Onewheel+ Battery Questions

[deanhuff]

I have been unable to find answers that I am looking for through any other means, and I see lots of detailed discussion about batteries on this forum so here goes...

I have questions about a processes known as Plug and Ride or "PnR" where a 56V EGO battery is used to connect directly to the charge port of certain older Onewheel + or Onewheel V1 boards. The battery is usually carried in a backpack or mounted to the fender of the Onewheel.

The purpose of this modification is to allow for longer distance riding. To be clear, this is a complete hack, I'm quite sure the manufacturer never intended the onboard battery to be charged or anything to be plugged into the charging port while the Onewheel is moving. It has been determined by removing the 3rd pin of the 3 pin XLR charging connector, the safety mechanism which immobilizes the motor while charging can be defeated. This only works on certain early revisions of the Onewheel+ and V1 Onewheel.

It is reported that a 2.5Ah EGO will yield about 2x distance where a 5.0Ah battery will yield 3x distance over stock. It is advised to plug in a 2.5Ah EGO battery around when the main battery is depleted to 20%, while the 5.0Ah EGO should be plugged in when the onboard battery is between 50-65%. I don't know the reasoning behind this advise.

Other fun facts:
When the onboard battery charges to 100%, the motor cuts out (i.e. you fall...the one onewheel literally has a single wheel and uses gyroscopes to keep you balanced).
Only the + and - terminals are used on the EGO battery, there is no under current protection from the EGO's BMS, so the operator needs to press the button on the EGO occasionally to look for a green/red light make sure it does not drain down below safe levels (42v)

There is another method among Onewheelers known as Vamp and Ride or "VnR" where an ego battery is wired in parallel with the onboard battery. I fully understand the need to match voltages when connecting batteries in parallel. For now, I am staying away from VnR setups because they all require internal modifications to the Onewheel.

The charger for the Onewheel outputs 58.4V at 3.5A so about 208 watts. Voltage falls inline with what an EGO battery can produce, however I have no idea how many amps an EGO can output. The 2.5Ah EGO is 14s1P while the 5.0Ah EGO is 14s2P....I'm guessing these batteries have the potential to output many amps greater than 3.5 from the stock charger.

The Battery on the Onewheel is a LiFePO4 battery, the board states it is 58V 130Wh, by my calculations that's about a 2.25Ah battery onboard.

With all of that explanation out of the way here are my questions:

1. Should I be concerned about initial current flows when hooking the EGO battery into the charger port?
2. Are there any tests I should run or things I should look out for to minimize damage to the onboard battery?
3. Could several EGO batteries be used in succession to maintain even longer rides?
4. Should I wire an in-line fuse between the EGO battery and the charge port to protect the Onewheel? If so, is there a certain product you would recommend for this application?

I have access to a Fluke Multimeter with a 10A / 600V fuse by which means I should be able to measure initial current flows...I have yet to do anything other than order the wiring harness and get some used EGO batteries off Craigslist.

 

[amberwolf]

There is another method among Onewheelers known as Vamp and Ride or "VnR" where an ego battery is wired in parallel with the onboard battery. I fully understand the need to match voltages when connecting batteries in parallel. For now, I am staying away from VnR setups because they all require internal modifications to the Onewheel.

FWIW, this might be a safer and simpler method of operation, because you will then charge and discharge both batteries at the same time, (assuming the EGO pack charges thru it's discharge wires and is safe to charge this way, meaning it has a way to protect itself from overcharging) and you aren't pouring current thru the charge connector at a possibly much higher rate than it or the OW BMS were intended or designed to handle.

The charger for the Onewheel outputs 58.4V at 3.5A so about 208 watts. Voltage falls inline with what an EGO battery can produce, however I have no idea how many amps an EGO can output. The 2.5Ah EGO is 14s1P while the 5.0Ah EGO is 14s2P....I'm guessing these batteries have the potential to output many amps greater than 3.5 from the stock charger.

