I see. I suppose there’s no reason not to go even bigger. But the strips withstand 10 amp continuous. And say it’s 10mohms for that distance (which it isn’t) then even with 10 amps that’s at very very most 100mv drop per strip. Cut across 4 that’s 25mv since. The current splits and quarters.
I measured a 6" strip with a 4wire meter to about 3 mohms per inch. So even those calculations are extremely conservative.
I agree that more would be more conductive but this should provide ample room for amps (giggle) and and extra just adds more. Points for failure at this point
Yeah I’d say so. Though 40A continuously. That I base.on my own test by which I ran 10A through a 6" (0.15mm x 10mm) strip. And it only got warm.to the touch. I should really do a more elaborate characterization. But that feels.too much like my job haha. As mentioned above I did measure the resistivity.to about 3 mohm per 2.5cm. You also have.to factor in the heat wicking of the copper wire and batteries, as well as the self heating of the batteries.
30s peak would be conservatively 2x. So 80A Based purely on edumacation guessing. I skipped all the power classes cause learning how a generator and brushed motor worked down to the magnetic fields. Just wasn’t for me. My game is FETs. Which also means I missed out on the electrothermal stuff. Oh yeah and I skippep heat transfer for electronics class in Lew of my ultimate frisbee league. Undergrad was good times
EE major? lol I had Circuits 1 & 2 and heat transfer. Kind of not looking forward to signals and systems this semester EEeeeeeh
That sounds like a pretty good amount cont, I feel like you could pull more than that pretty easily with good hardware though - just gathering data in my head for when I build my pack eventually lol
Correct, they are welded now and I think there are pictures of that further up. The tabs are also folded now.
Yessir, did my undergrad about a year ago and am going back for a masters in IC design. Cause ya know, I like pain and money but money more than pain.
Absolutely. Im eyeballing most of this and Im being very conservative for it. I wrote IC tests for my first two years in the business (partialy interning) and I follow the same method here as works for testing intel chips. We do a ballpark “feasibility measurement” (the 10A on 6 inches) as well as a model measurement (3 mohm/2,5 cm). Then we pick a no-fly zone-based purely on intuition. this zone is usually ridiculously conservative. In my case, I knew I could handle 10A continuous through 6" with an acceptable amount of heating. This was already way better than what I was going to do (10A cont through 1"). So my no-fly zone is anything above 15A per 8mm x 0.15 mm strip at any length. Now I know I won’t be near that zone and What I didn’t include was the much shorter strip. any 2nd order heating coming from/to the cells/wires and not to mention the active cooling I will have for the enclosure.
I think once my build is complete (UNITY IS SHIPPED!) I will build a rig to test the strips for real. If I see one more person reference that 2 amp per strip chart without proper referencing Im going to lose it.
So, I’m no EE so feel free to dismiss me, I won’t take offense … just going off your calculations: 100mv per P group for a 12S pack is 1.2V drop just from the nickel.
If it’s 25mv, that’s 0.3v drop from the nickel.
If doubling up means reducing voltage drop from the nickel from 0.3V to 0.15V, I’ll do it.
If 0.15mm nickel, 8mm wide is good for around 6-10A continuous and 30Q can do 20A, why not make your nickel good for 20A or more? I know at a certain point there are diminishing returns for reducing heat and voltage drop from the nickel, but from one strip, the old adage more is always better is at least partially true in my opinion.
@Skatardude10
I hope no offense is on the table. I’m just used to arguing my point , personal feelings be damned.
Yes 1.2 sounds like a lot but over 50v thats like 2%
I’d argue that 0.3V vs 0.15V is very much finishing returns. .
A big reason here.is that extra welds introduce extra possible failure points. 1.2v at 40A is 50W of heating. Not really all that much considering.
10A is what I’d argue for continuous nonsignificant self heating. And mainly because 20A per cell continuous is a ludicrous 80A continuous for the pack. I’d be genuinely surprised if I see data where anyone pulls more than 30/40A for more than 30sec.
I’d like to also point out that the shunt resistors on the vesc 6 are 4.7 Ohms.
Regarding amp draw, gearing for speed and direct drives make drawing high amps easy. On my 10S4P geared for 45+mph, drawing 80A was super common, enough for nickel to almost burn through kapton, or at least darken it like crazy where the nickel would get hot. On my 10S5P (VTC5a) with TBDDs, I see 150+ battery amps consistently, every time I hit the accelerator to max. Coming from this perspective, pulling 30+ amps per cell, maybe you can see why my inclination is to overbuild. Even at 20A per cell, id rather build headroom in past 1 strip per cell… It just makes me uneasy.
Ahhh now you’re changing the game. I think we both would agree you should build the pack to utilize the full ampacity. I thing I can safely pull 20A per cell cont. if I allow for significant heating. Which is the rating of the 30Q. I don’t expect more than 5 amps continuously for my ride style. Only the odd pull here or there.
Now the vtc batteries are a different story. And your riding style. Yes given those parameters I would definitely build a stronger pack.
All this makes me really want to build that test rig for. The strips. Need more data
That is crazy, I don’t even think I have pulled over 60 - granted my lipo packs are pretty old now and probably can’t deliver even close to that anymore
I wonder if I would get my full performance by replacing my packs haha
I have had these 25C lipo packs for almost 3 years now of riding 3 to 4 times a week, the sag has definitely gotten noticeable
Honestly it hasn’t been the biggest improvement. The major change is overheating. When pulling 80 battery amps on the same setup I never overheat.
At low to medium speeds, 80+80 motor / 80 battery feels pretty much the same as 80+80 motor / 160 battery. Where it shines though is keeping that powerful feel past easy cruising speed. This surprised me, that off the line it felt almost the same.
Hey, I have a question for builders using Cooper braid for series, what’s your work process, do you pre-tin the braid and then solder it, go straight away to the PCB/nickel or… ? You get the idea.
You should always pre-tin both sides. Pre-tin nickel, pre-tin braid. Place them, then heat both solder blobs till they melt together fully. It will work without pre-tinning, but you won’t be able to tell as easy if you got a cold solder joint on the pad without yanking or wiggling at it hard. Really melting solder good to the pad first and you can avoid cold joints easier. I’d recommend not pre-tinning the braid with as much solder as the pad because the braid will wick the solder, solidify down the braid, and become inflexible and brittle.
If holding my iron for a while when pre-tinning, I usually spread extra flux on both sides being joined, or at the very least melt a little bit more solder in there so it all flows together.
Also, are you using lead free solder? If I’m doing fat cables or anything requiring a lot of heat, leaded solder melts so much easier- lead free requires substantially higher temps to not get cold joints. I always try to use leaded solder unless I’m soldering in the living room or something and I don’t want bits of lead in the carpet
If you don’t need your product to pass a health safety rating go for good quality 60/40 solder and throw that lead free garbage in a bin.
I have been doing DIY for many years and if I learned three things it is:
Pre-tin both sides
Use more flux… the bigger the glob the better the job
Iv been trying out settings on cheep eBay battery and 0.3mm Nickle strip increasing then pulling it off with pliers. It started to get stronger about the 120j and I can feel the heat building guessing about 40 deg if I toutch it straight after welding heat gone after a second. I’m worried I’m using to much energy. What people’s opinions? More or less?
130j I started to rip a hole in the Nickle when pulling it off on 1 contact. 100j seemed to start to leave a little Nickle behind.
so it seems I need difrent settings from pos and beg terminals. My tests found that using a new batty and Nickle strip I was pulling it off early with pliers.
… just going off your calculations: 100mv per P group for a 12S pack is 1.2V drop just from the nickel.
