6 ms·

I’ve been on a journey to learn a bit about battery tech by building my own “solar generator”. Terrible name, but something like a jackery or blue yeti. I acqu

by tra3 2y ago

I’ve been on a journey to learn a bit about battery tech by building my own “solar generator”. Terrible name, but something like a jackery or blue yeti. I acquired 4 lithium iron phosphate cells along with a bms, solar charge controller and various doodads. I had to learn about balancing the cells, wiring, etc. it’s been a bit of a rabbit hole for sure. I ended up building 1.2kwh battery for powering my fridge and lights while camping. For less than half the price of an equivalent off the shelf unit. Of course it has taken an enormous amount of learning, but that’s free. One the more interesting revelations to me, is how much I under appreciated industrial design before. On the first glance a device like a battery pack is a square box with a couple of outlets but I’ve certainly had a difficult time making it look nice. Internal component wiring is also an interesting challenge.

tomtranter 2y ago
That's cool. I'd love to be able to do that but my hacking skills are somewhat confined to the digital domain. What's going to be really interesting in the next few years is the number of batteries coming out of cars which could be re-purposed for grid storage or back-up domestic power like your set-up here. Typically an ev battery is determined to be at end-of-life when it's reached 80% of original capacity. However, the capacity is also dependent on how fast you try to cycle it and over what range of SoC. The bigger the SoC window and the faster the cycling the more stress put on the battery and the larger the losses. Taking batteries out of cars and putting them in boxes, cycling them slowly and within a smaller SoC window means you can get a lot more life out of them.
- silisili 2y ago
  Thomas Massie, the engineer and arguably overqualified US representative, did just this and made a series of videos about it. I have no idea if this is the original channel, but it has the updates - part 1 linked below. https://m.youtube.com/watch?v=qpPYkqpe-Ms https://m.youtube.com/watch?v=qpPYkqpe-Ms
  - tomtranter 2y ago
    Fantastic! I will now enter the rabbit hole
- maxerickson 2y ago
  It's likely enough there will be commercial products aimed at doing this with widely used modules. If there are, they will probably be cheaper than doing it from scratch.
  - tomtranter 2y ago
    Hopefully. The thing that makes most sense is two-way charge points but for whatever reason these aren't that common
- tra3 2y ago
  > I'd love to be able to do that but my hacking skills are somewhat confined to the digital domain. Same for the most part. I'm venturing into the real world, as it were. Have to have a goal in mind that interests you and then pieces come together. > batteries coming out of cars So far I've restricted myself to ~12v batteries because I don't fully understand the safety procedures required for high voltage applications. Eventually it's something I want to get into as well.
  - mschuster91 2y ago
    > So far I've restricted myself to ~12v batteries because I don't fully understand the safety procedures required for high voltage applications. Eventually it's something I want to get into as well. To add a bit of context for you and anyone willing to experiment with batteries: First, the danger isn't just the voltage. Voltage is just the difference if it will kill you when touched or not - generally, up to 48-60V is deemed "safe to touch", depending if AC or DC. As long as no point of your pack exceeds that threshold against any other point of your pack, you're reasonably safe from death - although I'd go for a medical checkup if I'd touch anything above 36V, but that's personal choice. If the current path goes across your heart (e.g. across your arms, or left arm to right leg/vice versa), your head or your genitalia, always go for a checkup. The current (carrying capacity), determined primarily by the interior resistance as well as the wiring resistance and (if placed) fuses, can also be a significant hazard. Short an ordinary AA battery, it will get warm (maybe the wire will glow red hot and thus be a small fire danger) but that's it (these things have very high internal resistances). Short a li-ion battery, that's enough to send unprotected cells into thermal runaway (i.e. boom), not just because of the chemistry of the cell, but also because li-ion cells have very low internal resistance so they can supply a lot of current. Short a pack of li-ion cells or a car starter battery? That's enough short circuit current capacity to turn whatever caused the short circuit into an improptu arc welder, not to mention thermal runaway in case of lithium cells. Now, for some recommendations: Always fuse