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Upgrading wood chipper
2

Upgrading wood chipper

Upgrading wood chipper

(OP)
I am an owner of a wood chipper currently being powered by two 350 HP electric motors, each equipped with a soft start.  I am planning on replacing the chipper.  The HP requirement of the new chipper is 850 HP.  Therefore I am plannung on replacing one of the 350 HP motors with a 500 HP motor.  Two questions.  (1) Will I have to replace the existing soft start on the 350 HP? (2) How long does it normally take for delivery after ordering for a soft start?

RE: Upgrading wood chipper

If your soft starter is not rated for more than 350HP, of course you must change the soft starter...

Delivery is relative. If you need it fast, ask for it fast. Some people have them on the shelf, some take a week to make them, some take a month.

By the way if the motors are coupled to the same shaft of the chipper, they must be identical, both in size and slip. Otherwise one will drag the other as a load.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Upgrading wood chipper

(OP)
Thank you very much.  The motors are connected to a common pulley which is belt driven by the motors, same RPM but different HP.  the load varies depending on the amount of wood being fed to the chipper.  Will this be a problem?

RE: Upgrading wood chipper

If you feel very adventurous, you may try and start the chipper with ONE (the 350 HP) motor. The chipper has to be free of wood when doing this. Once the chipper is up to speed, it would be possible to DOL start the other motor. It will not be a very tough start because it is already up to speed.

It all depends on how strong your supply is. But if it is strong enough to feed an 850 HP load, I think that it would work. You can then either sell the superfluous soft starter. Or keep it as a spare.

I have seen this being done before, but then the motors were the same size. But, if you want to play it safe, just do what Jeff says.

Two motors on the same shaft could work, but you need to make sure they have similar rotor characteristics. A slight mismatch is not serious but do not run different NEMA classes on same shaft.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

(OP)
Again TYVM. As I understand it I may not have to buy a soft starter for the 500 HP. Right?
 

RE: Upgrading wood chipper

jraef; Would it be smarter to use three of the same 350s?

Hence having matched motors?  Also then only a new 350 would need to be purchased not a 500.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Upgrading wood chipper

Keith - you are even worse than I am!

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

Something not mentioned, both motors should have the same Design letter.
 See the Cowern Papers
http://baldor.com/support/literature_load.asp?LitNumber=PR2525
Look under:
GLOSSARY OF FREQUENTLY OCCURRING MOTOR TERMS
See.
DESIGN

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Upgrading wood chipper

Yes - that's what I meant with NEMA class. It is sometimes called Rotor Class in Europe - hence the mixing of terms.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

Replace the soft-starter on the 350hp motor that is still there? - No.

We could ship a soft-starter to you tomorrow if you ordered it before about 3pm tomorrow. But, if you want an enclosure and breaker and some extra controls it would take a little longer.
 

RE: Upgrading wood chipper

(OP)
We have an enclosure, breaker and controls already on both existing 350 HP motors.  Can we use same enclosure, breaker and controls for the soft starter for the 500 HP?  

RE: Upgrading wood chipper

You cannot use gear for a 350HP motor on a 500HP motor. You MIGHT be able to accelerate an unloaded 500HP motor with a 350HP soft starter that is going to be bypassed with a 500HP bypass starter, but that is a gamble.

I'm sorry, but if you are asking those questions, it is obvious that you need the help of a qualified electrical engineer who can visit your site and properly design a system to match your needs. This forum is not a substitute for proper procedures and engineering, it is to help qualified professionals who are stuck on particular issues and are looking for advice from those with experience; hence the "Tips" in the title. Please budget and hire someone who can do this properly and safely. A fire is VERY expensive!  


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Upgrading wood chipper

(OP)
I have had three PEs on site and each have had differing opinions on what is required.  I am not looking for a free design, just merely trying to better understand the complexity of it all.  For your info I have budgeted for this work to be done and I am not trying to save a buck as you imply.  Thank you for your input, it has helped me immensly to understand some of the issues. However your participation in this forum is voluntary. Sorry if you feel as though I am taking advantage of you. For all others, thanks again for your advice and comments.  It is much appreciated and I look forward to your continued involvement.   

RE: Upgrading wood chipper

Whoa. Just registered here for one day and going all judgmental on this forum's top ranked tip-master already ? Way to go kipawa.

