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RPC help needed - Will cedarberg model 50 power my tablesaw?

WhiteHawk

Plastic
Joined
Apr 21, 2021
Good evening all,

I found myself in possession of a 5hp 3phase 230v sawstop table saw and of course my garage doesn't have 3 phase power, so I'm looking into rotary phase converters. I saw a used cedarberg model 50 pop up near me which is rated to start a 5hp motor (with a 7.5hp idler) and was wondering if this would adequately run my saw. It looks like the rule of thumb is to have an idler at 2x the rated HP of the load motor you're trying to run, and cedarberg is the first place I've seen to recommend otherwise. My other question is related to the rated amperage of the manufactured leg - per cedarberg's catalogue (https://cedarberg.com/wp-content/uploads/2020/05/PhaseConvCatWeb.pdf) this RPC is rated at 6amp output, and I believe the saw is a 12amp saw...

Another huge limitation is that I only have 60 amp service running to my garage. I have a working 15hp 3phase motor at my disposal but believe I would need to upgrade power running to my garage to use that as my idler if I were to buy a panel for it.

Thanks in advance for any advice!
 
Good evening all,

I found myself in possession of a 5hp 3phase 230v sawstop table saw and of course my garage doesn't have 3 phase power, so I'm looking into rotary phase converters. I saw a used cedarberg model 50 pop up near me which is rated to start a 5hp motor (with a 7.5hp idler) and was wondering if this would adequately run my saw. It looks like the rule of thumb is to have an idler at 2x the rated HP of the load motor you're trying to run, and cedarberg is the first place I've seen to recommend otherwise. My other question is related to the rated amperage of the manufactured leg - per cedarberg's catalogue (https://cedarberg.com/wp-content/uploads/2020/05/PhaseConvCatWeb.pdf) this RPC is rated at 6amp output, and I believe the saw is a 12amp saw...

Another huge limitation is that I only have 60 amp service running to my garage. I have a working 15hp 3phase motor at my disposal but believe I would need to upgrade power running to my garage to use that as my idler if I were to buy a panel for it.

Thanks in advance for any advice!

"In general" 1.5 times is about the minimum, but works. EG: a 7.5 HP idler will start a 5 HP load-motor, so long as it is either de-clutched or otherwise not "loaded". And you aren't looking for "instant".

Your saw won't be "in the cut" at power-up, so it should JF work, even if it takes a second - or several - longer to spin-up.

I won't use above 10 HP in any one, single idler here even on 200A service. I simpy don't want the IDLER starting load to mess with the rest of the facility, nor my neighbours on the same transformer.

IF the Cedarberg struggles? Leave the 15 HP for somebody ELSE to utilize.

Just add a(ny) 2 to 5 HP 3-Phase motor as a supplementary idler, started as if it were any other "load motor". Even a 3 HP would do yah just fine, and go a long way towards "future proofing" you whole shop to 10 HP and a bit for other 3-Phase tools you might want, later.

eg: Fire it off AFTER the Cedarburg "pilot idler" is up onto its water-skis.

A more elegant way? Give it its own run/balance caps.

Simple-dumb "naked" way works, too, though. You can always add caps LATER if yah need to do.

For now, if you even NEED it at all.. just switch it ON like any other 3-Phase tool would be wired. It can even BE exactly that. Another 3-Phase machine.

So long as not running "loaded" when you start the saw ... or other largish load, going forward, it JFW to add a tad of inertia and "stiffen" the generated leg.

Dust collector, BTW is NOT a good "helper". Grinder or belt sander "can" be. Mill, lathe, or drillpress usually "just are".

RPC are just that simple.

That's why they still have a job in VFD-the-shop-cat's-ass-compulsion-fetish land.

VFD do not REALLY make yer dick bigger, BTW. Only variable-speed and easier to start.... slowly.... if .... undersized ... or ...overloaded...?

Hmm... I wonder...
 
Fantastic - thanks for that great info, especially happy to know I won't be losing out on the magic junk grower =D

Sounds like HP wise and electric feed wise I'm good to go, just want to verify there's no concern about the 'UL Listed Amperage Output of Mfg Leg" being 6.0 amps and my table saw being rated at 12?

Thanks again!
 
Fantastic - thanks for that great info, especially happy to know I won't be losing out on the magic junk grower =D

Sounds like HP wise and electric feed wise I'm good to go, just want to verify there's no concern about the 'UL Listed Amperage Output of Mfg Leg" being 6.0 amps and my table saw being rated at 12?

Thanks again!

Dataplates are but "snapshots" taken off an ANALOG device that actually WORKS to semi-linearized CURVES .. for different "slip classes" .. and any percentage of "duty" that is not continuous. Among other factors..

Note that the 12 A is "FLA" or FULL LOAD AMPS, thereby is associated with the "load"' being the whole dam' 5 HP, and SUSTAINED.

Saw is actually worked that hard, sustained? Your RPC won't be the biggest money-spender. New saw motors, rather. BEST an RPC can do is push a load to about 91% of unlimited utility-mains 3-Phase. Basic nature of the cheat. And nearly always more than good enough.

Starting INRUSH is a multiple of FLA. but.. mercifully very BRIEF.

THE IDLER start is the worser butt-kicker. Fool 3-Phase motor has to be started off but the ONE phase since there is no idler AHEAD of it going on-line. That's why you are saner with a stagger-start than a single too-large idler.

As said .IF it turns out to be problematic? Just add more idler contribution ... AFTER the primary is up "on step" and cruising. The total is the total.

No need of any extra starter nor RPC control alteration. As far as it knows, it just has a non-power-sucking idle load ... helping it keep the generated leg "stiff".
 
I suspect a 5 hp motor like that could easily be run off a 240 volt input VFD via a 60 amp branch circuit.
Given the saw is the only 3 phase load, this might be a more economical (space, and money) solution.
 
Yes do please explain to the man that a rotary converter is exactly what he needs and a VFD is absolutely the wrong thing to use as it will be much more expensive and will not work anyway for what he wants to do, and will be too much trouble to install and too noisy and take up too much room.

And will turn him into a republican.
 
The 5 HP corresponds to about 12-15A current at FLA.

A table saw is a somewhat hard starting load due to the inertia of the blade, and any step-up belting that may (or not) be present.

Plus, saws bog in the wood, and you do want ample current. But the 7.5A idler and being rated at only 6A seems very odd. FLA on a 7.5A motor is more like 20A, and half of that ought to be possible, given some voltage drop.

I say that it will work, but might not quite have the power it could, if you are really going to work it to 5 HP. A larger idler would not hurt you if you could do it. No clue what that unit is rated for as an idler.
 








 
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