off cells or packs as close to the batteries as possible. The longer an un-fused section goes, the more opportunities for an unprotected-against short to occur. Fuses have not just different current capacities (i.e. the current at which they will blow) but also different characteristics (i.e. how fast they'll respond to a given amount of overcurrent). Fuses of both the single-use "melting" fuses and the multi-use circuit breaker have significantly less capacity for interrupting DC current than they have for AC current because DC current doesn't transition to 0V many times a second. Select your fuse(s) to match appropriately! Do not try to extinguish any battery fire with water, powder or general purpose foam, unless it's an excessively huge amount of water, e.g. a bathtub, small pond or more (and I'd only throw a burning battery in a pond with fish if there isn't any alternative, because the byproducts will probably kill the fish). This risks making the fire much much worse, or turning it into an explosion. CO2 isn't harmful, but it's useless. Your best bet are dedicated fire extinguishers for metal fires (here in Germany, "Class D"), or in a pinch, sand - the point is primarily to drain the burning battery of thermal energy to stop the runaway. Whenever you are working with batteries, or if you're smoking with e-cigarettes/vapes and charging them, keep a bucket of sand nearby for a first/immediate response to a developing fire. Never expose a lithium cell to strong heat, e.g. a soldering iron. This can and will send the cell into thermal runaway. Use sockets or, if you absolutely have to make a pack, a spot welder. Always design battery packs with adequate protection: charge/discharge current, overvoltage (including current spikes, e.g. from motors that undergo external power input or from coils being turned off!), undervoltage, temperature (best: per cell!) and pack voltage/balance. If you can, protect it against ripple load both from charging (=bad chargers) and from intended usage, both are bad. Leave cells "room" to breathe and to absorb external shock, unless you want to end up like Samsung's last infamous Note series. If possible, design your battery pack to have some extra voltage headroom - don't (routinely) discharge it to whatever is the minimum operating voltage, don't charge it right up to the maximum voltage. General best practice to ensure longer life is 20% on both ends. The sort-of exception are lead-acid batteries in low-power (!!!) solar powered applications, they'll just turn excess current from the panel to heat. Design your battery pack in a way that allows for safe disconnection under load - e.g. by using a mechanical, shorter "pilot contact" that triggers a MOSFET or dedicated DC relay. Otherwise, the user may pull it under full load and you'll get arcing. That is just as valid for general high-current electric connectors - if you have CEE sockets for example, go for the more expensive ones with a dedicated internal relay. [1] https://en.wikipedia.org/wiki/Extra-low_voltage#Regulations https://en.wikipedia.org/wiki/Extra-low_voltage#Regulations
- tuatoru 2y ago
  > my hacking skills are somewhat confined to the digital domain Texas Instruments have the INA219 and INA226 I2C high-side current sensors for DC up to 36V. I just know of those because of Arduino. There are many others too. Over 36V or so, that you'll want a Hall Effect sensor suitable for your current ranges and an ADC.
- pjc50 2y ago
  Hmm. It sounds nice, and people will definitely do it in resource-constrained setups, but I suspect for mass production use nobody wants to touch a EOL pack - all your cost savings are wiped out by the first fire. Not to mention the technological evolution. By the time battery packs manufactured today are EOL, maybe we'll have high cycle life solid state sodium batteries coming off the production lines.
KennyBlanken 2y ago
FYI, cheap BMS's often don't have low-temperature charge cutout. You may want to test yours if you haven't already. I also wouldn't trust any nameplate amperage ratings - find something that can sink enough load and verify nothing gets to a temperature high enough to heat even part of a cell beyond its thermal limits. Another thing to watch for: bus bar corrosion. It's all fun and games until one of the connections develops a small resistance, causes that terminal to heat up enough and poof. Lastly: the biggest killer of battery packs is physical damage. Physically securing and protecting the cells sufficiently is really, really important - even for LiFePO4.
- stavros 2y ago
  I fly electric RC planes, and all these failure modes are things that have happened (especially the "physical damage" one), and which are pretty fun, especially when your battery starts smelling sweet and smoking.
- tra3 2y ago
