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NEED HELP! 3000W electric bike battery set up

3588 Views 30 Replies 7 Participants Last post by  Solarsail
hi to all!

i'm trying to build a DIY 18650 battery pack out of the samsung INR 3500mahs and my configuration is 23 in parallel and 30 in series = 100Ah 96V. my confusion is on charging this beast. what is a good charger that doesn't blow up the battery pack but can charge it quickly.

Any inputs on this set up would be much appreciated!


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that doesn't blow up the battery pack
That would be primarily up to you and your BMS, not the charger.

Quickly? This outfit makes some nice "quick" chargers.

Thanks for the reply! I'm actually planning on using no BMS. There are 690 18650 cells and in 23 paralel(23x30).. i cant find a bms matching this configuration so im planning on doing the resistor to copper situation build. The chargers you suggested are a bit pricey. Question.. does the voltage of the charger have to match with the battery pack?
Yes, of course the charger must match the pack voltage precisely..
For your 30 S pack that would be 126.0 v max, but 124 v would be a better
voltage to extend cell life.
It must also be a specific Li charge program with a CC/CV charge profile.
Dont expect to find a cheap solution.
You could use 3x 10s BMS boards.
Hi Jayson2

You can get away with a much more rudimentary battery charger - it's definitely NOT as good but it can be a lot cheaper

I charged my 44S Headway pack using a 230v - 110v transformer a full wave rectifier some capacitors and a JLD404 to switch it all off when it reached the target votlage

You could do something similar - but as you have 120v mains you would not need the step down transformer but you would need some resisters to ensure that the charging current was low enough

Not pretty - but it worked until I went to a higher voltage

Search for "Bad Boy Charger" - and you will find lots of suggestions
Jeeez Duncan !
The guy doesnt even know what voltage is needed to charge...
...and you are encouraging him to try a "bad boy" set up. :eek:
Jeeez Duncan !
The guy doesnt even know what voltage is needed to charge...
...and you are encouraging him to try a "bad boy" set up. :eek:
Steep learning curve??
... 3500mahs and my configuration is 23 in parallel and 30 in series = 100Ah 96V. ...
Hi J,

Your math doesn't add up. Perhaps you have S and P mixed up.

haha. i literally started researching about the setup yesterday and i did see some DIY chargers but im not thinking of suicide yet :D.

and for the numbers.. i just realized they are other way around (oopss). so 30cells in parallel and 23cells in series.

so its:

I found this on the web which a few people suggested to me.

i contacted the seller and the seller told me that he can customize it to do 96V while pushing max of 15A so the battery would be charged in about 6.6hours.

Do you think this charger could do it if it was optimized properly? Any other suggestions/ inputs are very much appreciated!
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If you are looking for 96V average, i.e. the controller can work with higher voltages but expects the average voltage to be 96V as the cells discharge, then you need to divide that voltage by 3.6 and not 4.2. The cells reach their average midpoint capacity at about 3.6V (actually 3.63V). 4.2V is the maximum voltage at full capacity. My understanding of motor/controller manufacturers is that 96V means the average voltage and not the maximum voltage.

In this case, you would need 96/3.6 = 26 cells in series. This is commonly written as "26s30p". So there are groups of 30 cells in parallel, and then 26 of these groups in series to make the pack.

With only 23 cells in series, you will be starving the controller half the time, and it may shut down prematurely to save itself. And you may be draining too much current from the battery pack when its voltage drops below 23*3.6 = 83V which may cause the battery pack to shut down or blow a fuse. If the system shuts down at 83V you still have half the battery capacity left, which will be unusable.
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My suggestion is that instead of building one huge 26s30p pack, which will weigh about 43 kg (95 lbs), to build four smaller modules, each 13s15p. So you get two modules and tie them in parallel, and then the other two in parallel, and then tie these pairs in series to get the 26s30p or 96V 100Ah.

There are several advantages to smaller modules. The weight is now down to 11 kg, and the size is a quarter, and you can distribute the four modules throughout the vehicle. The charger can also be 1/4 the rating of the full blown charger with half the voltage and half the current rating, and that will be a lot easier to find. You can now use 4 chargers if you are in a rush, and if you have the power supply to charge all at once.

