Siemens micromaster 420

[appletree]

Hi All
I don’t know if anyone can help/comment, i have just got a new old stock Siemens micromaster 420 single to three phase VFD, it did not come with the CD manual, however the manual is on the Web.
I  do not know how old the drive is, its modern but might be 7 or 8 years old.
Whilst looking through the manual i came across this section in 2.1of the link below. (unable to copy from PDF).

http://docs-europe.electrocomponents.com/webdocs/0391/0900766b80391560.pdf

Basically it talks about supplying the unit with a reduced supply voltage (Variac) and progressively increasing over a day.

I have a lot of experience of mitsubishi VFD’s and this idea is a bit new to me. I have a variac so could do it, just wonder what some of the clever electronics would make of low voltage e.g. 25% and rising.

Comments please Phil 

[philf]

Hi Phil,

I think this is fairly normal practice for electronics with big electrolytic capacitors to avoid a big bang and horrible fumes when you power up after years of sitting idle.

I was advised to do this with a big ABB inverter which I converted from 415v to 230v single phase operation. It had stood idle for probably more than 10 years. When the input approached the operating voltage of the inverter the display came on - maybe displaying under-voltage to start with.

The fact that they advise you carry out the procedure would give me confidence that no harm can come to the electronics.

Cheers.

Phil.

[John Rudd]

Phil,
Hopefully my comments will help.....

Basically what they are saying is that because your unit has been sat on some shelf for a prolonged period, the dc bus capacitors will need reforming.....the process involves applying a low-ish voltage to the unit for a period to aid the reforming of the electrolyte in the caps....it seems its a staged process they recommend..

A capacitor stored for a long period will lose capacity, by reforming, the capacity can be recovered...generally...hopefully the capacitors havent dried out and are recoverable, otherwise the only other course of action is to replace them with new ones....

[John Rudd]

Hi Phil,

I think this is fairly normal practice for electronics with big electrolytic capacitors to avoid a big bang and horrible fumes when you power up after years of sitting idle.


Phil.

An uncharged capacitor of largish capacity presents a short circuit when a voltage is applied to it....depending on the voltage, the current can be quite high sufficient to blow the bridge rectifier and/or up stream fuses....if the capacitor isnt reformed, then it wont charge up....hence the big bang and release of magic smoke ( and potentially other smelly substances.... )

[awemawson]

I understand that the mechanism is that the thin insulating anodised layer that is formed during manufacture, can dissolve back into the electrolyte unless there is a voltage potential applied occasionally in the right direction to reform it.

Anyone remember the 'wet electrolytics' that you could actually hear the electrolyte sloshing about inside? The can was the cathode, and the anode was an extrusion with loads of fins to increase surface area. Now they DID make a mess when they popped - AMHIK 

[seadog]

I remember a large paper electrolytic going bang one day, 600v rail for a transmitter. It filled the workshop with smoke and the smell hung around for days. Open frame too since I didn't have a case to fit it into. It certainly gave my heart a good work-out   
The can left left a nice mark on the ceiling too.

But I digress.
I believe the correct way to reform capacitors is to apply the full rated voltage but to limit current via a series resistor. In a perfect world you'd have a variable PSU with current limiting so that current could be increased incrementally.

[appletree]

Thanks for all the helpful replies, what you all have said follows what I was thinking, I was purposely vague as to entice considered answers. Before i retired I was an instrumentation technician, so had more than half an idea. Just didn’t like partial powering up of the clever electronics, but as philf has said its their procedure so should be fine. Will let you know how i get on will do it outside in case we end up "tuning for maximum smoke” if it ever stops raining.

Thanks again Phil

[Bluechip]

If anyone's interested I designed and built a cap. reformer some years ago.

Does most working voltages from 16V to 100V, current limited @ 10 mA.

If anyone wants I'll rake out the schematic. I think I still have it somewhere.

Dave

[awemawson]

When I did the ones on my Chipturn CNC lathe a few years back (as it had stood idle for 3 years before I got it) I just rigged up a lab supply, set to the rail voltage of the capacitors, but with the current limit wound down to a few milliamps. That way you could observe the voltage slowly increasing, and if it plateaued before it got to the rail value you knew there was an issue with breakdown.

