Friday, 9 April 2021

Nissan Leaf (gen-1) Old vs New Battery

Comparison of battery degradation (Nissan Leaf gen-1), before and after battery replacement:

Note that the top x-axis is for the new replaced battery, both plotted on the same date scale for easy comparison. My mileage usage is consistent every week, so using date scale for convenience:


The bump above, that was when I had recall from Nissan for battery software update, which I'm guessing is this one.

Now, for the difference in kWh/km reported by dash vs LeafSpy reading, comparing old vs new battery:

From my old battery below, 0.13kWh/km (dash) vs 0.18kWh/km (LeafSpyPro):


From new battery, which both has same figure at 0.12kWh/km:

However, do note new battery also suffers some difference (maybe depends on SoC?), as example below. I forgot to take photo from the dash on the day, but it was 0.13kWh/km on the dash (compared to 0.18kWh/km from LeafSpyPro):

Issue above causes the battery meter seems reporting discharge quicker, and then slows down later.


Tuesday, 29 September 2020

Nissan Leaf 2012 Fast Charge Curve

Some data from my Nissan Leaf 2012 fast-charge sessions:

Before and after battery replacement. Both data are for gen-1 battery, a.k.a canary battery:

Nissan Leaf Battery Fast Charge

Not too far from out there:


Sunday, 2 August 2020

eBike Long Term Reliability (2)

After clocking 54,000km since 2013, my DIY eBike conversion has indeed surpassed my expectation.

eBike


Photo of now and then.

Update since then:

Upgrade to a Bigger Battery:

The one on the photo above is my 3rd one (14Ah Tiger Shark Battery).

My 2nd set of battery has performed better compared to my first one by simply doing these:
  1. Fill any gaps with silicon grease. No more water ingress!
  2. Don't leave it fully charged and then leave it unused, especially on hot days.

Second bullet point above is important if you want to extend your battery life. My 2nd set of battery is now just under 9Ah capacity left (original 11.6Ah) after 1,000 deep cycles. Where as my first one degraded to just under 8Ah after same 1,000 deep cycles (see Note 1 below).

What happened to my previous batteries? Are they polluting the landfill?

Glad you ask! (of course you didn't)

They're joining my battery storage in my shed. I've upgraded my off-grid shed to include my ex-eBike batteries! Also, after getting an extra solar panel couple years ago (super cheap 2nd hand panel), my commute has been totally charged by the sun, even in winter cloudy days! Well, ok, half-lie there, as the other way charged at work, ha!

Note:
  1. 'Deep cycle' here is 7Ah average per ride after 1,000 cycles. Individual rides vary between 6 to 9Ah, which highly depends on head-wind.

Tuesday, 7 May 2019

Sin of Early Adopters

Ah, the sin of early adopters. The consequence from Nissan Leaf's engineers bad choice for their first generation EV battery, is now felt years later: The wrath of increased internal resistance (see UPDATE below)!

So far, my first-gen Leaf (i.e. 2012 built) decreased battery capacity (originally 24kWh) is not my biggest problem, thanks to network of fast chargers. The degrading internal battery resistance is!

My real issue is, instead of being able to 'fill' my battery in 6 minutes for a quick top-up of 5kWh, or roughly 30-ish km of range (so I can quickly get back on the road), the degraded battery has also 'slows' down the quick charge capability considerably. More than twice as long!

Prodding into cells' battery voltage during fast charge, revealed that the BMS deliberately slows down the charger in order to maintain cell battery voltage under 4.1 Volt at any stage. Fair enough. One can expect this 'slowing down' when the battery is closer to fully charged (i.e. 80% SoC or above). Due to massive degradation of 'Hx', this now happens very early on mine (under 50% SoC). Yikes!! (see UPDATE below)



I just never thought the 'Hx' degradation griefs me equally as the 'SoH' degradation. Sad.

Looking at the bright side (so I can feel better), other than batteries, Nissan Leaf is such a good car (said me who treat cars like a fridge, i.e. purely utilitarian). Definitely no disappointment to date (except the battery...)!

My battery history so far:


Nomenclature buster:

BMS:
Battery Management System.

SoH:
State of Health is another indication of the battery's ability to hold and release energy and is reported as a percentage. When the battery is new SOH=100%.

