No-clever-name build | Dual 6374s | 12S6P | homemade deck | SuperFlys | 218mm trucks | custom machined parts | carbon fiber

[birdus]

Starting on the battery packs now. I picked up some old laptop batteries from a local computer store for free and practiced soldering nickel strips to those. I’m very glad I practiced and I would highly recommend it if you haven’t done this before.

I’m soldering 3 pure nickel strips between batteries, each 8mm x .15mm (that’s about 5/16" x .006"). It’s pretty beefy and should handle high current nicely. My practice demonstrated that soldering one strip at a time is the way to do it. I wait a bit between iterations so the batteries don’t get too warm (i.e., I solder one each on all the connections, then cut more strips, etc., then do another iteration).

I’m aware of the warnings against soldering, but I have never seen any tests demonstrating any ill effects.

I sanded the terminals before starting and I used plenty of flux. I think I’m getting very good flow. Also, as you can see, I added insulators to the positive terminals. I experimented using hot glue between the batteries, but determined it didn’t really add much strength. I’ll just be gentle with the packs until I have the heat shrink in place.

I was going to use 10 gauge wire but decided that it would be difficult to make some of the connectors with wire that big, so I’m going to use 12 gauge. I think that’ll handle 20 amps continuous, so it should be fine. The batteries I’m using (Sony VTC6) will put out 30 amps up to 80° C (so temporarily) and 15 amps continuously. I doubt that I’ll ever have the guts to drive the board that hard.

[Pedrodemio]

Love the attention to detail

And nice to find another one with a homemade completely flat deck. My first was just two pieces of 10mm low grade plywood glued together, rode that for 1.5 years, just put a coarse grip tape and you are good

[Skunk]

Really like that idler set up. Do want.

[birdus]

Although I didn’t use hot glue, I did wrap some high-heat tape around the batteries to keep them tight. I really want to minimize movement between batteries to try and eliminate strain on the nickel strips.

I added some extra tape on top of the negative lead to add some protection against the positive wire wearing through against the sharp soldered wire of the negative lead.

Since I commonly do things without thinking (like building a $2,000 skateboard), I’ve really been trying to be careful as I build my battery packs. In this instance, I stripped the insulation off the positive wire, but left the negative one covered. Oh! Also, I made sure to put the shrink wrap on the wires before soldering! That’s definitely something I would typically screw up. Then, I shrunk the tubing. By following these steps carefully, I minimized the chances of shorting out the batteries. One interesting thing: while I was soldering, when I touched the solder to the bare wire, I got a few small sparks on a couple occasions. Turns out the solder was draped across the battery pack! No biggie. I’ll just be more careful as I go.

I was a tad sloppy and melted the connector just a bit. I’ll work on that.

One down, one to go.

Shrink wrap cut to length and ready to go.

I cut a slot in the shrink wrap to try and minimize pressure on the soldered negative lead.

The slit didn’t work out so well.

To fix the slit, I added several pieces of electrician’s tape, then added another shorter length of heat shrink. Turned out okay, I think.

Considering this is the first battery pack I’ve ever made, I’m pretty happy with the results. However, I still have 5 more to go and hope to do better on subsequent ones. In summary, this is a 12S pack. When I have all 6, I’ll just make a harness and plug them all together to get the 6P. I could easily have fewer or more packs, as desired.

[E1Allen]

@birdus. How do you plan on charging your battery pack?

Also, don’t make any more battery packs yet, I see some issues.

[birdus]

Here is my situation, as I understand it.

I’m using Sony VTC6 batteries. Each can put out 15 amps continuous and has a capacity of 3 amp hours. So, what I just built is a 12S pack, 43.2 volts nominal (3.6 x 12) which can output at 15 amps continuous with a capacity of 3 amp hours. I will build 5 more of those. Then, I will build a harness which will connect all the positives of those packs to one another and all their negatives to one another. I will tap into that harness at some point and add one more connector (probably on one of the ends). That will give me a 12S6P pack, 43.2 volts nominal (or 50.4 volts fully charged or 49.2 @ 4.1 volts per battery).

The final plug will go to a splitter which will feed the 2 VESCs. I will add an additional set of wires coming off that final plug which will go to an XLR connector in the battery cover.

My Cycle Satiator battery charger will plug into that XLR connector. I will set it to charge to around 49.2 - 50 volts and will probably use a current of 3.6 amps. 1C per pack is 3 amps (since each battery is 3 amp hours), so 1C for the whole pack would be 18 amps (3 amp hours x 6 packs). I understand that a good, moderate charge rate is .2C, so that’s probably what I’ll use (.2C x 18 amps = 3.6 amps).

