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Help with 18650 6s battery pack


#1

so i want to make my own 18650 pack and have some questions.

first do i need a bms? cant i just have a balance lead for each cell group and charge it like a normal lipo in a sense?

second how much amperage should a good pack be able to give out? i was thinking 4p so i could get 80-100 amps constant, is that to much would 60-75 be ok?

last is it really worth it? is it really worth it over the standard zippy lipos everyone uses? lets say money and time are not an object are 18650 packs worth it?


#2

Generally, they are safer and last for more cycles. If you have a good bms, you can charge them with a “dumb” charger. They are much more expensive than my 10c multistar lipos though.


#3

Personally I believe that people are using BMS simply because of ease of use. They want the single plug and charge solution, instead of plugging 2 cords and going through balance charging. It’s also safer in terms of protecting the batteries from shorts and low voltage. Hence I don’t think you really really need one.

100A continuous is way too much. VESC only draws peak 60A. Tested with multimeter, motor 200KV’ish only draw about 5 - 15A peaking at 20A tops on relatively flat ground (I weight 65kg). You will drain your battery super fast if you ever draw 100A and currently not much shady cheap chinese ESC that can handle 100A constant while pulling dead weight over kilometers of distance.

The reason i switch to li ion because of less risk in getting my entire build burned down due to bad lipo. Lipo has really descent -to- short charge cycle even though they have higher energy density per pack. I believe big lipo packs are also rejected by air ports and air carriers because of safety reasons.


If you’re not in a rush, wait for that graphene lipo packs are abit cheaper. If you have the money then try get one :smiley: Since I believe not getting a BMS is because it’s too hard to install or getting SPACE cel are too expensive, then it’s better to just stay with lipo and get new one if it’s shows bad symptoms.


#4

pretty much what @laurnts said. You can get a decent BMS on Ebay though for not a lot of cash, and if you can squeeze it in there, its a much better solution than an outboard programmable charger if you don’t have a whole stack of lipos to charge as well.

but i’m all about integration. I’m also about keeping my packs balanced, and a BMS can do that and extend the life of your pack in doing so.


#5

i dont use a BMS. i just attach balance leads on to it and use my lipo charger! lol i charge at low amps. and i monitor it constantly.


#6

ok well then my next question is would this be a good bms and if so how would i go about charging it with this laptop charger?


#7

BMS is determined most likely from the voltage and amps it could discharge. The one you have with your link seems to be good for 6S with a nice discharge capability. To be honest, I have not much experience with good or bad BMS. I have experience with a fake chinese product that uses bms and it appears to be fine.

The charger appears to be in good selection as well. 2A charging current is the safest route for long life cycle. I personally looking for 5A’ish power supply since I have 10000mah, charging 2A is really slow.


#8

So I ordered 48 Samsung icr18650 25r5 cells but have a question about charging.

If I use one of the following BMS boards where the charge and discharge leads are the same how should I change?

Option 1: one set of leads with a dean plug and use my old lipo charger.

Option 2: run 2 leads from both pads one for charging one for discharge with a 100A switch to close of the discharge leads when charging or not in use.

http://www.batterysupports.com/22v-24v-6s-60a-6x-36v-lithium-ion-lipo-battery-bms-pcm-pcb-p-478.html

http://www.batterysupports.com/28v-29v-30v-60a-8x-36v-8s-lithium-ion-lipo-battery-bms-pcm-pcb-p-264.html


#9

there is 3 pads, one is for the battery negative one is for the battery positive and one is for the charge negative.
you don’t need to use a lipo charger because the BMS will control charging.


#10

I was gonna use the lipos to supply the power not to balance. also there is no pad for positive on this bms and the negative pad is for both charge and discharge.


#11

ah sorry my bad, I misread the description. so in that case you just have B- to your battery -ve and P- to your charge port and ESC -ve


#12

So as long as I have cut-off switch between the esc and battery I can throw a charger on the battery aswell to have a spacecell like set up?


#13

thats right. thats exactly how the space cell works


#14

Well then when my spot welder and batteries show up that’s what I’m doing


#15

well got the batteries and tested the crap out of them. they are legit and so sexy… no im not aroused by batteries stop asking.
heres a link to the ones i bought. http://vitaltech.en.alibaba.com/product/60383730345-801914430/Wholesale_Authentic_Samsung_25R_18650_samsung_INR18650_25R_2500mah_samsung_sdi_18650_2500mah_battery_cell.html

if you want any ask to do the transaction via paypal.


#16

How do u know they’re legit? How much was it for shipping and can they sell less? 24? That looks like a great deal
I think li-ion has more energy density and less power density. Don’t know if that’s by weight or size compared to lipo.

I plan to wire two sets of 12 in series and two rows in parallel, (50 volts and 5amphour) and glue/pot them to my board with 70duro clear rubber without balancing wires but instead balance them individually with…a big light bulb or something. It will be very manual. And charge them with a 50 volt bulk meanwell charger I have.

Per mile li-ion maybe are cheaper. Safer. Thinner…my lipos skim the ground.


#17

The smallest amount they sell is 30 for 3.6 a cell. Shipping was 65. I know they are legit because I spent the last 30 hours running charge and discharge test to get the capacity of the cells and compared the discharge curve to what Samsung has published. Also they have all the little hidden markings that you find on Samsung 25r batteries.


#18

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#19

Not an expert but i think You can really save On BMS and get a lower amp rating and Just use it for Charing. Then for discharge you rely on the esc cutoff


#20

what do you mean just use it for charging? also lower amp rating? if anything i want a higher one but cant find a good 80A bms for around the same price.