2hp Bridgeport - VFD vs Static phase converter
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    Default 2hp Bridgeport - VFD vs Static phase converter

    Like the title says, I have recently acquired a 2HP Bridgeport mill with the variable speed head for home shop use. I need to power it but naturally only have single phase. In researching the options a rotary converter seems like overkill for this use (plus I don't want to listen to it). That leaves Static Converter or VFD options.

    As best I can tell:
    VFD
    - Much more flexible
    - Delivers full rated power
    - Rather complex to set up, wire and program

    Static converter
    - Easy to set up
    - Loss of power ~1/3 of motor rating

    Costs in this size range don't look terribly different between the 2 options, so I don't consider it to be much of a factor. I've been looking at Automation Direct and KB VFDs. Phase-a-matic for the Static.

    I can handle both options, I think, but it seems like a Static converter would be easier and in a home shop the need for full power seems unlikely. I have the variable speed head, so that feature of VFDs seems to be not terribly beneficial here.

    So I guess the question is if there are any other downsides to the Static converter that I am unaware of?

    Thanks,
    Dave

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    Quote Originally Posted by dstig View Post
    So I guess the question is if there are any other downsides to the Static converter that I am unaware of?

    Thanks,
    Dave
    All of them might apply?

    You don't "lose" 1/3 of motor nameplate power.

    1/3 is what you get to KEEP.

    Push it above 31% or so?

    A static gets progressively rougher and progressively harder on the motor, then trips-out.

    In the middle of a cut if you had been pushing it.

    A VFD won't necessarly gradually trash the motor. But for older motors, cheap ones can do.

    Your "gentlest" solution as well as EASIEST IS the RPC you skipped-over.

    No rewiring. Up to 91% of nameplate. Smooth, too.

    5 HP idler should do your 2 HP BirdPort just fine. Or any OTHER load of comparable power need.

    NO NEED to dedicate it to but ONE machine and wire it in and try to "integrate" the OEM controls ELSE run off the VFD's button-panel as one must with a VFD.

    RPC you just use the machine as-built.

    Noise? Put the silly thing behnd somthing, outdoors, or up in the attic. They aren't THAT noisy! Just an ordinary motor "idling".

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    You pretty well summed up the pros cons in your post.

    If the VFD install is not over your skill level, they are really NICE. Four knee mills in my shop, all use the VFD. And The shop has rotary phase converter power installed. Biggest reason for me is its so easy to change the speed. With a belt shiv crank, I just don't bother, the the speed its running is good enough. With the VFD speed pot right there, watch the cut for a second and change it to optimum.

    I do a lot of power tapping. Dial the speed way down with the VFD and go for it. Enough harder without the VFD that hand tapping is easier.

    BTW, I used to go automation direct. They lost my buisness to hitachi units from drives warehouse. I'd suggest this offer
    WJ200-015LF 2HP 1.5kW 230V VFD - Hitachi

    Also, if you don't mind a hobby site. Hobby-machinist.com has a guru that will walk you through the install. This site has a clueless troll that is already spewing pure BS to your thread. i suggest you ignore him.

    Nothing wrong with the static if you don't need the Hp.

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    I recently went through this and used a GS20 from AutomationDirect. It was easy to do and seems to work really well.

    Here’s my prototype controls setup:

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    Generally, the RPC is the easiest 3 phase solution. The Vari-speed does reduce the need for the VFD approach. I like either of them better as a general approach to the 3 phase issue, but I am somewhat biased, as I run my 3 phase equipment on an RPC.

    That all said, I know of folks using a "static converter" to run a Bridgeport, and it works fine also. It's probably your lowest cost approach. Of all the possible tools, the Bridgeport is possibly the one that is the least likely to be used to hog off material in full HP cuts. Especially a 2 HP unit, where you will still have over 1 HP of available power even after de-rating the motor due to using a "static converter".

    The mill is also a tool that will suffer the least from use on single phase, which is what the "static converter" actually supplies once the machine is started. If it were a lathe that you wanted to power, I would be "pushing" the RPC approach, or a VFD.

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    Quote Originally Posted by Karl_T View Post
    Also, if you don't mind a hobby site. Hobby-machinist.com has a guru that will walk you through the install. This site has a clueless troll that is already spewing pure BS to your thread. i suggest you ignore him.
    Good advice,

    This message is hidden because Karl_T is on your ignore list.


    Solves THAT little "pure BS" problem.