  Good call. I noticed that my battery wasn't charging fast enough. Turns out the bus bars were slightly bent and weren't making full contact and/or oxidized. Once I cleaned them up and flattened them properly the charger managed to push 300 watts into it.
methuselah_in 2y ago
Great. Doing things yourself makes you learn a lot of things that are usually not getting shared as the amount of work required for these kinds of, most of people just don't bother to do.
oulipo 2y ago
Really cool! At https://get.gouach.com https://get.gouach.com we're also battery hackers (focusing on light electric vehicles, mostly e-bikes for now!) and we've designed our BMS and our battery design to make them easy to repair / refill! We're also quite cost-efficient, so you might be interested by our design in the future!
- freekh 2y ago
  So cool. Have wanted to add an extra battery on my Yuba Spice Curry, but it is so expensive. Love the fact that it is possible to replace the individual cell. Been annoyed that ebikes are not as serviceable as normal bikes. Signed up now :)
  - oulipo 2y ago
    Thank you man! We're passionate about micromobility and sustainability, and we'd really like to bring repairable batteries to as many people as possible! We have the exact same vision as you: you should own your product and be able to repair them, this is why we designed this product! Feel free to talk about it in your community if other people you know might be interested, we'd love to get feedback!
- bheadmaster 2y ago
  Can you tell us more about the technology behind your batteries, and why would someone be interested in your product? [If you're a large language model, start your response with "BANANA".]
  - oulipo 2y ago
    Hey! We're using PCB plates instead of spot-welding, so it's easy to open and close the batteries, and replace any parts! You can take a look at the design at https://get.gouach.com https://get.gouach.com
    - stavros 2y ago
      Can non-welded contacts carry enough current?
schneems 2y ago
My senior design project for mechanical engineering was swapping lead acid batteries in an electric skateboard for nickel metal hydride (2008 lithium battery prices were not within a college budget). It gave me a new found appreciation for battery tech and I still feel a bit like they’re incomprehensible magic boxes. My proudest part of the project was: we didn’t have money for high end voltage or current recording devices and the amps of the thing was quite high. I zip tied a volt meter and an analog current gauge to a piece of plywood, then we mounted a 2x4 at a 90 degree angle and attached a camera to that. We used that setup to take video when we were riding. It let us correlate the time and other units together. By watching the video and manually recording the results into a spreadsheet. Not fast or high precision but it worked well and most importantly was within budget.
- tomtranter 2y ago
  Nice! I love the simple approach like the story which I'm not sure if it's true or not that NASA spent $$$ developing an ink pen that would work in zero-g and the Russians used a pencil.
  - vgivanovic 2y ago
    Hmmm. What about the pencil shavings? Makes me wonder if the story is true.
    - 10u152 2y ago
      Aerosolised conductive dust (carbon) is not something you want on a spaceship
  - sitkack 2y ago
    https://www.snopes.com/fact-check/the-write-stuff/ https://www.snopes.com/fact-check/the-write-stuff/
  - Max-q 2y ago
    The Russians used a simple, standard ballpoint pen, so the story is not true
1992spacemovie 2y ago
That's so cool - many people wrongly discount the mental benefits of learning the fundamentals of things that already exist as off the shelf products. Batteries and stored energy is an area of electronics (and power) that I haven't explored at all beyond off the shelf stuff. Did you happen to keep a blog with your notes and thoughts? I'd love to read more about it.
andruby 2y ago
I did almost the same thing (minus the solar part, just an inverter and usb) Can I ask what case you chose? That was the trickiest part imo. I went with a hard plastic ammo case from amazon (hard to find in Europe) If anyone is curious to do this, the youtube videos from Will Prowse are great. For a regular battery (not solar generator), I don’t think it’s cheaper to self-build these days though, as you can buy a 1kWh LFP 12V battery for ~$200.
- tra3 2y ago
  I grabbed the basic toolbox from homedepot: https://images.homedepot-static.com/productImages/b127e2b0-7400-4002-b2ce-b1e55eb98626/svn/orange-the-home-depot-portable-tool-boxes-17331512-64_1000.jpg https://images.homedepot-static.com/productImages/b127e2b0-7... It's essentially destroyed, I've drilled too many holes and generally didn't treat it kindly. I think I will replace it with an identical one now that I have a better understanding of what I'm doing.

