Can I solder directly to Headway 38120 cells?

[Little-Acorn]

I've seen Headway 38120 LiFePO4 cells (10Ah) that have screw terminals, and other Headway 38120s that appear to have no terminals at all. I know that some cells have flat tabs spot-welded on. But I can't spot-weld!

Does anyone know if it's possible to solder some flat tabs directly onto these no-terminal Headway 38120s? Screw terminals are too tall for my applications.

If I use a large-capacity soldering iron that can heat up the metal quickly, solder the tab, and get off quickly so I can cool the solder connection, do you know if this can still damage the cell internals? I've tried soldering to NiMH cells, and ruined my share of cells doing it. Don't want to ruin these (expensive!) Headway LiFePO4s!

Anyone know if it's possible to solder directly to these cells? (or, if these cells can come with solder tabs already installed?)

 

[julesa]

Doubtful. I wouldn't even try.

 

[Little-Acorn]

I've been told that soldering directly to a LiFePO4 cell isn't nearly as injurious to the cell, as soldering to a NiMH cell. But I'm not sure I'd want to trust such an unsupported word. I'd like to hear from people who have actually done it, good or bad.

 

[Zoot Katz]

According to EV Components they are available with tabs.
http://www.evcomponents.com/ProductDetails.asp?ProductCode=38120L

 

[frodus]

any warranty you get with the cells would be out the door.

heat can and will damage cells. You need a lot of heat to heat the end to get solder to stick, even with a hot soldering iron.

PM me, I may be able to help.

 

[julesa]

Try something like this?

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=2633&hilit=spot+welder

 

[Mark_A_W]

You can solder straight to them, I've/full-throttle's just done it.

You need a big beefy iron.

File the end of the cell lightly to clean it up, and solder with lead free silver solder.


Normal solder works too, but you've got to get the cell hotter to do it.


I would use a hot iron, as that actually means the cell stays cooler, I did some tests on a dead cell.

If your iron isn't hot enough, you end up having the tip on the cell for ages, heating the whole thing. With a hot iron the contact time is brief.

 

[liveforphysics]

File the end of the cell lightly to clean it up, and solder with lead free silver solder.


Normal solder works too, but you've got to get the cell hotter to do it.


I would use a hot iron, as that actually means the cell stays cooler, I did some tests on a dead cell.

If your iron isn't hot enough, you end up having the tip on the cell for ages, heating the whole thing. With a hot iron the contact time is brief.

Great advise about the iron of course, but I'm afraid you're mistaken about the choice in solder. Proper lead/tin solder melts around 183C, and has superior surface wetting properties than SnAg lead free blends melting around 218-230C, and higher surface tension to resist wetting.

 

[Mark_A_W]

Great advise about the iron of course, but I'm afraid you're mistaken about the choice in solder. Proper lead/tin solder melts around 183C, and has superior surface wetting properties than SnAg lead free blends melting around 218-230C, and higher surface tension to resist wetting.

Ah well, you can debate that with Full-throttle.

They both work.

 

[liveforphysics]

Ah well, you can debate that with Full-throttle.

They both work.

If it works, hey, it works. But I don't understand what is to debate, or who full-throttle is? Melting points for each different alloy blend of solder is widely available, and a consistent non-debatable characteristic of a given alloy. It would be like debating the temp ice melts, it's a pretty well researched and tested attribute.

Notice the leaded solder on the far left. Notice the lead-free stuff and silver stuff in the middle, and only the exotic bismuth solder on the far right is able to beat lead solder. Surface tension attributes are equally well documented, but I'm going to just leave the discussion as it sits.

 

[voicecoils]

I've seen Headway 38120 LiFePO4 cells (10Ah) that have screw terminals, and other Headway 38120s that appear to have no terminals at all. I know that some cells have flat tabs spot-welded on. But I can't spot-weld!

The 38120S cells are the screw type (hence the 's' designation)

The 38120L and 38120P have flat can ends designed to be tab welded to. The 'L' is a 10Ah cell and the 'P' is an 8Ah cell with higher discharge rate at the expense of 2Ah of capacity.

 

[voicecoils]

If it works, hey, it works. But I don't understand what is to debate, or who full-throttle is?

Mark_A_W is the ME
full_throttle is the EE (and E-S member)

The solder in question was 95.5% Tin, 4% Silver and 0.5% Copper

 

[liveforphysics]

If it works, hey, it works. But I don't understand what is to debate, or who full-throttle is?

Mark_A_W is the ME
full_throttle is the EE (and E-S member)

The solder in question was 95.5% Tin, 4% Silver and 0.5% Copper

95.5Sn, 4Ag, 0.5Cu melts at 217degC.