    Nothing wrong with the static if you don't need the Hp.

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    Yeah the GS20 was the one I was looking at from Auto Direct. I have used them in the past for other stuff and was quite pleased, and it seems like they have good instructions and support online for this. The VFD and Static converter seems about the same cost, but I can see a lot more in switches, enclosures, and wiring with the VFD adding up $$....plus all the time required.

    Karl, why did you go away from AD to Hitachi? Problems, or you found something better or???

    Nice install Mr Melvin.

    If I had plans for many 3 phase tools, I would get a rotary, but if I go that route it is going to be for a wide belt sander so it would be a big one (prob 20 hp or more). I kind of doubt I will need to do that, so it will be this mill and maybe a small lathe at some point too, both of which can be handled individually like this.

    Is there any real concern with long term damage to the motor on a static converter? I seem to recall hearing something like that back a long time ago but don't really have anything firm on it. This mill is a 1981 vintage per the serial number so not super old as Bridgeports go.

    Thanks again,
    Dave

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    Quote Originally Posted by dstig View Post
    .................
    Is there any real concern with long term damage to the motor on a static converter? I seem to recall hearing something like that back a long time ago but don't really have anything firm on it. This mill is a 1981 vintage per the serial number so not super old as Bridgeports go.

    Thanks again,
    Dave
    Only source of damage is overheating due to excessive current. If you have a 2HP motor, a "static converter", and you do not take cuts over 1 HP, you will not damage the motor.

    Even an RPC is not perfect, the slight normal imbalance slightly de-rates the motor, maybe to 90% for long term un-broken runs. And a VFD adds potential issues of voltage spikes and high frequency heating in an older motor (those are fixable issues).

    A static converter is a practical solution to needing 3 phase when you are not going to run the motor at over maybe 55% HP for longer periods of time. You already have variable speed, so that part of a VFD is not a big deal.

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    I use vector drives on my mills, they are all step pulley mills. I prefer those greatly to the variables heads, I hate the wobbly pulley noise and cranking that little wheel (or listening to the air motor on the BOSS). I leave it set to 1200rpm most all the time. Between option of driving motor to 120hz and backgear I very rarely have to change the belt to go between 1.5” face mills to drilling and tapping small holes.

    I thought static converters run the risk of jumping a phase when back-pluging the motor?

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    Not uncommon to use a static converter but a bit of old school and more popular before VFD's came down in price. An RPC if you plan to go that route, will cost more and for a single machine is a bit of a waste in my book if you only need 3 phase for a single 2 Hp motor. You can make it as simple as you want, since you have a mechanical variable speed head, you primarily want to use that for your speed changes and keep the motor at around 60 Hz. A 2 Hp VFD is small, not much more difficult than a static converter to wire in, and cost wise only slightly more. All you need is a 3 way sustained switch with two NO switch blocks F/S/R for 2 wire control and if you want you can use the speed pot on the VFD or do a remote speed pot. Program it so it will not start if there is a run command on start up. On these simple installs I usually recommend the Teco L510, it works and nothing fancy. The GS20 series and the WJ200 are the next level up, the GS20 is their newish line, they will all work well. I would not over speed the motor, and try to keep the carrier frequency around 8kHz unless it bothers you.

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    Quote Originally Posted by Nmbmxer View Post

    I thought static converters run the risk of jumping a phase when back-pluging the motor?
    Pardon my ignorance but what does that mean?

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    Quote Originally Posted by dstig View Post
    Karl, why did you go away from AD to Hitachi? Problems, or you found something better or???

    No complaints with AD.

    The Hitachi is a better drive for same or less $. Good support here too.

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    To the best of my knowledge you cannot plug-reverse a 3 phase motor that's being run on a static converter.

    1) set up the static converter.

    2) when that breaks or you buy another 3 phase machine, set up a rotary converter.

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    Quote Originally Posted by dstig View Post
    Is there any real concern with long term damage to the motor on a static converter?
    Two.

    First is if you run much about 40% long runs. heating is uneven. Takes years to do any real damage but...

    Second is that folks forget a static-NOT-converter is all about capacitors to trick a 3-Phase motor into running with two phases missing.

    The caps work harder than the balance caps on an RPC, age and fail at around half the life.

    IF all you have the budget for IS a static? Just change it over to a controller for an RPC "sooner rather than later" .. by adding an idler.

    Major maker? They provide the instructions. Not a new need.
    And then you HAVE an "RPC" and 90% of load-motor nameplate.

