INA 169 Current Sensing Board does not work reliably

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M123456
 
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INA 169 Current Sensing Board does not work reliably

Post by M123456 »

Hello,
I needed help!

I am using 12 of INA169 current sensing breakout boards (PRODUCT ID: 1164) to measure motor current draw on my automated monitoring equipment.

I am having issue with them stays working. From time to time, these current sensors died and I have to replace them. I just recently replaced 6 of the 12 due to no sensing voltage output (measured 0 volt from Vout to Ground pin). The power still pass through the board's Shunt resistor, but just no Vout signal to ground (0 volt at all time). I even added 5 amp fuses to protect each one of the current sensors, but it does not seem to help. I verifed it with a current meter connected in series to the motor circuit and there is current reading while the INA169 current sensor has 0V output. They just keeps on dying. Need to know why. Is the INA169 Chip not working?

My hook up info: 24V DC power supply connected to PWM driver ==> fuse ==> INA169 ==> DC Motor ==> Ground & Powr Suply Negative.

Hookup: PWM driver power output connected to Fuse box ==> Vin+ (J1), Vin- (J1) ==> DC motor ==> Gound & Negative of 24V power supply. The Vcc is jumped to Vin+ pin. Singal Vout is connected to data acquisition board to read voltage input and the DAQ board's ground is connected to the ground pin.

I am driving the motors with PWM Driver set at 15KHz. Voltage range 3v to 24v.

Thanks.
Jack

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primexandy
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by primexandy »

What are the motors rated at, what motors are they? On startup some will draw a lot of current in a spike, possibly too quick for your fuses. Are your motors being driven suddenly or do they have a softer start?

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

The motor are rated for 2.5Amps max. At stall, we are seeing as high as 3.0amps current draw. These are small brush DC motors. We are testing these motors with a simulated brake load.

We have two types of motor with independent test plan. One is the motor starts with full 24v without load for a brief second, then increase load apply gradually. The second is soft start at 3v, 6v, then 12v with a small contant load from beining to end. I am seeing INA169 board failures on both type of tests.

If in-rush current is the cause of the INA169 damage, what would you recommend I should do to protech the circuit? or change to a more robust board?

Thanks.
Jack

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adafruit_support_bill
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_bill »

With a 24v drive voltage, the brush noise and/or inductive spikes due to PWM could very well exceed the 26v absolute maximum rating of the chip inputs. Do you have access to an oscilloscope to look at the voltage across the shunt?

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

The TI INA169 spec page 5, Figure 1, note 1 @ bottom right corner.......stated the V+ voltage for INA169 range is 2.7v to 60v. Where do you see 26v Max. chip input voltage?

Jack

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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_mike »

The flyback voltage can also exceed 60v.

Try putting a voltage regulator between the motor supply rails and the INA169. That will protect the chip from whatever spikes of flyback voltage exist in the rails.

26v is the maximum voltage for the INA219 (another current sensor). I got caught by the similar names too.

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adafruit_support_bill
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_bill »

Sorry, I was looking at the sheet for the INA219. For the INA169, the max differential input is -40v to 2v.

See "Absolute Maximum Ratings" on page 2: http://www.adafruit.com/datasheets/ina169.pdf

The 2.7-60v spec is for the power supply. exceeding that would likely toast the entire chip.
The analog input limits are different. Exceeding those would damage the ADC.

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

Bill, Mike,
So, is 24v at V+ acceptable? I don't have a scope. I can tie another (separate) power supply to the circuit i.e. either constant 5v or 12v. But I don't have anymore good INA169 boards to use. I went through all 30+ boards in my few weeks of testing. My worry is that these boards may not be able to handle the steady 5A as advertised.

I can send defective boards back to you for Failure Analysis. I have plenty of them.

Jack

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

Hello? Bill, Mike?

Are you working on a solution for my issue? Can i return the INA169 modules for refund?

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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_bill »

So, is 24v at V+ acceptable?
24v is fine for v+, but that is not the inductive flyback voltage we are talking about. Switching power to an inductor like a motor causes large voltage spikes that can be many times the drive voltage. Switching circuits for inductive loads usually include a snubber or flyback diode to protect the electronics from the damaging effects of these spikes. http://en.wikipedia.org/wiki/Flyback_diode

Does your circuit include any protection for flyback? If so where is it installed?

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

There shouldn't be any inductive load fly back voltage issue. Our circuit is contineousely ON. We use PWM driver to bring the voltage to Zero in every cycle. We also have a 16bit voltage mointor in the circuit and we don't see any spike issue.

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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_bill »

Our circuit is contineousely ON. We use PWM driver to bring the voltage to Zero in every cycle.
If you are using PWM, your circuit is not continuously ON. PWM does not ramp voltage. It switches the drive current with a variable duty cycle.
http://en.wikipedia.org/wiki/Pulse-width_modulation
We also have a 16bit voltage mointor in the circuit and we don't see any spike issue.
It doesn't see the PWM pulses either because it is integrating over period longer than your 15KHz switching frequency. If you put a scope on it you will see both the PWM square wave and most likely a spike on the end of each one.

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M123456
 
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Re: INA 169 Current Sensing Board does not work reliably

Post by M123456 »

What I meant when I said Continueousely ON is that the cirucit does not physically switch OFF to generate the Fly Back voltage generated by the solenoid in the previouse Wikipedua link.

I am fully aware of how PWM works. We are using 5KHz to 15KHz to drive our motors. Do you see a concern of driving the motor with PWM?

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Re: INA 169 Current Sensing Board does not work reliably

Post by adafruit_support_bill »

PWM is switching the current ON and OFF to the motor at 15KHz. The example inductor in the Wiki article was a solenoid. But motor coils are inductive too and switching them ON and OFF with a PWM pulse will definitely generate flyback spikes.


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