This morning, the temp outside was -2. Opened the garage door from a balmy 17 degree C shop, so I knew the oil was not an issue. In retrospect, I don't think oil temp was ever the issue. I thought it at the time, but I've since changed my mind. Bad oil however still may be an issue. To be verified.
My first objective is to find the right balance of capacitors so that when the lathe is sitting idle, collets closed, the hydraulic motor sees a perfect balance. At least with this, I can have the lathe on and not worry that diagnosing for hours will harm the motor. From previous observations, I know that when the system is balanced, the current through each leg in the 3phase hydraulic motor is well below the FLA of the motor. The problem will then be how to balance the RPC so that during longer cutting operations when the spindle causes imbalance, it isn't so much that it trips the hyd motor breaker in the middle of the job.
For now, this is the data I compiled for various tunings. I first start by getting the system reasonably balanced with just the RPC running and no load whatsoever. When I get close, I start adding load. First, I just turn on the breaker to see how the load changes (this is where I wish I could actually measure the current flowing through the single and three phase lines). Once I get close to a balanced system under that load, then I turn on the control and activate the hydraulic system (what I refer to as "steady state" - the state I figure the machine will be in most of the time when it's not performing work). I will add a fourth state called operation which will be when the machine is actually cutting. But for now, I needed to look at the data compiled so far, presented here:
Attachment 390824
Having previously observed this steady state become grossly imbalanced again during spindle operations, I am having serious doubts as to my RPC's ability to handle the load. I think I need a much STIFFER voltage from the RPC. The problem with my RPC from WNY is that it only has capacitors between A-B, and B-C. There are no capacitors at all between A-C... unless the start caps are somehow involved, but I don't think so. Their "GOLD" series which I never new about has three banks and claims to have better balancing (?). Given this two-bank design, it is quite possible that my RPC is irreparably undersized. I also don't have a clamp meter to help me better understand the current draw on this system (relative to the RPC's supposed capacity of 20HP). I will head out today and get one; I need current draw to factor into my spreadsheet.
From here, I will progress to conduct more measurements with a new state called "Operating", which will be the instantaneous voltages during spindle/cutting operations. I think I will need to wire more of these meters into the hydraulic system so I can watch both the hydraulic motor, and the overall system voltage. If I can figure out a compromise between the two where the voltage drops during cutting operations, but not long enough (or imbalanced enough) to trip the hyd breaker, I might get away with my current RPC.
I strongly doubt I will achieve this with my current RPC though, but it's worth a try. I have a 20HP RPC, combined with a 20HP 4-pole Toshiba 3ph motor. When I get my ammeter and start measuring real currents in steady and operating states, I'll probably answer my own question as to whether this system is sized well enough.
The FLA on my lathe is a whopping 82A @ 230V, but that is the max with everything running full blast. My main spindle is actually 10HP (states 15HP but for no more than 30 minutes), my sub is 5HP, but they will NEVER be cutting at the same time. The FLA on the hydraulic motor is 3.8. Axes are what they are... 2kw each maybe, and then there are the various fans, pumps, control, relays, bells, whistles, etc. Boy, I really need an ammeter. I think I'll head out now and pick one up.
Torin...