Furthermore, it would be a lot easier to find a balancer and protection board for 13s15p compared to a 26s30p. All e-bike power packs have a balancer and a protection board. I really don't know how you want to get away without them.

I am building a 13s10p module, and have started a thread for that here. You may want to take a look at it. Cheers!
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For each of my 13s10p modules I will be using one 900W CCCV charger, such as:

This can supply about 16A at 54V, so it can charge the module in 2 hours (or 3 hours for a 13s15p module). Cost $20. It needs a 36V or 48V power supply, and there are many to choose from on eBay anywhere from $30. The power supply should be shared between the modules, and its wattage depends on how much power you can get from the plug. If you want lots of charging power, then get four 1000W supplies instead of one 4000W supply.

Then there is one balancer-protection board per module, such as:

Note the rating is for 20A which would probably mean that one should not draw more than 17A or 0.5C. Depending on how much power you want to draw from the pack, you need to rate this board to allow for the power. Cost is $10.
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wow i have a lot to learn. i think this splitting 1 to 4 modules would be a really good idea but im concerned about a few things.

First. The idea of using BMS (4 of them) could be a little too much limiting.. you say you can only draw out 17a from every module so that means a motor that peaks current at 65ah-70ah would barely have enough current. 17ah x 4 = 68ah? im not sure if this is right or wrong.

Second. There will be more batteries (exactly 780cells..13x15=195 x 4 =780) used which means more weight that can be moved around (not much room on a bike in the first place).

Third. The idea behind charging 4 modules and then reconnecting them back would be a troublesome thing to do and im not an expert on this so by all means correct me if im wrong. But if they are charged even slightly differently ( one has less or more than the other ), connecting them back together would throw off the controller (or something else) as the batteries are not synced.

But i love the idea and im not sure if anybody else has done this before. Anyone has any experience with this kind of setup? any inputs on my concerns and what have you would be great!
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Very good questions Jayson. Happy to say none a problem.

2) Your original layout was 23s30p 3.4Ah cells. That gives you 23*3.6 = 83V x 102 Ah = 8.45 kWh. The range depends on V*Ah and not just on Ah. So when you go to 26s you have more V, and you can reduce the Ah by reducing the number of parallel cells so that the range remains the same, and the number of cells are approximately the same. 8450/(3.6*3.4*26) = 26. So you can have 26 cells in parallel instead of 30 cells in parallel, and you will have the same power and the same range. (Power is volt * amp, and is not Ah). Therefore you can go to 4 modules 13s13p = 676 cells instead of 23s30p = 690 cells. Or you can go to 4x 13s14p = 728 cells.

3) You do not need to reconnect the modules because you will never separate them. They are always connected. Even if you have to occasionally separate and reconnect, it is not a problem because the two modules will have exactly same voltage when you connect in parallel. If they are not equal, just put a 1 ohm resistor between them, and let them equalize for a while before connecting. This said, it is not necessary to disconnect two parallel modules for charging. Thus let the charger charge both of them while in parallel. They will balance out. I also believe you can put two chargers in parallel as long as they are adjusted both to 13*4.2 = 54.6V - check the charger specs. Thus if one 900W charger is too slow, put two 900W chargers in parallel - both must be set at 54.6V exactly.
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1) If 17A is not sufficient, then use a bigger BMS. Below is a link to a 45A balancer. So now your pack can produce 2*45A or 90*3.6*13s= 4200W. I think your title says 3000W. So what you need is two parallel modules to produce 3000/(3.6*13) = 64A, or each module to produce 32A. So you could use a 35A balancer. Note that Ah is unrelated to power (W=V*A) and should not be confused. To get 3000W, you need 64A total or 32A per module.