Jeff is not "implying" anything as you are quick to assume. He is giving you a honest expert opinion given his tons of experience. I would listen to him instead of acting all offended.  

Muthu
www.edison.co.in

RE: Upgrading wood chipper

Try starting the chipper unloaded with just one soft start. If one motor can come up to speed driving the chipper and another 350 Hp motor you will probably be able to spin up the 500 Hp motor also and then go DOL when it is at speed. A quick test run on-site may be quicker and easier than several days of speculation.
Good call Gunnar.
If there is a little difference between the motor characteristics, mainly the full load speed, the motors may not share the load properly. It will be disappointing and expensive if the 500 Hp motor is limited to less than full output because the 350 Hp motor loads up at a slightly higher RPM.
If you find that one motor is loading up ahead of the other, you may consider having a machine shop reduce the size of one pulley slightly. If you have frequent short overloads and must trim a pulley you may want to match speeds at a little over 100% load.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Upgrading wood chipper

(OP)
Please don't misunderstand. I value  and respect Jeff's opinion as I do everyone else's opinion. However, I do not appreciate being lectured on how to run my business.  As Jeff says, this site is to help qualified professionals who are stuck on particular issues and are looking for advice from those with experience. The advice I received from professionals on this matter was inconsistent which prompted me in the first place to seek advice elsewhere.  I did not think for a moment that the forums were limited to professionals.  I may not be a PE but I have a substantial investment (4 mil) in my business and I am only looking for the best advice available before passing judgement. Nor was I looking for a substitute for proper procedures and engineering, only a fool would substitute advice for engineering.  Sorry for having offended you or anyone else. Please accept my apologies.

RE: Upgrading wood chipper

Sorry if I offended, I was trying to be as non-judgmental as possible. It's just that the nature of your last question had me concerned that you were in over your head and were not consulting a pro. It's unfortunate that you had bad experiences with PEs, but after 30 years in the Soft Starter business I can attest to the fact that a PE license is no guarantee of familiarity with every known technology. Even so, 3 opinions from 3 PE's is pretty good, in here you can easily get 5 opinions from 3 responders!

So back to your problem. Staged starting, the method espoused by Skogsgura where you soft start with one motor and run with both, is definitely a known and accepted strategy that works in a lot of cases. Since you have the 350HP motor already, it would not hurt to try to see if it will accelerate your chipper all by itself. If it does, then connecting the 2nd motor across-the-line once it is at speed should be fine. I do this all the time with some types of rock crushers, works great. But in my experience chippers tend to be very high inertia machines. I have had some barely accelerate quickly enough to avoid motor damage with all available horsepower connected. Acceleration is a factor of power AND TIME, in that you must get the motor to speed within the rotor damage curve time. So if you want to try this, make sure you have VERY GOOD overload protection. I would NOT trust a basic bi-metal thermal overload relay in this case, a solid state would be better and a programmable Motor Protection Relay would be best. If the Soft Starter has solid state OL protection built-in it's probably OK

So let's say for the sake of argument that this works. The next issue is one of motor matching. I cannot stress enough how critical it is that the motor slips be IDENTICAL for this to work. I did one chipper where the end user replaced one of a pair of 350HP motors with another of the same brand and model, but because they were made a year apart, the slips were slightly different (probably because of differences in materials). Before the change-out the motors shared the load within 1%, afterward the old motor was bearing almost the entire load and tripping on overload.

Bill (waross) had an interesting take, it may work but I never thought of nor tried that.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Upgrading wood chipper

(OP)
Good morning Jeff.

I am pleased we have come to an understanding.  I certainly appreciate your input on the matter and because of it I am now in a much better position to make an informed decision on next steps. I thank you all who have taken the time and patience to educate me. I wish all of you a very good day and many thanks again.

Kipawa

RE: Upgrading wood chipper

Say Jraef, more of a question for you than a suggestion at this point. If I'm off base here, please RF this thread to avoid confusion.
As you mentioned, my experience with chippers has been similar to yours; very high inertia and long starting times, but also very low power requirements running unloaded.
What could we expect with a small (20 Hp or so) motor with a VFD to run up the chipper until it may either go DOL or the soft start on one 350 HP motor may safely finish the acceleration? This technique has been discussed in other threads. Would this be a reasonable application?
Thanks Jeff
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Upgrading wood chipper

Or waross, a small motor with a VFD.  So you can take a minute or two get it all moving without thrashing the pony motor at all.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Upgrading wood chipper

Pony motor starting is what you are talking about. I have seen a few 1000HP and 1250HP whole log chippers started with a 150HP pony motor, so I doubt it's possible to start an 800HP with a 20HP even with a bigger belt reduction ratio and a VFD. But even then, these pony motors never were expected to fully accelerate the load, the required reduction ratio to create enough torque to move the mass prevents them from getting to full speed.

