Dbro172

Dbro172

Well Known Member
Need help wrapping my head around this. I understand my plane power 60 amp alternator needs a fuse. I didn't have one put in my panel so I ordered a 60amp ANL and holder. I gather that the ANL and Garmin supplied shunt should be mounted on the firewall near the batt.

Can I run the B-Lead (in series) from the alternator, to the ANL, from the ANL to the Garmin shunt and then from the Garmin shunt, to where?? Where does the B lead go from the shunt? (To the panel buss bar, master solenoid, starter solenoid) I'm confused.
 
Derek,

From the shunt (or ANL in my case), run a #4 wire to the Starter Contactor. See my schematic below. This is a basic Bob Nuckolls design on my RV-6, and only one of many ways to do it.



Here's a larger crop:



Everything from the alternator to the right is on the firewall. Hope this helps.
 
Derek,
Just as Pat says. I just thought I would add a picture.
The B-Lead from the ANL can be a copper strap for convenience and can connect to the starter or Master solenoid as long it is on the load side of the master.
2lwll6o.jpg[

Here is mine before I connected the B-lead to the top of the shunt.
 
There are two major was ways to wire the shunt to measure amps.

1. on the b lead, it measures the total alternator output.

Pros - one can tell if the alternator is overloaded due to direct measurement of output.
cons - since it measures all output from alt, then it sums battery charging amps, and system load. You don't know exactly what your systems demand is

2. mount shunt in line from battery to system. this always gives amp demand by system.
pros- always gives system demand on start up so you will have a consistent reference for demand.
cons - dont know what the actual battery charging amperage is. but voltage on G3X will give voltage to tell you it IS being charged, just not the quantity.

I chose #2, since the voltage will be measured and by reading amps I could manage power load if the alternator quit. Also, I will be able to remember what the load is for a typical configuration. Battery charge drops after a few minutes to a low number anyway. Digital voltage readouts are so good these days, I am confident that it will tell me if the output of the alternator is substandard, or non existent.

I read up on this and either is an acceptable practice per aviation standards, so both are "right"

What do you want to know, and why, will determine the selection.
 
BillL said:
What do you want to know, and why, will determine the selection.
Click to expand...

I'm not sure exactly what I want to see? But it seems that once the ANL and shunt are mounted on the firewall, relatively close to each other and close to the master & starter solenoids it would be pretty easy to swap wires & change configuration of whether im monitoring alternator output via the B-Lead or system demand through the panel power.
 
Dbro172 said:
I'm not sure exactly what I want to see? But it seems that once the ANL and shunt are mounted on the firewall, relatively close to each other and close to the master & starter solenoids it would be pretty easy to swap wires & change configuration of whether im monitoring alternator output via the B-Lead or system demand through the panel power.
Click to expand...

Absolutely! It is not a big deal, just a minor change in wiring. I just passed by this same situation a few months ago and decided to share the potential paths.

Like Yogi said: "when you come to a fork in the road, take one" (extra points for knowing why he said it)
 
I can't help but notice in the posted photo that the alternator bus is exposed. I am only posting this in the interest of safety, so please don't take these comments wrong.
I don't know if this is your final photo, but it is not a good practice to expose any bare wires, more importantly, high current lines, especially on the engine side of the firewall. Boots should be used on all terminations/ terminals, copper bus bar, while easy to install, should be replaced with properly sized aircraft appropriate wire. The ANL fuse should be enclosed in an insulated holder, as should the shunt. Fuses need to be installed as close to the shunt as practical on both wires leaving the shunt going to the measuring device (EIS).
IMHO the ammeter should always show the current draw from the power source. The power source is the alternator, not the battery. If the alternator quits, you should have a preplanned list of avionics to shed to reduce your power. Looking at the current draw from your battery as it slowly dies, is not a good use of the ammeter. Monitoring the current draw from your power source is.
 
Bill,

So, when your alternator dies, how will you know what your amperage draw is from your battery? Amps will read zero if the shunt is in the b-lead. When the voltage drops this tells me the same thing - no amps from the alternator. Granted, you can still read battery voltage, but it only tells you energy level (capacity), not power draw.

Is there some reason to quantify the battery charging amperage? or is the current draw of the system set up to potentially demand more than the alternator can provide? Wouldn't that be an undersized alternator?

I am not disparaging the B-lead shunt, I just don't see your implied advantage.
Admittedly, the b-lead shunt will give definitive information during the time after start-up and when the battery charging demand approaches its float demand. Does that information tell me something to prevent a failure or aborting a flight?
 