Some guesses: If you had the OW battery down close to empty, let's say 45v, and the EGO is fully charged at 58v. Let's say the OW battery has an internal resistance including all parts inside of 200milliohms (it's probably less), and the EGO has 50milliohms, then the difference in voltage 58v - 45v = 13v, then 13v / 0.250ohms = 52Amps. This doesn't account for voltage sag of the EGO under that load, nor does it account for any protection it might have that shuts it off under such circumstances, or voltage rise of the OW battery during this high charge current. (the math for all that is way too hard for me ).

If you can find out (or measure) the actual battery resistance of each pack, and know the actual voltage difference, you can guesstimate the initial current that will flow between them when connected.

1. Should I be concerned about initial current flows when hooking the EGO battery into the charger port?

Has anyone broken their OW by doing this, regardless of circumstances?

If yes, then concern is definitely warranted, becuase it's not designed to be used this way.

If no, then its' likely that it will "just work".

There are risks...but they can be minimized by simply always hooking up the EGO pack when boht it and the OW are at the same voltage, and leaving htem that way. If you have multiple EGO packs you wish to use, make a Y-cable that lets you plug all of them in at once.

Doing this means that the charge port connector and the BMS charge port FETs do not have to handle any high currents. They will only handle the current flow of the EGO pack into the OW pack as the OW pack drains, keeping all packs at the same voltage. The max current thru it will probably be about half of whatever the OW controller is drawing from the battery in total at any moment.

2. Are there any tests I should run or things I should look out for to minimize damage to the onboard battery?

If others have already done all this stuff and documented it well, then they have already done all the testing required, assuming that no one has any problems with doing this. If they do have problems, then you'd have to do tests to verify your system won't give you the same problems...but I don't know what those tests are, because I don't know what the problems are.

Any tests I can think of to tell you things about the system that would be useful are potentially destructive (like testing the charge port for max current capability--this usually requires testing until it fails or shows signs of imminent failure before you know where to stop). Finding out this sort of info without destructive testing is possible; it just requires disassembly of things to find out exactly what parts are in the charge current path, and then finding out what each of those is rated for.

3. Could several EGO batteries be used in succession to maintain even longer rides?

See above where I described connecting multiples with a Y cable. The limit will be whatever the OW systme itself has for heating. If it was designed with only enough heat capacity to survive the range/ride time of the onboard battery, and then cooldown during the recharge process time, then riding longer builds heat in amounts it can't get rid of fast enough, and eventually heat buildup will damage whatever parts can't handle it.

If it has good cooling, then nothing will ever overheat no matter how long you ride it, and you can use as many batteries as you can actually carry with you, to give you as much range as your butt can handle.

Other fun facts:
When the onboard battery charges to 100%, the motor cuts out

This is easily avoided by ensuring the EGO packs are never charged to a high enough voltage to cause the OW to be able to reach it's 100% full voltage. Assuming that it does things the cheap way, and measures capacity by voltage, which is the most common way.

If it measures by coulomb-counting (like a wattmeter) and shuts off when a certain number of Ah has passed thru the charge port, regardless of actual battery state of charge, then you would need to use a wattmeter on the charge port, with an alarm on it set to something far enough below that Ah limit to leave you time to pull over before it is reached. Then do whatever OW's do to reset that shutoff (presumably run down the OW battery to empty?) and repeat the process until your ride is over.

4. Should I wire an in-line fuse between the EGO battery and the charge port to protect the Onewheel? If so, is there a certain product you would recommend for this application?

Do you know how much current will need to flow thru the charge port during the ride? If not, it's tough to size a fuse small enough to protect the charge port stuff but big enough to not blow while riding.

I have access to a Fluke Multimeter with a 10A / 600V fuse by which means I should be able to measure initial current flows..

It's likely that the Fluke's fuse is well below the initial current, and will just blow. If you want to measure higher currents, either use a wattmeter (with remote shunt, useful for putting the meter where you can see it while riding, or builtiin shunt, useful for tests like this and embedding into the pack with the batteries in it for ride testing), or a clamp-on ammeter (whcih won't burn out from higher currents; it will just show you "OL" when beyond it's limits).