Help with electric table power supply

[ollihd]

Hi,

I have this electric table power supply that is used to supply power to the three motors adjusting the table. It has a weird problem. If two of the theree motors are connected, everything works fine. The order of the connected motors doesn't matter. I can connect M1 and M2 and it works or M1 and M3 or M2 and M3 and still it works. However the table wont't work if I connect all three of them. I can also see from the three leds that are on the board that they start to dim when all three are connnected and I try to adjust the table.

- I have changed all the caps on the board and the small DC-DC converter (8-leg) near the input
- All motor outputs (M1,M2,M3) get the same (correct) voltage out.

Something is capping the max output somehow when all motors are connected, I think? Where should I look next?

Pictures: https://photos.app.goo.gl/AKB3i16UdBUyaGfz6

[wasedadoc]

Have you checked whatever is feeding power into the barrel connector at bottom left?

[ollihd]

Yes, I checked the power brick supplying power and it is working correctly, confirmed by supplying with my bench power supply.

[ollihd]

Oh yeah and I think the correct term is "electric standing table" vs. my "electric table"

[bidrohini]

What is the recommended input voltage and current to drive 3 motors? I believe, there is not sufficient power to drive 3 together.Try to measure with a multimeter.

[Swake]

How much current does it pull with only 2 motors, keep an eye on the startup peak/surge?

Are 3 motors pulling more or less 3/2 of this or much more?

Double check your bench power supply is not maxed out. Trusting the sticker on it is nice, measuring is better.

[ollihd]

Thank you for the replies. Haven't been able to measure how much current the motors pull since the table is physically 1 hour drive away from me. Have to do that next. Power supply didn't max out, that I checked, just didn't check how much the motors pulled. I have now tried it with the power supply and 2x different bricks that are supplied witht he tables. The result is always the same, 2x motors fine, 3x motors = nothing. Could there be any component on the board that would underperform due to age/fatique?

[shakalnokturn]

Yes aged electrolytics (start with the large ones) could have this effect. (But if they do arguably the power supply is a bit close to the limit in the first place.)
Also check for poor / heated contacts on power input connector, excessive wire resistance. (How long and thin are the power supply wires?)

Edit:
Once you're sure nothing is wrong with the P.S. wires themselves my first suspects are:
-The point where the center pin of power jack socket is riveted to the solderable spade, very common poor contact point, I'll usually scratch and apply a little solder to be on the safe side.
-The large black capacitor behind the jack.

[fzabkar]

Please excuse my ignorance, but what sort of motor requires 2 relays plus a MOSFET? :-?

Would it be worth monitoring the voltage drop across the 0.1 ohm current sense resistor?

[shakalnokturn]

Please excuse my ignorance, but what sort of motor requires 2 relays plus a MOSFET? :-?

True there seems to be at least one device too many. I guess there's one relay for polarity, another for on/off, MOS for speed control or soft start or just killing the electrolytics with high current ripple...?

[ollihd]

-The point where the center pin of power jack socket is riveted to the solderable spade, very common poor contact point, I'll usually scratch and apply a little solder to

I have checked this, but will double check. Thanks.

-The large black capacitor behind the jack.

This has been changed already.

Would it be worth monitoring the voltage drop across the 0.1 ohm current sense resistor?

Will check!

[wasedadoc]

Do you really mean that the mere act of connecting a third motor prevents any of them from running?  Or do you actually mean that you can have two motors running at the same time, but not three?

The DC-DC converter is probably only for the IC and maybe some drive circuits, not for the motors themselves.  The electrolytics are unlikely to be a problem.

Is this something that has developed a fault?  Did it ever work as you expect or has it always been like this?

[ollihd]

All good questions.

Do you really mean that the mere act of connecting a third motor prevents any of them from running?  Or do you actually mean that you can have two motors running at the same time, but not three?

Thats is really what I mean. If two motors are connected, I can run them. When all three are connected, nothing runs. Order of connection does not matter or make a dfifference. It can be M1+M2 M3+M1 M2+M3, but not all three of them. When all three are connected and I try to control them I can see the three indicator LEDs on the board dim quite a bit. This does not happen when only two are connected and controlled.

