Zippy Flightmax / Turnigy lipo testing

[GGoodrum]

I agree, you don't want to get into shipping these things. Too much of a hassle now. The best option would be if you could maybe talk HC into setting up a "special" area on their site, that required signing into, so that the packs could be offered separately, at a special price. That way people would pay themselves and HC would do the shipping.

Regarding pack configurations, until the QC is improved, having a 10Ah pack, even using paralleled 5Ah cells, might reduce the number of interconnections, but if a "cell" goes bad it means you've lost twice as much, in terms of replacement costs. Right now, most people parallel packs at the 5Ah pack level, and charge/balance the packs separately. This has one advantage if a cell goes bad, because it won't kill a cell in the second 5Ah pack, unless the balance plugs are also paralleled. It seems that if a pack is going to have a problem, it shows up right away. Once a pack is used for a bit, they seem to stay balanced and work well. If you buy two 5Ah packs and plan to use them in a 10Ah configuration and one arrives with one, or more, weak cells, only that one 5Ah is affected. If you get a prepackaged 10Ah pack, made from paralleled 5Ah cells, and one 5Ah cell goes bad, it will take down the other 5Ah cell it is paralleled with, so it would be like saying both 5Ah packs went bad, not just one of them. I'm probably not making this very clear, but I'm not sure how else to explain it. :?

I guess there'd also be a problem with doing packs with double the number of cells in series, like 10s or 12s, if there's still going to be an infant mortality issue with these. If you have a single cell go bad in a 12s/5Ah pack, the whole pack is affected. If you have a single 5Ah cell in a 12s/10Ah pack go bad, the whole pack is now unusable. If the 12s/10Ah pack is made up using four 6s/5Ah packs, you only need to replace 1/4th of the "pack".

The QC problem is really more of a factory issue, not something HC can probably do anything about, except to maybe do some pack cycling ahead of shipping. The problem is if any moisture gets into the cell during manufacture. This is typically what causes cells to fail early. The problem is that it usually takes awhile before the problem manifests itself, so the pack might test fine at HC's warehouse, prior to shipping, but by the time it gets over here, the cell(s) start having problems. Cycling a pack a few times should help weed out these "weak sisters", so I would do this initially, before the packs are used.

To me, these prices are so good, even at the standard "list" price (I just bought six Turnigy 6s-5000 20C packs for $60 each...), that it is tough to complain too much about the occasional bad pack. I'd complain more, however, If I had a single 12s/15Ah pack that became unusable shortly after arrival.

What I'm going to do is cycle these packs individually, about 5-6 times, to make sure they are all good, and then I will connect them in parallel, at the pack and balance plug level, and then in series, to make a single 12s/15Ah pack. The parallel and series connections will be part of a single 12-channel LVC board with board-mounted connections for the main pack leads, and the six JST-XH balance plugs. The output of this board will have one set of main power leads, and one 14-pin VAL-U-LOK PE Series connector that will plug into my 12-channel charge balancer. I'm thinking I will arrange the six packs flat, in a 3 x 2 configuration with the leads all facing out. I'll put the LVC board on top, and then shrinkwrap the whole thing together. That will make a very compact pack that is roughy 2-1/2" high x 6" wide and about 12" long, and only weigh about 10-11 pounds. That is tiny for a 45V/15Ah pack.

If we can ever get past the 50V/12s controller issue, an HC pack configuration I'd like to see for HC packs is a 7s. The reason is that if you use 4.125V as the CC/CV charge limit, as Luke recommends, 7s matches up perfectly with 8s LiFePO4 and 24V SLA packs for charging. So a 14s LiPo configuration would be a drop-in replacement for a "typical" 48V SLA or 16s LiFePO4 setup, and could use the same charger. Three 7s LiPo packs in series, again charged to 4.125V, would be a drop-in for a 72V SLA/LiFePO4 setup.

-- Gary

 

[mwkeefer]

Gary,

Wow... good insight, especially on the potential issues with larger packs.

I believe we are all hoping that QC will be better if buying larger packs through Luke since he is such a good customer to them already.

From what Luke and others have posted HK essentially owns or controls the production facility although I have been told by others (of experience) that they merely are acting as a reseller and they are not even the ones who have the packs made up. In this instance I doubt if anyone is being dishonest, more likely that there is no clear cut answer from HK (why would they) in regards to this chain of manu/dist.

