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Smokin' H bridge

Started by petefrom bearswamp, April 14, 2014, 11:39:06 AM

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petefrom bearswamp

Sawed for 1/2 hr this AM when the head would go down but not up.
error message check cable connections which I did then called WM.
Tried a couple of other things Barry suggested, then when I tried to raise the head smoke poured out of the H bridge box.
Ouch.
$650 plus shipping.
So far this spring I have had a gross sale of $350.00.
Glad i don't have to rely on sawing for a living.
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Chuck White

Pete, is the H-Bridge part of the computer on your mill?

You're right though, good thing you are not dependant on the mill in order to put food on your table.
~Chuck~  Cooks Cat Claw sharpener and single tooth setter.  2018 Chevy Silverado and 2021 Subaru Ascent.
With basic mechanical skills and the ability to read you can maintain a Woodmizer  LT40!

pine

When I was doing my mill research I ran into what looked like at the time a plethora of H-bridge failures that folks were reporting.  I don't know if there was a batch from the manufacturer that had problems but heard/read about a bunch of failures (quite expensive ones) and since have seen very little about failures of the H-bridge. 

This is the first one in some time that someone has posted about.

Sorry for your troubles Pete.

Ga Mtn Man

Sorry to hear of your rather costly trouble.  How many hours on your mill?
"If the women don't find you handsome they should at least find you handy." - Red Green


2012 LT40HDG29 with "Superized" hydraulics,  2 LogRite cant hooks, home-built log arch.

stavebuyer

We went through one a couple weeks ago. Bearing going bad in the drive sprocket got the drive motor one day and the H-Bridge the next. I have been through several H-bridges and each time it was the end result and not the root cause. Bad connection on the power strip or a bad bearing in the drive system will burn out the H-Bridge.

ladylake

Any way to put a fuse or circuit breaker before that H bridge that would pop before it does.  Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

petefrom bearswamp

Mill has 650 or so hrs on it.
WM Hannibal  didn't have the part but Marty Parsons in PA does.
WM has always been very good about timely shipping so maybe it will get here tomorrow.
Barry at WM said to be sure the contact strip and bottom rail are clean.
How about the part that contacts the strip. It appears to be spring loaded and the hydraulics and forward /back drive all work.
I think maybe my helper over lubed the head drive chain and some may have gotten on the contact strip.
I did a cursory cleaning of both this PM and will do a thorough job tomorrow.
The bottom rail appeared dirty as the sandpaper i used loaded up with junk, but my thought is that with the weight of the head having some pressure on the lower rail wouldn't that take care of any dirt/crap on it?
Steve I don't know if a C B  can be done but I can't imagine that WM engineers wouldnt have placed  one in the circuits if possible.
Hey Chuck how come you  aren't sawing on such a nice day?
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Ocklawahaboy

I know the electronics are big time savers and one reason some of you can turn out many times the BF that I can with my old manual mill but there is something intuitive that says circuit boards on a big machine that lives outside and spits sawdust are set up for failure.  It seems like they would keep the electronics as simple as possible.

stavebuyer

That button under the bottom rail needs to be clean and making good contact too.

The bearing issue can be a little sneakier. The H-Bridge will handle the spikes of dragging back a large cant but not the heat from continuous resistance in both directions when a bearing fails. A circuit breaker or fuse would be constantly tripping whenever you dragged a cant off the mill.

Ga Mtn Man

I don't understand what the contact strip has to do with an h-bridge failure.  Isn't the hydraulic pump(s) the only thing powered through the contact strip?
"If the women don't find you handsome they should at least find you handy." - Red Green


2012 LT40HDG29 with "Superized" hydraulics,  2 LogRite cant hooks, home-built log arch.

petefrom bearswamp

Good point Ga mtn man
Thanks stavebuyer.
Oklawahaboy I sometimes wish I had kept my old hydraulic non computerized mill
Especially for a late life hobby.
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

barbender

I think the H-bridge is bypassed in reverse, when I smoked mine on my '97 the reverse still worked.
Too many irons in the fire

dgdrls

Quote from: petefrom bearswamp on April 14, 2014, 05:15:45 PM
Good point Ga mtn man
Thanks stavebuyer.
Oklawahaboy I sometimes wish I had kept my old hydraulic non computerized mill
Especially for a late life hobby.

