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12th Jul 2020, 08:09 PM #1Most Valued Member
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Brobo 2 speed cold saw - what type of motor are they
Helping a mate out with a 3 phase Brobo he needs to be able to run from single phase.
I was hoping the motor might have been able to be run from a 240v VFD, but turns out its a 2 speed motor.
I've got a dual voltage 3 phase motor here that just needs a slight massage to the bolt PCD and the locating ring to make it physically fit, but I'm interested in whether there are actually any practical options to be able to run the existing motor off single phase.
Here's the wiring diagram:
Brobo 2 speed wiring diagram.JPG
Steve
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13th Jul 2020, 02:41 AM #2
Hi Steve, Guys,
Plan "a":
The VFD would probably be your best bet if you can put up with just a single speed. Otherwise it gets complicated !
Plan "b":
To get the motor to run on a single phase you would have to create a phase shift network using capacitors in a similar way to to a phase converter, and then the capacitor values would only be right for one speed or the other.
I would stick with Plan "a" !Best Regards:
Baron J.
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13th Jul 2020, 08:44 AM #3Most Valued Member
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Thanks John.
I've found out that this style of motor is called a Dahlander type, and the switching changes the windings from delta to double-star to create the different speeds.
https://commons.wikimedia.org/wiki/Fileahlander.svg
That explains why both configurations are shown as 415v on the nameplate.
Other than breaking out the individual windings to use with a 240v VFD (perhaps using just 3 of the 6 windings, I can't see how it could be run at reasonable power from 240v at all.
Just academic discussion for my own interest anyway - I'll modify the bolt pattern and locating boss on the motor 240v motor I have here and there's a VFD being posted today from local supplier.
Steve
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13th Jul 2020, 09:20 AM #4Most Valued Member
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Practical? Certainly.
Economical? Well that's your mates call.
While I think you will have heard this from me before.... just in case you haven't. There are 240V to 415V VSD's, but they aren't what you would call cheap. A 2hp one is currently about $1262 delivered including gst.
Does the replacement motor match the high or the low speed of the current motor?
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13th Jul 2020, 10:18 AM #5Most Valued Member
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Yeah - fair call..
My "practical" always has the economical factor built in
Replacement motor is the lower of the 2 current speeds - 1400rpm.
That gives 42RPM blade speed which suits normal steel (mostly what he cuts). He has the negative rake high speed blades on a modified chop saw for cutting aluminium so isn't interested in trying to run the Brobo fast, but would like to be able to slow it down to about 15-20RPM range to use for stainless.
Steve
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13th Jul 2020, 11:36 AM #6Member: Blue and white apron brigade
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Here is a thread that discusses these two speed motors in a bit of grimy detail
https://www.woodworkforums.com/f271/...s-motor-183910
Towards the end you will see lamestllama posts how to retain the two speed option even at 240V.
However you should not leave the original 2 speed switch in place without some sort of protection as switching the speed while the motor is under VFD control and under load is likely to let some smoke out. You could rig some kind of interlock to the original speed switch so that as soon as you switch it the VFD power is switched off.
Alternatively, just leave it on the lower speed and use a vector drive VFD you should get about 2/3rd to 3/4 power at 25Hz. This should be enough to cut any small to medium in cross section SS.
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13th Jul 2020, 01:05 PM #7Golden Member
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Not directly related to the original question but may have some relevance.
I have two machines that came with 415V 3 phase two-speed Dahlander-wound motors (also called pole changing or consequent pole motors).
At the time I did a fair bit of reading and searching to see if/how these could be re-connected internally run from 240V, without finding any tried-and-true solutions.
The Arboga mill-drill has the motor built into the machine frame so it can not be simply replaced. I tried a VFD to run on the machine on 240V, but there was a significant loss of torque, and the machine was very underpowered at the higher speeds. My baby Deckel came with a very nice high quality dynamically balanced motor that I did not want to discard.
I had them both rewound as 240V three phase two-speed Dahlander wound motors, and was lucky to find an old rewinding shop that was acceptably affordable. I discussed options with them and they were not keen on trying to to revise the existing windings.
Retaining the original two motor speeds means you have the original range of speeds with full torque, but tweakable with VFD. Note: the VFD is at risk of damage if the motor winding configuration is switched while the motor is running. That's mainly an issue if the original manual motor speed switch is still used; ideally you would arrange the switching to eliminate that risk.
A basic V/F (voltage/frequency) type VFD seems fine in this application (switching between two motors with different characteristics), and I see no advantage in using a sensorless vector type VFD unless you are trying to extend the speed range a lot.
I have not bothered to see if it is possible to set up the VFDs with two sets of motor parameters automatically chosen to match the selected winding configuration, but no problems so far.
Edit: I see BobL posted a more directed response while I was writing!
Bill
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13th Jul 2020, 01:23 PM #8Most Valued Member
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13th Jul 2020, 04:47 PM #9Most Valued Member
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G/day Stu, I have mentioned these 220v to 380v VFD's a few times now but it's not sinking in......
