The International Cessna 170 Association

DaveF wrote:Depends on the design of the LED module. If it's just a string of LEDs or an LED with a series resistor, then reverse bias will mean no light. No idea what Richard's lamp is, but most LED lighting uses dc-to-dc converters, which are often designed to be polarity insensitive. Hook 'em up either way, the circuit takes care of it for you. My LED landing lights are that way.

That's not been my experience. I"ve bought several dozen various LED's intended for automotive use and they ALL are polarity sensitive. Even those little "wedge" lites intended to replace 194/164 indicator and parking lamps.... if you plug 'em in and they don't work..... reverse them and they do.

gahorn wrote:

DaveF wrote:Depends on the design of the LED module. If it's just a string of LEDs or an LED with a series resistor, then reverse bias will mean no light. No idea what Richard's lamp is, but most LED lighting uses dc-to-dc converters, which are often designed to be polarity insensitive. Hook 'em up either way, the circuit takes care of it for you. My LED landing lights are that way.

That's not been my experience. I"ve bought several dozen various LED's intended for automotive use and they ALL are polarity sensitive. Even those little "wedge" lites intended to replace 194/164 indicator and parking lamps.... if you plug 'em in and they don't work..... reverse them and they do.

Sounds like we agree.

Perhaps there is something to both John and Miles' comments. A truly parallel circuit should provide correct operation of both the LED and motor. Maybe there is something with how the light or motor complete their circuits to ground. The ground wire in this installation goes directly to the motor case which shares a wire that goes inside the motor case. The metal case is screwed to the beacon base which is where the LED gets its ground. I suppose it is possible that the polarities of the LED and motor don't match. Normally a DC motor will simply run backwards when polarity is swapped but when mixed with a capacitor and/or LED, things might not agree. In other words, maybe the LED will run with either polarity but it needs to match what the motor wants. Not sure if that makes sense anywhere but in my head!

BTW, I'm sorry George for your new RAM. But probably not as sorry as I am about my new Chevy!! What a disappointment!!

DaveF wrote:

gahorn wrote:

DaveF wrote:Depends on the design of the LED module. If it's just a string of LEDs or an LED with a series resistor, then reverse bias will mean no light. No idea what Richard's lamp is, but most LED lighting uses dc-to-dc converters, which are often designed to be polarity insensitive. Hook 'em up either way, the circuit takes care of it for you. My LED landing lights are that way.

That's not been my experience. I"ve bought several dozen various LED's intended for automotive use and they ALL are polarity sensitive. Even those little "wedge" lites intended to replace 194/164 indicator and parking lamps.... if you plug 'em in and they don't work..... reverse them and they do.

Sounds like we agree.

I'd swear you said that "most LED lighting uses ...converters, which are ...polarity insensitive. Hook 'em up either way and the circuit takes care of it for you."
And I was sayin' that was NOT what I'd experienced. I find them polarity sensitive. You can only hook the ones I've had up ONE way if you want them to work.

How does that sound like we were saying the same thing, in agreement?

gahorn wrote: I'd swear you said that "most LED lighting uses ...converters, which are ...polarity insensitive. Hook 'em up either way and the circuit takes care of it for you."
And I was sayin' that was NOT what I'd experienced. I find them polarity sensitive. You can only hook the ones I've had up ONE way if you want them to work.

How does that sound like we were saying the same thing, in agreement?

Sounds like "most of the LED's Dave bought" had circuitry to make the module polarity insensitive, and "most of the LED's that George bought" did not have that circuitry. Not hard to fathom at all. Neither is indicative of how "most" LED modules are designed.

Thanks Miles!!

DaveF wrote: If it's just a string of LEDs or an LED with a series resistor, then reverse bias will mean no light.

gahorn wrote:if you plug 'em in and they don't work..... reverse them and they do.

So it does sound like we agree.

But that whole thing was a distraction from the real problem of why Richard's beacon doesn't work with an LED lamp but does with a normal bulb or with no bulb at all. It sounds like the unit isn't wired as we assume it is. Richard, send it to me and I'll figure it out!

DaveF wrote: Richard, send it to me and I'll figure it out!

Ha! Sorry Dave, but this one is too interesting for me to give to someone else!! I haven't had a chance to get back to the hangar to look into this. My CFII checkride is on Sunday so airplane disassembly is not an option until next week! I'll let you know what I find when I get a chance to dig into it.

Dang!

This is a continuation from the off-topic discussion on page two of this thread regarding dampened crankshafts. The connection to LED lights is that these lights use less current and thus provide an alternative to installing 35 amp. generators which require dampened crankshafts, i.e. crankshafts with counterweights.

canav8 wrote: ↑Sun May 10, 2009 3:55 pm Hi Karl, no I am not referring to the hole. That is not a true indication of an undampened crank according to the IPC. Please look at the pictures Johneb has posted. The comparison is looking at the crankshaft part numbers on all C-145,C-145H, C-145-2, O-300A,B,C,D motors. If you look near the front of the Continental engine IPC, there is a chart that shows an on list with codes. These codes show which crank part number applies to which engine. All of the part numbers indicate a crank that is dampened by part number. I hope this helps.

As shown in the attached service bulletin, this 1/4” hole in the prop flange is not to distinguish a dampened crankshaft from an undampened one, it is there to distinguish the C-125 crankshaft from the C-145 crankshaft. Many of us have confirmed that our cranks have the hole and the counterweights. The C-145 has a 1/4” longer crank throw than the C-125. Continental used the hole in the flange as an easy way to tell the two nearly identical cranks apart. From page six of the Overhaul Manual:

C-145 crankshafts have a slightly longer crank throw than those of the model C-125. … Early production C-145 crankshafts had no counterweights and were identified by a 1/4” diameter hole drilled between propeller bolt bushings through the propeller flange. … The letter “D” in a C-145 serial No. denotes a dampened shaft.

If you have an 8-bolt crank without the hole, it’s possible you may have a C-125 crank.