How do I detect if a component is working if it's circuit is open?

sghioto

Joined Dec 31, 2017
2,335
I am not familiar with this semi conductor set up, could you run me through how this works?
When the normal power is applied the output of the 4N25 going to the MCU is basically a closed switch. If the resistor is open then the switch is also open. This just a basic schematic, additional component and values will depend on Battery voltage, resistor value capacitor,etc.
Steve G
Edit: the reason for the 4N25 is it completely isolates the MCU.
 

Delta prime

Joined Nov 15, 2019
843
it would be necessary to test the resistor with a discharge current.
Just knowing that the resistor is present by passing a low test current etc.. is not good enough
Hello their... all of you :) you need a who's watching the Watchers. That is a real scientific term that I just made up. :D
have a gander at this circuit
1597429103270.jpg
you can integrate any of and all of your wonderful circuits & idea's this is merely an option.Trip Circuit Supervision Circuit senses any fault either in the trip coil of breaker or trip circuit.:cool:
https://electricalbaba.com/how-does-trip-circuit-supervision-work/
 

LesJones

Joined Jan 8, 2017
3,133
I am guessing (As no information on values has been given.) that this is a high power (Hundreds of watts.) resistor and the working voltage is quite high (A few hundred volts..). I would suggest having a low value current sense resistor (Or hall current sensor.) in series with the negative end of the resistor. Use two ADC inputs on a microcontroller, One to measure the current sense value and one to measure the voltage on the positive end of the resistor. These two values monitored during the discharge would confirm that the resistor was working. I think a third ADC input should be used to monitor the voltage on the positive side of the capacitor to confirm that the relay was closed as this is a more likely point of failure as others have pointed out. (Monitoring the decay time of the voltage would be an alternative to using a third ADC input.)

Les.
 

MisterBill2

Joined Jan 23, 2018
8,460
It's a safety measure; the resistor discharges the circuit in an emergency, therefore ideally I want to be able to monitor it and make sure that in an emergency, the discharge relay will be opened and the discharge resistor will be able to discharge the circuit. It may not be possible, but I thought I would post it up here to see whether any of you guys (which almost definitely have more component knowledge) knew of a way of checking that it is still a working resistor.
This purpose does not make sense. A more detailed explanation pf what is intended to happen when that resistor is switched on may provide some understanding.
 

jpanhalt

Joined Jan 18, 2008
11,088
It made sense to me that a "safety" device needs to be checked. I check it on my guns, and when I worked, we tested fire showers, masks, and other safety devices routinely.

Here's a specific example using relays. For launching model sailplanes, we use high power (contest limit is 200 A, but some designs can exceed that) 12-V winches. A heavy-duty starter relay is used for control, but occasionally even those contacts would weld closed. There is a second battery cut-off switch for emergency. In some cases, a safety person with an ax stood by the battery cables. Very soon thereafter, two relays in series were implemented, and those relays had diode indicators as described above. If both diodes weren't on before launch, which indicated both relays were open, you didn't launch.
 

MisterBill2

Joined Jan 23, 2018
8,460
Once again, the purpose of that"discharge resistor" is not adequately explained. What is it discharging?is it intended to discharge whatever energy remains in the inverter assembly? Or is it intended to discharge the battery pack? The difference is rather huge. If it is intended to remove drive power in the event of a controller fault that prevents shutoff, then having a redundant series contactor would be a far better choice.
That option has just been described.
In addition, there are a wide variety of double-break contactors available that will still open the circuit if one side contact welds shut. And as a last resort, as part of the system protection scheme, circuit breakers with external trip connections are also available. Two double-break contactors in series will provide four breaking points in the circuit, and a monitor for each contact would certainy provide enough protection.
One more point is that if the "discharge circuit" is activated with either of the drive power relays closed, the power dissipated in that related resistance will be very large, and the heat generated will be a serious hazard. So that condition must also be considered.
 

MisterBill2

Joined Jan 23, 2018
8,460
Post #4 shows that the resistor is to discharge the inverter capacitance, not the battery.
There is nothing in any of those figures to indicate that the battery connection must be off for the discharge circuit to enable. Thus my comment. If the need is simply to assure that all capacitance in the inverter circuitry has discharged, the very simple scheme of multiple LED plus dropping resistors would both discharge and indicate the presence of charge in the circuit. And the cost for a quadruple redundant scheme will be far less than the switching device shown.

And now one more question is "just who is to be protected and under what circumstances and conditions?" An inverter in an electrical vehicle is in an enclosed package not quickly openable. And the connectors outside are designed to prevent unintentional contact with the conductors. So just what emergency situation is anticipated that would require such a function?
 

jpanhalt

Joined Jan 18, 2008
11,088
It's an electric car. You might consider discharging the battery to "zero" and damaging it as a reasonable precaution before servicing the electronics; I don't. Usual procedure with any car is to disconnect the battery.
 

MisterBill2

Joined Jan 23, 2018
8,460
It's an electric car. You might consider discharging the battery to "zero" and damaging it as a reasonable precaution before servicing the electronics; I don't. Usual procedure with any car is to disconnect the battery.
Running the battery to flat dead is the poorest possible choice that there is! Disconnecting the battery is far more sensible, but that still possibly leaves the hazard of a charged capacitor inside the inverter package. Evidently that is the hazard that the TS is intending to reduce. It may be possible that in the event of a violent collision the vehicle may be damaged enough so that the inverter package is opened and the internal connections could be touched. It might also be that an individual not familiar with the internals of an automotive inverter system would open the package and contact a charged capacitor.
In some countries the safety rules have been written to protect drunks bent on self destruction, and it may be that this EV is intended for such a market.
 

jpanhalt

Joined Jan 18, 2008
11,088
Running the battery to flat dead is the poorest possible choice that there is! Disconnecting the battery is far more sensible, but that still possibly leaves the hazard of a charged capacitor inside the inverter package.
Congratulations, that's what the TS is trying to do and is the problem my comments tried to address. But then, your comment (below) indicates you needed the TS to clarify that the battery was disconnected despite clearly showing it that way and making common sense.

There is nothing in any of those figures to indicate that the battery connection must be off for the discharge circuit to enable.
1597500176262.png
 

MisterBill2

Joined Jan 23, 2018
8,460
Congratulations, that's what the TS is trying to do and is the problem my comments tried to address. But then, your comment (below) indicates you needed the TS to clarify that the battery was disconnected despite clearly showing it that way and making common sense.



View attachment 214806
What we see is that it is possible to disconnect the battery before engaging the discharge circuit, but there is nothing that demands it being disconnected.
There is a quite simple circuit change that would automaticly discharge every time the maim power switch was operated. That would require changing the main power control switch to include a normally closed contact, and then using that normally closed contact for the discharge function. very simple and inexpensive.
 

sghioto

Joined Dec 31, 2017
2,335
The TS said: "This is a generic schematic, with the resistor I need to monitor in red."
I asked the question about disconnecting the battery before activating the discharge circuit back in post #13.
To my understanding that was verified in post #19.
Steve G
 

MisterBill2

Joined Jan 23, 2018
8,460
The TS said: "This is a generic schematic, with the resistor I need to monitor in red."
I asked the question about disconnecting the battery before activating the discharge circuit back in post #13.
To my understanding that was verified in post #19.
Steve G
OK, and here is a generic answer: In many fire alarm systems there is a function called loop monitoring, where a smal current is constantly flowing through all the devices in the circuit being monitored. The supervisory system constantly observes that current and signals an alarm if it changes beyond some limits. You could monitor a small current flowing through that resistor and verify that it was within some limits, indicating that the main resistor was still in place.
 
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