Okay. Fill me in. Where am I going wrong?

Jay

[TheMrLarin]

Lithium ion cells need to be balance charged. Using a BMS for charge only is the typical way to do it if you dont want a bms for discharge. Smart chargers with balance leads can be used to but I’ll end with that. Others will fill in the voids I’ve left

[pat.speed]

Yep your right, he needs balance leads to keep the cells balanced.

@birdus sorry to say but you will need to remove the shrink wrap and add balance leads

[trigger4point7]

I know it’s possible to go balance-less but it is very dangerous and you have to keep check the voltage for over or under discharge which will be difficult with the shrink wrap and you’d need to be able to rebalance the pack when they inevitably fall out of sync.

Basically, for your own peace of mind throw a BMS on there.

[pat.speed]

That’s the other problem, it’s not like he could even check the voltages because it’s covered in shrink wrap

[trigger4point7]

One other issue could be that the negative lead is not shrink wrapped but still in contact with the cell. This is more so a problem if on the anode side of things with the positive lead cuts through the cells shrink wrap and shorts on the cathode but still something that I would personally wrap and shield.

[janpom]

I’m afraid it’s not just about adding balance leads. As I understand, you’re aiming for 12s6p and the way you want to do it is by building six 12s1p packs (like this one) and wire them in parallel. That won’t work for balance charging though. You need to do it the other way around. Build the 1s6p packs first and wire them in series.

[trigger4point7]

You could build it as he is but you’d need 6 packs with their own BMS and then split the charger leads to each of them. That is how I would do it but I agree with you, 12 1s 6p packs with one BMS.

[E1Allen]

I went to bed, basically the BMS problem was what I was going to get. I don’t use a BMS for my packs. I have four 3s6p batteries with balance leads. These I connect to my hobby charger. That way I still properly balance the cells. Currently you have no way to balance so it’s a hazard in the making. 100% have to balance the cells at some point. The problem with going 1s6p is not balancing. It’s the fact you will have 12 connectors under your board which is plenty.

This is my method which is not typical on this forum but works for what I wanted which is 3s packs I can use on other projects.

You need to unsolder that pack and go a different route. It’s okay though, a solution isn’t far away.

[pat.speed]

Why would it not work? He would just need to wire all of the balance leads together into one plug… yes it would create a lot of bulk but it’s definetely possible

[E1Allen]

That sounds like a nightmare setup.

[Sender]

I am with @E1Allen yoo much bulk, nightmarish

[trigger4point7]

@birdus don’t stress too much dude, we’re just trying to keep you safe.

[birdus]

Hey, guys.

I just want to thank you all for your input. You did it in a kind way, and I genuinely appreciate your concern. However, as stated in the first post of this thread, I’m not going to use a BMS.

There are two schools of thought regarding a BMS (Battery Murdering System?). First is that it’s absolutely critical and you’re likely to die a horrible death unless you have one. Second is that if you use brand new, high quality batteries, never charge up to 4.2 volts nor drain past about 3.6 volts, the batteries will stay almost perfectly balanced for many, many cycles.

Over on endless-sphere.com, there are a number of threads with quite a few folks who have gone the second route trouble free. What I’ll probably do is just check the voltage on a per-pack basis from time to time. That will give me an idea of battery health and would certainly make it easy to locate a pack with a bad battery in it.

Anyway, I’m going with the second school.

Thanks! Jay

[E1Allen]

@birdus I don’t use a BMS either. However my batteries have balance leads so I can balance charge. The method you plan on using is called Russian roulette. You have 12 batteries and not a single way without tearing your pack apart to check the voltage of each battery. Since you’re not balance charging at all, only charging one battery could be lower than the rest but the pack voltage is correct. Now when you discharge the pack that low cell goes lower than the rest. It will continue to do so until it dies. Your pack will still read the correct voltage but one battery is going to take a hit and that creates a fire hazard. None of us know how long this process will take. Even if you don’t fully charge or discharge the pack it will still happen. Plus you will have this issue with all the packs you’re making. I think most of us would highly recommend you change your pack design.

“Over on endless-sphere.com, there are a number of threads with quite a few folks who have gone the second route trouble free. What I’ll probably do is just check the voltage on a per-pack basis from time to time. That will give me an idea of battery health and would certainly make it easy to locate a pack with a bad battery in it.”

This is where you are missing the point. You need to check CELL voltage not pack voltage.

Yes, they can go probably quite a few cycles without balance charging, but the point is after a while it has to be done and you are unable to do that with your current configuration.