I do a fair amount of VFD's but have yet to try one on single phase.

I understand that the rule of thumb is the VFD needs to be somewhere around 2-2.5 times the driven HP. 5HP motor=10-15HP VFD.

Of course, Jraef is the resident authority on this stuff, so maybe he'll see your post and comment.

Don't forget that whatever one you choose, you verify it can take single phase input. It wouldn't surprise me that you will find several different brands that may fault and not be able to reset if they only see single phase input, with the fault being a phase loss on the third leg.

 

Watts are watts.

Start with that.

Allow for losses.

It's actually pretty easy to back out Amps from the Watts.

Round UP for horsepower.

 

I agree, the 200% rule works well, I've used it successfully on a number of single phase sources.

You need to multiply your single phase current by 1.73 to account for the manufactured phases, and then the extra 0.27x is just for switching inefficiencies in the drive.

There may be cheap drives that won't run 1ø, but every major manufacturer I've run into had that ability, you just have to set up the parameters.

 

Thanks guys. Looking at the hitachi sensorless vector drives from driveswarehouse.com. Any experience with hitachi drives? Will these drives work?


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Yes. Good choice. What I sell.

2x hp for 1ph so buy a 6, 10, and 20hp size.

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You also need to look at how much load those motors have. I have gone as little as 125% on lightly loaded motors.

 

Bad idea.

Most people focus on the simple current difference based on phase difference, but that's actually the least important factor. Much more important is how the diodes conduct and how the capacitors react to the highly increased DC bus ripple.

50% de-rate (VFD = 2x motor amps) is a MINIMUM number to use, and that should only be used for VFDs that have an internal DC bus choke. Most Asian drives do not, because it's (relatively) expensive to ship that steel and copper on a boat. So my rule is with no DC choke, a 65% de-rate (VFD = 3X the motor FLA) or de-rate the ambient operating temperature by 30% if using a 50% de-rate. So if the Asian VFD is rated for 40C, you can use a 50% de-rate if you ALSO make sure it is never used above 27C (80F) ambient, which is next to impossible if it's in any kind of industrial environment and enclosed to protect it.

Mind you though, there are a LOT of small Asian drives, 230V 3HP and down, that come designed FROM THE FACTORY to accept single phase input without de-rating (or really, they are already over built because at that size, the components are cheap enough). There are a couple of suppliers selling a 5HP version that says "No de-rating", but that's basically a marketing ploy because if you compared the cost of their 5HP single phase input unit to a 10HP 3 phase unit, you will see they are the same (Lenze / AC Tech does this).

Be VERY wary of a cheap junk Chinese product from Huanyang, but usually sold with no name. They claim on their websites on eBay that they are 4HP or 5HP with no de-rate, but it's an outright lie. AFTER you buy it and get the manual, you find out it is only 5HP at 3 phase, 2HP at single phase. But by then, you can't return it because the eBay seller has disappeared (really, they just change their name).

 

I never heard of a grain auger that did not jamb up (aka, full load)... Do they exist?

 

Lol....if they do, I've never seen one......

I'm not sure I'd even put a VFD on a grain auger. If I did, I'd oversize it by quite a bit.

A VFD, unless it's grossly oversized, cannot get a motor to develop as much locked-rotor and pull-up torque as across-the-lines.

 

It's never a bad idea to know what your loads are.

 

No argument from me on that. If know for absolute sure that your motor is never going to be loaded at more than 60% of it's rated capacity, then a 125% up size of the VFD to the motor rating will likely be fine.

But then you have to ask why the motor is so over sized to start with...

 

Why wouldn't your beginning point be determining the HP of the 3 ph motor, then decide on a brand and model # of drive, say ABB then simply look in their manual? Usually there is a table and it will show both 3 phase and single phase rating. Or call the distributor. That's what they get paid for. Finally, upsize it at least one size.

 

UFA had some auger specific setups for sale a while back. The customer decided to hack them in himself so I never looked any further into it.

 

easy on Hitachi... they are well known for badly written converted to English manuals...

They actually DO recommend using ANY of their 3ph models on 1 phase and have their well documented application note on their website how to do it:

http://www.hitachi-america.us/ice/support/ac_drives_inverters/?WT.ac=ice_rm_acdinvrtr

Specifically:

http://www.hitachi-america.us/suppo...rtingdocs/forbus/inverters/Support/AN032404-1_Rev_A_Sizing_for_Single-Phase.pdf

But you are right, many other mfgrs of VFDs do leave it very vague.

 

easy on Hitachi... they are well known for badly written converted to English manuals...

They actually DO recommend using ANY of their 3ph models on 1 phase and have their well documented application note on their website how to do it:

http://www.hitachi-america.us/ice/support/ac_drives_inverters/?WT.ac=ice_rm_acdinvrtr

Specifically:

http://www.hitachi-america.us/suppo...rtingdocs/forbus/inverters/Support/AN032404-1_Rev_A_Sizing_for_Single-Phase.pdf

But you are right, many other mfgrs of VFDs do leave it very vague.

Well whadaya know... someone who knows what he's talking about! :thumbsup:

I guarantee you, 99% of the people I have run into that sell Hitachi drives have never seen that document... but it's good to know they do back it up in writing.

Interesting side note that I know amuses you... their reference to 1.732 in that paper!

To explain, Mike and I were involved in another website debate where I brought this up and the argument among the EEs went on for something like 400+ posts as to the validity of that statement...

 

Yep, the square root 3. I actually argued with Hitachi engineers on that a few years ago and won. Argument was that since they rated a lot of drives as both variable torque and constant torque, variable T being 1 size higher HP (and continuous amps rating) that the cont torque ratings for the same drive, we should be able to just increase 1.5x not 2.0 times for single phase use...

Knowing what was learned in 400 posts of study you mentioned elsewhere, I now realize 1.73 is the least of our issue, the added ripple in cap bank and 2-3-4x higher Irms on AC input says double the drive size minimum! And add input choke if customer will pay a tad more to extend the life of their VFD (my guess by 200%)...

 

That Hitachi document doesn't mention the issue of DC bus chokes though. Do their drives have them? The only Asian VFD mfr I had seen (before now) that supplied a documented de-rate method was Yaskawa and they are specific in mentioning that the 2x value is predicated on adding a DC bus choke. A-B are the only ones I have seen saying that without a DC bus choke you either have to use 3x (actually, 65% de-rate), or keep the ambient at 30% lower if using a 50% de-rate.

But I guess it really boils down to what a manufacturer is willing to accept as far as risks vs rewards. It might be that Hitachi is saying that the added failures with a 50% de-rate but no DC choke are going to be on small cheap drives anyway, so they will simply absorb the cost risks to gain a little extra market share by replacing any drives that fail, knowing that the total number is likely low because most people don't run machines at full load anyway. For A-B and Yaskawa the volume of drives they put out is so much higher that their exposure to risk is higher as well.

 

The Hitachi are low cost drives too; no dc choke, but with large terminals (jumpered) to ADD one if wanted.

I would not bother with adding a DC choke tho; I think a much bigger bang for the buck would be adding a 3% or so series line reactor to the input AC side - get similar results as a DC choke but also widen out those hi peak hi Irms current spikes potentially more than the DC choke would - a lot of failures we see are diode input failures...