# Differences between old and new VFD's ?



## backstay (Feb 3, 2011)

Upgrades to capacitors and firmware. Caps have always been the weak link. Firmware is getting wild, a 1500 parameters on the last one I worked on. So the newer ones can be used on a wider variety of installations.


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## SWDweller (Dec 9, 2020)

I found an article that said the S700 was being released in England. 
Comparing a known to an unknown is impossible. How old are you going to go?
All you can do is look at the specs of the two your choosing between and see if the less expensive model is worth the risk. I never cared for the concept of changing drives as often as the mfgs do. Keep in mind with older equipment is production going to stop soon. 
Most of these do not have user servicable parts, but if the process is critical you might want to buy two and keep one on the shelf.


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## paulengr (Oct 8, 2017)

Aside from that VFDs pre 1990s were terrible. The smaller ones used MOSFETs which is still true of micro drives today. We could speak of MG sets too as “VFDs” but that’s stretching things. The early ones used actual timer circuits and were true scalar drives…putouts were controlled by adjusting timing on VCO or similar circuits…basically analog drives in the truest sense of the word. For higher power they used forced commutation SCRs then GTOs. So in this design triggering the SCR is easy, just slow. But to turn it off a second SCR was fired to short out the first one or a big inductor was used to reverse current by resonance. Typically components blew up and had to be replaced every couple years.

When IGBTs came along, VFDs became reliable in the late 80s. As an example I found a Westinghouse manual. 11 pages, half size. One page of warnings and a couple “this page left blank”. The entire wiring diagram was 1 page. The settings (pots) were roughly 2 pages.

We didn’t get full vector control and later space vector modulation until computer technology caught up in the 1990s. This is typical of VFDs. We get a major evolution roughly every 10 years. These days full vector or sensor less is “free”. Back then it was a huge upgrade and price.

The next jump was from discrete to IPMs and similar engineered modules and thermal designs and faster IGBTs.

Got smaller again around 2010. USB started showing up. UL came on the scene greatly improving short circuit reliability.

Smaller again more recently and faster still. A lot more application profiles,


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## micromind (Aug 11, 2007)

With the older ones, if just about anything went wrong, it'd blow the drive. The newer ones certainly can be wrecked but it's much harder. 

Also, some of the newer ones are much more difficult to program. A lot of them can be programmed without a book but some have parameter numbers rather than descriptions and the choices are also numbers.


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## paulengr (Oct 8, 2017)

micromind said:


> With the older ones, if just about anything went wrong, it'd blow the drive. The newer ones certainly can be wrecked but it's much harder.
> 
> Also, some of the newer ones are much more difficult to program. A lot of them can be programmed without a book but some have parameter numbers rather than descriptions and the choices are also numbers.


Do you mean newer or older? With the really old drives you sat with the manual, a calculator, and about a dozen pages. You had to calculate resistor sizes and dip switches. It was very “hands on”.

The AB Bulletin 1336s were their first “digital” drives, all numeric settings.

Newer drives especially micro drives often have parameter numbers only. Only the more “advanced” drives have text. On some you can often buy the text display as an option.


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## glen1971 (Oct 10, 2012)

paulengr said:


> The AB Bulletin 1336s were their first “digital” drives, all numeric settings.
> 
> Newer drives especially micro drives often have parameter numbers only. Only the more “advanced” drives have text. On some you can often buy the text display as an option.


We're still running a small handful of 1336's in the area I'm in. And a few older Toshiba's.


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## just the cowboy (Sep 4, 2013)

paulengr said:


> You had to calculate resistor sizes and dip switches. It was very “hands on”.
> The AB Bulletin 1336s were their first “digital” drives, all numeric settings.


I remember when they came out.
We used to have Volkmann Drives before that, like you said hands on no parameters just dip switch and resistors. For troubleshooting we would call MR. Volkmann himself.


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## francois3 (Oct 19, 2021)

Thank you all... I now can see quite more clear. But still have to learn on how to... if some of you have good links for beginners... I will appreciate. also if there is some good pdf to learn or ebooks... thanks.


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## CMP (Oct 30, 2019)

Download some manuals for drives that are popular in your area. Study them as long as it takes for you to understand the meaning contained within. Get yourself a used one and a motor. There is nothing like doing it for real, reading can only take you so far. 

Fill out your profile and location for better assistance.


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## CraziFuzzy (Jul 10, 2019)

Just in the same model of drive, there can be huge differences between 'old' and 'new'. Old drives were installed and worked for decades, new drives are installed, then replaced every three years...


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## Creatine (Nov 1, 2021)

One manufacturer is using smaller IGBT in their newer drives, at least the ones we use. It's caused issues in some of our installations, which has been a massive headache for me. I'm sure they're sacrificing reliability / durability for profits. IIRC you can get drives with the larger IGBT but you have to pay for the heavier duty drives. I guess it's whatever, you don't get braking resistors for free either, but manufacturers should be required to make equipment that's going to last if it's used as the MFG intended.

As for how older drives can differ from newer ones in my experience newer drives have a lot more options and are a lot more sensitive to the settings. If the drive isn't set up correctly, as in you miss a couple of options you didn't realize were very important, you can see a lot of issues arise while its in operation. New drives don't seem to be bulletproof, while older drives I dealt with in 2007 had already been in operation for a decade and are still going strong today. Lots of shaft voltage issues too which I didn't see as often forever ago... Then again, back in the day, I wasn't aware of motor shaft voltage issues and proper grounding stuff.


