2kwh Headway pack build.... opinions??

[nebriancent]

2kwh Headway pack build.... opinions??


so i plan to build a 20s 3p headway pack using the 10ah 38120S i have sorced from ebay
i have 2 orders recived to date with one on the way
i will have a ttl of 8 orders of 8 cells ea.
i have decided to break up into 4 sub packs (found this to be the way to go wile working with doc pack makita cells)
i choose to break up into subpacks for the folowing reasons

1 it is far easyer to disperse the weight load
2 repairs would suck on one large pack
3 i am still using my rc charger (4 chargers in one--non isolated) and i need a way to easily break up the packs for charging

i know you may be thinking .. no 5s bms easily scorcable
i have found a solition

http://www.batteryspace.com/balance-module-for-3.2v-lifepo4-battery-pack.aspx?ssaid=204502

its a single serries balancer that can ballance at up to 1.4 amps (so way overkill)
it has no negitive ocsilation wen run in serries

and yes i did prototype a balancer BUT i found the end resalt to be..... time consuming and ....slightly more expensive then this one inc shipping

and yes i know BUT WHAT ABOUT THE OTHER FUNCTIONS OF THE BMS>>>>>LVC>>>>CURENT LIMIT>>>CHARGE CURENT

*/*&*(#% that (*&^@$ i have no need for that
my ca has a pack wide lvc (i know still not cell level lvc but i will check it ocationaly and dont plan on more than a 20% dod on pack for most rides
my controller is set up for 100amps batteries will alow 300amp so i cant realy see a problem here
and finaly the charge current and cutoff function of the bms
my charger only will allow a 6 amp charge batteries should be good for up to150 amps of charging .... no problem here
my charger will self terminate after a set time,and or ah put into pack,and will terminate the charge by itself

so the thing i need real help with is should i mount the cells horizontily or verticly
btw i plan on using copper pipe as bus bars to make conections ... opinions on this?

here is a pic of the first subpack... i will uipdate it once i get the balance boards installed in the next coule of days

 

[nebriancent]

btw the top cell holder is redundant
and i do plan on manualt balancing cells before any parilell connections are made

 

[dogman dan]

Seems to me, you don't need a balancer if you continue to use an RC charger. Nor would you need to select balance charge very often if you practice a conservative dod, say 80%. Should stay fairly balanced for quite a few cycles, at a minimum, till the weekend if you are doing 10 cyles a week commuting or something.

Then you could just charge, check voltages, and zap a low cell group with the RC charger set to 1s, using a 1-2 amp current through the balance taps.

So all you really need is a lvc, or monitoring you are paying attention to.

Same deal as many of us do with our RC lipo.

I would upgrade the charging system for a pack that size of course. Perhaps a pair of 10s Hyperions, or at least 4 150w chargers that each can do 8s. Each pair of150w chargers could run on a meanwell 350w PS.

Current limit. What are you running? 3p headways would be good for a few amps. Would you need it? We typically don't with RC lipo due to the good c rates.

 

[nechaus]

if you have an icharger that you can charge 10 s, you could split the pack up in 2 sections and charge them in parallel or just charge one section at a time.
then you dont need to worry about a bms.
You really dont need a bms with them, but it depends on how you want to charge really.

 

[Lemlux]

I'm considering building a Headway pack using this BL20 balancer for each parallel group. It is a couple of bucks more expensive and is set at only 0.5A balancing discharge current, but it:

a.) has 2 LEDs, 0 or 1 are lit showing if cells are (i) red (lit while discharging down to 3.55V) or (ii) green (when charge > 2.5V but <= 3.55 V)

b.) has bolt on connections which avoid soldering, and

c.) are considerably smaller than the balancers you reference whichappears to make it easier to bolt the balancers to a single board along side the cell groups.

http://elitepowersolutions.com/products/product_info.php?cPath=42&products_id=151

 

[dogman dan]

Lots of ways to do it, if all you need is low voltage monitoring. But a solid cell level lvc can still be a good thing. Relying on it, maybe not so good... So monitoring at the very least at pack level is advisable.

Couple of cheap voltmeters, one for each module should be easy. At least lets you know if the charging happened, or not.

 

[nebriancent]

i am always checking my packs for voltage (espesialy if i see somtihing funny on the ca)
if a cell group falls too low i wil disconect the whole subpack from being used untill i can reballance

so far i have been running this single headway subpack in serries with my doc batterys (had to give a subpack away to a friend) for about 50 km now and i notice a huge gain in proformance (less sag at 100amps off the line)

they dont seem toi be heating up at all iether doc makita pack cells get realy warm fast at >4c and start getting warm >2c but the headways stay cool

not to take away from docs product i found them resonably easy to dimantle measure charge assemble and ballance and i had no problems with the pack i built that wasnt self inflicted in over 6000km (over did it with them in the winter)

i plan on building anoither 2 subpacks to compleatly replace my doc packs but am currently unable to due to tight funds at the moment (lost main job about a month ago)

so in ttl i will have 4 subpacks by the end of this and be running about 2kwh on a peddle bike

by the way i have built a ballancer out of the single cell ballancers i found on the site i mentioned in another post (see ealyer post in this thread by myself)

i got 5 of them in serries and have ballance wires commin off of it

seems to ballance all cells within 1mv of each other (2mv first charge)



one thing i find though is that this ballancer dose not let me reach end of charge on my charger so i was thinking i have 2 available options and wanted any relavent opinion

option 1

limit charge capasity and ignore it (built into charger)

option 2

plug and unplug ballancer as needed

option 3

put a diode inline with the chargers output to limit voltage so the balancer dose not always come on and mabee have it on a switch or somthing so i can ballance charge when and if i want (liking this option as it will leave the ballancer on the pack and will only come on in a gross pack inbalance (make it little more dummy proof if i fail to moniter voltages)