SoC:
State of Charge indicates the amount of charge currently in the battery.

Hx:
The meaning of this number is not fully understood but it appears to be inversely related to the battery internal resistance. As the internal resistance of the battery pack increases it is thought this percentage decreases. As internal resistance increases more energy is lost within the pack and the pack heats up more under load.

UPDATE 24 June 2019:
I had another fast charge session from 20%SoC, and I was expecting the 50kW charge lasted longer. I was wrong. After self-research, I've just found out something called polarisation effect. So, the aging of my Leaf battery grief is mostly due to this, not internal resistance.

Presented below in equivalent circuit. There you go!


Friday, 7 September 2018

Electric Bicycle Long Term Reliability


After clocking up almost 40,000km since mid-2013 (half of it clocked up in the last 2 years) in my e-Bike to commute to work, here are 2 major lessons learnt:
  1. Stop water ingress;
  2. Think about spares requirement.
Electric Bicycle

Photo: Now and then.

There is a huge exponential jump in reliability requirement when I use my eBike as a sole commuting machine. One simply can't afford a major breakdown, and there should be minimal maintenance required even with daily usage (the last thing you want to do is work on your bicycle at the end of daily commute).



Lesson#1: Waterproof Your eBike

Most bicycle components are not designed to be waterproof. These are 5 major components (from most expensive to the least) that need special attention:


Component#1: Battery

I have a tube style battery that is not designed to be water-proof (the big yellow sticker said so). However, who heed the caution tape anyway, right?

So, depending on your battery type, you need to find the gaps where water ingress is possible. On mine, it's the indicator button that tells you the battery charge remaining:



Opening the battery (voids the warranty of course), I applied (very) copious amount of silicon grease (gel type) behind every gap I can find: buttons, screws, switches, etc. To date, it's been proven very effective (true and tested in flooded road and heavy rain).

My second set of battery get silicon gel treatment, whereas my first set didn't get it. On my first set, the water ingress caused the BMS (Battery Management System) developed salt bridge and cut the output off . Luckily, after cleaning the salt bridge, it fixed the problem and continue to serve my machine until it has 70% charge remaining (after 1,000 deep cycles). It's still functioning to today, but not good enough for my commute, as I need at least 80% charge to cover strong head-wind condition (5% time of the year).

Note that I don't mention the controller in this list. Mine hasn't given me any grief whatsoever!

Lesson learnt: Silicon grease gel type is your electronics best friend.


Component#2: Electric drive hub

Considering there are so many different types of electric drives out there, I have to be specific here. I only can give you feedback on my experience with solarbike electric front-drive 500-watt kit (which looks almost identical to any other electric hub kit).

Although the electric motor is not advertised as waterproof, I'm happy to report that by simply applying light oil (I use Inox) on the shaft and cable entry time to time, it has been clocking up more than 30,000km without any issue even in flooded road.

My first front-drive electric hub motor lost its free wheeling after 10,000km. Upon opening the hub, I've found that the stator has rusted and created too much friction between the stator and the rotor. It was hard work to get the rust cleaned off due to the super strong magnet (metal scraper and magnet, hmmm...). However, after cleaning, my first set of motor is back functioning again (I keep this as a spare now).

The bearing is a sealed type on the front motor. Although the interface between the sealed bearing and the axle is a snug fit, it's still not hard to slide through, which I suspect moisture still can seep through this. The cable entry is protected by a putty, but cracks have developed after some time. These 2 factors, my guess, is where the water ingress can get through:

Electric Bicycle Hub Motor Cable Entry


Lesson learnt: light oil as corrosion inhibitor is your wheel hub best friend.


Component#3: non-electric wheel hub

Most wheel hub bearing is not water-proof, unless you have a sealed bearing type. Mine is definitely not (I've learnt this the hard way). Rusty balls anyone?

Rusty Ball Bearings


You definitely can tell when you have water ingress in your wheel hub bearing. Please don't ignore that clanging noise. Walking and dragging a bicycle with a destroyed wheel wasn't a pleasant experience (true story).

After 2 re-grease occasions in the space of 4 months (it's been a really wet 4 months), I've learnt that the best way to block water ingress is to grease them like there's no tomorrow.

