# What type of DIY homemade rechargeable battery or fuel cell would you recommend to power an electric car?



## OR-Carl (Oct 6, 2018)

I hope you meant a scale model of an electric car! Modern batteries are sophisticated; they can not be made at reasonable scale in a home shop. You would be lucky to make something robust enough to power a remote control car. The good news is that major car makers are already making batteries for you, you just need to find a crashed EV car and salvage the used pack.


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## afidegnum (Aug 17, 2020)

how do i find salvaged EV car batteries?


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## Mustang101 (Apr 17, 2008)

You can make your own pack if you don't want to gamble with used batteries that have been in a wreck. That's what I did.
18650 Cells are the way to go.

I'm actually sick of all the people on here telling people not to make their own packs. It does take time and depending on the salvage yard, might not be any cheaper but you'll get new batteries that haven't suffered an impact.

Attached are some pictures of the packs I've made for my 94 Camaro. It'll have 8 packs total when I'm done, 4 in the front and 4 in the trunk.


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## remy_martian (Feb 4, 2019)

Most cells/modules are unaffected by an impact unless they get dented/pierced, which is rare because the cell has a Roman Candle "indicator."

Nice looking packs. Are they sealed for dust and getting water into them?


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## DrGee (Aug 22, 2018)

Mustang101 said:


> You can make your own pack if you don't want to gamble with used batteries that have been in a wreck. That's what I did.
> 18650 Cells are the way to go.
> 
> I'm actually sick of all the people on here telling people not to make their own packs. It does take time and depending on the salvage yard, might not be any cheaper but you'll get new batteries that haven't suffered an impact.
> ...


Woah! These look really nice! I've dreamed about building my own packs for quite a while. How much did you pay for the 18650s? Are your packs sealed against dust and moisture?


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## Duncan (Dec 8, 2008)

The trouble with buying "new cells" is that they are either very expensive or low quality - or both!
The ones the OEM's use have gone through a very thorough quality control process
The ones we can buy have either not gone through that process or have been the ones rejected


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## Mustang101 (Apr 17, 2008)

Duncan,

That's not true. You'll have to make phone calls and talk to dealers but my NCR18650PF are new from Japan. They went through a quality control process and of the +2000 batteries I bought very one was within a tenth of a volt of 3.4v. 

3.4v is what they ship them at because it's better for storage. 

DrGee, yes they are sealed from water and dust and I have a thermal management system I'm trying out with water cooling. The black tubes you see are standard quarter-inch sprinkler tubing.

I paid around $1.75 per cell.


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## OR-Carl (Oct 6, 2018)

Hey Mustang, those are nice looking modules you have put together. I may have misinterpreted what the OP was asking, but based on the chemistries he mentioned, I thought he was talking about making the actual cells - which I do believe is a non-starter. 

Building your own modules out of commercially available cells is another matter entirely. I am curious what you estimate your cost per kwh will end up being when all is said and done. Did you invest in a spot-welder to make all the those interconnections? Also, 18650 modules generally have cell-level fusing in case one of those 2000 cells develops into a short circuit - are you at all worried about that? I dont know what the odds are of a cell failing shorted, but with that many, it seems like eventually you might find out. Have you done any testing with that black plastic tubing to see how much heat it will actually transfer away from your cells? It seems that the low thermal conductivity of polyethylene is going to limit its effectiveness somewhat.

I feel like building modules is a great learning experience, but there is something to be said for leaning on the engineering and production acumen of the big car companies. If price is not a factor, and learning is more important than longevity, then I think building modules is probably perfect. The OP did not really make his priorities very clear, but hopefully some of this info is relevant...


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## Mustang101 (Apr 17, 2008)

OR-Carl,

Agreed making cells would be ridiculously difficult.

The price per kilowatt is around $15. That's including nickel strips and copper wiring and Anderson connectors. I haven't estimated the final kilowatt/hour.

I built my own spot welder with a car battery, PIC microcontroller, and some power MOSFETs. It wasn't that difficult and cost around $80 including the battery ($40).

















I only spot weld the bottom of the cells. The top I do solder a small fuse and then connect that fuse to a copper bus bar.









