It’s gone pretty quiet around here as we wait for Batch 2 to be delivered. So quiet, that we will soon be telling Knock Knock jokes to pass the time…
Given this, I thought I’d reserve a little corner to document the build progress.
May I present my charging system! Yeah. I know. Not as exciting as flight video’s but still a crucial part of the openPPG ecosystem
I’ve mounted my chargers and power supply inside a semi- ruggedised case for ease of transport. It also means I don’t need to dedicate permanent bench space in my shed for charging. Just pull it all out when needed or throw it in the car when going out on safari.
Here’s what it looks like when being used in anger.
At full power, it will charge all 4 batteries in 2 hours. Today was it’s first full power run while I was on smoke guard. I cycled the batteries up and back down to storage and all seemed to go OK
I also decided to re-terminate the batteries with different connectors. Not that there is anything wrong with the XT150’s they come with but I believe there is better out there.
The chosen RC Pro Plus snap-lock together and are spec’d for higher current loads.
I drew the line at replacing the 10AWG battery wire with heavier duty 8AWG. Open LiPo surgery makes me nervous and I’ll see how these guys cope in real life conditions before going that next step
There was a surprising amount of work creating all the parallel charge / balance leads and fabricating the aluminium brackets to screw the hardware into the case but so far, I’m pretty happy with the result
Specs -
Chargers: Hyperion Eos capable of 20Amp charge at 6S. Had one for last 7 years. Bullet-proof performance in compact form factor and added a second just because I could and got it cheap.
Power Supply: generic 50 Amp, 30 volt jobbie in bling red! Will see how it stands up to full power runs from both chargers sucking on it.
Connectors and wire: Rc Pro Plus from Hobbyking global warehouse and 12AWG wire for dual, parallel charge harnesses.
I look forward to adding more to this thread in the coming weeks…
I use the same connectors - they are great! I love the 3 different color codes > black, red, orange
Since we have to put two 6S packs in series to have a 12S pack, it is just more logic to use the
orange color code for the series connection…
@Lukas and @tarifachris for my project (13S15P Battery Pack Build - #25 by etienne ) I will also need to select a cable for the connection to the openPPG. Do you know what amount of current your connectors and the 8AWG silicone/copper cable can handle?
I sort of doubt that they are sufficient for the 300A current that the openPPG will require …
It even says on the sticker of the bag of the connectors: Continuous Current 190A whereas I can’t find any information about the 8AWG wires…
And: Are these connectors also the type the OpenPPG kit is equipped and shipped with?
I’ve had some experience in the e-bike world with 8AWG pulling 200+ Amps.
The thing to watch is the quality of your solder join from the wire to the connector. I once got lazy and ended up with a cold, shitty join in a connector. That much current with a rising resistance melted the solder in the join and it popped out under load, blowing the ESC.
Knowing where the mistake was, I think the 8AWG and RCProPlus should be OK due to the shorter cable runs and better connectors. There will defiantly be a testing phase of the build.
My plan - Put unit on a jig of some sort. Full power run for a complete battery cycle to simulate a max power climb to max altitude. Monitor the temperature of batteries, cables, connectors, ESC’s and motors. Be great if you could hire a thermal camera for a day for this bit.
If there are hot-spots. Double up with another wire and connector.
Just had another thought - using the frame as a negative earth part of the power system (like in automotive design). Anyone had any experience pushing big currents through carbon?
Might drink some idea’s beer and try it out on some scrap carbon tonight
Using the carbon fiber frame as a “negative earth” would be a bad idea in my opinion and there really is no need to. Yes carbon fiber does conduct electricity, but not nearly as well as copper wire which will reduce the system voltage and be less efficient. There really isn’t any need to in this application since the distance the wires need to run is relatively short. The only reason the automotive industry uses the frame as a ground return path is due to cost and weight. Even if you did use the carbon fiber frame as a “negative earth” you would be damaging the structure in the process and increasing your risk of a short circuit occurring. If you pass current through carbon fiber you will eventually melt the resins and epoxy that strengthens the structure.
I wouldn’t recommend pushing that much current through 8AWG either. Even if it they are just short cable runs 8 AWG is only rated to 40-50 amps so you are talking about exceeding that rating by 4 times. Even if you have done it before in an eBike application it is still not a good idea. After all if your eBike catches on fire you can just hop off. If you pull too much current mid flight and burn up your wire or start a fire while you are in the air you are out of a motor and potentially have a fire on your back. Just my 2 cents. Stay safe out there.
Forgive my ignorance Lipo’s are new to me, but I do not understand how the Bonka batteries can say " Max Continuous Discharge: 25C(550A)" yet they come with wires and connectors that are not rated for that continuous amperage draw.
I understand if that rating is for what the battery is safely capable of but maybe they should give a realistic rating for the limit of the wire and connector it comes with? So do to wiring each pack can only do 50 amps continuous?
Also, nice build log Lukas! I too received my bonkas, I assume they’re at storage charge or do you suggest using a charger to put them in that state? I also picked up a Hyperion charger.
