Could someone recommend a Diode (part#) to put across the posts on the relay/solenoids that I can easily purchase. Want to reduce spark jumping back at the switches.
Can I use the same diode part# for all three (trying to keep it simple)
Those diodes are significantly underrated for flyback application. I would look for something in the 3A If and 1000V Vr range, like the RGP30M-E3.
Even the 1N4001 (1A 50V) is adequate
I've seen 430V spikes from my intermittent duty starter solenoids. In fact, one such spike blew out my 400V rated flyback diode, shorted it to ground, and disabled my landing gear.
...I might be a little bit passionate about this!
I installed large MOVs across my starter contacts and - I'll probably be soundly flamed for this - I didn't run my starter solenoid in series with the master relay. It's on it's own separate circuit. The risk I'm taking, of course, is that the starter solenoid contacts weld themselves and the starter keeps cranking until the battery is dead. Since I had protected the contacts with the MOVs, I decided to take that risk. Flame away!
Yup, I have one of those, too.The diode discusison above is for the coil terminals here to short out the back current from the field collapse.
Hi Joe, I think these are two different topics - the diodes (or snapjacks) on relays is recommended, but Bob says that "spikes" going back into the electronics is an OWT.Bob Nuckolls posted, "Some ol' hangar tales just never die. . . . . The 'cranking spike' thingy doesn't exist."
Read his complete post HERE.
From my perspective Nuckolls is a new guy. He didn't start monkeying with this stuff 'till Cessna had begun using alternators, so he is not well placed to be the last word on this subject.
[snipped]
Nuckolls has done some really good stuff and I tip my hat to him, but I can demo blowing a small diode out with a starter spike any old time.
Cumulo, that is a very interesting scenario. But why does the master contactor drop out before the starter contactor? I assumed, maybe incorrectly, that the starter contactor has a stronger spring and would drop out first. If the starter contactor did drop out first, then most of the starter induced energy would be dissipated across the starter contactor contacts.
When you conducted the experiment that demonstrated blowing a small diode that is across the starter contactor coil, did the start contactor coil fuse also blow?
if the solenoid is powered directly from the bus, the grounding starter switch, on my aircraft at leased, is not fused.
If the battery is so weak that it can not hold the master contactor closed (less than 1/2 amp), then how can the battery send hundreds of amps to the starter motor?
Yeah, you could.
Let's start with why we install protection devices at the supply end of the wire (instead of on the device).
Explain that, and then we'll move forward.
Stalled starter current is greater than turning current because there is no back EMF. That is why lights dim when motors start.
A stalled motor is a fixed resistance (but will increase slightly as the wire heats up).
Stalled starter motor current is directly proportional to the voltage.
.
Correlation cannot be assumed to be causation.
Can you cite lab tests demonstrating starter current spikes failing current technology a/c electronics? Be aware that there *were* lab tests demonstrating early solid state a/c electronics failing during the start sequence. But the cause wasn't flyback spikes from the starter. Hint: Silicon isn't the only substance from which you can make a semiconductor, and wasn't what was used in early solid state a/c electronics.
Correlation cannot be assumed to be causation.
Can you cite lab tests demonstrating starter current spikes failing current technology a/c electronics? Be aware that there *were* lab tests demonstrating early solid state a/c electronics failing during the start sequence. But the cause wasn't flyback spikes from the starter. Hint: Silicon isn't the only substance from which you can make a semiconductor, and wasn't what was used in early solid state a/c electronics.
I still have CK722 transistors and 1N314 diodes. Hoping they make a comeback, like vinyl records. Anyone who understands the last sentence is ooold!
Did you buy those from Poly-Paks?I still have CK722 transistors and 1N314 diodes...
Did you buy those from Poly-Paks?