Van's Air Force
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Ground strap for battery?
- Thread starter crabandy
- Start date
Flying Scotsman
Well Known Member
Just out of curiousity...why? Is there a problem with using a large wire of which you're aware?
Cause if there is, I'd like to know
Cause if there is, I'd like to know
Just out of curiousity...why? Is there a problem with using a large wire of which you're aware?
Cause if there is, I'd like to know
Theory has it that the BRAID is more flexible and will hold up better with the engine vibration between the engine and firewall.
In actual experience, I have seen one braid break where it was soldered into the lug that attached to the firewall. I have only see large gauge wire fail when the lug was not properly crimped. (The wire fell out of the lug because it was not crimped correctly.)
Regardless of weather you use a braided cable or a large gauge wire, it MUST be sized to carry the max current the system will see. Typically that is the starter. It must also be low enough resistance that there is no voltage drop from one end to the other. Typically one needs a milliohm meter to read the resistance.
And another to the engine case.......
Cable from the battery to firewall is OK.
Then cable from firewall to the motor case. And another braided from firewall to engine case makes a good system. Welding cable works very well for these connections.
MauiLvrs
Well Known Member
Which is why it should be crimped...
I have the braided ground strap (crimped only) from B and C from my forest of tabs to the engine case. I can make a 2 AWG battery cable but it must have a rather large service loop, I was wondering about using the same braided ground strap from B and C because it's flexibility lets it lay out of the way.
Dbro172
Well Known Member
(As you may be welll aware). You can buy the exact ground cable with pre-crimped connectors direct from vans. You'd have to get the exact part number from Vans but if you go to "the list". They can be seen towards the very bottom near part numbers WH-P10.
Last edited by a moderator:
Flying Scotsman
Well Known Member
Yes, and that's what I have...the OP was asking about from the *battery* to the *firewall*, however, not the engine to the firewall.
I hope I can repost from the aeroelectric matronics list..
The legacy rationale for ground straps of many
finely drawn wires was common in vehicles for
grounding an engine to the vehicle frame or maintaining
electrical continuity across moveable joints in
the machine. The engine needed to move around in
its mounts but often needed grounding integrity
for starter motors and generators/alternators.
Electrical connections that are in motion with
respect to each other demand a conductor that
is exceedingly resistant to flex failure (See
explanation of design goals for 19+strand wire
on airplanes in the 'Connection).
How long a strap are we talking about? Have
you considered welding cable for BOTH battery
(-) and (+) connections? It's a good thing to
reduce the bending moments on battery terminals
due to stiff wire. Some builders have experienced
battery post failures when short lengths of 2AWG
'aircraft' wire was used to jumper a battery(+)
to the contactor.
I would recommend that you consider 4AWG welding
cable jumpers for both battery connections. Then
consider what materials make the most sense for
cost, weight, system performance, or wire that your
hangar mate donated to the project.
A braided strap from fire wall ground to crankcase
is a good thing. A welding cable jumper is equally
good. I'm aware of no particular advantage for
using a fabricated braid-strap to make connections
to the battery . . . but it wouldn't hurt anything
either.
Bob . . .
The legacy rationale for ground straps of many
finely drawn wires was common in vehicles for
grounding an engine to the vehicle frame or maintaining
electrical continuity across moveable joints in
the machine. The engine needed to move around in
its mounts but often needed grounding integrity
for starter motors and generators/alternators.
Electrical connections that are in motion with
respect to each other demand a conductor that
is exceedingly resistant to flex failure (See
explanation of design goals for 19+strand wire
on airplanes in the 'Connection).
How long a strap are we talking about? Have
you considered welding cable for BOTH battery
(-) and (+) connections? It's a good thing to
reduce the bending moments on battery terminals
due to stiff wire. Some builders have experienced
battery post failures when short lengths of 2AWG
'aircraft' wire was used to jumper a battery(+)
to the contactor.
I would recommend that you consider 4AWG welding
cable jumpers for both battery connections. Then
consider what materials make the most sense for
cost, weight, system performance, or wire that your
hangar mate donated to the project.
A braided strap from fire wall ground to crankcase
is a good thing. A welding cable jumper is equally
good. I'm aware of no particular advantage for
using a fabricated braid-strap to make connections
to the battery . . . but it wouldn't hurt anything
either.
Bob . . .