[appletree]

Thanks for the further comments,
Dave I imagine your circuit will be for capacitors sat on the bench as opposed to in circuit? I don’t intend removing mine.
The manual says to start at 25% supply for 1 hr so I shall start lower than that maybe 5 or 10 volts using my variac.

Does that seem like a plan?

Phil

[John Rudd]

Phil,
Using your variac to modify the voltage is good, you can limit the current by adding a 60 watt light bulb in series with the supply to the inverter.......

[Bluechip]

Phil:

Yes, it is for bench use.

And I can't seem to find the cct. diag.  Dozy ole pillock has lost ALL the schematics and PCB layouts for all the stuff I've made ... 

I think they probably AWOL went when I changed my old PC to Linux 'cos that does not support Express PCB which I use. ( Nor MikroC for that matter. )

Linux is better than W7 or W10 for t'net IMO but a lot of other stuff  won't run on it. Bugger ....

I may have copies on a USB stick somewhere 

When I was in the RAF the stock of spare electrolytics were reformed at intervals, at least the big ones, 'cos the date was on the packaging when it was done.

Wot John sez ... 

Dave

[appletree]

Is that a fluorescent or LED 60w bulb John LOL yea that would be easy to do cheers.

Don’t worry on my behalf, hope you find your stuff though, my dogs more use than w7 or w10, in total frustration i moved over to apple, much better but not perfect.

Phil 

[Bluechip]

If the CFL or LED bulb don't work try a daffodil ... 

I'm right in the S H 1 etc. with PC's.

This one is a new one with W7 & W10 loaded ... I still use W7 though. Just can't get on with W10 .. uSoft must be going for a Nobel Prize for convoluted crap ...  The old one ( on W7 ) kept invoking DSKCHK and complaining bitterly about the hard drive but a surface analysis sez it's fine ..  .. so I shovelled Linux Mint on it and it works just fine. And no ads.   
My Toshiba Satellite laptop now has W7 & Linux on it but I'm used to a 24" screen and I can't see the l/top screen now ... poor old scrote ... 

D.

[John Rudd]

Phil,
A cfl or fluorescent is no good.....neither is led......
A good old fashioned incandescent lightbulb is what you need....even one of the halogen type will suffice.....
You are making use of the cold dc resistance of the bulb to limit the current....ok that changes as the filament warms up but its sufficient to stop things going bang.....oh and one more thing....change any fuses to 3 amp ones......less likely to go bang badly....
The number of electric drills that have cime my way with 13 amp fuses un the plug is unbelievable...!

[awemawson]

For a depolarised electrolytic I'm not sure (*) that an incandescent lamp will reduce the current sufficiently to prevent damage - a depolarised electrolytic will present a very low resistance and you want a controlled current of a few milliamps - just maybe a few tens of milliamps. A cold filament of an incandescent lamp also presents a very low resistance until it heats up where upon the resistance increases. The damage to the capacitor is done well before that happens 





(* read that as I'm certain that it won't !)

[appletree]

Hi John the comment about florescent and LED was for a laugh , obviously no good, might try a couple of daffodils in series (Bluechip) as they are plentiful just now failing that tulips will be along soon. I have some of those nice gold anodised power resistors somewhere 100 ohms or so, if only I can remember where.

Phil 

[John Rudd]

Andrew,
You are correct....( as usual.... ).....
I would normally use said bulb if I were testing a power supply to limit the current and prevent blowing it up if there was a fault....a common use in servicing brown goods....where a variac isnt available...I've also made good use when repairing inverters, limiting the power available and preventing the things from destroying themselves...

In this instance where a smaller current is needed, then my approach is inappropriate....I apologise for giving misleading information....

[Bluechip]

OK had a stab at re-creating the schematic. It's screwed together from essentially 3 bits:

[1] The full-wave doubler giving some 136V DC .and 68V DC

[2] A string of zeners to set the o/p voltage of the pass transistor.

[3] A 10mA current limiter, 0-20mA meter and a switch to discharge the cap.

