Is it safe to short wires together?

5 years 2 months ago #29530892 by Peter Balch
We are using an HBL2360 in a differential-drive vehicle. The vehicle will have to pass an ISO test. Part of the test involves choosing any pair of wires in a multi-core cable and joining them together to see what happens. Fuses can blow or whatever but the vehicle must remain in a safe state and must be undamaged.

The 25D connector on the HBL2360 contains a 5V supply with a max current of 200mA. What happens if that is connected to ground (or any other wire in the 25D connector)? Does the HBL2360 limit the current to 200mA? Does it shut down? Or is it damaged?

Peter

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5 years 2 months ago #29530893 by TechSupport
Not sure why you would ever feel the need to short the 5V directly to ground unless you are looking to damage the logic control circuit.

You will draw high current that will ultimately cause the logic voltage to collapse and further damage the logic card.

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5 years 2 months ago #29530894 by Peter Balch
As I said, part of the ISO test is to check that the system can survive damage to cables. To simulate that, the testers short together the conductors in a cable, two at a time. It's part of a single component failure analysis.

No doubt many Roboteq products are used in systems that are expected to fail safely. For instance, The HBL2360 joystick input features safety guard bands in case the joystick cable is cut. So your designers have assumed that such faults may occur. What happens if the joystick cable is crushed and the conductors touch each other?

Normally, once might put a fuse at a suitable point in a conductor. But in the case of the 25D connector, it's hard to see how to fit a fuse before a wire leaves the connector housing as part of a multicore cable.

Presumably, the HBL2360 5V supply comes from a 48V-to-5V buck converter. The majority of converter chips have short circuit protection. Are you saying that the converter used in the HBL2360 does not?

If the logic card supply falls to zero, why would that damage it?

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5 years 2 months ago - 5 years 2 months ago #29530895 by TechSupport
The 5V circuit is created to the MCU on the I/O connector is recreated on the logic card. The original down converter dc/dc converter is on the main power board. The HBL2360 is a 2 part system, logic card, and power board. So if for whatever reason your joystick wires get crushed and short together, anything can happen. The likely result is that either the voltage at the analog input would read a 0V or +5V depending on what is shorted(5V or ground to wiper pin).

There are cases where if something is mis-wired on the I/O connector, it prevents the controller from turning on. But if it is a direct short, the 5V rail on the logic card will do what any direct short to power does, draw high current and then damage the circuitry.

If ground is shorted across other pins on the I/O, the likely result is you'll fry the MCU preventing the controller form working.

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5 years 2 months ago #29530896 by Peter Balch
> If ground is shorted across other pins on the I/O, the likely result is you'll fry the MCU preventing the controller form working.

Are you sure? According to your documentation, all the outputs are open drain. So shorting them to ground would have no harmful effects. The inputs can be shorted to ground of course.

I don't know of any MCU that is damaged by a short circuit to either Vss or Vdd.

Can you provide a circuit diagram of a typical output stage?

> a direct short, the 5V rail on the logic card will do what any direct short to power does, draw high current and then damage the circuitry.

That's hard to believe - your products seem better designed than that. Any half-decent engineer would do it properly. Can you ask them please?

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5 years 2 months ago #29530897 by TechSupport
The digital outputs are the open drain. The 5V is a power source.

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5 years 2 months ago #29530898 by Peter Balch
> If ground is shorted across other pins on the I/O, the likely result is you'll fry the MCU

> The digital outputs are the open drain.

So shorting them to ground would have no harmful effects. In fact, shorting ground across any of the data I/O pins would have no harmful effects.

I find it hard to have confidence in what you're saying.

According to Table 6 of the manual, "Output Short circuit threshold" of an Output 1.4A whereas the "5V Output Current" is 200mA. So the "5V Output" is unable to provide enough current to damage an "Output pin".

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5 years 2 months ago - 5 years 2 months ago #29530899 by TechSupport
The worse thing that can happen if there are shorts at the 25pin
connector wires is that there will be a short between 5V and ground.

The DCDC converter inside the controller is protected against shorts.
So when the short goes away, the controller will work normally again.

No other shorting of any pin and any other pin can do any damage unless you are shorting higher voltage sources(separate external power source) to the I/O.
The following user(s) said Thank You: Peter Balch

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5 years 2 months ago #29530900 by Peter Balch
Excellent.

That's what I was hoping to hear. It makes our job a lot easier.

Thank You

Peter

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5 years 2 months ago #29530901 by LROBBINS
Whew, I too am glad that you straightened out this information. I was already thinking about things like using a 5V wire only in the DB25 and gnd only in the DB9 to make sure they can't be shorted; over-current protections is much better!
Ciao,
Lenny

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