stuart(at)stuarthutchison
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 Posted: Tue Mar 01, 2022 2:21 am Post subject: WAS: Sizing a B-lead ANL now "master fuse" on the battery |
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No, the master contactor interrupts the positive side of the circuit between the battery positive lead and the main power feeder wire. The Master Switch connects a thin positive wire from an insulated post on the contactor body to ground when closed, energising the master contactor solenoid. Obviously this small wire needs to be physically protected, but I’ve never seen that wire fused (I could be wrong) … potentially because it is small enough to burn through without starting a fire. You certainly wouldn’t want nuisance CB or fuse trips on Master Switch power. | Quote: | On 1 Mar 2022, at 8:54 pm, Bob Verwey <bob.verwey(at)gmail.com (bob.verwey(at)gmail.com)> wrote:
But....the master solenoid is actuated by a negative wire right? So now if the thinner switching wire is earthed forceably to the fuselage, then rhe fat wire is live? What am I missing?
On Tue, 01 Mar 2022, 11:01 Bob Verwey, <bob.verwey(at)gmail.com (bob.verwey(at)gmail.com)> wrote:
| Quote: | ..of course when someone else points that out it makes perfect sense...lol..thanks!
On Tue, 01 Mar 2022, 09:54 Stuart Hutchison, <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)> wrote:
| Quote: | G’day Bob,
In anticipation of the in-rush and persistent current through that wire during prolonged starting, a pretty large gauge fusible link would be needed … do you really want that much current available at the site of a short hoping the large slow-blow fuse will eventually isolate power? Weight is obviously at a premium, but it seems to me like a solenoid and master switch are a much safer bet.
Kind regards, Stuart | Quote: | On 1 Mar 2022, at 5:02 pm, Bob Verwey <bob.verwey(at)gmail.com (bob.verwey(at)gmail.com)> wrote:
Sort of related query.
A J3 Cub is being converted to accommodate an 0-200 engine with electric start.
The battery box is behind the baggage compartment, and for the sake of simplicity, there is no master solenoid back there, so there is a hot #4 wire all the way top the firewall.
The only electrical load is the radio and intercom, for which there is a switch and circuit breaker.
I want to add a fuse of some kind at the battery box to prevent a "shower of sparks" welding event if there is an incident which causes the steel bits to cut into the hot battery cable.
What is the likely current draw on a typical lightweight starter for an 0-200, and what is the suggested "fuse " mechanism?
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