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Shunt location

Best place to install a shunt


  • Total voters
    38
On the battery. The health of the alternator to run the system and keep the battery charged is voltage. Amps will show what the system demand is if the alternator quits.

On the B lead, if the alternator quits, you can not manage the amps. In that event, volts will tell you the battery condition as it is used up.
 
For this discussion, and assuming only one Amp meter which I have, I used the following reasoning/logic for my setup.
- On the Battery, I would expected to read mostly about a negative reading close to zero. If the alternator fails, I would expect to read a positive reading which might be for the first time or possibly during a test flight when I had shut the alternator to see what my typical amp draw is. So, to a good degree I would be unfamiliar with typical amp draw at different stage of flight. Reading on the Batt may help me during a Alt failure situation but then again, I have the volt meter which probably is just as good of indication if not better for that emergency situation.

- On the Alt, I get a reading of my typical usage at any time when the engine is running and the Alt is working. If my Amp reading changes for any appreciable amount, it may be a good indication of possible issue and investigation might be on order. For instance, Amp suddenly goes up, volts comes down might indicate a short somewhere. If my draw goes up for any long period of time, I may want to check the health of my battery or find out what has changed. If it reads zero, I know my Alt has gone south but most likely I will have other indicator to confirm that.
So, I like measure my usage and for that I installed it on the Alt side. With that, I know how much my LL draw, what my heated seat use or the fuel pump.
But it is only $$$ so why not install two.
 
The voting choice "On the Battery" means to measure all current into or out of the battery EXCEPT starter current.
I vote for none because if it is not installed, it can not fail or make sparks during a forced landing.
A voltmeter reading of 13.5 or more indicates that the alternator is working. If you really want to know the current,
put a hall effect sensor around the alternator B lead to measure how hard the alternator is working.
The RV-12 ammeter was designed to measure battery current. Their reasoning is that in case of
alternator failure, the pilot could shut off loads based on current flowing out of the battery.
Why not just shut off everything that is not needed and fly the plane?
 
What do you want to measure?

1. Amp output of alternator?
2. Amp load of lights, instruments, etc?
3. Amps to/from battery?

If you do 1 & 2, you can derive 3 in your head.
 
I have two alternators, I did two alternator shunts off the B leads... This is mainly because I have a VPX and that gives me a good bit of info as well.
 
I put mine on the B lead. In most of my flying it tells me load on the system. I can also see the condition of my battery right after start when additional amps are drawn for charging. If more amps or more time than typical is needed to charge the battery I conclude that the battery is getting weak. In the unlikely event I lose the alternator volts will provide what I need to know.
 
What do you want to measure?

1. Amp output of alternator?
2. Amp load of lights, instruments, etc?
3. Amps to/from battery?

If you do 1 & 2, you can derive 3 in your head.
And if you add #2 and #3 you get #1. At least for me, adding is easier than subtracting.

:cool:
 
Curious to best location for a shunt on a Garmin single alternator system and why?

On the BATTERY.
That always tells me the battery state, with or without the alternator working.

In normal flight with alternator online, I will see +14 volts with 0 amps drawing from the battery. Good. I know the battery is fully charged and the alternator is carrying the full load. How many amps is the alternator producing? Simple. Turn off the alternator and read the current draw from the battery that was provided by the alternator. Want to see if your landing light is working? Turn on the switch and you'll see a momentary load on the battery before amps returns to zero.

Now...If the alternator fails in flight, I again see the discharge RATE of the battery. That helps me reduce the load if necessary by turning off high-draw items... extending the time I can stay flying. If the shunt had been wired to the alternator, amps would show zero. No useful info. I have a red alternator off light that tells me that. No value added.

Also, before starting the engine, I always see the discharge rate of the battery which is useful for reducing the loads while waiting.

One final good reason: I use the experimental EarthX battery which handles huge surges of current during start. It draws a lot of current from the alternator to bring the charge back to zero. I like to keep close watch on the EarthX voltage and amps... In fact, that battery requires a blinking status light to troubleshoot malfunctions. Putting the shunt on the battery gives me a way to constantly monitor volts AND amps.

My opinion: There is no advantage to putting the shunt on the alternator, while wiring it to the battery gives me constant power monitoring from before engine start until after engine shutdown.

Of course, this a lot like our "Primer Wars" debates...lots of opinions!
 
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I agree with Joe on this one.

