I just bought a battery pack welder

[LuxLuthor]

OK, I'm in a groove with this baby. Snap Snap, Shrink Shrink, Sweet Sweet. Doing some packs for people now, and throwing in these magnet (1/4" cube K&J N-50 stronger magnets) leads that I am making.....have to get your technique down to avoid demagnetizing from the soldering.

Next up.....Li-Ion setups with tap leads.

 

[dulridge]

throwing in these magnet (1/4" cube K&J N-50 stronger magnets) leads that I am making.....have to get your technique down to avoid demagnetizing from the soldering.

Couldn't you weld the leads to the magnets? Just a thought. Low heat etc.

 

[Silviron]

So how would I go to weld using capacitors?
I'm thinking of something like this:

Possibly with a multi-capacitor circuit to allow for rapid welding without having to wait for recharge times and/or to allow for stronger welds by discharging more than one cap into the joint.

Put the probes on the tabs, press, push button (with foot?), zap, tab welded.

Now, this all looks theoretically sound, but I'm guessing if it was this easy there would be no need for expensive $1000+ welders and everybody would be welding with homemade cap rigs.
So where's the catch?

I built one about 17 years ago, used a big bank (about 3-4 farad or so, at 25 or 40 V (if I remember correctly)), of surplus power supply grade electrolytic caps in parallel.

A mechanical momentary switch, even a massive one won't handle that kind of current without welding itself shut. You have to use a high current (hockey puck type is best) SCR to switch that much current.

Mine worked OK, but nowhere near as well as a professionally made one. and weighed three times as much.

 

[orionlion82]

I built one about 17 years ago, used a big bank (about 3-4 farad or so, at 25 or 40 V (if I remember correctly)), of surplus power supply grade electrolytic caps in parallel.

A mechanical momentary switch, even a massive one won't handle that kind of current without welding itself shut. You have to use a high current (hockey puck type is best) SCR to switch that much current.

Mine worked OK, but nowhere near as well as a professionally made one. and weighed three times as much.

yeah, high amp DC switches are tricky like that with the internal arcing.
but thats why we weld with high amp DC... ever see the massive knobs on welding machines?

 

[Fallingwater]

I posted here about this and they suggested I build a welder with a microwave transformer, which seems a pretty good idea to me.

 

[65535]

Really cool Lux, much faster than soldering, and no temp degradation of the cells. Seems like a fun project involving high output caps and some control circuit to charge them. Probably could work out something cheaper than $1k.

 

[LuxLuthor]

Couldn't you weld the leads to the magnets? Just a thought. Low heat etc.

The soldering is easy, fast, and secure. Once you learn the technique you can do the soldering without any significant loss of magnetism.

The wire strands make it unlikely that the pointed tips of the welder leads would be able to include the entire wire in the weld...then there is the relative difference in metals between copper and what you are welding to which make it difficult.

 

[dulridge]

The soldering is easy, fast, and secure. Once you learn the technique you can do the soldering without any significant loss of magnetism.

The wire strands make it unlikely that the pointed tips of the welder leads would be able to include the entire wire in the weld...then there is the relative difference in metals between copper and what you are welding to which make it difficult.

Yes, with a bit of practice, the soldering is easy.

My brain really wasn't working. If you weld a nickel strip to the magnet then solder the wire to that, you've added another step. Brain failure here.

I suppose a crimp connector that was welded to the magnet and crimped onto the wire would be faster (And possibly slightly more reliable if done properly) but hardly worth the effort for the minimal gain.

 

[OhMyGosh]

That magnet lead looks really clever - never seen that beforeoo:
Any idea what the voltage drop under load for that is?
How does it compare to spring tabs?

 

[LuxLuthor]

That magnet lead looks really clever - never seen that beforeoo:
Any idea what the voltage drop under load for that is?
How does it compare to spring tabs?

I get no resistance with my Fluke 179 DMM between the bottom surface of the magnet and end of wire, so no voltage drop under load should happen from these.

These are the much stronger N50 magnets with 1/4" x 1/4" surface area contact. I use high strand 16AWG and have used these to charge a 16 cell (Elite 2/3A) 19.2V battery pack up to 24+ Volts, and it works perfect. There is very strong contact made with battery end plate...and I like the color coded, thicker wire.

 

[orionlion82]

I get no resistance with my Fluke 179 DMM between the bottom surface of the magnet and end of wire, so no voltage drop under load should happen from these.

These are the much stronger N50 magnets with 1/4" x 1/4" surface area contact. I use high strand 16AWG and have used these to charge a 16 cell (Elite 2/3A) 19.2V battery pack up to 24+ Volts, and it works perfect. There is very strong contact made with battery end plate...and I like the color coded, thicker wire.

well, whats the electrical resistance of iron?

 

[LuxLuthor]

well, whats the electrical resistance of iron?

I give up.

 

[orionlion82]

Heh, i dunno either, but magnets is iron...

 

[dulridge]

Heh, i dunno either, but magnets is iron...

But nickel plated - these high power magnets are a ceramic (i.e. fragile) material made up of neodymium, iron and boron among other things and conduct fairly poorly. The nickel plate conducts just fine.

 

[OhMyGosh]

For a connector the resistivity is not as important as how much surface area you can maintain in contact.

A good rule of thumb for copper wire is: 10 gauge = 1 mOhm per foot, every 3 gauges is 2x the resistance. ie 16 ga = 0.004 Ohm/ft.

Resistivity of some metals in microohms*cm
copper - 1.72
aluminum(pure) - 2.83
gold - 2.44
brass - 6.2
iron pure - 10.1
iron cast - 75-100
steel - 15-50
nickel - 8.54
lead - 22
tin - 11.6
tungsten - 5.5
zinc - 5.97