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Member postings for Martin of Wick

Here is a list of all the postings Martin of Wick has made in our forums. Click on a thread name to jump to the thread.

Thread: DIY induction motor rewind
23/03/2020 23:13:29

DC3,

thanks for that, hadn't come across the name before so very useful.

OM and G8R Hmm... hardly seems worth the effort as you say. I suppose I could remove the flange.

Anyway, I think I will price up how much the materials for a rewind are and see if it outweighs my thirst for knowledge and satisfaction.

Thanks to those that responded.

Thread: vfd question
23/03/2020 23:06:20

Sounds good John, Check the back of the VFD too. There is a thermal trip parameter. I think the default may be 85c, you may want to reduce that by 15 to 20c to protect the unit if it runs hot (there is also the possibility of fitting a fan).

The display current and voltage could be anywhere in the VFD, on the DC bus for example, so would treat them as indicative readings but always best to check the equipment.

Just all part of the fun from those whacky xsy guys!

Thread: DIY induction motor rewind
23/03/2020 18:30:28

I have a small 0.375 kW 3 phase induction motor where one of the coils is in continuity with the case, not obvious where, probably deep in one of the coils.

Clearly not worth paying for a commercial rewind (circa £300) but thought could try a rewind myself.

so has anyone attempted this? was it successful?

Does anyone have a ballpark figure for the weight of copper in the windings? only asking as the enamelled wire is about £20 per kilo and was hoping that would be enough, any more ad it probably isn't worth it.

Are there any UK sources for the material for coil shrouds and separators? I guess rustins shellac will be ok to stick it all together.

Thanks for anyone willing to share advice.

Thread: vfd question
23/03/2020 10:05:43

mgn

The XSY's that have passed through my hands all look like that (but in varying colours and plus or minus a fan or pop out keypad).

22/03/2020 21:18:30

John,

non conforming display nothing to do with shielding. The best guide is to check motor temperature. If really drawing 5A on 750W motor when you put your hand on it will get 'aargh S***' hot very quickly.

I assume that the display current is measured on the output phase, but I don't know for sure.

I have seen on various setups higher than expected current on the display. For example, I am setting up an 8 pole 370W motor at the moment -

plate indicates 1.3A at 400V 50Hz. display shows 1.9-2.1 A no load at 410v from a 220v in 380v out dual stage VFD (spindle not connected). For an 8 pole fractional motor I would expect about 1 A current draw no load. If I run the motor for an hour or so, it gets warm but not hot - stabilises at about 45-55c (without the fan).

I could be very wrong, but that suggests to me the motor is not really drawing 2A and similar logic may possibly apply in your case but you have to proceed with care.

In other applications I had noticed a similar discrepancy at the pad display relative to plate, but it was not as large as in this instance. I have been awaiting the arrival of a replacement clamp on meter to check phase currents at the motor for comparison, but it has been a long time coming. If I get it any time soon I will update.

22/03/2020 19:30:32

John,

VR =potentiometer or the little knob used to increase or decrease the motor frequency. on some setups if I turned it too quickly it could cause a trip if the overcurrent was set close to run current.

Those indicated currents are a fair bit higher than I would expect for no load and load, but as noted in my previous post the display V I are not always completely accurate so treat as suspect initially (at indicated 5 A power draw would be just over 1kW if it were true) .

Just keep a watch on your motor and check it isn't getting unacceptably hot when the lathe is working. some people use one of those cheap digital temperature displays to check initially.

Edited By Martin of Wick on 22/03/2020 19:41:24

22/03/2020 17:56:04

Eeeek!!!! is it a new virus?

John, good news - reducing the start ramp rate to limit the surge is fine for interim, but for my peace of mind are you really using a 1kW motor that would actually account for approx. 5A current draw? Should really try to get to the right over current settings for your situation rather than skirt around the issue.

Need to also check that using the VR rapidly doesn't cause a similar effect.

22/03/2020 17:26:02

mgn,

the little screw on cover protects all the low voltage control terminals.

the high voltage connection wire go directly into the oval slots on the base below (one terminal per slot for avoidance of doubt). However, this appears to be a common feature of most VFDs.