.75kw $115.00 https://www.aliexpress.com/item/4000...archweb201603_
2.2kw $131.00 https://www.aliexpress.com/item/4000529305916.html?spm=a2g0o.productlist.0.0.63b6215cIGvLA7&algo_pvid=3bae0d38-2741-4b1f-8dfe-72c75a38a3ca&algo_expid=3bae0d38-2741-4b1f-8dfe-72c75a38a3ca-5&btsid=0ab6d67915946184834033275e15e8&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
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13th Jul 2020, 05:31 PM #10Most Valued Member
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Thanks Shed - I recall you posting about those now but had forgotten.
I ordered a Folinn 240v VFD from Conon motor for my mates Brobo to use with the motor I have here.
Just bought one of those 220-380v ones from Aliexpress and will have a play with it on the original Brobo motor when it arrives.
Steve
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13th Jul 2020, 05:59 PM #11
I have cut probably a 1000ton of SS tube and bar on Brobo's and their Asian equivalents in my lifetime. I doubt that there is much value in going to slower blade speeds than for MS for cutting it. The primary factors are to keep up a very good flow of coolant and to use blades configured for the task at hand.
Better coolant flow is needed to clear chips and stop them pressure welding to the sides of the blade, which leads to blades cracking and breaking. Blades need to be cobalt for best life between sharpenings, and need to have an appropriate number of teeth for the material size being processed. High tooth count blades are fine for thin walled tube, but as the wall thickness increases or you move to cutting bar, angles etc, you need to go to fewer teeth to minimise the number of teeth engaged in the material and allow enough gullet space to clear the chips. As a rough guide, for 304/316, a tooth count of approx 80% of that for MS should be ideal.
Your mate needs to make the acquaintance of a very good saw doctor, preferably nearby, for advice on tooth counts for particular sized stock. A decent saw doc getting regular work from him will understand what he wants from the blades and can suggest variations to make the blades last longer. Blades are supplied to the doc as blank disks, and the doc tooths them to requirements prior to delivery. They can also grind the existing teeth off and retooth them if you break a tooth out or need a different tooth set for different stock thicknesses. Our plan was to tooth new blades (max diameter) for our heavier barstocks ( to 4" x 1/2" flat, 2" dia rounds, angles to 1/4" thick) and gradually increase the tooth count as the blade diameter decreased, to transition through thick walled tubing (4" x 2" x 3/16 RHS etc) down to a variety of thin wall tubes. That way, the larger blades were available for the heaviest cuts, while lighter cuts for thin wall etc could be handled by the well used and retoothed blades.
One issue with the Brobo's is that they can be a bitch to change blades on, because of the guarding employed, which tends toward operators doing the odd heavy cut with blades not suited to the task rather than blow time dismantling and reassembling the guards to change to a more appropriate blade. This can really compromise time between sharpenings as a high tooth count blade working in thick walls or bar will have most teeth rubbing in the material rather than cutting, which wears the cutting edge away.
In order to improve coolant flow, your mate may be better going to an external coolant pump and reservoir wired into the trigger contactor to run whenever the motor does. The Brobp's I have used have used the piddly Holden fuel pump mounted on the gearbox as a coolant pump, and they don't flow enough coolant to flush the chips if you are cutting anything thicker thn thin wall tubing. The reservoir that these use is a plastic dish with about 4 litres capacity, which is not really enough for continuous thick wall cutting.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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13th Jul 2020, 06:48 PM #12Most Valued Member
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But has anyone tested one of those yet?* They have been misunderstanding the specs for years. A good sign the same seller has 220V ones for $30 odd less.
If I didn't already have more than enough VSDs I'd get one just to find out, but Steve has saved me the money.
Fingers crossed!
*In fairness I havent actually tested my UK one. Pretty sure running 25Hz or less on a 415V motor at 240V would show up pretty fast )
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13th Jul 2020, 06:59 PM #13Most Valued Member
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I fitted one to a mate's 5 hp herbert capstan lathe, single ph 240v in and 380v 3 ph out, the lathe has plenty of grunt.....
this one https://www.aliexpress.com/item/3283...27424c4dQHn2FELast edited by shedhappens; 13th Jul 2020 at 07:03 PM. Reason: link
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13th Jul 2020, 07:22 PM #14Most Valued Member
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I'll report back on the Aliexpress VFD once it arrives and I've had a chance to play with it.
Malb - thanks heaps for the detailed info on saw use. I've passed it on to him and I'm sure he will be grateful for the info as he hasn't actually used them before and it will be a decent learning curve. Hopefully a happier less expensive one with that sort of info up front.
Steve
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14th Jul 2020, 11:44 AM #15
A couple of points to mention about powering the Brobo via a VFD.
1. You would have to rearrange the trigger switch wiring so that it switches the control inputs on the VFD rather than operating the contactor on the saw, VFD's don't like going from zero load to applied load and back again when the contactor operates the motor, they prefer to control the load.
2. The two speed switching will effectively disconnect the load and reconnect it if the selection is changed while the motor is running, which the VFD will dislike immensely. There are two possible remedies here, one is to hardwire the speed selector switch for single speed operation by moving the motor cables to the corresponding power input terminals for which ever speed the user wants, the other is to leave the speed select wiring as is, and either remove the switch knob or use a mechanical interlock of some sort to prevent the switch selection being changed while the motor is running. There should not be an issue with changing the speed switch when the motor is completely stopped and the VFD is not supplying power to it.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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