Hi everyone,
I'm very new to electric circuit design, a mechanical engineer here so excuse me for my lack of knowledge on the matter. I worked with another coworker to put together this circuit however am running into issues which neither of us can figure out and was hoping that I could use your guys' knowledge to help guide me through this troubleshooting, as I have a feeling it is probably a rather simple problem that us MechE's are just overlooking. Note: I've linked each of the components listed to their respective datasheets for reference, and vendor part numbers.
The circuit is a control circuit which I am putting into a testing device in order to ensure that the lithium ion battery does not succumb to a low voltage which would damage it - the circuit's intention is to provide 2 set points which will trigger different battery protection actions:
I tried to draw a diagram of how the circuit is arranged:
With this set up the transistors and everything works just fine at ambient temperature (~25°C), however when I've tested it in a freezer at about -10°C the transistors act really weird, prematurely giving off signals which light up the red LED at a voltage higher than the 7.3V set point, and will get to a point where the system shutdown transistor is pretty much flipping the relay, such that if you hit the NC off pushbutton the system will shut down and not turn on again (as the transistor is not permitting it). You are able to simply put your finger on either transistor and you can notice either the relay coil voltage getting further away from the trip voltage, or the red led fade away....it seems as though this is a temperature issue? I used to have a 10kOhm where the 1.05 kOhm is now and a 72kOhm where the 10kOhm is - we changed these to lesser resistances thinking this would fix the problem to no avail.
The only thing is that these transistors are rated to -65°C so we are just completely flabbergasted at the whole problem.
Is there something simple in the design of the circuit that we are overlooking? Are we using the transistors in an appropriate manner for this control circuit?
ANY help would be GREATLY appreciated...I've been hitting my head against the wall for weeks over this problem.
THANKS,
Jeff
I'm very new to electric circuit design, a mechanical engineer here so excuse me for my lack of knowledge on the matter. I worked with another coworker to put together this circuit however am running into issues which neither of us can figure out and was hoping that I could use your guys' knowledge to help guide me through this troubleshooting, as I have a feeling it is probably a rather simple problem that us MechE's are just overlooking. Note: I've linked each of the components listed to their respective datasheets for reference, and vendor part numbers.
The circuit is a control circuit which I am putting into a testing device in order to ensure that the lithium ion battery does not succumb to a low voltage which would damage it - the circuit's intention is to provide 2 set points which will trigger different battery protection actions:
- Signalling a low battery red LED, turning on the LED at a battery level of ~7.3V
- Signalling a relay to switch off and kill the system when the battery level reaches ~6.3V
I tried to draw a diagram of how the circuit is arranged:
With this set up the transistors and everything works just fine at ambient temperature (~25°C), however when I've tested it in a freezer at about -10°C the transistors act really weird, prematurely giving off signals which light up the red LED at a voltage higher than the 7.3V set point, and will get to a point where the system shutdown transistor is pretty much flipping the relay, such that if you hit the NC off pushbutton the system will shut down and not turn on again (as the transistor is not permitting it). You are able to simply put your finger on either transistor and you can notice either the relay coil voltage getting further away from the trip voltage, or the red led fade away....it seems as though this is a temperature issue? I used to have a 10kOhm where the 1.05 kOhm is now and a 72kOhm where the 10kOhm is - we changed these to lesser resistances thinking this would fix the problem to no avail.
The only thing is that these transistors are rated to -65°C so we are just completely flabbergasted at the whole problem.
Is there something simple in the design of the circuit that we are overlooking? Are we using the transistors in an appropriate manner for this control circuit?
ANY help would be GREATLY appreciated...I've been hitting my head against the wall for weeks over this problem.
THANKS,
Jeff