Homemade Battery Packs

[67spyder]

You are right, the 32ah capacity just barely eclipsed the fact that they are pink! I went with 12p config because the C rate is so low with the laptop chemistry and there are six cells in each laptop battery.

Some shots of the jig.

A string of cells ready to be soldered

The tabs folded over and tinned.

soldering a piece of 12Ga wire

One end done, going to remove the string, flip it over, put it back in the jig and solder the other end

The finished string of 12

Repeat 28 times

I charged each string individually to get a feel for capacity and to start with a reasonably balanced pack. All the strings took right around a 27Ah charge

I assembled them into a pair of 6s packs with a 2s pack to make 14s because that is what fit into the battery box.

I will post pics of the finished battery in the battery box tomorrow.

 

[67spyder]

Forgot to mention, BMS and charger ordered from Paul last week

 

[chilledoutuk]

Nice build but i wouldn't rely on the heat shrink alone on those laptop cells to separate your battery banks the shocks/vibration involved in ebiking could easily wear through those very thin heatshrink wraps potentially causing a short/fire.

 

[67spyder]

So maybe a strip of duct tape in between each parallel string of cells?

 

[DrkAngel]

So maybe a strip of duct tape in between each parallel string of cells?

1st
I like your method of soldering to the paired cells using the excess tab length folded back.
This should greatly simplify soldering and help protect the cells from excessive heat, also allows a bit of durability-flexibility.

16,000+ recycled battery eBike miles!
In 5+ years, including packs carried in fabric bags (high density cardboard as protective shell around batteries), I have never encountered any wear through ...
Duct tape ... couldn't hurt tho ...

I do recommend "stabilizing" cells, to prevent movement-"rubbing", but more to prevent cracked solder connections.
My later builds are taped with clear boxing tape (to allow visual inspection), then firmly retained in oem eZip battery packs.
Doe to my initial problem with cracked solder connections, I began using tinned copper braid and seem to have eliminated that problem.

 

[etriker]

Being able to solder to the tabs is a real big plus when making packs out of recycled laptop packs.

The tabs were welded on with spot welders that made nice spot welds.

Good spot welders cost a lot and I don't like the welds that cheap spot welders make.

I gap them a little by wrapping each cell with a few turns of plastic packing tape.

 

[67spyder]

I took a couple more shots.
In this first one you can see the whole pack. The top and bottoms and the sides of the pair in the middle have rubber pads on them that I get from the bottoms of the small 5 cell Makita battery packs.

After approx 10% DOD the cells are still pretty much in balance. I was going to run the battery through a few cycles, charging it part by part with my HK charger, just to make sure it will be OK but I am pretty confident so I ordered the BMS and charger last week

And the gratuitous ebike porn (with my Leaf in the background)

 

[Judoka]

Here's an update on my battery testing, would like some feedback to make sure I'm doing everything correctly. ...

Results - I was surprised to see a poor discharge time on a couple batteries that performed well on the bleed down test, thus making me believe this discharge test is essential in gathering a good lot of batteries to build my pack with.

So my question to those who have done this several times is, do my numbers appear normal and do my test procedures seem solid? Battery G1 has high resistance and sag, poor discharge time, but look at it's end volts... seems weird, might try retesting. Similar results on battery B1.


Method seems sound.
Likely, as indicated by initial "sag" and final "recovered" voltage, G1 has one cell bad. Separate, test and keep good one for flashlight etc?
B1 ... possibly 1 bad, more likely 2 "poor" cells, as indicated by moderate initial sag.

Also ... Regard "bleed down test" as only step 1 in a series of elimination trials.

I'm done testing all my batteries and have a Resistance and Capacity testing done. My thoughts are to take the battery with the best capacity and pair it with the worst (but in the acceptable range) and continue to do that for my 12p groups. For example; A = Best Capacity and L = Least Capacity I would pair them like this....

Group 1 ABCDEFGHIJKL
Group 2 Same as above but differences between capacity is getting slimmer as I continue to make groups of 12p.

