Noob question thread! 2020_Summer

When at 99 it’s much higher and at 10 (which is minimum) much slower, I guess I could try until I get a good approximation but I don’t have an accurate way to measure the boad speed

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Ride the board and measure the speed with gps, change the remote until it fits the measured top speed.

Probably the most accurate you’ll get.

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I have a question about voltage sag… people say increase p-value of your pack = less voltage sag. I imagine that is purely because AH of the pack are increased… am i right?
I am asking because I am considering doing a Lifepo4 pack with Headway cells (
only 12s1p but a 15 AH pack and rec. constant discharge goes up to 75 Amps. I know others have used these cells or at least talked about them as a viable option. It would be a very cheap but heavy pack I would use for a dual motor longboard with 110mm street wheels. I figure with 15AH I wouldn’t even stress the battery or test it’s sag until mile 10 or so. Even though its a 1p. I currently have a 14s2p lifepo4 a123 cells and while theyre great… I find myself not going full throttle on some hills to be gentle to pack/ trigger low voltage. just looking for something completely bulletproof that I could abuse if i wanted to

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I think some people use voltage sag to describe two slightly different phenomena.

The main one in my mind is “draw more current from the battery and the voltage dips”. This is because there are actual resistances in the pack (weld points, solder joins, wires) that obey ohm’s law, so when you run a current through a resistor there is a voltage drop developed across it. There are also parts of the chemical reaction in the batteries that act sort of like resistance, so you can pretend they’re a resistive element. Same thing applies, current through a “resistor” drops voltage. The reason that adding P groups helps you with this is because adding parallel paths for the current reduces resistance. Think water in pipes, if you add more pipes alongside your existing one you can push more water through without having to add crazy pressure.

The other version that I sometimes see (and don’t really like calling sag but I could be wrong) is related to this:

That’s not the battery responding to a high current draw and the voltage dipping under the load, it’s just the battery going dead. This would be helped by having bigger capacity, because the battery doesn’t go dead as quickly. The voltage produced by a pack reduces depending on how much charge is left in it.

Small bit of extra nuance is that LiFePO4 has some different characteristics to Li Ion. Specifically, it doesn’t change in output voltage as much depending on its state of charge. If you’re comfortable reading the graphs this shows as a flatter discharge curve, basically just that the change of voltage with respect to capacity is more flat (for the majority of its discharge, there’s a spike near fully charged but just don’t charge to 100% and that goes away).

Lithium Ion - you can see the slopes are a bit steeper, meaning they lose voltage relatively quickly with regard to charge level

LiFePO4 - a bit flatter

If you want a really quick and dirty way of reading the graphs, mentally change the labels on the axes to “Miles ridden” on the bottom, and “available speed and power” on the vertical. That lets you plot how much power is available at different points on your ride.

TLDR; P groups help you from reduced power at high battery draw (+ also adding capacity), just adding capacity by itself helps you avoid the feeling of limping home with no power left on a nearly dead battery because you just don’t hit a nearly dead battery as often


What’s your VESC voltage cut off settings? 14s2p of those A123 should get you like 140 battery amps, so maybe it’s the pack construction or too high of a voltage cut-off that’s limiting performance?

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I use LiFePO4 a lot and love them. For commuter boards where range isn’t as large an issue, they’re actually ideal as they excel in every single characteristic except range.

I second @jaykup — what are your cutoff settings?

This is what I like:

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empty post


Awesome, thank you

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Good helmets in late 2021?
Will a TGS pass or Avitar v2 protect me at 40mph?

soo…I’ve got 2 samsung 30q cells that have been discharged to 1.5v. I’ve tried reviving them with the Imax B6 but it spits out an error to check the main line (because the voltage is too low)

what other options do i have? The only other charger i have is this liitokala charger, though i’m not sure if it punches too much energy into the cells relative to the voltage they’re at.

Check the manual, see if it has a low-voltage “pre-charge” mode that uses a reduced charge rate.

Though I would recommend just buying two new cells. :slightly_smiling_face:


This would be the best way, yes. The reason i’m trying to revive them is because they are spot welded together and are being used in a small JBL speaker that barely takes any power. (which is no excuse, i know)

i just don’t want to buy A: new cells and B: send them to someone that can spotweld them ^^ (i’m cheap and lazy) is a fire worth it though? definitely not.


See if you have a 100mA charge rate setting. Use that until they are at about 3.0V or higher.

Make sure they never get hot while charging, charge on a non-flammable surface while you are around and awake. Let them sit for a week and see if their voltage drops below about 4.15V or so. If yes then they’re probably damaged.

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i just remembered that i don’t know for how long the cells have been at 1.5v. They were connected to the JBL speaker but is hasn’t been used for months now, Likely they have been equally as long at 1.5 as they have been not used.

so tossing is most likely the only way.

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If you feel like tinkering, you could set the imax to NiMH or Pb mode and trickle-charge them up to ~2.5-3v that way.
I ended up flashing my imax with this open-source firmware to give it more flexibility and the ability to be calibrated more easily


I mean…this might be a really stupid idea but…seeing as a EDF is a motor with a propeller attached I thought what other stuff one could attach a motor to and…what about a flywheel? could that work? (excuse my ignorance)

It could, but you’d probably need a more specialized controller than the rheo board. Also to store a meaningful amount of your braking energy, you would need either a very heavy flywheel, or one spinning at STUPID speed. Most KE storage/recovery systems use carbon-fiber flywheels spinning at tens or hundreds of thousands of RPM, spinning in a vacuum chamber and supported on magnetic bearings so they don’t catch on fire due to friction.

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Seems right…it’s a load for the motor so the motor would use up some regen current.
Steering with one or two flywheels on board though could be…umm…exciting. :grin:


Not directed at you but just for the record because it’s a noob thread, this is a terrifying idea because large amounts of stored kinetic energy are crazy dangerous. Split your board or take out a shin if it came loose


Yeah, fully agree. Of all the common energy storage systems, I think KE is definitely pretty high on the scary-o-meter if it fails.