I tested my Li-ion pack 10s 9000mah on flat ground and got 27 miles Then I tested it on a a road with long hills and only got 10 miles. My 12s 5000/25 would go 12 miles on flat or hills. My 10s 5000/60 went 13 miles with using it up. I’m not just throwing theory out there. Like I said, I learned this the hard way and have proved it myself.
I can see your concern, which is why I said I’m oversimplifying it. The discharge curves of lipos vs li-ion are different and thus, it screws any data immediately. But what I also said is from real world testing, this was the case. I knew my limit with the 18650s very well, and with the lipo, I got 2 miles more past that limit.
By the way when you set the cutoff for the Samsung 25R to 3.2V the you only use 40% of the capacity under 20A load.
@Namasaki what were your cutoff levels with li-ion and lipos?
My BMS cutoff was set at 2.8v so if any cell hit that, the BMS would shut down. I ran the Li-ion pack till the BMS shut down. But really, I see your having trouble believing our report even though we have tested and proven what where saying. So the best solution if you want the truth is to go build different types of battery systems like @evoheyax and I have and prove it to yourself.
Doesn’t make sense to me. The 12S 5Ah battery has the same range on flat or hills. The 10S 5AH battery goes further than the 12S battery. And the li-ion does great on flats but fails on hills with 80% more capacity. I am confused now. One last question. What li-ion cells where that? And I hope you don’t use the same bms for the lipos.
This is how voltage sag affects range. More load = more sag More sag = less range. I did not use a BMS on my 12s Lipos. I monitored Voltage. I’m using the same BMS on my 10s Lipos but monitoring voltage and not depending on BMS cutoff. My stoping point with 12s Lipo was normally 42v Which usually got me around 12 miles The 10s Lipo, I have not yet gone below 36v and have not had a chance to finish testing it however, I did get 13 miles with the battery still above nominal voltage. The Li-ion cells I tested where Basen black 26650’s 4500mah 30a continuous in a 10s 2p pack.
According to this test the Basen has 24,6mOhm internal resistance, pack total is 123mOhm, and with at 60A current will sag 7V approximately
Using the VTC6 in 10S3P that has a 20mOhm resistance(calculated from the actual discharge charts from lygte) you get 66mOhm pack resistance and 4V sag, lower if you use 4p, in my opinion your experience with Li-ion used the wrong cells and configuration for your specific requirements
Voltage sag sucks, I made the same mistake in my current board and went with Panasonic NCR B that has a 110mOhm IR, I sag more than 7V at only 20A, but if arround me had less hills, it would be perfectly fine
Good point, The internal resistance is a very important factor. This is another fact that I like about Lipos is that they generally have very low internal resistance. I’m currently using Turnigy packs that are around 1.5 milliohm per cell.
I know where @Ackmaniac is stuck. Let’s see if I can explain it better…
Basics: Power §= ViAi = W Energy (E)= integral(ViAi*dt)= Wh
Total Energy content varies with how hard you push, push 1A on a 10A cell and you get ~12.6Wh of energy. Push 7A on that same cell and your total energy drops to ~10.75Wh. If you have a 40cell battery in ANY configuration (1s40p or 10s4p don’t matter) and you’re drawing an average of 1000W, you just lost at the very least 14.7% of your range this is because your performance differs when you get on the board to halfway through your ride to towards the end of your ride, to draw 1000W at 3.8V/cell it takes 6.6A/cell, at 50% and 3.44V/cell it takes 7.27A/cell and towards the tail end at 3.0V/cell it takes 8.33A/cell So you can see how 14.7% is lost is really conservative.
Now if you have a lipo with the same rated capacity at the same nominal voltage and a 60c discharge rating your voltage sag is non existent and your discharge curve is pretty flat which means your battery energy doesn’t change regardless of how much power you draw.
So yes, hills do reduce range. Same as a car.
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Yeah, and what about cycle life? The only ones I saw test was the Graphene series, but they too expensive at the momment, even the bare generic turnigy cells are pretty expensive, and with that I get half of the range than 10S3P
@PXSS that’s pretty much it, and is important to remember the resistance relation between load and cell, at 60A, without sag, 37V, your load is approximately 600mOhm, this number goes lower with increasing current, to the point where the load resistance is equal than the battery internal resistance, this is the maximum power transfer point, the same amount of power going into the motors is heating the battery, not good since half of the energy is being thrown away and things will get hot quickly, I believe @Namasaki was getting here pretty often with this crazy 100A draw, and thus explains the 50wh/km
You should never even be in that region imo. The internal resistance of the cells is less than 40mohm, 10 in series: 400mohm, 4 in parallel: 100mohm at the battery level. For their internal resistance to quadruple, you would need to be running them hot (60+c) near their low end while pulling ridiculous amounts of current. If you require to constantly pull 100A, your system has been designed wrong. Hell, if you’re constantly drawing 60A on a 10s4p, your system has been designed wrong. You most likely needed a different kv motor with more torque
I just bought some Samsung 25R from NKON. All batteries weighed in as genuine and within 0.01 of a V on delivery, positive cap pattern is correct too so I’m pretty confident they are the real deal. I sacrificed a bit of capacity to gain on the amp draw and price which means I can put together a 10s4p.
If you want a speed monster with great torque you will probably need 100A?
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Then use the appropriate sized battery. A 10S4P is definitely not it.
Depending on your top speed/torque/max power draw, you could run 8S9P, 10S7P 12S6P. They will all be most efficient at different rpms so take the most efficient system and run that for something that could easily provide 2000W+ with @ 7A/cell.
This setup would be very costly as it requires 72cells, but you’ll be running for days and days.
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how much amp and capacity has the 18650 u have?
2500mAh and 20 amp max draw per cell. 10s4p 10000mAh and 80amp max draw (to be set at 80amp via VESC)
Additional cost of 3000mAh and lower max draw wasn’t worth it for me.
80A will kill your endurance and your max power draw is 2500W avg. I would suggest 60A as your max: you gain a good amount of endurance, increase life cycles and you can still pull 2000W avg. l say average because your max power draw decreases as your battery discharges.
Is this right: Does your board drive around 30km in distance?
10s * 3.7 * 10Ah = 37km
Depends on more than that. You need wheel size, gear ratio, motor kv etc to calculate range. It cannot be calculated from the battery alone unless you assume a specific W/km consumed by the mechanicak system
What @PXSS said. Also I have no idea as I haven’t finished my build yet. I am a heavy guy but in pretty much 100% flat terrain. I am not expecting that distance though. Probably more like 10miles or 16km on 14/36t , 90mm wheel and 192kv motor.
Maybe I will go 60amp (to begin with for sure) I doubt I will have many occasions to go max amps anyway.
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