Harold gave me the bug! (Andy builds a mill)

Fla._Deadheader · April 03, 2003, 05:32:53 PM

The Pulse Width Modulator is what I have. First, the guy said I had a Series wound motor. I needed a Permanent magnet motor. I bought one. Then, I had him build a board that would handle 120 Amps and use the 80 amp PWM to run the 120 amp board. That worked for 2 hours, NOT a steady run, but, probably 75 minutes total. The cheap pot he supplied quit working, so I got a better pot. That lasted about 6 hours and that control feature quit. The pot still works, according to my ohmeter. Then the PWM board blew a mosfet and it quit working altogether. That's where it stands.?????

Dave_Fullmer · April 06, 2003, 03:16:41 PM

Harold,
I was hoping you would have that feed thing all worked out and tested by the time I got back so you could just give me a list of all the details and I would go out and purchase the stuff and make it work on mine. Now what am I going to do? ??? ??? ;D ;D

Fla._Deadheader · April 06, 2003, 03:36:50 PM

Hi Dave. The controller for the motor is $240.00. I MAY go to hydraulic feed. I have the power for it and total would be about $300.00 including hoses. Money is tight, so, I'm sitting here trying to figure the best approach.

I COULD sell you the 12 volt motor, and then I could get the hydraulics??

Dave_Fullmer · April 06, 2003, 03:52:31 PM

Harold,

I just might be interested. Why don't you give me an email message at dfullmer@aeneas.net.

Dave

D._Frederick · April 07, 2003, 04:32:10 PM

Fla._,
If you are thinking about going to a hydrualic feed system, give some thought about a hydrostatic drive. One lever gives you forward and reverse plus speed. This system does not over heat the oil.
How did you make out with the smaller hoses for your log lift?

Fla._Deadheader · April 07, 2003, 06:01:50 PM

Hi D. Went from 3/8th's to 1/4" and it works very well. Don't have to lift-wait-lift anymore.

Fla._Deadheader · April 08, 2003, 05:51:12 AM

Dave. The guy I got the controller from is going to repair it and work with me to get this figured out. I am buying a second unit and that will give me a spare. The first has been through h***. I will keep you informed.

Dave_Fullmer · April 08, 2003, 12:44:50 PM

Harold,
That sounds like a good solution for you.

It really surprises me about your hose size. Obviously, I don't understand all I should about the principle. I would have thought bigger would have been better in the application.

Dave

Fla._Deadheader · April 08, 2003, 04:03:45 PM

Dave, the pressure doesn't fully build until the load gets real heavy. Even so, a smaller hose will allow LESS oil to flow and therefore the load will move slower and not stall the motor. May not be according to Hoyle, but, works for me !!

Mark M · April 08, 2003, 09:17:18 PM

Andy are you talking about a hydraulic motor to drive the band? if so is there a certain reason you want to do that?

Mark

Dave_Fullmer · April 08, 2003, 10:39:25 PM

Harold,
I think I am beginning to see what I missed. I think I remember you saying that your were using a Ford starter motor. What didn't register to me was that you were stalling the motor. I can see now why smaller hose could limit the volume of flow and prevent the motor stalling. How did you connect the starter motor to the pump and what size pump are you using (gpm)? I'm just curious.

I bought an 11 gpm pump from Northern. Also bought the cylinders and tank from them. The $900 plus was a little bit of a shock, but I'm ending up with 7 cylinders on this thing. I have to admit that I'm going over my budget a little.

Jason_WI · April 09, 2003, 12:16:07 AM

All this talk of smoking traces off of boards and popping MOSFET's has got me interested in your problem. ;D

What is the make and model of your DC motor?

Where did you find this motor controller? Is there a big a$$ heatsink on the FET's? There should be and maybe even a fan too to keep them cool. Are the gates of the FET's being properly driven? If they are sitting in the linear reagion for any amount of time it will generate a lot of heat and eventually smoke your H bridge.

Links to the specs is what is needed to see if you have a mismatch of parts here. Schematics would be great if you have them for the controller.

Creating a PWM signal is the easy part. Putting that signal to an H-bridge and driving a load is a whole different ball game.