I also love your foresight into the 7S configuration... it would fit right into existing SLA and LiFePo4 style if only we limit the charge v cutout as you indicated (and as Luke proposes). Currently I charge my 2x12S5AH Turnigy Packs (made of 4x3S packs series then paralleled for discharge) using a 1010B+ which works well enough. A full (per pack) balanced charge takes a bit less than 2 hours (1 hr per 2x 3S cells in series @ 5A). My charging cutout is set at 4.18v per cell and I use trickle charge balance method so I end up with 4.18v per cell and rarely if ever do I see cells overcharge and drain balance (reviewing logs). This is a bit higher than Luke's recommended 4.124v per cell but I am hoping that it will extend the life cycle of the packs a bit. My LVC is pack based currently and configured for 38.5v. So long as I am balanced, I have never seen a single 3S pack go below 3.16 at full discharge cutout. Again that is (I assume) becuase my cells are all balance charged.

All in all, if the QC (just checking for bad packs by voltage and IR) were stepped up prior to shipping from HK... it would eliminate the problems we all seem to have with dead packs.

Of the 30 cells I received, 28 are now salvaged and working. I use my few spare cells (4) in parallel as a 12v 20AH supply for accessories and such although I may make them into 2x2S packs and series them in with my existing 12S 5AH packs to bring them up to 14s.

I guess the ones which puffed upon initial charge must have had moisture or contamination inside the cells (if they did even a single cycle to full charge then back to storage voltage for shipping this would have been caught by HK also, but since these two packs had bad solder tabs they would have failed the simle QC check above so they wouldn't have made it to shipping anyway).

Based on my own experience and that of everyone else here on ES who has posted... if a pack works when it arrives, it will be okay.

-Mike

 

[Dave-s]

My 2 cents.
Since you can't agree on a preferable battery configuration, wouldn't it be best to ask HK to sell loose 5Ah cells (preferably with copper tabs for easy soldering) and the small circuit board they use for connecting cells in series/parallel?
Then each user can assemble his own pack. This way you also get the benefit of being able to replace a single cell if it goes south (I hope I used the correct expression).
We should also ask HK to carry higher power chargers to charge the bigger packs.
Maybe we can also convince them to carry some more E-bike hardware like controllers/throttles/high current connectors etc.

 

[mwkeefer]

Dave-s,

Not that your idea is bad, however I see several issues:

1.) Without assembly it would be next to impossible for HK to automate QA testing (IE: Charge / Discharge / Storage V Charge) further increasing the risk of bad cells

2.) Without purchasing as a pack, the price would likely be higher.

3.) The aluminum tabs require special solder and skills, not everyone possesses.

4.) the HK circuit boards are junk. To build a true high capacity discharge pack you would want to get the cells with the tabs unbent and perform spot welds to either a nickle busbar or somthing stronger then the tabs will still protect against dead short (like a fuseable link) while the electrical quality would be 100% better with much less impedance - resistance

-

In regards to larger or larger cell count chargers...

You are 100% correct, it would be nice to get 12S 10A chargers and supporting power brick style 13.8 -> 15v @ say 30-40 AMP power supplies. The issue is with quality, believe you me the first 1212B+ charger available I will buy and will be very happy with it.

In regards to deciding on AH capacity and voltage range:

We have reached a consensus:

1.) 10S 5AH Packs
2.) 12S 5AH Packs
3.) 8s 5AH Packs

All the above could also be offered by HK as 2P (2 cells in parallel) x 8,10 or 12S
Finally they could also be offered in 10AH capacities although keeping them at 5AH 1P8-12S will allow for nearly any configuration required to match any existing power chemistry and cell count.

So really I think we have a consensus of what is needed for the vast majority of eBikers (80-90%) right out of the gate with the above configurations. Those can be combined to serve the elite.

The real issue is as it always has been Quality Control.

Great ideas and good insight!

-Mike

 

[johnrobholmes]

I do like 6s packs for compatibility with the vast amount of charging systems available today.

 

[mwkeefer]

6S 10AH would be beautiful
Personally I like the 6S 5AH and then rewire myself but I would buy the 10AH if available in stacks.
-Mike

 

[Grinhill]

1.) 10S 5AH Packs
2.) 12S 5AH Packs
3.) 8s 5AH Packs

These option may be more palatable to Hobbycity as they would also be useful to the RC crowd.

 

[ktm_paul]

i just noticed a new listing - 'bulk buy'!