Also, this image http://www.endless-sphere.com/forums/download/file.php?id=98637 has me wondering the best way to connect the cells together. It appears from this image I should attempt to join them as illustrated on the bottom right, but I'm unclear how the best for low power is connected... that part of the diagram is not clear to me. I bought some flat tinned copper braid and plan to use it for all connections.

 

[Judoka]

67spyder,

I like your jig and that's a nice solder job, the only thing that caught my attention was the way you are connecting the batteries... it appears you are connecting them on the end, from the diagram I referenced in the above post that is not the ideal way to do it... unless I'm missing something? See this thread a little over halfway down... http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=28285

Btw, what's the speed and range on the scooter?

 

[knighty]

quick check before I buy...

going to build a big laptop cell pack

but I'd like a parallel something with higher C rate to take some of the strain off them (cromotor - going to run high power)

can I parallel these in on a cell level ?

if I parallel on a cell level it lets me charge/balance the pack as a whole

might have to be a little bit cunning when I wire the pack up, to make sure the power from the nanotec cells comes via there main power connectors, and not via there balance connectors into my laptop pack and then out through there power connectors...

 

[etriker]

quick check before I buy...

going to build a big laptop cell pack

but I'd like a parallel something with higher C rate to take some of the strain off them (cromotor - going to run high power)

can I parallel these in on a cell level ?

if I parallel on a cell level it lets me charge/balance the pack as a whole

might have to be a little bit cunning when I wire the pack up, to make sure the power from the nanotec cells comes via there main power connectors, and not via there balance connectors into my laptop pack and then out through there power connectors...

I don't know that anyone on this forum has tried to do it.

A big reason to do it with A123 m1 cells is that they can handle being overcharged or overdischarged a little and they will still be ok and do a huge # of cycles.

You can charge and discharge A123m1 cells and 18650 laptop cells together. 8s m1 cells and 7s 18650 cells pack level not cell level.

Try it and let us know.

Smaller packs are easier to keep an eye on.

 

[knighty]

I was thinking if I'm keeping the cells inside the laptop cell voltages, then I should be ok ?

google said I'm ok between 3v and 4.2v for those hobby king cells

which is the same for the laptop cells ?

(I obviously won't charge that high or run them that low)

 

[Judoka]

After hours upon hours of reading, I finally completed my first battery pack yesterday. I want to thank all of the regular posters on this forum for all your help. Here is a quick rundown on my project.

- I disassembled approximately 30 battery packs, leaving batteries in pairs.

- Purchased a Genuine Imax B8 to charge do initial charging (also used some wall chargers), then did a bleed down test. Next time, I need to streamline the charging, doing two at a time took a few weeks.

- I choose cells that had .02 or less discharge after a week, then started capacity testing.

- I did a discharge test using my Imax set at 4 amps. I'm glad I did this part, I had several cells that passed the bleed down test, but poorly on the discharge test. Also worth mentioning, the resting voltage did not mean much when determining how well a cell performed. I had several cells that were 1.x that did very well, and surprisingly some that were 3.x that were bad. I only used batteries that could make it over 50 minutes during my discharge test.

- Assembled my batteries in 12p, then my wattage meter arrived so I was able to measure the amps I could put into the batteries. From 3.70 - 4.15 I was able to put in approximately 25 Ah... whoo hoo, much better than the approximate 6 Ah from the SLA's. I can't think drkangel enough for recommending the tinned copper braid, that stuff was EASY to work with. Additionally I purchased a good soldering station... I was laying down the solder pretty quick, so much so, I decided to solder to each individual battery even though I left them in pairs. I thought if one of my solder joints didn't hold up, I'm at least connected in two spots on a battery pair.

- I had to really hack up the ezip case to squeeze those batteries in there. I used a large paint stick, some corrugated signs, and a small amount of packing material to make sure the batteries stayed in place. I drilled holes in the case for external balancing leads, and a deans connector to charge via my Imax. Cat5 cables seems to work well for balancing leads.

Anyways, here's some pictures... the bike gained about 2 miles per hour on the flats. I'm 205 lbs, towing a 40 lbs "furry child" in a 40 lbs trailer. Bike performs well, I'm happy with the 18 mph I get from it.

