An Equals Zero Quickie: Adjusting the Voltage and Current on Your Inexpensive Chinese E-Bike Charger

So over the last few weeks I went back to my roots a little and spawned an electric bike out of basically just the hot garbage in my robot/van/go-kart storage totes and a $20 yard sale frame. That post’s for (yet) another day, but what I also needed to do is charge it… and that is where things got funny.

I still have several standalone e-bike/scooter chargers from the 2.00gokart and Power Racing Series days, but they’re all for 10S (37V for LiCo chemistry or 33V for LiFe) lithium packs. I also have a 12 LiFe-only one that I used for Melonscooter, which is the one I will be hacking up.

This new e-bike runs 12S regular lithium cobalt, with a nominal voltage of 3.7V instead of 3.3. I just had to figure out how to crank the charging voltage up some, from the 43.2V of charging 12S LiFe cells at 3.6 volts apiece, to 49.2 volts for charging lithium cobalt at 4.15 volts per cell.

So let’s crack it open. Basically every switching power supply architecture has means to do fine tuning and calibration on the factory floor, you just had to find it. They usually can’t adjust far, which is why I started with my highest-voltage charger.

I did a quick scour of the Internets for whoever has done this before. Luckily, the usual suspects at Endless Sphere (still alive and buzzing in this day of easy social media share buttons) have done this before, and I found some useful information in this thread. I seem to have a visual match with one of the chargers posted in the thread.

These things haven’t moved much technologically for over a decade if not more, so it was easy to make the visual correlations with mine. Here’s the potentiometers on my model, which was sold by ELifeBike, still around today as PSW Power:

From the schematic posted in the thread, I deduced that the termination voltage adjust trimpot was right by the output status LEDs. They usually are some place obvious for the technician. At the time I didn’t know what the other two trimpots did, but figured they were charge current and charge termination current threshold (At some point, your charge current in CV mode falls so low you might as well call it good).

The way I was going to make these adjustments, obviously, was all live, all the time. So if you do this, just remember that even if the output sounds relatively harmless like 24 volts, switching power supplies still will pack a few hundred volts right next to that. So, avoid poking the wrong thing.

We begin the prodding by checking the charger as-is after scattering it on the bench. Hmm, 44.3 to 44.4 volts on the output, you say. That’s above the termination voltage you’d want for LiFe/A123 cells, but not enough to really hurt anything.

I began cranking the CV trimpot and (many many turns later) got the voltage up to about 49 volts. Counter-clockwise is increasing voltage, at the rate of what seems like 0.2 to 0.3 volts per full rotation. I was scared of running out of potentiometer, but it got there. These small vertical trimpots are usually 25-turn.

I generally bulk charge my EV batteries, so I don’t take them all the way to 4.20 volts. Historically I’ve popped them out once every few months and balanced the packs manually…. if at all. Beyond that, you make an assumption about how far apart you can stomach having the cells drift, and assign a little safety margin. For instance, by charging to 4.15V per cell, you are saying that the summation of all cell voltage deviations both high and low shall be no more than 50mV…which is quite a lot, by the way.

So that’s why I didn’t adjust it all the way up to 50.4V, which is 4.20V/cell for 12 cells. You only get 3 or 4 percent of charge going that high compared to 4.1-4.15V/cell and it just makes for a much more relaxing experience. I dunno why, but I expected some kind of instantaneous catastrophic failure as soon as the thing hit 50.0 volts.

Next, I wanted to mess with the charge current not for any hot-rodding reasons, though you know me, but to see where the adjustment is made. On the PCB, the two (what I think are the) current-adjustment trimpots are located right next to a dual op-amp chip, part number HA17358. One of them probably adjusts the CC stage current, and the other the cutoff current.

I just picked one and started messing with it, and hey, it’s the correct one.

Pursuant to the “You know me…” up there, I gave it a few whirls to bring the charge current up to 10 amps. The “rate of adjustment” seems to be about 0.3 amps per rotation, so I was turning this thing forever to get to 10 amps from 8.

To dial the current in, you have to actually be charging the battery. Luckily, this bike uses salvaged Overhaul and Sadbot batteries. They’re 6S and 6Ah each, and I run them in a “2S2P” arrangement to get 12S 12Ah. They’ve been sitting a while, so were discharged somewhat.

Finally, after keeping an eye on it for a nervous 30-something minutes, I decided to see if I could change the threshold current for ending the charge cycle. This is probably something that is utterly unnecessary, but curiosity!

