DIY lightweight battery

[frediiii]

not a car progress thread, but my latest mod. might be interesting for the lightweight fetish people on here

everything started about a year ago when I was looking for lightweight batteries for my twingo RS. all I found was the typical hawker 7kg bike battery, the varleys and all their lookalikes. but 7 kg battery would only safe 7kg of weight compared to the 14kg twingo stock battery... so I dismissed the idea

few weeks later at a local RC drift meeting one of the guys tried his brand new LiFePO4 battery pack... I asked him about it and he told me it's a nice technology... not as much punch as LiPo batteries but you can charge it with high current like a car battery so it is full in minutes... wait... did he say "like a car battery"?

later at home I did some research and found out that LiFePO4 is indeed a worthy alternative for crappy lead-acid cells. so I dug out a few manufacturers, found a cell that was easy to handle, offered huge capacity and even was nice to look at:

enter: the headway 40160 LiFePO4 cell

the beauty of those cells is that they are huge, compared to other cells. so you only need a few of them limiting the assembling time and point-of-failure rate. quickly I ordered a bunch and upon arrival I started to assemble a 12v 16Ah battery pack

the sheet underneath outlines the stock twingo battery dimensions. just to see how small the pack actually is, there's a standard issue redbull can right next to it

I charged it using my RC car charger and found out they came pretty well precharged. then all I needed to do was hooking it up to the twingo to test it... but that weekend I was attending a slalom race and in the class I was entering I was not allowed to modify the car and the tiny blue battery would have caused disqualification. so I put it aside for "later"

much later, as turned out. few months after building the cell I traded the twingo in for the clio which I am now driving for over 3 months... but today, I stumbled over the cell and couldn't resist to finally test it:

[youtube]FnaC7peUCrc[/youtube]

voila... it works. now it's time to do an endurance winter test

 

[Foxspeed]

very interesting that :jase2:

be good to see how it copes with winter...

how does it compare with a standard battery in terms of amps and cranking amps etc?

 

[frediiii]

I will leave it in this winter. tomorrow morning will be the first cold start at about -4°C

this configuration has 16Ah and 160A Peak power. doesn't sound too promising but consider this:

LiFePO4 cells have a much less steep discharge curve compared to lead acid cells. so you get more bang out of the capacity...

here is a comparison of smaller lifepo cells (A123) with 4.6Ah compared to a 12Ah lead acid battery...


you see even though the capacity of the lifepo cells is not even half of the capacity the lead acid battery is offering, it lasts more load cycles (one cycle is 70A discharge for 20 sec, 20 sec pause).

my cell has more than 3 times the capacity of this tested cells so it will outrun a 40Ah lead acid battery easily...

 

[Yiannis197]

Very interesting. Well done to you, top effort!

 

[Fernandez]

That is awesome, top work...could very well be interested in one of these if they perform well.

 

[smoggy mark]

Top work would free more space up if it was flat rather than been up right,what would be the costs for this?

 

[frediiii]

Top work would free more space up if it was flat rather than been up right,what would be the costs for this?

there's tons of space either way. I didn't want to modify the original plastic casing so everything still looks stock. without cutting the box the cables only allow upright mounting.

in the video the battery is just hooked up somehow to see if it would work. meanwhile I tidied up and temporarily secured the battery so it won't move around. have to find a proper, lightweight way to hold it into place though

price for the setup is around 100gbp

 

[marshall]

That seems to do the trick.

Got a feeling you could make money putting these together and selling for track cars.

 

[frediiii]

First lets see if it survives this winter

 

[Foxspeed]

might be good if you can find a securing type of strap to hold it in position

 

[frediiii]

might be good if you can find a securing type of strap to hold it in position

this as well needs cutting. I'm more tempted using velcro. as the battery is so light this will withstand hard driving. in case of an accident it might become loose though.

 

[smoggy mark]

Think if you could get it flat like this by using a L bracket it would work well with a maxogen setup providing they are ok over the winter.
I did this with no cutting and all can be put back to standard.


redtop and maxi 003 by chickster2012, on Flickr

 

[frediiii]

if mounted flat the terminals would be 2cm from the ground of the plastic-casing. all those wires would be too short. the varleys terminals are higher up due to it being thicker.

update: battery is still in and no problems so far not even after 2 days of standing outside. measured the battery temp -2°C when I started it and it started like a charm. I also noticed that when I turn off the engine whilst having the lights on and closing a window, the lights don't dim and the window doesn't slow down like they did with the stock battery. that's also an indicator that there is less voltage drop on load like the graph I posted earlier already indicated.

 

[marshall]

All is looking well then!

 

[smoggy mark]

sounds promising hope it works

 

[EviLNeeDs]

I hope this doesn't happen.
Link

 

[Benmc]

Subbed!!