tweaking up your charger

Warning:

Firstly I don't recommend this to anyone who is not comfortable with electrical work and who has no history of electrical work.

So with that out of the way its pretty common that the chargers supplied with our scooters are not really "dialed in" to voltage (you're shocked I'm sure that a charger that you can buy on eBay for $20 wasn't bench adjusted) ... sure someone does some "gross adjustment" but not really careful dialing in (and don't start asking about the accuracy of the 240V supply to your house).

Why?

well as it happens batteries need a particular Voltage to charge, which must be a bit more than the voltage you want them to charge to. It doesn't need to be by much but it does need to be more. Further a reality of electronics is that everything (no matter what) takes some voltage out of the circuit, so even if the charger is supplying 54.4V the BMS will inevitably take a little nibble out, as will all the wires. So its best to tweak the supply to be a little bit over the level of the BMS.

Below is a picture of my charger now charging (in the final phase) my 500W mercane which has ridden just a few Km after its last charge (which I noticed wasn't getting up as far as I'd like it to have gotten) on the "other charger" which I keep at work. I've tweaked all my chargers here.

You can see that while the light has gone green indicating (to those who think they are in the know) that charging is complete, the charger is still supplying a small current (for the saturation of cells to 4.2V)  which still (because of the voltage) amounts to 7.1W or the equivalent of a modern efficient bulb. All in all the battery has had pushed in about 40Wh, which is pretty consistent with the small running around I did before putting it on charge now.

What did I do

Basically I just carefully opened the charger (mine has screws under the bottom rubber feet) and then identified the "trim pot" and with it plugged in and live adjusted that up to where I wanted it. See this Video

This basically went very well and I was then able to see good charging voltages and indeed show the difference between what the handlebar volt meter shows and the voltage at the entry to the BMS (using my inline meter)

Job Done

Hope that is helpful to someone.

Mercane single motor 8.8Ah battery range test

This post is a follow on from my repair post here. Well, looking at all this I'd say that my scoot has passed its battery test. and is pretty much "up to spec" despite nearly a year of use and some problems with the BMS and construction.

Introduction

To test the battery in the scoot I took it on this course:

So while I didn't tackle any significant hills (read mountains) I did indeed do some long uphill slogs. Here's the GPS data

When I got it home it was pulling Volts down to 44.2 or so on the milder hills, but still pulling better than it ever did on hills, and note how steady the speed was almost to the end.

Analysis

The interesting thing was the recharge: It took 271Wh to recharge (using my 150A meter to count that), and as the battery is rated at 422Wh this means I've used up about 60% of the battery total rated capacity. Now as anyone who knows much about batteries would know, getting that last part of the energy may be hard to get to and even predictable about how far you can go, perhaps even may damage the cells if getting to it (if you don't have a good BMS). Here is why: the discharge curve.

Looking at this test discharge of Volts vs Ah working out the area under the curve (using a near approximation and I've chosen to be a bit conservative) gives me 7.11Wh per cell. So with 13S4P that gives me 13 x 4 x 7.11 = 369.72Wh of actual usable Watts. Note how quickly that last bit of voltage at 3.4V per cell just dies off.

So while my cells are 2200mAh the difference will be small (if indeed it is any different and not just "rebadged").

For all intents and purposes I'm willing to call the 271Wh I put into it (on recharge) to mean that my ride took out 271Wh Effectively 75% depth of discharge. Given also that rapid fall off at the end that last unit may be quite unpredictable (and depend on hills), its best to not be relying on that being available. Meaning I won't get much more out of it than that (as you can see how the voltage plummets towards "out of juice" and I'm walking levels.

So a real world range of 20km "flat stick" on cruise control is reasonable. The less you do stops and starts of course the better because re-establishing speed will suck more energy than just maintaining it.