I did run some tests with the thermal management system. I had one cell sitting in my garage in Las Vegas this summer with 115-degree heat. The outside temperature in the garage was around 101 but I had the controller keeping the packs average temperature to 85 degrees, never got above 87. I'm using standard automotive coolant with a Peltier system and pumps to run the coolant through the packs. I think the thermal conductivity of the vinal tubing is perfect for not stressing the Peltier elements but still cooling the pack to a nominal temperature range.


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## brian_ (Feb 7, 2017)

Mustang101 said:


> The price per kilowatt is around $15. That's including nickel strips and copper wiring and Anderson connectors.


My guess is that this was supposed to be the price per kilowatt-hour (of stored energy), not per kilowatt (of power output).



Mustang101 said:


> I haven't estimated the final kilowatt/hour.


Perhaps this means the final kilowatt-hour capacity hasn't been estimated? "Kilowatt per hour" doesn't mean anything.


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## OR-Carl (Oct 6, 2018)

It looks like you have a pretty good setup there, Mustang. It is interesting to me to see what actually goes into building up a module from the ground up. I bought some tesla modules that also use 18650s, and I paid about 130$/kWh, going off the nameplate rating (in reality one would want to figure 80% DOD, plus some derating for the age of the cells to get a real-world price per usable kWh). Someday I hope to actually measure what they are capable of putting out, but my project is on summer break. It is nice to see that with enough time and ingenuity it is possible to make your own modules, although if I have learned anything so far it is to not underestimate the complexity of an EV conversion!


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## Duncan (Dec 8, 2008)

Hi Mustang
You are aware that a tenth of a volt is a HUGE HUGE tolerance for a new cell! - 10 mV - or a 100th of a Volt is more usual

I've been on this site for a number of years - people who buy NEW cells - even expensive ones - have had a failure rate over 5%
Including me when I bought new cells

Cells from a crashed production EV? - I'm not aware of ANY problems 

2000 batteries and $1.75 each so - $3500 - you claim $15/kwh ??
So 233 kwh in that dinky little pack - 

I call BULLSHIT!!

That looks more like a $10 kwh pack - and that makes a lot more sense - $350/kwh - 

Compare that to a Volt pack - like the one I bought for $1800 - that was $112/kwh 
Just a wee bit LESS than your $350/kwh

AND I pull 1200 amps from my pack - 360 Kw - only for a few seconds 

It's great to see people making their own packs - but expect to be severely disappointed compared to using a pack from a production EV


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## MattsAwesomeStuff (Aug 10, 2017)

Mustang101 said:


> The price per kilowatt is around $15. That's including nickel strips and copper wiring and Anderson connectors. I haven't estimated the final kilowatt/hour.


$15 / $1.75 = 8.57 cells per $15.

Amps = 1000 watthours / (3.7 volts x 8.57 )
= 31.5 amps per cell.









Panasonic NCR18650PF 2900mAh 10A Battery


Panasonic Battery - Panasonic NCR18650PF 2900mAh 10A Battery




www.imrbatteries.com





"Discharge Current: 10A Maximum Continuous"

You're going to get 31.5 amps out of 10 amp batteries?

And, do you really care about power out of a battery?

You've already got 2000 of these you say... that's already 2000 * 10a * 3.7v = 74kW, or 100hp. Or, supposedly, 31.5 amps or 300+ hp short term.

And you're planning on having a lot more than 2000 I presume?

Power isn't really your limitation, energy will be.



> I think the thermal conductivity of the vinal tubing is perfect for not stressing the Peltier elements but still cooling the pack to a nominal temperature range.


So... what happens when PVC tubes, in a vibration-heavy environment, through sharp bends, in heat and cold... break?

You're going to hose your batteries with water and antifreeze?

I like your solution but, I'd worry about imitating it. I am also doing 18650s, but I have no cooling solution other than perhaps forced air and a prayer (my are square packed, which does leave a fair amount of airspace for cooling).


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## OR-Carl (Oct 6, 2018)

Duncan said:


> 2000 batteries and $1.75 each so - $3500 - you claim $15/kwh ??