Jason

ADfields · April 09, 2003, 03:31:28 AM

Mark, what I am looking at is working inside in Alaska in the winter and still be able to go portable in the summer, set a pony pump in the corner and pipe the exhaust (via a heat exchanger) to outside. The more I kick this around the more I think I will go electric with a big genset. I found a guy that has 5 horse motors for 60 bucks up hear, I'm thinking a stack of 3 for the band and a 4th for the pump. I been doing income tax stuff :P for 4 or 5 VERY long days now :

and have not had time to think on the mill much let alone work on it. >:( Got that all done and as always I just get a very small part of my money back from Sam, I think I just payed for one of the J-dam gifts we sent our Friend in Iraq.

I have 2 big fears in going all hydraulic. First is enough constant power with heating the oil to death, and the other is price. The price part is more that I don't want to put the money into it that it calls for and find I did it wrong and have the wrong parts payed for, been down that road and don't like the town at the end!! :

I would get way better fuel mileage from hydraulics then the gen set also.

I'm sure open to input! ???
Andy

Fla._Deadheader · April 09, 2003, 05:51:08 AM

Dave, I am using a 4 piston pump @3.9 GPM. I got the unit as pump, res, valve, from Surplus Center. We used it on our punch press, until we had a problem. I bought another and kept this one as a spare. It is belt driven with a variable drive pulley on the motor. New, $320.00. Find an outboard mechanic and see if you can use the tilt cylinders. They are short and when the pump goes bad, the guys here throw the whole thing in the yard for parts. Cylinders rarely go bad, just get eaten up from salt water.

  Jason, where were you when I started this project ????? :D :D :D

  I have limited info on the motor. Papers are at the shop. It is 12 volts, permanent magnet, 3/4 HP @ 58 amps. Leeson.com
  I got the controller on Ebay. I exchanged several messages with the guy, before buying.

  There is a big?? heatsink on the board with 5 fet's attached. When I use the mill, the top of the control box is laid back and the board is completely exposed to the air, no fan, YET ???

  From there, you lose me. When I got the unit, I had a starter motor driven by it. It worked for a short time. I sent it back and it was replaced with a heavier amp model (120). A board was added to be driven by the PWM and actually run the motor. It worked for about 4 hours of actual use. Then it melted a mosfet. It had 2. Tere is a controller that matches the motor, but, at $240.00 and no-one that seems to know how to make this thing reverse, I am hesitant to buy it. That's all I can tell you. Thgere may be a diagram on ebay that shows the PWM. If you want, go to (motorspeed control) and click on 80 amp PWM. I think?? I saw the diagram there??

  When I burnt the track, it was on a used WM board that was sent to me. I am NOT sure if I had it hooked up right. It MAY still be OK, if I solder some small wires to the track?? That is the only thing I can see that is burned?? :

Andy, I think Timber Harvester is all hydraulic, BUT, they drive the blade with belts. Get their free video. You can always hook the exhaust to the outside.

Mark M · April 09, 2003, 08:14:22 AM

Hi Andy

We I'm not sure I can be of any help, but I think if you can direct drive the band with a belt it would be more efficient. As you know there is always some loss when you convert from mechanical to something else (hydraulic, electric, etc) and then back to mechanical. Most applications I am familiar with that use hydraulic drives is because of a need for speed, gear ratio, and or direction control as in the case of a hydrostatic drive. Also it works well in the case where it is difficult to attach a drive shaft or when the power source must be located remotely.

As for heating the oil, unless you are dumping across a relief valve a lot or operating wet clutches that slip on engagement (as in the case of a powershift transmission) you shouldn't build much heat. Oil circulation through a closed loop doesn't really get that hot. We have trouble with our hydraulic excavators running too cool when it's cold out. Even in the summer they only run around 140F which isn't even hot enough to get rid of condensation. You might have to use an oil cooler, which could provide heat in the winter, and you might have to use a fairly large sump (say maybe 30-50 gallons), but I don't think it will be hard to cool. Also I would recommend using a 0W20, 0W30, 5W30 synthetic oil such as Mobil 1 or one of the Petro-Canada products. This will give good oxidation resistance if it does run hot.

I think you are right about hydraulic being more efficent than electic drive, but my choice would be belt drive.

Good luck

Mark

D._Frederick · April 09, 2003, 04:01:21 PM

Fla._,
Glad that the smaller hoses solved your problem. It sounds to me that your piston pump is a veriable displacement type pump. With the smaller hose, the flow is restricted and your pump reduces the volume it will pump at a given pressure. If you had a constant volume pump like a gear pump, the hose would not have helped.

Fla._Deadheader · April 09, 2003, 04:15:11 PM

"D", you may be correct. I'm no hydraulic mechanic. It just works.

