this is how it looks alltogether.
The triple layer board on top is the BMS, which is right now only lying on there. still have to find a way to attach it to the battery somewhere.
And the other side, which shows the not-yet connected balancing wires of the BMS.
still looks kind of messy, as mentioned above, I’ll need to find a way to put it all together.
The tricky thing is, that I really really need to pay attention to not shorting the battery by accident.
I have purchased a large sheet of foamed rubber, which I will use for insulation and wrapping the battery.
However before I start wrapping this battery up, I want to make sure how and at what position I will attach the battery to the OpenPPG frame.
By the way, I received my batch 3 kit a couple of days ago, and I am already at 80% completion.
As I am eager to get in the air with this thing, I will be wrapping up things pretty quickly now.
Note that the OpenPPG now comes with two switches, and that the community has come up with an idea of how to prevent the arcing effect, when turning on the power circuit (a lot of current going from the batteries to charge the capacitors when connecting the circuit), and that is the pre-charge solution
with a 22 ohm Resistor and a special 3D printed switch with a very smart feature
Thanks @GliderPilot
(explanation and files here: Paul B & Braedin B (GliderPilot & Glydrfreak) Flights & Build Modifications - #76 by GliderPilot)
So my two sets of 8 AWG wires are on one hand to dissipate the current onto two sets of wires,
and to be able to connect both switches to the battery at the same time.
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Great looking battery well done! Hope it works as good as it looks. Could you build a plexiglass or thick plastic box around it with vent holes? This would protect it from getting touch by any metal screw head on the paramotor frame. Then mount with industrial Velcro and strap around it to the frame as well.
Amazing you built your kit to 80% 2 days. Would like to know how to battery fits between the motors, lots of room?
Could you connect to the copper bus bars to power cables by tapping holes and securing the cables down with bolts? Add an eyelet crimp connector to attach the wires to the bolts.
After I was done, I kind of thought about the same thing. Soldering the thick 8 AWG cables to a thick copper bus bar requires a strong soldering iron and a lot of heat. (I ended up using a small gas torch to solder).
Using ring terminals and screws would probably have been much more elegant. But hey, hindsight is easier than foresight!
I am scratching my head about what kind of enclosing would be best.
I was first thinking about acrylic sheets as well, lasercut and with fittings just like the carbon sandwich concept of the OpenPPG, a couple of screws, done!
The I was thinking about a sleek aluminum case.
Last, I decided to wait until I actually receive the openPPG kit, to actually see how and where it would fit.
To be able to handle the battery with the conductive screws and carbon plates, I needed to wrap the battery first. This is crucial to avoid an explosion!
This is what I used: a sheet of foamed rubber (I bought two thicknesses, to have a choice whatever is best) and stretch film
And finally, the OpenPPG aaaaand the battery.
the OpenPPG is laid flat on the floor, battery just loose on top, quickly wrapped in the stretch film to roughly protect all the contacts.
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Nice build - looking forward to seeing static test run numbers - wishing you all the best, you put a lot of effort into this and I hope it pays offs - it looks very promising.
I tried building a pack from old laptop batteries some yrs ago for my E-bike. It did not work out and I no longer have the patience for these detailed projects. That is on of the reasons I picked the headway kit for my bike after that.
Thus I admire those that attempt them and envy them when they are successful - I hope to envy you!
Cheers
Thanks @E-pusher!
So after I finally wired everything up (OpenPPG as well as the Battery) I was finally able to fire Up the Battery.
And it looks like as if I had scratched my head to much about the pre-charge circuit and the switches,
as the BMS seems to allow me to turn on and off the Power from the Battery.
The display also reads the Voltage and the Current/Amps once it’s running:
This is a picture of the BMS’s display before I charged the battery. That’s the state the battery is in since the cells were delivered (I never charged or discharged them).
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I then charged the battery for the first time. Charging went smooth, all the way up to the max Voltage.
LG HG2 cells nominal 3,6V; maximum 4,2V and minimum 2,5V
with 13S this sums up to nominal 46,8V; maximum 54,6V and minimum 32,5V for the whole battery pack.
So above I wrote:
and that’s where I seem to have an error.
The BMS display, after charging, shows a battery Voltage of 54,7V.
A Fluke Multimeter reads 54,25V (measured directly at the battery’s positive and negative terminals).
When I measure the output at the terminal of the BMS, it reads 47,8V and drops to almost Zero once I connect the OpenPPG.
