ANL Fuses

·         John McGlynn

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I am building a JABIRU 3300 powered RANS S-19 and starting to work on the electrical circuit. I am using the JABIRU J160 as a starting point for my wiring diagram. That circuit uses a 40A ANL fuse from the hot side of the starter selonoid to the master switch relay. It seems to me that the JABIRU J160 circuit doesn't protect a direct short on the starter motor.

I am thinking of changing it so I have the ANL fuse connected to the hot side of the battery, then to the master switch relay, then to the starter selenoid. Does the starter motor draw in excess of 40a? I have the aero electric manual on order and will see how they suggest wiring.

I also have a DYNON 120 EMS which I plan to have on during the start. Another builder suggested the EMS might reboot due to low voltage while cranking. Finally I am also protecting the buss with a crowbar circuit in the event of voltage during starting or shutdown.
Regards
John

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·         Doug Smith

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Hi John,
Seems the search I ran before only looked at approved posts, not those still pending. Oh well, you should learn something everyday they say 🙂

The 40A fuse is there in the J160 so that if there is any damage to the big wire running from the starter solenoid to the main bus it just takes out the fuse. It doesn't carry starter current.

From memory the starter does draw well in excess of 40A, I suspect you'd fry a 40A fuse. Admittedly most fuses will carry more than their rated current for a short time but even so. I've worked with bigger aircraft where there is a "contactor" - effectively a thumping big relay - between the battery and everything else but the contactor itself can fail and cause its own troubles so it's a personal choice...

Yes, it's pretty normal for EMS's to black out during starting, same as the radio in your car (or my car anyhow). I think systems with internal battery backups can address that issue if you want to be able to see the whole thing on the screen. The D120 restarts pretty quickly though.

Regards,
Doug.