3 Phase compressor, single ph service: What options?

[mike_s]

if the appliance you are using does not have a ground wire (hair dryer) the GFCI doesn't really provide any level of protection.

Kinda off topic of compressors with my reply on this, but most hair dryers have a GFCI built in the plug/cord now days...

according to one reference I found on the web, it's been a law to have GFCI built into the hairdyer plug/cord since 1991 in the US.

Reference NEC 422.41, and US Code 422-24, and UL 859,

 

[Fl_Key_Guy]

Dereck, I'm told by Brownie's that you need a 10 hp VFD to run a 7.5 hp motor on single phase input. The cheap ebay VFDs appear to be Asian- could be okay, could be junk and they have your money before you know which. Also, some VFDs will accept single phase and some need 3 phase in.

Right, Mike- you DID say GFCI breaker, I just saw receptacle. Tired I guess... And yes, $900 seems pretty good for a 20kw propane generator. A 12 KW one just sold on ebay for $1500- also a good buy.

Craig, it appears that I have a Mariner block based on your description. However, it is already specified as running at 1200 rpm, so if I can't go below 1100 rpm, using a smaller hp motor is not an option - at least not at full pressure. Rough measure of the current pulleys is 12" motor and 17.5" pump with 1750 rpm motor which is about right for specified speed.

Which makes me wonder if a 5 hp motor would run it if I settled for lower operating pressure? I'm not sure if it is linear, but 2/3 of the hp might yield 2/3 of the pressure which would be 3300 psi which is acceptable. Would that work- just lowering the operating pressure?

The other possibility was using a 7.5 hp single phase motor. Brownie's says they are about 50% bigger and might not fit, but that is not what I seemed to be reading on the dimensions of two that I checked. I found one reasonably priced motor 7.5 hp at 1680 rpm which would spin the pump at 1140- not much cushion on the 1100 rpm minimum, but not much less than current design. Are single phase motors really that much bigger than 3 phase?

Another possibility is to sell this compressor and buy one that I can run without modifications. It should be pretty desirable as it only has 11 hours on it and it is nicely mounted in a heavy stainless steel frame. This Yachtpro reportedly cost $18,000 new, but a Mariner II is much less. What's this thing really worth?

 

[tlawler]

Dereck, I'm told by Brownie's that you need a 10 hp VFD to run a 7.5 hp motor on single phase input. The cheap ebay VFDs appear to be Asian- could be okay, could be junk and they have your money before you know which. Also, some VFDs will accept single phase and some need 3 phase in.

All VFD's will produce three phase output with single phase input. The electronics are similar, whether it is a purpose built phase converter or a standard VFD. Here is a paper with a lot of good info. It deals with using single phase generators to run three phase waste water pumps through a VFD in an emergency when three phase power isn't available. Checking ebay, you will find a lot of good name brand used and even some new VFD's for reasonable amounts. Names to look for are : ABB, Danfoss, Magnetek(now Yasgawa), Square D(Altivar, Telemechanique), Siemens, Toshiba and Hitachi. The trick is locating a 208/230 VAC model, as there are probably five 460 VAC drives for every 208/230 one out there. And keep in mind the 2/3rds rule as you stated above when sizing a VFD: a three phase VFD will only produce 66% of rated output with a single phase input.

 

[CraigAClark]

Craig, it appears that I have a Mariner block based on your description. However, it is already specified as running at 1200 rpm, so if I can't go below 1100 rpm, using a smaller hp motor is not an option - at least not at full pressure. Rough measure of the current pulleys is 12" motor and 17.5" pump with 1750 rpm motor which is about right for specified speed.

Which makes me wonder if a 5 hp motor would run it if I settled for lower operating pressure? I'm not sure if it is linear, but 2/3 of the hp might yield 2/3 of the pressure which would be 3300 psi which is acceptable. Would that work- just lowering the operating pressure?

Where did you get the info about pressure? The only thing that will be effected is output volume. Actually the Mariner, if set up at the max speed would run at 1250 rpm. You can do what you want, but like I said earlier, I just converted a Mariner from 7.5hp, single phase to 5hp single phase. Basically, you would be turning a Mariner into a Capitano.

Craig

 

[Fl_Key_Guy]

Good information on VFDs in Diversolo's link!

Some manufacturer's specify that their VFDs MUST be supplied with 3 phase power ONLY. However, that may just be the VFD manufacturer covering his butt for possible improper use, or they even be changing the color of the box and selling the same device for more money as a phase converter!

Craig, I was just exploring possibilties in discussing a lower pressure setting. That possible option would run the pump at full design speed and presumably give full cfm at lower pressure. Or not.

