Making a better motorcycle battery with LiFePo4

A typical motorcycle battery costs between $100 and $250. I usually - I admit - go for the cheaper option because I always plan to drive this thing at least once in a while - which I usually don't. What thing you ask? My 2008 Triumph Speed Triple 1050. A rather hefty bike that wants to go fast in a straight line but requires some serious courage to go around corners quickly. The 1050cc engine requires a bit of oomph to be moved and as such the starter is stronger which in turn requires a powerful battery with a lot of cold crank current / cold crank amps.

A lead acid battery that's sitting around is dying. Always. Apparently, based on my brief research, sulfur deposits on the lead which eventually causes a short in between the cells. This is especially true when the battery looses charge at the same time. A sulfur overgrown battery makes die even faster and reduces the current it can put out.

My plan is to get rid of all this antiquated technology and use something more sustainable and durable like LiFePo4 cells. New(er), much more durable, and very hard to kill.

DISCLAIMER: Batteries are generally dangerous to work with. Once shorted, it's easy to cause a thermal runaway which is likely going to cause a fire or worst: an explosion. This is equally true for over-discharging as well as over-charging. And the latter is one of the primary considerations when putting LiFePo4 batteries to work in an automotive environment: A car generator's charge controller assumes the battery is fully charged at 14.7 Volts but a 4S LiFePo4 battery's max charge voltage is 14.6 Volts. Doesn't sound like much but could present a hazard.

Project Logs

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Next Steps...
Timo Birnschein • 03/24/2022 at 03:47 • 0 comments

Now that I have an enclosure that I can work with, I need to put the actual battery together.
I have a spotwelder that I built a few years ago which thankfully still works. I already made a few tests during shaver-repair and plan on spot-welding the new pack together over the weekend if I find the time. All cells are still very well balanced (down to 0.01V) and can be welded together without any additional balancing action on my part. I'll double check each cell again, though, just to be safe. LiFePo4 won't burst into flames but hot wires are also not needed here.
Once I have the cells welded and the pack somehow stabilized, I'll try and solder the power cables to the nickel strips and run the wires through the hole in the top cover straight to the screw terminal. I did it this way so that the power doesn't go through the bolt but instead connects directly to the leads to the motorcycle. I hope this will generate less heat, stressing the PLA less. Honestly, this is going to be an issue. I'm aware of it but I don't like it either. But it was the material I had available at the time of printing.
After (maybe before) the power cables are attached, I'll solder the 4S balancer into place. It says it doesn't like high capacity packs but since it's probably analogue it will just take longer to balance. And since I don't draw much continuous current from the pack and also have the pack sitting for long periods of the time it will (hopefully) eventually balance.
Then, I'll run the ground wire to the pack and the positive lead from the pack to the battery shut-off switch and from there to the positive lead of the bike. All this, in theory, should be pretty straight forward. There will be a bit of improvisation and probably incorrect terminals but that's an issue for a later day.
A looooong time of nothing and then some action!
Timo Birnschein • 03/24/2022 at 03:09 • 0 comments

I know, I know. I neglected my four followers on this project for way too long ;-)

Prologue

The reason is that I decided to sell the bike instead of ... well I guess restoring it further. That has changed at least a bit when I drive her last weekend, enjoying it, and realizing that the biggest reason I never like to use her is the hassle of getting things going.

With some people, Triumph is kind of known for destroying batteries. They never really turn off like my old Honda did. When that thing was off, it could sit for months over the winter and when pulled out of the garage or even a tent in March she would fire right up! No charging or bridging required. No, not to with the 2008 Speed Triple. She kills batteries like no other bike I have ever owned or heard about. If the battery isn't absolutely full and brand new from the factory, it's gonna be dead dead in two months. In my book, that is entirely unacceptable and it needs to change.

Most people would just add a trickle charger. Okey, so I bought a 7.5 watts solar panel with charging cable for my bike. No idea how to mount it, yet, but that's probably gonna end up like a removable rear spoiler or something silly like that.

But I also want to stop the leak current altogether, so I purchased a 200A starter battery shut-off switch that I'm going to mount under the seat. So when I'm not using the bike, I'm gonna kill the main switch. It's at least very unlikely that it's gonna open by itself to burn out the alternator as well as charging circuits so it's worth risking.

The Battery

Then, I also decided to continue the actual project: Making a better motorcycle battery. As you know, I ordered parts. These have arrived a long time ago and have been patiently sitting here to be put together. The main blocker I had was the enclosure. There is not much space in the battery compartment. Especially on the long edge, it's only 150mm total. If you want the 3D printed battery case to have any strength at all, it's not a lot of space to work with considering the 26650 batteries that I going to use for this.

