The build manual for my Kitfox IV call for the shunt to be installed between the battery and the master relay. I noticed that all of the options shown in the installation manual have the shunt somewhere on the switched side of the master relay. Do you anticipate any problems with a shunt installed between the battery and master relay (I.e., the unswitched side)? If it matters, I'll be running a Rotax 912UL which uses a generator/rectifier rather than an alternator.
Shunt Location
- Thread starter m1bondo
- Start date
Raymo
I love aviation!
My shunt is installed between the alternator and the relay and battery. I mounted it on the engine mount tube with Adel clamps. I like seeing the load on the alternator. Working well 450 hours later.
FWIW I have my shunt between the master relay and the alternator, like Raymo. This is basically the same "electrically" as between the battery and the master relay. The reason I did it this way is to remove battery power from the shunt when the master switch is off. Just a little bit safer. I attached an image of my electrical system showing the shunt location.
Where you place the shunt decides what you are actually monitoring. By placing it between the battery and the master relay (or master relay and alternator) you monitor if the battery is charging or discharging. If you mount it between the alternator and the main bus, you monitor alternator total output. IMHO, either way is perfectly acceptable.
Where you place the shunt decides what you are actually monitoring. By placing it between the battery and the master relay (or master relay and alternator) you monitor if the battery is charging or discharging. If you mount it between the alternator and the main bus, you monitor alternator total output. IMHO, either way is perfectly acceptable.
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Tango Mike
New Member
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- Jul 14, 2021
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A bit of advice from an engineer. Yes, it's a good idea to put the shunt on the switched side. But, and here's the advice part: a current limiter (aka fuse) should be installed immediately following the battery and immediately following the alternator output. I know these are not commonly shown on drawings, but doing so can prevent fires. Fuel and fumes usually creep along slowly after a tank is breached tank. But if an electrical arc is allowed to continue to burn after an accident, a fire is much more likely to start than if a fuse breaks the connection first. Locating a current limiter (fuse) very near the positive terminal on the battery a good idea. A 400 A current limiter is sufficient for my IO-360's starter. Now I know you might think that the 400 A required to blow the current limiter will create quite a whollop of a spark, but the battery will blow it easily in a direct short to frame. The alternator should be so protected also, but with a 60 A current limiter. Part numbers are ANL-400 and ANL-60. They require a Bussmann 4164 fuse block or equivalent. All this will add about $150 to your project, but your battery is a big source of energy that can ignite things.
airguy
Active Member
I wired my shunt to read amps in/out of the battery only, AFTER the starter connection so it doesn't see the starter load. System voltage will tell me whether the alternator(s) are healthy, I have voltage alarms on the bus and current alarms on the shunt. If I'm running large amounts of current in/out of the battery, that's the number I really want to know about since that means the alternators are on vacation and my battery is depleting - in that case, I need to know how fast.
As Tango Mike indicated, it's a good idea to use fuse limiters, I have them on both alternators but not on my starter - so I'm only a partial hypocrite.
As Tango Mike indicated, it's a good idea to use fuse limiters, I have them on both alternators but not on my starter - so I'm only a partial hypocrite.
Bill Putney
Active Member
I’m more curious about power than some people. I have 2 Shunts. One is wired between the alternator “B” Terminal and the main electrical bus. That one reads the “Load” on the alternator. The second one is between the main electrical bus and the master relay. That one reads “Charge and Discharge” to the battery. The starter doesn’t go through any shunt.
Both of these shunts are pretty close to bus voltage on both sides. Because of that I have 1A automotive mini fuses right at the terminals at each end of both shunts before those connections go into the wire loom headed back to the instrument inputs. That keeps any short from in those sense wires to the airframe from trying to pass way more current than a #22 wire can handle back to an unrestricted connection to the battery.
Both of these shunts are pretty close to bus voltage on both sides. Because of that I have 1A automotive mini fuses right at the terminals at each end of both shunts before those connections go into the wire loom headed back to the instrument inputs. That keeps any short from in those sense wires to the airframe from trying to pass way more current than a #22 wire can handle back to an unrestricted connection to the battery.
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My setup is similar to yours, as you can see on my diagram. One shunt shows battery charge/discharge while the other (CS-02, 50A Hall Effect Sensor) shows the rest of the electrical load. If you add the values, you get total load on the alternator. Just like your setup, starter current doesn't flow through a shunt.
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