13S15P Battery Pack Build

After I watched the video above, titled “The most advanced BMS ever” I kind of decided to also take the LCD Display of the BMS out of the equation. less electronics and cables to worry about, and it’ll also easier to build a case for the battery pack later on.

The app on my android smartphone works just fine, and it displays all the parameters that the LCD display would show as well: Voltage, Amperes used, Watts used, the Voltage of each cell and the temperature of the four temperature that I added in between the cells. (I think there’s also a temperature sensor on the BMS itself as well).

I also already decided to remove the two switches, which I’ll have yet to do.

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Just as I am done with the build (I also attached the Dudek Powerseat in the meantime) it started to rain heavily, and it looks like it’s going to continue to rain the next couple of days. :frowning:

When I noticed this morning that the rain had stopped for a moment, I immediately ran outside for a first testrun.

Here’s a short Video

You’ll notice me fiddling with my phone - that’s because I wanted to take a screenshot of the BMS Bluetooth App showing live data.

I was “almost” full throttle, there were maybe a couple of millimeters left to press the button further down,
but I already had difficulties leaning against the sheer power of the OpenPPG and I also wanted to take that screenshot, which takes two hands.

Here’s the screenshot that was taken during the video:

And a second screenshot that I took on a second testrun two minutes later (I just could not resist):

Please note that I should be able to set the total capacity of the battery, which is 2.1 kWh or 45 Ah, in the App, but I simply did not do this yet. The factory default was 100, so the screenshot read a value slightly below 100. It is therefore not (yet) accurate.

You can see that this time I went slowly over the 300 Amps, but again, there were still a few millimeters left to press the throttle further.

And you can see that the battery got a little warmer between the two runs, but still far away from problematic heat. The BMS would stop the current anyways, if the battery got too hot.

From the thrust I felt, comparing it to my gas powered two stroke engine, it has plenty.
And I know from experience that I hardly have to go full throttle when flying, maybe for a few seconds when taking off.

I can’t wait for my first testflight, but’ll be a few days until it eventually will stop raining.

At this point, I can say that I am pretty happy with my battery decision and the whole OpenPPG setup!

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Looking good!

Do you know what the voltage was before going full throttle? I’m curious how the resistance of your pack compares to the Bonkas and we can tell that by the voltage drop and amp readings.

Edit: actually we need to know throttle position too but the only way to know that is to give 100%

unfortunately I did not check it.

but since I did the testrun, I did not do anything else but shutting off the BMS.
So let me turn it back on, and read the voltage, it should be very similar to the voltage right before the testrun, since the motors weren’t spinning for longer than a minute or so.

Here you go:

notice the ambient temperature of the battery, which is located in my living room right now.

Outside this afternoon it was around 6 degrees celsius.

I most likely can’t go full throttle if the lawn is that soakin’ wet or unless I stand against a wall. The OpenPPG would toss me around like in a hurricane :slight_smile:

Actually, we don’t need full throttle to calculate this because we know the amps. I use throttle position to calculate amps for the capacity correction programming I’m working on. Anyway… voltage drop divided by amps equals 0.0259 ohms of resistance for the whole system. I think almost all of that resistance comes from the batteries.

With four Bonka batteries I get a resistance of 0.0143 ohms.

I’ve read that Li-ion can’t handle the higher amps as well as lipos and I think that’s because the resistance is higher. You’re totally fine though with that nice BMS… much safer.

Higher resistance means more voltage drop which means you will also have lower amps but you are dropping from an already higher voltage with 13S.

What charger did you get for your pack?

I ended up buying a standard Li-Ion 48V ebike battery charger, which perfectly fits my battery.
cost me 70 Euro for a 6 Amp charger instead of the 300 Euro Cycle Satiator that I mentioned far up in this thread.

I had my first testflight yesterday, and a second one right after! Yay!

TL;DR

The good thing: I was up in the air and the BMS works as designed: keeping the Battery Pack secure!
I love the OpenPPG, it’s just so light, no stinky gas engine running idle when getting ready for launch, no torque, instant power on the press of a button, motors stop and don’t run idle when I let go off the throttle up in the air, no vibration!

