thanks again for the insight on my problem........at least it not dead dead, and I can still cut some wood and plastics but its metal cutting days are over for now..........at least temporarily.
Re: DC motor controller........no control........help
Well Roy, since I don't really know your saw, this may not be what you want but it's maybe something to consider. Convert it to a three step pulley with an AC motor. My feeling is that while continuously variable speed is nice, it's not really necessary. You may find that three steps of slow, medium and fast will do everything. AC motors are plentiful and cheap and there's no electronics to fail. The round rubber belt on this one is just stretchy enough to make changing speeds easy.
"The machines are gaining ground upon us; day by day we are becoming more subservient to them" ~ Samuel Butler (1863)
Re: DC motor controller........no control........h
I would have a hard time modifying may saw to adapt jackshafts etc to it at this stage of the game. Be a lot of redoing for sure.
If you never seen my homebrew saw check it out on my website. Its a real brute and has the guts or should say had the guts to cut anything and everything I ever tried. Been totally trouble free since day one up until now.....Guess a new controller is what I am gonna have to go with. I may have another suitable motor of less amps and IIRC may be different voltage( 90) and of 1 hp somewhere out in my yard full of treadmills..... I can probably get by on a 1 hp on it without sacrificing any power.
My bandsaw project is at: http://www.frugalmachinist.com/3wheelbs.html
It is quite extensive and covers 5 pages........was a good interesting project to make.............
If you never seen my homebrew saw check it out on my website. Its a real brute and has the guts or should say had the guts to cut anything and everything I ever tried. Been totally trouble free since day one up until now.....Guess a new controller is what I am gonna have to go with. I may have another suitable motor of less amps and IIRC may be different voltage( 90) and of 1 hp somewhere out in my yard full of treadmills..... I can probably get by on a 1 hp on it without sacrificing any power.
My bandsaw project is at: http://www.frugalmachinist.com/3wheelbs.html
It is quite extensive and covers 5 pages........was a good interesting project to make.............
-
heavy_groover
- Posts: 37
- Joined: Fri Jan 21, 2005 2:18 am
- Location: western PA
- Contact:
Re: DC motor controller........no control........help
Your monster bandsaw is quite an accomplishment by itself. As the others have commented, I'd also agree that the power devices are shorted, causing the input power to just be "full on".
The power device in this controller appears to be a SCR module, most likely mounted directly to the back plate or heat sink. These are typically a 6-pin module that contains 2 SCRs and diodes.
The parts list shows it to be Q3, Q4, D5, D6, and D7 all in one "package" like a little brick. The number they give is L512FY131 Gentron.
If you were to repair your existing controller, it would probably last a while, but the SCR module may fail again.
I'm not sure which model you were using, but I suspect that the failure may have been heat related.
The practical limit of many 120VAC input controllers is about 1HP. When some manufacturers show their 120VAC input controllers can be used at the higher end of the output currents in their models, they strongly recommend that an optional heatsink be used.
Large heatsinks and cooling fans are fairly critical for long life of most controllers, particularly over 1/2HP.
Unless the manufacturer recommends isolating the controller plate, choose a mounting method that maximizes heat dissipation.
For controllers that are mounted on a flat aluminum plate, they can be attached directly to the back panel of an enclosure (removing the enclosure paint and adding heatsink compound is advisable).
In addition to mounting the plate to the back panel, a large finned heatsink can be attached the same way to the rear of the enclosure.
If the entire assembled controller can't be mounted in a location where the heatsink surfaces are in free circulating air, a fan should be used to provide cooling.
Heatsinks should be mounted where they won't accumulate a build-up of dust and debris, which will reduce the efficiency of the heatsinks.
You will probably be limited to only about 3/4 to 1HP of useable power from your existing motor, by using a 120VAC input controller.
If you should decide to use a 240VAC input controller, you can expect to get the full 1-1/2HP from your existing motor (or more from one of your other motors).
HG
The power device in this controller appears to be a SCR module, most likely mounted directly to the back plate or heat sink. These are typically a 6-pin module that contains 2 SCRs and diodes.
The parts list shows it to be Q3, Q4, D5, D6, and D7 all in one "package" like a little brick. The number they give is L512FY131 Gentron.
If you were to repair your existing controller, it would probably last a while, but the SCR module may fail again.
I'm not sure which model you were using, but I suspect that the failure may have been heat related.
The practical limit of many 120VAC input controllers is about 1HP. When some manufacturers show their 120VAC input controllers can be used at the higher end of the output currents in their models, they strongly recommend that an optional heatsink be used.
Large heatsinks and cooling fans are fairly critical for long life of most controllers, particularly over 1/2HP.
Unless the manufacturer recommends isolating the controller plate, choose a mounting method that maximizes heat dissipation.
For controllers that are mounted on a flat aluminum plate, they can be attached directly to the back panel of an enclosure (removing the enclosure paint and adding heatsink compound is advisable).
In addition to mounting the plate to the back panel, a large finned heatsink can be attached the same way to the rear of the enclosure.
If the entire assembled controller can't be mounted in a location where the heatsink surfaces are in free circulating air, a fan should be used to provide cooling.
Heatsinks should be mounted where they won't accumulate a build-up of dust and debris, which will reduce the efficiency of the heatsinks.
You will probably be limited to only about 3/4 to 1HP of useable power from your existing motor, by using a 120VAC input controller.