As I watched the current drop below 1 amp, I decided to give this trimpot a few spins to see if I could induce the cutoff. This time, clockwise seems to raise the cutoff current. I spun it forever counterclockwise before I realized I should probably go back the other way, as I did not actually count any of the revolutions.

A few turns clockwise later and the green LED turned on, indicating the cycle is complete. Again, there’s probably no need to mess with this at all.

While I was inside, I decided to also go ahead and shore up the completely unprotected PCB with some conformal coating around the chips and sealing the connectors. This thing no longer lives in a climate-controlled building, so I figured it wouldn’t hurt.

Some day you’ll hear about the bike itself, I promise!

Beyond Unboxing: A Dive into the Gear Vendors Overdrive

We’re going to skip ahead a little from the Summer of Ven into more the “Autumn of Ven” because I get to ramble about a cool mechanical thing. As one of the categories on this site, I often take apart neat things and make snide comments about their construction or internal parts. This time, it will be the Gear Vendors overdrive unit that lives under Vantruck, which I got for it in 2018 in a already very well used state.

I didn’t know how many miles it had on it already, and kept up with the recommended maintenance interval for fluid changes. It was just fine from 2018 until this past summer when it began slipping under load, and even worse, would occasionally seize in the overdrive state, leaving me barely able to reverse (and you’ll see why soon). Hauling so many vans back home probably did the unit in, finally.

I tried a few hacks, like flushing the fluid with a lower viscosity oil for a little while and cleaning the high pressure filter, neither of which really resolved anything decisively. Well, that’s how things shake out I suppose, so I called Gear Vendors to send the unit in for rebuild. What they do is go ahead and send you the new one and refund a core charge once they get the used unit. The total cost afterwards is about $1200 for a rebuilt unit, $500 of which is the core charge.

I’ll get to the install itself – first is the interesting bit, which is taking the old unit apart!

Here it is on the surgery ward floor after dismounting from vantruck. Notice that the input shaft is pulled out? It’s not actually attached by anything, and all you need to do is ensure it mates with the internal spline on the right side. I’ve pulled some kind of inspection lid off already, as my MO with anything on Beyond Unboxing is to start popping bolts off.

Inside the lid is the tail end of the output shaft. There’s nothing much going on here to speak of. I think this port is to install retaining clips.

The real bolts are around the perimeter on M8 studs. They come off fairly easily.

On the front, you need to remove the four nuts that holds the shifter piston’s end effectors, little bracket things, to the internal shifter ring. They’re gently spring loaded in this position, so the studs will pop inwards as you take the M8 nuts out.

When the shifter solenoid valve is enabled, oil pressure fills the two shifter cylinders (the round things behind the brackets). These two brackets then pop outward and collide some parts together inside that they’re linked to. We know from cutaway diagrams that it’s cone-clutch based, so presumably it’s connected to the cones.

Where does that oil pressure come from? The shaft that fell out has an eccentric lobe on one end, which rides in the circular socket seen in the center. That’s connected to a simple rod pump. So when you move, there is oil pressure. When you don’t move, you pray the seals are still adequate (though it seems like one or two pumps of the rod is enough to fill up the shifter piston chambers. Typically, to prevent leak-down from causing inadequate pressure to operate the pistons, the automatic controller you can get (which I didn’t install, because fuck using phone jacks as connectors) has a speed-based lockout.

And with those bolts removed, the whole thing just kind of splits open. Well there’s my first sign of something being wrong, the clutch cone has no… clutch on it.

Here are all the fun bits laid out in order left to right: the casing with the fixed clutch ring, the cone clutch assembly, the gearset, and the output. So what in the epistemological hell is going on inside these things, anyway? They rely (as most good things do) on the magic of planetary gears and their ability to add, subtract, and multiply speeds.

So the big showrunner of this basket of skulduggery is the cone clutch assembly, pictured center left. It’s coated on the outside (usually……..) and inside with clutch lining, and is the object being rammed into everything else.

I pushed the shaft back in for the assembly photo, but notice that the shaft doesn’t engage with the cone clutch, but actually with a splined bore inside the planetary carrier (center-right). When you spin the input shaft of an assembled Gear Vendor overdrive that’s at rest, you are applying torque to this carrier.

The sun gear of the planetary gearset is attached to the big clutch cone. This means the clutch cone controls whether the sun gear is fixed (grounded) or free to spin with everyone else including the clutch cone itself. This is important, because on the very right is the output cup, which acts as the ring gear (asteroid belt?) of the planetary gearset. It, too, is a cone shape on the outside, fitting tightly into the interior of the cone clutch under rest conditions.

