48V ebike battery pack - 91 cell 14Ah

Hey guys, as the title says, this will be my first ebike battery build. As I hope to use my saved parking money over time to build a bigger/better/more capacity battery down the road, I'm hoping I can get one to get me by with my 4-5mi commute...
I'm planning on a:

• 13 cell in series for 48v nominal battery
• 6 parallel 48v banks for a total of 10-12Ah @ 48v
• Use of 9 unbranded 2000mAh rated cells (I've tested them to be around 1800-1950mAh, Samsung ICR18650-30A cells, and Samsung ICR18650-26F cells
• BMS - 13S here: http://www.ebay.com/itm/13-S-Packs-...269155?hash=item489178f6e3:g:S10AAOSwHoFXtAjS
• Heat shrinking each battery again to ensure double protection...
• Deans Ultra connectors
• Pretty hefty gauge wire, likely 12-14AWG

Let me know how that sounds.

I'm planning on building a custom battery housing for my bike once I have it. I'm planning on a fiberglass enclosure where the batteries will stay safe but I'll also be able to remove them from the shell and do any type of maintenance on them if needed. I also plan to shape the fiberglass to fit the frame of the bike...hopefully.

Some people have said 20A for a BMS is too low. I'm planning on a 1000W motor, local restriction is 500W so I'm not really planning on using a ton of power over 500w to get me to and from work... I want decent power but enough where it can get me to work without much effort on a pretty flat commute and in decent time ~25-30mph.

Few questions:
Can I test internal resistance of the 18650 cells I have? I have a few used ones and right now my only tests are timed and calculated discharges with a multimeter testing current and calculating capacity...

Hi,

Philaphlous said:

Let me know how that sounds.

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Sounds like you are building a 13S6P pack. Adding cell level fuses might be a good idea.

Philaphlous said:

Some people have said 20A for a BMS is too low. I'm planning on a 1000W motor, local restriction is 500W so I'm not really planning on using a ton of power over 500w to get me to and from work... I want decent power but enough where it can get me to work without much effort on a pretty flat commute and in decent time ~25-30mph.

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The 20A I believe is for discharge. The BMS that you posted will take a long time to fully balance the entire pack (it says 30mA). 10Ah of capacity might take days to complete.
I have 48V 1000W ebike kit and currently running on 14S12P recycled 18650s. It does consume over 20A. I am not sure about 500W though as it depends on how efficient your motor controller is.

Philaphlous said:

Few questions:
Can I test internal resistance of the 18650 cells I have? I have a few used ones and right now my only tests are timed and calculated discharges with a multimeter testing current and calculating capacity...

Click to expand...

I used a homemade constant-current load to quickly judge the cell's health. It is not super accurate, but it will give relative readings which allow test for under a minute for each cell:
https://twitter.com/AfdhalAtiffTan/status/820386064187559936/photo/1

1) A lot of hobby chargers will measure internal resistance
2) I would go with a 40 amp BMS since even a stock 1000W controller usually draws 30+ amps.
3) How are you connecting the cells together electrically? How are you securing everything physically?
4) Your post doesn't make it clear quite what you're doing but under no circumstances do you want to build a battery pack with no-name cells, ever. You want to use ONLY good name brand cells with decent discharge rates. DO NOT IGNORE THIS.

flat tire said:

1) A lot of hobby chargers will measure internal resistance
2) I would go with a 40 amp BMS since even a stock 1000W controller usually draws 30+ amps.
3) How are you connecting the cells together electrically? How are you securing everything physically?
4) Your post doesn't make it clear quite what you're doing but under no circumstances do you want to build a battery pack with no-name cells, ever. You want to use ONLY good name brand cells with decent discharge rates. DO NOT IGNORE THIS.

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2) Would 30A suffice? I'm new to the whole BMS thing so I just noticed the balance current.
3) I'm using desoldering wicking copper strand to connect all the cells. After that I plan on physically connecting all 3 via heatshrink and tape combo
4) I've already tested individual cells I've harvested from a battery pack and I can easily get 3A out of them no problem per cell... I think those should be ok for my needs. I'm trying to keep the draw under 3A per cell under full load.

Maybe this BMS is better: http://www.ebay.com/itm/BMS-PCB-for-48V-13S-45A-Li-ion-Lipolymer-Battery-with-BALANCE-for-ebike-escooter-/172593421675?hash=item282f5e9d6b:g:rygAAOSwuxFY1nxl

You can use a 30 amp BMS but then your BMS may slightly bottleneck the rest of your system...not a big deal for your low power setup. 30 amps will give you reasonable performance and you should see 30+ mph depending on your motor and the rest of the equipment used.

I looked up the 30A + 26F cells you mentioned. Those are not good for ebikes, even if you scavenged them. You will need way more cells in parallel than you're planning on if you want the battery to provide its full capacity, have a good life span, and not voltage sag like a mofo. You can try to make the pack and use your experience to build one with GOOD cells once you learn that ebikes are awesome, but your battery sucks. As for the no-name cells, THROW THEM AWAY. Do not include them next to those name brand cells or you will REALLY ruin the battery.

