Monster Moto Shield VNH2SP30 current sense problem

Thread Starter

paulus_v

Joined Nov 19, 2017
11
Hello all,

I am using a Monster Moto Shield VNH2SP30 Board wired in dual half-bridge configuration to increase power (second diagram).

Everything works fine except the current sense output (CS). I get no voltage output.

I am not that good at electronics but I have a feeling that it could be something about the added components (resistors, condenser) on the board (third diagram) to convert the -3/+15V CS output to arduino usable signal (0-5V)? Or the common CS output of both H-bridges working in paralell is canceling out somehow?

Any suggestions are really appreciated.

vnh2sp30 diagram.JPG VNH2SP30 wiring.jpg sparkfun monster moto shield.JPG
 
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dendad

Joined Feb 20, 2016
3,921
What current is being drawn by your motor? Have you measured any voltage at all on the current sense outputs?
And I'm not sure what you mean by "-3/+15V".
The CS outputs will generate a voltage in proportion to the load current. If you are only running a small motor, like 100mA, the CS voltage will be pretty small too.
 
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Thread Starter

paulus_v

Joined Nov 19, 2017
11
What current is being drawn by your motor? Have you measured any voltage at all on the current sense outputs?
And I'm not sure what you mean by "-3/+15V".
The CS outputs will generate a voltage in proportion to the load current. If you are only running a small motor, like 100mA, the CS voltage will be pretty small too.
The current drawn by the motors is huge, more than 10A. In normal dual half-bridge configuration I get consistent voltage reading but in parallel configuration it remains on 0V.

-3/+15V is from the ICs datasheet (page 8) but the board converts the voltage to 0.13V/amp.
 

dendad

Joined Feb 20, 2016
3,921
What is your circuit in parallel?
Without looking at the data sheet, I think the CS outputs get their reading from the top FETs so if you have the motor running from +V to the FET to ground, the CS will not read if I'm correct.
Please put a diagram of your full connection so we can see.
Yes, I checked the data sheet.
Oh, that CS -3/+15V is the max voltage allowable on the pins, not what comes out.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
Please look at the second diagram from the op. I am using one driver IC to run the motor in one direction using both half-bridges and a separate one for reverse direction.

Here is a descriptive setup example.

MotoMonsterSetup_single-motor-driver_final.jpg
 

dendad

Joined Feb 20, 2016
3,921
I don't think that is a valid connection you are using. The FETs will be running in the Brake mode so the current sense is disabled. Look at table 13A. When both A and B inputs are the same, the CS outputs are hi impeabance.
Do you need two like that? One H bridge will work ok. Or hook both H bridges in parallel, A1 to A2, B1 to B2, and same with the inputs. Then just drive them as one bridge.
 
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dendad

Joined Feb 20, 2016
3,921
As above, the current sense is turned off. Give it a try with just one package. It will have a high enough current rating(30A), and monitor the CS to back the PWM off if the current gets too high.
I'm off to sleep now, hopefully. Best of luck on your project. Please keep us posted.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
First I tried to connect both h-bridges in parallel but I get inconsistent motor move in reverse direction. I thought the board was defective but tried several and all behaved almost the same. In reverse direction is working only one H-bridge, the other is in fault condition (EN pin low). And the working one will shut down rapidly as the motor power is 20A.

When I connect them in dual h-bridge everything is working fine except the current sense output.

What do you mean by "The FETs will be running in the Brake mode"? Could you explain?
 

dendad

Joined Feb 20, 2016
3,921
First I tried to connect both h-bridges in parallel but I get inconsistent motor move in reverse direction. I thought the board was defective but tried several and all behaved almost the same. In reverse direction is working only one H-bridge, the other is in fault condition (EN pin low). And the working one will shut down rapidly as the motor power is 20A.

When I connect them in dual h-bridge everything is working fine except the current sense output.

What do you mean by "The FETs will be running in the Brake mode"? Could you explain?
Have a look at the table 12 in the data sheet. When you have both A and B hi, both top FETs will be on, shorting out the motor to Vcc in normal bridge connection, applying a brake to it. And both low in brake to 0V. Both conditions disable the current sense. See table 13.
And yes, it will still PWM when using 2 as you are, but probably disabling all protections built in.
Study the data sheet.
And try just one H bridge.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
Many thanks for the explanation!

In other word they will work without protection until the magic smoke escapes...

Have you any idea why is one IC disabled in reverse direction when connected both H-bridges in parallel?
 

dendad

Joined Feb 20, 2016
3,921
Many thanks for the explanation!

In other word they will work without protection until the magic smoke escapes...

Have you any idea why is one IC disabled in reverse direction when connected both H-bridges in parallel?
My only guess would be a crook connection.Try each half of the board separately to see if they both work before connecting the outputs together.
(I'm having trouble getting to sleep tonight so decided to get up again.)
Then when you do connect the outputs together, do it with equal lengths of wire from each A and B pin to the motor, not just across the board. That way, there is a small amount of series resistance from each driver to the motor and that helps the drivers to share the current load more equally.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
Wow, you could be right!
I wired them in series, the motor wire goes through first driver output and ends up in the other. I will try with equal length wires.
 

dendad

Joined Feb 20, 2016
3,921
I had a read through the blog that you got your diagrams from and noticed there is a big difference in quality of the boards. Probably the better ones have a good thick copper layer and the ICs are properly bonded to it. You will need cooling heatsinks and fans it seems too.
I don't think I still have some of these boards but if I do, I'll try them out tomorrow maybe. Now it is almost tomorrow so I'm going to have another go at getting to sleep :)
Good night.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
Thank you a lot for your help! I wish you a good night!

I have six boards with six motors. Just tested one board's each drive IC separately and one chip is faulty in one direction. So the board is crap! I will test all six boards and report back.
 

Thread Starter

paulus_v

Joined Nov 19, 2017
11
After all the troubles I searched the internet and found out that these boards are using fake or defective VNH2SP30 chips. This chip model is not manufactured anymore but the Chinese are selling tons of them...

I have tested each driver individualy.
Using the same input voltage (12.5V), with the same motor, the same pwm speed (30%) I have measured the output voltage for both directions and here are the results:

board 1: A1 1.6V; B1 5.37V; A2 5.5V; B2 5.37V - first chip defective

board 2: A1 5.5V; B1 0V; A2 1.4V; B2 5.37V - both chips defective

board 3: A1 0V; B1 0V; A2 5.98V; B2 6.07V - first chip defective

board 4: A1 5.61V; B1 5.73V; A2 5.72V; B2 5.78V - good board

board 5: A1 6.19V; B1 0V; A2 3.51V; B2 6.48V - both chips defective

board 6: A1 0.24V; B1 4.9V; A2 4.97V; B2 4.97V - first chip defective

In the end I replaced the boards with similar original ones, Pololu Dual VNH5019, ten times the price :)
The original chips get a little warm at motor acceleration where the Chinese get so hot that I can not hold my finger on.
 
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