Clearly you don't want to 'hang one on the wall' in that set up condition!

should have said that the screws to tighten the terminals for the HV side are also beneath the cover but recessed below the case  (and hard to see too!)

Edited By Martin of Wick on 22/03/2020 17:32:12

Edited By Martin of Wick on 22/03/2020 17:37:54

22/03/2020 16:55:47

Ian, you are absolutely correct.

I would go further, these low cost devices are cut down versions of 'proper' VFDs, so hard to know what other compromises have been made. However, I am not aware that they are inherently less safe or inherently less reliable than any other VFD - just more awkward to use.

In short, you don't get what you don't pay for! In addition these devices...

have very limited functionality bar the basics,

have very poor guidance manual or safety advice - barely sufficient to get it going and no parameter explanation

have no back up or warranty

have some rather basic operational oversights

users are entirely on their own and absolutely need to consider all risks.

If these issues are significant to anyone contemplating VFD use or you are rightly wary of electrical installations, then I would say make your purchase from one of the established UK distributors. It will cost a bit more, but you will get good advice on purchase installation and set up assistance.

ps I don't have shares in the XSY company!  but being at the bottom of the food chain have found them to be affordable and useful  and not had any significant issue with one yet.

Edited By Martin of Wick on 22/03/2020 17:01:58

22/03/2020 15:52:12

Indeed, in that case we are agreed...

...VFDs in general are relatively high risk devices that need to be installed and used with considerable care.

A fact that no one would dispute...

Thread: Working mild to hard steel
22/03/2020 15:18:30

Ian

plenty of choice available within your budget in the generic Chinese mini lathe market - various suppliers advertise on this site. Bear in mind you will have to have some budget for tooling as well - at least 20-30% of lathe cost as a start.

You won't get much of a mill for your quoted budget, I have had some of those at the small end SX1 or SX 2 class of machine and found they are just about OK with non ferrous and a pita for anything harder. You may need to budget between 1 and 2 times your lathe budget for a new machine compatible with the capacity of a mini lathe, the lower end being OK if you are sticking to small stuff. It seems manual mills just need to be that much bigger and stiffer to do decent work otherwise you are in for a lot of handwheel twirling.

Second hand is always an option. You need to know what you are looking for. It can also be a bit of a long and drawn out process and in the end the savings rarely turn out to be that significant for the smaller stuff. Avoid old British iron in the smaller sizes, unless it is immaculate with all tooling etc. or unless you enjoy the tedious prospect of lengthy refurbishments.

Edited By Martin of Wick on 22/03/2020 15:26:01

Thread: vfd question
22/03/2020 13:04:59

NDY

Nobody here is recommending using an unsafe product or creating an unsafe installations.

I think if you look at most commonly available VFDs, you will see in general they do not have cable anchoring or secondary covers. Does this mean you consider all such VFDs 'unsafe' and not fit for purpose? (better tell inverter supermarkets to withdraw their full range in that case )

Or do you really mean that VFDs in general are relatively high risk devices that need to be installed and used with considerable care. A fact that no one would dispute I would think.

22/03/2020 11:42:39

Well, Robert is right in his way. you have to be aware of all the various risks, assess them correctly and mitigate them in the appropriate manner.

But that is different from baldly stating that ' most' low cost VFD are substandard or inherently more unsafe than other similar products. If I saw a reliable body of factual evidence to support such statements, I would probably avoid using them.

Regarding the rating of Chinese equipment - I think it is just a cultural thing. British/European equipment is or used to be, rated conservatively and for continuous duty. It appears to me that the Chinese seem to rate their equipment at the maximum capacity. So if for example I need a PSU to deliver max 1000VA, I make dammed sure to get the one rated at 1500VA! It avoids disappointment.

22/03/2020 08:22:36

John,

can you tell us exactly what the power of the motor is / plated current rating etc. at all voltages etc, or provide a photo of the motor plate and inside of the motor connection box.

Are you using the supplied keypad or a pendant?

Do you have access to a clamp on meter to measure true motor current or at least a regular meter to check motor coils?

