Static converters loose 1/3rd to 1/2 the motor Hp depending on the design, in particular with a 2 speed motor. I have also seen a number of reports of surface finish issues with static converters vs. RPC/VFD. On a mill, less of an issue, lathe and surface grinder I would just go with an RPC/VFD. Cost wise, a VFD is a reasonable alternative to an RPC for smaller motors, beyond 3 Hp the costs of a VFD increase significantly. VFD's have many features like speed control, soft start, electronic braking, slow speed jog, etc., but if you do not need these then an RPC is probably a better choice. I have done a few shop system installs where the shop was run off of an RPC, and we installed several 3 phase input VFD's on specific machines that benefited significantly from there additional features. One doe not negate the other, and there is minimal to no derating of the VFD in this arrangement.
Cost wise up to 3 Hp, VFDs are probably more cost effective and simpler to install on machines like mills and surface grinders, but lathes take a little more effort to do it right. As far as VFD whine, depends on the VFD, motor and software/parameters. My mill and lathe (both 3 Hp) with Yaskawa VFDs, the carrier frequency is 12 kHz, I no whine whatsoever. The Yaskawa also has programs for variable switching frequency settings as opposed to fixed. Higher switching frequencies can lead to more motor heating and insulation breakdown, but this is not an issue with newer motors. Old motors should use a lower carrier frequency.
Machines are an investment over time, we spend numerous hours adding accessories and modifying the machine to fit our needs, adding a VFD is no different. The time consuming portion is figuring out the design, materials and getting everything in house. Building the system correctly and understanding the wiring connection the VFD and the programming parameters are a bit of a hurdle, so sharing one's experience helps others to get started. The system build time is trivial in relation to the years of use and benefits if you use the features of a VFD. Investment/cost wise, you can go super cheap these days with a VFD, or invest a bit more and get more features. I have installed numerous VFDs and worked with 100's of people doing VFD installs, I can't recall anybody that would have done otherwise and almost everyone wishes they had done it sooner. Also know many RPC owners that are just as happy, recently I have seen a number of small shops using the AMP RPC's which are plug and play, they were super quiet. Plug the cube into the wall, plug the machines into the cube and you are up and running. There are also other less expensive RPCs that work great.
AMP Mobile - The AMP Mobile rotary phase converter is plug-and-play ready for a quick and cost-effective installation. Equipped to run 208-250V equipment in three tiers: Tier 1: 1 Breaker and 1 Receptacle Tier 2: 2 Breakers and 2 Receptacles Tier 3: 3 Breakers and 3 Receptacles These...
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Below is an old thread on a G4003G VFD conversion, it is a very simple 3 relay design, and did not take very long to install. If this is something you are interested in, I will update the schematic to include provision for the foot brake, differential braking etc. to the VFD of your using and provide you with a basic parts list. I have previously outlined the suggested VFD enclosure components, etc. in other posts. It is a more expensive proposition at 5 Hp and above, but I think you will be very pleased at the end of the day. Otherwise, buy a static converter as a band-aide to get you started, or add a motor to get you to an RPC and then go from there.
Hi everyone.... Well My warranty is up on my G4003G. These dam chinese motors are garbage. this is Number 3 and it has developed some noisey bearings. So I've decided to go with a Leeson 192205.30 2HP 3ph motor. And i also purchased the Automation direct GS2 3 hp VFD I ordered the motor...
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