Thoughts

Knowing this curve you can more accurately use your Volt meter to understand how voltage (while riding) reflects your actual remaining range. For instance, when you see certain voltages under load (you'll note that flat road cruising voltage is different to that going up a hill, because of the load). To get the chart below I used the 2A discharge measurements of the Parkside battery (because I expect its pretty close to what I've got having observed my own discharge and the battery markings) and simply altered the scale on the Volts axis by multiplying cell voltages x 13 (because I have a 13S4P pack)

So seeing anything dropping down to 45V while under load means you're getting close to the end. If you're seeing 48V you've still got at least half your power left.

Next interesting thing is that if one considers that I needed (to supply to the scooter) 271Wh to travel about 19km that works out to about 1.4kWh/100km which (as mentioned previously in the article about my dual motor variant) is stunningly good efficiency and no electric car gets anything like this. Supporting my view that for short distance frequent trips a scooter is far more the efficient transport solution for cities.


It remains to be seen if I need to give this pack any more attention, but hopefully this shows how resilient they are and how easily rebuildable they are.

For how this started please refer to this post here

Mercane 8.8Ah pack repair

This all started back at this post. However I think that this time I've nailed it, mainly because unlike last times I've identified a very significant physical factor: a rusted through connection bus strip across the postives of one parallel bundle of cells (yes, the one that was down on that last BMS test).

I found it (and as you can see it was buried beneath the paper where the BMS sat) while trying to identify which set of physical cells that wire loom (just to the right of the picture) connected to, as I'd been making my voltage measurements off that. Its hidden under the paper behind the BMS as seen in this picture:

(featuring a Reddit Approved Kitchen Utensil as a tool).

Anyway, the voltage measurements at the pack didn't marry up with what the BMS was seeing, so I dug in to see. When I peeled it back I saw a big scab of rust across the cells, which basically just crumbled away when I hit it with the vacuum cleaner.

So essentially this leaves the last three cells unconnected to the BMS and so only one cell was getting charged and supplying power.

I cleaned it up with the wire wheel on my Dremel tool ...

which showed me that I just needed to bridge that set of cells and I'll be right.

Now lacking a spot welder I pondered how to best do this, and decided that because it was the positive ends I could prepare that lone cap with some solder if I worked fast, because the top of that cap is not directly connected to the electrode. So if I worked the right way I could solder with minimal damage. The cells left and right of it I could solder onto the nickel (hah ... fucking nickel my arse) strip.

First however I gave them a balance charge with my iMax and then soldered two strands of copper ~1mm in diameter across those three cells.

I charged it till it was only pulling 0.1A and took it for a 5km ride to test it.  All went well, so over night I charged it again. This morning when I checked the pack it was at 54.6V, with 0.00Amps going in to it. I thought that was very encouraging and ideal at about 4.2V per cell (bundle).

So maiden voyage on the repaired pack was one of my standard test routes.

which is an excellent result and compares very well to what I got before I put in the new BMS and just balance charged the pack by hand (hoping that would fix the issue, but it didn't):

Comparing those two results in more specific details:

shows that the pack has a bit more pep in places but what is really significant is the voltages were way up when I got back, suggesting I'm going to have increased range (as well as I'm sure the cell balances will be better with the new BMS).

This is the voltage upon return of that trip (and an additional little 2km victory lap I did). Further as I found in my pull down and mentioned in that post, the balance charging is doing much better with the new BMS than the old one:

the blue columns are the result of a "full charge"with the old BMS, which clearly wasn't balancing anywhere near as consistently as the new one. Probably equally important is that my testing to BMS shutdown yesterday (which prompted this new pull down) gave this result:

V discharged
4.03
4.04
4.03
4.03
4.03
4.03
4.03
4.03
4.03
4.04
4.2
3.66
4.03
4.02
0.12
50.7

which:

1. shows how bloody well balanced the cells were after initial "full charge" levels are shaved off by a few km riding and
2. is what led me to to this pull down to investigate why the BMS shutdown was happening and why that cell was low.

