Noise problems can be infuriating! Do you need a VFD for the coolant pump? Most people just get a large Little Giant pump or a Superior pump and run it off 120VAC. If you want to control the amount of coolant, you can open a valve to divert some of the output back to the reservoir, or close a valve to partially restrict the output.
There are two basic approaches to solving RFI/EMI problems. 1) The Shotgun Approach. Start with the most likely culprits and/or easiest fixes. It sounds like you've been doing a great job of that so far. Most often, this is a matter of revising a machine to electrical best practices, so it's worth doing even when it doesn't fix a specific problem because it may prevent a future problem. 2) The Scientific Method. This is my favorite, although I usually spend an hour (or ten) on step 1. The scientific method requires data. The idea is to see what type of noise you have and what causes it so you can have a better chance of directly fixing the problem. The first step is to determine whether you have radiated noise or conducted noise. Radiated noise would be one conductor acting as a transmitting antenna and another acting as a receiving antenna. It may be that your encoder cable is the receiving antenna and the cable between the VFD and coolant pump is the transmitting antenna, in which case shielding the coolant pump motor cable could fix your problem. It could also be that the coolant pump VFD is the source of radiated noise, and short of building a Faraday cage around it, you're not going to stop that radiated noise source. In either case, shielding the encoder cables would be a good idea. You could also have conducted noise. The coolant pump VFD may be injecting electrical noise onto the power lines that feed it and whatever powers your encoder circuit. This seems unlikely. The VFD may be adding noise to the line, but the power supply for the encoder circuit is probably immune to most noise of this variety. The fact that you already added an EMI filter to the power leads of the coolant VFD without any success would keep me from barking up that tree any more, but you could always add an isolation transformer to block higher frequencies. I wouldn't bother, as that's likely to be more wasted effort, which is common when trying to solve noise problems. I'd put a digital storage oscilloscope on the encoder signals and watch them while turning the coolant pump VFD on and off. I'd also watch the power lines on both sides of the coolant pump VFD EMI filter while turning the VFD on and off. If you don't have a DSO, an analog scope will work too. It's very difficult to fight a monster that you can't see. If your encoder cables are not shielded, I'd replace them with shielded cables regardless of whether that cures this problem. It's just the right thing to do. Ditto with the spindle motor power cable and the coolant pump motor cable. The shields should all terminate at the same grounding lug in the electrical panel (star configuration) that's connected to an earth ground, although some people have a power panel and an electrical panel and each has its own common grounding lug. The simplest solution might be to upgrade the coolant pump VFD to something less noisy. I've been using the Huanyang VFDs for some of my CNC projects, and they're very noisy. So far, my biggest problem has been noise on the VGA monitor. I wish I had HDMI video. On 01/22/2016 12:51 PM, Jim Craig wrote: > Hey all, > > I have been troubleshooting some noise that I have on my servo encoders. > I have isolated the noise source to be the 1/4hp Automation Direct GS1 > VFD that I have running my coolant pump. If the coolant pump is not > running then there is no noise on the encoders and the machine maintains > correct positioning. If I turn the coolant pump on then the encoders get > false signal that in turn changes where the machine thinks it is. This > problem showed up immediately after I retrofitted the machine this last > summer. I have just now been able to diagnose where the issue is > originating. > > In attempts to improve the situation I have done the following. > Installed EMI filters on the supply lines to both the coolant and > spindle vfds. > worked on ground system to try to isolate the noise. > rerouted the coolant pump motor power cable completely away from > any other cables and completely away from the machine. > > All of these things have failed to improve the noise issue. > > I also tried the following to try and diagnose the issue. I disconnected > the coolant pump motor cable from the coolant pump vfd. Disconnected the > spindle motor from the spindle vfd. Connected the coolant pump to the > spindle vfd. Note that the spindle vfd is a 3.0hp Automation direct GS2 > drive. > > When I did this and ran the coolant pump via the spindle vfd there was > no noise on the encoders. > > Does anyone have any ideas on how to get rid of this issue. I really > want to make some parts but I can't with the noise issue. > > I talked to a EE buddy of mine and he mentioned running both motors > (spindle and coolant pump) off the same 3.0hp GS2 drive just to get me > going. What do you think about this? Will running two different sized > motors on the same VFD cause any issue. Right now I don't run my spindle > in reverse so I would not have any trouble with the coolant pump running > backwards. > > I talked to Automation Direct and they said that the GS1 is more prone > to noise than the GS2. I am contemplating getting a 1/2hp GS2 to replace > the GS1. > > So frustrated right now. > > Let me know if you have any ideas. > > Thanks, > > Jim > > ------------------------------------------------------------------------------ > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. 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