When I was considering a new mill, WM in Hannibal had a hydraulic
converted LT-28 which, as I understood at the time,  was purpose built for the Amish
as a Demo unit. 

I'm certain you will be back running in no time Pete.

best
DGDrls

stavebuyer

Quote from: Ga Mtn Man on April 14, 2014, 05:08:14 PM
I don't understand what the contact strip has to do with an h-bridge failure.  Isn't the hydraulic pump(s) the only thing powered through the contact strip?
You are right that the contact strip is only supposed to power the hydraulics. When there is a bad connection the power sometimes finds an inconvenient path through the H_bridge,

Peter Drouin

And can go though A bearing and burn out the grease out of it.
A&P saw Mill LLC.
45' of Wood Mizer, cutting since 1987.
License NH softwood grader.

Chuck White

Quote from: petefrom bearswamp on April 14, 2014, 05:15:45 PM
Good point Ga mtn man
Thanks stavebuyer.
Oklawahaboy I sometimes wish I had kept my old hydraulic non computerized mill
Especially for a late life hobby.



Want to trade!  ;D  :o

Quote from: petefrom bearswamp on April 14, 2014, 03:35:09 PM
Mill has 650 or so hrs on it.
WM Hannibal  didn't have the part but Marty Parsons in PA does.
WM has always been very good about timely shipping so maybe it will get here tomorrow.
Barry at WM said to be sure the contact strip and bottom rail are clean.
How about the part that contacts the strip. It appears to be spring loaded and the hydraulics and forward /back drive all work.
I think maybe my helper over lubed the head drive chain and some may have gotten on the contact strip.
I did a cursory cleaning of both this PM and will do a thorough job tomorrow.
The bottom rail appeared dirty as the sandpaper i used loaded up with junk, but my thought is that with the weight of the head having some pressure on the lower rail wouldn't that take care of any dirt/crap on it?
Steve I don't know if a C B  can be done but I can't imagine that WM engineers wouldnt have placed  one in the circuits if possible.
Hey Chuck how come you  aren't sawing on such a nice day?
Pete

Just finishing up sugaring!

In a couple of weeks I'll be out there, at it again!

~Chuck~  Cooks Cat Claw sharpener and single tooth setter.  2018 Chevy Silverado and 2021 Subaru Ascent.
With basic mechanical skills and the ability to read you can maintain a Woodmizer  LT40!

backwoods sawyer

Sand your rails and oil with ATF, clean the contact stip and contact (park off strip to clean) clean and sand the ground this will allow the bearing to turn with less resistance and insure the ground takes the path of least resistance. 
Backwoods Custom Milling Inc.
100% portable. . Oregons largest portable sawmill service, serving all of Oregon, from our Backwoods to yours..sawing since 1991

Brucer

An easy way to fry and H-bridge is to reverse your carriage down the track and then bump it back into forward while the carriage is still moving. As the carriage is still coasting backwards the motor becomes a generator. If you put it into forward just then, you'll be trying to push current backward through the H-bridge.

The bypass diodes are supposed to provide some protection by conducting reverse voltage around the H-bridge. Doesn't always work, though.

I used to build H-bridge controllers for small hobby motors and I came up with half a dozen ways to toast them.
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

petefrom bearswamp

thanks everyone
Backwoods where is the ground?
Barry at wm said the bottom rail.
Is this it?
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Dave Shepard

There is a pad that rides on the bottom rail. I was just looking up at mine yesterday as I was aligning the mill. I really don't like laying on the ground looking up at a machinery anymore. :D
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

drobertson

It will be bolted to a small assembly, it has springs just like the one that rides on the contact strip.  Saw dust can interfere with the springs at times causing them not to push the contactor firmly against the rail.
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

petefrom bearswamp

I wish that when i bought my mill and the salesman was going over the operation, he had included some of the tips regarding routine maintenance and cleaning contacts etc.
Maybe this stuff is in the manual I will have to check.
But thank you all for the info.
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

backwoods sawyer

The logs we have been milling have a lot of pitch so while I was oiling the rails this morning I wanted to watch the lower rolls to make sure they were turning and noticed the ground was flipped off the bottom rail, it springs right back. I keep an eye on it when the sawdust and sticks start getting deep.   
Backwoods Custom Milling Inc.
100% portable. . Oregons largest portable sawmill service, serving all of Oregon, from our Backwoods to yours..sawing since 1991

