REFLECTOR: Intercom Noise

Wed Mar 9 19:19:39 CST 2011

Oh yeah.  What's the rectifier for?

On 03/09/2011 09:01 AM, aminetech at bluefrog.com wrote:
>
>
> --- michalk at awpi.com wrote:
>
> From: Brian Michalk <michalk at awpi.com>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Intercom Noise
> Date: Tue, 08 Mar 2011 22:58:07 -0600
>
> You mention that 1, 8 and 9 show 11.8 volts with the mag on., and 
> voltage goes up with mag off.  That difference is because V=IR.  The 
> higher the current, the larger the voltage drop.  It's either a lot f 
> current, or a lot of resistance on the wire from the battery to that 
> terminal strip.  I would not expect an EI to pull that much.  Now, the 
> coil packs do draw a lot of power, but I'm not familiar if your EI has 
> them integrated.
> *The coil packs are powered from the same lead, but do they use power 
> when the engine isn't running?  Also there are other components.  I 
> think Power comes into #8 then to #7 (rectifier) then to #9 which 
> connects to A then to #5 (voltage regulator?) and then to #1 which of 
> the + lead to the EI.  Maybe all this contributes to the voltage drop?
> *
>
> Also, what is your voltage relative to?  Ground, yes, but which ground?
> *The ground at the starter, which has triple 0 wires, so there 
> shouldn't be much voltage drop there.*
>   Just like you have the forward voltage drop, you'll also have a 
> voltage rise on the ground before it gets back to the battery.  Get a 
> long piece of wire for your voltmeter.  Any small gauge will do, 
> because we are only needing a milliamp or so for the voltmeter.  
> Attach to the battery for your ground reference.  Now check your voltages.
>
> 1) battery -- probably 12.4 from your data
> 2) at positive terminal -- probably going to be above 11.8
> 3) at negative terminal --- probably going to be about .2 volts or so.
>
> For test 2), you want to be as close to 12.4 as possible.
> For test 3), you want to be as close to 0v as possible.
>
> See if you can clean some contacts to get those numbers better.
>
> On 03/08/2011 11:55 AM, aminetech at bluefrog.com 
> <mailto:aminetech at bluefrog.com> wrote:
>
>     A while back I reported that I found a bad ground and eliminated the intercom noise. After 20 hours of quiet operation, the noise is starting to return. It's infrequent and not to annoying, but I don't want it to get worse. I've attahced a pic of the barrier strip where I found the bad ground. (I'm sending the pic of the left side separately). My plane was built with a second battery and I believe this barrier strip was part of the backup system. The backup battery and alternator were removed before I bought the plane, so I'm not sure.  Here is what I know.
>
>     Terminal B is the EI mag wire.  It goes to the mag switch and the circuit returns through the shield and terminates at terminal C which appears to be grounded to the firewall.
>
>     Terminal 1 is the power wire going to the EI.  With the EI mag switch up, B is grounded and 1 has 11.8 v.  With the mag switch down, B is not grounded and 1 has no voltage.  Is this how EI s are normally wired?  I figured the mag switch would simply cut off the power.
>
>     Terminal 8 has 2 wires.  One is power from the master.  I don’t know where the other wire goes.  It reads 12.4 v with the master on.
>
>     The terminal 2 wire goes to the EI ground.  I need to check where it is grounded to.
>
>     Terminals 8 and 9 are connected and read 11.8 v when the EI mag is on and the voltage goes up to 12.4 v with the EI mag off.
>
>
>
>     Terminal 3 is the bad ground, and 4 is a mounting screw that is also grounded to the #3 wire. I didn't replace anything, just removed #3 and 4 and put back on. Before I removed them, the #3 screw was reading 5-900 ohms, now it is 0. With both 3 and 4 removed, the EI did not operate. With 4 connected the EI ran, but rough at low rpm. With 3 also connected it ran fine.
>
>     I would appreciate anything anyone can tell me about all this.  If there is something that I can remove, I would like to do so.
>
>     John
>
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