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Old 08-10-2019, 08:36 AM   #1
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New 3PH irrigation service using VFD that provides overload protection, do I still need a mag starter before the VFD?
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Old 08-10-2019, 10:18 AM   #2
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Originally Posted by pfactor2 View Post
New 3PH irrigation service using VFD that provides overload protection, do I still need a mag starter before the VFD?
99% of the time, only fuses or a breaker are installed in front of the drive.


I don't see why it would be any different for what you're doing with an irrigation pump.
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Old 08-10-2019, 01:25 PM   #3
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Gotcha, my thoughts as well, additionally, I’m drawing plans for review for permitting. Never used to this point a VFD, only Breaker or fuses, mag starter and whatever control is applicable.
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Old 08-10-2019, 09:21 PM   #4
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New 3PH irrigation service using VFD that provides overload protection, do I still need a mag starter before the VFD?
Majorty of the time it will not be needed for mag starter at all .,

Just a fuse or circuit breaker that it.
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Old 08-14-2019, 02:14 AM   #5
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In fact putting a mag starter ahead of a VFD is a BAD idea.



All VFDs have what is called a "pre-charge circuit", used to avoid having the instantaneous charging current of the DC bus capacitors in the VFD causing damage to themselves and other components. So inside of the VFD, the pre-charge circuit is a current limiting resistor in series withthe caps, but it has a relay or contactor that shorts across the resistor after about 1 second to avoid having it burn out. But that circuit is normally only used when the VFD is first energized and are designed for around 1,000 to 5,000 cycles. If you put a starter or contactor ahead of the drive and open the circuit every time you want to use it, that life span gets used up really fast, leading to premature failure of the drive.


There is no need for it, all UL listed VFDs since 2005 are required to have the OL protection built in as part of their UL listing. The only time to worry about it is if you use one of the cheap no-name Chinese drives sold on the internet for impossibly cheap prices. There is a reason they are so cheap...
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Old 08-14-2019, 01:23 PM   #6
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In fact putting a mag starter ahead of a VFD is a BAD idea.



All VFDs have what is called a "pre-charge circuit", used to avoid having the instantaneous charging current of the DC bus capacitors in the VFD causing damage to themselves and other components. So inside of the VFD, the pre-charge circuit is a current limiting resistor in series withthe caps, but it has a relay or contactor that shorts across the resistor after about 1 second to avoid having it burn out. But that circuit is normally only used when the VFD is first energized and are designed for around 1,000 to 5,000 cycles. If you put a starter or contactor ahead of the drive and open the circuit every time you want to use it, that life span gets used up really fast, leading to premature failure of the drive.


There is no need for it, all UL listed VFDs since 2005 are required to have the OL protection built in as part of their UL listing. The only time to worry about it is if you use one of the cheap no-name Chinese drives sold on the internet for impossibly cheap prices. There is a reason they are so cheap...

That’s almost becoming a joke. Ever heard of TMEIC? It started as a joint venture with GE and Toshiba. They also make VFDs for Schneider and Mitsubishi that I know of. Also LSIS which is the industrial part of LG (Lucky Goldstar) private brands theirs as Benshaw, Franklin, and others. Not Chinese of course but South Korean! They’re all mass produced on the same production lines so cheap that Chinese manufacturing doesn’t even make sense. That’s just the assemblers.

Drill down to the chip level and look at Semikron on their web site. Most drives now are MPMs or IPMs. The only difference in brands is the plastic color, the software (to some degree...), and the label on the front. The big names stopped doing their own design and manufacturing. It’s a commodity product.


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Old 08-15-2019, 09:35 AM   #7
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on some machines i see mag-starter before vfd, but they are there only for e-stop circuit when the vfd don't have a e-stop function built-in (a lot of small vfd don't have it). they should not be used for frequent start-stop
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Old 08-15-2019, 11:30 PM   #8
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Well you have some stuff mixed up. TMEIC has no connection to GE, never did. There was a brief Joint Venture of Toshiba and GE announced in around 2000 to develop and market large drives, but it never got off the ground because GE decided to buy Converteam instead. So Toshiba took that momentum and instead formed a JV with Mitsubishi Electric in 2003, calling it Toshiba Mitsubishi Electric Industrial (systems) Corp. or T.M.E.I.C. The JV was formed for the specific purpose of developing LARGE LV and MV drives, larger than Tosh or Mitsi made in their standard product lines, then expanded into solar inverters for utility level stuff, motors, large DC drives etc. They (TMEIC) do NOT make small LV drives, i.e. nothing under 500HP.

The connection to Toshiba and Schneider is that they formed a DIFFERENT JV called Schneider Toshiba Inverter SAS, a holding company (60% Schneider, 40% Toshiba) that owns Schneider Toshiba Drives in Europe, Toshiba Schneider Drives in japan, ST Drives America in Houston and a few other smaller plants around the world. All of the plants make products that are marketed by both Schneider and Toshiba, with only a few minor cosmetic differences.