Live for physics - can you ask them to do something similar for 5ah, 5S 20C cells?

http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=8930&Product_Name=Turnigy_BULK_BUY_2200mAh_3S_20C_($14.99ea_/_36pc_box)

 

[bearing]

You only save half a dollar a piece though.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=8932&Product_Name=Turnigy_2200mAh_3S_20C_Lipo_Pack

 

[bearing]

I have a question which is a bit off topic, but may be of general interest. I'm thinking about buying 24 6s 5Ah Turnigy packs for an electric motorcycle build. The weight of 24 packs is too high for air shipping, it has to be split into 10 kg groups. 11 packs is 10 kg, so the pack would have to be split into three groups. Shipping will be about 20% of the battery value. Since custom fees (and I think also taxes) in my country are based on the total value including shipping, in the end shipping cost will add an an even bigger amount to the total. So, shipping is a cost I would like to reduce.

Have anyone of you had Hobbycity ship heavier stuff than their air mail limit, or got a shipping in a cheaper way?

I might be able to help you save some cash with a large LiPo purchase. I can often get special prices from HC, and even special shipping on large orders. I don't know what country you are in, but I could always send it on to you as a gift, with a declared value of $40 or something. However, it could be that the cost of shipping the package twice could out-weigh the cost savings.

I can assure you that HC will use a customs declaration form that will make you smile when it comes to pay dutys. I've had >$2,000usd single orders, and the customs form said "$38usd of hobby toy parts".

Thank you, thats a kind offer. I will remember it when it's time to buy the packs. I'm in Sweden though, so it may be as you suspect; extra shipping outweighing the savings.

Good to hear they put a lower value in the customs form, it may even slip through customs with such a low value.

 

[mwkeefer]

In regards to the BULK BUY!

Please notice these are 3S 5AH packs - The very same packs I received 10 of over two orders, about a week apart. My end result was 5 packs DOA because of bad solder joints... when opened and repaired, 1 cell of 1 tab had broken weld tab at crease and couldn't be repaired to provide sufficient current to meet pack requirements and 2 of the other packs puffed up within 1 minute of charging on a 1010B+ as single 3S packs using 1/5th C (1A) charge rate. Only 1 of the two puffers actually blew or outgassed (no fire or heat, just nasty dangerous fumes.

In the end, I would up with 28 working cells of 30 purchased after having a friend aluminum weld some nickle tab material to the cell with a broken tab. So I paid $29.99 ea for 10 3S packs or $9.99 per cell but since only 28 were useable the per cell price jumped up ever so slightly to: $10.71 per cell.

As I have stated already this was a good buy for me and still a reasonable cost per cell for the living cells which perform quite well (far above ratings) however remember I had to fix 5 of these, had 2 puffers and in the end redid the entire packs into new packs (incorporating the new cells).

You will need to have:
Good soldering skills
Aluminum Solder (or thin guage aluminum brazing / welding rods)
Aluminum Flux (to allow the solder to flow properly)
Stable Hands
Time

I only post this as a warning because I assume this BUY BULK deal is likely the same batch of batteries that I had such an issue with (I wasn't the only one who had issues with these 3S packs)

Good News:
Seems HK knows these were bad packs and is dumping them so they do care to sell working product not just rip the "little" customer off.
The new 3C 5AH packs should be much closer to 0 DOA or 100% viable on receipt from now on. This caused them lots of headaches and they don't have time fro those.

Bad News:
When you factor my averages the BULK price is actually not any better than the std retail price so I would rather order these 3S the normal way but in truth I will not be ordering 3C packs from HK until I see their stock flip over. People buying the 5S and 6S packs seem to have had better luck with them than those of us who went with 3S. Bad for HK as 3S is a very common airplane and heli power source.

-Mike

 

[mwkeefer]

Hello All,

For anyone interested, I had a long talk with my friend the "battery guy" from mtobattery.com in regards to the actual current laws around lithium (yes I did just get certified, by a CBT?)... here is the real deal on the laws:

It is legal for anyone to mail up to 25 grams of lithium based battery via the USPS, this would cover most cell phones, PDAs, digital cameras, etc.

The formula the FED / USPS / FAA use to calculate the lithium content of your package is:
AmpHourCapacity x .3 = Grams of Lithium in battery

Before you jump up and down and point out how inaccurate this is for various chemistries as some have a higher concentration and some a lower, I know and YOUR RIGHT, IT'S NOT ACCURATE ACROSS various lithium types but I didn't come up with this formula... one guess, that's right YOUR GOVERNMENT.