The DC-DC converter is probably only for the IC and maybe some drive circuits, not for the motors themselves.  The electrolytics are unlikely to be a problem.

Good to know.

Is this something that has developed a fault?  Did it ever work as you expect or has it always been like this?

The desk had been sitting in storage for a few years, no physical damage. It was working when going in storage and came out not working.

[wasedadoc]

Still not clear to me and perhaps others reading here.  I'm not familiar with any motorised, never mind the particular one that you have.

Does the control system always attempt to run all connected motors at the same time?  Are there any modes where only one or two motors should run.  If yes, you are finding that with two motors connected then one or two can be run?  But with three motors connected, not even when a single one should run that does not happen?

[ollihd]

Does the control system always attempt to run all connected motors at the same time?  Are there any modes where only one or two motors should run.  If yes, you are finding that with two motors connected then one or two can be run?  But with three motors connected, not even when a single one should run that does not happen?

So basically the table has three legs that can go up or down. The three motors are connected to the three legs. A controller is connected to the power board in question. The controller has 3 switches: up, down and a dead mans switch you have to press before you can press up or down (so that you won't accidently move the table with your leg or something). If one is connected, it will move. If two are connected, they will move. If three are connected, nothing moves, not even a little bit.

[wasedadoc]

Does the control system always attempt to run all connected motors at the same time?  Are there any modes where only one or two motors should run.  If yes, you are finding that with two motors connected then one or two can be run?  But with three motors connected, not even when a single one should run that does not happen?

So basically the table has three legs that can go up or down. The three motors are connected to the three legs. A controller is connected to the power board in question. The controller has 3 switches: up, down and a dead mans switch you have to press before you can press up or down (so that you won't accidently move the table with your leg or something). If one is connected, it will move. If two are connected, they will move. If three are connected, nothing moves, not even a little bit.

That doesn't categorically answer my question but I think you are saying that either no motor should run or all three motors should run at the same time.

[Swake]

What is the yellow rectangular thing near the big black cap? Is it a fuse? If it is then check it's good and measure voltage over it when acting the motors. Should read like 0 volts all the time if not you've found something is with it.

Please excuse my ignorance, but what sort of motor requires 2 relays plus a MOSFET? :-?

And a microcontroller! Total over-engineered board with 100 parts when all you need is a couple decent push-button switches.
Of course it is more fun having soft start and blinky blinky LED's and that can be sold for many more dineros.

[Swake]

I have the impression the power socket is melted on the back, please confirm it is still in working condition, also when loaded.

[ollihd]

That doesn't categorically answer my question but I think you are saying that either no motor should run or all three motors should run at the same time.

Sorry for being unclear. Yes that is correct, all three motors should run at the same time or no motor should run.

What is the yellow rectangular thing near the big black cap? Is it a fuse? If it is then check it's good and measure voltage over it when acting the motors. Should read like 0 volts all the time if not you've found something is with it.

You are correct, that is a self recovery fuse (X30 UF700). Will measure when acting the motors.

I have the impression the power socket is melted on the back, please confirm it is still in working condition, also when loaded.

Socket is in working condition, also under load.

Thank you everyone for the replies. Will do some measurements during the weekend and report back asap.

[ollihd]

Hi all,

Finally got to test table again. Before testing I replaced the DC input terminal, just in case.

The problem remains, although this time I discovered something very interesting.

I connected each motor one at a time to each motor output and tested UP/DOWN movement. The only terminal that was acting suspiciously was the middle terminal. When ever a motor was connected to the middle terminal (didn't matter which motor) and I would press UP on the control unit, the motor would move UP and then for a brief second DOWN (automatically). The only terminal that did this was the middle motor terminal. I also discovered that when all three motors were connected I could move all of them DOWN, but not UP. I'm thinking downward movement requires less power.

My thinking now is that something in the middle motor terminal is causing this. The component groups for all three terminals are identical so it "should" be pretty easy to find what is wrong.

[shakalnokturn]

Is there any position information (end of run) return on motor connectors?
Did you get round to any current measurements?