NB 

In accordance with my lifelong habit of not getting anything error free, the transistors are MJE 13005, not MJ 13005.

The 2 resistors with *** may need small changes as the load regulation of the transformer may give a higher o/p voltage.

If anyone builds it,

[1] Do the doubler first and check the volts are fairly near, although they won't be precisely the same.

[2] Make the Zener circuit, then set VR1 for 20V on the 16V range. [ you'll see why in a bit ]. Measure from Q1 emitter to 0V. Check the other voltages, make sure you ain't got a cranky Zener. They should all read about 4V high.

[3] Make the rest. Put a short circuit instead of the cap. and set VR2 to give 10mA on the meter.

[4] With a 10R resistor instead of cap. tweak VR1 again to read 16V from the -ve to +ve test terminals on the 16V range. Then check the other ranges.

The -ve test terminal actually sits at some +4V because of the Q2 limiter action, hence the 4 extra volts in [2].

Poke a GOOD biggish cap. in and set up. [ Not in that order ] 

The meter should whip up to 10mA and stay there. When the cap's charged up it will swiftly drop to zero.

As this contraption is sort-of linear you can make a fair stab at finding out what a cap. really is.

CV = It ... 

Capacitance x Volts = Amps. x Seconds

Or:

C = ( I x t ) / V

So:

Suppose we have   25V, Amps. = 0.01, time to when the needle starts to drop,  6 seconds.

We have (6 x 0.01) / 25  = about 2400uF.

Have done this with caps. marked 56,000 uF, 25V and then with my Peak capacitance meter and it's pretty accurate.

D.

EDIT S1 is a 1P 12W rotary switch, stopped off @ posn. 8 ..

S2 on mine is a  ON [ON] 2P 2W  just flick it to discharge the cap.    DVM should drop to 0V, then cycle cap. again if it's not been used for a long time. The 'slow' drop from 10ma to 0 gets sharper as cap. improves.

[appletree]

Thanks for posting the circuit Dave, I shan't be using it this time, but I am sure someone will find it useful.

Phil

[appletree]

Gents (and Ladies)
I have some 1k ohm wire wound pots if I put a couple in series to give 2k and apply 20vac I will have a maximum current of 10ma (disregarding anything in the VFD).
Leave it like that for an hour or 2, ramp up the voltage to 60vac (siemens starting voltage) which will give 30ma, then what?
1 Carry on increasing voltage in 60vac increments with resistance in place?
2 Remove the resistance start at 20vac ramp up to 60vac then follow Siemens recommendations (60v increments)?
3 Do something different?

Regards Phil

[John Rudd]

10ma at 20v is one thing in terms of power, (200mW..) but as you wind up the volts, the watts are going to rise too, maybe exceeding the power rating of your pot?

I'd be inclined to follow the ramblings of Mr Siemens......

BTW, have you got an isolation transformer?.....( that would be the way I'd do it....rather than live mains direct from a variac.... )

[appletree]

Hi John
I think I will start as suggested, then option 2 above, still much gentler than Siemens recommendations, most people would not even read the manual, just bang it on line and maybe watch the smoke rings. The pots will be used as a fixed 2k resistance, they are just something of reasonable resistance that can dissipate some power.

Phil

[appletree]

A result, I supplied the VFD at 10vac for an hour then ramped up to 60vac over another hour, then followed the manufacturers instructions, basically 2 hours at each of 60,120,180 and 240vac.
The VFD display lit up at around 140v saying low supply voltage, had difficulty programming could JOG and reverse JOG, you could run and the motor “locked” but the frequency would not increase, got there in the end.
The next decision the VFD is capable of 1.5 kw, I want the use it to drive my Raglan 5 inch which is currently fitted with a 1 HP single phase motor.
The motors are both older frame sizes which will fit straight on with the correct shaft size.

1 Unused 550w 2800rpm fully sealed fan cooled

2 little used 750w 1425rpm open frame internal fan

I have a 375w 3 phase 1425 motor fitted to my little John Mk2 which is a bit underpowered (basically the same lathe), I fancy the power of the 750w but the sealed aspect of the 550w motor, additionally there is the RPM issue.

Phil