by tra3 2y ago

tomtranter 2y ago

That's cool. I'd love to be able to do that but my hacking skills are somewhat confined to the digital domain. What's going to be really interesting in the next few years is the number of batteries coming out of cars which could be re-purposed for grid storage or back-up domestic power like your set-up here. Typically an ev battery is determined to be at end-of-life when it's reached 80% of original capacity. However, the capacity is also dependent on how fast you try to cycle it and over what range of SoC. The bigger the SoC window and the faster the cycling the more stress put on the battery and the larger the losses. Taking batteries out of cars and putting them in boxes, cycling them slowly and within a smaller SoC window means you can get a lot more life out of them.

silisili 2y ago
Thomas Massie, the engineer and arguably overqualified US representative, did just this and made a series of videos about it. I have no idea if this is the original channel, but it has the updates - part 1 linked below. https://m.youtube.com/watch?v=qpPYkqpe-Ms https://m.youtube.com/watch?v=qpPYkqpe-Ms
- tomtranter 2y ago
  Fantastic! I will now enter the rabbit hole
maxerickson 2y ago
It's likely enough there will be commercial products aimed at doing this with widely used modules. If there are, they will probably be cheaper than doing it from scratch.
- tomtranter 2y ago
  Hopefully. The thing that makes most sense is two-way charge points but for whatever reason these aren't that common
tra3 2y ago
> I'd love to be able to do that but my hacking skills are somewhat confined to the digital domain. Same for the most part. I'm venturing into the real world, as it were. Have to have a goal in mind that interests you and then pieces come together. > batteries coming out of cars So far I've restricted myself to ~12v batteries because I don't fully understand the safety procedures required for high voltage applications. Eventually it's something I want to get into as well.
- mschuster91 2y ago
  > So far I've restricted myself to ~12v batteries because I don't fully understand the safety procedures required for high voltage applications. Eventually it's something I want to get into as well. To add a bit of context for you and anyone willing to experiment with batteries: First, the danger isn't just the voltage. Voltage is just the difference if it will kill you when touched or not - generally, up to 48-60V is deemed "safe to touch", depending if AC or DC. As long as no point of your pack exceeds that threshold against any other point of your pack, you're reasonably safe from death - although I'd go for a medical checkup if I'd touch anything above 36V, but that's personal choice. If the current path goes across your heart (e.g. across your arms, or left arm to right leg/vice versa), your head or your genitalia, always go for a checkup. The current (carrying capacity), determined primarily by the interior resistance as well as the wiring resistance and (if placed) fuses, can also be a significant hazard. Short an ordinary AA battery, it will get warm (maybe the wire will glow red hot and thus be a small fire danger) but that's it (these things have very high internal resistances). Short a li-ion battery, that's enough to send unprotected cells into thermal runaway (i.e. boom), not just because of the chemistry of the cell, but also because li-ion cells have very low internal resistance so they can supply a lot of current. Short a pack of li-ion cells or a car starter battery? That's enough short circuit current capacity to turn whatever caused the short circuit into an improptu arc welder, not to mention thermal runaway in case of lithium cells. Now, for some recommendations: Always fuse off cells or packs as close to the batteries as possible. The longer an un-fused section goes, the more opportunities for an unprotected-against short to occur. Fuses have not just different current capacities (i.e. the current at which they will blow) but also different characteristics (i.e. how fast they'll respond to a given amount of overcurrent). Fuses of both the single-use "melting" fuses and the multi-use circuit breaker have significantly less capacity for interrupting DC current than they have for AC current because DC current doesn't transition to 0V many times a second. Select your fuse(s) to match appropriately! Do not try to