My Bullit build using the Repairable and Refillable Gouach Battery

M

Mael

10 mW
Joined
Aug 13, 2024
Messages
22
Location
France
Hi guys! I'm one of the co-founders of Gouach, the Repairable and Refillable e-Bike Battery, we're designers/engineers from France who set up to design the best DIY e-bike battery ever! We'd love your feedback!

Here's our custom Bullit which includes the battery, more details and videos coming soon!

IMG_6575.jpg
IMG_6577.jpg

And here's our founder riding it!

And about the battery itself (check https://get.gouach.com/1 if interested! Technical details: Gouach Battery Framework)

👉 whole presentation here:
👉 Repairable in <5 min with nothing but a screwdriver thanks to its weld-less design (check this video!)
👉 Fireproof (yes it works!) we extensively tested it, videos coming
👉 Connected (get your data with the app, and configure it for your motor, 90% of brands supported)

IMG_6529.jpg

Some intro videos you can check on the casing and pack:
👉 Presentation of the casing (Fireproof and waterproof)
👉 Presentation of the battery features
 
Last edited:
Mael said:
Thanks so much! For now there is no option to buy just the case but if enough people are interested we might!
Click to expand...
I'm going to spend more time looking at this and your other material today. But in general, if you guys have successfully made a durable pack geometry with easily removable cells, that provides good contact on the cells and can deliver high current, that's going to be a pretty valuable and in-demand product for DIYers.
 
What mechanism are you using for cell contacts? Springs or something? Close up pictures of the inside of the case would be great.

What current is the case rated for, if we want to swap to higher power cells? What current is each cell/location/contact area rated for?

When swapping new cells in, it would be possible to put a cell in backwards. Is there any built-in protection about that kind of user error?
 
harrisonpatm said:
I'm going to spend more time looking at this and your other material today. But in general, if you guys have successfully made a durable pack geometry with easily removable cells, that provides good contact on the cells and can deliver high current, that's going to be a pretty valuable and in-demand product for DIYers.
Click to expand...
thanks! yes, we plan to also deliver custom batteries, check our builder at Gouach Builder
 
harrisonpatm said:
What mechanism are you using for cell contacts? Springs or something? Close up pictures of the inside of the case would be great.

What current is the case rated for, if we want to swap to higher power cells? What current is each cell/location/contact area rated for?

When swapping new cells in, it would be possible to put a cell in backwards. Is there any built-in protection about that kind of user error?
Click to expand...
You can check Gouach Battery Framework for the details!
 
harrisonpatm said:
What mechanism are you using for cell contacts? Springs or something? Close up pictures of the inside of the case would be great.

What current is the case rated for, if we want to swap to higher power cells? What current is each cell/location/contact area rated for?

When swapping new cells in, it would be possible to put a cell in backwards. Is there any built-in protection about that kind of user error?
Click to expand...
yes! the cells have fuses, so if a cell is wrongly put, there is no danger!
 
I really like the idea, and above all the fact that you've reverse engineered so many vendor lock-ins. I think there are many good old ebikes rusting away just because its impossible to get a new battery for them. Good luck with hacking, i wish there were some regulations forbiding such practices (i mean vendor locks, not hacking).
 
Thanks for sharing, and especially the engineering test data... much appreciated. So, BOM-wise, for a customer, a rebuild of the pack entails new cells, and... anything else? what sizes of cells are supported? also realize that it's early in the documentation process, but would love to see shake and bake data for assembled packs at elevated temperatures as well. well done!
 
Very interesting! For the heat shedding mechanism you only model radiation it seems (see Fireproof casing), so are you thinking of space applications ? Naively I'd have thought that convection carries away more heat (if you have an atmosphere). Maybe 300°C is already hot enough for radiation to be sizeable.
For radiation I get 0.11*5.67*10^-8*(270+300)^4 ~650W/m^2, and for convection in still air (assuming htc of 5W/m^2K) I get 300*5=1500W/m^2. But maybe that coefficient is not right at elevated temperatures.
 
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Still fooling around with vape pen cells, I see.

Maybe you can advise ESA on how to go to orbit with lots and lots of model rocket motors. Repairable and replaceable!
 
I think nothing wrong, even with vape pen cells (they need to provide quite good current without catching fire). And they can be swapped for anything to one's liking.
The whole thing makes a lot of sense to me and their BMS is a strong point (but i dont believe producers will be very happy about someone exploiting the inner workings of their security/vendor lock-in protocols). The only claim i find too optimistic is the fireproof casing - there was a post with silverfish battery exploding in a lift and killing a person - the aluminium casing did nothing to stop the fire as the burning gases had no problem with escaping. So i don't think it's possible to keep burning batteries in an airtight box - false feeling of security, you'd get an explosion first and then the fire.
I think the box is good for keeping water out and protecting the cells from damage, but the security should be provided by the BMS detecting any suspicious behavior of cells and alerting user to check/replace them (a loud siren when the temperature inside is rising fast would be useful too).
And i'd imagine the BMS could also estimate the capacity of each section and inform when there's some underperforming part - makes sense even to even replace few cells instead of all.

