Custom LiPo (dangerous)

[LibertyMKiii]

Recently I have been running my Hobao VTE 2 on 2s speed runs.
The runs often are over 400 amps and it can be hard on the batteries. After looking around I noticed that some of the top of the line LiPo brands do not have offerings of the commonly used 6000 mAh cells in a 2s configuration.

Long story short I went with SMC and fried a cell after 3 runs. Not saying SMC is bad as many have good experiences.
I went to order another but it was sold out.

I then started looking for alternative solutions and decided I would finally make my own custom lipo.

I had laying around 2 Revolectrics 4s packs that I have never used because they were 4800mAh. The pack is 4 cells in series.

Cut the pack in half and you have 2x 2s packs.

Before I get much further I wanted to point out a few things. This is extremely dangerous and shouldn't be done anywhere inside your home.
I am doing this in my garage with the door open where I can toss the pack out into the driveway away from the house in a moments notice.

First step was to open it up very carefully. If a cell gets punctured and allows oxygen in its basically over and should be disposed of properly.
I began by separating the series connection in the middle making this 4s pack into 2x 2s packs. (I had a second one so now i have 4x 2s packs)

I removed the balance plug as I would be soldering on a new one and just taped those ends off so that no shorting would occur.

I followed a guide from Peter Dirks where he mentioned getting the packs cold before applying the soldering iron on them to help avoiding damage. He also mentioned you need to apply the heat for a short duration of time. He recommends a large chisel type soldering iron of 80 or more watts. I ordered a Weller 100 watt off amazon and this thing rocks!!!

Old 30/130watt Weller vs New 100 watt Weller

At this point I had 4x 2s packs ready to begin the process. I used tape to isolate any connections from an accidental short.

Next I used the freezer to cool down the packs but not very long like 10 mins. If they get too cold then you deal with condensation issues....

I started by removing the main power wire leads with the soldering iron.
Next came soldering on my new heavy ga. wire (8ga castle wire and you could go with 6 ga.) I had already set this wire up on QS8 connectors.

(notice how close on the other side of the tape that was already there from Revolectrics how close the opposing cell tab is.

At this point I have 2 separate 2 cell packs that I need to make parallel. So as they saying goes..... Red to red and black to black...
Be cautious and tape over any tabs/exposed metal that could be touched accidentally.

2 Wood working clams worked awesome to hold the pack straight up, very stable, and could work on it.

Final step was to install a new balance plug for 2s. (available on amazon)

Then tape everything up and wrap it up!

Found PVC shrink wrap the right size also on Amazon

Now I have a high output 9,600 mAh 2 cell pack to use with 8 gauge wiring.

I just hope it does not blow up and catch fire!!!!

Already tested it on the charger and cells are still balanced and look good!

 

[Moirae]

This is impressive, I would have been terrified.

 

[norcalsc]

pushing the limits

 

[Jon NC RC]

U r crazy sir

In a good way......

U r an evil rc scientist

You speed guys, what will you think of next!!???!!!???

And yes, unless you REALLY know what you are doing, DO NOT try this at home !!!!!!

I won't be.....

 

[*420+3RC*]

Skill......all skill.

 

[LibertyMKiii]

This is impressive, I would have been terrified.

U r crazy sir

In a good way......

U r an evil rc scientist

You speed guys, what will you think of next!!???!!!???

And yes, unless you REALLY know what you are doing, DO NOT try this at home !!!!!!

I won't be.....

I have been terrified to try this for years and finally now that I had these 4800 mAh batteries that I was considering trashing I said why not give it a try!
I will say if you take it slow and take precautions it is not that bad.

This took me about 1 hour to do on my lunch break.

 

[fpvmiller]

If I read everything correct, you still have a 4800mah 2s pack.

Parallel increases capacity.
Series increases voltage.

If you had a 4800mah 4s and split it down to 2s packs it's still 4800mah but at 2s instead of 4s.

