Ammeter Shunt Location Question

[daveg]

I understand the A, B and C locations of ammeter shunts suggsted in the Dynon installation manual. I am designing my electrical installation to have an e-bus leg coming off before the battery contactor to power essential items in case of alternator or battery contactor failure. In this configuration, I will not be able to see my amp load when I am soley on the e-bus as the ammeter and shunt will be out of the loop. Can the Dynon ammeter shunt be installed in between the negative side of the battery and ground? In this location, it would read the battery amps in all instances, but would would also subject it to the high 200-250 amp starter loads. Would this high intermittent load harm the Dynon EMS?

Thanks,

Dave G

 

[dynonsupport]

You cannot put the shunt on the negative battery lead for two reasons. The shunt physically cannot handle the starter loads, and the shunt must be connected to a wire that has 6-30V on it. You wouldn't harm the EMS, but it would read wrong all the time and your shunt would overheat during start.

 

[daveg]

OK, thanks for the prompt reply.

Dave G

 

[David_Prince]

I understand the three possible shunt locations. Of the three which is the most useful?

A: Between Master Relay and ACLoad/Alt to measure amps to/from battery seem good. Zero would indicate aircraft load being handled by Alternator.

B: Between MasterRelay/ACLoad and Alt to measure alternator output seems good (Might detect problem quicker)

C: Between MasterRelay/Alt and ACLoad to measure Aircraft load (Not sure what monitoring this would do)

I know personal preference would dictate but does Dynon have any preference?

Option B seems to be my preference to detect alternator failure...

 

[dynonsupport]

We don't have a recommendation, but here's what each location gets you (refer to any EMS manual here for the diagram):

A tells you the amount of current going into and out of the battery, and is the way a conventional cessna style ammeter works. It will give you a slightly negative reading when the engine is off but the electrical system is on, a positive reading as the alternator recharges the battery after start, and 0 when you're cruising and the battery is all topped off. From this indication, you can learn whether your alternator is pumping way too much current into the battery, or if the battery is discharging, but you might not be obvious where the drain or surplus power is coming from.

B tells you the output of the alternator. It will definitely tell you how much current is flowing out of the alternator, but you can't be sure if its ending up being absorbed by the battery or aircraft load. You can definitively detect an alternator failure though.

C tells you the current of the aircraft load, but you can't be sure whether they're being powered by the alternator or the battery. It can tell you if something in your aircraft is drawing excess current.

 

[SaroDude]

You cannot put the shunt on the negative battery lead for two reasons. The shunt physically cannot handle the starter loads, and the shunt must be connected to a wire that has 6-30V on it. You wouldn't harm the EMS, but it would read wrong all the time and your shunt would overheat during start.

So I'm wiring my ems and have this same question. The starter issue is moot for me because I don't have one. I don't follow the voltage issue though. Can you please clarify?

-Saro

 

[dynonsupport]

On the D10/D12/D180, the amps shunt must have 6-30V on it relative to ground. Basically, it must be on a positive wire, not the ground wire. The EMS cannot read the output unless it has this "common mode" voltage on it.

SkyView does not have this restriction.