Wheel Hub


From the photo above, you can see the fresh grease oozing out, where other parts are dirty. Ensure to wipe it off time to time as they get flicked off to everything else. Of course, you can get a sealed bearing type. But who can afford them?


Component #4: headset bearing

Remember the fender advice above? Depending on your headset type, water ingress on the headset bearing can cause early failure due to rust.

In mine, there is no protection whatsoever:

Lower Headset Bearing


So, I have no choice but to grease it like there's no tomorrow. I can't find an aftermarket fender that covers half circle of my front wheel.

Exacerbated with my choice in front wheel drive, my headset bearing needs replacement at least once a year. The headset bearing is definitely not designed to cope with front wheel drive.

If I've chosen rear wheel drive from the very beginning, I wouldn't have this issue. However, there are different issues in choosing rear wheel drive (more on this later).


Component#5: Chain

After trials and errors with different type of grease, light oil, etc, I've found that immersive wax is the very best for longetivity of the chain, coupled with the least number of maintenance.

The basic 'science' is not to have sand and grit trapped in the chain during wet weather riding, which becomes abrasive to your drivetrain (chain ring, the chain itself, and the rear casette). Immersive wax basically makes your chain clean at ALL times (even riding in a flooded road).

However, you still need to dry your chain (quick wipe with a dry cloth) after each wet ride. I left them wet once and ended up with surface rust on the rollers and plates:

Rusty Bicycle Chain


 I still need to re-wax my chain after cumulative 300km (really) wet ride. In the dry season, I haven't found the upper limit yet. Usually, I rewax after 600km cumulative dry ride (it can definitely go longer).

The other thing I've done to my eBike is to convert it to a single speed. This simplifies the drivetrain considerably for easy cleaning after each wet ride (you don't need gears with eBike). The conversion process itself is a big steep learning curve for me (and not trivial). Let's park that for another time.

To mention the obvious, chain quick-connect is essential.

My last chain has stretched about 1/32" out of 12" length after roughly 10,000km ride (the limit is 1/16" from here). Half of it had light oil (Inox) bath treatment, the other half had immersive wax. Mind due though, the electric assist has also contributed large part of the longetivity, i.e. the chain has been barely 'stressed' :). If you have a mid-drive electric motor, that'll be a different story!

There is another choice: simply replace drivetrain every few months or so. I didn't do any maintenance at one stage (wrong choice of lubricant was also largely responsible) and managed to get a 1/2" stretch (out of 12" length) after more than a year. Yup, the drivetrain was completely destroyed (some teeth were reduced to a blip). Sorted!

Moral of the story: Chain maintenance takes time and money (wax is not cheap). I'm seriously considering the no maintenance approach and treat them as a pure consumables (which includes the chain-ring and rear sprocket).


Lesson#2: Spare Philosophy

Getting cheap parts for your eBike build is one thing, but to keep using it for long term is another thing.

I've seen many special built eBikes entering the market in the last 2 ~ 3 years with its beautifully packaged system (and expensive of course). However, when you need to replace its parts (with components mentioned above). Will these parts available when you need them? How expensive are the replacement parts?

This is when building your own eBike shines. These days, finished products are built to Apple-like system, locking consumer to a specific manufacturer where you can't get replacement parts anywhere else (and super expensive).

On the other hand, using stock standard frame (with special attention to components I mentioned above) ensures your system can last a long time and replaced with cheap available parts when required. New 27.5" and 29-er with disc brakes are not helping one's decision, but, let's park that issue for other times.

I mentioned above that rear wheel drive eliminates the issue with headset bearing (so you don't need to replace it too often). However, from my 40,000 km commuting experience, it has always been (100% of the time) the rear wheel that experiencing punctures (don't know why).

I always have Schwalbe marathon plus with its awesome anti-puncture capability. However, that still doesn't stop steel wire debris (no thanks to industrial area where I need to go) going through the thick layer of rubber.

If I use rear wheel drive and got a puncture, that will be super difficult for me to replace on the road (no such thing as 'Quick Release' on electric motors). I haven't tried tubeless tyres though. So, it might be in the far future when I'm going to experiment with rear wheel drive and tubeless tyres.


