The "Brave Combo" Lithium Pack

NickF23 said:
...don't forget lithium should be charged in parallel arrays. how would this work with the cells end to end in a tube?
Click to expand...

Good point... better to stick to Nickel based batteries for tubes... But then again, these have built in PCB's so they "should" balance no matter how you charge them... wouldn't they?

Isn't that the whole "magic" of having the PCB and the cell together... no worries about "weird" situations that could cause a meltdown?
 
NickF23 said:
I suppose you could build a side by side battery the case that the cells slot in?
Click to expand...

I'll bet you could buy those in a "prefab" kind of way. Buy a bunch of "trays" and then simply squirt a little silver paste on each spring loaded metal plate to get the resistance down. Maybe lightly sand the metal to create more pores to get the paste into?
 
Check this out:

D-Cell_www.jpg


http://www.batteryholders.com

BatContacts.gif
 
Safe - before deciding on lithium, I seriously explored the idea of employing 600 AA NiMH 2300mah batteries in a 60s10p array, connected by common plastic holders with extra metal plates against the springs for the higher current the springs wouldn't likely carry.

AA Nimh at <$1 per battery was the cheapest non-lead solution I could find. The AA batteries, if I remember right, were also significantly lighter than a similar capacity pack of NiMH D's.
 
As far as those PCB-endowed lithium cells, I don't know if the PCB still does its thing correctly when in a multi-cell environment. BMS's like on the dewalt powertool battery packs fry when also connected to other dewalt packs.

I'm pretty certain with those lithium cells you'd need (or should) go parallel-first, then series so they'd balance -- else after some number of charges the pack will appear to have lost significant capacity.
 
xyster said:
AA Nimh at <$1 per battery was the cheapest non-lead solution I could find. The AA batteries, if I remember right, were also significantly lighter than a similar capacity pack of NiMH D's.
Click to expand...

I noticed that too, but that's just too many batteries to fiddle around with. If I could build on my own a battery tray that could hold 50 per tray then stack them it could work, but all it takes is one loose battery and things go bad. The "tubes" idea is simple and "contained". It's "tempting", (the AA's) but I don't have any feel for how to do it.

The Lithium with the built in PCB's would be good in parallel in some sort of battery tray. You wouldn't need 600 of them either. You could rearrainge the wires for runtime verses charging.
 
The spring loaded battery holders usually suck long term. The contact material tends to oxidize and develop high resistance. They are not designed for high discharge rates either. It's hard to beat solder.
 
fechter said:
The spring loaded battery holders usually suck long term. The contact material tends to oxidize and develop high resistance. They are not designed for high discharge rates either. It's hard to beat solder.
Click to expand...

For my "tubes" idea I was going to use a spring, but the contact itself would be something that was more ideal. What WOULD be the best material to make contact with the two "end batteries" in a series of 10 batteries in a row? The battery-to-battery issue is resolved with silver paste, but the spring and plate on the ends are still "undefined" for me so far...
 
Hi guys!
A very successful higher-amp spring contact in mass use is the plastic 3AG fuse holder, the one with wire leads.
Study that 20 amp design to get ideas for 200 or more amps.
It is quite clever! and cheap! and easy to change fuses! NOT SOLDERED!
IT WORKS!
Odds are, even the naysayers are using them!
 
I would say a fuse holder doesn't have to contend with much heat dissipation, at least nothing like a voltaic pile at high current draw.