The bad thing: I have to re-think a few things. The BMS shut off the battery three times. once on first launch (because of too high amps), and twice up in the air, because of battery temperature.

I am not mad, because I think I know how I can fix it, and these three shutdowns confirm that the BMS was the right choice, it works as designed, keeping the battery (and me, the pilot) safe.


Here’s the long story:

When launching with a paramotor on my back, I am used to go full throttle, even with my strong gas paramotor. I usually very quickly gain altitude.

Against my expectations from my post above…

… I am now thinking there could be a little more thrust, but it will work as well as is.

As mentioned above I had three shutdowns: once due to high amps being drawn out of the battery, and twice because of temperature. Here’s the details:

Problem 1)
After pushing gently, and then stronger, during launch, I did not feel any lift.
So I went full throttle for probably a couple of seconds (the BMS settings has a factory default of 5 seconds shutoff delay on exceeding the set Amperage maximum of 300A).
So it happend, the BMS shut down and I had to abort. The bluetooth App on my phone confirmed the shutdown due to too much Amps draw.

Possible solutions:

  1. add a second battery of the same size, so any power needed is devided between the two
  2. loose some weight (yeah, that would be awesome)
  3. reprogram the throttle controller, so that all the way down is equal to max 95%, or allow 100% for maximum 4.5 seconds, then reduce to 95% automatically
  4. not sure if it’s possible or advisable, but change the settings in the BMS from 5 second delay to 10 second delay before shutting off.
  5. a mix of the above

Problem 2)

The first flight was around 9 minutes, I did not gain much altitude (approx. 190 meters. Divide that by 3.3 for feet :slight_smile: ), because I did not want to go full throttle due to the experience above (problem 1). Flying was great. I really enjoyed it, until all over the sudden the motors went out.

The battery temperature reached 60° Celsius, and the safety measure kicked in.
I landed safely and checked the App again. The temperature of the BMS was fine, the four temp sensors that I placed evenly spaced in the middle of the pack however were showing 60°, 60°, 59° and 58°. I took off my gloves to feel the battery, but I felt… nothing.
I touched below, on top, on the sides, no heat at all.

And that’s the key takeaway here! I did insulate the battery too much, not only to protect all the terminals (which are all over the place on four sides) but apparently also thermally.

I wrapped the battery, mainly to protect it from shorting, with foamed rubber. I secured the foamed rubber with stretch film which I tightly wrapped around the whole battery. It did give a nice pack in the end, but apparently it was too much!
So even though the battery was at 60°C, I did not feel a thing. I then reached with my fingers underneath the wrapping (I left vent holes on the bottom and top), and there was the heat.

That was the moment were I knew that I had insulated the battery too much, and that I need to rethink securing the battery against shortage.

For the fun of it, I waited like ten minutes until temperature was low enough again (the ESCs at some point just start to beep again, which tells you that power is back and you can arm your ESCs again).

This time I was about 6 minutes in the air before another shutdown. The temperature had reached it’s maximum of 60°C again!

Possible solutions:

  1. replace the foamed rubber and shrinkwrap with a (plastic) case that has plenty of vent holes on all 6 (!) sides
  2. possibly add active cooling with fans
  3. add a second battery so that the load is evenly split between the two batteries
  4. don’t place the battery directly onto the carbon fiber backplate, leave at least 1cm space for the air to circulate

I’d like to add that changing the BMS’ settings for max temp of more than 60°C is NOT an option, because that’s the recommended maximum discharge temperature by the manufacturer.

My personal opinion: the thermal insulation was so good, that it’s no wonder that the pack overheated.
leaving 1cm of space for between the pack and the backplate, as well as leaving away the thermal insulation and replacing it with laser-cut acrylic sheets with plenty of vent holes on all sides should be enough.