The BMS is so cheap and easy to install, but it does many important protection jobs that you must use it. It saves your cells from going below 2.8V each, which will partially destroy them, and is a safety issue. If you leave your lights on one night, and the cells go down to 2V or 1V, you have lost $3,000. It saves the cells from going over 4.2V each, which will shorten their lifespan and is dangerous if the charger goes bad and keeps on raising the voltage. The BMS will also balance the cells to make sure they are all equal to 4.2V when fully charged. Also in case of short circuit, it will cut the current. If too much current is requested from the pack by the controller, the BMS will cut the current. And if too much current is forced into the battery during charging, it will cut that too. Finally, the BMS detects the module temperature and cuts off the current if it becomes too hot during a runaway event.
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Thanks for the info! really loving this setup now. I have more questions though:D.

1) So for charging them, do you make a charging port for every module or just do 2 modules per charging port and then do parallel charging? which is better?

2) how do you eyeball calculate the range for a 26s30p? as you said the range depends on the Watt hour of the battery and the motor. In my case the motor peaks power at 4200w and peaks current at speed 74.5 miles an hour (with load). i found this formula on the web and did it based on this setup:

watt hour per mile= 96Vx (65ah/74.5mph)= 83.75.

96v x 100ah=9600w

so, 9600/83.75= 114.6 miles.

Is this an approximate measure or even correct?

many thanks!
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watt hour per mile= 96Vx (65ah/74.5mph)= 83.75.
96v x 100ah=9600w
So close - just a couple of typos:

watt hour per mile = 96 V x (65 A / 74.5mph) = 83.75 Wh/mile
96 V x 100 Ah = 9600 Wh (or 9.6 kWh or 34.6 MJ)

You just had the time component (hours) misplaced in both expressions, but the logic and the result are correct (if the input values are correct).
Now for whether the values are correct...
2) how do you eyeball calculate the range for a 26s30p? as you said the range depends on the Watt hour of the battery and the motor. In my case the motor peaks power at 4200w and peaks current at speed 74.5 miles an hour (with load). i found this formula on the web and did it based on this setup:

watt hour per mile= 96Vx (65ah/74.5mph) ....
If the motor is getting 65 amps at 96 volts, that's 6240 watts, not 4200 watts... so something is not right. Perhaps you are looking at current to the motor from the controller, but voltage to the controller from the battery? Perhaps the 4200 watts is output power and the motor is only 4200/6240 = 67% efficient when producing this peak output?
1) So for charging them, do you make a charging port for every module or just do 2 modules per charging port and then do parallel charging? which is better?
Yes, each module can be charged independently. In case you remove one for testing, etc. So each module has a charging port. When you install the module and put it in parallel with the other, then the two charging ports should go in parallel, and you can connect one charger to charge both, or connect two chargers in parallel, one on each port. Or you can have a separate charging port in a convenient location that connects to both charging ports in parallel.

The other module pair that is in series, must have its own port, and you cannot charge two serial modules in parallel (unless you install hefty switches or contactors to rewire for charging, and not forget to switch it). However, you can have one big charger 2x13x4.2V = 109.2V and charge the whole system with a single charger. I still prefer at least two chargers, each 54.6V, in series, one for the upper pair and the other for the lower pair. If you lose a charger in a trip, you still have the other one that can charge any pair.

I will also put an ammeter with LED display on each module, as they can point to problems. Also one LED voltmeter that can measure the module voltage, or using switches measure the voltage for each group of cells. So the switches will allow 14 readings by the voltmeter. One for each group and one for total. Occasionally upon charge and discharge one must check all 13 groups in the module. If there is one that is different, then it probably means one cell has gone bad. You need to replace that cell in the group as not only it reduces total energy storage disproportionally, but could result in future safety issues like a fire.

If you plan to go 26s30p, then I would suggest you split that into 6 modules: 2 series x 3 parallel x 13s10p. The modules become smaller and may be easier to install. Also, if you lose a module (due to a bad cell), you can disconnect two modules, and still have 4 working which gives you 2/3 range. On the other hand if you had 4 modules total, and one goes bad, your range drops to 1/2. Also if you have one or two bad cells in a group, or you are unsure, you will have to open all cells in the group to find which one it is. In a 13s15p module, you will have to open 15 cells. In 13s10p, you open 10 cells.
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