Bill,
Let's say that you have your ammeter on the power source (alt output). You know from many hours of flight that your normal current draw is 18 amps. You set an alarm on the EFIS or EIS to let you know when the current reaches 90% of your alternator capacity. The alarm sounds, you look down and see this unusually high current demand. You land and investigate. If your ammeter is on the battery, you wait until there is a fire or smoke, because you will never know until the current exceeds the alternator capability and the battery begins supplying current to supplement the alternator and feed the short.
Why would you want a meter to help you only if you have already had a failure. I would much rather continually monitor the health of the alt. rather than the aforementioned.
In either case, if your alternator fails you would probably be best served by landing immediately to investigate, even if you have a standby alt. If you have an alt. fail, just shed everything but a previously chosen list of essential equipment and find the nearest airport to investigate.
The great thing about these aircraft is you can build them any way you desire:)
 
Bill,
Let's stick to actual failure possibilities here. If "something" causes a high demand, it would have to occur between where the b-lead shunt would be, and where the battery out shunt would be. Otherwise, the amp reading from system fault (downstream of the battery ) would still be measured by the shunt in either location.

The actual configuration difference between the two options is only one connection a couple of inches apart.

I am not hearing a failure mode not already considered, but thanks for the dialogue. It has been educational. I will take some pictures of my connections, and post in another thread. I am interested in your comments about shielding the high amp potential connections. I don't like them exposed, but even boots are not complete. Your kitlog link seems to be inop.
 
a third option

There are some good points here on where to put the shunt to measure current in the system. The two options already mentioned have each been built by many and work just fine.
However there is a third option I will try to explain for educational purposes. I'm not suggesting this method is appropriate for a small single engine plane as it's a system used on a twin turboprop.
How about putting the shunt in the ground wire? On the twins I work on there are three shunts in the electrical system, one for each generator on the engines and one for the battery. The battery ground wire goes through a shunt before terminating to ground, same with the ground wires from the generators. It allows a measurement of the current draw or output of each power source in the plane as indicated on a loadmeter in the panel.
Advantages are if/when the generators fail the loadmeter in the cockpit still indicates current draw of the battery, it's default indication. Load shedding is not a guess it's visible.
For a single engine plane with an Essential bus this is handy info to have as it's an indication of the power available in the battery. Similar to putting the shunt in the battery to bus wire only more accurate. If there are items not on the bus there would be no indication of the power being used. With the shunt in the ground wire, even the power being used by the master solenoid is indicated. It uses almost one amp, hence the Essential bus is before the master solenoid.
If the alternator output is X amps then there are X amps in the ground as well. When the alternator quits there are no amps indicated on a B-lead shunt but there are still X amps in the ground wire. May be helpful to someone.
Phil
 
Phil,
The only issue with this option is it requires a floating ground on the generators, which is fairly common in the large aircraft fleet. It's a great way to monitor power consumption and load, just not practical with the alternator based systems with non-floating grounds. I guess a person could install 2 shunts, one on the alternator output and one on the battery lead. The G3X has multiple shunt inputs.
 
ground

Bill
The generator grounds are bolted to the airframe same as the one at the battery. They are DC generators, I think perhaps you may have thought they were AC?, with the floating ground.
With multiple shunts and different sources of information, you can be in information overload (possible while reading these forums too). Can you determine in a heartbeat where that information is coming from and what it means in an emergency?
Phil
 
Phil,
I guess what I was trying to say was the shunt is placed prior to the ground, in that way it can measure the current flowing through the generator. In our simple alternators, the whole frame assy is grounded and there would be no way to measure the current on the ground side unless you could isolate the frame.
I agree, with all the new electronics out there it's easy to see how you could get overloaded with information and forget to fly the plane! :eek:
 
simple is best

Bill
Keep it simple. I was offering the method for educational purposes as it has advantages with monitoring power consumption as was said.
However putting it in practice on an alternator equipped single engine plane would be best if kept simple. To me that means; put one shunt in the battery ground wire.
The alternator is bolted to the engine and it's grounded to the plane, so trying to put a shunt somewhere in that side of the system is not easily possible as the engine ground is also the ground for the starter.
About the alternator load, it's included in the total load indicated by the shunt. Time in service will show you normal loads for different phases of flight. If the alternator quits the voltage will drop to 12.5-ish and a low voltage alarm should alert you to the problem.
I agree with the statement "In either case, if your alternator fails you would probably be best served by landing immediately to investigate, even if you have a standby alt. If you have an alt. fail, just shed everything but a previously chosen list of essential equipment and find the nearest airport to investigate."
A Z-11 architecture with an Essential bus makes this possible with a planned for procedure you can use. Alternator alarm = flip a switch and keep flying the plane.
And this, from the good book (the Aeroelectric Connection, App. Z) "As you craft your dream project, keep in mind that the e-bus
and your battery maintenance philosophy can provide
system reliability that few single engine airplane drivers
enjoy. But you MUST understand how it works, what it?s
for and how to maintain it."
Good luck however you decide to build it.
Phil
 
Heres what I did

After the help here - this is what I ended up doing:

Later I wired in the Alt out indicator light to my panel and hooked up the alternator wire to the shunt. I spun up the alternator with a cordless drill and verified the red light extinguished.

16c41tu.jpg
 
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