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Member postings for Russ B

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

Thread: Help wanted, DC motor speed controller issue
28/01/2022 10:28:14
Posted by John Rudd on 27/01/2022 13:08:41:

The Chinese lookalike boards similar to the KBIC control boards are essentially copies using thru hole components, although some later derivatives use smd devices too.

The mains AC is used to drive a full wave bridge rectifier comprising 2 S*025L thyristors and similarly rated diodes.A third diode is connected directly across the output. The F+ and F- supply is generated using two low current diodes( typically around 1 amp).

The full wave bridge uses phase angle control with a zero crossing detector to generate the speed control.

A startup ramp is generated using a resistor and capacitor network that is adjustable to give a soft start, current overload sensing and motor load compensation is also featured on these boards.

The Seig speed controllers are similar but principally operate the same way.( are some subtle differences in how the 12v rail is provided).

Repairing these boards is not for the faint hearted.
Be also aware that the scr/diode devices that are heatsinked on the KB boards have isolated tabs, the Best controllers I’ve encountered are isolated using mica washer sets, the devices not having isolated tabs…Using the wrong type of device can result in failure of neighbouring parts.

Fake parts abound, beware where you buy replacements from

Edited By John Rudd on 27/01/2022 13:09:11

John,

I wrapped my head around the concept of the full wave bridge using SCR's to control the output, but I'm afraid the purpose of the diode across the output is beyond my understanding, when I think of a diode I think of a check valve (converting in to my more familiar mechanical/pneumatic engineering knowledge). Also these have 3 pins, I don't know if each one is a pair of diodes sharing a common annode/cathode or if one pin floats - I should know because I tested them and believed them to function, I have perhaps have misunderstood them but without reviewing the data sheet and what/how I tested them I can't say either way.

As for mica washers..... the board and wiring had been fettled and given that the armature was accidentally connected to the field terminal adjacent I would guess finer details like mica washers slipped the attention of whoever dissasembled it in the first place. That said, when I tested it, it was on a non conductive bench, out of the machine, the heat sink was attached, however where as the SCR's and Diodes connected dry, directly to the annodised aluminium, I slipped a 0.3mm thermal pad under them believing it would be useful?

I feel like I shouldn't be touching this at all but as it didn't work, I felt I had nothing to lose and when I identified a clearly faulty SCR I thought I'd cracked it! I hope I haven't done more harm that good!

28/01/2022 10:09:17
Posted by Les Jones 1 on 27/01/2022 13:00:32:

You have not answered the question of which connections measured 110 volts (Field connections or armature connections.)
You start by saying "This link" but you do not give any details for the link.
Two of the diodes and the two SCRs form a phase controlled bridge rectifier. This output will be to the armature and the average voltage output is controlled by how much delay there is between the zero crossing point of the AC waveform ant the point at which the SCRs are triggered.
The 3rd diode provides a half wave rectified of a constant voltage for the motor field winding.
As the motor only has two wires coming out of it you will need to dismantle it to bring out the field and armature connections separately.

Les.

Sorry Les,

110v was measured at the armature connections.

I don't think there is a field, its a brushed permenant magnet motor, all in good condition and running smoothly to my untrained eye.

The manaul is here Link I didn't do the link correctly last time.

27/01/2022 11:36:41
Posted by Les Jones 1 on 26/01/2022 14:42:53:

The controller should have two outputs to the motor. The one that goes to the field winding will be a fixed voltage. The one that connects to the brushes will be controlled by the speed potentiometer. Which connection did you get a constant reading of 110 volts ? I have not been able to find the schematic online for your speed controller But I do have a schematic of the KBIC 240D controller. If yours is a similar design it would explain why you get a reading of 110 volts rather than about 240. The 240D uses half wave rectification for the field supply so you will be reading the average voltage of half wave rectified 240 volts. I suggest that you measure the voltage to the armature and see if that is present and varies with the speed potentiometer setting. It would be helpful if you could provide a link to the information on your controller and any information on the motor.

Les.

This link is also referencing a KBIC, and later refers to two models, a BC2000 and a BC2200, and everything in it, seems to match almost exactly to the board in hand.