Summary:
Knowing what I know now, I would've save at least AUD600 in the last 5 years, i.e. no need to buy a new motor, and less drive train change-out due to less wear and tear.

So far, I clocked up around AUD3,500 in cost (the bulk of the cost are 2 sets of motors and batteries). Predicting my second set of battery will be good for the next 500 cycles, that translates to AUD1.75 cost per trip (6.5cents per km). If I implemented my lesson learnt from the start, that would've brought the cost down to AUD1.45 per trip (5.4cents per km). Not bad!

Wednesday, 6 June 2018

Powerwall 2 Time Base Control Algorithm

Since PW2 (Tesla Powerwall 2) introduced the new TBC (Time Base Control) algorithm, I had a great difficulty in trying to understand the actual algorithm, especially during shoulder period. Consulting forum (such as here and here) only confuses me further, especially when the forum started to discuss incentives and local regulations (US centric). This, however, makes me appreciate the herculean task for PW2 engineers. You simply can't make everyone happy.

The ever evolving nature of PW2 algorithm (typical Tesla my guess), makes any 'User Manual' writing attempt a futile exercise. Reverse engineering the algorithm also requires different permutation, such as state of charge, how much PV production during the day, etc that can affect the PW2 behaviour.

Still, little documentation is better than nothing. Since I don't have the stamina to try all permutations, I deliberately write down as much details below (trying to be as neutral as possible, i.e. no incentive and regulation jargon):

Off-Peak Cost Saving Mode:
In this mode, PW2 does try to aim a certain State of Charge prior entering shoulder and peak period (by charging from the grid if necessary). Based on the limited 2 days experiment (see screenshot below), this State of Charge (SoC) is not a fixed value. How does PW2 decides this SoC level? Me no idea.



Also, some charge from PW2 is used during off-peak period (see bubble number 1 in the screenshot). I don't know how PW2 decides when to use the battery. One thing for sure: it mostly uses the grid to conserve the SoC for peak period.

I haven't tested what happens when you have solar production during off-peak period.

Shoulder Cost Saving Mode:
Now this gets interesting. In day 1 of the test (see bubble number 2), my PW2 behaved as I wanted it, that is: no grid activity (i.e. to behave exactly like peak). Too bad I didn't record the SoC, but I remembered it was roughly 40-ish percent at this stage.

In day 2 (see bubble number 3), my PW2 started to be less agressive (despite higher SoC compared to the previous day), i.e. grid activity is allowed by importing and exporting. Uh oh, for me, who has a power provider that value exported PV close to zero (yup, zilch, nada), this is bad news. Also, why PW2 allows a significant grid import when the battery SoC is relatively high (roughly 60-ish percent at bubble number 3). Is this because PW2 hasn't learnt that I don't usually use lots during peak period? My guess at this stage, this is due to the PW2 algorithm is based on US-centric market, where they have incentive to export PV to the grid (such as net metering). Pure guess though.

At this stage, my panic mode was on, and I switched it back to 'Self-powered' mode (as commented by the red line), which explains why the screenshot is no longer showing peak/off-peak on the 14-th May, and also 100-ish watt grid consumption during solar production after the switch (see my previous post).

After 14th of May, I changed PW2 to 'TBC Balanced' mode and extended the peak period to also cover shoulder (i.e. only peak and off-peak, no shoulder). This has worked perfectly for me, but...

In the last 2 days, I haven't had enough PV production to cover my shoulder and peak. This has caused me grief since now I need to import from the grid during peak period (see bubble number 4). So, I changed it to TBC 'Cost Saving' mode, thinking that PW2 would've charged from the grid during off-peak to cover my PV production shortfalls. To my surprise, it didn't (although the SoC was just a tad below under reserve).

So, here I am, finding another quirk in PW2 algorithm. If you don't set the shoulder period,  PW2 will not charge from the grid (despite the PW2 SoC at the reserve level). What the??

In the screenshot below (see bubble number 5), you can see that as soon as I bring back the shoulder period, PW2 behaves as I expected again by start charging from off-peak grid (I've found this by coincidence).

In short, for those who want exporting to the grid at the very lowest priority, I recommend to use 'TBC Cost Saving' mode with a wee bit of shoulder period (just enough to activate 'charge from off-peak grid mode').



