Bauer K17 re-motor help needed

[broncobowsher]

So the shop I deal with picked up a used K17 compressor with a 3-phase 15HP motor. I didn't pick it, I didn't spec it, I didn't buy it. But I am trying to get it to work. The building doesn't have any 3-phase. So we are trying to figure out the best route to go. Looked at some phase convertors, but they are not cheap and the amp draw would push the limits of the old panel.

But it has been rumored that the motor can be swapped out with a 10-HP. That is what the old compressor is. I know the wiring is there and can supply it. Not having to rewire the building will go a long way to getting this up and running. Finding a 10HP motor is a lot easier, and cheaper. But this leads me to a problem, I know that the compressor that was engineered for a 15HP motor won't pair very well with 10HP unless something changes. My understanding is we will need to change pulleys to slow the compressor down. But my googlefu isn't good enough to figure how much it needs to be slowed down. Quicky math says with 2/3 the HP, the compressor should run 2/3 the speed. But I suspect that it isn't that easy. And will the compressor even run right at a lower speed?

So any tips on derating a K17 into a 10HP compressor? The 15HP motor is 3490 RPM based on the data plate. I forgot to measure the pulley sizes before I left.

 

[Namreg 58]

Dive Shop Utility Software

" Go figure "

 

[tbone1004]

the motors will only pull what they need to pull to run, so just because it is a 15hp, doesn't mean it will take all 15hp, but if you put a 10 on there, it may not get up to full pressure.
I believe that is a splash lubricated compressor which means you can't slow it down all that much. The manual should have it's max and min rpm for lubrication purposes and you can only go to the min.

How much electrical service do you have and what voltage is the motor? You're going to want at least 60a of 220v fwiw.

Your best plan is to put a VFD on there. Will cost about $1500, but it will allow you to give variable speed, use the existing motor *3phase motors ALWAYS run better*, and you can do the phase conversion in there.

 

[broncobowsher]

Well I did spend a lot of time going through those links. Ran the numbers and as built it should pull a touch over 14HP, so I will say the 15HP motor is correct. I like the idea of the VFD and keep the 15HP motor that is in there now. But that is going to be upwards of nearly 100A. Right now all the wiring is set up for 50 or 60A (I can't remember exactly which). If the VFD can be used to throttle down the load (run at 40Hz instead of 60Hz) and stay in the limits of building wiring I would be interested. This is getting to the top of my electrical skill set. What would be really nice is a pressure feedback on the output where we could run the compressor fast under low load and throttle back as the load builds.

But all that comes back to how slow can we run this compressor? I have looked for an RPM range. I can't find it. I can calculate what it runs with the factory setup. But that doesn't tell me how slow or fast it can be run, just what it is now. As for splash lube, I think it is pumped. I thought I saw an oil pressure gauge, but I can't guarantee that. Even splash lube should have a pretty wide RPM band. For reference a splash lube Briggs & Stratton engine that is purely splash lubed will run from a bit over 1000 RPM idle to nearly 4000 RPM governed and live a long happy life.

Anyone know where I can find an RPM range for this compressor? Maybe an output chart for those speeds as well?
The limiting factor is turning into the buildings power. Trying to avoid the needing a new panel and rewire the building and maybe even the power feed to the building.

 

[tbone1004]

why would 15hp pull 100a? I assume you have 220v, 1hp=746w=3.4a @ 220v. 15*3.4=51, assume 85% efficiency through stuff blah blah=60a at max load. VFD will soft start so you won't surge it.

I'm not familiar with the k17, but if it doesn't have splash *with Bauers there is often a combo of splash and pump*, then you can slow it down. That should be in the manual, but there shouldn't be a reason you can't run it full out.

WRT the B&S engine, splash lubed motors that are designed for wide bands are designed to lubricate at the low RPM. Compressors like this are designed to be run at a fixed RPM and they usually have a pretty narrow RPM band they're happy with. Typically no slower than around 80% max rpm for the ones I have paid attention to

 

[broncobowsher]

One of the VFDs I was looking at for a 15HP motor stated input amps of 99A. But now you have me thinking and that probably included the 150% overload for startup. Which would put it at 66A full load. And I bet it would still be happy with a 10% underdrive if needed. You do have me thinking. The original plan was to replace the motor as it was 440V and we didn't know it could be rewired down to 220. I just saw the data plate for the first time yesterday and saw the dual voltage rating. I was looking at rotary convertors for a little bit but that looked ugly. VFD had not really entered the picture until now. I still have worries about the 50 year old panel in the leased strip mall. I need to look that over again.

 

[TrimixToo]

It should not take all 15HP to start the compressor if it's bled down (autodrains or by hand) before it starts, even if it needs 15HP running at its rated pressure.

 

[tbone1004]

One of the VFDs I was looking at for a 15HP motor stated input amps of 99A. But now you have me thinking and that probably included the 150% overload for startup. Which would put it at 66A full load. And I bet it would still be happy with a 10% underdrive if needed. You do have me thinking. The original plan was to replace the motor as it was 440V and we didn't know it could be rewired down to 220. I just saw the data plate for the first time yesterday and saw the dual voltage rating. I was looking at rotary convertors for a little bit but that looked ugly. VFD had not really entered the picture until now. I still have worries about the 50 year old panel in the leased strip mall. I need to look that over again.

monetary surge vs running is different though and with the VFD you can set a slow startup curve without any issue. I'd just use the existing motor if it will do 220v 3p

 

[Kayakingphotos]

Make sure if you go the VFD route, you make sure it is rated for the HP requirements with SINGLE PHASE INPUT. Typically you need to oversize a VFD when you run single phase input. Depending on what model, it could be that you would need one that is rated for 30% or more HP than the motor you want to run.

 

[Billy Northrup]

I've used Invertek VFD with success. You can configure it for a constant current mode as well. It will run as fast as the current rating will allow and slow down as the load builds.