I have taken things like the rotary switch and NVR etc out of circuit although I have tested them all and they do work as they should so I'm focused on the board. There was also some sort of filter box or something, I recall trying with and without it, it made no difference before or after changing the S6025L thyristor

27/01/2022 11:31:04

Hi,

The motor just has two wires, the documentation I found online for the BC2000-TA explained to me what the F+ and F- terminals were for, and that is how I knew whoever connected the motor had done so by mistake.

When I measured 110v I had the board wired correctly (to the best of my knowledge and by the book) - I assumed this was because one of the thyristors was stuck closed circuit and passing half the rectified AC sine straight though (again, I'm not knowledgeble on this stuff, but at the time I think I recall seeing that one thyristor was connected to one of the diodes, and the other thyristors was connected to the other diode, so I assume they combined the two halves of the AC in varying amounts, and the 3rd diode I guess did something else, but, I don't know, I'm not really clued up on complex electronics like this, I can wire up basic machines and follow diagrams, that's about it!)

26/01/2022 13:34:43

I have an issue on a motor speed controller that I've been unable to solve (I seem to have created or uncovered a different issue!?)

This lathe has never run and the guy who gave me it had been tinkering with stuff, he perhaps knew even less than I do as I found one of the motor wires connected to field terminal by mistake, I'm not sure if this could have damaged something.

Any, there was a bank of 3 diodes and 2 thyristors, all but one thyristor seemed to function as it should so I went ahead an replace it with a like for like unit.

The machine was constantly outputting 110v DC seemingly regardless of pot position (but it did pop the 3a or 5a plug fuse when turned up despite not changing the voltage) - now after changing the tyhristor, it just trips the mains out.

I checked the motor brushes and communtator and after cleaning it all seems absolutely fine, it'll run from a little 9v radio battery smooth as silk, and generates quite a bit of power, when run from a 12v supply, more smooth running, more speed, more power, it looks good.

I'm afraid my knowledge on this repair comes from a google search and a bench test based on my limited knowledge of what is to me, a complex piece of electronics.

Can anyone recommend or offer any expert advice or diagnosis/repair services please, I believe these boards are known universally as KBIC or something. Mine is a BC2000-tb and there is a comprehensive manual online detailing many many different things, wiring configurations and all sorts, it seems like quite a useful board...... if it worked.

Thread: Workbench top
26/01/2022 13:21:41
Posted by JasonB on 26/01/2022 12:59:14:

White bounces more light back into the workshop and also probably easier to see a small nut or screw on the surface if you drop one.

+1 for this comment

I have smooth metallic white sparkle worktops in the garage, when I'm rebuilding engines I have an area set aside for circling and naming unique bolts/valve shims etc.

Thread: Myford 280 Manual and Sales Brochure
23/11/2021 15:27:20

When I got my Myford 280 I scanned the manual and sales brochure that came with it, and shared it around. Since then, multiple copies seem to have surfaced on the web for £10-20 for a download or paper copy, and I can't find the free link that I shared originally.

Don't pay for 1's and 0's, download and share please.

Manual

Brochure

Edited By Russ B on 23/11/2021 15:28:06

Thread: Chester DB7 speed control board? NVR switch doesn't lock
22/11/2021 10:22:27

After a good clean, the motor works perfectly and spins smoothly on the bench from a little 9v battery, and consumes around 200ma on 12v.

I went on to do the light bulb test on the motor output and found constant 110vdc with a 50hz flicker which was a big clue..... as I see it with my very basic electrical knowledge, the board uses 3 diodes and 2 SCR's, one SCR for each half of the rectified AC sine, and one of them was stuck closed, allowing the 110v flicker as half the AC flowed constantly.

New parts ordered sub £10, I think I'll change the pair and keep the old one as a spare, time will tell if my diagnosis is accurate but I did test the SCR with the 2v given by the diode test function on my meter (spec sheet says it should switch at half that) and one opened and closed nicely, the other was just constantly passing current no matter what I did to try and shut it.

Hopefully nothing else is damaged. All the diodes played nicely, nothing on the board appears burnt or damaged.

Thread: Another chinese lathe rises through the smoke
18/11/2021 09:11:02

Anthony, I love the new thread title wink

My motor (now) runs perfectly smoothly and spins up in just a fraction of a second off a little 9v battery much to my surprise, and draws 190 to 210ma when connected to a 3a 12v regulated supply. If I brake the shaft with my fingers it’ll draw around an amp as it slows to just a few revolutions per second.

Testing the resistance however, I have just 4ohms all round, and in fact, 4 ohms between any two at any angle, i don’t know if this is right, but it’s all very consistent.