    Might find it a better deal to buy an RPC starter/controller and find yer own idler motor, even so. Be aware than transport cost can matter as much as motor cost.

    Even so, all of my ones were NEW motors, not used. One light 10 HP Weg. three heavy-bugger Reliance Duty-Master XES with minor cosmetic scratch & dent. Zero or near-zero work to sort for use as idlers.

    Keep that in mind, ever you go for 20 HP or more.

    FAR easier to start a 10 HP, add a second 10 HP than to fire-up a single 20 HP in one go. Nice to be able to run partials from a "pool" as well to better suit that day or hour's load. Only one starter/controller needed.

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    Quote Originally Posted by dstig View Post
    Pardon my ignorance but what does that mean?
    When you flip from fwd to rev and the motor reverses direction (nearly) immediately, for power tapping mostly. On a single phase motor it will just keep going in the same direction. A 3ph motor stop and restart as fast as it can. I think on a static converter since the generated leg isn't very strong compared to the other legs, just enough to get the motor to start under a normal load, that plug reversing runs the risk of not stopping.

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    Quote Originally Posted by Nmbmxer View Post
    When you flip from fwd to rev and the motor reverses direction (nearly) immediately, for power tapping mostly. On a single phase motor it will just keep going in the same direction. A 3ph motor stop and restart as fast as it can. I think on a static converter since the generated leg isn't very strong compared to the other legs, just enough to get the motor to start under a normal load, that plug reversing runs the risk of not stopping.
    As I keep saying a static converter does not actually "convert". It tricks the load motor.

    There isn't really a "generated" leg except within the load-motor itself.

    The very one you are asking to reverse!

    Lottery ticket might be the better deal?



    No "free lunch", BTW.

    IF.. a rotary phase converter's idler does not have enough of an "advantage" over the load motor?

    It now and then happens that the command results in the IDLER reversing. Even if the load motor obeys.

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    To reverse, you obviously have to stop, then switch to reverse on the machine. Starting should then be in reverse.

    You are running single phase when you use a static "converter", so there is absolutely no plug reversing whatsoever.

    The way the static converter works is generally to connect a start capacitor to the 3rd wire get the motor started, and then to automatically disconnect it, running on single phase via the other two wires.

    A few types may leave a "run capacitor" in place after the larger start capacitor is disconnected. That somewhat smooths the operation of the motor by providing a bit of the 3rd phase operation, similar to a capacitor start/capacitor run single phase motor.

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    Quote Originally Posted by JST View Post
    To reverse, you obviously have to stop, then switch to reverse on the machine. Starting should then be in reverse.

    You are running single phase when you use a static "converter", so there is absolutely no plug reversing whatsoever.

    The way the static converter works is generally to connect a start capacitor to the 3rd wire get the motor started, and then to automatically disconnect it, running on single phase via the other two wires.

    A few types may leave a "run capacitor" in place after the larger start capacitor is disconnected. That somewhat smooths the operation of the motor by providing a bit of the 3rd phase operation, similar to a capacitor start/capacitor run single phase motor.
    I tend to avoid them like a bad rash, given the last "10 HP" Phase-A-Matic to cross my radar had done-in the motor on the HBX-360-BC, prior owner's hand. The good news as that Milacron sold it to me cheaply with a bummed motor! Motors, I have in surplus!



    But.... "AFAIK" some circuits it is much the same as start and run caps of an RPC's idler.. just that it is NOT "idle" but also carrying the mechanical load directly.

    One might see some advantage in use of a static-converterNOT for running a 3-P OEM coolant pump at low-load and predictable? Then again, with drop-in Taiwanese 1-P 120/240 pumps as cheap as they are, Cast-Iron, stainless, or plastics in all sizes .... and the OEM pump usually old and grubby anyway? Why bother?

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    Thanks for the info guys. I'll think it over and figure something out...

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    Quote Originally Posted by dstig View Post
    Thanks for the info guys. I'll think it over and figure something out...
    End of the day, it's your mill, your ACTUAL operating needs, your expectations and plan for future additions, if any.

    RPC works. VFD works.

    Static converter is sort of a band-aid side-trip, best case, and "best case" kinda sucks, even on its "best days", anyway.

    Rank it last.

    Pick one out of the better two.

    A Phase-Perfect could be nice. I still have a 10 HP one. But USD$ 4,000 might not be on your dance-card?



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