I recently got an M7 and was going through some posts, here and on the internet in general, recommending to calibrate the charger.  As I was reading about that I also came across recommendations to calibrate the current sensor on the FC.  Something I had never thought of during my almost 1 year in the hobby.


I have multimeter, so I thought I could have this done no problems (given my limited options in tools, the way I would do it is to check the lipo first, get all the readings, and then validate them on the calibration screen. Same for the input). But then it occured to me that the multimeter itself is not calibrated and it is a cheapo one from amazon, so I'm not sure if this would be adequate to use for such scenario.
- Question 1: Does this matter for the process of calibrating or am I overthinking it? Should I calibrate the multimeter first somehow?
- Question 2: Is my method ok or would this create even more discrepancies ?

Now the other bit... For the FC current calibration I was thinking of using the trial and error method described by Oscar on his blog (use the mAh consumed on flight and the mAh charged, throw those on the formula along with the existing scale and get the new scale, repeat the process a few times to fine tune).
As I was marking down the values, the one from the charger after charging the lipo caught my attention.  This is a 550mAh 3s lipo, during flight the FC reported 520 mAh consumed, the charger marked 594 mAh charged.  I'm not used to reading these things out, but since its over the presumed capacity I thought there might be a problem.
- Question 3: Is this situation normal?  Could there be a problem on the lipo itself or the charger?

I would say to skip on calibrating the meter unless it's super cheap. Most of those are pretty close. As for the flight controller's current reading, I almost always find that they're somewhat out of whack, and it can be helpful to tune them for specific purposes. If all you're doing is ripping around, it's probably better to make sure voltage reads right, and ignore current and capacity. On your charger, make sure voltage reads right and you should be set. Also be sure to check your total against the sum of your balance connections.

Tks for the tips...

Whats super cheap for you? lol Mine was just under £6, which I consider super cheap at least, assuming you would too, do you have any ideas of what to use as a voltage reference to calibrate it? For example, if I set my charger to power with a specific volt, would this be ok even though the charger is not calibrated?

Do you have a cell checker? How does it compare to your volt meter on various battery readings?

(16-Apr-2023, 06:42 PM)cst3x6 Wrote: Tks for the tips...

Whats super cheap for you? lol Mine was just under £6, which I consider super cheap at least, assuming you would too,  do you have any ideas of what to use as a voltage reference to calibrate it? For example, if I set my charger to power with a specific volt, would this be ok even though the charger is not calibrated?

Good things to check are fresh batteries from the store, USB power, and various regulators. If you get the expected result, good enough.

(16-Apr-2023, 08:21 PM)sevro Wrote: Do you have a cell checker? How does it compare to your volt meter on various battery readings?

Just the one on the m7, don't remember the values now (forgot to write them down the other day) but they might of been something around the .05 to .1 difference. Only checked the one lipo I have with balanced cables. Having said that, I do have a bunch of rechargeable AAs and a charger that shows some info on them, could use that as well..

Quote:Good things to check are fresh batteries from the store, USB power, and various regulators. If you get the expected result, good enough.

I'll try checking with some things around that have some sort of reference, such as mentioned above. 
However, after I last wrote, I opened up the multimeter to check it out and it turns out its so cheap it doesn't have a rotary potentiometer to calibratre it.. lol So with this one, If I find that its really not balanced, I would have to know by how much and apply that to the readings I make. No big deal..

All this is just to ensure I don't mess up the bigger lipos I have started to get into (only 1s so far and 2x1s for 2s)..

Whilst on the topic somehow..

I'm planning to make an extension lead with multiple connectors to allow me to plug on the XT60 of the charger into Xt60 and XT30 lipo (to allow me to have the lipo inside a lipo safe bag with the charger outside) and drone (to use as a power source for the drone to work on bench), so four connectors in total.

Should I follow wire gauge guidelines used on the battery leads on the esc/fc or because there is no burst in this case, can I use thinner wires without any problems?
For reference I'm thinking if I should go with 16 or 18 for everything or 16 for the the xt60 parts and 18 for the xt30. So coming out of the charger would be 16, at some point the split to the xt30s would become 18, and for the xt60x remain on 16.
What do you reckon?

It really doesn't make sense to use different sizes of wires as the smallest will always be your bottleneck. Another thing to consider is how much amperage you actually plan to draw. If it's a light duty task, the wires can be pretty tiny and not have an issue. Plus, we're dealing with short wires, so we can bend the rules a bit as most wiring guides are for home use. Unless you plan on ramping up your motors on the bench, even a USB cable could provide more than enough.

The plan is to make it around 20-25 cm long and when connected to the drone, would be to do basic checks no ramping the motor, at most low throttle to check functionality.

18 all the way or 16?

I'd feel pretty safe on 18. My 2S Mobula7 runs on 20 gauge and it's not bottlenecking anything at 100% throttle.

Cool.. I'm not planning on 6s anytime soon, 3s is the highest at the moment with 4s on the radar already. So in terms of voltage, 4s would be the max this would be used for...

Oh, don't worry about voltage when deciding on wire thickness. You can push a million volts through a tiny wire as long as you have low amperage. The POE standard pushes 48 or 52 volts through 23 gauge wire all the time. As long as you don't try to push like 30 or 40 amps through yours, you almost won't even notice the wire getting warm.

Ha.. didn't know about that, learning all the time. Max output of the charger is 10A in any mode, so no chance of going higher.

Tks a lot for that Suros!

Went through with the 18 for the extension, all good so far.  Here s how it came out:

Very clean! Well done!