Since you have already converted a Mariner from 7.5 to 5 hp successfully, would you share the details?

I may be getting confused here, but gather that you reduced the speed by less than 150 rpm (1250 to 1100+) and were able to run on 5 hp. Is that correct? If so, do you still have continuous duty cycle?

I am obviously not familiar with the various Bauer pumps: Does the Capitano actually use the same pump as a Mariner? Please excuse my ignorance- I'm still learning and just trying to solve a challenge that might be simple for some of you...

 

[pescador775]

I agree with Craig. If this is a old style Mariner which is just repackaged then it can be run at lower output with no effect on final press. However, if you install the 5 hp motor with no other changes there may be an unacceptable increase in current draw. IOW, one would have to monitor current and heat at the git-go. It is a small possibility that the motor would not start at all. A smaller pulley may have to be installed.

Craig, I recall that this mod has been done more than once. Is there anything else in the way of details to share? Is there a "best fit" for 5 hp motor vs rpm?

Keys; where are you getting the advice? I mean, you have surfaced with some information that is hard to verify. However, identifying the compressor is a break through, thanks.

 

[CraigAClark]

For the conversion I did, I used a Leeson 120554 motor (145T), AK56H pulley and H-7/8 bushing. This reduced the rpm to equal the approximate output of a Capitano. There was no effect on the pressure, which the machine is rated to 5000 psi.

I can't link to the specs so try the search at:
http://www.leeson.com/products/

Without seeing your machine, I can't tell whether you will need to add a motor base or not, nor can I tell you what size belt you will need. The belt will be an "A" cross-section though.

For those of you that keep mentioning VFDs, you better check closely to make sure the maximum output amps of the drive are equal to or greater than the FLA on the motor. Just seeing an ad that says the drive will run a 7.5hp, 3 phase motor with single phase input may not be accurate. Plus you will still be drawing the same amperage as a single phase motor between the drive and the 3 phase motor. Unless I had the drive specs, I wouldn't take the sellers ad at face value.

Craig

 

[Scuba Duck]

The primary purpose of a VFD is to control the frequency (speed of rotation) of the motor powered by the VFD. To do this they convert AC current into DC current, and then back into AC current at whatever frequency you desire. The middle state is this DC current. Most all VFDs designed to be powed from 3 phase will run with only single phase AC applied but at a lower output considering you are essentially starving the amount of power applied. Some VFD's are specifically designed to be powered by Single Phase (don't event have the connections for 3 phase input) and there is no loss or reduction in output. Just make sure you read the discription of the item.

Here's another one on EBAY specifically for single to three phase.
http://cgi.ebay.com/7-5-HP-PHASE-CO...ryZ42894QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Having a fairly large capacity VFD around is also nice for the workshop, as used 3 phase shop tools typically sell very cheaply as the general homeowner cannot use them. You can purchase very expensive industrial tools for pennies on the dollar.

mike_s - I guess its been a while since I purchased a hair dryer, considering I don't have enough hair to warrant its use... I should have chosen another household appliance for my example.

 

[Fl_Key_Guy]

Much of my info is coming from manufacturer's literature and internet info sites. Some is from Brownie's.

One VFD spec says that it will only feed half the motor size if fed from single phase. That surprised me as usually they just say go to the next bigger VFD- i.e., 10hp VFD for 7.5 hp motor.

I think there is some misrepresentation on motor sizes out there, too . (No! Say it isn't so!) I see 7.5 hp motors with amp ratings of 28, 35, 38 amps. The low amp motor had double the speed of the other two and is quite a bit cheaper. Off brand and probably Chinese, with Chinese Manufacturer's Association rating criteria. (I don't actually know if there is a CMA, but I do know that sheet metal manufacturer's in the USA have an association that says they can use different gauges numbers than the standard ones. In other words, they sell you a "20 gauge" roll-up door that is made with 24 gauge metal, but it is okay because they are using the manufacturing association's "gauges").

Thanks for the great information, guys!

 

[pescador775]

Craig says that he used a 5hp, 3450 rpm motor and 5.5 inch pulley. It's worth consideration. Go with Leeson, don't experiment, IMO.

The actual output of that compressor is possibly no more than 6.5 cfm. Bauer advertises it as "7 FAD" but I am pretty sure that it is lower. Running it with a 5 hp motor may draw some extra juice over that recommended for the motor but I doubt that it will be a killer, particularly at press less than 3500. Moreover, the high rpm motor has greater cooling capacity (higher fan speed) over that of a 1750 rpm type. My est of current draw < 24 amps. Est output, 5.8 cfm.