Anyway for the rest of it that sounds good...just make sure your solder joint to the negative case of the battery is solid as there is lots of thermal mass and it can be really hard to heat up. The positive part is easy to solder to HOWEVER it is also easy to damage the insulation covering the positive / negative transition on top of the battery and if this part is compromised it will give you a bad day. The desoldering wick is a decent choice. Also, make sure your battery assembly is fully structurally sound and solid before you begin soldering as you don't want the soldered connections to be structural or they'll undergo a lot of stress and can fail.

flat tire said:

You can use a 30 amp BMS but then your BMS may slightly bottleneck the rest of your system...not a big deal for your low power setup. 30 amps will give you reasonable performance and you should see 30+ mph depending on your motor and the rest of the equipment used.

I looked up the 30A + 26F cells you mentioned. Those are not good for ebikes, even if you scavenged them. You will need way more cells in parallel than you're planning on if you want the battery to provide its full capacity, have a good life span, and not voltage sag like a mofo. You can try to make the pack and use your experience to build one with GOOD cells once you learn that ebikes are awesome, but your battery sucks. As for the no-name cells, THROW THEM AWAY. Do not include them next to those name brand cells or you will REALLY ruin the battery.

Anyway for the rest of it that sounds good...just make sure your solder joint to the negative case of the battery is solid as there is lots of thermal mass and it can be really hard to heat up. The positive part is easy to solder to HOWEVER it is also easy to damage the insulation covering the positive / negative transition on top of the battery and if this part is compromised it will give you a bad day. The desoldering wick is a decent choice. Also, make sure your battery assembly is fully structurally sound and solid before you begin soldering as you don't want the soldered connections to be structural or they'll undergo a lot of stress and can fail.

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You think the 26f's are a bad choice because of their consumption limit? Maybe my math is wrong? If I have 6, 2-2.5Ah packs of 48v in parallel that get me around 10-14Ah. Each 13 series of cells would see a max draw of maybe 4A... Probably more around 2A.

That math is right correct?
4.2V fully charged X 13 cells in series for 54.6V.
6 "Lanes" or, 6 packs of 13 cells connected in parallel to make up the entire battery
3A draw per cell @ full voltage would give me 982W calculated.

Those controllers draw more like 1.5kw and believe me you're going to want every bit of it cuz it's not very much.

So your understanding of the pack configuration, capacity and C rate is correct. The issue is you will be stressing the batteries and dropping the voltage a lot + reducing performance whenever you go full throttle which should be very often if your ebike is working correctly. A battery made from those cells would be OK for lower power cruising.

The controller is really going to determine the current draw on the pack. Your cells need to handle the current without overheating. The BMS should be rated for about 2x the current limit on the controller. The BMS should only trip if there is a fault. If the BMS is rated too low, it will tend to trip from normal startup current surges.

I have a 14s, 9p pack of similar cells. it handles 40A draw OK.

Holy crap...

So the BLDC controller is that inefficient? gooosshh. That's unreal...

So in essence I'd be building like a 600w real power ebike but with a 1000w capable motor...

I'm trying to think up ways to include more batteries in my build, still not there yet. I won't be able to tell till I get my bike and determine what exactly is all going to fit.

The controller efficiency is good, that's not the problem. It's where the current limit is set and how accurate that is. Many of the newer ones have a programmable current limit, so you can dial it in for the max your batteries are good for. The max discharge current for the batteries will be your limiting factor. Having more parallel cells will increase this.

So for designing the pack...

What's better? Hooking the batteries in Series first then parallel or parallel then series?

Here's my batter housing idea:


I may stack 3 deep since I'll have to go ~16" long for all the batteries to fit...

First parallel, then series. You want all the parallel cells to be connected at each series connection so they will be protected by the BMS. There are a few good pack building threads to look at.

Working on getting my batteries! Unfortunately received some duds... 0v

All batteries and name brand Samsung or LG which is good. Hoping to do my big battery purchase over the weekend with the easter sale.



I think the 3 layer is going to work... It should actually be a pretty compact battery...


Ended up getting a 35A BMS for 48V.

So all batteries in Parallel will balance but its the series that needs balanced?

Cells are assembled into groups. Each group is a bunch of parallel connected cells. The cells within each group are forced to the same voltage by the parallel connection, so will be balanced. When the groups are placed in series, the BMS tries to balance between the groups to get them all the same.

When building a pack from recycled cells, it will be hard to get good matching between cells and groups. Pre-testing each cell is highly recommended. Even then, you can easily get one group with a dud cell that will be a bottleneck for the entire pack. A good BMS is more important here too, as it's more likely a single group will be significantly weaker than the rest.

fechter said:

Cells are assembled into groups. Each group is a bunch of parallel connected cells. The cells within each group are forced to the same voltage by the parallel connection, so will be balanced. When the groups are placed in series, the BMS tries to balance between the groups to get them all the same.

