High current connectors

[[email protected]]

Can anyone comment on what's the 'right' way to connect high current
sources to a PCB? Can anyone recommend a particular connector? Assuming
I don't want to do something like solder the cable directly to the
board.

I'm looking at 40A, but for the sake of learning something, I'd be
curious to know what people use for 60A, 80A, 100A or above, and for
that matter, what the limit is.

Thanks,

Chris

 

[Yukio YANO]

Can anyone comment on what's the 'right' way to connect high current
sources to a PCB? Can anyone recommend a particular connector? Assuming
I don't want to do something like solder the cable directly to the
board.

I'm looking at 40A, but for the sake of learning something, I'd be
curious to know what people use for 60A, 80A, 100A or above, and for
that matter, what the limit is.

Thanks,

Chris

Look up the Fork-lift servicing people in the phone book . They have
standard Connectors for wheel-chairs to Industrial Fork-lifts !

Yukio YANO

 

[[email protected]]

Yeah, but are the PCB mount?

The forklift we had in our back shop had a nice high current connector,
but it was cable to cable, rather than cable to PCB.

Chris

 

[John Larkin]

Can anyone comment on what's the 'right' way to connect high current
sources to a PCB? Can anyone recommend a particular connector? Assuming
I don't want to do something like solder the cable directly to the
board.

I'm looking at 40A, but for the sake of learning something, I'd be
curious to know what people use for 60A, 80A, 100A or above, and for
that matter, what the limit is.

Thanks,

Chris

I sometimes use a regular nylon-shell Amp or Molex connector at, say,
5-10 amps per pin. Inter-board cables are run with one modestly-sized
wire per pin pair; that's cheap, easy to fab, flexible, and the wire
resistance equalizes pin currents if you plan it right.

Somewhere north of 50 amps RMS, current crowding and power dissipation
in the PCB traces becomes a problem. A big connector with lots of
smallish pins helps here, by spreading out the current footprint.

John

 

[Terry Given]

I sometimes use a regular nylon-shell Amp or Molex connector at, say,
5-10 amps per pin. Inter-board cables are run with one modestly-sized
wire per pin pair; that's cheap, easy to fab, flexible, and the wire
resistance equalizes pin currents if you plan it right.

Somewhere north of 50 amps RMS, current crowding and power dissipation
in the PCB traces becomes a problem. A big connector with lots of
smallish pins helps here, by spreading out the current footprint.

John

AMP now make them, but we designed our own. Make a big fat (red) cross,
out of 1mm Cu, with fingers on each of the protrusions, and a hole in
the middle. Fold the protrusions down, to make a little box, and drop
into a suitable PCB footprint (fingers thru holes get soldered). Then
unsolder it, and pop a suitable sized nut underneath (appropriate hole
on PCB) then re-solder, and voila - a nice high-current connector you
can bolt too. After you forget the nut once, you wont forget again

careful choice of dimensions mean the nut is contained but cannot spin
freely. poor choice of dimensions renders the idea useless.

Others just bolt big fat lugs directly to PCBs, but beware the Z-axis
CTE of FR4 is about 10x worse than X- and Y-axis CTE, and that near Tg
it'll happily flow. Still, thats what Mithras invented Schnorr washers
for

Cheers
Terry

 

[John Larkin]

AMP now make them, but we designed our own. Make a big fat (red) cross,
out of 1mm Cu, with fingers on each of the protrusions, and a hole in
the middle. Fold the protrusions down, to make a little box, and drop
into a suitable PCB footprint (fingers thru holes get soldered). Then
unsolder it, and pop a suitable sized nut underneath (appropriate hole
on PCB) then re-solder, and voila - a nice high-current connector you
can bolt too. After you forget the nut once, you wont forget again

Why solder/unsolder/resolder?

careful choice of dimensions mean the nut is contained but cannot spin
freely. poor choice of dimensions renders the idea useless.

Others just bolt big fat lugs directly to PCBs,

Yup, did that whan I was young and foolish. Lots of trouble.

The problem isn't so much the connector as it is the current
distribution and heating in the PCB traces. It's fairly easy to get
most of the current squeezed into a relatively small part of where you
expected it to be. The Amp block-o-pins thing has such a low
resistance that the pcb pad/trace geometry is going to determine the
current sharing. I like the multi-wire thing because it can be made to
force a nearly equal current on each pcb pad, and can spread out that
current over a wide area. Plus, the octipus of wires just above the
shell housing provides much better air cooling than you'd get from a
single equivalent fat wire.


John

 

[Terry Given]

Why solder/unsolder/resolder?

just a cheeky comment. And because most people do that, at least once.

Yup, did that whan I was young and foolish. Lots of trouble.

oh yes. a terrible idea.

The problem isn't so much the connector as it is the current
distribution and heating in the PCB traces. It's fairly easy to get
most of the current squeezed into a relatively small part of where you
expected it to be. The Amp block-o-pins thing has such a low
resistance that the pcb pad/trace geometry is going to determine the
current sharing. I like the multi-wire thing because it can be made to
force a nearly equal current on each pcb pad, and can spread out that
current over a wide area. Plus, the octipus of wires just above the
shell housing provides much better air cooling than you'd get from a
single equivalent fat wire.


John

and a split-washer (cheap shit spring washer) exacerbates the problem,
by heavily loading one point.

Cheers
Terry

 

[[email protected]]

Can anyone comment on what's the 'right' way to connect high current
sources to a PCB?

I have used wire-mounted "Singlepole" and "Multipole" Anderson connectors
http://www.andersonpower.com/ for DC (150 V, 150 A) and AC (300 V, 70 A)
connections and they seem to work well. It looks like they do a PC-mount
version of some of their connectors (which I haven't used) for up to 55 A.

Can anyone recommend a particular connector?

Big copper land on PCB, big bolt, ring terminal...

Thinking out loud: do you know about the lugs that are used to terminate
larger stranded wires to fuse holders, etc? Like
http://www.gardnerbender.com/whats_new/products/ima_prod/alu_lugs.jpg .
Maybe you could use a lug like this, bolt the thin part to your board
permanently, and have the user insert a stranded wire into the hole and
tighten the screw. Essentially it's a DIY high-current terminal strip.

Standard disclaimers apply; I don't get money from any of the companies
mentioned.

Matt Roberds

 

[Rich Grise]

Why solder/unsolder/resolder?


Yup, did that whan I was young and foolish. Lots of trouble.

The problem isn't so much the connector as it is the current
distribution and heating in the PCB traces. It's fairly easy to get
most of the current squeezed into a relatively small part of where you
expected it to be. The Amp block-o-pins thing has such a low
resistance that the pcb pad/trace geometry is going to determine the
current sharing. I like the multi-wire thing because it can be made to
force a nearly equal current on each pcb pad, and can spread out that
current over a wide area. Plus, the octipus of wires just above the
shell housing provides much better air cooling than you'd get from a
single equivalent fat wire.

And less impact from skin effect. ;-)

Cheers!
Rich