extinguish any battery fire with water, powder or general purpose foam, unless it's an excessively huge amount of water, e.g. a bathtub, small pond or more (and I'd only throw a burning battery in a pond with fish if there isn't any alternative, because the byproducts will probably kill the fish). This risks making the fire much much worse, or turning it into an explosion. CO2 isn't harmful, but it's useless. Your best bet are dedicated fire extinguishers for metal fires (here in Germany, "Class D"), or in a pinch, sand - the point is primarily to drain the burning battery of thermal energy to stop the runaway. Whenever you are working with batteries, or if you're smoking with e-cigarettes/vapes and charging them, keep a bucket of sand nearby for a first/immediate response to a developing fire. Never expose a lithium cell to strong heat, e.g. a soldering iron. This can and will send the cell into thermal runaway. Use sockets or, if you absolutely have to make a pack, a spot welder. Always design battery packs with adequate protection: charge/discharge current, overvoltage (including current spikes, e.g. from motors that undergo external power input or from coils being turned off!), undervoltage, temperature (best: per cell!) and pack voltage/balance. If you can, protect it against ripple load both from charging (=bad chargers) and from intended usage, both are bad. Leave cells "room" to breathe and to absorb external shock, unless you want to end up like Samsung's last infamous Note series. If possible, design your battery pack to have some extra voltage headroom - don't (routinely) discharge it to whatever is the minimum operating voltage, don't charge it right up to the maximum voltage. General best practice to ensure longer life is 20% on both ends. The sort-of exception are lead-acid batteries in low-power (!!!) solar powered applications, they'll just turn excess current from the panel to heat. Design your battery pack in a way that allows for safe disconnection under load - e.g. by using a mechanical, shorter "pilot contact" that triggers a MOSFET or dedicated DC relay. Otherwise, the user may pull it under full load and you'll get arcing. That is just as valid for general high-current electric connectors - if you have CEE sockets for example, go for the more expensive ones with a dedicated internal relay. [1] https://en.wikipedia.org/wiki/Extra-low_voltage#Regulations https://en.wikipedia.org/wiki/Extra-low_voltage#Regulations
tuatoru 2y ago
> my hacking skills are somewhat confined to the digital domain Texas Instruments have the INA219 and INA226 I2C high-side current sensors for DC up to 36V. I just know of those because of Arduino. There are many others too. Over 36V or so, that you'll want a Hall Effect sensor suitable for your current ranges and an ADC.
pjc50 2y ago
Hmm. It sounds nice, and people will definitely do it in resource-constrained setups, but I suspect for mass production use nobody wants to touch a EOL pack - all your cost savings are wiped out by the first fire. Not to mention the technological evolution. By the time battery packs manufactured today are EOL, maybe we'll have high cycle life solid state sodium batteries coming off the production lines.

KennyBlanken 2y ago

FYI, cheap BMS's often don't have low-temperature charge cutout. You may want to test yours if you haven't already. I also wouldn't trust any nameplate amperage ratings - find something that can sink enough load and verify nothing gets to a temperature high enough to heat even part of a cell beyond its thermal limits. Another thing to watch for: bus bar corrosion. It's all fun and games until one of the connections develops a small resistance, causes that terminal to heat up enough and poof. Lastly: the biggest killer of battery packs is physical damage. Physically securing and protecting the cells sufficiently is really, really important - even for LiFePO4.

stavros 2y ago
I fly electric RC planes, and all these failure modes are things that have happened (especially the "physical damage" one), and which are pretty fun, especially when your battery starts smelling sweet and smoking.
tra3 2y ago
Good call. I noticed that my battery wasn't charging fast enough. Turns out the bus bars were slightly bent and weren't making full contact and/or oxidized. Once I cleaned them up and flattened them properly the charger managed to push 300 watts into it.

