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Old 10-20-2014, 12:22 AM   #1 (permalink)
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Default Current sensor repackage

i got the 40A smart sensor for my X3, it's kind of bulky and doesn't really stealth install too well.

So, i split the boards and made the sensor board remote.

The current sensor is just a current shunt. Current is measured by reading the voltage drop across a resistor on the +(high side).

on the sensor board there are 3 points coming out, each side of the resistor and a ground connection.

the resistor points are for measuring current
the ground connection is for the voltage readout from the sensor.

splitting the boards takes some effort and a good soldering iron. I removed the yellow housings and desoldered the pin/sockets from the board. I put on my own sockets and some wire with a connector on it. Then i just tied the boards back together with a length of wire. Now i can have the logic part of the sensor some where else and out of the way.
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Old 10-20-2014, 09:27 AM   #2 (permalink)
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Very nice! Looks much better!

That is interesting how they measure the amps, is this the best way to do it?

I have noticed it runs about 30-50 mah low on my X3. I always put in about 30-50 mah more than what the sensor told me I used.
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Old 10-20-2014, 11:21 AM   #3 (permalink)
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Nice job!

@Jmann841: The difference could be due to balancing (assuming you balance charge your packs). It's not super accurate on any of my setups, but I give myself enough of a buffer that it doesn't worry me. And it's still better than flying with a timer.
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Old 10-20-2014, 12:51 PM   #4 (permalink)
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Nice work, P.I.Engineer!

Jmann841, personally I don't care a whole lot about the actual accuracy. I just want it to be consistent/repeatable. If it says 800mAh, and my charger puts back 900mAh, and this is consistent, I'll simply scale my alarm thresholds as needed.

It's when the results vary significantly from flight to flight that things get annoying, to me. If I fly to the same mAh-used number, but put back 900mAh one time, 750mAh the next time, and 1000mAh the time after that, it becomes much less useful.
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Old 10-20-2014, 12:54 PM   #5 (permalink)
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I agree, it is simple to just scale the difference. I wonder what the cause is though. Is it a sensor inaccuracy or is it like chris suggested and the balance charging is throwing the numbers off?
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Old 10-20-2014, 01:57 PM   #6 (permalink)
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it's inaccuracy, you can offset the value(telem page, FAS Offset). I compared to my watt meter, no blades on spooled up. watt meter 1.8A, telem 1.0A

using a current shunt is not the best way, but it does work. A hall effect sensor is much better, but much larger.

I agree with not caring about the number not being accurate, just find a good number to fly to.

i flew 3 packs today and only got to charge one back up.

telem for flight was 733mah
charger mah put back in 800mah.

pretty happy with the result.
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Old 10-20-2014, 03:42 PM   #7 (permalink)
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Hmm, I wonder if those offset settings will help what I'm seeing with the 150A sensor? My consumption is pretty accurate, based on recharge data, but the amp draw shown on the Taranis screen is WAY off. Like it shows 600 amps when hovering around. I'm not sure what I've jacked up in the configuration on the Taranis.
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Old 10-20-2014, 04:01 PM   #8 (permalink)
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that's weird, because the consumption should just be some math based on the current and time.

Jmann841: this is the hall effect sensor
http://www.alofthobbies.com/sp-150a.html
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Old 10-20-2014, 04:38 PM   #9 (permalink)
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Quote:
Originally Posted by P.I.Engineer View Post
that's weird, because the consumption should just be some math based on the current and time.

Jmann841: this is the hall effect sensor
http://www.alofthobbies.com/sp-150a.html
very cool, I have 2 of those that I will use on my G570 and the 6HVU if I don't sell it.

Glad it is more accurate! I wonder if it is more accurate than using Jlog and running the data from the ESC.
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Old 10-20-2014, 06:15 PM   #10 (permalink)
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Caveat: I'm a mech engineer, all the Elec stuff i know i learned from asking questions at work.

but, I was doing some reading and i forgot to take into account efficiency. It will be unlikely that you will put the same amount of mah in that you took out.
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Old 10-20-2014, 07:57 PM   #11 (permalink)
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Good point. Due to internal resistance, wasting energy heating up the packs during flight, you'll have to put more back in, vs what actually came out of the leads during use.

Thanks for mentioning FAS Offset, I hadn't realized you could add an adjustment on the TX.

As far as comparing the watt meter and FAS reading, doing it at 1-2A is probably asking a lot. That's 2.5-5% of the total measurement range. It's unlikely to be very accurate when reading that low; this isn't a laboratory-grade instrument. I'd hope it's fairly accurate when reading 20-30A, something that's a bigger percentage of its total range.

I was just buying some current shunts for some stuff I want to try at home. The ones I saw all have a 75mV drop across them at their rated current, whatever that is (5A or 100A). If this drops 75mV at 40A, then down at 1-2A, you're trying to accurately measure a 2-4mV drop across it. That's pretty small, especially for a ~$20 device, IMO.
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Old 10-20-2014, 08:43 PM   #12 (permalink)
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that's true, i had the same thought that measuring with a watt meter that's chinese calibrated prob isn't the best. And that the measurement is so low.

I don't care enough to spool that thing up with blades. I glanced down while flying and noticed that i'm at about 9amps in a hover. i'll have to log some flights just for curiosity sake.
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Old 10-23-2014, 11:55 AM   #13 (permalink)
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Quote:
Originally Posted by JustPlaneChris View Post
Hmm, I wonder if those offset settings will help what I'm seeing with the 150A sensor? My consumption is pretty accurate, based on recharge data, but the amp draw shown on the Taranis screen is WAY off. Like it shows 600 amps when hovering around. I'm not sure what I've jacked up in the configuration on the Taranis.
Any more info on this? I'm curious as to how well the 150A sensor works, as it's my backup plan if I can't get the results I want using a JLog with my Castle Edge.
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Old 10-23-2014, 12:14 PM   #14 (permalink)
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Quote:
Originally Posted by RedOctobyr View Post
Any more info on this? I'm curious as to how well the 150A sensor works, as it's my backup plan if I can't get the results I want using a JLog with my Castle Edge.
I haven't investigated it any further, but nobody I've spoken with really had any suggestions. Like I say, it is accurate when it comes to the consumption, but the value shown on-screen in my Taranis is miles off for the actual current draw.
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Old 11-25-2014, 07:06 AM   #15 (permalink)
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Finally got around to hooking up my 40A sensor on my X3 last night. Everything is working but I'm running out of places to mount things and this puppy is bulky! I'd like to see pics of where you X3 guys mounted yours if not too much trouble.
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Old 11-25-2014, 08:12 PM   #16 (permalink)
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I found this to be the best solution...

Battery wires go in to the rear then come down through the bottom plate and into the unit. It works very well and if you set it up right you can plug it in with the canopy on.

It also gives the canopy more room in the front without hitting the wires so it fits much better!

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Old 11-25-2014, 11:38 PM   #17 (permalink)
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Thanks. My sensor is a little longer because I have deans converters on each end, but this might work.
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Old 05-06-2016, 11:44 PM   #18 (permalink)
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So this is as far as I've got with mine. Not sure where to solder leads on the resistor board.
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