EDIT: I actually see it now. Yes, from a single 4s you gained a 9600mah 2s @ 4800mah 2s x2 in parallel.

 

[Jon NC RC]

Skill......all skill.

And now you know why I won't be doing something like this....

I have been terrified to try this for years and finally now that I had these 4800 mAh batteries that I was considering trashing I said why not give it a try!
I will say if you take it slow and take precautions it is not that bad.

This took me about 1 hour to do on my lunch break.

You get a pat on the back for your using your time in a constructive way.....

Well done

 

[LibertyMKiii]

If I read everything correct, you still have a 4800mah 2s pack.

Parallel increases capacity.
Series increases voltage.

If you had a 4800mah 4s and split it down to 2s packs it's still 4800mah but at 2s instead of 4s.

EDIT: I actually see it now. Yes, from a single 4s you gained a 9600mah 2s @ 4800mah 2s x2 in parallel.

Right in its original configuration it is series 4800 cells making it a 4s pack 14.8 nominal volts.
Now it is 2s2p making it 7.4v nominal and 9600 mAh.

You could do this with a connector outside of the lipo pack and would be considerably safer, but I am going to run 2 of these giving me a total of 19,200 mAh and only wanted 2 be running 2 lipo packs. + I gained bigger better solder connections and 8 ga wire in the process. It was originally 10ga wire.

Packs with 2s2p configuration is not uncommon at all. Now seeing how this works I could see how bad cells could be hidden as each wire in a 2p configuration is actually used for balancing 2 of the cells.

 

[bt224]

My daughter was into the electric motorcycles. Most of the guys built custom Lipos because the off the shelf stuff was insanely expensive.

 

[olds97_lss]

I've had varying experiences with soldering to the tabs. I eventually got some aluminum solder/flux for it and it made the job waaaaaay less annoying. I've pulled packs apart to remove bad cells or pulled a couple apart to make a 4S or 6S pack out of 2x2S or 2x3S packs. I've been able to use the tabs on the packs to solder to the other tabs, but the aluminum solder/flux made that go a lot easier on tabs that had zero solder on them.

Couple 4S packs I made, was hoping to make 3 of them out of 4x3S packs, but I knicked one of the cells outer layers when taking it apart and didn't want to risk using it... so I ended up with 2x4S packs.

I later made a 6S pack out of a couple 3S liperior packs to try 6S in my maxx4s:

I've since also bought some heat shrink for rewrapping old packs or wrapping ones like these. Even after measuring, I still ended up with shrink wrap WAAAY to big. Luckily though, cutting it to a more appropriate size and using CA glue to connect it back together worked out surprisingly well.

This was a buddie's 6S pack that dropped a cell. He asked if I could make it a 4S pack for him:

Cutting open my first SMC hard case packs with a dremel was terrifying... but I've done enough of them now, it's not so bad. Soft packs are way easier to deal with though.

This stuff is good for keeping all the wires insulated from each other and to also hold the pack together before you get the outer covering on it:
https://www.amazon.com/gp/product/B07S1Z877Q

This was the solder/flux I used for the tabs. Worked great:
https://www.amazon.com/gp/product/B010UMSB9Y

But, it ruins your iron tip. I have a cheapy "choice" brand 100W iron I got off amazon and an adjustable rheostat to plug my irons into. This tip worked in it and I just keep the aluminum soldering tip in the aluminum solder/flux package for next time:
https://www.amazon.com/gp/product/B083F5B1YH

 

[TheBadazz]

Bro you're a brave man!

 

[LicketySplit]

I'm pretty good at soldering but thinking about doing lipo's I'm like that

 

[Surchaufeur]

I tried soldering broken tabs on my zeee and it never worked. Solder never wanted to stick to it. As long as you don't punch the lipo you are fine. Show it respect and it will give you respect back

 

[LibertyMKiii]

I've had varying experiences with soldering to the tabs. I eventually got some aluminum solder/flux for it and it made the job waaaaaay less annoying. I've pulled packs apart to remove bad cells or pulled a couple apart to make a 4S or 6S pack out of 2x2S or 2x3S packs. I've been able to use the tabs on the packs to solder to the other tabs, but the aluminum solder/flux made that go a lot easier on tabs that had zero solder on them.

