DC Treadmill motor and cheap Chinese 10000watt power supply suitability-Getting Hot.

Thread Starter

oldman2

Joined Mar 28, 2020
16
I have a treadmill that the motor speed controller board has failed, I bought a Chinese 10kw power supply and added a 50amp bridge rectifier. The treadmill now runs with the speed control pot from the psu mounted on the upper panel so speed is adjustable by hand. I use the machine at a brisk walking pace and the motor appears to get too hot now, at 77V DC input to the unloaded 1.5HP 230V DC motor I can measure 59V AC. The current draw is 2 to 3 Amps DC with 6 Amps AC supply load.
Do I have too dirty a psu with that amount of AC showing on my meter?
I have attempted to repair the original KXTL 230 controller board but after replacing IRFP460C and F10U60DN plus the 390microfarad 400v Cap I still have no motor Volts on the output terminals.
Although I would still like to repair the board its now past my capabilities without guidance.
I wonder if KBmg 212d controller would be my best bet to get a clean supply to keep the motor from cooking?
Being on lockdown I have plenty of free time to explore all the options if anyone would like to give an input please.
 

MaxHeadRoom

Joined Jul 18, 2013
20,458
If the motor current is 2a-3a then it is barely loaded.
It should not be getting hot at that current.
How is the power supply voltage controlled? is it a PWM output or ?
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,458
There are a couple of Utube videos of someone doing the same, it should not stress the motor as basically this is how the triac bridge versions work with the same output.
Check motor loading, belt friction etc.
Max.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
Thanks Max, as you have already seen the motor loading is 2-3amps on the dc side driving the belt, the bed under the belt is well siliconed. The belt will move with just 18 Volt drill battery connected & the fan attached to the drive motor is intact.
Should I be seeing 59V ac on the dc motor terminals?
motor (2).jpgmotor (2).jpg
 

MaxHeadRoom

Joined Jul 18, 2013
20,458
Your voltage will depend on the setting of the pot.
Running on 230vac I would expect a maximum of almost that on the DC side.
Presume you have wired the bridge correctly?;)
Max.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
Oh, ok I feed the controller with 240V AC and yes the bridge is correctly connected though I will double check tomorrow and I will even change it as I bought more than one, just in case. I didn't realise I would see that much AC on the DC side of the rectifier though, so I will check and get back to you.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
So I couldnt wait to check so its done now Max. The bridge double checked and its correctly connected, I even changed it for another new one just in case.
I have 240V AC supply into the variable speed controller, I set the pot output to 77V DC into a 100watt lamp and reading 91V AC across the dc supply to the lamp.
I used a 100watt lamp as its easier than lugging a treadmill into the workshop!!
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
So Max I am back to the original question :) The motor runs hot, is the chinese supply unstable in some way ie not smooth enough DC after the bridge?
Comparing this application with those using the motor for mini lathes, I would say the lathe is less load than dragging several mrtrs of belting around with a hefty lump jumping about on it ;)
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
Bad form to reply to your own post I know but I just got this snippet from someone designing a treadmill motor to mill conversion.
"Just doing PWM off straight rectified mains is going to be electrically noisy for one. I also have a suspicion that even though a limited PWM duty keeps motor speed down, the high-voltage peaks that still go through the motor are what causes the most common failure; overheating. "
Any input on that Max?
 

MaxHeadRoom

Joined Jul 18, 2013
20,458
The popular T.M. board for machine usage is the MC2100 series, this used PWM to the motor and works like a charm.
The SCR bridge (mains rectified) types MC-60 etc, usually have a series choke on the motor power in order to smooth the DC somewhat.
Max.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
Thanks Max for the info, the MC60 is it seems quite a rare board here, the MC2100 is out of my price range at over £100 and still needing some sort of extra circuitry to get it up and running .
Would a Kbmg 212d dc motor contoller board be suitable? Looks like it is 10amp capable. I can get one of those cheaper.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
Hi Max, I now have a Kbmg 212d on order so I will see if that fixes the motor heating once it arrives.
I wonder if I could try once more to repair the original control board, I will put some detail up on what I have done so far over the next day or so to see if I can get any guidance on what may be wrong with it.
 

Thread Starter

oldman2

Joined Mar 28, 2020
16
So just to refresh,
I have a treadmill that the motor speed controller board has failed, I have attempted to repair the original KXTL 230 controller type board. It had a blown 10A fuse caused by full motor volts being applied at startup due to a dead short on mosfet IRFP460C but after replacing IRFP460C and F10U60DN plus the 390microfarad 400v Cap I now have no motor Volts on the output terminals even when selecting start on the main user panel.

Although I would like to repair the board its now past my capabilities without guidance.

I cant find a circuit diagram for it so ive attempted a pencil sketch of what I can trace out.
mywiring3A.jpgI checked the values of the resistors R1 through R4. I had to desolder all to get a true reading. R1 across Gate to sink of the 460C was slightly low at 1985 ohms (15ohms low) and R4 paralleled across the 390mf cap reads 994kohms and should be half that at 470k. The large white ceramic case has 3WR02J stamped and it reads around 3ohms so I guess thats ok.
topside.jpg
Refitted the motor control board, powered it up and its still the same with no output to the dc motor on + and - terminals.
DC Voltage tests between the + motor terminal and the gate and sink of IRFP460C was 330V. R1 is 2k and across G & S on 460c, 330V is on both sides of R1.
Between R3 & the speed control trimmer pot was the only lower voltage at 276V.

I did find some more out about the user control side of the board. The white 5 pin socket has 5 wires which go up to the user control panel. The red and yellow is a 10V AC feed to the top panel. The 3 wires blue white and black are for the motor speed up down signals from the user control panel.

Black is +8V
Blue is ground
White is output

I measured white to ground .75V DC at the lowest speed setting rising to 4.92V DC on fastest speed.

Close to the white 5 pin socket are 2 voltage regulators, one is L7808CV 8V 1amp.
The other is L7812CV 12V 1.5amp regulator.
KHXKEM~1.JPG
close wiring.pngSo Max or anyone else would like to give me some clues please I would like to beat this problem if possible.
 
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