I have got my cells fron nkon over the past years( vapoting) no problem , the other day a sanyo GA died on me just like that … I will go with 30q i think
Yeah Nkon is the best in Europe, the US has it’s preferred one aswell, can’t remember
Anyhow I wanted to mention over the fact that, at least for 25R, 3.0 volts means 500mA left in charge of 2500mA, but you never go below 3.0V, people ofttimes use even 3.2 and 3.3 voltage cutoff parameters and charge only up to 4.0 so you get better battery longevity
The LiFePo seems very interesing, I think Chaka or somebody from Esk8 tried to use them for both the long battery life and safety reasons
It all depends on battery profile but generally li-ion will have bigger voltage drop. It is ok to go bertween 2.5-3.0v under load as long as temperature is under control. Take a look at the link below great test results for lg hg2
Efoil needs a controller like flight controller. So it can communicate with BMS, temperature sensor, so it can control these things and outcome could be derating power and torque based on battery state and other parmeters and potentially some autonomy for assisted riding
Lifepo4 is nice from the specs, but the cells weigh almost double of Li-ion. Not great for efoils that are already really heavy. You need to carry those things into and out of the water all the time.
As i understood , voltage drop : high internal resistance , even higher with heat : waste of energy : lower rpm for our propeller , not a good thing
We need a good cell that can discharge 10-15a for take off so the battery pack can stay light , and i would aim for 5-8a /cell for flying
I still don’t know if i use 13s to keep the voltage around 48v under load
Or 2x6s :12s to keep using my lipo Chargers …
Most esc have cut off voltage and some current control for the motor and some for the battery as well , for me bms is not needed for discharge
Any li-ion will have some DCIR. HG2 cells has high discharge rate which is what efoil require. So we are looking for high discharge (at least 15 to 20 amp), low DCIR, and high capacity and reasonable life cycle. Life span of li-ion is highly depended on battery management system. Thats why for example Tesla battery packs loses just 10% of their capacity over 10 years and they are not re-inventing the cells, they buy them from big manufactures.
Can’t we just rely on a overbuilt battery coolant system, VESC/ESC automatic voltage cut-off and current limiting in our builds? And use BMS only for charging?
Thats what all builders here do usually. But the problem is those off the shelf BMS usually they dont have dynamic State of Power calculation (SOP). SOP in advanced BMS (which you get 10 years and more life span with Li-ion) gets calculated based on cells temperature,SOC (state of charge) and it means power that battery pack can deliver or can consume while in charge. This helps to keep the cell in their specs and keep them healthy and eliminate safety risks. In this case a controller comes to play and command/control esc not more than what battery provide. So no ESC, contractor or battery blow up.
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Has anyone found a good quality cell for a good price yet?
This guy is heavily involved in diy powerbanks and does group buy batteries. Has Brand New Panasonic NCR18650BD for $3.15 Per Cell.
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Awesome find @g.gregory8 !! I think his Sony VTC6 cells might be a better options for us since it can hold over 15a of continuous discharge! I am interested in buying 200 cells of the VTC6 but I would have probably 50 cells extra if anyone is interested! Anyone tried this site?
Hi everyone. Its probably a dead thread and I just got google hits on my modules here.
Tested current on these modules where 200A per 6P with Sony vtc5a, from nkon.nl. This was full to 0. Cells went to 90C at the end of a test while contacts were in low 40’s. Cell contact area with the tab is far greater than that you can get with spotwelding and tabs are made out of 0.6mm copper tin plated for corosion restance. Spotwelding usually done with 0.15mm nickel and its conductivity by IACS % 24% when copper 100%, silver 106%.
Here is a test video:
If you can do that with spotwelded group, then I know far less than you guys.
Cheers
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I would be worried about the authenticity! Go to jehugroupbuy.com . They have authentic Sony VTC6 for 3.50$ per cell. This is a steal. I got 200 cells from them and they come factory sealed.
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Too bad that I am from Europe, and this site provides shipping only to US. Maybe this one Sony+US+18650+VTC5+2600mAh+30-Amp+High+Drain+IMR+Li-ion+Battery+Flat+Top for sale online | eBay
I would be careful on eBay too because a lot of fakes are going around. If you are in Europe, I would buy directly from nkon.nl I think. You guys probably have online retailers with dedicated websites that guarantee authenticity!
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Here is a site that gives , i think the correct discharge value on 18650 pack
I didn’t try them since i am building my own pack , but it gives nice specifications
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