First Engine Start-Master Relay Help

Just had my first engine start today. WooHooo!!!
I did realize an electrical problem prior to the start where the solenoid & Master relay join. I placed a red jumper to bridge the circuit on the master relay. (See image link below) I had to remove it once started to enable my eis4000 and avionics to run. I'm running the exp2 bus which isolates the avionics bus in start mode.
The engine ran terrific, nice & smooth through all rpm ranges up to 1700.
That's as high as I went today
Ran it for .2 hr, here's the readings just prior to shutdown

Oil Temp=119
Oil Pressure=68
EGT 1177, 1191, 1146,1184
CHT 309, 342,342,358

Any advice on my electrical problem?
Should my diode be connected in the place of my jumper?
Would the diode there enable the starter to engage, then release to enable the closed circuit to power the avionics bus?

SolenoidRelayConnection

you do have two .063 copper bars inbetween master and starter solenoids? it's hard to tell from the photo, but it doesn't look like.. not sure if that'd cause any issues..

The solenoid has left side to batt +.
Center is from the bat switch terminal.
Right side has 1 copper bar to the relay.
This is where I had the diode connected incorrectly.
The center master relay lug has the starter switch wire.

My red jumper is connected to the relay left post to the center lug.
Although from other pix I've seen, has the diode connected from the left bat side to the center solenoid.

My thoughts where, will this enable the starter to engage, then release to enable the avionics bus to power up?. I guess I don't completely understand the diode.
I know it provides a one way current but, once the starter switch is disengaged, does the circuit close?

It's difficult to test with that prop turning.

TIA.

Aeroelectric Connection

Hi Dan,

I think there is a little more to wiring the battery contactor than I can see in your picture. Here's a picture from the Aeroelectric Connection website that shows how to wire the battery contactor. Note the diode. Perhaps your contactor is different.



There are other things that can be used in place of the diode as "spike catchers", like the Perihelion Design "snapjack". http://www.periheliondesign.com/

If you don't already have the Aeroelectric Connection book, I strongly recommend it. It really helped me a lot.

See the above photo for how I wired my VAN'S battery and starter contactors. NOTE that the contactors are slightly different than what Bob Nuckolls describes in his AeroElectric photos, but the concept is the same.

In the above photo, here's the deal with the diodes...

Diode type: Radio Shack #276-1141 (2-pack, 3A, 50V barrel diode)

Battery contactor diode: stripe side to ground, other side to the switch terminal

Starter contactor diode: stripe side to the switch terminal, other side to ground

Also, is it just me or are those pretty fat wires going to your switches? Those appear to be 12 AWG or so?

Iirc, I used 22 AWG (maybe it was 20 AWG) for the master & starter switch circuits. There wasn't a lot of current going through those wires.

Here's another photo with my switch wires connected (no boots, no heat shrink covering the copper bars, and no alternator connection yet), in case that helps...

DanLandry said:

The solenoid has left side to batt +.
Center is from the bat switch terminal.
Right side has 1 copper bar to the relay.
This is where I had the diode connected incorrectly.
The center master relay lug has the starter switch wire.

My red jumper is connected to the relay left post to the center lug.
Although from other pix I've seen, has the diode connected from the left bat side to the center solenoid.

My thoughts where, will this enable the starter to engage, then release to enable the avionics bus to power up?. I guess I don't completely understand the diode.
I know it provides a one way current but, once the starter switch is disengaged, does the circuit close?

It's difficult to test with that prop turning.

TIA.

Click to expand...

Dan,

I think you are trying to get the the solenoid to do too much? Apologies if you know this already, but the whole point of a solenoid is to apply a very small current to switch a much larger one - that avoids bringing large currents to the panel switch (heavy wires) and trying to switch large currents with a simple switch (switch would burn up in no time). So the solenoids are just heavy duty switches. The diode just stops unwanted power spikes - you don't have to have them. You seem to be missing a feed to the exp bus? There should be a feed from the switched side of the battery solenoid to the exp bus. I think you will have to use the switch of the exp bus to switch on the avionics bus, the only other way is to bypass the switch and have the avionics come on line with the battery master - the exp bus will then cut that circuit during cranking (as long as you feed the starter switch in the cockpit to the "start" terminal on the exp bus, as well as to the starter solenoid). It really is easier to use the Av Master Switch provided with the exp2bus to bring the avionics up after engine start. If you need a radio or an EFIS on before start you can use the CDEL input, with a switch, that applies power to the AB6 output - however - If you switch on CDEL I don't think that output will be switched off when the starter is engaged.
Hope this helps, Pete

dan said:

Also, is it just me or are those pretty fat wires going to your switches? Those appear to be 12 AWG or so?