Yeah, this must have been a typo - as it seems to be off by a factor of 10. If they were indeed 2.9Ah cells (there are other capacity ratings available, I believe) they would hold something like 11 Wh/ cell if charged to 3.8v. So $1.75/11Wh = .159$/Wh or 159 $/kWh. Part of me feels like 5% failure seems like a lot if you are indeed getting fresh cells from a reputable supplier, but I do not have any actual experience to back that up. Also, with so many small fused cells in parallel, a few failures here or there is going to be less of an issue than with larger format prismatic cells. It does make me wonder how much of the capacity loss over time in a Tesla module could be explained by a few cells dying off completely vs degredation of the individual cells. 

The use of plastic piping in the cooling system seems like a bit of a gamble to me too. I do think thermal managment is important, though, so I dont think it is wise to forgo it entirely. If price was not an object, I would think of using malleable copper tubing that was maybe rolled or hammered out into an oval shape? 1/4" runs north of a dollar per foot, though, so it would add up. I suspect all the auto manufacturers use aluminum, but getting set up to make aluminum water tubes with tight radius bends would not be easy for the DIYer I suspect. 

If one were to try air cooling, what about putting aluminum bars between the rows of cells, and then putting in a 18mm aluminum tube in place of every 5th cell, say? Your pack would get a bit bulkier, but it might actually give you a fighting chance of forcing some air through. Or make it into a short-circuit-prone fire-waiting-to-happen?


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## Mustang101 (Apr 17, 2008)

Duncan said:


> Hi Mustang
> You are aware that a tenth of a volt is a HUGE HUGE tolerance for a new cell! - 10 mV - or a 100th of a Volt is more usual
> 
> I've been on this site for a number of years - people who buy NEW cells - even expensive ones - have had a failure rate over 5%
> ...


This is why I don't put out numbers, you guys are asses (looking at you Duncan). Yes I made a typo


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## Mustang101 (Apr 17, 2008)

MattsAwesomeStuff said:


> $15 / $1.75 = 8.57 cells per $15.
> 
> Amps = 1000 watthours / (3.7 volts x 8.57 )
> = 31.5 amps per cell.
> ...


I'll let you know how vibrations cause issues with the cooing if any. I do have a temperature, voltage, and moisture sensors in each pack. I'm not worried


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## Mustang101 (Apr 17, 2008)

MattsAwesomeStuff said:


> $15 / $1.75 = 8.57 cells per $15.
> 
> Amps = 1000 watthours / (3.7 volts x 8.57 )
> = 31.5 amps per cell.
> ...


26 cells in parallel then 9 parallel sets in a pack for a total of 260 amps continuous at 36 volts. 4 packs in series to make 144vs and then 4 more packs in parallel to make a total of 144v at 540 amps continuous. I'm limiting my controller to 500 amps which should be completely safe for my batteries. 

Maybe someday if people stop trolling I'll post my videos, schematics, code, and 3D printing STL files so others can see exactly how I made these packs. 

BTW I have a master's in EE so I'm not a newbie at this. I've been driving EVs since 2005.


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## Duncan (Dec 8, 2008)

So you spend a LOT more money to produce a pack with dubious cooling that can supply a fraction of the power

It's your money !


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## Mustang101 (Apr 17, 2008)

I made a pack that I controlled completely, that is less weight, more efficiently cooled and will last much longer than any salvaged pack.


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## brian_ (Feb 7, 2017)

Mustang101 said:


> BTW I have a master's in EE so I'm not a newbie at this.


Then you should know to be more careful to avoid miscommunications. I'm sure that you would have had trouble passing engineering courses making order-of-magnitude errors in answers and using incorrect units of measure, so you can get this stuff right. There's no good way for another member of the forum to distinguish between careless typos by someone who understands the subject, and nonsense by someone who does not understand it.


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## Mustang101 (Apr 17, 2008)

Be careful of what? Did you not notice the question was cost per kwh.


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## Duncan (Dec 8, 2008)

Mustang101 said:


> I made a pack that I controlled completely, that is less weight, more efficiently cooled and will last much longer than any salvaged pack.


Bollocks

Cost we have discussed
Weight - possibly
Cooling - nothing like as well cooled as the Volt packs -
Last much longer - in your dreams

On this forum we have had a lot of cars completed using new large format prismatics - these have unfortunately had a high failure rate - about 5% in the first year

We have had a lot of people using salvaged OEM modules - with no failures

We have had a lot of people who START to use the small cells you are using
I don't remember anybody actually succeeding and getting them working in a car

It may well be that you will be the first - but as an EE you SHOULD know the difference between kw and kwh - and you should understand heat flow enough to know that you cooling system is not in the same league as the ones used by the OEM's


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## OR-Carl (Oct 6, 2018)

Gentleman, please! Everyone gets so defensive and snappy on here. Nobody should feel the need to defend their project as being done "the right way." We are all just wasting time and money in our own creative ways - we really do not do the community any good by getting all dogmatic and telling each other how to best waste time and money. 