YellowHammer

Quote from: Brucer on April 15, 2014, 02:31:17 AM
An easy way to fry and H-bridge is to reverse your carriage down the track and then bump it back into forward while the carriage is still moving. As the carriage is still coasting backwards the motor becomes a generator. If you put it into forward just then, you'll be trying to push current backward through the H-bridge.

The bypass diodes are supposed to provide some protection by conducting reverse voltage around the H-bridge. Doesn't always work, though.

Great tip, I was wondering why those diodes were there.

YH
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

petefrom bearswamp

H bridge came yesterday, too cold to work on the mill.
In the package is a sheet with 14 steps to follow when replacing.
I did find a technical service bulletin from 2011 which had several maintenance steps to do and did them then, but have failed to keep the bottom rail and grounding block clean.
Hard lesson learned.
Pete

Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Ga Mtn Man

The control box has a ground wire that runs directly to the battery.  I do not believe that the bottom rail/grounding block had anything to do with your H-bridge failure (unless your mill is wired differently than a standard LT40HD).
"If the women don't find you handsome they should at least find you handy." - Red Green


2012 LT40HDG29 with "Superized" hydraulics,  2 LogRite cant hooks, home-built log arch.

petefrom bearswamp

Well I followed the steps to the letter.
Wouldn't work so called WM Hannibal.
Actually called several times.
After trying several things the WM tech said I must have gotten a bad part.
Now am waiting again for a new H bridge.
Lost 4 days sawing so far.
Also paid my man for about 6 hrs non productive time so far, but Oh well.
Such is the lot of the sawyer.
I think yellow hammer may be right in reversing before a complete stop but this of course will effect production.
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Brucer

Add up all the production you'd lose by not stopping your carriage before shifting back into forward. Compare that to how much production you've lost so far :(.

And just for you hydraulics-only types, you can also blow out the seal on a hydraulic motor by reversing it while it's still traveling in the other direction.
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

ladylake

 After over  9000 hours  with no feed problems I'd say hydraulic feed works good and I'm not easy on it.  I did have to put a couple of $7 bushings in the front idler and a $50 part in the speed control, neither shut the mill down. Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

petefrom bearswamp

I Like the modern stuff but sometimes think it is too sophisticated and obviously is prone to electronic failure.
I only have 650 hours on my 2008 mill.
Have maintained it judiciously except for the ground which i didnt know about or overlooked so far.
Have lost 4 days sawing so far and am glad I do not have to rely on the mill for my livelihood.
steve i dont understand how the forward and reverse issue talked about earlier has a bearing on my problem.
Brucer so far I have lost the 4 days and hadnt had a problem previously.
Maybe sparks will join in and explain it to me.
 
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

stavebuyer

When my last H-bridge went out it was due to a bad bearing on the drive sprocket. That bearing fried my drive motor and the newly replaced motor overloaded the H-bridge. Be sure to check that your head travels freely and that your drive motor is good. H-bridge can be the symptom and not the problem.

petefrom bearswamp

Up and running one week later.
Yippee
Pete
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

Magicman

Hopefully you have also conquered the "whys".  You certainly do not need a repeat. 
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

petefrom bearswamp

Thanks Lynn
Everything went well today finished an order of 2x10x12 Hemlock and 2x2x 12 stake stock.
Glad i have a young 53 yr old to help me.
Someday I'm going to weigh one of those green hemlock planks, but they must weight 70 80 pound each for 2x10x12.
Had one hiccup when the head wouldnt go up but it seemed to correct itself.
Kubota 8540 tractor, FEL bucket and forks, Farmi winch
Kubota 900 RTV
Polaris 570 Sportsman ATV
3 Huskies 1 gas Echo 1 cordless Echo vintage Homelite super xl12
57 acres of woodland

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