I’m not sure what was going on with my motor, initially I couldn’t get any sense out of the resistance it was jumping all over, I cleaned up the contacts with a soft brass suede brush and then it all seemed to measure as above.

I’ve no professional expertise here bar 6 months studying DC and AC theory as part of mechanical engineering qualifications - i’m just handy at working stuff out, I assume the lower resistance is due to my higher output (claimed) 750w motor. The DC controller quite an output of 0-180vdc

I will research this light bulb test, I assume it’s a circa 50w 240vac light across the motor controller output.

17/11/2021 13:28:31

Anthony,

Thanks for another update and the resistance values new vs old, I will be checking exactly the same thing later tonight as my motor struggles to turn when run off a little 9v battery and I believe if the motor is good, it should spin smoothly and quietly even on a battery as small as this.

Could you do me a favour, and measure the current when the new motor is connected to a 12v supply, it should be circa 100-200ma if my googling is accurate - I'm not sure I would suggest doing the same with the old motor unless you can limit the current to protect your meter somehow.

The Chester DB7 I'm working on for a friend is a similar age to your clarke machine, and I think under the fancy clothes, they are very similar machines, although this one has had a pretty hard life by the looks of it!!

I have a Myford 280 and a Warco Super Mini (basically identical to your Clarke but green!). Now if you think a Myford Super7 is a sturdy lathe, or the Myford 254 is supreme, wait till you see a Myford 280!! It's a hell of a piece of kit. I love them both, they are both excellet machines, I'd buy another chinese lathe tomorrow if I needed one. The myford, I wouldn't replace, great machine, too expensive, unjustified. When I bought it, they were cheap.

Thread: Chester DB7 speed control board? NVR switch doesn't lock
16/11/2021 19:08:44

Fuses aside for a moment….. motor testing didn’t check out, I think there may be an issue with the brushes or commutator which will require investigating thoroughly.

16/11/2021 17:01:48

Well, I finally got round to looking at this machine. Can anyone help me confirm a few things?

The main plug had a 3 amp fuse in it, which after testing & sorting a few things.... blew as soon as I pressed go, but it did spring to life very briefly and all appeared fine! Since the machine is (should be) protected by the small internal fuses, I think the main plug fuse can be 5 or 10 amp to protect the cable alone, however....... as below...

I notice it has a pair of 10 amp fuses in the back, should these be 5amp fast acting, there is no information in the Chester Manual or on the parts diagram about any of the fuses rating or types - good old Chinese manuals!

I'm reluctant to try a 5 amp main fuse till I know what the control board and motor fuses should be.

I found a couple of faults, the side panel interlock was smashed, and the chuck guard interlock wasn't quite positioned correctly.

I also found that the neutral line (which runs though the stop switch and interlocks not as per above) had been connected to a terminal called F- which is right next to L2..... a mistake perhaps? It runs though some sort of separate EMI filter first that is glued to the bottom of the enclosure.

I tested the NRV and that works and latches as it should when the control board is disconnected. Looking at the wiring, someone has been at this in a big way which is never comforting, either that or the Chinese are fond of sticking insulated crimp terminals in various lines to and from the various switches, board, motor etc etc. I tested the pot and apart from going though a dodgy almost open circuit patch just before full speed, it checks out exactly as it should.

When I tried to start the machine, I had to pot turned to minimum. I have now disconnected the drive belts and will try 9v and 12v across the motor while measuring current to quickly assess general motor health/cleanliness.

26/09/2021 17:44:27

I’m picking up a faulty DB7S tonight, so this might well come in handy, thanks!

He said the motor won’t run, but he seems to think someone’s tested the motor and it checks out ok, and i’m guessing he’s checked all the internal fuses as he said there were a load, I wonder what mysteries I’ll find!

smiley

Thread: First try with a 3D printer
15/04/2021 09:13:47
Posted by Ady1 on 15/04/2021 04:59:54:

Very nice, you gets what you pays for

30 quid a spool for the media

How many nose caps will a spool make? 15?

Edited By Ady1 on 15/04/2021 05:02:43

I only the buy the best filament for final parts as cheap stuff can (but doesn’t always) cause terrible quality prints. I’m typically paying £20-£25 a kg for Verbatim branded filament and £15 ish for cheap draft quality filament.