Normally there should be zero volts across a fuse (or pretty close to it) & when it blows there's zero amps. So volts or amps times zero equals no power ergo no heat. Just a guess tho...
 
for proof of concept, one only needs to take apart a toggle switch.
U will find a spring loaded contact in all its glory.
They will pit as the years go by, from switching.
A spring loaded contact against a cell never switches. Doesn't arc and pit. The spring does NOT conduct(unlike cheap battery cases).
This would be a great final exam Q!
Half would flunk! LOL
:roll:
 
safe said:
For my "tubes" idea I was going to use a spring, but the contact itself would be something that was more ideal. What WOULD be the best material to make contact with the two "end batteries" in a series of 10 batteries in a row? The battery-to-battery issue is resolved with silver paste, but the spring and plate on the ends are still "undefined" for me so far...
Click to expand...

safe
did u figure this out?
 
i cut the top terminal off an AA cell, and used it to start my vette. so stainless steel can flow ~350 amps.
i held it with my finger against the battery post.
so i would match the cell with a ss stud. spring behind a lock nut
 
i cut the top terminal off an AA cell, and used it to start my vette.
Click to expand...

That's one heckuva AA battery! :shock:

Just kidding, I remember that thread.

Since you're happy with your grocery getter, can I have your vette? Trade ya another controller for it!
 
Matt Gruber said:
For my "tubes" idea...
safe
did u figure this out?
Click to expand...

Have not done anything so far.

For $600 I can have a 44lb and 1440 Watt/Hour battery pack if I go with NiMh and so far I haven't seen any other option to beat that... so unless there is some "last minute" alternative I'll go with that idea. (can you suggest something that beats that on price/performance/simplicity?)

As for the springs themselves... I'll probably try the hardware store first and if that doesn't produce anything then I'll have to order something online.
 
Beware the DIY NiMH pack is not as simple as it should be. For those cheaper ~5$/10ah individual NiMHs, other users have reported failure rates upon delivery of around ~ 1 out of 20 -- so extras are necessary. As is individual cell testing. I just noticed BS is now selling the West Mountain CBA:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3200
 
xyster said:
Beware the DIY NiMH pack is not as simple as it should be. For those cheaper ~5$/10ah individual NiMHs, other users have reported failure rates upon delivery of around ~ 1 out of 20 -- so extras are necessary. As is individual cell testing. I just noticed BS is now selling the West Mountain CBA:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3200
Click to expand...

That is one nice battery tester. $109 is "proper", but that places it out of my budget. I was planning to buy about 8 extra batteries on top of 120 to get 128 and the lower price tier. Do you think that's enough? Total price out the door is $608 for 128 plus shipping whatever that will come to...
 
Do you think that's enough? Total price out the door is $608 for 128 plus shipping whatever that will come to...
Click to expand...

Should be. Most of the problems were not dead cells, but cells on the low end of NiMH's often widely varying capacity. I recall DIY'ers noting a couple 10 ah batteries in every batch tested at ~7 ah's after cycling. How would you know which one's unless you test each one? If you don't test, it seems to me, because capacity is decided by the lowest common denominator, there's a high likelihood you'll end up with two ~7ah strings of 60 batteries. I chose the lithium 18650s in part because of their much tighter capacity variances, and lower DOA rate.
How do you plan to separate the two strings for charging?
 
hardware stores have loads of springs. should be easy to find some to slip over a ss bolt.
as far as tension, my wild guess is 10-30#, and ~3/8" end play.
i'm still having fun with sla, so i have no info on others. good luck!

next i plan to try 3, 18ah sla's @$30 each delivered. should last me 2-3 years, rides twice a week, at 33% DOD.
 
xyster said:
How do you plan to separate the two strings for charging?
Click to expand...

There would be more than two strings. With 120 batteries you have 4 sets of 3 tubes that have 10 cells per tube:

4 sets X 3 tubes per set X 10 cells per tube = 120 cells.

And since there is NO SOLDERING I can every once and a while give the tubes their "routine checkup" and pull all the cells out and test each one individually.

:arrow: Would it be easier to identify the "weak cell" before or after charging?

I would think before charging, but it's almost as though for the "checkup" I might need to run a separate single cell charger on each cell to see how much capacity each one really can hold. Then from that I would identify the "weak link".

Ideas?

I might begin with the "overall" tube voltage and if it's "fine" then I can skip it and only do the "checkup" on ones that are showing problems. I was figuring to use a charger for each tube, or maybe for every two tubes (24V)... not sure yet.
 
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