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
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
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RE: Upgrading wood chipper
RE: Upgrading wood chipper
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
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
RE: Upgrading wood chipper
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
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
See the Cowern Papers
ht
Look under:
GLOSSARY OF FREQUENTLY OCCURRING MOTOR TERMS
See.
DESIGN
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Upgrading wood chipper
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
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
RE: Upgrading wood chipper
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
RE: Upgrading wood chipper
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
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
RE: Upgrading wood chipper
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
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
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
Keith Cress
kcress - http://www.flaminsystems.com
RE: Upgrading wood chipper
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
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
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
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Upgrading wood chipper
Keith Cress
kcress - http://www.flaminsystems.com
RE: Upgrading wood chipper
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 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
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
Keith Cress
kcress - http://www.flaminsystems.com
RE: Upgrading wood chipper
It's good to see you back from your working holiday.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Upgrading wood chipper
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
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
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
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
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
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
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
RE: Upgrading wood 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
The RPM of the new disc is 480.
RE: Upgrading wood chipper
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Upgrading wood chipper
RE: Upgrading wood chipper
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