L

lr172

Well Known Member
I was thinking about my connections between my solenoids today. I thought that I followed the standard convention, but not sure.

I ran a copper bar from the switched or output side of the Master Solenoid to the input of starter solenoid. I now realize that I am passing over 200 Amps through the master solenoid and I don't believe it is rated for that. I am thinking that the starter solenoid should be fed from the battery with the solenoid activation circuit run through the master to prevent inadvertent starting. The only downside is that I cannot break the circuit in case of a short.

How do others do this? Did I do it wrong?

Larry
 
Larry - your technique is common to many "certified" airplanes and homebuilts. It's the way I would choose to wire it up, too.

With respect to rating of the solenoids, they are rated for the amount of current they can regularly handle when making and breaking connections, or in other words, how much current they can reliably switch on and off.

In the case of the master solenoid, it is not normally being asked to actually switch the starting current. In fact, one expects the master to be closed and conducting long before one kicks in the starter. It's only in the rare event of the failure of the starter solenoid in the "welded closed" state that one relies on the master solenoid to switch off the current flow to the starter. Again, this is something we're asking the master solenoid to do as a highly abnormal condition.

Contrast this with the starter contactor that's being asked to switch a huge current surge to the starter motor EVERY time we hit the start switch. The start solenoid lives a tough life and we can almost visualize how its contacts take a beating with every start cycle. This is very different duty than asking the master solenoid to, maybe once or twice in its entire life, shut off current flow to the starter. We would almost never expect the master solenoid to be used as the primary means of applying juice to the starter.

All of that to say, you're good to go. As I'm sure you've already done, make sure you've got diodes across your solenoid coils to lengthen the life if your master and start switches, and do your best to ensure the exposed solenoid terminals are covered with insulating materials so as to avoid an accidental short from them to airframe ground.
 
You are following standard convention.

I offer however to use caution with copper bars. Nice terminal boots on solenoids connected via insulated wire provide protection against accidental shorts. Copper bars do exactly the opposite.

Carl
 
A short piece of heat shrink tubing on the exposed portions of the buss bar reduce the possibility of a short as well.
 
Toobuilder said:
A short piece of heat shrink tubing on the exposed portions of the buss bar reduce the possibility of a short as well.
Click to expand...

In all of the plans recommended installations the two contractors are mounted very close to each other so the amount of exposed bar is very small but this is a very good solution if someone is bothered by the exposed bar.
It takes some effort but it is also possible to get two insulating boots over the bar.
 
Thanks for the input here. Makes sense about the the rating tied to switching current and not through current. My bar is quite short and I covered most of it with shrink insulation. I did that install diodes on both solenoids.

Thanks!
 
Last edited:
Just did that very thing last week. And I need photo posting practice.

Tony

lwt5k.jpg
 
copper area

Van's copper bus bar material is 0.063 x 0.500 copper and is equal to just a little better than 6 gauge wire.

It certainly will work, but I prefer two strips which makes it just about equivalent to 2 gauge wire.
 
You must log in or register to reply here.