So if we look at a single cell 3.7v nominal 5AH Turnigy Lipo under the governments rules we have a total of:
1500 grams (5000mah x .3 = 1500)

As you can tell we are 1475 grams over the limit with a single cell as 12S1P of these would be 17,975 grams of lithium.

For us in the USA (public school was useless eh?) to figure out how many lbs any specific grams weight is (low precision but close enough for government work and amazing for US educated people) Weight in Grams x .0022 = Pounds.

17,975 x .0022 = 39.545 lbs of lithium content.

Here's my question for the government, if an entire 3S pack of battery only weighs a total of: 412 grams / .906 lbs how the hell can it have 39.545 lbs of lithium content. I spoke with the postal Hazmat rep about this and he claims it's right.

I say BS, they are calling for AH capacity not MAH so we need to redo the calculation using AH instead of MAH (though they will not verify this is right and are sticking by their story.)

Our new method gives us 1.5g of lithium per cell. hmmm, if we follow the letter of the law (they will ask if package is lithium) then we have a 25g limit so the most cells we could ship of these Turnigy Lipo by USPS legally would be: (25 / 1.5) = 16.6 cells or 16S.

If what I have uncovered today is correct, these idiots at the post office are instructed to read the rating on the batteries if they inspect (they will if they don't know you) they are supposed to take the capacity written on the pack. The thing they don'
t get is the law refers to Capacity In Amp Hours not MAH. We could solve this problem (and it would be fully legal) to request the 5000mah rating be replaced with the words 5AH. Then they would do the math correct and we could legally use the USPS to ship up to 1P16S or 2P8S.

Remember the less wire / connectors the better as they are also calculated by the postal person as lithium content weight (they don't have a clue how to determine how much your solder, pcbs, 10G wire, etc weigh so they can't do it. They must use the package weight to perform their calculation. In this case your best bet is cut off the discharge leads untilabout 1/2 - 1" remains... on 15-16 cells this will make a huge difference.

Also because fo the way the laws are worded it would be best to leave teh balance connecters in palce so they can't claim you modified the battery packs (which are supposedly already UN certified according to HK).

All that stated, I am not a lawyer but I'm sure someone here is (they are everywhere aren't they) and could confirm my analysis of the federal and postal statute.

Hope it helps,
Mike

 

[Rassy]

Mike, you have confused me. You said the formula was AH X .3, but you did your calculations using MAH. Since this makes a factor of 1000 difference your results may be off by a factor of 1000.

Edit: Sorry, I didn't read very carefully, and see you have already addressed this issue.

 

[mwkeefer]

Sorry,

I forgot to post a link to a very valuable file with all the information about the new laws, weights, etc... (it confirms my mah vs ah observation, the people at the post office where i live just dont get it.

http://www.ultralifebatteries.com/documents/whitepapers/Ultralife_Batteries_Lithium_Battery_Transportation_Regulations.pdf

You will want to read down a bit I noticed several other important things:

1.) Starting on October 1, 2009 all cells and batteries (apparent distinction between cells and batteries seperating them properly in legal terms) must pass UN T1-T8 tests. Until that date we are grandfathered and exempted from regulation based upon lithium metal or equiv. - This means that before October 1, 2009 (a few months still) we are exempted from these regulations... hurry up!!!

2.) Packages which contain more than 12 batteries (note this would be the battery not cell counts since they draw the distinction above) or 24 cells - (for us this means larger than 2P12S) have all sorts of special labeling requirements.
That confirms a 1P16S (actually a 1P24S would be okay without labeling or a 3P8S) is okay.


3.) Cells and batteries must be shipped Hazmat Class 9 (Unless transported by rail or automobile - Does this technically mean just riding our eBikes is a federal crime, after the federal law makes ebikes legal? JK - Idiotic Government Legislatures)

I don't want to recap the entire document, read it if you want to.... talk to your post master or call the post office and ask to speak with someone concerning hazmat... see how flexible your local USPS is.