D._Frederick · April 09, 2003, 04:41:21 PM

ADFields,
A hydraulic drive to power your band requires a large displacement pump and hydraulic motor, also it takes a large diameter hose to handle the high flow rate. A hose this size is very stiff and hard to handle. If I was setting-up a hydraulic system for the rest of your mill functions, I would go with a closed loop system and use a veriable displacement pump. With this type system, you have no oil flow until a value is open. Since there is constant pressure in the system, two or more controlls can be operated at the same time. If you want to go first class for your carriage feed system, either go hydrostatic drive or a veriable frequency drive with a ac gear motor.
Using a motorgen set will allow you to saw inside and not have all the noice and exhaust of engine. It will also give a more even power to your saw blade and will not lug-down like a small engine.

Jason_WI · April 09, 2003, 05:34:21 PM

Harold,

I looked on ebay and only found one 80 amp, 12V PWM motor controller. It looked pretty whimpy for a 3/4 HP motor.

This may not be the same one that you have though as it said it was made in Yugoslavia. ???

I think that you will need a larger controller. Something like 200 amp or so to handle the startup current. The plate rating I believe is for continuous current and the startup current for a few pulses of the PWM could be higher than the controller can provide under a load. I think this is what is killing your PWM controller boards. Although I am just speculating this, the only real way to prove it would be with a current probe and an oscilloscope.

The only other thing that may cause controller failure is if the voltage sags going to the controller under a load. With the amount of current that you are pulling from the battery you should be using 6 AWG copper stranded wire at a minimum. Keep the wires as short as possible from the battery to the controller. Use the same size wire to the motor. Also sheck to make sure that your alternator can keep up with the demand.

Jason

Fla._Deadheader · April 09, 2003, 06:45:11 PM

Jason. That is about what the controller is that I have. Mine is 120 amp. The guy I deal with thinks that there are "spikes" returning from the motor and he thinks they have to be arrested with Varisters.

   I have #4 battery cables going to a terminal strip. From there, I use 2 #8 wires to the PWM and to the drum switch for each connection. From there I connected #4 welding cables to the motor.

  I run a 10 amp battery charger all the time on the separate battery for the motor feed only. Could it be that low voltage is causing the burn-outs??

  Really appreciate yer input. ;)

Jason_WI · April 09, 2003, 07:44:56 PM

Harold,

I took another look of the picture of the board on ebay. There is no physical way that board can supply 80 continous amps of current. There is only one thick trace on the board going to the pairs of MOSFET's and even with 2 oz copper on that one layer there is no way it can supply the rated current.

I talked to a analog engineer here at work that has experience designing PWM motor controllers and he had mentioned that it would take 1/8" thick copper buss bar 1/4" wide to supply the current that you are trying to supply to your motor. So with that one wimpy trace there is going to be a large voltage drop across it.

Also he noticed that the package size of the MOSFET's that are being used are only TO-220. He calculated with 80 amps of current and a on resistance of the device at .010 ohms the power disipation for each part would be 64 watts each. Way too much to dissipate for a TO-220 package size and for that size heatsink.

He had also mentioned that if you have voltage spikes coming back to the controller that you can snub them with a 0.1uF, 50 volt polyester capacitor attached directly across the terminals of the motor. You might be able to get one at radio shack or I can send you one via mail if needed. The varistors the vendor mentioned would do nothing to snub out the voltage spikes.

Also check to see if your battery voltage is staying anywhere from 12 to 15 volts. The lower the voltage is the more current the PWM controller has to provide to the motor to maintain the same speed setting.

Sorry I don't have good news...

Jason

Fla._Deadheader · April 09, 2003, 08:04:32 PM

Jason. What would be your guess on how much actual current is being used by the motor? 1 person can push the sawhead while it is sawing. It can't be running at half of it's rated load, with the gearing I have, or, am I figuring wrong??
My son tried to push against the sawhead while it was cutting, and it didn't even know he was trying??

Jason_WI · April 09, 2003, 08:34:14 PM

Hmmm

With the gear ratio that you have and with the ease of pushing the saw head there should be little load on the PWM controller, say maybe 30 amps. Hard to tell with out more specs on the motor and the acutal pulling force required to move the saw head.

Do these fail under similar situations every time or is it a random poof and smoke rolls out?

I would try the cap across the motor leads. Maybe those spikes are breaking down your MOSFET's over time and then poof.

Jason