 

[voicecoils]

95.5Sn, 4Ag, 0.5Cu melts at 217degC.

Cool. Perhaps full_throttle will chime in on the solder choice.

It may simply boil down to: it was on hand & it worked

Perhaps their workplace is lead-free...I don't know though.

On a completely unrelated note, I just got back from my first ride ride on lico lipoly (a baby 15S1P 5Ah 15C pack). Max discharge current was 45A. It was fun! I kept riding. Then the voltage plummeted, the chargery buzzers (set to 3.3v/cell) started going spastic. I watched my Cycle Analyst show the voltage dip down to 39V for a second , I switched off the controller & the voltage rose to 45V. Still, for a second the cells averaged 2.6v/cell and I imagine some cells were lower, some higher.

20 min of fun & $200 of lipos and shipping costs are likely down the drain. I'll try to find a safe spot to charging them, but I don't think I can parallel them with the other 15S2P of the same packs now :? ah well... might have a little cry and start a thread about it :lol:

 

[ejonesss]

well it depends if it is the internal screw terminals you should be ok.

if they are the external screw terminals like the psi green cells then that is where you run into problems.

I've seen Headway 38120 LiFePO4 cells (10Ah) that have screw terminals, and other Headway 38120s that appear to have no terminals at all. I know that some cells have flat tabs spot-welded on. But I can't spot-weld!

Does anyone know if it's possible to solder some flat tabs directly onto these no-terminal Headway 38120s? Screw terminals are too tall for my applications.

If I use a large-capacity soldering iron that can heat up the metal quickly, solder the tab, and get off quickly so I can cool the solder connection, do you know if this can still damage the cell internals? I've tried soldering to NiMH cells, and ruined my share of cells doing it. Don't want to ruin these (expensive!) Headway LiFePO4s!

Anyone know if it's possible to solder directly to these cells? (or, if these cells can come with solder tabs already installed?)

 

[liveforphysics]

95.5Sn, 4Ag, 0.5Cu melts at 217degC.

Cool. Perhaps full_throttle will chime in on the solder choice.

It may simply boil down to: it was on hand & it worked

Perhaps their workplace is lead-free...I don't know though.

On a completely unrelated note, I just got back from my first ride ride on lico lipoly (a baby 15S1P 5Ah 15C pack). Max discharge current was 45A. It was fun! I kept riding. Then the voltage plummeted, the chargery buzzers (set to 3.3v/cell) started going spastic. I watched my Cycle Analyst show the voltage dip down to 39V for a second , I switched off the controller & the voltage rose to 45V. Still, for a second the cells averaged 2.6v/cell and I imagine some cells were lower, some higher.

20 min of fun & $200 of lipos and shipping costs are likely down the drain. I'll try to find a safe spot to charging them, but I don't think I can parallel them with the other 15S2P of the same packs now :? ah well... might have a little cry and start a thread about it :lol:

You've done no damage my friend!

It's not what the voltage gets dragged down to under load that matters a bit, it's entirely the SOC voltage. If your SOC voltage was still 45v, you were at a 4v SOC on the cells still. lol No harm done at all. The cell damage is only caused by an irreversible chemical change that happens of the level of ions shifts excessively inside the cell once the SOC drops below the safe point. Just pulling the voltage down hard from discharge doesn't hurt a thing, unless you let the excess resistive heating get them too hot and melt something, otherwise you're golden.

-Luke

 

[voicecoils]

You've done no damage my friend!

It's not what the voltage gets dragged down to under load that matters a bit, it's entirely the SOC voltage. If your SOC voltage was still 45v, you were at a 4v SOC on the cells still. lol No harm done at all. The cell damage is only caused by an irreversible chemical change that happens of the level of ions shifts excessively inside the cell once the SOC drops below the safe point. Just pulling the voltage down hard from discharge doesn't hurt a thing, unless you let the excess resistive heating get them too hot and melt something, otherwise you're golden.

-Luke

*slowly reaching for celebratory beer in fridge...*

Thanks for that great info.

According to my Cycle Analyst I discharged 241.6Wh.
My math for the pack energy is: 15 cells x 3.7v/cell x 5Ah/cell = 277.5Wh
The 15S1P pack started out at at just over 4v/cell however (60.5v) so the full pack energy may not have been available.

Now that the pack has been sitting for a few hours, it has risen to 47.1v, with the lowest cell at 2.98v and the highest at 3.44v.

I don't quite understand your comment on the pack being 4v SOC on the cells still. Do you mean that if the pack's resting voltage had gone down to 41v, then it would have actually be dangerously discharged 100%?

 

[liveforphysics]

I just fumble fingered the 4 key when i meant to hit he 3 key.

