VAF Forums

VAF Forums (
-   Electrical Systems (
-   -   Just ditched my Ammeter... (

wcalvert 02-08-2021 07:23 PM

Just ditched my Ammeter...

I am building a system based on Nuckolls Z-19 diagram (2 pc680 batteries, 1 alternator, low voltage sensing with automatic Endurance buss backup). B&C external regulator with over volt protection, 55 amp Denso alternator. There is a 60 amp ANL fuse on the output of the alternator.

Aircraft is Dynon equipped, VFR only platform. The display will show voltage for each battery.

The engine is run of the mill IO-360 except for the EFII ignition (no mags), hence the redundant electrical power scheme. Superior fuel injection servo.

So I was looking over the schematic and thinking through failure modes, and it occurred to me that there may not be a need for an ammeter. If the alternator fails, I will get a low voltage warning from two sources. If alternator output is too high, the regulator will shut it down and I'll get a low voltage warning soon enough.

The only use for the ammeter I can see is to monitor the load after start to get a feel for the condition of the start battery... how long it takes to get back to a "normal" charge level. Or a slowly running away overdraw on the alternator (can't think of an example).

I realize that the shunt and accompanying wiring will only be another pound or so, but space on the one Dynon display is limited and will need to be prioritized.

Anyone have another opinion? Ok, that's a loaded question. Thoughts then? :rolleyes:

Aluminum 02-08-2021 08:11 PM

A Hall effect sensor weighs way less than a pound and adds no failure points to the critical wiring, unlike a shunt. Had one in my Skyview system since '12, no quirks. Helped me detect a stuck starter relay, which was not audible on that engine so the quickly draining battery was the only noticeable symptom. Highly recommended. Dynon EMS already provides a quiet 5 Volt output to power it, easy-peasy.

wcalvert 02-08-2021 08:21 PM

Ok, I do like that kind of solution...

JLuckey 02-08-2021 09:08 PM

If you put the shunt in the battery circuit (sounds like that's where you may have it) then if/when the alternator fails, you can see the exact load on the battery (as a negative number). May be helpful in load-shedding/time-remaining arithmetic.

I understand that with an Essential bus that you theoretically have already done that calculation, but could not hurt to see actual current drain in that situation.

Larry DeCamp 02-09-2021 04:00 AM

Voltage is truth
My Garmin stuff came with a very nice shunt. When ordering panel components, I ask BJ at B&C, what a shunt tells that the voltage does not. The answer is 14.2 volts is the goal and anything less is caused by proportional current flow. Ammeters just make some happier than others, was my takeaway from the conversation. Also, a red light for stuck starter gives a good clue when the voltage cant keep up.

Carl Froehlich 02-09-2021 03:30 PM

Three RVs flying, and none have an ammeter - and never missed.

Voltage is a superior indication of system operation and I need not know what current flow is all the time. I measure it once during hangar flying and have POH emergency procedures to cover load shedding.


Walt 02-09-2021 04:54 PM

I find amp meter provides useful info on system loads and battery condition, costs nothing to install except a few extra wires.
Basically a piece of wire with terminals, so why not?

David Z 02-09-2021 07:53 PM

In all the work planes I have flown, they're full of ammeters (and voltmeters). One on each generator and battery, inverter and rectifier. Granted some of these have limitations set by the manufacturer.

They're great at knowing the condition of some equipment as it's being turned on or off. For example, pitot heat. Watch the alternator load increase when turning the pitot heat on means it still works.

Battery load shows the condition of the battery. Longer recharge time means either an old or significantly discharged battery.

We also can't stick load meters everywhere on every device. Those with backup batteries or backup alternators, we'd be looking at 3 or 4 ammeters. Seems a bit excessive and unnecessary.

Not really answering any questions here, just trying to figure out where it's best to put the ammeter. Weigh the pros and cons of each location.

JDeanda 02-09-2021 11:12 PM

Just My 2 Cents
If’n it was up to me (it’s not) every airplane with an electrical system would have an ammeter, loadmeter, voltmeter and an idiot light. And pilots would be trained to look at them now and then, and be able to at least understand what’s normal and what’s not. I’ve had at least two conversations with pilots who had had alternator failures but did not notice until radios and lights started falling offline while never thinking to look at an ammeter, loadmeter or voltmeter. Neither did any load shedding, both those at night. In one case, the pilot still had not thought about the loadmeter years later, actually, until I asked him about it.

All times are GMT -6. The time now is 03:49 PM.