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@GliderPilot I’d like to hear your thoughts, especially about my suggested solutions.
if you care to read my (long) post :slight_smile:

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The ESC’s are rated at 80 amps which is 320 amps total. They are well cooled and have handled 90 amps each just fine at least during takeoff. That’s 360 amps total. Why are you holding it to 300 amps? Is it to protect the battery? Can you change it to 320? Do you know what your amps and volts were when it shut down? Or what it was at max throttle? I take off with 45 volts and 360 amps which is 16,200 watts and that’s plenty of power for me. I assume your total watts is much less than that and you could allow more.

Limiting the throttle is an easy option. If you decide to go that route I’ve modeled throttle position vs percent of voltage which we could use to calculate where to limit the position to get the amps you want.

As for the case… acrylic is too brittle. Polycarbonate would be much stronger. Hopefully you can get the temperature under control so the pack could handle more amps.

How much does your pack weigh? Doubling the pack would certainly help but that’s a lot of weight. Maybe you could add more parallel cells instead of going double.

Good question! the BMS is rated for 300A, and the “overcurrent discharge protection setting” is set by factory default at 300A

The setting actually reads 300,0
yes, with a comma!
when I change that to 320,0 and click on save I am getting some chinese error message and everything sets back to 300,0 !
Same for the total battery capacity. It reads 100,000
and when I change that to 45,000 I am getting that error message again.

However I just had an idea… and it worked. instead of inputting 320,0 and 45,000 (with the comma)
I just set 320 and 45 … and Voilà, I was able to update and save the settings.

■■■■ the chinese software :slight_smile:

Unfortunately not, I had the app on my phone attached to my cockpit, but I could not constantly watch.
I will have to find a solution for a screencast next time.

yeah, you’re right, I thought about that for myself. maybe acrylics will do, but polycarbonate would definitely the better option. I had difficulties finding someone who offers lasercutting on polycarbonate, though. well, just have to search again.
And yes, I am sure the thermal insulation is the problem.
on the large front and back I used double sheet of the thick foamed rubber.
Look at that picture again:


underneath the rubber foam I felt the heat, on top, on the outside, nothing! no wonder it got too hot!

As for the weight,
last time I measured was a couple of months ago:

after measuring I added the two solid copper bus bars, another layer of nickel, a couple of screws, a bit of solder, but I discarded the LCD screen.
I am guessing that I am at 10.5 or 10.6 kg of weight.

Bottom line: since I was able to change the overcurrent discharge protection setting to 320 and since I’ll get rid of the heat problem when I remove the thermal insulation, I should be fine!

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Supposedly sheets of mica are thermally conductive, but not electrically. I’m not sure if it will disperse enough heat, but it will definitely do better than the heat insulating foam :slight_smile:

OR You can order some Aluminum Oxide infused ceramics: Oxide Ceramics – Aluminum Oxide (Al2O3)

Congrats on your first flight! Many more to come I’m sure. Sounds like this bms works very well, I’m happy to hear this. The heat most likely is due to your insulation wrap. I agree with gliderpilot you could add more parallel batteries to your pack this would reduce heat/stress on cells, but a new breathable case should also greatly help. Have you considered Lexan? https://www.homedepot.com/p/LEXAN-24-in-x-18-in-x-0-093-in-Polycarbonate-Sheet-GE-07/202038064

Glad you are able to adjust the amps beyond 300 on this bms!

If I end up building a pack I think I would try sandwiching the pack between two plates of lexan, or building a box out of it and install a fan to suck air through the pack.

Congrats.
I am certain you will get your issues corrected.
Cheers

Watch this space…14s28p coming soon…hopefully.

How did you attach the battery to the frame?

I have no practical experience but feel that you do not need the cooling fans if you create some vent holes. The props probaly generate enough airflow. A frame standoff would certainly help to dissipate the heat.

Great project! Today I bought the Arduino spot-welder and will practice first with retrofitting the 18600 cells in my ebike with 21700 cells so that I get double capacity:)

Keep up the good work…I am closely watching your progress.

Happy flights!

I’m new to this… how much flight time would you get from this setup? How much were those batteries? Shipping? Overseas? Thanks.