And, finally, i think if the company wants to really support reuse/repairability, they should guarantee availability and reasonable pricing of parts. Or make parts of the design open source/publicly available.
 
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rafalg said:
I really like the idea, and above all the fact that you've reverse engineered so many vendor lock-ins. I think there are many good old ebikes rusting away just because its impossible to get a new battery for them. Good luck with hacking, i wish there were some regulations forbiding such practices (i mean vendor locks, not hacking).
Click to expand...
Exactly!! We want to fight planned obsolescence and give back power to people, there's no reason you could not use your bike if you bought it, just because a company decided to stop making the parts
 
kuromaku said:
Thanks for sharing, and especially the engineering test data... much appreciated. So, BOM-wise, for a customer, a rebuild of the pack entails new cells, and... anything else? what sizes of cells are supported? also realize that it's early in the documentation process, but would love to see shake and bake data for assembled packs at elevated temperatures as well. well done!
Click to expand...
Exactly! Just changing the cells, so perhaps $150 every 4 or 5 years or so, depending on your use! For now this battery uses 18650, but there will be a 21700 model soon!
 
Gruesome said:
Very interesting! For the heat shedding mechanism you only model radiation it seems (see Fireproof casing), so are you thinking of space applications ? Naively I'd have thought that convection carries away more heat (if you have an atmosphere). Maybe 300°C is already hot enough for radiation to be sizeable.
For radiation I get 0.11*5.67*10^-8*(270+300)^4 ~650W/m^2, and for convection in still air (assuming htc of 5W/m^2K) I get 300*5=1500W/m^2. But maybe that coefficient is not right at elevated temperatures.
Click to expand...
Thanks for your comment! We'll check that with the engineering team haha
 
Chalo said:
Still fooling around with vape pen cells, I see.

Maybe you can advise ESA on how to go to orbit with lots and lots of model rocket motors. Repairable and replaceable!
Click to expand...
Those are standard 18650 lithium-ion cells, the most common in e-bike battery packs, and we will also have a model with 21700 cells!
 
rafalg said:
I think nothing wrong, even with vape pen cells (they need to provide quite good current without catching fire). And they can be swapped for anything to one's liking.
The whole thing makes a lot of sense to me and their BMS is a strong point (but i dont believe producers will be very happy about someone exploiting the inner workings of their security/vendor lock-in protocols). The only claim i find too optimistic is the fireproof casing - there was a post with silverfish battery exploding in a lift and killing a person - the aluminium casing did nothing to stop the fire as the burning gases had no problem with escaping. So i don't think it's possible to keep burning batteries in an airtight box - false feeling of security, you'd get an explosion first and then the fire.
I think the box is good for keeping water out and protecting the cells from damage, but the security should be provided by the BMS detecting any suspicious behavior of cells and alerting user to check/replace them (a loud siren when the temperature inside is rising fast would be useful too).
And i'd imagine the BMS could also estimate the capacity of each section and inform when there's some underperforming part - makes sense even to even replace few cells instead of all.

And, finally, i think if the company wants to really support reuse/repairability, they should guarantee availability and reasonable pricing of parts. Or make parts of the design open source/publicly available.
Click to expand...
Thanks for your comment! Yes the BMS has safety alerts and is connected, so you get notifications (app or SMS) if there's something wrong on your battery! And the fireproof casing works to prevent explosions and flames, although indeed the fumes would escape
 
I read the case as holding 40 cells, so one can have a 36V 10S-4P or a 48V 13S-3P. It ships with Panasonic GA cells, based on picture and other docs? I consider GA's the workhorse cell for ebikes at 3.5AH and 10A peak. The Sanyo GA's cost me about $4 each from US vendors.

If they have solved the pressure contact problems, this is great,

I would suggest selling the case alone as an option. It will save you and customers money in shipping costs because you avoid the hazmat regulations.
 
docw009 said:
I read the case as holding 40 cells, so one can have a 36V 10S-4P or a 48V 13S-3P. It ships with Panasonic GA cells, based on picture and other docs? I consider GA's the workhorse cell for ebikes at 3.5AH and 10A peak. The Sanyo GA's cost me about $4 each from US vendors.

If they have solved the pressure contact problems, this is great,

I would suggest selling the case alone as an option. It will save you and customers money in shipping costs because you avoid the hazmat regulations.
Click to expand...
Exactly!

We might actually sell the case alone at some point, although it's been designed to fit our pack!
 
Gruesome said:
I assume/hope that docw009 means 'everything but the cells', so case, cell holder, BMS & connectors. Essentially a kit that you can ship, and the customer fills it with cells.
Click to expand...
Oh yes! Then that's definitely possible, it will be around $110 less than the pack
 
Interesting system, i'd probably buy one if they came in huge sizes ( IE will accept 1-1.5kwhrs )
 
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