Volts will tell you everything you need to know. One could argue that you don't need to "manage" the load if the alternator fails. Just turn off things you don't need and watch the voltage drop over time.

You should already know the high current items from the low current items as part of your electrical system planning. So knowing what to shut off is not too tricky.

While a shunt is not too complicated, it is one more thing to break.
 
Hall Effect Sensor

I just put one hall effect sensor between the B lead and the battery. It seemed much more reliable and simpler to install than a shunt.

grtsensors_11.jpg

https://www.aircraftspruce.com/catalog/inpages/grandrapidscs-01.php
 
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I agree with Joe on this one.

Volts will tell you everything you need to know. One could argue that you don't need to "manage" the load if the alternator fails. Just turn off things you don't need and watch the voltage drop over time.

You should already know the high current items from the low current items as part of your electrical system planning. So knowing what to shut off is not too tricky.

While a shunt is not too complicated, it is one more thing to break.

Marc,

If I understand a shunt correctly, it is just a place for us to read/measure the current of our system by tying it to our fancy glass screens?

My existing VM1000 shows load from equipment I have selected on at any given time. I would like to be able to see the loads when I install my Dynon system. Where would I install the shunt to see this? Would a Hall Effect sensor be better?

Thanks!
 
I just put one hall effect sensor between the B lead and the battery. It seemed much more reliable and simpler to install than a shunt.

grtsensors_11.jpg

Mickey,

Where did you purchase this from?
Was it easy to install and hook up?

Thanks.
 
BAttery ground

Per aero electric on the ground side of battery. I want to know draw if alt fails. If this happens, i probabaly wont remember all those numbers from flight test. With this amp draw and voltage, i can tell if i am gonna have enough battery to make my landing; cant assume battery is as good as new when the alt fails because may have a worn battery. With volts and amps, i can tell if battery is old and going down faster than planned. also can tell when battery is charging after start or if alt cant keep up with load. And on ground side. Leads to cockpit cant cause short circuit if they wear thru. I plan to use a small pad mount B&C alternator, and forgo the belt (and suspenders) of traditional installations. This takes advantage of lower current draw LED lights to offset the extra weight of all those BBQ flyins the pilot will be carrying around.
Plan:
* all Garmin
* Garmin brownout module
* Flyled lights
* B&C pad mount alt
* B&C overvoltage crowbar on field circuit breaker
* fusible lonks thru firewall
* batt on engine side of firewall
* regenerate gas lead acid battery ( no li-po)
 
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Per aero electric on the ground side of battery. I want to know draw if alt fails. If this happens, i probabaly wont remember all those numbers from flight test. With this amp draw and voltage, i can tell if i am gonna have enough battery to make my landing; cant assume battery is as good as new when the alt fails because may have a worn battery. With volts and amps, i can tell if battery is old and going down faster than planned. also can tell when battery is charging after start or if alt cant keep up with load. And on ground side. Leads to cockpit cant cause short circuit if they wear thru. I plan to use a small pad mount B&C alternator, and forgo the belt (and suspenders) of traditional installations. This takes advantage of lower current draw LED lights to offset the extra weight of all those BBQ flyins the pilot will be carrying around.
Plan:
* all Garmin
* Garmin brownout module
* Flyled lights
* B&C pad mount alt
* B&C overvoltage crowbar on field circuit breaker
* fusible lonks thru firewall
* batt on engine side of firewall
* regenerate gas lead acid battery ( no li-po)

John,
With AMP draw from your battery, does it show how much is left in your battery or how much your system is using? If it show much your system is using, how do you know how much is left, other than looking at the volts creeping down and isn't that a good indication of the status of your battery?
 
Hall effect

Heres a link to the Amploc key 100 which is specifically mentioned in the Garmin G3x manual. At $25 each, I might just buy two and monitor both the Alt and the battery. Can someone who has installed one please post a pic of how they did it?

Another interesting issue is the location of the shunt. For example, Garmin specifically say on the battery line to install in between the positive terminal and the battery contactor. Meanwhile Dynon, specifically says after the contactor. :confused: I guess install as recommended by whatever mfr you are using.
 
Ok, you're measure amps and volts..............

Are any of these systems smart enough to predict how much time left you have on your battery?
 
picture

Any chance of posting a pic of your install?
Sure - here are a couple.

img_2130-1024x1024.jpg


img_2108-1024x768.jpg


Please keep in mind that I'm not flying, so this installation may not be a good one. I know it functions, but will it last 2000 hours? Not yet sure.
 
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