Then the other problem always was getting the pony motor disconnected from the shaft before the main motor is energized. I saw some pretty dangerous and scary things done to accomplish that, the worst one being a rubber tire pressed up against the coupling and kept in place with a come-along. Before energizing the main motor, they snapped the ratchet latch on the a come-along and let the tire pressure push it away. The guy who had the job of flipping that latch only had 3 fingers on his hand...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Upgrading wood chipper

Bill, Jeff

I don't understand how a smaller pony motor would be able to start the load (and the main motor) when the main motor itself is not up to the task. I understand using a pony motor on a synch motor but not on an induction motor.

Muthu
www.edison.co.in

RE: Upgrading wood chipper

edison123; F = ma

You can use a small amount of F regardless of m if you don't mind a being small too.

Getting a bunch of rotating mass up to speed is an exercise in energy management not in overcoming static friction.  If you can take a while you can store that 1/2mv2 over whatever time you want.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Upgrading wood chipper

I think that my previous suggestion was a little unclear. I was proposing a small motor driven by a VFD to bring the chipper and the large motors up to speed gradually as itsmoked suggested. Then either using the soft start or going DOL to kick in the 350 HP motor and then going DOL on the 500 HP motor. The small motor could remain belted. Some of the chippers I remember had quite a bit of windage but the fan laws being what they are, the chipper will be going quite fast before the windage load starts to build up. It may take several minutes to build up enough speed to be able to kick in the soft start but that should not be a problem with a VFD.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Upgrading wood chipper

You can take care of the sequencing by having the small VFD signal the soft starter to start.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Upgrading wood chipper

How can a bunch of smart people mess things up like you've done?

Forget 20 HP or whatever power you are thinking about. Forget the VFD. Just use the existing 350 HP plus soft start to bring the chipper up to speed. Then go DOL with the new 500 HP motor. Taking care, of course, that the motor slips are similar.  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

I suppose..

I was gonna say a 20HP triggering a 50HP followed by a 100, 150, 250, THEN the 350!  But NooOOOOo! You want to just cut to the chase.  How droll.

 

Keith Cress
kcress - http://www.flaminsystems.com

RE: Upgrading wood chipper

Tough but unfair. That's me!

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

That was my first suggestion, Gunnar but it was shot down on the basis of the very high inertia of a large wood chipper.
It's good to see you back from your working holiday.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Upgrading wood chipper

It should be asked - what are the existing starter ratings? You keep asking if you can re-use the starter. Why do you think that can be done?

You need a 500hp rated starter and about a 750A or greater rated breaker on that 350hp if you want to use it for the 500hp motor. So, buy a new soft-starter for the 500hp motor and set them both with the same ramp settings so the motors share during the start. That way, it will work once everything is installed. If you put in a full-voltage starter and the 350hp with soft-starter is incapable of starting the chipper you will have even more expense to get it working.

If the extra 350hp starter is fairly new then sell it or use it on another motor.

Bill - He can't test starting one motor today because he is changing the chipper to a larger chipper.

And I agree with Gunner - a pony motor is way off the mark in this case.
 

RE: Upgrading wood chipper

(OP)
Hello All

Thank you one and all for the interest you have shown in my wood chipper operation.

Perhaps I could have been a bit more descriptive of the situation earlier but here it is again.

I currently have a 4 knife, 96" disk diameter powered by two 350 HP motors.  I plan on replacing the chipper with a 6 knife, 83" disk diameter chipper.

Because of the additional knives (2), the full load HP requirement is greater than what is currently powering the 96" chipper and it has been suggested by the manufacturer to replace one of the 350 HP motors with a 500 HP motor to meet the new requirement. However, because the new chipper is smaller in diameter than the existing chipper the weight of the disk is less than the old chipper and may be a factor in the final assessment.   Therefore, even though it is a higher production chipper on full load, it is essentially a smaller chipper when starting up.