I did not mean to create a big stir, I was just legitimately curious how much it costs to put together a module from scratch - clearly 15$/kwh of capacity was not accurate, right? It is a moot point for me, because I am not an electrical engineer of any sort, and it is way more work than I would have time to take on. Money does always seem to come up, though, so I thought it would be interesting to have a ballpark figure for anyone who wanted to go down that road. I am pretty certain if I tried it, it would end up being a real nightmare, but that does not make it a bad idea for anyone more competent than I (read: anyone else).

Mustang, I do think you are getting out on a limb trying to (needlessly) defend yourself. A brand new OEM battery is an engineering feat - a hobbyist is unlikely to do better without access to serious skills and major investment of both time and money. Judging by what you have made, you seem to have skill and resources, so keep up the good work, and keep sharing your findings. Of course, when you buy a used pack, there is no guarantee as to its condition. You have no idea how many miles are on it, or how it was abused. But, even with a significant derating, I think it is fair to say it would be high standard to match. I think the most compelling argument for doing yourself should be 

1) to say you did it yourself - even if it is not better, or cheaper, its still a huge accomplishment and an opportunity to learn something new
2) to make a battery that fits in a very specific space
3) possibly to shave weight for a really high end application (with money to burn)

anyway, thats my take on it all, and if you all dont like it, you can write me long angry screeds 😀


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## brian_ (Feb 7, 2017)

Mustang101 said:


> Be careful of what? Did you not notice the question was cost per kwh.


Yes, the question was about cost per kWh. As I already posted...


brian_ said:


> Mustang101 said:
> 
> 
> > The price per kilowatt is around $15.
> ...


There's no need to keep discussing this - it was a minor error.


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## MattsAwesomeStuff (Aug 10, 2017)

Mustang101 said:


> Maybe someday if people stop trolling I'll post my videos, schematics, code, and 3D printing STL files so others can see exactly how I made these packs.


I'm curious, but not about your attitude. Everyone here is trying to understand what you're trying to say.

You've made multiple mistakes in what you wrote, and then you lean on your credentials and accuse people who're trying to understand you, of trolling?

No one's trolling here. I presumed you were talking about power, because your answers were foolish if they weren't talking about power, so I ran the numbers for that and came up with the same thing you did. Other people presumed you were mistaken about your costs or calculations and pointed that out.

The same people did the same thing to me when I did the same thing as you in the past. I didn't lash out at them, I'd say "Whoops, yes. Good catch."



> I made a pack that I controlled completely, that is less weight, more efficiently cooled and will last much longer than any salvaged pack.


Making a pack that you control completely is the thing I like most about using 18650s. I'm not picky about specs (I'm using waste-stream 18650s I test), and, regardless none are especially great for specs, but *the unbeatable value of an 18650 pack is that you can design your own form factor*. So many builds are constrained by where they can fit batteries, and, whether they'll have enough voltage to do so (too big is usually the problem, not too small). Not a problem with 18650s.

*Less weight* is highly debatable.

*More efficiently cooled* is almost certainly wrong. Look at Tesla packs, which are at least comparable. They use a thin aluminum foil loop as their cooling path through the battery packs. You're using plastic irrigation hose. You think your design will be superior? They have a heat pump to chill or heat the batteries when needed and keep them at optimum temperature, hot or cold. Your design is superior? Let along the fact that 18650s are kind of a ghetto solution and custom-formed cells designed for EV use with cooling channels are the alternatives if you go with another brand.

And *lasting longer*, I disagree with both you and Duncan. Duncan is arguing more about large format prismatic cells, and is correct (they're garbage), but that doesn't apply to your build. Large prismatics are small batch cells of weird design. 18650s are bulletproof, mass-produced by the best battery manufacturers in the world.

