mmarien
Murray M.
Do the voltmeter pins need any fuses like the AMPS shunt pins? or can I just connect pin 1 and 2 to the main or avionics bus directly?
EMS Voltmeter Pin Connections
- Thread starter mmarien
- Start date
mmarien
Murray M.
That sounds logical. But how far do you go then? So far we have fuses on the Voltmeters and AMPS pins.
What about the RPM input. Is the 30kohm resistor enough protection or do you also need a fuse?
I suspect thermocouple pins and the general purpose pins are fine as long as they are connected to the sensor they are intended for.
What about the RPM input. Is the 30kohm resistor enough protection or do you also need a fuse?
I suspect thermocouple pins and the general purpose pins are fine as long as they are connected to the sensor they are intended for.
- Joined
- Mar 23, 2005
- Messages
- 13,226
What really matters is if what the wire is connected to can source a lot of current.
Clearly the battery and any part of your main bus can. So the AMPS and volts input should be fused. A resistor works as well as a fuse for wire protection, but in these cases, it would mess up the readings so you can't do that.
The RPM input wants a resistor, not a fuse. In that case, we want to make sure that if your wire shorts, the engine doesn't turn off. The P-Lead is designed to be grounded in order to turn the engine off. This means it develops very little current and can never harm a wire. You'd be hard pressed to find a fuse that would blow on a short. So the resistor limits current to the point that the wire is fine for sure and the engine stays running. It's all you need. The resistor doesn't mess up the readings since we count pulses, not voltage on the RPM wires, so the voltage drop the resistor creates isn't a problem.
Other sensors like oil pressure and thermocouples just can't produce more than a few mA no matter where they are shorted. So no fuse is needed.
Clearly the battery and any part of your main bus can. So the AMPS and volts input should be fused. A resistor works as well as a fuse for wire protection, but in these cases, it would mess up the readings so you can't do that.
The RPM input wants a resistor, not a fuse. In that case, we want to make sure that if your wire shorts, the engine doesn't turn off. The P-Lead is designed to be grounded in order to turn the engine off. This means it develops very little current and can never harm a wire. You'd be hard pressed to find a fuse that would blow on a short. So the resistor limits current to the point that the wire is fine for sure and the engine stays running. It's all you need. The resistor doesn't mess up the readings since we count pulses, not voltage on the RPM wires, so the voltage drop the resistor creates isn't a problem.
Other sensors like oil pressure and thermocouples just can't produce more than a few mA no matter where they are shorted. So no fuse is needed.
mmarien
Murray M.
Thanks - That answers the question - and more.
I guess if I was thinking ahead, I would have just added a 1A breaker to the bus and connected the voltmeter wire there. If the inline fuses go I'll have to be crawling under the panel looking for them.
I guess if I was thinking ahead, I would have just added a 1A breaker to the bus and connected the voltmeter wire there. If the inline fuses go I'll have to be crawling under the panel looking for them.