Discussion and Conclusion

I think that this time I've got it nailed, and unless there are other cells in this condition the only reason I'll need to pull the pack down again is if the solder joints I put on need repairing (which will only happen if the solder melts because the copper heats up under power: meaning my calculations on the required diameter are wrong).

Its pretty clear that this pack has failed (dead pack walking) by catching it early I've minimised cell harm and saved money. because of improper assembly and cheaping out on materials. I'd speculate that in the Chinese Sweat Shop where this was assembled the worker involved dripped some sweat right there on that part of the bus connector and started this rust process right then and there, before the pack was even sealed. I've seen the impact of a single drop of sweat on a circuit board before (the salt in sweat just helps electrolysis and oxidation reactions go nuts). Had they used decent nickel this wouldn't have happened.

I don't believe that there are other cells with suspect (rusty) joints because I can see all those other joints and this one was the only one hidden by the paper under the BMS.

This highlights the importance of pack construction being at least as important as cell choice. For even if these were LG cells and even if said LG cells were better, it would still fail because the assembly of the pack was flawed.

I'll do some range testing and perhaps do another pull down to check again.

Basically for

• my time, and 
• 2c worth of solder and scrap copper wire

I've saved a $250 pack which I anticipate will go on to last another year (its already lasted nearly one).

I hope this is also helpful to someone else.

difference in BMS outcomes

This is sort of a part 3 in the ongoing issue of (what I believe to be) the BMS caused issues in the battery pack of my 2019 (supposedly, but I somehow think 2018 fluffed up) Mercane Wide Wheel single motor 500W scooter. For other parts see here and here.

What happened

I was riding to work and then suddenly the battery voltage just plummeted and I had to take an Uber the rest of the way. The failure happened on a flat just a km or so from work.

So I've pulled the pack apart a few times now (of course after the first pulldown it was only sealed back up with duct tape, so no cutting required after then) so that I could measure cell situations. This has been prompted by an early "flat battery" situation (at about half the range I normally got) before. Investigations ensued.

Firstly this is the situation of state of charge after a full charge (defined by observation of no further amps going into the battery monitoring with my 150A charge monitor tool).

V 1st represents the first full charge still using the BMS that came in the pack, the other V readings represent state of charge with the new BMS and all readings are taken with the pack having had an hour or so to "settle".

What stands out to me is:

1. just how badly the original BMS behaved, with the lowest cell after charging being 3.86 (or just over nominal) and most cells not getting a proper saturation charge.
2. just how much better the new BMS has managed to balance these cells after the punishment of the last 9 months of 3 or 4 times a week discharge <-> charge cycle
3. how tolerant the cells are of mild abuse (given by the old BMS which probably dragged at least one cell bundle below an ideal low level.

Analysis and Speculation

I have been unable to find much on the BMS that it came with but what I've found implies it was an older design (initially made for 3 cells and then simply scaled) which is a passive system (not active, and reading this supports that view and why its failed) that I anticipate used the following simple triggers:

• shut down pack at a pre-determined whole of pack voltage (which seemed to be 42.5V based on my experience, which would be a safe 3.2V per cell if all cells were equal (less likely in a bigger pack)
• shut off charging when the highest cell got to above 4.22V (even if bleeding hadn't raised the others much)

So pretty clearly this new BMS (which is active looking at the video below) is doing a much better job.

But the over discharge seems to have done some damage to a couple of the cells in parallel bundles in at least one bundle because even with 49V showing on the display the pack goes into shutdown. When I get it home (often 30 min later) I can see this:

V discharged	diff
3.94	0.26
3.9	0.3
3.94	0.26
3.96	0.24
3.91	0.29
3.92	0.28
3.94	0.26
3.91	0.29
3.76	0.44
3.96	0.24
4.06	0.14
3.47	0.73
3.92	0.28
3.89	0.31
0.14	0.14
50.7

where the bottom rows are average and standard deviation of the column.