Charge those babies up, and enjoy.

 

[themotorman]

NO NO!! do not solder onto any cell... I know it sort of works but that's Ok for a Nicd that costs a few bucks but why ..OH why waste money destroying ( or risking to ) a Lipo.. Get the correct cells for the job and treat them like gold. The areas at the end are right next to plastic insulation so the chance is high that you will damage the cells. Make a spot welder and be careful you don;t overheat the cells with this as spot welders put out a lot of heat ( for a very short time ) . I even have had cells damaged by too many welds causing early failures. For hobby use the screw terminals, or the tabbed ones, where with care you can solder correctly are my choice.

 

[Mark_A_W]

NO NO!! do not solder onto any cell... I know it sort of works but that's Ok for a Nicd that costs a few bucks but why ..OH why waste money destroying ( or risking to ) a Lipo.. Get the correct cells for the job and treat them like gold. The areas at the end are right next to plastic insulation so the chance is high that you will damage the cells. Make a spot welder and be careful you don;t overheat the cells with this as spot welders put out a lot of heat ( for a very short time ) . I even have had cells damaged by too many welds causing early failures. For hobby use the screw terminals, or the tabbed ones, where with care you can solder correctly are my choice.

Bah, it works fine.

My soldered cell is by far the strongest in the pack (cell-log 8 ), it took no damage from soldering it.

 

[Jeremy Harris]

NO NO!! do not solder onto any cell... I know it sort of works but that's Ok for a Nicd that costs a few bucks but why ..OH why waste money destroying ( or risking to ) a Lipo.

LiPo packs are pretty much always soldered together, as are all the other pouch type LiFePO4 cells. There seems to be a massive body of evidence that supports the safety of soldering some cylindrical cells (A123, for example; take a look at the RC fora) with very little evidence that, done properly, it causes any harm to the cell if done properly.

I agree, spot welding is better (I made a spot welder just to build a pack of Headways, the old type without screws), but knowing what I know now I think I'd just set up to solder a pack together in future.

Jeremy

 

[The Mighty Volt]

any warranty you get with the cells would be out the door.

heat can and will damage cells. You need a lot of heat to heat the end to get solder to stick, even with a hot soldering iron.

PM me, I may be able to help.

Yes, you need a lot of heat, but it need not necessarily damage, or for that matter, even heat the cell. I have been experimenting at length with these things to see what solutions I can get. I have used all sorts of flux, all sorts of solder, all sorts of heat appliers- rods, guns, butane torches, irons etc, wire brushes, you name it.

1. The cells should be tabbed using a home-made welder or the existing nickel tabs that come on some batteries. Then tin the tabbed area with lead-free solder.

2. Take copper shim, tin one side of it using a basic butane iron and some lead-free solder.

3. Place the tinned shim, tinned side down, onto the battery.

4. Tin a 100w iron with the same solder used on the shim. Press into the shim over the terminal of the battery for 2-3 seconds. Hey presto- done.

5. The tinning of the iron is KEY. For some reason, the temperature, or the heat transfer characteristics, of a tinned tip are significantly different to that of a red-hot but non tinned tip. You can lean all day on the shim with a red-hot tip and you will never get the solder on the underside to melt into the solder of the tabbed battery. But once the tip is tinned, one seems to get results quite easily.

The trick with all of this is not temperature per se but heat transfer over a specific range of time. You want solder, on one surface, melting into solder on another surface, and then you want the heat transfer to abruptly end at that very point. Pay attention to small things like "drafts"- a stream of cold air can significantly mess things up for you.

Practice Practice Practice.

 

[frodus]

TMV,

Thats exactly what I'm saying. I wouldn't directly solder the cells. When you say to tab the cells, thats kind of what I was getting at. Its much easier to solder to a tabbed cell without heating up the cell itself.

 

[AndyH]

well it depends if it is the internal screw terminals you should be ok.

if they are the external screw terminals like the psi green cells then that is where you run into problems.

There is no problem with PSI cells, Eric, because there's absolutely no reason to solder to a cell with a threaded terminal.

 

[The Mighty Volt]

TMV,

Thats exactly what I'm saying. I wouldn't directly solder the cells. When you say to tab the cells, thats kind of what I was getting at. Its much easier to solder to a tabbed cell without heating up the cell itself.

Docbass himself says the same thing. He prefers to use existing A123 tabs, present on cells from Dewalt packs, and fold the tab back on itself a few times, like an accordion, and then he feels it is safe for soldering.

Using a liquid-acid flux also has advantages in that any excess heat is used to bubble away the flux before that heat can get around to damaging the cell. Of course this raises issues of it's own vis a vis corrosion, mess etc.