If you should decide to use a 240VAC input controller, you can expect to get the full 1-1/2HP from your existing motor (or more from one of your other motors).
HG
Re: DC motor controller........no control........h
Heavy Groomer.......The controller it had used the entire chassis as a heat sink as it wa all finned and such. I also removed the original face plate as its mounting flanges were broken and it wa had to retain it on the chassis, and replaced it with a piece of aluminum plate to which I attached yet another large heatsink I acquired, and the aluminum cover I made was sealed and such to keep out any possibility of chips entering it. Then I mounted this controller directly in the airflow from a fan I had attached to one end of the motors double shaft that I used to pull in yet more air to flow over motor and controlle and the controller was mounted on a portion of the frame which again is steel and very cool. The fan mounted on the motor pulled in a heap of air, so much that i ducted a portion of it upwards through the 4 x 4 steel tube fame and had iot exit above the upper blade guide and it kept chips etc blown away from the cutting line etc, and also blew any accumulated chips out of the chip tray under th bottom drive wheel and made them fall out through the discharge chute......It worked great........and would find it hard to believe it got overheated in use......The shop is also air conditioned to the point you can hang meat in it...its cold in the shop to say the least. I guess I just have to chalk it up to age and use. Once I find another controller, I'll see what I can do to this one to possibly fix it, as I have a lot of other motors just dying to get used on various projects.......
Regards
Regards
Re: DC motor controller........no control........h
Heavy Groomer ?.......
That don't sound like the HG I know!
Personal Hygene is important, but I just can't see him saying "Mirror, mirror on the wall".........[img]/ubb/images/graemlins/grin.gif"%20alt="[/img]LOL! [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
DC
Re: DC motor controller........no control........h
Wow, I really did miss that "V" on the keyboard by a few letters didn't I? I guess I really need to do something about that missing index index finger.........
Sorry bout that [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
Sorry bout that [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
-
john58-
Re: DC motor controller........no control........help
Your scr or triac is shorted ......It controls your current to motor check with ohm meter from tab to pins one should be 10 ohms the other should be open ......if you have zero ohms its gone..replace with same amp rating or a little more 2-3 amp ...
the gate 10ohmsshould read open when leads of meter reversed also the collector
should read open to the emitter both ways....(.pnpn junction)
the gate 10ohmsshould read open when leads of meter reversed also the collector
should read open to the emitter both ways....(.pnpn junction)
-
heavy_groover
- Posts: 37
- Joined: Fri Jan 21, 2005 2:18 am
- Location: western PA
- Contact:
Re: DC motor controller........no control........h
That reminds me.. I didn't get a haircut last week.
By the professional work you put into your saw, I didn't really think you had hung the drive circuit on a nail in the wall (as I've seen some done).
The mounting info was for anyone considering a DC drive, which is a popular retrofit.
The Dart controller's power module is also used in the Leeson Speedmaster 174902/174903 models (and probably other brands/models).
You might try contacting Dart, Leeson or www.galco.com for a substitute/replacement module. I'm fairly confident that a replacement part is available, since there are other producers of these power modules (Crydom), used in both 120 and 240VAC models. Polyspeede refers to the modules as "power cube".
Examples of these power modules can be seen here
http://www.nteinc.com/specs/5700to5799/NTE5700.html
I believe your power module could be the NTE 5700 type, but I'm not recommending that part as a replacement, since I don't know the original Gentron part specs (Gentron appears to be defunct).
If the power module is faulty, the NTE pinout might help you confirm it with an ohm meter/diode check feature.
The KB Electronics controllers are available from dealers, surplus suppliers and ebay. They're well engineered and reliable.
They're available in 120 or 240VAC input, and 90 up to 180VDC outputs.
For extra protection, in addition to the motor controller fuses, there are other ways to protect the power modules in SCR-based controllers.
There are fast fuses that prevent module damage from high short-duration current surges which can cause the SCRs to short immediately, despite the AC input fuse protection and heatsinks.
Use of fast-acting rectifier-protection type fuses are required by some manufacturers.
HG
By the professional work you put into your saw, I didn't really think you had hung the drive circuit on a nail in the wall (as I've seen some done).
The mounting info was for anyone considering a DC drive, which is a popular retrofit.
The Dart controller's power module is also used in the Leeson Speedmaster 174902/174903 models (and probably other brands/models).
You might try contacting Dart, Leeson or www.galco.com for a substitute/replacement module. I'm fairly confident that a replacement part is available, since there are other producers of these power modules (Crydom), used in both 120 and 240VAC models. Polyspeede refers to the modules as "power cube".
Examples of these power modules can be seen here
http://www.nteinc.com/specs/5700to5799/NTE5700.html
I believe your power module could be the NTE 5700 type, but I'm not recommending that part as a replacement, since I don't know the original Gentron part specs (Gentron appears to be defunct).
If the power module is faulty, the NTE pinout might help you confirm it with an ohm meter/diode check feature.
The KB Electronics controllers are available from dealers, surplus suppliers and ebay. They're well engineered and reliable.
They're available in 120 or 240VAC input, and 90 up to 180VDC outputs.
For extra protection, in addition to the motor controller fuses, there are other ways to protect the power modules in SCR-based controllers.
There are fast fuses that prevent module damage from high short-duration current surges which can cause the SCRs to short immediately, despite the AC input fuse protection and heatsinks.
Use of fast-acting rectifier-protection type fuses are required by some manufacturers.
HG