We simply haven't seen enough 18650 packs put into DIY use to really have much to say about their reliability. Duncan's correct that many people start and few finish, but that's true of any project and isn't necessarily a condemnation of 18650 packs. Especially not in your case, as someone succeeding more than most. He's not correct that no one has finished a project. I ask for example a few times a year that this comes up, and I think 2 people so far have mentioned that they use 18650s and their builds are surviving, but, low sample size.

You lean on your credentials as a masters in EE... but you're competing with the efforts of dozens, or hundreds of people just like you all on the same team. There's no way you're better than dozens of you combined on the same project. You are absolutely worse at this than efforts of hundreds of millions of dollars of braintrust in the automotive industry, who have economies of scale, and potential 6-figure quantity of events, of each 5-7 figure liability per event to consider in the robustness and safety of their designs. Your quality is not going to successfully compete with them. Not by 2 orders of magnitude, if not 3 orders.

That's okay, it's a DIY project. I'm sure with a modicum of respect for safety you can make it safe and successful _enough_. And that's good enough. But, come on, no, you're not some world-class fabrication genius that's superior than the entire industry. Lose the ego man. You'll have a lot more fun.


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## Mustang101 (Apr 17, 2008)

Matt, seriously? Stop and think for a second. This has nothing to do with ego.

A company that sells EV has to not only design a car and all the systems that go with it but also must satisfy a laundry list of regulations the government forces on them. Most of those regulations focus on safety...that means overly engineered parts...meaning weight and redundancy. Both hinder engineering efficiency. I never said my pack and system are safer because they're not. They don't have to be. They are safe enough for me. 

Point two, not all the regulations are about safety. Some are simply because bureaucracies are slow at updating laws. For example a requirement to have rivets on a part because there "isn't enough data" for carbon composite parts to be the only binding medium. Yes, that's a real issue. 

Last point. America was made by men and women making things in their garage BETTER than industry. If you feel that only big companies are the ones that can make technological breakthroughs then I'd read: Great inventions that were made in garages

I'm not claiming any breakthrough. I'm saying have a pack that works extremely well and I'm happy with it.


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## Duncan (Dec 8, 2008)

90% of regulations have piles of dead bodies as the root cause

A huge amount of the other 10% are related to stopping fraud or other crimes

There are some regulations that are basically anticompetitive - more of a problem in the USA with your "finest democracy that money can buy" than in other countries
But those are NOT NOT NOT likely to be anything that will bother your battery construction


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## MattsAwesomeStuff (Aug 10, 2017)

Mustang101 said:


> Most of those regulations focus on safety...that means overly engineered parts...meaning weight and redundancy. Both hinder engineering efficiency.


Please list what regulations due to battery packs are at the expense of weight and redundancy.

Take for example, the Tesla 18650 packs if you want something equally comparable.



> Point two, not all the regulations are about safety. Some are simply because bureaucracies are slow at updating laws.


Please list what regulations due to bureaucracies being slow to update laws, result in added weight and redundancy.



> Last point. America was made by men and women making things in their garage BETTER than industry.


No it wasn't. No country pats itself on the back more the US, and it's largely the laughing stock of the rest of the world for it's baseless smugness.

It's a vague description, that the US was "made by" X, makes it easy to run around loose with the definition any time the facts don't fit. I presume you're talking about innovation.

If you're talking about innovation, America was "made by" giant corporations and research centers that can afford to concentrate brainpower into complex problems. The biggest advantage America had going for it was simply its size, and the bigger the size, the bigger the organizations that can tackle the bigger problems. 10 countries 1/10th the size can't set their sights on as ambitious of targets as 1 large country.

Much like how the pyramids were once built. Big government with big goals.

The Manhattan project wasn't dreamed up in a garage. We didn't go to the moon on someone's garage. And specifically the automotive industry exists because of the effect of cramming thousands of engineers together over decades doing tedious R&D.

1/1,000 of America's innovation was even possible at a home based level. Sure you can find some cute examples, that's only an interesting story because of how much it's _not_ the common case.



> If you feel that only big companies are the ones that can make technological breakthroughs


Go on then, tell us about how your plastic irrigation pipe is a technological breakthrough over the sophisticated and cost-effect solution that Tesla engineers implemented. Or, really, any one single solution you can come up with.

What a bizarre stance to take.



