Variable frequency drives

[nymapleguy607]

Does anyone have knowledge about sizing these to electric motors. I bought a vacuum pump with a 1/2 hp 3 phase motor on it I would like to hook it up to 1 phase 220v, so I think I need a VFD inverter but I'm not sure on the sizing. The plate on the motor gives a rating of different rpms for various Hz but the voltage is 200. Will a VFD do this? Sorry if this is hard to understand I'm new to 3 phase stuff. Once I get the drive I plan on having an electrician wire it up. I'm just hoping to save some money buying a drive off e-bay. Thanks

[Amber Gold]

If it's a 3 phase motor, you'll need a VFD to convert phases. If you call www.driveswarehouse.com, tell them what you have, and they'll set you up. I have an electrical engineer friend who says by code you need the VFD to be twice the size of the motor...0.5hp motor you'll need a 1hp VFD. I have a 3hp VFD on my 1.5hp pump. I've heard from others though that the smaller can be 1:1. The VFD's nice because there's lots of parameters you can set to protect the motor from undervoltage, overvoltage, and etc. It's also nice because mine has a restart function...if it shuts down because of undervoltage (for instance), it'll restart the motor for me.

I have an Hitachi VFD. The first one fried mid-season in the first year (of course they said it wasn't covered because it was my fault), but I've had no issues with the second.

[Teuchtar]

I strongly suggest you replace the motor with a 1/2 HP Single phase motor. Get one that's rated "farm duty". It's all you need.
The trouble with VFD's is that they get fried. And often they will fry your motor. The one's available on ebay are notoriously "buyer beware".
Just my 2-cents worth.
( I design electric power plants for a living. The golden rule is "keep it simple" )

[nymapleguy607]

Thanks for the replies, Josh have you seen a reduction in your power consumption with the VFD verses without. I'm starting to realize that there seems to be a lot more involved with trying to use a VFD.

[GeneralStark]

I strongly suggest you replace the motor with a 1/2 HP Single phase motor. Get one that's rated "farm duty". It's all you need.
The trouble with VFD's is that they get fried. And often they will fry your motor. The one's available on ebay are notoriously "buyer beware".
Just my 2-cents worth.
( I design electric power plants for a living. The golden rule is "keep it simple" )

VFD's are a very common industrial tool. Don't you think suggesting they fry motors is a bit extreme? Are you sating that using them to convert single phase to 3 phase is not wise?

If they are good quality, sized correctly, and maintained well they are reliable equipment. Most running Busch pumps are using VFDs. There are many advantages including using a vac. sensor to turn down the motor when lines freeze.

What am I missing here?

[mountain man maple]

Why do you want to use a vfd on this motor? If you change it too 1 phase it would be much cheaper than a vfd. Savings on the 3 phase motor as far as electric usage for a 1/2 HP would never pay for vfd. As far as frying motor have never seen that but have never used a vfd that changed 1 phase to 3 phase if something happens with vfd to cause you to lose a phase then a motor being destroyed could easily happen.

[Amber Gold]

In retrospect, change the motor to a single phase. You won't notice the power savings during the course of the season. And I agree, keep it simple...one less thing to go wrong. You might need a motor starter though...forget at what HP these are required by code...a simple switch style works fine and is ~$30.

3 phase motors are much more efficient. My 1.5hp motor running on 230V uses 4.6amps. When I had a Delaval 73 on a 3/4hp motor it would use 5.5 amps at 220V. I also bought an A5 with a single phase 1hp motor and it uses more amps than the 3 phase.

[Teuchtar]

Sorry for the abrupt reply earlier. Here's my thinking:
Case 1) Run the 1/2 HP motor 6 wks at 12 hrs/day. Use $0.18/kWh electricity cost. Thats $35.38 electric bill for the season.
Case 2) Reduce its speed and load using VFD. At 50% load. the kW is 0.287 (per Leeson motor site). Thats now $26.04 for the season.

Option a) If Single phase motor used: $170 at TSC for farm duty motor. It has overload and reset switch. Plus $15 for a 115v power cord. Say $285 total.
Option b) If Three phase motor used: $0 (you have the motor), plus $30 for cord and plug. Plus whatever bill for the electrician. Plus $275 for the VFD. Maybe less on ebay. Say $305 plus the electrician.

My point here is that 115v is well understood by most of us, and plugs into a 115v/15 amp circuit. But maybe the VFD route is a bit of a technology and cost mystery to most of us. And the savings are in $10 range for the season for a 1/2 hp motor.

I have worked with VFD's for years. They are great when the driven machine demands a definite speed change (such as a conveyor drive ). But the benefit is less obvious when they are used on low power motors to reduce fan/pump delivery. In those cases, its maybe simpler to throttle the flow. If the motor and drive have been properly selected and come in a package with manufacturer's guarantee, hey I'm all for it. But if you have to piece together the components yourself, it can very quickly become a science project. And maybe you'll be in the middle of Big Sap when you find out some problem.

[DrTimPerkins]

There are two additional advantages of a VFD, besides any (admittedly reasonably small) savings in energy efficiency. The first is that when combined with a vacuum sensor the motor is throttled down automatically during low flow times (low leak times really) such as when the system freezes up. This means you can just turn on the motor at the start of the season and shut it off at the end, and only need to check on it when you have the time in between sap runs. There is no turning on, turning off, throttling down....so if simple is good, a VFD, once properly set up, is quite good in that sense. The second advantage is that the speed of the motor (or amperage draw) is probably the best indicator (far superior to vacuum level) of how tight your system is (unless you happen to have a CFM meter in line somewhere), and makes the decision of whether or not to head out into the woods to look for leaks quite easy.

[nymapleguy607]

Thanks for the replies, after doing some more research I think I'm going to change out the 3 phase 1/2 hp for a single phase 1 hp motor. The bigger motor gives me a few more cfm out of the pump. Than

[ClarkFarmMapleSyrup]

Hi, My dad is an electrician and deals with this alot, and says you should double the Hp capabilities of the VFD.

[nymapleguy607]

Hi, My dad is an electrician and deals with this alot, and says you should double the Hp capabilities of the VFD.

Not sure what you mean by double the hp capabilities, is that just by over speeding the motor say to 100hz instead of 60hz

[ClarkFarmMapleSyrup]

Double the "capacity" that the Vfd can run with, that way, if the motor is running hard, or something, the vfd will react better. Dont quote me on this, because this post here is what I think he meant, but Ill ask him again when I talk to him.

[wiam]

My guess it means that a 1hp single phase motor should have a 2hp rated VFD.

[ClarkFarmMapleSyrup]

Yes. I think thats right