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I have a OneWheel electric skateboard with a 58V LiFePO4 battery 130Wh (I believe 14s1p configuration).

There is a method in practice where owners wire EGO LION battery packs (56v 2.5Ah=14s1p, 5Ah=14s2p, 7.5Ah=14s3p) in parallel to their OneWheel onboard battery. Due to their internal parallel configurations, I believe the EGO batteries can flow AMPS as follows: 2.5Ah=20A, 5Ah=40A, 7.5Ah=60A.

I have measured the AMP flow @ 5.5A spike then ramp down to 3A within about 30 seconds when connecting a full 5.0AH EGO to a 85% charged OneWheel (voltage differences of roughly 58V connecting to 54V).

I do not know the internal resistance of the onewheel battery other than my observation above.

My questions are, what is a practical safe voltage difference to connect a full EGO battery to a slightly discharged Onewheel for use in the real world?

Is there a way to graph initial expected amperage currents given onboard battery voltages of the onewheel? (58v=100% - 48v=0%)

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  • $\begingroup$ What do you mean by "safe"? $\endgroup$ – Bob D Feb 4 at 16:15
  • $\begingroup$ I guess I'd quantify "safe" as low enough current that damage to the onboard pack would not be expected in practice. I realize the technically correct answer is exactly equal voltages. $\endgroup$ – deanhuff Feb 4 at 16:30
  • $\begingroup$ But if you don't know what that current level is, how can you expect an answer to the title of your post? $\endgroup$ – Bob D Feb 4 at 16:33
  • $\begingroup$ If you re-ask this question somewhere else, you should say whether you are asking about the safety of using batteries with different nominal voltages in parallel, or about safe methods of equalizing the voltage of batteries before you (semi)permanently connect them. $\endgroup$ – Solomon Slow Feb 4 at 18:08
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This is kind of like asking "how hot is too hot?" It will depend on how fast a battery can be charged and discharged- weakest link. You can always connect through a resistor, let it sit for some time so they equalize (current through resistor drops to zero or voltage across resistor becomes zero), then connect directly. Practically it doesn't have to actually reach zero though.

130Wh @ 58V = 2.24Ah. 5A equalizing current is 2.23C which I would argue is pushing it as far as uncontrolled charge currents go for batteries you know little about. I'd be a lot more comfortable at 0.5C or less with so many unknowns.

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  • $\begingroup$ your last sentence...practically it doesn't have to actually reach zero is what i'm asking. if charging @ 3.5A is what the manufacturer does. how many amps in practical use would result in damage of a direct DC-DC connection? 5A, 10A, 60A? $\endgroup$ – deanhuff Feb 4 at 16:45
  • $\begingroup$ I just added edits. You have no idea how conservative the manufacturer was when choosing a charge current of 3.5A. For all you know that is the very limit in the absence of more info. So do not exceed. Fast charging isn't healthy for batteries anyways. $\endgroup$ – DKNguyen Feb 4 at 16:51

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