I bought one of these boards
https://www.amazon.com/gp/product/B078M1NC3L/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
It came with no documentation and I emailed the vendor through Amazon and he said "sorry for you but".
No documentation is available.
I can figure out every connection like IN1, IN2, and EN. But there is a connection called CT whose function I don't know.
Anybody know what CT is? How is it used?
thanks.
First things first.
WHAT EXACTLY is you criteria ? (what is your application load current requirement ?)
All I need to know is the function of the connection CT. I was an engineer for 30 years before I retired.
I know what I need to know except for the functionality of CT. I was hoping that someone here might know.
I'm working on using an arduino UNO as a source of PWM. Just got started with it.
If you were an engineer wouldn't you guess that CT probably means Current Transformer ?
That would be my guess, although , honestly I wouldn't know if it is an input or output.
There's only two meanings for CT that I know, Center Tap (for a transformer) , and Current Transformer.
Since there is no transformer on this board I would go with the latter.
There are two pins so I would put a meter on it to see if it is the output of an onboard CT and
figure out what the mv/A ratio is an amplify it with
an op amp if it's too low to use as an analog input.
If it's well designed it is 100mV/per A and the output is 0 to 5.00 V dc (1 V/per 10A)
Alternately , I suppose you could surmise that CT means Current Threshold, (input) but is that a voltage ?)
The question is , is it optional or mandatory ?
My money is on Current Transformer output voltage intended to be used as an Arduino analog input,
having a maximum output of 5.00 V.
There is a BRAKE function that can stop the motor quickly.
Maybe CT is short for Control , and acts as Brake input signal.
On the other hand, the brake might engage automatically when you turn off EN.
My money will go with the braking circuit. Since the description says:":This motor driver has a brake function, which can stop the motor quickly", and all the other pin connections make sense. the only option left is to control the circuitry that disables all the motor drive circuitry and shorts the motor leads.
Be aware the DC motor braking merely slows the motor, it will not hold it in position.
Paul
I did suggest the brake...
We should start a pool...
Hi,
This may be of help;
CT looks like an voltage output from the bridge, representing the current measured by the bridge.
Tom... 
I win.
I was wrong about the pins. There's two current
channel outputs not one as voltages. I forgot it's a
dual motor driver , not a single.
There's probably a shunt built in similar to
the type used for RC with an onboard amplifier
to amplify the voltage drop across it.
The only question is what's the mV/per A
conversion factor ?
I'll stick with my first guess of 100mV/per A.
I must confess it caught me off guard that "CT"
was just the word 'CurrenT' abbreviated. I would never
have guessed that.
Okay, that link was a good one as that board also has a CT on it. The description is a bit obtuse but it's better than the response I got from the vendor.
"The manufacturer tells me it that the connected CT function is to dial the connection terminal and perform the login process." ???
That response kind of counterpoints the surrealism of the underlying metaphor.
I was thinking it could be a current sense because some of the motor controller chips have that functionality. So I guess I'm in experimental mode or reverse engineering mode. I'll try some things and try not to blow it up in the process. I'm used to getting specifications so that I don't have to guess at these things.
Hi,
When you experiment, you should be able to leave the CT terminal of the motor controller disconnected.
The spec does not say what voltage may appear on that terminal and the Arduino controller analog inputs are not tolerant to voltages above 3.3 or 5V, depending on the model Arduino controller.
So I would advise when you begin to apply power and try to get the motor running, just connect a DMM, on DC Volts mode, between CT and gnd.
You will then see what voltage you will have to work with if you want to include current limiting.
Tom...
What would be the point in including current
sense output voltages on a motor controller intended to interface with an Arduino microcontoller
that cannot interface directly due to incompatible voltages ?
In what universe does that make any sense
from a design standpoint ?
Dollars to donuts it's 100mV/A because at the maximum current of 50A ,
50 * 0.1mV is 5.0 V
It sounds like you've been wasting your money. Big time.
That thing is advertised to handle 50A - which is of course total bs as the screw terminals used are suited for no more than 3A or so. That's the first give-away it's a horribly fake and misleading listing by a seller that has no idea of what they're selling (or they know and intentionally try to mislead you).
The listing is also missing a voltage rating for the driver. That's a serious omission, as it's one of the key specifications.
Reading the comments, it appears to be based on the ancient and rather inefficient L298N motor driver, which can do no more than 2A continuous. The chip is conveniently hidden under that heat sink. You have to connect it as you would an L298N... That chip is indeed so lossy you need a heat sink like that to stand a chance of running two motors at full power (i.e. 2A per motor, at which it has a voltage drop across the chip of up to 4.9V, making for almost 20W total dissipation!). Back in the day that may have been acceptable, nowadays it's not.