1kg goes a very long way, as most parts aren’t solid infill (especially test fits and draft parts), they’re a shell with a matrix inside, which can work out to be tougher though more flexibility (although this part probably is solid). I’d guess it’s no more than 10g, so you could make around 100 finished parts, and typical standard 3d prints are around 25% infill and you’d get double or triple the quantity.

I just printed a pair of exhaust manifolds for a classic Honda I’m restoring, bores have to be machined as it’s not super accurate, but test fit was spot on, now thinking about quotes for laser/water cutting from 5-6mm aluminium, it’s handy to have that ability! I did some carburettor adapters for fittings webber carbs years back, easy to knock out 5+ revisions inc test fits and tweaks in a day, and due to the CAD side of things I was able to properly design the flow though the part to ensure smooth transition between flanges.

Thread: supercharged V12 2 stroke
19/02/2021 21:43:28

Great to see an email notification pop up from you relating to a thread update!! I've loved this from the start!

Thanks for putting it all online!

Thread: Lidl Portable Bandsaw
05/11/2020 13:06:03

I think you may have just got a bad one, my blade tension can't be adjusted by any other means, but it works perfectly fine, so I see no reason why it might need to be changed.

 

Perhaps one defect accoutns for you both your complaints, a stray guide perhaps not holding the blade vertical, and as a result, shortening the correct route of 1140mm in length preventing you from tightening as the blade its literally cutting corners?

Edited By Russ B on 05/11/2020 13:06:58

Thread: Parkside (Lidl) Cordless Angle Grinder
05/11/2020 12:58:14

ahhhhhhhhhhhhhhh..................I think I might have unknowingly had the brushed version? it did a few good jobs albeit at a drastically reduced speed vs my 240v/110v gear but hammered my 4ah battery, which normally lasts a week or more of daily odd jobs M16-M20/pipe/flanges etc on the 1/2" impact gun.

I sold it practially brand new for about what I paid for it (£29.99 without battery/charger)


I think I'll keep an eye out for this brushless version, it took me so long (12+ months!) to find to the first one I got I won't hold my breath

Thread: Lidl Portable Bandsaw
05/11/2020 09:55:53

Martin, I have the Aldi one (£149.99 delivered last year I think) - the blade tension is fine, I could play a tune on it and the weld is flat and smooth, I'd be taking it straight back before they have none left to exchange it with if I were you! (And hoping its not a crap batch!)

I bought a 3 pack of Milwaukee variable pitch 44.7/8" blades (1140mm) but I'm still on the original M42 blade after over a year (although I recently chipped a tooth manhandling dexion profile, my own fault) - they were very cheap delivered, worked out circa £6-7 a piece or something?

Milwaukee do 10, 14, 18, 24 TPI and 10/14 and 14/18 TPI variable pitch. Not all of those are available in europe in the more economical packs of 3 or more blades, so it takes a bit of looking around on the net. I can't for the life of me find where I got mine from, I'll have to check the bag/box in the garage for clues.

Thread: I'd like a simple plastic injection machine or designs
03/11/2020 14:15:19

Jeff,

As I suspected, very expensive to do properly! I already have polyurethane and silicone casting equipment as I made a valve head and cast a PU sealing face onto it for a small (by my standards) injection machine (typically pulverised or pellet fuel injection)

I might contact the local supplier to see what other options might be available as the PU i have would be too soft although probably chemically compatible.

I’m still going to gave a look at this DIY machine, i’m too curious.....

03/11/2020 08:04:10

Chris/Jeff,

What if I only want 10-20 of a particular part, what are the costs involved?

Jeff, the piston is connected via a gudgeon pin, you can't see it in the screenshot as it's the same colour as the conrod, I just modelled the one in for stress anaylsis, the opposing pin will obviously feature equal and opposite stress. The head of Cylinder is flat and removable to aid cleaning when the jobs done.

I have one of the finest, if not the finest FFF 3d printer on the market so I can print the model myself. I'm looking at a small 6mm pipe connector with a 1-1.5mm wall thickness. We're looking at about 55mm total length, the most difficult part I want to make is a 4 way cross.

Chris, it's always good to have some companies to call up, thank you, putting injection moulding terminology and quieries into google is a waste of time, I was trying to find out how NBR parts are made the other day to see if I could make my own and it was like I was asking the meaning of life, every answer was totally different and none hit the mark!

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