There is no connection to Mitsubishi in the small drive arena, and there is no connection to Schneider in the large drives arena, there is no connection to GE at all (and GE no longer exists except as a brand name for ABB). GE was brand labeling LV drives from Fuji, then abandoned that deal for Danfoss for a couple of years, but now that ABB owns the GE name, that has one foot in the grave.

The cheap junk Chinese stuff I am referring to is stuff you can buy on Fleabay or Amazon with no name on it, many of which are made by Huanyang (aka "HY/Verter, or sometimes just HY) or any number of made up names. Absolute garbage; I've taken some apart and the solder traces on the PCBs are flaking off right out of the box, components are grossly undersized, no UL listing, terminals are not suitable for US installations, the list goes on and on, including outright lies about capacity; for example saying on the Fleabay ad that they have a single phase input 5HP drive, then when it arrives it says it is only good for 2HP with single phase, 5 HP with 3 phase.

But the Fleabay / Amazon sellers move a LOT of them because the prices are impossibly low, as in >$100 for a 2HP drive sometimes. When the drives fail, if the Fleabay sellers have not sold out their stock, they might replace them. But once the inventory is gone they disappear, then resurface with a new name and new inventory, denying any connection to the previous sellers. It's all a big scam to move high volumes of absolute garbage onto the unwary who are desperate to have VFDs but want to avoid spending money on them.
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Old 08-17-2019, 12:54 PM   #9
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on some machines i see mag-starter before vfd, but they are there only for e-stop circuit when the vfd don't have a e-stop function built-in (a lot of small vfd don't have it). they should not be used for frequent start-stop
E stop can just be a pushbutton or break glass in series with the command. Just make sure hand or fire overrides aren’t past it in the circuit
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Old 08-19-2019, 10:52 AM   #10
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E stop can just be a pushbutton or break glass in series with the command. Just make sure hand or fire overrides aren’t past it in the circuit
this is ok if the vfd has a e-stop function built-in (basic vfd don't have this function), if not you need a way to remove power from vfd (just having a e-stop in series with stop button is not ok
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Old 08-19-2019, 11:16 AM   #11
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this is ok if the vfd has a e-stop function built-in (basic vfd don't have this function), if not you need a way to remove power from vfd (just having a e-stop in series with stop button is not ok


Have done many e stops in a system that way. Fire alarm shutdown is also done via the control ckt same way. Smaller VFD’s sometimes give you internal points for stops and overrides but larger systems with BMS, purge, e stop etc do the stops and overrides externally via the control ckt


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Old 08-19-2019, 10:45 PM   #12
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Don’t get excited about E-Stops.

First let’s mention SIL. Other standards are similar. SIL stands for Safety Integrity Level. It means that in an emergency situation like where an E-Stop would be used, a SIL 1 system might fail 10% of the time. SIL 2 is 1% failure. SIL 3 is 0.1%.

Standard controls are rated SIL 1. SIL 2 is supposed to require redundant inputs and no single points of failure throughout but a lot of equipment can hit SIL 2 without redundancy. SIL 3 gets pretty crazy with double or triple redundancy.

There are two kinds of “safety” interlocks on VFDs. One type is just a digital stop type input. It can be “hard wired” and older ones almost always were, or purely software. From a safety system point of view all the hard wired input does is prevent programming errors. Practically wiring it in series with a run input or a stop input is exactly the same thing. This is essentially SIL 1. If there are redundant inputs and some other things it can reach SIL 2 Since it is pure software they can also do fancy things like “safe slow” or a powered stop.

Drives with a “safe stop” run the IGBT gates for instance through a relay which can block firing from the main board. This is a second independent input so it can theoretically make it a SIL 2 as well,

Various safety relay schemes can have redundancy (no single points of failure) and an E-Stop can be used with dual NC and NO inputs to make the BUTTON SIL 2.

BUT all safety standards only consider operators have an error rate of 10% and ONLY if they aren’t panicked, stressed out, in a hurry, etc. Otherwise tons of military studies have shown human error rates go up to about 40%. So under the best of circumstances the human button pusher is only SIL 1 but in the real world not even that good. So that’s the limit on the system. It doesn’t matter how reliable the control system is because operator performance limits the system. So anything past SIL 1 performance on an E-Stop is impossible to achieve. I’ve done tons of accident investigations. It is a rare day that an operator doesn’t flee or freeze. There was a case at a chemical plant I worked at about 7 years ago where two operators argued with each other over the radio on who had authority to hit the E-Stop while an entire rail car of anhydrous ammonia dumped from a blown line. The cloud went down wind and sent 8 rail car mechanics to the hospital before it dissipated over a river. There were tons of “findings” but the obvious one is that their super reliable dual redundant E-Stop buttons failed to work when the operators spent the whole time freaking out. The system was redesigned with a pressure switch system to eliminate operator error and the rail car mechanics next door were issued emergency equipment and training.

So nothing special is needed on an E-Stop. Any input scheme will work. I normally wire it up though on a separate enable/interlock input simply so the E-Stop wiring is separate and clear. It can be in series with the normal stop because that’s all it is.

SIL 2 or more makes sense with automatic machine safety systems like area scanners, light curtains, gates, and other types of true safety systems.



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