10hp air compressor....how to power it.

[LD1]

Ok guys, I have mentioned in a few other threads that I acquired a locked up old screw compressor. A joy twistair TA010....40cfm compressor.

I didnt want to invest too heavily in this project because I honestly didnt know weather or not I could save it.

Well, so far with minimal investment in new bearings and an oil filter.....the thing lives and breaths very well. It will go from 0-100 psi in 3min flat and thats with an 80 gallon tank:thumbsup:

And pressure on off being 100psi and 120psi......that recovery time (if no air is being used).....a mere 30 seconds:thumbsup: So I think its safe to say this thing makes way more air than I will ever use.

Being it is a screw compressor with vent/unload/load valves....its not a hard starting machine at all. For test purposes I have been running it off my 15hp American rotary phase converter. But I am not liking the amperage imbalance I am seeing.

At the machine.....I am pulling 38-40 amps on L1 and L2....and 22a on the generated L3. All the while the nameplate amperage for 230v is only 25.6. So this is not a good way to run, and would assume the converter is simply too small??? But certainly worked for my test stages to make sure this compressor was even worth investing more money into.

And while running on the RPC......my single phase supply supplying everything.....right around 55a. So that certainly doesnt sound efficient at all since a with only ~40a single phase I could be running a single phase motor.

And options get alot slimmer for VFD's to power 10hp motors that I am starting to shy away from that as an option.

I can get 10hp/3600rpm single phase motors for ~$750-$800. Which is certainly worth it for this beast of a compressor considering that even spending that for a motor, I'd still have under $1000 total in a 40cfm screw machine.

Another option I am considering....is drop to a 1800rpm motor. Currently the pulley sizing has the airend running 4000rpm. Cutting motor RPM in half.....and upsizing the pulley a bit but not quite doubling it....get the pump to maybe 3000rpm is what I am thinking. 40cfm is way more than I need, slower will pull less amps, and make things last longer....and 1800rpm motors in the 10hp range are alot easier to come by and a few hundred bucks cheaper.

Whats everyones thoughts? Dont really think there is a wrong way to do it. Just trying to decide what is most practical/economical.

Also came across some old references on practicalmachinist about Ronk add-a-phase static converters. That use an autotransformer or something. Supposed to be able to use a 3ph motor up to rated HP with their static device...and have good amp balance too.

 

[Bingo9991]

Get a Wisconsin thd/tjd with 100lbs compression and run it at idle, not exactly efficient but bulletproof

 

[LD1]

Get a Wisconsin thd/tjd with 100lbs compression and run it at idle, not exactly efficient but bulletproof

Don't think I can make that run on electric

 

[Mendonsy]

The current readings that you are seeing are not particularly surprising for an RPC running a loaded motor. The phase angle of the output from an RPC isn't the same as true three phase power so the two phases connected to line draw much more current than the generated phase.
About the only option with the existing motor would be a phase converter VFD. That would allow you to adjust the motor RPM which should improve the situation, but I'm not sure how rpm effects a screw type compressor. Slower speed might reduce both CFM and pressure?? The other option would be to go with one of your single phase motor choices.

 

[oldnslo]

seems like the 10 HP 230 VAC single phase would be the simplest solution. Only failure I ever had on larger single phase motors was capacitors in cold weather. This was in central MN at -15 to -25 degrees. Doubt you will see that to often in central Ohio.

 

[LD1]

The current readings that you are seeing are not particularly surprising for an RPC running a loaded motor. The phase angle of the output from an RPC isn't the same as true three phase power so the two phases connected to line draw much more current than the generated phase.
About the only option with the existing motor would be a phase converter VFD. That would allow you to adjust the motor RPM which should improve the situation, but I'm not sure how rpm effects a screw type compressor. Slower speed might reduce both CFM and pressure?? The other option would be to go with one of your single phase motor choices.

RPM wont effect the pressure....within reason.

As I said, this compressor airend is the exact same one used on 7.5hp/29cfm models......the 10hp/40cfm model that I have, and 15hp/60cfm models. they just did the speed change with pulley sizing. So yes it is feasible to run a drive and reduce speed.

But from an economics standpoint.....I cannot buy a drive big enough for any less money than a single phase motor.

 

[LD1]

seems like the 10 HP 230 VAC single phase would be the simplest solution. Only failure I ever had on larger single phase motors was capacitors in cold weather. This was in central MN at -15 to -25 degrees. Doubt you will see that to often in central Ohio.

No cold issues in a heated shop

Still trying to decide if I want to spend ~$800 for a 10hp and have a 40cfm compressor......or spend $400 for a 7.5hp and ~$25 for a new pulley and have a 29cfm machine?

Decisions decisions.

 

[bigdeano]

I put a 10hp 3ph motor to use on single phase by using capacitors and a starting relay. I used 220ufd run capacitor and 900ufd start capacitor. I had the relay, the caps cost a little over 100 dollars total. It works real well, runs just like on 3ph, but I suppose it wouldn't develop full power. I'm probably using about 7 or 8 hp. I bought the run caps at surplus center, the start caps on Ebay.

 

[LD1]

I put a 10hp 3ph motor to use on single phase by using capacitors and a starting relay. I used 220ufd run capacitor and 900ufd start capacitor. I had the relay, the caps cost a little over 100 dollars total. It works real well, runs just like on 3ph, but I suppose it wouldn't develop full power. I'm probably using about 7 or 8 hp. I bought the run caps at surplus center, the start caps on Ebay.

Yea, you basically made a static converter. And no they dont run full power. You are probably closer to 6-7hp rather than 7-8

 

[Erik M]

If you want simplicity and have the current to do it, just get the single phase motor and the starter as it will be cheaper than any three phase solution. It will need plenty of power when you start it though so I wouldn’t do it if you have only enough power to run the motor. The inrush current will be very large as a compressor is a hard start. If power is limited a three phase solution with a VFD will use less current on start.