When building a pack from recycled cells, it will be hard to get good matching between cells and groups. Pre-testing each cell is highly recommended. Even then, you can easily get one group with a dud cell that will be a bottleneck for the entire pack. A good BMS is more important here too, as it's more likely a single group will be significantly weaker than the rest.

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My entire goal of the battery build is to build an easily accessible case for the batteries to be housed in. That means, if needed, I can pull all the cells out and test as needed. Additionally, if I want to replace a bank, I'll be able to do so. Once I get more involved with the build and sure up my job situation, I hopefully will build the entire battery the correct way. With where it stands right now, I'm expecting to get around 12+Ah out of the 48V pack which is going to be a pretty decent output. Heck if I used Panasonic cells I'd be around 19Ah...lol

I just ordered a 150Amp watt meter from ebay. That'll be my primary logger of my power consumption and voltage meter for the battery. I hope to integrate this right on the battery. That way I get a true number of my power draw before the controller.

Which solder is going to be a good solder for the cells? I've got a rosin core 60/40 right now and not sure if that's a good choice... I ordered some super flux so hopefully that help adhesion.

Spot welder. You can build one out of an old microwave.
You could buy a battery and a running bike. An also do your battery hobby.

If you're going to solder, you need a huge soldering iron to solder them right cuz the battery case wicks away heat like crazy. 60/40 is the right choice. Be careful.

If you go nickel strip I wouldn't recommend making a spot welder out of a MOT. It will suck for welding batteries. Instead you can make one out of a thyristor, a couple car audio capacitors and a car battery charger / other power supply.

Where are you from ? There are 175.00usd 1,000 watt kits. No battery.

I would get a bms with blinking balance lights. Very fun to watch.
Plus if I brought a battery it should have blinky balance lights. .

Ok changes are happening! Here's what's up

I got my charger and watt/amp meter for the battery!


I also got the charger which is what this is being powered from in the pic. Looks like it uses around 0.02-0.03A @ the 57V which is around 1-2W of power which I can deal with... Sounds fine to me. I might add a switch to turn it on and off so it doesn't constantly drain the battery when not in use. Oh, and I also took apart the charger and carefully inspected everything before trying it out. I also modded the housing that has a small 40mm cooling fan. I cut the very restrictive grill out and turned the fan around so its blowing cold air in the charger and not sucking air out. That should yield better cooling for it. I'm debating if I want to add another 70mm fan to it for super cooling so nothing gets overheated and blows...lol

I'm planning on going with a bigger battery. 91 cells to be exact. Even if the cheapo batteries I have only produce say 1500mAh, that should still give me over 10Ah of juice. I'm hoping its more like 12-14Ah in reality.

So I did a little experiment with soldering yesterday. Found out that soldering the + side of the battery is super easy and quick. Maybe takes a few second for the solder to pool and stick. Heck I didn't even need flux. Question, When I make my connections, Should I connect all the batteries in series first then add parallel or do parallel first then series? Just trying to understand what is the best method of construction.

I have 29 18650 cells right now and they're all charged to around 4.00-4.10 just to keep them energized at a decent level. I should be getting around 50 more this and next week. my BMS is on its way and I'm still working out the details of actually getting my bike here. I still haven't ordered my rear hub kit and I likely won't do that till I have my job situation figured out and my bike here with me. I plan on doing a bunch of upgrades to the bike even before converting it so I'll definitely take some time for that.

I also have an ImaxB6 charger coming so I'm going to capacity test each cell. Gosh its going to take forever...lol

When are even voltage parallel first then when the two groups of parallel cells are at even voltage connect. Parallel first then series of same voltage cells. A wet sponge will cool solder joint fast . Do use gaskets to insulate the pos tit from the neg case. I use a 80watt weller iron fat tip. Haven't made a spot welder yet.

999zip999 said:

When are even voltage parallel first then when the two groups of parallel cells are at even voltage connect. Parallel first then series of same voltage cells. A wet sponge will cool solder joint fast . Do use gaskets to insulate the pos tit from the neg case. I use a 80watt weller iron fat tip. Haven't made a spot welder yet.

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Whops...
My soldering iron is only 15w...lol Looks like I'm going to have another ebay buy on this one...

I also got a hot glue gun (I guess people call it hot snot...). Hoping to get my fiberglass in the next few weeks also so I can be ready to start building the custom battery case.
Another idea I had was after I was done building the battery and box is to wrap the batteries in aluminum foil, of course making sure nothing shorts out with sulifane underneath, then filling the voids around the battery in the fiberglass with expandable foam. That way I can make the shell a perfect fit for the cells and they will have a snug fit. I think I can really do a good job with the battery box and something transferable to any bike...

Ya the big fat tip let's you a very short time soldering on the cell also pre tin the strip. Let the tip get hot. I wire brush the tip tin it and can but cleaned with hot with wet sponge. All must be clean. I also like a set of sense wires like 6s ect that way you can use a cell meter. This with or without bms.

Drbass has a good thread on pack building.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=28285#p407768