always on +12V connection in dash - 63 M20C

[bavareze]

Hi.  Looking to install a gt-50 chrono/g-meter in my mooney.  I need an always on +12V connection for the clock in order to have it remember the time.  The most obvious one was on the hot side of the master switch.  But I noticed that is not directly hooked to the battery and the voltage drops once the master is turned on.  Other than running a new wire through the firewall, do I have an option?  Thanks

 

http://www.fdatasystems.com/gt-50/

[Mooneymite]

A small rechargeable 12 volt battery?

[N601RX]

You could use 2 diodes to feed it and provide isolation between the two feed sources. One would feed from the màster switch you mentioned and the other could feed from any of the busses that are hot once the master is on.  You might also need a small capacitor to bridge the gap for the few milliseconds between when the master was flipped on and the other busses became hot.   The only problem this would cause is the voltage to read .7 volts low on the ground-50. 

[Yetti]

The later mooneys have a hot lead for the clock and the cabin light from the battery.  It's about 15 feet of wire from the comm bay.  Is your battery on the firewall?  Just run a wire.

Edited May 11, 2018 by Yetti

[carusoam]

How sensitive is the clock to the voltage drop?

The clock will have specs for it, that will indicate how crappy the power supply can be...

Some clocks actually have memory in them, a battery, or a capacitor, to hold enough power to be out of power for a while...

The M20C doesn’t have any hot circuits after the Master is off... The newer Mooneys keep interior lights, cigarette lighters and radio memory alive...

Expect the clock manufacturers have figured this out already.  Finding the right clock may be the next challenge...

PP thoughts only,

-a-

 

[bavareze]

10 minutes ago, N601RX said:

You could use 2 diodes to feed it and provide isolation between the two feed sources. One would feed from the màster switch you mentioned and the other could feed from any of the busses that are hot once the master is on.  You might also need a small capacitor to bridge the gap for the few milliseconds between when the master was flipped on and the other busses became hot.   The only problem this would cause is the voltage to read .7 volts low on the ground-50. 

I'm not the best in electronic design.  why would your design cause a .7 volts error?

 

what about this design, with a 12V rechargeable battery to power the GT-50, recharged (when the master is on) through a diode from the main bus...

[carusoam]

Why not just follow the instructions for install...?

http://www.aircraftspruce.com/catalog/pdf/10-03691manual.pdf

A few wires, hot, ground, interior lighting, and a CB...

Or follow advice about installing from the AS site...

(Great clock and easy to use. Installation is simple but you need a inline fuse holder for the wire from the main buss and a 1/2 amp fuse for the light feature.)

Check with your mechanic on the Best way to run the wires...

Where is your Master relay?  On the firewall, near the battery?  This is the place to get the hot juice, not the actual switch on the panel....

The switch only activates the relay. The relay does the actual switching from off to +12V...

PP thoughts only, not a mechanic...

Best regards,

-a-

[N201MKTurbo]

Just install a continuous duty solenoid like the master relay. Hook one side to the ships battery positive and the other side to the standby battery. Hook it up so it turns on with the master relay.

The only downside to this is if the standby battery is dead when you turn on the master, it will put a big load on the system. You could put a resistor in line with the relay to limit the current between the batteries. It will slow the charge rate of the standby battery but it will allow the standby battery to eventually get fully charged.

[N201MKTurbo]

I would just hook it up like you said originally.

[ragedracer1977]

I have the same clock.  We ran a wire from the battery.

[Piloto]

On the M20C the battery is next to the firewall so is only a matter of running a wire through one of the wire bundles. To avoid a possible fire, install a 1 amp  inline fuse next to the battery side. For accurate time set the clock to https://time.gov/ on your cell phone.

José

 

[bavareze]

On 5/10/2018 at 7:02 PM, carusoam said:

Why not just follow the instructions for install...?

http://www.aircraftspruce.com/catalog/pdf/10-03691manual.pdf

A few wires, hot, ground, interior lighting, and a CB...

Or follow advice about installing from the AS site...

(Great clock and easy to use. Installation is simple but you need a inline fuse holder for the wire from the main buss and a 1/2 amp fuse for the light feature.)

Check with your mechanic on the Best way to run the wires...

Where is your Master relay?  On the firewall, near the battery?  This is the place to get the hot juice, not the actual switch on the panel....

The switch only activates the relay. The relay does the actual switching from off to +12V...

PP thoughts only, not a mechanic...

Best regards,

-a-

the only problem is the instructions don't say where to get the continuous PLUS because they don't know the kind of plane I'm putting it in.

 

I'll run the wire to the main solenoid with an inlnie fuse then....

[carusoam]

The M20C, like most planes, doesn’t have many continuously hot wires to choose from... your mechanic will know you have an M20C...   

The POH has a complete electrical diagram.  You and your mechanic can choose the best spot to get the 12v source from... The hot side of the Master solenoid sounds pretty good.  Got a POH?

The source for the variable voltage / dimmer / interior lights is only slightly more tricky to find... there is a post where all the instruments lights get connected to behind the pilot side instrument panel...

Select a ground wisely too... often the instrument panel may lose its ground over the years... so plan on adding a ground or running a wire to the ground.

This is typical mechanic kind of activity. You can help him by having the parts, and POH and electrical drawing ready for him... be ready to update the WnB and make a proper note detailing the installation in the log...

Are you going to be able to assist in the install?  Removing and replacing cowling and anything else that gets in the way will save you about an hour of the total job...

PP thoughts only, not a mechanic...

-a-

[bavareze]

On 5/14/2018 at 9:10 PM, carusoam said:

The M20C, like most planes, doesn’t have many continuously hot wires to choose from... your mechanic will know you have an M20C...   

The POH has a complete electrical diagram.  You and your mechanic can choose the best spot to get the 12v source from... The hot side of the Master solenoid sounds pretty good.  Got a POH?

The source for the variable voltage / dimmer / interior lights is only slightly more tricky to find... there is a post where all the instruments lights get connected to behind the pilot side instrument panel...

Select a ground wisely too... often the instrument panel may lose its ground over the years... so plan on adding a ground or running a wire to the ground.

This is typical mechanic kind of activity. You can help him by having the parts, and POH and electrical drawing ready for him... be ready to update the WnB and make a proper note detailing the installation in the log...

Are you going to be able to assist in the install?  Removing and replacing cowling and anything else that gets in the way will save you about an hour of the total job...

PP thoughts only, not a mechanic...

-a-

to me it looks more like a job for an electrician not a mechanic... 

 

 

Edited May 21, 2018 by bavareze