Couple 4S packs I made, was hoping to make 3 of them out of 4x3S packs, but I knicked one of the cells outer layers when taking it apart and didn't want to risk using it... so I ended up with 2x4S packs.

I later made a 6S pack out of a couple 3S liperior packs to try 6S in my maxx4s:

I've since also bought some heat shrink for rewrapping old packs or wrapping ones like these. Even after measuring, I still ended up with shrink wrap WAAAY to big. Luckily though, cutting it to a more appropriate size and using CA glue to connect it back together worked out surprisingly well.

This was a buddie's 6S pack that dropped a cell. He asked if I could make it a 4S pack for him:

Cutting open my first SMC hard case packs with a dremel was terrifying... but I've done enough of them now, it's not so bad. Soft packs are way easier to deal with though.

This stuff is good for keeping all the wires insulated from each other and to also hold the pack together before you get the outer covering on it:
https://www.amazon.com/gp/product/B07S1Z877Q

This was the solder/flux I used for the tabs. Worked great:
https://www.amazon.com/gp/product/B010UMSB9Y

But, it ruins your iron tip. I have a cheapy "choice" brand 100W iron I got off amazon and an adjustable rheostat to plug my irons into. This tip worked in it and I just keep the aluminum soldering tip in the aluminum solder/flux package for next time:
https://www.amazon.com/gp/product/B083F5B1YH

Very nicely done!
I wish I had those GT500 chargers. My Venom charger does not read the cell resistance and I really wish it did....

 

[L3phturn]

Very nicely done!
I wish I had those GT500 chargers. My Venom charger does not read the cell resistance and I really wish it did....

A $15 voltage checker will give you internal resistance. https://www.amazon.ca/dp/B0178P8H9U?ref_=cm_sw_r_cp_ud_dp_ZHRW7034PB9DJ634891F

Everyone should have 2 of these. Very handy. They will even balance and discharge (very slowly) your packs. I have two and use them regularly. One in the shop near my charger and LiPo storage, and one comes with me when out running.

 

[LibertyMKiii]

A $15 voltage checker will give you internal resistance. https://www.amazon.ca/dp/B0178P8H9U?ref_=cm_sw_r_cp_ud_dp_ZHRW7034PB9DJ634891F

Everyone should have 2 of these. Very handy. They will even balance and discharge (very slowly) your packs. I have two and use them regularly. One in the shop near my charger and LiPo storage, and one comes with me when out running.

Thanks for pointing that out.
I have the ISDT Battgo cell checker which is rather fancy with the color digital screen etc, but it does not display cell internal resistance.
I love how it shows all cell data on the same screen at one time. I really wish this one had the cell resistance data too...

I'll order one like you linked as that is a simple and low cost solution versus looking to replace my lipo charger.

 

[L3phturn]

Thanks for pointing that out.
I have the ISDT Battgo cell checker which is rather fancy with the color digital screen etc, but it does not display cell internal resistance.
I love how it shows all cell data on the same screen at one time. I really wish this one had the cell resistance data too...
View attachment 213146

I'll order one like you linked as that is a simple and low cost solution versus looking to replace my lipo charger.

They are cheap and you can also use them in the field with the battery still connected in the car. Just take the body off and plug it into the balance lead. Very handy. One goes with me along with my temp gun and wheel wrench.

 

[Hammer Down]

A $15 voltage checker will give you internal resistance.

How do you do that? I have two of those meters and all’s I’ve ever been able to is check voltage..

I can use my charger to check IR but it would be cool to use that meter.

 

[L3phturn]

How do you do that? I have two of those meters.

It’s not obvious. Here I made a video.