That is not lifepo but Samsung 25Rs
The Samsung 25R can deliver 20A until the cutoff of 2.8V till 2.25 mah. That means for 90% of itās capacity it can deliver 20A. Sounds good to me.
Got it. Thanks!
So when your cells hit the cutoff at 2.8, what is the voltage of your cell after you stop the discharge?
I would say maybe Iāve messed up with my battery, which is causing the sagging numbers and poor range numbers, but I had these issues before with the space cell. I had the 10s3p space cell, and I was lucky to get 4 miles on my route (had to be very conservative with the throttle and run stop signs when possible). You logic there seems good, but it the real world, I had very different resultsā¦
Of course it jumps back. But the shown discharge curve is under load.
What is your theory than for my poor range?
I could get 4 miles with a 10s3p and 6 miles with a 12s4p (LG HE2ās). The calculations I did sowed I should in theory get 4 times this.
The most likely cause would be fake cells, but I would expect the space cell to have legit cellsā¦
I think we need a battery selection/technoly/voltage sag guide thread. I think we all agree on some basic points but all the thread jumping is making the info hard to find.
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Thought you mentioned before that you set the cutoff end to 3.3 or 3.2V because we had this discussion already. Maybe you should do a little test when you find the time. You also have a app to show the data in a video. I would recommend to show a video with Lipos and Li-Ions on the same board with the same setup but of course correct voltage cutoffs. Would be very interesting.
@Ackmaniac. You are wrong in your watt hour calculation. At 20A your average voltage is NOT 3.7v on the samsung 25r. Itās more like 3.1v. Look at the discharge curve. Do your math with that number and youāll see why @evoheyax gets crap range from his cell.
From the voltage sag thread a few weeks agoā¦
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.
And what happens when you discharge the cell with 20A continious, and once you reached the 2.8V then you continue with only 1A. How much Wh do you get then from the cell?
That is an unrealistic scenario but sure, Iāll bite.
Scenario 10s4p samsung 25r pack on a quad drive, that pulls 80A total on a hill, you discharged till 2.8 but then itās flat home and you can cruise at 4Aā¦
Here are both curves on a per cell basisā¦
You ride at 20A until you reach 2.8v. Average voltage: 3.1v Total Ah: 2.2 Total energy used: 6.82Wh/cell
Continue riding at 1A until 2.8V again. Average voltage: 3.1v Total Ah: 2.45-2.2 = 0.25Ah Total energy used: 0.775Wh
Sum of energy used: 7.595Wh/cell Times 40 cells: 303Wh
āRatedā = 403.62.5 = 360Wh
You lost 16% of your rated energy by running at 20A continuous.
Very nice. Now we get closer. A realistic average discharge rating for a average ride would be around 16A (4A a cell on 4P) in total. That is more than 500 watts on average which is quite high. Can you do the Wh Calc please for that.
If I am not wrong it should somewhere around 3.6V * 2.45A * 40 = 352Wh Sounds good to me. Of course you have some bursts with 20A but we are very far away from 20A continuously.
Problem with average is, average for who? Since we are all using different motors and configurations, are different weights, and ride in different environments, there is no average discharge. This is why I focus more on max discharge. If it works well in the harshest of conditions, than its good.
Even calculating average amps is tricky, because how do you calculate it with real world data? I ping the vesc every .25 seconds, so I just add them all up and divide by however many amp data points I have. This is bad though, because I factor in the times when Iām not moving. so say I have 10 10 0 15 8 8 0 0 0 0 4 as your amp data points, that would be 55/11 = 5 amps average. But thatās not a good indication because while pulling 0 amps, I likely was not moving, so It shouldnāt be counted. If I leave the zeros out, thatās 55/6 = 9.166, which is more accurate. So how you calcualte average amps even could skew your numbers.
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Load up his custom vesc firmware or attach a wattmeter in line and find out what your average power draw is. Iām sure we can get you to give up lipos 
I can understand your statement. But your board is something I would definitely not call average. For me the average rider is 80 kg with clothes and the board has a max speed of 45 km/h. And there are some hills in the area. But of course not like in SF. And 500 watts average would already be a average speed above 30km/h. And I donāt think many of us even ride that speed on average. So I think that those values are not bad when it comes to the average rider.
(3.55v * 2.125ah + 3v * .25ah) * 40 = 331.75Wh ish
You cant really relate average power to average speed as that is truly dependent on road conditions, riderās weight, gear ratio, etc.
Why do I feel like we are repeating the same conversation from 2 weeks ago? Lol
Iām working on some new data points for my app. Iāll be able to give you more info about my board soon that should explain more. Iām mostly curious as to how many Wh I actually get from my 12s4p li-ion battery.
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San Francisco hills are crazy though. I see why you run LiPosā¦ @evoheyax. You could probably get away with a liion pack but it would be extremely expensive, although if you solve the power issue, you could be looking at twice the range as your lipo counterpart.
Give me numbers and Iāll get you a solution.
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