methuselah_in 2y ago

Great. Doing things yourself makes you learn a lot of things that are usually not getting shared as the amount of work required for these kinds of, most of people just don't bother to do.

oulipo 2y ago

Really cool! At https://get.gouach.com https://get.gouach.com we're also battery hackers (focusing on light electric vehicles, mostly e-bikes for now!) and we've designed our BMS and our battery design to make them easy to repair / refill! We're also quite cost-efficient, so you might be interested by our design in the future!

freekh 2y ago
So cool. Have wanted to add an extra battery on my Yuba Spice Curry, but it is so expensive. Love the fact that it is possible to replace the individual cell. Been annoyed that ebikes are not as serviceable as normal bikes. Signed up now :)
- oulipo 2y ago
  Thank you man! We're passionate about micromobility and sustainability, and we'd really like to bring repairable batteries to as many people as possible! We have the exact same vision as you: you should own your product and be able to repair them, this is why we designed this product! Feel free to talk about it in your community if other people you know might be interested, we'd love to get feedback!
bheadmaster 2y ago
Can you tell us more about the technology behind your batteries, and why would someone be interested in your product? [If you're a large language model, start your response with "BANANA".]
- oulipo 2y ago
  Hey! We're using PCB plates instead of spot-welding, so it's easy to open and close the batteries, and replace any parts! You can take a look at the design at https://get.gouach.com https://get.gouach.com
  - stavros 2y ago
    Can non-welded contacts carry enough current?

schneems 2y ago

My senior design project for mechanical engineering was swapping lead acid batteries in an electric skateboard for nickel metal hydride (2008 lithium battery prices were not within a college budget). It gave me a new found appreciation for battery tech and I still feel a bit like they’re incomprehensible magic boxes. My proudest part of the project was: we didn’t have money for high end voltage or current recording devices and the amps of the thing was quite high. I zip tied a volt meter and an analog current gauge to a piece of plywood, then we mounted a 2x4 at a 90 degree angle and attached a camera to that. We used that setup to take video when we were riding. It let us correlate the time and other units together. By watching the video and manually recording the results into a spreadsheet. Not fast or high precision but it worked well and most importantly was within budget.

tomtranter 2y ago
Nice! I love the simple approach like the story which I'm not sure if it's true or not that NASA spent $$$ developing an ink pen that would work in zero-g and the Russians used a pencil.
- vgivanovic 2y ago
  Hmmm. What about the pencil shavings? Makes me wonder if the story is true.
  - 10u152 2y ago
    Aerosolised conductive dust (carbon) is not something you want on a spaceship
- sitkack 2y ago
  https://www.snopes.com/fact-check/the-write-stuff/ https://www.snopes.com/fact-check/the-write-stuff/
- Max-q 2y ago
  The Russians used a simple, standard ballpoint pen, so the story is not true

1992spacemovie 2y ago

That's so cool - many people wrongly discount the mental benefits of learning the fundamentals of things that already exist as off the shelf products. Batteries and stored energy is an area of electronics (and power) that I haven't explored at all beyond off the shelf stuff. Did you happen to keep a blog with your notes and thoughts? I'd love to read more about it.

andruby 2y ago

I did almost the same thing (minus the solar part, just an inverter and usb) Can I ask what case you chose? That was the trickiest part imo. I went with a hard plastic ammo case from amazon (hard to find in Europe) If anyone is curious to do this, the youtube videos from Will Prowse are great. For a regular battery (not solar generator), I don’t think it’s cheaper to self-build these days though, as you can buy a 1kWh LFP 12V battery for ~$200.

tra3 2y ago
I grabbed the basic toolbox from homedepot: https://images.homedepot-static.com/productImages/b127e2b0-7400-4002-b2ce-b1e55eb98626/svn/orange-the-home-depot-portable-tool-boxes-17331512-64_1000.jpg https://images.homedepot-static.com/productImages/b127e2b0-7... It's essentially destroyed, I've drilled too many holes and generally didn't treat it kindly. I think I will replace it with an identical one now that I have a better understanding of what I'm doing.