I agree that the absence of details is very
suspicious.
Okay, here's what I've discovered. I looked at the chips I could see on the board. The mosfets are hidden under the heat sink, but I might take that off (if it's not glued, there are a couple of screws) and see if I can see the mosfet numbers.
The control chip is an IR2104S. There are four of them on the board. There is also an LM393 comparator for each channel. It's not perfectly clear, but the comparator may be looking at current sense in order to turn off the 2104's.
There is also a MC34063 switching regulator on board which is cause for some confusion.
So I wired the thing up by itself with jumpers first with a resistive load then with a small motor. The board works and if I take EN low, the motor turns off. I monitor CT with a voltmeter. When I grab the motor shaft and load it down, the voltage on CT goes to around 20mV. So MAYBE it is set up to limit the thing to 50A. Who knows? I'm not ready to test it to destruction just yet.
But there is something that bothers me and I guess I need to study the 2104 data sheet some. I at first reasoned that the board required two supplies. One to power the motor and one for the logic. But it seems to work only with the supply for the motor. So as one responder put it, I better be careful about connecting the Arduino. More testing to be done but thought you would like to know what I've found so far.
I did actually get another response from the vendor who claims he will get the information I want. We'll see.
Well, at least it looks like the thing is indeed MOSFET based, that's good.
The LM393 may also act as level shifter... by making any input voltage of say >1V is a high signal, and <1V a low signal. You did mention logic is driven by motor voltages.
Still I don't believe the 50A rating at all, the screw terminals I see on the photo are simply not up to it. You also have to take care of the voltage: there's a 16V rated capacitor, so that's probably your upper limit for the motor supply voltage. A very low voltage for such high current motors, normally you'd try to increase the supply voltage to reduce the current well before you reach 50A.
Let's consider the obvious, ie
The LM393 is amplifying the shunt voltage
and outputting it to the CT pins.
Put a voltmeter on the output pins when running it and compare it the CT voltage.
Finally got a reasonable response from the vendor.
"The manufacturer tells us that CT is just a Output port
It's function is to output the current value of each channel of the driver, and the current value has been converted into a voltage value output,"
That is consistent with what I see experimentally. Thanks for all the comments, folks.
Little bit more info. i took the heat sink off. There is an LM358 op amp and 8 N channel mosfets NTD70N03 by ON semi.
Also the board is called a DBH-12 and is available from Banggood for $17 and other sources for $14. These other sources list it as a 30A controller.
Also at Banggood I found some specs.
"Operating Voltage: DC 5-12V
Standby Current: <30mA±5mA
Current: 0A-30A(Max)/each channel
PWM Mode: Duty Cycle: 0-98%; Frequency: General Motors: 16kHz; Coreless Motor: 80kHz; TEC: 500Hz-80kHz
Input Voltage Level: Low:0-0.5V; High: 2.5V-13V(typical drive level: 3.3V, 5V, 12V)
Current Sampling: CT Pin Output Voltage(V)=Current(A) x 0.155
Item Size: 6.2 x 5.3 x 1.8cm / 2.44 x 2.08 x 0.71inch"
wvmarle:
Well, at least it looks like the thing is indeed MOSFET based, that's good.The LM393 may also act as level shifter... by making any input voltage of say >1V is a high signal, and <1V a low signal. You did mention logic is driven by motor voltages.
Still I don't believe the 50A rating at all, the screw terminals I see on the photo are simply not up to it. You also have to take care of the voltage: there's a 16V rated capacitor, so that's probably your upper limit for the motor supply voltage. A very low voltage for such high current motors, normally you'd try to increase the supply voltage to reduce the current well before you reach 50A.
The comparators are for current limiting. MOSFET drivers don't need level shifters on the input.
Its not clear if the MOSFET drivers are running direct from the motor supply, I suspect so (with the inductor to
protect from the spikes on the main supply?). If so this board is designed for 12 to 15V operation only.
The screw terms are probably >20A or so, certainly they've handle wires capable of that, its the pcb traces that will fail first. Upto 20A is a reasonable level to expect from this kind of construction, I agree 50A is not realistic (except as a brief pulse rating)
[ On further consideration that inductor might be part of a boost supply to give 12V to the IR2104S's, allowing the board to run at lower voltages. ]
Not easy to find a datasheet for the NTD70N03. Not too shabby specs, 32A wire limited maximum drain current.
The inductor may also be part of a boost circuit to get a voltage some 5-10V above motor positive supply voltage, to be able to properly switch on the high side MOSFETs.