Following up on last night. @bkennedy027 is completely right with his assessment of the carbon as a -ive earth system. A 30cm carbon strip lost its structural integrity pretty quickly when a sacrificial lipo was shorted at both ends to simulate big current. . Different forums also describe other problems such as galvanic corrosion as an issue. A tin-foil-hat idea, but was fun to try. So forget I mentioned it and lets move on.
@maxem I believe a very valid point. Though as drone batteries, I can see why they came like this for RC drone application. If the factory is minting them for us and they are open to custom orders, perhaps next time they could install heavier gauge discharge wire for round 3 and beyond. The 10AWG they currently come with looks a bit err… thin for this application.
I am curious with @Pdwhite setup in the video running the 2 x Bonkas. How hot do the battery wires get once you land?
I also take my hat off to @etienne who has gone straight to the ‘pro-build’ option and can parallel up as many discharge cables as needed and side-step this whole issue: If there is one.
Look forward to receiving the unit and having some actual data to work with.
My Tattu’s have 8 AWG wires as well. Hard to find bigger than 8 AWG Y parallel adapter!
My original idea was anyway to split my batteries > 38000mAh to two ESC’s and the other 38000mAh to the other two ESC’s. The load will be halved.
I have no idea how this will work out, because I don"t know how the OpenPPG wiring is designed.
I even think at level flight we will pull 100 A and only at climbing we would pull 300 A…
DIY Lipo Hard-cases for the Bonka’s.
Why?
There big, expensive and I’ve done enough RC to know that batteries are prone to mechanical damage out in the field. Figured they kind of deserved it.
The cases are also snug enough to resist puffing.
Made from 2mm acrylic sheet I cut to size - score with blade and snap
Use heat gun to thermo-form around wooden block, the exact size of the battery.
There’s heaps of Y.T videos about how to do this. Just buy a few extra sheets to practice on and wear gloves when folding the plastic. Finish join by gluing aluminium angle - score both surfaces with sandpaper for best bond.
@dzubot these are the ones that I purchased about two weeks ago:
I bought those, as the 6mm ones are indeed sold out. I chatted with Hobbyking to find out if they would be available soon again, but they could not tell me anything, so I decided to just buy the other ones
My Bonka batteries also came with 10 AWG wires and after flying this morning I am wondering the same thing that maxem asked:
I flew with 2 Bonka batteries. I felt like I couldn’t climb very high without running close to full throttle. The batteries were hot but not uncomfortable to the touch. Then when I removed the batteries I noticed the wires had melted the Velcro that was holding batteries. Here is how I route the wires:
@Pdwhite and whoever else wants to chime in… Now what do I (we) do? Why did our group battery buy come with 10 AWG when even 8 AWG doesn’t support the full C rating of the pack. Shipping batteries is quite expensive and wires have to be welded to the pack not just soldered so this isn’t something I can fix myself.
I have 4 packs but prefer to use 2 at a time. However, using all 4 should help, right?
Fark! There’s some heat in there… Nylon / Polyester break down at 280°F / 138°C so says an online MSDS…
You’d have a voltage drop due to the resistance in the wire which is where all that heat is coming from. Causing the motors not to reach full RPM’s-hence your riding the top of the throttle range to climb.
I have the exact same setup but my order is still in transit. Thanks for posting and here’s my thinking…
Stage 1- Running all 4 batts should definitely help the situation by spreading the load on batteries and wiring. Perhaps you can do this and report back how much less throttle was needed compared to today (if any).
Stage 2 - Shorten all the battery and harness wires as much as you can get away with (cut and re-terminate) Upgrade connectors. Check all soldering
Stage 3 - Open Lipo surgery - Solder on additional discharge wires where the factory ones join the battery (2 positive and 2 negative per batt scenario).
These are still drone batteries made to pull low / moderate current for a longer time. Not big numbers for 10 or so minutes.
Running 4 batteries would certainly help - the power loss in the cable is proportional to current squared, so halving the current will quarter the power loss instantaneously (and better over a few seconds, as the previous higher temperature increases wire resistance, increasing power loss - repeat).
Can I make a little suggestion? For ALL builds (regardless of who did them), PLEASE put the paramotor up against a hard stop (racking etc), and simulate your real flight. So, for example, put it up at 100% throttle for 2 minutes (climb to 900ft), then down to half throttle for as long as you have battery afterwards. This simple simulation should give you some more confidence to actually strap the unit to your back, or will find where the failures happen. If you have a thermal imaging camera (FLIR,Seek Thermal, etc - they don’t cost much) record the on-ground test cycle, and treat any temperature over 120C as ‘critical’
With regards to batteries and ESCs, take any data with a pinch of salt. There are almost no batteries sold for hobby purposes that will achieve the ‘specified’ maximum current rating (550A through 10AWG wire being a prime example), and I have stripped ESCs which have had capacitors that have a lower voltage rating than the manufacturer specifies as an input voltage, and have FETs that are rated at or below the specified maximum current of the ESC (i.e. the non-switching current is being exceeded, let alone the switching current!). Remember, these parts are normally on RC models, so no one cares if they work or not.
So test, test, test, test, and build some confidence first!