In addition, set out your stored parameter values P00 to P26 and P65 to P78

Then we might have a clue as to what parameters need modifying to solve your problem.

Don't implement factory reset at this stage - my experience with this type of inverter is you may well get additional complications depending on the exact type of inverter (they look the same but not always set up the same!).

Thread: Coronavirus
21/03/2020 19:36:47

excellent!

cant be any worse in that mode than it was when used on PCs!

21/03/2020 18:15:40

,,,Ady1

and after coronavirus - National Socialism

21/03/2020 18:12:40

hmmm...

Howard, where were you from super Mac's 'you've never had it so good...' to the heady days of 20% inflation, the humiliation by the IMF and 17% mortgage rates? The printing presses were rolling pretty much flat out in that period, but just made matters worse. The only difference was the most of the money was going to the population in general rather than to financial institutions and billionaires, and just like then QE is part of the problem and not the solution.

They never learn.

Thread: vfd question
21/03/2020 16:30:52
Posted by Robert Atkinson 2 on 21/03/2020 16:12:26:

I would note that regardless of being "Commercial" or not, most of these cheap far eastern VFDs do not meet accepted safety and quality standards. Additionally tthe internal components may be sub-standard or under-rated. This is why many sources (including at least one UK reseller) recommend buying a larger unit than should be needed.
Even quallity units need to be mounted in a proper enclosure and most also require a EMI filter on the mains unless te VFD specifically states it has one internally. A good filter can cost more than the VFD.

Robert G8RPI.

To be meaningful you would have to define who's safety standard and what quality requirements. If you are in the market for a £60 VFD you would be inclined to assume it was built down to a price in terms of component spec. and had limited functional software. If your 'standard's are high, then better units are always available.

My safety requirements are you don't get electrocuted while setting the parameters and as long as it runs more or less as expected for a few years, my quality requirement has been met. I will put up with all the other shortcomings.

No point ranting and raving about iniquities of Chinese hobby equipment, real or imagined. It is what it is. Ya pays yer money and takes yer choice.

21/03/2020 15:02:56

John,

Bear in mind that while a VFD is very useful, it is no substitute for speed reduction via belt ratios, gearbox etc.

I wouldn't recommend that you regularly use your VFD at above 60 Hz, as torque will decline significantly at frequencies above design - so ok to go 65 Hz for a short burst of small diameter work or polishing but not for an extended bout of turning, because just you cant be bothered to change the ratios and run the motor at closer to design frequency.

Similarly, if you run the VFD at 20 Hz output, remember effective power at the motor is 2/5 of design and at 15 Hz it is 1/4 (approx.). Induction motors are pretty robust, but extended high torque use at low powers should be minimised.

Just because you can, doesn't mean you should!

Don't know what spec your motor is, but assuming 1kW should show approx 4.5 to 5 A setting the trip to 7A is 40% higher than design and will warm your motor somewhat if you operate at that current, might be OK for the odd peak but not for general operation. I would set a good deep cut on the auto and observe the indicated current and draw your own conclusion.

Secondly, if it is a 1.5 kW inverter, what is 220x7 ? If those are true V I, you would be running your inverter quite hard. I always treat Chinese specs as being at maximum output prior to magic smoke release, not an indication of continuous duty.

 

Edited By Martin of Wick on 21/03/2020 15:04:24

Edited By Martin of Wick on 21/03/2020 15:27:43

21/03/2020 12:29:35

I suppose it depends on motor power?

As stated, the display current doesn't always reflect true motor current draw in my experience. If the OP has a clamp on meter, it is best to confirm real current. I have found that P67 and P73 to P75 seem to impact offset and span on the display pad - but I haven't been able to work out how to apply them, or whether they do more than impact the displayed V A, so have been inclined to leave at factory setting.

Even so, the VFD interlocks reflect what is shown on the key/display pad, so if the overcurrent trip is set at 6 amp, then when the display shows 6 amp, it will fault. I take from that if the real draw was say 2.5A at an indicated 5A then cutting out would occur at a true draw of just over 3A. Difficult to be sure, but have not had a problem with overheating motor so far....

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