Lipo Questions

[Eujangles]

Hi All,

My goal with my next build is to be quite a bit more light weight than my super heavy last one. As such, I'm going the geared hub route (probably a MAC or an eZee), and despite my hesitation (due to my complete inexperience) would like to have a go at assembling a lipo pack...no matter what way I look at it, I'm not really getting any lighter while retaining a good top speed without it.

I have read the Wiki on building lipo packs as well as searching the forum, so please forgive me if the answers to my questions are available elsewhere here as I couldn't find them, and thanks in advance to anyone who can help.

1. Since it's very dangerous to discharge the cells below 3.0v, is it possible to have an automatic low voltage cutoff, or would I have to monitor the pack during rides with a CA or something?

2. I'm a bit confused by bulk charging and pack balancing. Is there no simple way to set up a lipo pack to be "plug and play" when it comes to charging, or is it always going to be a matter making sure the cells are balanced each time, and having to charge the cells separately if not?

3. Speaking of charging, is it possible to get a "smart charger" where I would be able to plug it in overnight and sleep safely knowing that it will cut off at 4.15v, or is there no such product reliable enough for this?

4. My electronics knowledge is next to nothing and my previous build was assembled from, more or less, turn-key products. Would you guys advise that I stay the hell away from lipo due to my massive ignorance and just bite the bullet on a heavier battery, or should I go for it?

Thanks again for any advice...as always this forum is ridiculously helpful!

-Eugene

 

[docnjoj]

Both Methods and Kfong make lvc cutoff switches. I use the one by Kfong and it works fine and is programmable. Methods one is also hvc for charging.
otherDoc

 

[neptronix]

Sounds like what you're looking for is a BMS. A BMS will prevent 95% of all awful things that could happen from occurring.

 

[Eujangles]

Thanks guys, do I need a lipo-specific BMS, or will any one (that of course fits my amp requirements) do?

 

[wesnewell]

1. Match the lipo to your controller and the controllers LVC will shut it off when the pack gets low. 12s for 48V controller, 18s for 72V controller, etc. You can also change LVC in controllers if you know how.
2. A good lipo pack rarely needs balancing. However, with the right balance charger you can balance charge the whole pack at once up to a 14s pack. You should never have to charge a single cell with a decent pack.
3. Well, I do it sometimes, but it's never a good idea for ANY battery.
4. If you're a forgetful idiot stay away from all batteries. Otherwise, use proper cautions and any are fairly safe.

Been using lipo for over a year without incident. I wouldn't use anything else.

 

[o00scorpion00o]

I set my controllers lvc to 53 volts 3.5 volts x 16S - some sag. that usually keeps them pretty well in balance sacrificing a little capacity. I could probably go lower only I have a low cell that always goes lower than the rest if I allow too much discharge, because of that 1 cell i get only 8.5ah out of the pack.

It's sagging more now because I have not been too kind to it, it sags as much as 6 volts. I will still get the same capacity out of it if I turn down the amps in the controller, but lvc kicks in now around 5.5 amps. When I get my mac back running I won't need to use such high amps!

I bulk charge most of the time now, but occasionally I need to balance charge on the icharger.

Once you get used to LiPo you won't go back and the Zippy compact seems to be the lightest and smallest battery available atm, worth considering. But to me small packs light weight is far more important than cycle life!

A bms would be useful if you can't remove the battery form the bike, but other than that it saves you a lot of money if you can manage your pack yourself.