I'm hoping to find someone out there that Knows pump multplexing two 25 hp.pumps , one pump on the VFD and one on a across the line starter on a community well system (I'm a board member of the water system and the only one who will go over to the pump house to see whats going on and we have lots of lawn irrigation on timers) I'm having issues again with the Yasakawa P-7 drive . The pump system demand is right where the issues are created. What's going on is the system has minimal demand and the lag pump (across the line) is being turned on and off within every 3-4 minutes. What I'd like to see is widening of the time that vfd pump stays on at higher Hz (58 Hz) even at the expense of lower pressure say even down to 55 PSI (70psi setting). Any kind of parameters change/setting to keep the lag pump from kicking in so frequently. I just feel it's kinda mean to the pump couplings and electricity to have turning on and off so often. I can only hope I've laid out enough information on the problem so someone can maybe tell me which parameters to look at. Oh yeah and as the post will state it's Sunday afternoon. I have a regular week day job so trying trouble during the week is next to impossible. bjr
You should set up a 0~10VDC transducer and install it onto the water pressure system. Use that as the primary pressure/freq control to use the VFD correctly in an analog mode so the main VFD controlled motor runs 100% of the time as 5 to say 75Hz. The 5 to 75Hz is a guess and would represent a 0~10VDC pressure reading set so that your MAX water line pressure = 10VDC and MIN water pressure (30psi?) = 0VDC. It will need a small calibration setup and once set as long as power stays your pressure should stay very constant as the pump RPM increases & decreases to maintain your set point pressure.
By running the VFD drive motor the secondary across the line starter should be off MOST if not all the time.
Yasakawa has a pretty good support lines from a quick search you can find it and they have both engineering and customer support lines. Couple of the maintenance guys at work have used them a lot, I like ABB as well. For inexpensive transducers look at Automaton Direct or Keyence or Amazon/Ebay. You should be able to power the transducer from the VFD power supply if you dont have extra 24VDC handy.
I agree with Spiker. If the demand is normally below the capacity of yone 25HP pump then the VFD pump needs to be the lead pump. When the demand exceed that pump the other starts and the VFD has to ramp down and pickup the excess load. There is a low limit on the VFD though so the lag between restarting has to be set at the optimum low load. This setup puts all the wear on the one pump. To equalize the run time and be assured of always having a variable load pump you need a VFD on both pumps and an Industrial Programmable Logic Control system such as ABB makes. Setting one up is a job for the experts to get it right. That way you will never have a short cycling motor.
I am assuming this was not an engineered system from all your dialog. You need a Mechanical engineer experienced in these systems. I used to work in the Industrial Control business in my younger day (back when we used air instead of computers). Give me an offline personal and I can may be able steer you to the right solution via my consulting firm.
A little update: I did get in touch with local Yasakawa rep. and while on the phone, we went thru the parameters while I was right at the pump controls. I'm a little foggy on all the settings we went thru but we reset some times and a What they call "Delta" setting. Basically what ever is the set pressure number is it subtracts a number from that and has to remain at that point for another setting in seconds before the lag pump kicks on. There was another parameter that had to be "turned on" to operate some more parameters. It does get a little much for a old goomer such as myself to read and follow "all instructions". Somehow me and the water Association president muddled thru it and everything works now. Thanks for the input though. bjr