One last note: Whenever possible keep the packs you have as "packs" meaning leave the shrink wrap and balance connectors in place, build a harness to parallel the balance connecters if you need to. This means your "packs" are "unmodified" so if they were UN tested (should have been by HKs manufacturer) then you can just assume they are UN tested and send out 8 of them to a US destination with the proper Hazmat 9 label. The package would meet the requirements as posted of not exceeding a 12 cell battery, not having more than 24 cells total and each sub pack is UN tested by hobbyking (or so we will assume) so that should be cool too.

Yea it will be a pain in the ass for larger packs but I would rather break them down into useable / chargable subsections and keep them small enough for shipping within the US via USPS (I will check pricing tommorow).

-Mike

 

[Hyena]

What I'm going to do is cycle these packs individually, about 5-6 times, to make sure they are all good, and then I will connect them in parallel, at the pack and balance plug level, and then in series, to make a single 12s/15Ah pack

Thats exactly what I'm doing. As you said if they don't fail initially they'll probably be ok, and its worth a bit of testing and running in considering the packs will be around relatively long term. I have no problems with the individual 5ah packs, I'm happy to solder and tape them all together and then if one does go bad down the track atleast I can replace it. As you say if you get a failure in a pre-made 10-12S 10ah pack you'd be a bit upset.

I just had my second shipment arrive from HC, only 3 this time but all 3 well balanced. I noticed these ones are actually labelled as 20-30C, unlike the first lot which said 15-20C.

Also, those bulk buy ones are only 2200mah, a bit fiddley for our application

EDIT: For reference, here a shot of the turnigy boards / solder connections for those thinking about unsoldering or reconfiguring packs

 

[GGoodrum]

I just had my second shipment arrive from HC, only 3 this time but all 3 well balanced. I noticed these ones are actually labelled as 20-30C, unlike the first lot which said 15-20C.

My 1st shipment of 6 packs is "out for delivery", so I should be receiving them today some time. Not bad, as I just placed the order on Sunday afternoonl. It takes me longer to get stuff from the east coast. Anyway, I will do my cycle tests as soon as the get here, and hopefully get the 12s/15Ah pack built by later today. My 12s LVC board, with active cutoff, is done.

-- Gary

 

[ZapPat]

I just received 12 of my 16 turnigy 6s packs, and they all initially seem in great condition. All cells are around 3.85V, with a maximum voltage difference of about 30mV, although one pack has it's two first cells about 100mV lower, so I'll mark these and keep an eye on them. Has anyone noticed any problems with cells that arrive a bit lower than the others?

I'll be getting the other 4 packs in a week, and so I'll cycle them all to test them and report back.

BTW, has anyone noticed their iCharger 208B charger reading a low voltage on the last cell in a 6 cell setup? On mine this cell (#6) always reads about 50mV low, which annoys me for some reason... maybe maybe because this is otherwise a great charger?

 

[bearing]

ZapPat, is the weight limit 10 kg for you Americans as well?
12 packs is slightly over the weight limit. Did they still send them as one shipment?

 

[mwkeefer]

ZapPat,

I have not noticed any issues (other than the puffers and received packs with bad solder joints.) with any of my 12S turnigy 3S 5000mah packs in the 22 cycles I have on them (actually one 5AH segment 12S of my 2P pack has 4 more cycles than the other).

The balance always remains within tight tolerances (+- 10mv) throughout discharge.

With regards to your iCharger 208B - I havent had any issues with my 1010B+ but I have seen docs out there on how to calibrate your charger. You may have received a unit with poor factory calibration and you might need to perform the calibration manually with a good DVM and known voltage source. If your readings are always off by a consistent mv on one specific balancer channel - sounds like recalibration is required.

Normally I would say ignore it (any other chemistry) but with these, it's better to get as close to balanced as possible and since your reading is 50mv off... that will keep charging and trying to trickle charge balance that final cell. Sadly it will never balance according to the "firmware" programming in the iCharger (set to balance to +- 30mv I believe).

Did you perform the firmware update when you received your 208?? Which firmware are you running with the charger?

Hope they work well for ya!

Regards,
Mike

 

[ZapPat]

ZapPat, is the weight limit 10 kg for you Americans as well?
12 packs is slightly over the weight limit. Did they still send them as one shipment?

I never use regular air mail, only EMS. I've decided that the best shipping choice for me (I'm in eastern canada BTW) is using 4kg EMS packages. I never get charged duty nor taxes with EMS, and this nearly makes up for the difference in price with the air mail option. And it takes less than 1 week to get here...

