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Magneto and VM1000 Dimming

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dean.psiropoulos(at)veriz
Guest

Posted: Sat Nov 10, 2007 11:57 pm Post subject: Magneto and VM1000 Dimming

Functional checkout of my (Nuckolls inspired)electrical system has gone well

so far with no smoked wiring or equipment.  I bought an equivalent of an

Odyssey 680 a couple years ago and trickle charged it occasionally hoping it

would at least be good enough to do electrical checkout, first engine start

and maybe a few times around the pattern. But it appears that is not the

case. Voltmeter says there is 12.5 volts at the terminals but it can't

produce enough amps to fire the battery contactor or even make some sparks

when shorted, pretty pathetic. I substituted a Panasonic 4.5 amp hour sealed

lead acid battery that I bought second hand about 6 years ago. It's got

enough oomph for the checkout but I'll need a new 680 for 1st engine start.



I did a test on my magneto P-lead (one mag on left side, electronic on right

side)with an ohm meter.  Thinking that when the key switch is in the off

position, the resistance across the p-lead should measure close to dead

short and, it does.  By the same logic, I thought that when the mag was

ungrounded the resistance across the pleads (I used a shielded wire with the

shield grounded at the magneto through the key switch as Bob recommends, no

local grounding).  But when I measured across the p-leads at the magneto the

resistance only went from 0.2 ohms to 0.4 ohms when I turned the key.  Not

an appreciable increase in resistance but it was consistent (happens every

time) and measurable. I thought maybe I had a faulty key switch but not so,

I removed one p-lead from the mag and made the same measurement and the

resistance with the key in that mag's position read infinite.  I suspect

that there is some thing about magnetos I don't know and that this is not a

problem but would like to be sure. Anybody ever done this test?  Did you get

the same results?



Also checked out the VM-1000 and it seems to work fine except for dimming.

I used one of the B&C dimmers connected to the VM-1000 dimming input but I

don't seem to get any dimming action (backlight works ok).  Anyone else

experience this? Have I missed something in the VM manual and it doesn't use

an external dimming input?  Any thoughts? Thanks.



Dean

RV-6A N197DM

closer to 1st flight.

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Bruce(at)glasair.org
Guest

Posted: Sun Nov 11, 2007 1:08 am Post subject: Magneto and VM1000 Dimming

Yea, I believe the VM1000 only dims from the front panel.



Bruce

www.Glasair.org

 

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mprather(at)spro.net
Guest

Posted: Sun Nov 11, 2007 7:06 am Post subject: Magneto and VM1000 Dimming

I went through that too, Dean..



If you measure the resistance between the p-connection on the mag and 

the mag case, you are either measuring the resistance through the 

primary winding of the coil in the mag, or through the breaker points in 

the mag (depending on where mag/engine are positioned - making the 

points open or closed).  In either case, it's a low resistance value.  

Normal behavior.

Regards,



Matt-



DEAN PSIROPOULOS wrote:

 	  Quote: 	
		   



 Functional checkout of my (Nuckolls inspired)electrical system has gone well

 so far with no smoked wiring or equipment.  I bought an equivalent of an

 Odyssey 680 a couple years ago and trickle charged it occasionally hoping it

 would at least be good enough to do electrical checkout, first engine start

 and maybe a few times around the pattern. But it appears that is not the

 case. Voltmeter says there is 12.5 volts at the terminals but it can't

 produce enough amps to fire the battery contactor or even make some sparks

 when shorted, pretty pathetic. I substituted a Panasonic 4.5 amp hour sealed

 lead acid battery that I bought second hand about 6 years ago. It's got

 enough oomph for the checkout but I'll need a new 680 for 1st engine start.



 I did a test on my magneto P-lead (one mag on left side, electronic on right

 side)with an ohm meter.  Thinking that when the key switch is in the off

 position, the resistance across the p-lead should measure close to dead

 short and, it does.  By the same logic, I thought that when the mag was

 ungrounded the resistance across the pleads (I used a shielded wire with the

 shield grounded at the magneto through the key switch as Bob recommends, no

 local grounding).  But when I measured across the p-leads at the magneto the

 resistance only went from 0.2 ohms to 0.4 ohms when I turned the key.  Not

 an appreciable increase in resistance but it was consistent (happens every

 time) and measurable. I thought maybe I had a faulty key switch but not so,

 I removed one p-lead from the mag and made the same measurement and the

 resistance with the key in that mag's position read infinite.  I suspect

 that there is some thing about magnetos I don't know and that this is not a

 problem but would like to be sure. Anybody ever done this test?  Did you get

 the same results?



 Also checked out the VM-1000 and it seems to work fine except for dimming.

 I used one of the B&C dimmers connected to the VM-1000 dimming input but I

 don't seem to get any dimming action (backlight works ok).  Anyone else

 experience this? Have I missed something in the VM manual and it doesn't use

 an external dimming input?  Any thoughts? Thanks.



 Dean

 RV-6A N197DM

 closer to 1st flight.

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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recapen(at)earthlink.net
Guest

Posted: Mon Nov 12, 2007 5:04 am Post subject: Magneto and VM1000 Dimming

My VM1000 would dim with my B&C dimmer....then I started having problems with the backlight not working at all.  JPI told me there was something wrong with my wiring - checked that.  I haven't flown yet but they wouldn't repair it - and wanted too much money for me to give JPI.  I bought an Advanced Flight Systems AF3400EM - used most of the existing wiring and am a happy camper now.



Parting out my VM1000 to keep others going.....



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