Of course with the new Active BMS it will trigger a pack shut down to protect the lowest cell at 2.8V and not release the pack until that cell recovers at 3.0V, from the seller specs (assuming they're correct):

Type of batteries: lithium cobalt oxide / manganese lithium / ternary materials
Temperature protection: 55/65/75
Rated Discharge current: 20A
Equilibrium voltage: 4.18v
Equilibrium: ≤ 30MA
Overcharge protection voltage 4.25V
Overcharge recovery voltage: 4.1V
Over-discharge protection voltage: 2.8V
Over discharge recovery voltage: 3.0V
Protection Current consumption: ≤30μA
Short circuit protection current: 60A
Short circuit protection time: 500MS
Fine workmanship and durable.
Applicable: 48V13 string lithium battery protection board.

Meaning that when those low cells get down to that level (probably well before the others) the pack will shut down to protect them.

I'm now going to see if I can "groom" those two bundles up a bit with my iMax charger but if I can't it's going to mean more serious pack surgery to slice out those two bundles and replace one or more cells in that parallel bundle.

PostScriptum:

Further surgery and exploration after a failure to be able to cover even 1/4 of previous ranges revealed this:

which essentially presented two different halves to the BMS and the Discharge. This has clearly been coming for a while, and I believe fits my (and many other peoples) experience of a hesitation when hitting bumps.

Essentially only one cell in that bundle was carrying the load.

I'll repair this and report.
Lets see how this goes.

detachable mudguard

I got a bit tired of applying and removing the duct tape for my "mark 1" mudguard (mainly because rain has been so sporadic but that's changed now) and so I decided to mung up one that's operable more permanently and conveniently.

basically its just a piece of plastic (from an empty 2L plastic milk bottle) which I cut to a shape, then put some duct tape over it to make it "black" and then affixed it with self adhesive velcro.

Loop side on the flap to keep it from getting clogged:

hook side under the guard

Make sure the underside of the guard is cleaned first.

The easiest way to make sure its all "aligned" is to put the two parts of velcro onto the flap, take off the adhesive cover paper and put it in place. Press firmly...

...  make sure that the adhesive has taken, then just rip off the mudguard.

Done

Cost breakdown:

• milk bottle (fished out of the kitchen bin) = $0.00
• velcro ($2.5 / 1.5 meters = 60c / meter, used 3cm) = about a cent
• duct tape ($4 /  30 meters = $0.13 / mete, used about a quater of  a meter) = about 3 cents

and people want to buy this sort of thing from eBay and pay $15 for it.

hmmm

Mercane (single motor) new BMS

So I decided that I didn't like the way things were appearing on charging since I did my strip down - rebalance - tape back up, so I pulled the battery out and stripped it down again. The first thing I did was measure it.

so while no cells are down below 4V and none at 4.2 (which is safe but not ideal); one is close, and two are below 4.1V.,But given it was charged till it "would take no more" over night and in repeated phases with a timer to boot more should be at or nearer to 4.2.

So up on the ($20 folding) bench (in the kitchen, because I still haven't built my workshop!!) I pull the battery and reopen it after the last surgery.

and am able to plug the new BMS (red arrow) directly into the existing balance wiring harness (yeah), but will need to redo the input wires because the new BMS is a 3 wire BMS and the old is a two.

so this new BMS should be better. So it went in with some minor adjustment, where the charging, battery and power -ve each gets its own port.

Plugged in and working.

Seems good ... lets see

---

But alas it was too good to be true, on the way to work this morning:
Speed dropped, voltage dropped and then everything went dark.
So either:

• my soldering failed
• the BMS failed
• something else

Either way, it was an Uber back to my accommodation, stuff it in my truck, and drive that to work.

Worth noting for anyone who thinks having only one scooter is a good solution.

More to follow,turns out it was "something else"; see here.