One way to counter that is to use more cells in series, that’s what boosted done in their extended range pack, if I’m not mistaken it will be 13S2P, so even if the cells sag you won’t loose top speed or significant power, it’s basically to have a 10S board that has 25km/h top speed with the cells almost empty, so you limit the top speed to 25 and the rider will not notice the performance reduction
Some day i have to try a board with 65 km/h. Really curious how that feels. The difference from 45 to 50 is already like from fast but i can handle that to fuck that is fast and don’t do a mistake now. But 15 km/h more must be quite impressive and scary. I think i will try next summer. But then with motorcycle leather gear.
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This doesn’t make any sense. Why would voltage sage under max load shorten your range? You shouldn’t be pulling max amps all the time, so you should also not see sag all the time. Now if you are riding only uphill and weigh 200kg, then you’re a special case and should be treated as such.
I totally agree with @evoheyax I started with 12s Lipo 5000/ 25c 125a continuous They where ok. Then I tried Li-ions 10s 9000mah 60a continuous I was very disappointed. 40% sag going up 10% grade. Ok on flat ground with light wind. Then I built an other Lipo system 10s 5000/60c 300a continuous. Now I can power up that 10% grade and my total pack voltage only sags 1 volt. Range also improves as sag is decreased. I learned this truth the hard way, you just can’t have too much battery! So if you want to eliminate voltage sag, I recommend a battery that’s capable of 10 times the current your pulling. It not easy to do this with Li-ions. You’ll need a lot of cells. Lipos offer the most power per pound and are safe enough if you treat them with respect. Btw, my batteries don’t even get warm pulling my 190lbs up hills.
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Still doesn’t make sense that a 10S 9000mah battery should have less range then a 10S 5000 mAh battery. What where the voltage cutoff start and end on both setups?
It’s simple. The closer your amp draw is to the battery limit, the more it’s voltage sags, The more its voltage sags, the more amps you need to maintain power. The more amps you draw the faster your battery depletes. As your battery depletes, its voltage gets lower compounding the problem. It’s a vicious cycle.
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Even on flat ground, I sag a decent bit and on slight up hills, I sag pretty bad. I have very little flat ground anywheres to ride on. San Francisco in the sunset district is almost exclusively hills. Probably under 10% of the roads here are flat or under 2% grade of steepness. This means I’m always sagging pretty heavily. So when I get my cells down to 3.6v, I must stop. If I have steeper hills to tackle, I must tackle them before I hit 3.8v or I’ll sag down past 3.2v per cell. In effect, I’m losing about 30% of my range due to sag. Now with high discharge lipos, I can get my cells down to 3.3v before I sag before the cutoff. The effect is most range. I know I’m over simplifying this, but my real world tests with lipos and with liion showed me that a 12s 10 Ah li-ion got 6 miles of range while a 12s 8 Ah lipo got 8 miles of range. This is one of the reasons why I nag so much about sag. It slightly dampens performance (which may not be a big deal to some, it should be if your buying the quote un quote “most powerful” direct drive board IMO), but also reduces range, as you must stop at a higher voltage. With the VESC, this will just mean I can’t climb the hills I need to climb when my battery is suppose to have 50% left, as my voltage cutoff will start to kickin. Even with 25% of my lipo left, I can climb the hills I need to without sagging below 3.2.
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That’s not correct sorry. Because watts is voltage multiplied by amps. So the power drawn from the battery is still the same. As long as you don’t reach maximum duty cycle the motor doesn’t care where the watts he needs come from. But more amps is also more heat so you might loose a bit but 80 % (5000 compared to 9000) is beyond my imagination. Expecially when you take into account that the voltage difference is only 15 %. So at a full charge under 80A load you need 15% more amps for the same power. But this is only for the short moments when you draw max amps. To me it sounds that your cells had issues.
With li-ion you can go down to 3V or even 2.8V as cutoff. I set mine to 2.66 for example. With lipos a cutoff at 3.2V is already very low. So this is of course a explanation for the range difference. And you don’t need to worry about the cutoff. Because it doesn’t switch off the board. It starts to reduce the power until it reaches that level. So the vesc helps you to stay in the range you have set as cutoff end. That means it starts to reduce the power when it reaches the cutoff start and doesn’t give any power anymore when it reaches the cutoff end. With a lipos you can get the feeling that it shuts off if you go as low as 3.2V. Because the lipos cells collapse at that low voltage already. Should mean when you reach that voltage under load it is OK. But when you reach that voltage without load then they can jump from 3.4V to like 3.0V in a couple of seconds. Of course that also depends on the lipos. So you need to set different cutoff start and cutoff ends for a lipo and a li-ion battery. That is also the reason why I said that you can’t compare the voltage sag in % if you have the same cutoff start and end.
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