need help building my first LiPo pack

[Matthew]

Hi, I'm new to LiPo and would like some help building my first pack. I've done plenty of reading on the subject so I have some ideas of what I want to do, but given the dangerous nature of LiPo and the cost, I wanted to check with you guys first.

So here is the situation:
-I want to commute on a daily basis (about 5 miles each way and very little hills)
-I want to go fast, around 30mph
-I want to use a 10T mac motor form EM3ev (but I'm persuadable to other motors)

I've found some reasonably cheap batteries on Hobby King http://www.hobbyking.com/hobbyking/store/__26675__Turnigy_5000mAh_6S_20C_Lipo_Pack_UK_Warehouse_.html
and I was thinking of arranging them into 3s 2p for a 66v 10Ah pack, so are these any good, and will 66v get me to 30mph with a 10T mac motor?

Also; what will I need for harnessing and charging/balancing?

Thanks,

Matthew.

 

[wesnewell]

What you're calling 3s 2p is really 18s2p, 66.6v nominal and 75.6V fully charged. I don't know much about the mac motors, but with a DD hub you can get 30 mph with a 12s lipo pack, which makes charging much simpler. And it will have less noise and no gears or clutch to wear out down the road. But, to the point.

You don't need anything to connect the main battery leads together. Just plug + from one to - of the next as in the diagram. If you really want to go with 18s2p here's a a link that should help.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=39666
There are several other ways to safely charge.

 

[Matthew]

Thanks.
Any charging docks you recommend?
and do I need anything like a BMS?

 

[wesnewell]

If you go with 18s, then either a high power 6s charger to parallel charge, or an 18s bms and charger, or a 75.5V bulk charger and 3 battery medics.
If you go with 12s, http://www.hobbypartz.com/75p-1220-charger.html?gclid=CNa3z9_N57ICFayPPAod10MAPw
If you go with 14s, http://www.ebay.com/itm/HYPERION-EOS-1420i-NET3-CHARGER-1S-14S-20A-MAX-550W-/290974096869

 

[dogman dan]

14s or 15s is the best configuration for "48v" controllers. If this is your first E bike, I'd suggest you just get an easy to care for battery from Em3ev.

I'm told the 10T motor will go 30 in 26" wheels.

 

[Matthew]

If this is your first E bike, I'd suggest you just get an easy to care for battery from Em3ev.

This isn't my first build, but still only my second, I already have a safe and reliable commuter but now I want a more challenging and fun bike for off road.
I was thinking maybe go for the new GNG 60v 650wmiddrive (http://www.gngebike.com/60v650w-brushless).

 

[dogman dan]

In that case, 18s is a nice voltage to play with. Slightly more compact than 20s, but still pretty fast.

But I still don't like lipo for daily riding, a battery you can ignore is nice for a commute.

I will confess, I run only lipo now, but only because with no job I couldn't afford 15 ah of anything else. But with no job, I have endless time to dork around with checking the cells and storing properly so I don't burn the house down.

 

[friendly1uk]

You will need some form of battery management system (bms) which can be endless dorking around or a circuit board that does it all for you(and better).

I use lipo and do no dorking about at all. Some of my cells are getting towards the end of their service life, and have never had a voltmeter on them. Charging my pack is no different to charging your phone. If I didn't use the $25 circuit board I would have to use a more complicated charger. More importantly a more expensive charger. $25 would not cover the difference.

Of course you don't have to take the cheap and proper option. You can spend more on less effective solutions. There are plenty of fire threads that show you how they did it if your interested. Some leave the pack connected so it drains down and flares up. Others re-wire the pack to charge it, then rewire it again to put it back in service, eventually getting a wire wrong. Others pull the balance wire's apart, because there not designed for repeated disconnection, they have nowhere to get hold of them. It is always some sort of user error that a proper bms would of avoided. Overcharging through the poor balancing that occurs in all older packs. Lots of fires that should not of happened.
On Rare occasions a cell will just go up in flames because of a manufacture or handling error. Nothing will stop this, but I have not seen a bms protected pack burn. The common denominator across all fire threads is the lack of a proper bms.

30mph won't need 18s you would be fine with 13s but if you want 18s you will end up buying a bms from bestekpower(if at all) for around £50 while an ecitypower 13s smart board could come in at $19 along with your motor order, if you got a bpm from bmsbattery to run at 48v to get your 30mph.

 

[dogman dan]

I'm not anti bms at all. Just anti trusting a bms. So having an easy way to put a voltmeter on the pack is good.

I advise that now for lifepo4 packs too. Not so much because of fire, but because letting a faulty bms wreck a pack is costly.

Fortunately, lipo bms is now more available than it was 3 years ago.

That first post talked about distance to work, so I was thinking riskier lipo at work.