4kg packages allowed for 4pcs 6S 5000mA packs, and I filled up the rest of the weight of each box with sticky foam pads, 6S balance wire extensions, silicone wire, velcro and the likes. Their 4mm bullet connectors are a much better value than andersons IMO so I loaded up on these too, so it was easy to fill up the 500 or so grams in each of the four packs.

 

[Hyena]

I got a heap of the 4mm bullet connectors as well but I found they're very hard to connect - not so much the contacts themselves but the plastic cases seem to be a bit roughly made and they don't go together well. For one or 2 its ok, but for my config with 8 terminals it was much easier to go with andersons (albeit I'm limited to ~45a now, but my controller can't handle more than that anyway)

I used the 3.5mm EC3 plugs previously. They connected well and but after 6 months of pulling 30 amps several of them melted, which is a real pain when both sides of the plastic cases fuse together!

 

[liveforphysics]

I just received 12 of my 16 turnigy 6s packs, and they all initially seem in great condition. All cells are around 3.85V, with a maximum voltage difference of about 30mV, although one pack has it's two first cells about 100mV lower, so I'll mark these and keep an eye on them. Has anyone noticed any problems with cells that arrive a bit lower than the others?

I'll be getting the other 4 packs in a week, and so I'll cycle them all to test them and report back.

BTW, has anyone noticed their iCharger 208B charger reading a low voltage on the last cell in a 6 cell setup? On mine this cell (#6) always reads about 50mV low, which annoys me for some reason... maybe maybe because this is otherwise a great charger?

Werid, mine reads right on with my Fluke 92. If I remember correctly, there are 8 pots you will find inside there, and you can make adjustments to dial in the voltages as you please.

As far as cells reading low, I've not had any problems. Ideally, they should all ship around nominal voltage, as it's LiCo's optimal storage SOC. As long as they come in above ~3v and below ~4.2v, balance them, cycle them, and everything should be fine.

 

[ZapPat]

I just received 12 of my 16 turnigy 6s packs, and they all initially seem in great condition. All cells are around 3.85V, with a maximum voltage difference of about 30mV, although one pack has it's two first cells about 100mV lower, so I'll mark these and keep an eye on them. Has anyone noticed any problems with cells that arrive a bit lower than the others?

Werid, mine reads right on with my Fluke 92. If I remember correctly, there are 8 pots you will find inside there, and you can make adjustments to dial in the voltages as you please.

Ah! That's great news, thanks for the tip! I had only opened up the little 50W turnigy charger I have (not the larger chargery one), and had not noticed any pots so I assumed that the icharger didn't have them either. This should solve cell #6's reading problem, so the only small grumble I have left about this charger is the cell internal resistance measurement function. It reports values fairly close on par for the first cell or two, but some cells read almost double their real Ri. I guess this is more of a gadget function, unless something is thowing it off for some reason?

As far as cells reading low, I've not had any problems. Ideally, they should all ship around nominal voltage, as it's LiCo's optimal storage SOC. As long as they come in above ~3v and below ~4.2v, balance them, cycle them, and everything should be fine.

OK, I hope these two slightly low cells do end up as good as the others, maybe they had just been batch charged a bit lower than the rest at the factory? I guess I might be a bit crazy, but anything visibly deviating from the "norm" makes me a bit suspicious. From over 15 flightmax packs I bought in the past few months, not one had an "off-norm" reading.

 

[liveforphysics]

Many of the 5Ah packs seem to give 5.5Ah, or even more. It could be that you happened to get a couple cells with a little extra capacity. If the first charge for all the cells is constant current, as I imagine it is, the cells with greater capacity would end up with a lower voltage if all the cells in a batch get constant current charged for the same amount of time.

Just a guess

 

[GGoodrum]

I got my packs yesterday, and all had 3.865-3.870V. I've been cycling them since about noon yesterday. All appear to be rock-solid. I too got a bunch of 4mm bullet connectors, and spent quite awhile making a 2s3p series-parallel harness, using 10-gauge wire. Man what a pain that was! I ran into the same problem with the little red holders that match up with the packs. It turns out the only way they go on is if you slide them from the back. I figured this out, of course, after I had soldered all the bullets on. I also managed to put the holders on wrong, on about half of them, before I figured it out. It took me about 4 hours to get this silly thin done. I'm not going to go through this again, so I will definitely do a series-parallel board for hooking these up, and use board-mounted bullets.

I'm now ready to put the pack together. I'll post some pics when I'm done.

-- Gary