Van's Air Force
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Need Help; current sensor location
- Thread starter Mycool
- Start date
GalinHdz
Well Known Member
Depending on what you will use to display the value, a properly sized DC Shunt or a Hall Effect Sensor will work just fine.
Andrew Anunson
Well Known Member
Shunt
Between + battery terminal and master solenoid.
Between + battery terminal and master solenoid.
No, but not everyone wants an indication of alternator output.
My opinion is that it is of far less value than it is installed in the battery feed line (though you will likely now get a wide variety of explanations why other methods are better).
Here is my reasoning......
For the most part, an alternator either works or it doesn't.
It is rare to have an alternator fail in a mode that only allows partial output.
It does happen occasionally (rectifier diode failure....) but that can still be detected with the amp shunt in the battery feed. For that reason, being able to measure the actual output of the alternator is of far less value than monitor the battery.
That means we really only need to be able to determine whether it is working or not. You can do that with buss voltage. If the voltage is above nominal battery voltage (12.7, or so) then you know that the alternator must be working. Another indicator of it working well, with the shunt in the battery feed is an indication of a strong + charge right after engine start (working to restore the battery level) and a low + charge current after flying for an hour or so.
The plus side to having the shunt in the battery feed is that if you do have an alternator failure in flight, there is no guessing on how much battery life you have.
If you have a health battery with an amp hour rating of 16 (Odyssey P680), if you shed loads until you are indicating -16 amps from your battery, you should have about 1 hr of battery endurance. If you can shed load down to -8 amps you should have about 2 hrs.
If you have something other than a traditional battery there my be specific reasons for having the shunt in the alt. feed, but I am not aware of any.
My opinion is that it is of far less value than it is installed in the battery feed line (though you will likely now get a wide variety of explanations why other methods are better).
Here is my reasoning......
For the most part, an alternator either works or it doesn't.
It is rare to have an alternator fail in a mode that only allows partial output.
It does happen occasionally (rectifier diode failure....) but that can still be detected with the amp shunt in the battery feed. For that reason, being able to measure the actual output of the alternator is of far less value than monitor the battery.
That means we really only need to be able to determine whether it is working or not. You can do that with buss voltage. If the voltage is above nominal battery voltage (12.7, or so) then you know that the alternator must be working. Another indicator of it working well, with the shunt in the battery feed is an indication of a strong + charge right after engine start (working to restore the battery level) and a low + charge current after flying for an hour or so.
The plus side to having the shunt in the battery feed is that if you do have an alternator failure in flight, there is no guessing on how much battery life you have.
If you have a health battery with an amp hour rating of 16 (Odyssey P680), if you shed loads until you are indicating -16 amps from your battery, you should have about 1 hr of battery endurance. If you can shed load down to -8 amps you should have about 2 hrs.
If you have something other than a traditional battery there my be specific reasons for having the shunt in the alt. feed, but I am not aware of any.
rv7charlie
Well Known Member
Scott,
I'm not that comfortable disagreeing with someone with your extensive knowledge, but since this could be a serious safety issue, I feel that I must ask you to review the Odyssey tech documents related to capacity and its relation to load. I believe that you'll find that the 16AH rating on Odyssey & similar batteries is the '20 hour rate'. In other words, divide 16 by 20, and that will tell you how many amps you can use to get a full 16AH out of the battery.
I'm looking at the Odyssey PC680 doc right now, and you can draw only 0.8amps continuous, over 20 hours, to get the full 16AH out of the battery. To last an hour, you can draw 12.3amps, which yields only 12.3AH total from the battery.
This is a big deal if someone with an electrically dependent a/c isn't aware of the fairly steep capacity curve with increasing loads.
Link to the Odyssey document:
http://www.odysseybattery.com/documents/US-ODY-TM-002_1214.pdf
I do agree about the very limited usefulness of current measurement during actual a/c operation.
Charlie
I'm not that comfortable disagreeing with someone with your extensive knowledge, but since this could be a serious safety issue, I feel that I must ask you to review the Odyssey tech documents related to capacity and its relation to load. I believe that you'll find that the 16AH rating on Odyssey & similar batteries is the '20 hour rate'. In other words, divide 16 by 20, and that will tell you how many amps you can use to get a full 16AH out of the battery.
I'm looking at the Odyssey PC680 doc right now, and you can draw only 0.8amps continuous, over 20 hours, to get the full 16AH out of the battery. To last an hour, you can draw 12.3amps, which yields only 12.3AH total from the battery.
This is a big deal if someone with an electrically dependent a/c isn't aware of the fairly steep capacity curve with increasing loads.
Link to the Odyssey document:
http://www.odysseybattery.com/documents/US-ODY-TM-002_1214.pdf
I do agree about the very limited usefulness of current measurement during actual a/c operation.
Charlie
Last edited:
Mycool
Well Known Member
Good conversation
I think im sold on the idea of monitoring the battery health in the event of a alt failure, especially since ill be operating the dynon d-180.
VANS aircaft can be flown safely without any instrumention in day VFR OF COURSE.
The worst case scenario for this aircarft would be night VFR, and in the event of an alt failure it would be safe to know EXACTLY how much time time i have until everything goes black.
Another question, what will the amp meter read after engine start if i have the current sensor on the BATT side and the alternator is working?
I think im sold on the idea of monitoring the battery health in the event of a alt failure, especially since ill be operating the dynon d-180.
VANS aircaft can be flown safely without any instrumention in day VFR OF COURSE.
The worst case scenario for this aircarft would be night VFR, and in the event of an alt failure it would be safe to know EXACTLY how much time time i have until everything goes black.
Another question, what will the amp meter read after engine start if i have the current sensor on the BATT side and the alternator is working?
You are right. I shouldn't use my memory of data for stuff like this.
So, don't use the actual #'s I quoted above... research and use the data specific to your battery(s). But the recommendation is still relevant.
It depends on how much cranking is done for the engine start, but there will be an initial jump of a + charge in the 20-30 amp range which will progressively reduce to just a couple amps once the battery has been fully recharged.