 

[67spyder]

I like your jig and that's a nice solder job, the only thing that caught my attention was the way you are connecting the batteries... it appears you are connecting them on the end, from the diagram I referenced in the above post that is not the ideal way to do it... unless I'm missing something? See this thread a little over halfway down... http://www.endless-sphere.com/forums/vi ... 14&t=28285

Btw, what's the speed and range on the scooter?

You are correct, I connected the strings of cells on the ends which is less than ideal but this is a stock controller and does not pull huge amps. I made the decision to go with ease of building and put the connections at the pack end.

The speed is pretty much stock 35kph as I didn't change the voltage significantly, it is a little faster than with Pb batteries as there is no voltage sag. The range is way better than original, the bike is still running on the first charge although it does not get ridden every day. My Ah for this pack is around 32 where the Pb was under 10. The Pb was rated at 14Ah but the discharge rate is higher than the 14Ah discharge rate.

 

[999zip999]

Be careful how hot you get the cells with the solder iron as when soldering the pos. end the neg. case is very close to the copper wire and wire braid. This is a place when you can have a short very easily. Try not to over solder as small balls of solder can jump off and get lodge under the tabs ect. Plus pushing down to hard with a hot iron on the tab betwwen the cells can bow the tab downwards and touch the neg. rim of the case. I like a gasket on the pos, end. So be careful.

 

[Judoka]

I just got a second batch of batteries and I'm hoping to improve on my next pack build. This time I should have enough batteries from the same manufacturer (Panasonics 2400 mah). My first pack is doing great (see a few posts up), but it took forever to test all the batteries. I think I've learned a few things during that build that can help me cut down on some time... hoping to get some feedback.

During my first pack build, I charged all batteries to approximately 4.20, then monitored for a week or more for bleed down results. Batteries not dropping more than .03 were selected for the next phase of testing, a 4 Ah (per pair) discharge test on my iMax. I set the iMax to discharge to 3.0, then kept track of the time. The iMax would take 30 seconds to build up to a 4 amp discharge so I would check voltage at exactly 35 seconds to get my resistance. Of all the batteries I tested, I did not have any that with a low resistance that performed badly... so this has me wondering if it's necessary to do a complete discharge test, possibly a resistance only test? This would save me many hours of waiting approximately 1 hour for each battery pair.

See attached chart, batteries highlighted in blue were used on the first pack... thoughts?

 

[7tronics]

On the VERY simple end, I have two Clean Republic Bamboo LiFEPOs in an eZip RMB pack. This was a 30 minute job to install in an older eZip Mountain Trailz (2009 model) RMB gray battery container. It is a wonderful step up from an aging SLA pack. Not sure it is even worth posting a photo this upgrade was so simple, but may do so...

A few things I have done to improve some RMB battery pack issues:

• Put electrical tape around the rack rails; wrap enough to stop the rattling but allow the pack to be pulled in and out.
• Add more padding in the RMB pack for the batteries. I've used rubber shelf liner material and blocks of wood wrapped in shelf liner as the 12v10ah LiFEPO is smaller than 12v10ah SLA.
• Clean out pits made where plunger makes contact on bottom battery box contact and use contact enhancer such as DeoxIT often.

Now I have a Currie 24v charger already from my daughter's iZip via Rapido, so I didn't even think about getting a separate charger. Clean Republic site has a cheap one ($20 extra for 12v Li charger when you purchase battery from them). I'm thinking of getting one of the 12v chargers with next order so that I have a way to occasionally balance the charge between the two "12v SLA replacement" Bamboo encased LiFEPO packaged batteries. So for $200 you have a 24v 10ah LiFEPO drop-in replacement. These Bamboo LiFEPOs have some low voltage and overheat protection, but no internal BMS is claimed.

Question though:
? Does anyone know where to get an extra eZip RMB battery case and would prefer it with the old SLA batteries removed ?

 

[DrkAngel]

On the VERY simple end, I have two Clean Republic Bamboo LiFEPOs in an eZip RMB pack. This was a 30 minute job to install in an older eZip Mountain Trailz (2009 model) RMB gray battery container. It is a wonderful step up from an aging SLA pack. Not sure it is even worth posting a photo this upgrade was so simple, but may do so...