Needless to say that the OpenPPG does not react at all.
The Android App, that came with the BMS reads an error:
It says that the ChargeMOS and DischargeMOS Balance lines are missing,
but I have no clue what these are. I wired the battery exactly as per the instructions of the BMS manufacturer
which is also similar to what a couple of youtube tutorials point out
Here’s my wiring diagram, that I also sent via email to the seller of the BMS today:
If anyone has an idea, let me know.
Did I say that the manual of the BMS is written in really bad english?
I think I may have the solution, after searching the web.
I found, that pretty much the same BMS is sold by other sellers as well. The layout of the circuit board looks more or less the same, also the Bluetooth App.
This seller offers the same BMS with a different name. However the explanation of how to use the BMS is already on the product page much better:
There’s a label on the BMS that says the same thing as the text further down in the description:
If battery cell is not full enough 24S, ignore it
After connecting the wires, connect Bluetooth to set the battery parameters and the number of cells to use
The “secret” here is, that this is a flexibel BMS that can handel any amount of Cells in Series between 8S and 24S
(I knew that before).
So you can connect (minium) 8 Balance wires, if you have 8S, up to 24 balance wires, if you have 24S, the balance wires of the non-existant cells are just “left away” as illustrated in this image:
What the the vendor, from whom I purchased the BMS, did not say (and neither do his documents): I most likely have to go back to the App (an up to date Android Smartphone is required) and set the amount of cells that I actually have (13S). I think the BMS just assumes that I have 24S, which seems to be the factory default, hence the error…
I can only test this later and will surely report back.
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I really like that BMS I’ll have to get one when i do a battery pack like this. if you can solve the “no balance lead” issue. Good luck, looking forward to real flight time results.
just a quick reply, my above suggested solution (setting 13 cells in the App) worked!
Motors are spinning!
More info later!
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Congrats etienne, well done. Thanks for posting your findings. I bought same BMS, but will hopefully buy battery from Chris at VeConcepts now.
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Carful not to go full throttle with those volts as you will draw too many amps. You are the first I’ve seen go above 12S and fully charged batteries with 12S draws over 90 amps per motor (360 total).
I’m curious about the details of what else the BMS can do. Does it have a built in solid state switch making it so you don’t need the precharge feature?
Good job with the build… it’s been awesome to watch.
Hi @GliderPilot,
thanks for checking in.
Good point, I will definitely not go full throttle without being on the ground, and keeping an eye on the LCD Panel (which measures the amps) and not without keeping an eye on the battery temperatur (the LCD Panel also shows the temperatur of four sensors that I added to the battery).
Your question about the pre-charge circuit actually is in direct connection with what I wanted to post anyways.
You may remember that I commented on your pre-charge switch design, which I then decided to implement as well.
And you’re right, switching the battery/current on and off is as easy as pressing the button for 3 seconds.
The BMS also measures the voltage of the whole pack (plus of course it’s most important feature, measuring each parallel group’s/cell’s voltage, so that the pack can be balanced - this is even done automatically while charging, of course)
It measures the Amps, the temperature and of course shuts the current off if the voltage is reaching it’s minimum or the pre-set temperature reaching it’s maximum.
I have turned the whole unit on and off about four or five times since I wired everything up, all of the times with the switches being in the on position. The battery fires up with a beep, and immediately the ESCs start beeping as well.
So I will definitely take the switches out of the equation and just discard them.
Next step is, besides building a case for it, to rewire the LCD Panel (adding longer wires), so that I can put it into a separate box that I can place onto my front container, next to my vario, of course together with the on/off button for the battery.
By the way, in this picture, you can see the MOSFETs that are actually responsible for turning the current on and off:
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I like the idea of not needing the switch. At the same time, I wonder if it would be beneficial to keep the switch as a mechanical cut off in case the BMS switch fails for some reason.
That’s awesome how the switch works. I was hoping to be able to add a switch like that for LiPo use but it looks like that won’t be possible… or would it? Could we connect the balance leads from the LiPo packs to a BMS like that and be able to switch it the same way?
The pack from VeConcepts has a BMS and switch that works similar if not the same.
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I think you can even hook up LiPo Pouch Cells to that BMS and monitor and turn them on and off.
When I was searching for a solution for my problem (setting the 13 cells in the App) I found this video:
that guy is using the BMS with LiPo Pouch cells.
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You can see the two LiPo packs starting 6:45.
The link above should start the video where he starts to talk about the BMS (before there is some content about a charger)
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