> I'm not claiming any breakthrough. I'm saying have a pack that works extremely well and I'm happy with it.


No you're not. Does it normally work in your life to just move the goalposts every time you overstep your claims? Because everyone here can literally just scroll up to see this isn't true.

I won't put words in your mouth, you literally said you had already made a pack: "that is less weight, more efficiently cooled and will last much longer than any salvaged pack". Direct quote, that's your claim.

I won't dance around the word "breakthrough" and its threshold for significance, since those goalposts are just going to keep a'movin', so, I'd be happy for you to show us how anything you've done is even an improvement over salvaged OEM packs like you're stating.

Bold claims require bold evidence, how are you even attempting to quantify what the lifespan of a salvaged OEM pack is vs. what yours will be, without any data to back it up? (other than theory, since, you have no practical observation as you just built yours).

...

I don't care what you make, there's no "right" way to DIY something you're passionate about. It doesn't have to be better. It doesn't have to make sense. It doesn't have to be practical. It's yours, there's no rules. Do whatever makes you happy.

You know what my answer is to people saying "18650s are trash, bulky and complicated and prone to failure, you'd be way better off with salvaged OEM packs" is? "That's probably true, but I just want to do it this way anyway". And no one's ever given me sh#t over it. Everyone's been helpful and encouraging.

... you're souring how cool your project is going to be by continually making these unprovable, outlandish claims and then acting like you didn't.


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## Mustang101 (Apr 17, 2008)

Nice try Matt, I don't owe you anything. Judging from your condescending attitude you aren't even America. You can do your own research on American manufacturing laws.

You've given no facts just your own opinion. Move on


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## MattsAwesomeStuff (Aug 10, 2017)

Mustang101 said:


> Judging from your condescending attitude you aren't even America.


You are correct. I am not America.



> You can do your own research on American manufacturing laws.


Why would I do research to prove _your_ false points?

You are the one making the claims, which means you already have that information. Yet when people are rightly skeptical about your outlandish claims, rather than be dismissive you're given the floor and everyone's attention to share your information.

... instead, as expected, you continue to play the game of moving the goalposts. You moved them so far this time, you moved them the other side of the field and are saying everyone else has to prove your (false) points for you.



> You've given no facts just your own opinion.


You are the one making claims. You are the one who has to provide facts. The only fact I have to provide is the fact that you made these claims and then lied about the fact that you made them.

How could possibly I provide facts about whatever imaginary technology you think you've invented in your garage that is superior to OEM vehicle batteries? I've done as much as I can to be open minded about your absurd claims and provided some facts about the construction of things we know exist, that aren't fantasy, that you have to compare to.

How am I suppose to provide facts about whatever imaginary faults you perceive there to be with vehicular regulations, that you vaguely handwavingly refer to? I'm not inside your head. I might as well be trying to guess what your favorite meal is and how to cook it.

You seem to like attention and praise, so much so that you award it to yourself. Well... the floor is yours to earn it.

We're waiting with bated breath for you to reveal your gound-breaking garage-made technology.


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## remy_martian (Feb 4, 2019)

Can you guys chill, step back and dial the testosterone down from 11?

Well, I think you did a great job on the car & pack and it's your wallet, not Duncan's, Matt's, or any future builder's, that knows the dent put in it. 

Cell price & quality varies so much that the discussion (it's not trolling, it's having reference info that's accurate that people 5 years from now can reference) challenging your numbers is out in the open. You responded. 

Engineers have thick skins, so don't take it personally. And, yes, we can all be assholes here (like my first postings towards Brian) - there's always a price to be paid for knowledge, lol. Once you know the cast of characters you'll see we're just assholes and it's not personal 🤓

More detail on the cooling tubes please. A Tesla Model X/S uses plastic tubes as well for their battery box coolant manifold and module connectors - people seem to have missed that part. What was your strategy for contact cooling the cells?


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## brian_ (Feb 7, 2017)

remy_martian said:


> A Tesla Model X/S uses plastic tubes as well for their battery box coolant manifold and module connectors - people seem to have missed that part.