PS: Peak period behaviour is consistent as expected, i.e. no import from the grid.

Monday, 13 November 2017

My Observation of Tesla PowerWall2

My Tesla Powerwal 2 (PW2) summary, freshly installed just 3 days ago:
[UPDATED 7 May 2018: see point 6 below]
  1. PW2 can be installed in multiphase (mine is 3-phase). PW2 monitors each phase current using Current Transformer (installed by the installer of course).
  2. PW2 basically absorbs all your solar power instead of injecting them back to the grid. What is worth to be noted, although you have load on different phases, the PW2 will compensate this so that your electricity meter reads export as 'zero' (since Australian domestic electricity meters don't care on which phase you're consuming). So, in my example, I was using an induction stove top at 1000 Watts on the 'white' phase, and the PW2 injecting back to the grid at 1000 Watts at 'red' phase, resulting net zero export. To mention the obvious, PW2 inverter maxed out at 5kW power.
  3. Non-noticeable transfer time when the grid has failed. I've tested this 2 times: at first attempt, the solar panel inverter anti-islanding has to reset (causing the solar power to cut for about a minute). In the second attempt, the solar inverter didn't trip at all (as if nothing happen). I'm definitely impressed on this one. To mention the obvious, only 'red' phase of my home is backed up by PW2. Other phases are not. Now I can officially welcome mad max scenario!
  4. During daytime (when the solar panel is active), I've noticed PW2 constantly draws around 100 Watts from the grid, but not at night time. I can't find any info in the internet on the why, yet. My guess, PW2 requires power for its own functionality and ineffeciencies in converting AC to DC and somehow only compensates during daytime? 
  5. It is also worth to be noted, unlike the Tesla cars, users can't set the maximum charge level on PW2. My guess, Tesla is now extremely confident that this is no longer required. Maybe combination of newer chemistry and internal software to limit when required during hot days?
  6. My particular one consistently under report kWh used and exported to the grid by roughly 15 - 20% (compared to my grid provided meter). However, the solar energy kWh is spot on (compared to my soalr inverter kWh measurement). No idea the why. Anyone experiencing the same issue?


What it doesn't do and I wish Tesla will update this functionality sometimes in the future:

  • Change the timing on the 100-Watt constant draw from the grid. I wish this is user configurable. For example, to draw this at night time, or to use solar panel instead. For me who on Time of Use plan, this total of 1kWh on daytime is something I'm not willing to pay the grid for. Call me stingy.
  • Ability to charge PW2 from the grid during off-peak via the app. At the moment PW2 only absorbs power from solar panel. Since my solar panel is not enough for my usage, I'd love to have the ability to get cheaper electricity at night to be used by my household during peak time. Quicker ROI anyone?


Now, to how I use the Tesla app:

  • Once the installer enter account holder details via the installer page, your PW2 will be immediately visible on the Tesla app (you'll need wi-fi router for PW2 to connect to Internet). I haven't accessed the PW2 directly via the ethernet router (no reply). Will try again next time.
  • The visualisation of the app is indeed very useful. For a data hoarder like me, the visualisation has altered my energy usage. For example, now I know my inverter reverse cycle Air Conditioner doesn't have linear energy consumption (I thought it does). It has step changes, i.e. 2.4kW at full power, then 1.5kW, then 900 Watts at lowest power (in cooling mode). When the PW2 is low in charge, I deliberately turn off my air-con to minimise grid usage and happy with slightly higher room temperature (but still comfortable). My guess, sometime in the future, all home appliance will talk to each other (via ethernet router, just like the PW2 at the moment) and have AI (Artificial Intellegence) based on user preference on how and when to consume energy (whether to save energy, or maximum comfort).


So here is my data, just 1 day after it's being installed (grid data not shown for clarity):

Tesla PW2 App Visual





The data above is definitely not my average day. I had to travel 120-ish km on that day, so most consumption gone to EV (I'm guessing around 18kWh).

Now my debt has increased significantly again (thanks to PW2 as an expensive toy), so the family now have to be content living from boiled water and salt. At least we have a good-lookin' dead weight on the wall now (wheel added in MS Paint to make me feel less guilty by the dead weight):


[UPDATE 12 Oct 2020 for 2018 annual figure]: