# static or rotary converter for grinder



## bosephus (Jan 27, 2015)

i bought a 5 hp 3 phase baldor grinder on Craigs list for a whopping $25 .
 i have a 10 hp motor to build the rotary converter with , and everything i need to build a static converter as well. 

 whats the best option for a grinder ,.. while i do understand how to build a converter i know very little about electrical in general , my first instinct is to just build a rotary converter as then i can power anything else i might happen to pick up in the future . 

but then again .. i do not have any other three phase machines and not having to start a converter every time i want to use the grinder is attractive as well


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## randyjaco (Jan 27, 2015)

Go rotary. RPC or VFD- your motors will  appreciate it.

Randy


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## Ulma Doctor (Jan 27, 2015)

Hi Steve,
Dependent on how intricate you'd like to get, you could have the RPC start and stop by the controls of the grinder, if you were worried about the RPC running for only the grinder at this point.
adaptations can be made to to the generated 3 phase circuit later on for additional machinery.


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## bosephus (Jan 27, 2015)

i like to keep things simple , i get easily confused when it comes to wiring .

either of two is with in my comfort zone to do , but getting fancy with it ... well lets keep in mind i am fairly ignorant of electical once things go beyond a simple on and off switch


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## ironmonger (Jan 27, 2015)

bosephus said:


> i bought a 5 hp 3 phase baldor grinder on Craigs list for a whopping $25 .
> i have a 10 hp motor to build the rotary converter with , and everything i need to build a static converter as well.
> 
> whats the best option for a grinder ,.. while i do understand how to build a converter i know very little about electrical in general , my first instinct is to just build a rotary converter as then i can power anything else i might happen to pick up in the future .
> ...


 

 Congrats on the find! 

I have a 3 HP 2X71 grinder and I first ran it with a rotary converter and have since installed a VFD. They both work, but the VFD of course, can slow the motor down with the twist of a knob... which I find quite handy.


 FWIW I just bought a cheap chicom water mister, if you do a lot of heavy grinding its supposed to help. Haven't tried it as yet.

paul


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## Karl_T (Jan 28, 2015)

Build yourself a 10 hp rotary converter. Then you're all set for the next deal too. plenty of guys here to help you "cookbook it" so its simple to do. I made a couple of mine just run when you flip on the circuit breaker - VERY simple wiring.

Or sell me the grinder and save all the pain and heartache of getting hooked on this hobby :roflmao:


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## bosephus (Jan 28, 2015)

aah its always nice to know theres plenty of people out there willing to take a headache off your hands , lol 


this morning  i figured my first best step was to make sure the grinder actualy works , so i spent some time and wired my 10 hp motor up and grinder , and with the flip of a switch and a pull on a rope to start the idle motor it came alive . 

so now after lunch comes the hard part for me,.. making my converter self start . ok so thats not the hard part for me , what i am only about 25% sure of is wiring in the magnetic switch/relay thingamabob so i dont have to worry about the converter coming back on after a power outage ( very common in the winter months in my rural area ) if i forget to switch it off . 

i think i am going to have a a slew of wiring questions in the near future ... it apears that i may have a two speed motor , and i dont have a clue how to make it two speeds again . 

in another bit oh honesty ,.. no i did not check the grinder out in the slightest when i bought it , i showed up handed the fella his $25  and wrestled it into my nephews pickup truck ,.. i just didnt care , the cast iron base alone was worth a lot more to me then the measly $25


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## xalky (Jan 28, 2015)

I'd take that 10hp motor and make an RPC out of it. Like others have said, then you'll have 3ph power for whatever comes down the pike. You'll save a lot of money too, since you already have the motor. There are quite a few threads here on making an rpc with capacitors to have it self starting etc.


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## larryr (Feb 3, 2015)

bosephus said:


> i bought a 5 hp 3 phase baldor grinder on Craigs list for a whopping $25 .
> i have a 10 hp motor to build the rotary converter with , and everything i need to build a static converter as well.
> 
> whats the best option for a grinder ,.. while i do understand how to build a converter i know very little about electrical in general , my first instinct is to just build a rotary converter as then i can power anything else i might happen to pick up in the future .
> ...


since you already have a 10hp motor i would build a rpc . the static converters will cut your available power. i use a rpc in my shop and have a 3ph circut wired thru the shop to use with other machines. it works great. thats a mighty big grinder.probably uses 12 inch wheels? very expensive. rpc's are very nice and have a lot of programable features, but you pretty much need one for every machine to take full advantage of all the functions. if i were starting from scratch and didn't have access to a free motor i would certainly consider that route.


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## Ulma Doctor (Feb 3, 2015)

Hey Steve,
 if you decide to go RPC, i have a thread on how to make one from spare parts.

i'd be more than happy to assist you or even build the control box for you if you are not comfortable doing it yourself.
here is a link to a working model and the second link is plans for it.

https://www.youtube.com/watch?v=xD8xwh_P8mI


here are the plans:

http://www.hobby-machinist.com/showthread.php/12712-Rpc-simple-design-unbalanced


Let me know what you need, i'll do my best to help out!!
mike)


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## bosephus (Feb 10, 2015)

i got caught up on my work this afternoon and wired up my rotary converter  and grinder .

it works... the converter self starts just fine and the grinder spins right up to speed , unfortunately one of the ratty stones blew up about 10 seconds after i started it 
so no grinding until new my new wheels show up later this week . 

 i do have a couple issues .. the biggest one is that while i thought i knew how to wire up the magnetic starter properly i goofed somewhere , if i leave the switch on and cut the breaker the converter fires right back up once i reset the breaker .
i was a bit tired so i didnt attempt to trouble shoot it . 

the second issue is the two speed on the motor ... havent a clue how to make it a two speed again , the last genius who fubar'd the wiring just stuck some random on off switch on it ... it would be nice to have both speeds . 

and yes it takes 12 inch wheels ... not cheap , but they wasn't as expensive as i thought they would be , but then they should last for quite a few years .  


 next up ... as i now have three phase power its time to ditch the chicom motor on my g0602  and find a good three phase motor for it . 
luckily three phase motors are dirt cheap and easy to come by in the rust belt 
i do plan on buying a vfd in the future for the lathe .. but no hurry now


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