Then, there was the second big issue: How do I get the power from inside the pack to some type of terminal. I'm not sure I found a good solution, yet. I'm sure it's a pretty bad one since I printed the case in PLA and the terminal won't be as tightly screwed together as on a regular battery. So this is a risk I have to evaluate under test and under different temperature conditions.
The one who spots the typo may keep it. It's ahm, artistic freedom!

I printed the entire case in matte black PLA at a 0.33 layer height to reduce print time. I am also beginning to like the esthetics again as it really has its own charm after printing lots of 0.1mm parts "because it looks like Markforge3D parts".

The pieces fit together nicely and with a little bit of flexible glue, this will be almost water tight. 3D printed parts are really not water proof, though, but the compartment is in a reasonably dry place. No high pressure washer for me!
Ordering parts
Timo Birnschein • 02/28/2021 at 05:37 • 0 comments
I just ordered this active balancer board: https://www.ebay.com/itm/3S-4S-6S-10S-12S-Li-ion-Lifepo4-LFP-Battery-Active-Equalizer-BMS-1-2A-Balancer/402273591810?ssPageName=STRK%3AMEBIDX%3AIT&var=672205559543&_trksid=p2057872.m2749.l2649
as well as 25 x https://www.18650batterystore.com/products/jgne-26650-3000mah-battery
The battery case and all the cell block holders will be 3D printed. This is gonna be an interesting overall experiment with lots of unknowns:
- Will my printer last for the duration of the print?
- What will the total final cost be?
- Can the motorcycle charge this pack with no issues?
- How long will the pack last?
- How heavy is it going to be?
- Is the balancer any good?
- Is my DIY battery spot welder going to last?
We will see when I start building this. At the moment, I'm definitely curious about all those questions!
All things start with a bit of research...
Timo Birnschein • 02/28/2021 at 05:06 • 0 comments

I have been looking for a better motorcycle battery for a while and was severely disappointed when I came to the realization that good batteries no matter how small are very expensive. Motorcycle batteries definitely count as small in my book - in comparison to, say, boat batteries.

For the DIYer, there are several interesting building blocks out there, some more, some less <del>explosive</del> volatile.

First, I looked at LiPo 18650s. Typical laptop batteries, or in recent years also known as Tesla electric vehicle batteries. The market is huge but so is the danger in case something goes wrong with your battery pack. Overcharging, overdischarging, shorts, overheating, the list is long and result is almost always: fire, a lot of smoke and usually the total capital loss of the device they powered. Apart from the very good power to weight ratio, LiPos are quite terrible to work with. On top of that, the fully charged voltage is too high:

4.2*4 = 16.8 Volts (fully charged 4S)
4.2*3 = 12.6 Volts (fully charged 3S)

Both is incompatible with automotive battery management systems.

Here comes the LiFePo4 battery chemistry. It's a bit different than LiPo in that it usually does not burst into flames at all. Or at least, it is considerably harder to get them into this undesired state. Also, their voltage levels is completely different, making them entirely incompatible with LiPo batteries:

3.65*4 = 14.6 Volts (fully charged 4S) !!
3.2*4 = 12.8 Volts (nominal voltage at 4S) !!

As can be seen from this quick math, four cells in series give almost exactly the same voltage range as normal automotive batteries and can therefore be used with no issue. The difference is 0.1V at the max voltage end but according to their datasheet, LiFePo4 batteries are being tested up 1.5V overcharge and still no fire.

Similar to LiPo batteries, LiFePo4 also requires a balancing circuit. Nowadays, these exist in passive, as before, and active which supposedly a couple percent more efficient as it doesn't burn energy to equalize the cells but transfers the energy instead. We will see how that works and how precise this is but that's a topic for later.

I did some math and calculated the following:

I compared two different sizes, the typical 18650 cell and the bigger, higher capacity, 26650 cell. In theory, both cells work equally fine in the motorcycle environment but there is one thing that stood out that made the difference to me:
Cranking the engine is fine in both cases but leaving the lights on will kill the 18650 battery in less than a work day while the 26650 battery would last much longer in this scenario providing much more buffer for me to notice that I forgot to turn the lights off. And yes, this is extremely easy on some motorcycles.
The next thing I needed to figure out was of the cells even fit into the packaging space of a motorcycle battery. To my big surprise, the answer is yes!
Length, width, and height are no issue. Even wiring and nickel-strips are no problem. Space for the balancer on top of the cells is also available. All I need now is a frame that holds the cells in place and the terminals to allow connecting the 4S6P LiFePo4 battery to my motorcycle.
One last mystery is, though, how the charge controller on the motorcycle will react to the battery and vice versa. I will have to take lots of measurements to ensure the battery is being treated well and never leaves 14.6 to 14.7 volts.