Highly recommend a 2nd pack, run in parallel.
Otherwise you will be exceeding recommended, will also prolong life!
"Specifications

-Discharge: 20A max continuous, 60 max 2-second pulse. 8v max discharge, 11v max recommended discharge. For longest lifetime recommended discharge rate 1-5Amps

-Charge: 10A max, 14v max recommended, 15v max. Compatible with most SLA chargers, use recommended Clean Republic charger for max performance, sold separately.

-Operating temps: Much better than SLA or other lithium’s, -20'F min, +120'F max recommended environmental operating temps.

-Capacity: 10Ah rated up to 80% capacity for 2,000 cycles in recommended conditions.

-Safe, fire resistant internal construction, stable, reliable LiFePO4 chemistry with proven production and market history. "Multiple fail-safe architecture" combines three layers of overlapping safety features including inherently stable chemistry, fireproof internal materials, and multiple heat-activated electrical shutoffs.

-151x65x95mm form factor"

 

[7tronics]

Thanks for the advice. The two Currie TrailZ we have are equipped with the 250w motors so I thought running these as a single series combination would be adequate, but should we upgrade to a 450w motor we can see that running these LiFePO in series + parallel would be essential to battery life.

again a question as posed above:
? Does anyone know where to get empty Currie RMB battery cases?

 

[etriker]

Thanks for the advice. The two Currie TrailZ we have are equipped with the 250w motors so I thought running these as a single series combination would be adequate, but should we upgrade to a 450w motor we can see that running these LiFePO in series + parallel would be essential to battery life.

again a question as posed above:
? Does anyone know where to get empty Currie RMB battery cases?

Are you in the USA ?

 

[7tronics]

Yes in Central NC

 

[etriker]

Yes in Central NC

I have one empty black one.

$20 + shipping. Shipping from Fl to NC should not be much,

pm if you want it.

Thanks, Steve

 

[knighty]

I just got a second batch of batteries and I'm hoping to improve on my next pack build. This time I should have enough batteries from the same manufacturer (Panasonics 2400 mah). My first pack is doing great (see a few posts up), but it took forever to test all the batteries. I think I've learned a few things during that build that can help me cut down on some time... hoping to get some feedback.

During my first pack build, I charged all batteries to approximately 4.20, then monitored for a week or more for bleed down results. Batteries not dropping more than .03 were selected for the next phase of testing, a 4 Ah (per pair) discharge test on my iMax. I set the iMax to discharge to 3.0, then kept track of the time. The iMax would take 30 seconds to build up to a 4 amp discharge so I would check voltage at exactly 35 seconds to get my resistance. Of all the batteries I tested, I did not have any that with a low resistance that performed badly... so this has me wondering if it's necessary to do a complete discharge test, possibly a resistance only test? This would save me many hours of waiting approximately 1 hour for each battery pair.

See attached chart, batteries highlighted in blue were used on the first pack... thoughts?

I got a battery resistance tester on ebay.... was only £20 iirc... haven't used it yet... no idea how good/accurate it is/will be... but it'll be fine as long as it helps me sort the good cells from the bad cells

I went a little crazy buying cells, and have about 6,000 used laptop cells here to charge/test :-o

got a psu and loads of cell holders, so I can charge 100 at a time

 

[arkmundi]

I got a battery resistance tester on ebay.... was only £20 iirc... haven't used it yet... no idea how good/accurate it is/will be... but it'll be fine as long as it helps me sort the good cells from the bad cells

Pardon me for a real novice question, but what is a "battery resistance tester?"

 

[knighty]

it tests the internal resistance of the cells... which should give a pretty good indication of how well they'll preform

tbh... I don't really know what much about it.... the lower the ir the better

high ir = means the cells are probably damaged inside and/or the chemicals inside are breaking down / not as efficient

if I can charge up all the cells, then check the ir of them, it should help me eliminate most of the bad ones before I have to bother discharge testing them