Iirc, I used 22 AWG (maybe it was 20 AWG) for the master & starter switch circuits. There wasn't a lot of current going through those wires.

Here's another photo with my switch wires connected (no boots, no heat shrink covering the copper bars, and no alternator connection yet), in case that helps...

Click to expand...

Dan,
You're setup closely resembles mine. It's probably because I modeled it from yours originally.
My confusion on my setup, is the relay left post has 12v but does not open the circuit to the center lug when engaging the starter button unless I jump the circuit. Can you explain what the diode to ground accomplishes here?

Thanks everyone for your help here. It's difficult to assess & meter.

DanLandry said:

You're setup closely resembles mine. It's probably because I modeled it from yours originally.
My confusion on my setup, is the relay left post has 12v but does not open the circuit to the center lug when engaging the starter button unless I jump the circuit. Can you explain what the diode to ground accomplishes here?

Click to expand...

I'm sure somebody will step in here and correct me, because my understanding of the electromechanics of it is limited...but the diode is there to "catch spikes" in voltage that are created when the coil of the contactor collapses (i.e. as you release the starter engage switch or what not). I believe the idea is to preserve the life of the switch and possibly avoid the spike propagating to the bus as well. Again, I'm no expert, and my terminology is likely off here. Somebody who knows this stuff cold can hopefully comment.

I followed Bob Nuckolls' recommendation and other RV builders' examples on the diodes and haven't had any problems whatsoever in many hours and lots of starts. Would I have had an issue had I left the diodes off? No idea!

With Van's contactors (at least the ones I got from Van's in my FWF kit circa 2003), the master contactor's switch terminal needs to be GROUNDED to close, whereas the starter contactor's switch terminal needs VOLTAGE to close. This is a key difference in these two contactors' design.

Dan, you are pretty close in your description.

Lemme give it a try now.

The "theory" for a diode is to impede any voltage generated by the starter motor from entering the wiring system.

How it "can" happen is kinda techy, buuuuuut... the starter motor has all three things necessary for generating electricity.

1) Magnetic field
2) Motion
3) A coil cutting flux

The theory goes like this:

At the moment the key is released after activating the starter there is a possibility of "generator action" from the starter. This is due to the fact that the starter is still spinning within a magnetic field and the armature and rotor fields are cutting flux from the residual magnetism remaining in the poles.

This "generator action" theoretically could allow an errant, unregulated voltage to find it's way beyond the starter solonoid for the split second it may still be in the closed position.

It will also extend the longevity of the starter solonoid by keeping this "generator action" from the electrical system, as it could be reversed in polarity and at the very least cause severe arcing within the solonoid leading to eventual premature failure of the component.

Blue connectors I think are 16-22 AWG. I forget, though.

I hope this helps!

CJ

Thanks Dan & John.
I believe you guys may have nailed it.
With the starter key engaged I get 12v across the master relay.
Disengaged, I was getting 2v. Someone suggested it may be "ghost" voltage, but it may be enough to deactivate my avionics bus.
Dan, I'll try your setup with the master relay diode to ground & see if that resolves the problem.

Starter solonoid

Does it matter which large (left or right) terminal you install the battery cable to on the starter solonoid? It works better in my install to connect the battery cable to the right terminal ( small ?s? terminal being left side)
Thank you
Bob

The correct answer is, 'it depends'. Many Starter solenoids (typically ones designed for engines with old Kettering ignitions) have an additional 'small' terminal that may be tied internally to one of the 'fat' terminals. It's intended to bypass the ignition system's 'ballast' resistor during starting. So if you hook up the fat wires backwards, you may have an additional always-hot terminal on the contactor. Not really a problem, as long as you're aware & make sure you don't hook anything else to it.

Charlie