So Many Lipo Questions! Please Help (First Build)

[akrenits]

HI ES,

I'm completely new to Lipo. I've done some research, but I'm struggling to find a bunch of answers still. Please help with as many questions as you can!

I want to put 5 of these in series making 74v: http://www.amazon.com/dp/B01CCSMS6Q/ref=sxr_pa_click_within_right1?pf_rd_t=301&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=2329824862&pf_rd_i=14.8v+floureon&pf_rd_r=1BJSN79ATE6WEG3083JH&pf_rd_s=desktop-rhs-carousels&psc=1

Questions
1) will 74v fry a cyclone 40amp 36-72v controller or will the voltage drop be enough? Do I put in a resistor? Do I need to downgrade to 6 11.1V cells in series? What is the highest voltage I could get away with?

2) Should I put something like a 50amp breaker before the controller as a safety measure/primary on and off switch?

3) Whats the best way to wire these in series? Is something like a lipo bms necessary?

4) According to this video, balance charging them in series shouldn't be a problem.. should it? https://www.youtube.com/watch?v=7CDuWSBqIM8

5) Is there a better way to charge them all together though, or would the alternative be to charge them all individually?

6) EDIT

7) Is there any other basic Lipo knowledge I should know? Lipo 101 please

 

[wesnewell]

1. The voltage won't fry it. If you run max amps for too long, that will.
2. Most people use a fuse, but it's up to you.
3. In series means positive to negative. Do you know some other way? I've run mine for over 5 years without a bms.
4. You're not going to find a 20s balance charger, so forget that. You'll need some external balancers like battery medics or a bms to charge a 20s pack in series.
5. see 4.
6. see 2.
7;
http://www.rchelicopterfun.com/rc-lipo-batteries.html
http://scriptasylum.com/rc_speed/lipo.html

 

[akrenits]

That was super helpful! So all I need now is this: http://www.aliexpress.com/item/20S-Li-ion-Lipo-Batteries-Protection-Board-BMS-System-72V-84V-80A-Continuous-Discharge-Current/32500068377.html?spm=2114.30010308.3.2.kxeyKT&ws_ab_test=searchweb201556_0,searchweb201602_3_10017_10005_10006_10034_10021_507_10022_10009_10020_10008_10018_10019,searchweb201603_9&btsid=6ec02aa7-91b2-472c-be60-a872125d9747

1) That has a balance function correct? all BMS do?
If not that BMS, surely this one: http://www.batterysupports.com/72v-84v-20s-80a-20x-36v-lithium-ion-liion-lipo-battery-bms-p-294.html

2) Then all I need is a 20s (84v) wall plug and just plug the negative to the bms and the positive to the battery and leave it to charge overnight because the BMS will prevent overcharging and will balance cells?

3) What kind of connectors go in the BMS from the balancing wires (is it just soldering)? and what connectors do you recommend for all the heavy gauge connections? have a good place to pick them up cheap? Are wire nuts okay for between my battery cells?

4) For wiring the BMS I will need to know which cell is "first" in its balancing wire. Is there a way to tell if the black balancing wire below is the first or last in the series? (Aka first as definted by the BMS wiring diagrams).

If these questions get answered, I think I should be kept busy for a long while! Thanks so much for the help

 

[wesnewell]

1. Either of those bms's should work fine.
2. Yes, 84V charger, 10A or less charge current.
3. I'd use some kind of connector (DB25 maybe) for the balance wires so I could easily remove the bms form the pack, but you could solder direct too. I like 4mm gold bullets for the mains. I would never use wire nuts.
4. The lowest cell is the first cell. Cells number from low to high.
http://scriptasylum.com/rc_speed/lipo.html

 

[akrenits]

^ this guy deserves a raise

 

[akrenits]

3 more questions if youre still here,

The maximum voltage will be 84v on my 20s pack. Are you sure it wont cook the 36-72v controller on a full charge?

Can i use a 20s bms with only 16s if i decide against having all that voltage?

Why no wire nuts? I would be using them between the battery packs

 

[wesnewell]

1. A 72V controller should have 100V caps and fets. About any 72V nominal battery will charge to 84V, so if it fry's the controller, the controller is defective to start with. I run my 72V controller up to 100.8V.
2. Maybe, but not likely without mods. Check with the bms seller.
3. Because wire nuts suck. They tend to come loose, corrode and provide a poor connection which will cause them to heat up and cause you nothing but problems over time.
if your lipo has XT connectors, you can buy or make serial adapters to put them in series. If they have bullet connectors, just split the housing and pug in series direct.

 

[dogman dan]

Wire nuts are fine for an emergency fix, for a temporary test, that sort of thing. They aren't used on vehicles for sensible reasons. On a house, fine, the house doesn't hit potholes.

One or another of the soldered on connectors is best for RC packs, my preference the 4 or 5 mm bullets. I also like Anderson power poles, but use them only on the final connections to the controller.