Opinions on LIPO PCM & BMS

[auraslip]

http://www.batteryspace.com/pcmwithequilibriumfunctionfor24cells888vli-ionbatterypackat60alimit.aspx
# Prevent 88.8V Li-Ion Battery pack from over charge
# Balance each cell at Max. 4.325/cell (required voltage tolerance within 0.2V for each cell)
# Protect 88.8V Li-Ion Battery pack from over discharge ( 2.50V/cell)
# Limit 88.8V Li-Ion Battery pack's discharging current below 60 A ( continuous )
$220.95

I like plug and play. As a daily e-biker it is needed for safety and sanity. My ping pack is as simple as unplug controller and plug in charger, but sometimes I manage to mess even that up!

Of course the problem is sourcing Lipo cells large enough. To make a 20ah pack out of hobby king packs would take 4 sets of BMS, and that is just to expensive!

 

[amberwolf]

Not if you parallel all the packs first.

 

[auraslip]

Is that dangerous? What if a cell fails in a parallel cell?

 

[dogman dan]

What you'd do is buy 1s packs, then paralell them to 20 ah. Then series connect them. Just like in a ping pack. The paralell cells will keep each other at the same state of charge.

But lipo likes to balance to 4.2v, so 4.325 might set the house on fire.

And the cells will die at 3.0 volts, or at least be risky to charge after that forever. So the bms is going to let you know you just killed the whole pack when the lvc pops off. Must be a bms aimed at another chemistry from the one in HK turnigy.

 

[AussieJester]

Is that dangerous? What if a cell fails in a parallel cell?

The good cells continue to charge until the set voltage is reached, this means instead of 4.15v a cell they go waaaay over to compensate for the dead cell in the string
... has happened to me ...twice, all 16 packs of mine were overcharged to 5v due to cells failing (0.0v) have 6 left that have been rebuilt from de-puffed/re-sealed packs. You

You can use monitors on every cell, they trigger an alarm if any cell fails below set point

http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=7227&Product_Name=Hobby_King_Battery_Monitor_6S

You should read the battery section theres heap of info there.

4.325v wont even see the cells puff Dogman takes near ~6v before anything dramatic happens with these Turnigy and Zippy 6s packs.

KiM

 

[amberwolf]

WEll, it does mean that it could take down the rest of the parallel cells. So if your intent is to protect each individual cell, then yes, you would need a separate monitor and/or balancing device for each one. Costs go up.

It is potentially cheaper to replace all the paralleled cells killed by a failed cell if that ever happens to you, than to buy multiple BMS units. You'd need to work the costs out.