RE: Upgrading wood chipper

kipawa,
That helps to understand. Most likely you will be able to accelerate it with the 350HP motor, and as I said, you already have it so give it a try. Just disable the other 350HP soft starter and see if it gets to speed with one before the overload relay trips out. If it works, just close an across-the-line contactor on the 500HP motor after the disk gets to full speed, probably no need to soft start that motor. But here are the caveats:

1) The control gear for the existing 350HP soft starter is not going to work for the 500HP unless it was seriously over sized when originally purchased, and chances are since starters this big are expensive, it was not. So you will need to replace that 2nd 350HP starter with a 500HP starter of some sort.

2) The power circuit must be sized for 500HP, by which  mean the switchgear breaker feeding it, the cables etc. There is a significant difference in all component sizes.

3) Your power system must be capable of delivering the added kW, meaning the transformer feeding this machine switchgear. If the transformer is too small to take the additional load, you could end up with a severe voltage drop that damages BOTH motors. In addition, closing an A-T-L contactor on a 500HP motor, spinning or not, will entail a brief but very high current transient when the motor magnetizes. This must be supplied by that same power system and if it can't, you can get other severe consequences.

So this is back to where I said you must engage the services of a qualified PE who will thoroughly investigate, calculate and engineer the entire system, not just the one aspect of the motor starter. I say go for a fourth try, but interview people to make sure they have experience with large motor systems and soft starters. Ask around fr recommendations. Post your general vicinity, maybe someone here knows someone.


Keith, I'm going to talk your ear off about your VFD idea when we get together with Marke this weekend... but I don't want to bore everyone else with it.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Upgrading wood chipper

Sorry that I can't be with you. Have some serious doubt about talking Keith's ears off. Would be an interesting experience.

To remind you what proper behaviour is, I attach picture with Mark, Ozmosis (was SED2developer then) and me from a meeting in Nuremburg, Germany.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

(OP)
Folks, thanks ever so much for your valuable input.  Here is more data.

Old chipper disc and arbor weight = 18,000 lbs.
New chipper disc and arbor weight =  9,950 lbs.

Old chipper rotational inertia = 129,300 lb.ft2
New chipper rotational inertia =  55,070 lb.ft2

Jeff, we have an electrical engineer to do the work for us.  However, your excellent input has been priceless and has made us all much more wiser to say the least. I am now feeling much more confident in working with and understanding our engineer.  He is French speaking and I am English speaking so there is a language problem as well.  But I believe I am much more able to comprehend him than before. All thanks to you and your chat buddies. I'm sure he will appreciate as well your taking the time to educate me.  Again thanks ever so much.

FYI we are located in eastern Canada on the Quebec/New Brunswick provincial border.

 

RE: Upgrading wood chipper

Well, getting the details really makes a big difference. Oddly enough, even though you post "here it is again" I fail to find any of that information in a previous post.

A single 350hp motor should have no problem starting with only 42% of the inertia as before. If both 350hp motors could start the old chipper then one can start the new chipper.

Of course, this is assuming the new chipper speed is the same as the old chipper speed. You haven't left out some important speed change data?

 

RE: Upgrading wood chipper

(OP)
The rpm on the new chipper will be a bit higher than the old chipper.  The rpm on the motors will be the same.  w expect to use the same driven shive but will install new drive shives on the motors.  

RE: Upgrading wood chipper

A "bit higher"? What is the rpm of the old chipper and rpm of the new chipper.

The inertia reflects back to the motor as rpm^2 so it can make a bigger difference that it would appear to.

RE: Upgrading wood chipper

(OP)
The RPM of the old disc is 397.
The RPM of the new disc is 480.



 

RE: Upgrading wood chipper

A 20+ % speed increase means around 50 % more inertia. But it was already less than half of old disk. So, no sweat.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Upgrading wood chipper

(OP)
Thanks Gunner. That's reassuring.  I was somewhat concerned.

RE: Upgrading wood chipper

Reflecting the inertia of the new chipper to the old chipper speed I get 80,503 lb.ft^2.

So, the new chipper is the equivalent of about 62% of the inertia of the old chipper. This means you still need to investigate starting it with a single 350hp motor before assuming that will work. Being at 62% of the old chipper inertia I'd give you a high probability it will work but it is more than 50% of the old load.

See how the info can change the answer?
 

RE: Upgrading wood chipper

(OP)
Yes, much clearer now.  Thanks again for the advice.   

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