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## paulengr (Oct 8, 2017)

CraziFuzzy said:


> Just in the same model of drive, there can be huge differences between 'old' and 'new'. Old drives were installed and worked for decades, new drives are installed, then replaced every three years...


This should not be happening. Virtually all drives (ignoring Eatons bogus claims) should be good for 100,000 hours run time or about 10-15 years. This is partly a planned obsolescence issue.

You can switch to sintered IGBT modules and metal film caps and this increases lifespan to 200,000+ hours but that’s for very high end applications like power plant systems and trains where it’s cost effective.

What often happens that I see a lot is you have to figure in if the drive is 95% efficient, where does the other 5% go? I constantly see panels loaded with drives with no thought whatsoever about cooling. Every 10 degrees rise in temperature cuts drive life in half. The other problem is it’s not bottled up in a box but it gets filled with dust and fibers. Finally as mentioned a lot of them have incredibly bad short circuit ratings. Like 5 kA. That sounds like a lot but as a rough rule of thumb if the transformer kVA is more than 10 times the VFD kVA it probably won’t survive a motor failure. This is typical of micro drives especially. As mentioned they’re getting better. This is where adding a line reactor or better fuses (RK1 or J) makes a dramatic difference over say a typical thermal magnetic breaker or RK5 fuses, even without exotic semiconductor fuses.

A final issue is that drives these days are application specific and marketed with some goofy numbers. So if you buy say a “10 HP” pump/fan drive either intentionally or because it has the lowest price it will work fine on a standard inertia centrifugal pump or fan application. As soon as you get into any other application or get into a high inertia web site, it is under rated. Plus if you need braking without resistors it can’t regen so braking will be very rough on it. So with today’s drives you need to order the right model for the application. But this isn’t clearly stated in most catalogs. So if you put that 10 HP fan drive on a 10 HP conveyor that starts and stops frequently, it will be short lived as an example. A larger or more expensive drive or some optional parts may be required.


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## Creatine (Nov 1, 2021)

paulengr said:


> A final issue is that drives these days are application specific and marketed with some goofy numbers. So if you buy say a “10 HP” pump/fan drive either intentionally or because it has the lowest price it will work fine on a standard inertia centrifugal pump or fan application. As soon as you get into any other application or get into a high inertia web site, it is under rated. Plus if you need braking without resistors it can’t regen so braking will be very rough on it. So with today’s drives you need to order the right model for the application. But this isn’t clearly stated in most catalogs. So if you put that 10 HP fan drive on a 10 HP conveyor that starts and stops frequently, it will be short lived as an example. A larger or more expensive drive or some optional parts may be required.


Where can I read more about modern drives? Specifically drive sizing and proper installation practices? My boss is old school so caveats of newer drives are throwing him off and I'd just like to be educated on the more modern stuff. I'm asking the supply house we buy drives from (2HP - 800HP) so I can better verify how they're installed and catch any issues before they're started up. 

I'm seeing some obvious stuff, like the motor being wired up to the inputs on the drive by local electricians doing the install (I'm based in NC but equipment goes out nationwide), and some not so obvious stuff like a deep setting being missed or braking being used when they should just use a freewheel stop, or whatever.


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## CraziFuzzy (Jul 10, 2019)

paulengr said:


> This should not be happening. Virtually all drives (ignoring Eatons bogus claims) should be good for 100,000 hours run time or about 10-15 years. This is partly a planned obsolescence issue.
> 
> You can switch to sintered IGBT modules and metal film caps and this increases lifespan to 200,000+ hours but that’s for very high end applications like power plant systems and trains where it’s cost effective.
> 
> ...


Obviously, this shouldn't be happening. Doesn't mean it doesn't happen. Primarily, it's the same issue of poor quality electronic components (caps, mostly) that affect the entire power electronics industry for the last decade or so. Most of the failures we are seeing ate in the low voltage power supplies, not the meetings drive components. As a more specific example, ABB had made the ACH-550 series of drives for a very long time, but there is a very significant difference in the robustness of one made 15 years ago vs. one made 5 years ago - with the exact same model number.


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## JRaef (Mar 23, 2009)

> ...if I buy and old VFD for half new price such as Mitsubishi S500 , what do I loose ? or better choice a new model ?


To directly address this part of your question, often what you give up by buying an older version are features and bug fixes that customers had asked for. Responsible drive mfrs that care about their customers solicit feedback from them about what could be fixed, improved or added. Subsequent iterations of drives are generally the result of this kind of feedback (plus market research and component changes). So by buying an older model, you are missing out on those improvements or bug fixes.

I don't know the specific Mitsi model series in question, but if you go TOO far back, you will get into drives that were not capable of "Sensorless Vector Control", which was a quantum leap in improvement of the drive's capability to provide consistent torque at a wide range of speeds. Some older drive lines had Flux Vector Control, but required an encoder feedback. The advance made with SVC was to eliminate the need for that encoder, which made it MUCH more widely available for applications. SVC is not "as good" as FVC, but it's fine for 99% of common applications.

But most importantly in my opinion, if looking at buying older drives, you expose yourself to a failure risk that many people are unaware of. Opinions vary on the time frame, but at BEST, if a drive has been sitting on a shelf without being powered for more than 2 years, the capacitors must be "reformed" in a procedure that is best done with equipment that most people do not have access to. If you even CONNECT the drive to full line power without doing so, you can blow out your capacitors and your cheaper drive becomes a door stop. Reforming requires applying a low voltage to the capacitors and SLOWLY increasing it in small increments over the course of hours. There are many tricks and shortcuts that people take, but they have risks associated with them that may end up damaging the capacitors and thus the drive. So be VERY careful about what you buy when buying used.


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