So you have two choices for the position of the clutch cone. Either it’s spring-loaded (with a big throwout bearing seen below) into the output cup, or it’s pushed against the fixed clutch ring on the casing by the shifter solenoids.

In the rest condition, the cone clutch is shoved against the output cup. They rotate as one. With the sun gear affixed to the cone clutch, it’s forcing the planetary gears to also not rotate. If you overtorque the system and overcome the cone clutch friction, there’s one more line of defense left: the planetary carrier on one side is a very large spline that fits into the corresponding spline in the output cup, around which is a one-way bearing.

Therefore, in the rest condition with the vehicle powering forward, the torque is taken up by either the cone clutch friction or the one-way bearing forcing the carrier’s torque (which is your input, remember) straight to the output shaft.

In the overdrive condition, the cone clutch shifts forward a half inch or so and mates with the fixed clutch ring on the outer casing. The sun gear is stopped dead, and the planetary gears are forced to mate in orbit around it.

The good trick here is when you have a planetary gearset in that condition, the rotational speed of the planets adds to the rotational speed of the carrier. A gear that mates with the planets, like the output cup, will get flung faster than the rate at which you spin the carrier (/the input shaft). You might say it’s overdriven. In this situation, the one-way bearing capitulates and spins freely as the output cup is now moving positively (faster, in the same direction) relative to the carrier.

So there you go. That’s how the thing works in forward. Here’s a better view of the stackup from the end view, showing the big throwout bearing that controls the cone clutch and the also-conical shape of the output cup, and its one-way bearing inside.

When using a GV unit, you’re advised to not reverse while the unit is active (shifted in OD). The automatic controller (which I didn’t install, because fuck using phone jacks for anything) has a reversing switch lockout so it automatically disengages. Also, if a unit is severely worn, reverse is also generally difficult or impossible as it slips even in the rest state. The reason this happens is a unique property of the angle of cut of those planetary gears (they’re helical cut) and the liability of having a one-way clutch.

Cone clutches work on the principle that the two cones crammed together create an outward normal force many times the force pushing them together axially. The same principle governs tapered spindles in machinery. To work properly though, you generally have to keep holding them together. If a force exists that pulls the cones apart, they’ll decouple quickly.

The helix angle of the planetary gears creates an axial thrust load when the gears are transmitting torque. The direction of the helix is very important here. It turns out, by observation, that the helix is purposefully set to 1. Pull the clutch cone tighter in the OD and forward-torque condition, as well as 2. failsafe in the off (rest) position.

In the overdrive position, with the input shaft applying positive torque “Forward”, the helical thrust force pushes the sun gear into the clutch cone, which forces it more into the fixed clutch ring. That is, to the left in my explosion photo. It took me a while of staring to realize this is the case, and it makes the engagement more solid: As long as you’re applying drive torque, the system will tend to keep itself engaged.

Reversing in the overdrive position is a problem, because now the thrust force is pulling the clutch cone away from the fixed clutch ring (Towards the right, in my first exploded photo). At this point, you’re fighting the oil pressure in the shift pistons. At low-to-no speed, the oil pressure is not high, and likely leaking down slowly. The applied reverse torque at standstill wins, the cone clutch begins disengaging from the fixed clutch ring, and you don’t go anywhere fast while slowly grinding the clutch down. In real life, this is manifested as a really ugly squealing sound as you only maintain roughly idle speed in reverse, if at all.

Oh yeah, that one-way bearing isn’t helping you in this case either, because if you’re spinning the planetary carrier the wrong way, it doesn’t engage.

In the rest position, however, with the clutch cone now forced against the cone of the output cup, reversing torque now turns into thrust load which shoves those two cones together. The one-way bearing still doesn’t help, but at least your system is trying to be in a positive-feedback state. The reversing torque is still ultimately limited by a 3/4″ wide clutch band, and if this band becomes too worn or disappears, you could lose reversing power entirely. However, the general story seems to be it’ll try its darndest even severely neglected going metal on metal, because of the thrust of the planetary gears helping keep the cones together.

So there we go. Quite a clever mechanism with a few foolproof design choices to improve overall reliability. If the helical gears were cut with the spiral the other way, everything would have sucked more. That’s easily something I see myself doing, so good thing I didn’t design this thing, huh?

Alright, I’ve satisfied my curiosity and am now ready to put it back together so I can ship the unit back to Gear Vendors. I dunno what it is that I did, but I can’t quite get the thing to close again.

So I just left it halfway open, put the nuts and washers in a baggie, and left a note explaining myself.

That’s all for this episode of Beyond Unboxing! The installation of the unit itself will be covered separately as the Summer of Ven progresses.