My understanding was that there were two concerns raised with the PVC tubing: thermal conductivity, and durability. Tesla apparently uses aluminum tubing between the cells; that would provide much better conductivity, but Mustang101 says apparently believes that lower conductivity would be desirable to limit heat transfer rate or coolant temperature. Tesla (like GM, in at least the Volt, and probably everyone else with liquid cooling) uses polymer tubing and fittings outside of the modules... but there are many polymers and the mounting of fittings and tubing is important in a high-vibration environment. Even with awareness that Tesla uses "plastic" there are still reasons for concern, or at least questions.


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## OR-Carl (Oct 6, 2018)

brian_ said:


> My understanding was that there were two concerns raised with the PVC tubing: thermal conductivity, and durability.


Having seen one of the Tesla packs up close, It is true that they use a mix of aluminum tube and some sort of polymer in the delivery pipes - and as previously stated, inside the modules they use a sort of flat aluminum tube. The plastic parts look like a smaller version of radiator hose, probably with some sort of fiber layer. I am certain that it was rigorously tested, and spec'ed from materials with a known compatability with both the temperatures, chemicals and vibrations involved. I will also note that all the modules connect to a rigid manifold with short sections of flex hose, and that all the connections occur in a water-tight compartment with a float switch to sense leaks.

Vinyl irrigation hose is designed for cold water. It is not wrong to wonder if running warm or hot antifreeze through it is going to be a problem. It is also not wrong to ask, how long would a failure take to develop? It might work great for 100 heating and cooling cycles, or 1000, or 10000 - it might last for the lifetime of the car. But without knowing, its pretty bold to say that an untested method is better than the highly engineered method. If it works for you, that is great, the community will no doubt find that info useful. Personally, Mustang, I hope your system does work, and gives you a nice long service life. The next person to try a self-built cylindrical pack can lean on your garage inventing and not have to start from scratch. If you overhype it, and then downplay your problems out of pride, the community does not benefit.


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## remy_martian (Feb 4, 2019)

brian_ said:


> My understanding was that there were two concerns raised with the PVC tubing: thermal conductivity, and durability. Tesla apparently uses aluminum tubing between the cells; that would provide much better conductivity, but Mustang101 says apparently believes that lower conductivity would be desirable to limit heat transfer rate or coolant temperature.


The Tesla "tubing" is actually a fine-channel aluminum extrusion, coated with conductive goop. It's total crap for coolant flow rate because those channels are so small.

If you know what you are doing, thermal conductivity in this application is a _secondary_ desirable trait, given the low temperatures and heat flux levels encountered during charging. If your batteries see more than 130F or so, you have a bigger problem than the concerns expressed here over tubing choice.

Funny how nobody is actually interested in the cell to coolant hear transfer design and everyone is concerned about a frikkin piece of pipe whose job it is not to leak under gravitational pressure.


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## OR-Carl (Oct 6, 2018)

remy_martian said:


> It's total crap for coolant flow rate because those channels are so small.
> 
> Funny how nobody is actually interested in the cell to coolant hear transfer design and everyone is concerned about a frikkin piece of pipe whose job it is not to leak under gravitational pressure.


I might not be following you, but it seems that the debate that is raging is about if it is possible to make something in your garage that is better than what a team of automotive engineers can come up while only using affordable off-the-shelf components. I suspect most of us would be incapable of doing any sort of rigorous analysis of a DIY system, let alone designing it from the ground up to be more efficient than what a team of engineers could come up with. You say the coolant flow rate is low - but compared to what? Which DIYer would even take the time to to measure the coolant flow, let alone compute if they are getting enough heat transfer through the tubing? I suspect a group of experts spent a lot of hours crunching numbers and making prototypes before Tesla decided on the coolant arrangement they went with. I just dont see how an idividual could hope to compete with a team of experts on the design phase. 

What we might actaully hope to have a meaningful argument/discussion about is: does the benefit of brand new cells outweigh the fact that our hypothetical home-brewed design falls short of the OEM one? It might be true that we could never hope to design a better coolant loop, but, does that part of it really matter all that much? If the goal is max range, maybe the new cells have an edge. I suspect it will be hard to know, because most people will not spend the many man-hours needed to come up with all the data, but it is an interesting topic to discuss....


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## Duncan (Dec 8, 2008)

_if it is possible to make something in your garage that is better than what a team of automotive engineers can _

Everything is a compromise - always

So you can make something that is "better" for your own needs by changing the compromise 

My car would be an example - I have swapped comfort and range for performance


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