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I want to make a power connection between my PCB and an accumulator. I need it to handle up to 100A, and to be mechanically very strong, because it will be on board of a buggy car model.

In the prototype I made with a Perfboard (dot pcb) I split the big wire into 16 smaller sections, and I pass each of them through a different hole. Then I solder all together in the bottom.

Two big wires split in 16 small portions Can't fit a PCB bus bar

Wires and connectors are standard from model hobby:

That works really well, as it is both strong and accommodates the large wire in quite a small footprint. I've used a similar technique to retrieve output current from the half-bridges underneath the dissipator.

Now I would like to make a printed circuit, and I would like to replicate the same kind of connection, but I'm unsure how to proceed:

  • Creating a component that contains multiple through-holes, too close to each other fires up plenty of design rules error.
  • My PCB editor (Proteus - Ares) believes that each through hole is a different connector, so it is awkward to create a component.
  • I prefer to remain as standard as possible because I order my PCB to a commercial manufacturer.
  • Some comments suggest to use a PCB bus bar. I understand that this would make a great connection, but I don't see how I could possibly fit them in a circuit that goes onboard of a model car. Circuit is a BLDC controller, and has 2 power inputs and 3 power outputs.

I would welcome any idea, including creating the connector in a different way, or using a different PCB editor.

Edit

Chris Stratton suggested to look at an actual commercial ESC module. I should have started by that. Here is the disassembly of one:

550X ESC Disassembly - HeliFreak 550X ESC Disassembly - HeliFreak

Now I have more questions:

  • It looks like the power cables are soldered to a metallic area reinforced with small dots. Someone knows what it is?
  • On the other face there are a kind of slab. Is this a power bus?
jmgonet
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    You won't convince me that PCB trace has the same cross section as the wire. – Marko Buršič Sep 04 '16 at 09:19
  • The large wire is standard in model hobby to handle high current. It is oversized in my case, but it is still the standard size. Underneath my prototype I had to hand-made a trace by welding a braided shield extracted from another wire to avoid the soldering paste to melt when in full power. – jmgonet Sep 04 '16 at 09:28
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    Directly soldered wires aren't the best for vibration; you want PCB bus bars with terminals: https://electronics.stackexchange.com/questions/59735/creating-a-high-current-bus-on-a-pcb – pjc50 Sep 04 '16 at 09:32
  • The reason being that the wire mass goes up quadratically with radius, but the holding surface only goes up linearly. – Ignacio Vazquez-Abrams Sep 04 '16 at 10:35
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    The bus bar or the stiffener is definitely a good idea. You can also add some cutouts on the smask and pour solder on them, you can sometimes see that in high current traces. Also consider using multiple layers for the trace. And of course keep the tracks **short**. Anyway, the problems you are encountering are cad related and should be trivially solved, I have done something similar with KiCad, so any tool can do that. – Vladimir Cravero Sep 04 '16 at 11:16
  • Also consider using several, smaller section cables. The final cable volume is higher but there are huge benefits: better heat dissipation, easier routing, possibly better transient response, neater soldering job (what you did is quite good but you can do better)... – Vladimir Cravero Sep 04 '16 at 11:19
  • I understand that PCB bus bars make the best possible connection, but I don't see how I can possibly fit them in a circuit that goes onboard of a model car. I've added another image to show it. Also, it is a BLDC driver, so there are two power inputs and 3 power outputs. – jmgonet Sep 04 '16 at 11:21
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    I'm using standard cables specifically designed and manufactured for model cars of the same size and power as mine. – jmgonet Sep 04 '16 at 11:23
  • Out of curiosity, why wouldn't you just buy a pre made one? Anyway, which kind of connectors are you using? If there is the solderable connector I would go with that. – Vladimir Cravero Sep 04 '16 at 11:23
  • Why not use a board mount terminal block with spring wire clamp? – Tyler Sep 04 '16 at 11:30
  • @VladimirCravero: I want a controller that is able to drive in high speed and also as stepper. The car is able to position itself within 1cm of precision, and run up to 30km/h. I'm using EC5 connectors to the accumulator, and 3.5 bullet connectors to the BLDC engine. – jmgonet Sep 04 '16 at 11:31
  • @Tyler When building the PCB I considered using terminal blocks, but I had two problems: first is that Perfboards have a hole diameter of 1mm, and terminal block able to drive this amount of current have bigger connectors (this problem would disappear in a custom PCB). Second is because terminal blocks mainly address industrial applications that have higher V and lower I than mine, so they're quite big. – jmgonet Sep 04 '16 at 11:59
  • @Tyler But I would definitely consider a mount terminal block if I was able to find the right one. Which I haven't been for the moment. – jmgonet Sep 04 '16 at 12:00
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    Seems like a cool project! I had a quick look and it seems you can solder EC5 and bullet connectors to a PCB, maybe you have some laying around and you can make some does-it-fit tests. I am still quite convinced you need to find room for the bus bars. I tried some quick numbers and I get 6W dissipated on the track, not sure if this is acceptable. – Vladimir Cravero Sep 04 '16 at 12:28
  • Just search Digikey for terminal blocks 100s to choose from, above 100 amps.... – Tyler Sep 04 '16 at 12:32
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    If you don't want to bother with buying specific components, you can just use solid copper wire of larger diameter. Drill the holes in your test PCB large as the external wire, put wire through hole and solder it to solid copper wire. Solder this solid wire to copper side of PCB, but just to hold it in place, NOT to have high current going through PCB traces. This thick solid wire you need to bend appropriately and place all the way to pins of transistors, or wherever it leads to, and solder it directly to pins. – BJovke Sep 04 '16 at 16:45
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    Why don't you look for ideas at the physical assembly of proven ESC products intended to drive this size motor in this type of application? For that matter, you can probably achieve your goal by rewriting the firmware for an existing product, possibly after changing out the MCU a version having more resources in the same pinout. – Chris Stratton Sep 04 '16 at 20:15
  • @ChrisStratton Yeah. Well. Looks an obvious suggestion, but I didn't thought it before. I feel silly now. – jmgonet Sep 05 '16 at 07:58
  • Just for those curious, the "dots" are probably multiple extra vias. Instead of using a single large via connection, using multiple vias is better (for much the same reason as why you use stranded wire over solid core wire - the skin effect in AC circuits). It also can be important because some manufacturing processes have fixed via sizes, so you need multiple to be able to carry the current. – techdude Feb 03 '17 at 00:15

2 Answers2

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From the photos it looks like you are desiging a brushless driver for RC car , the RC car motor and batteries are sized for short pulses of high current and not continuous , so the limit in your case is not the PCB traces .

BUT anyway i will present some of the methods used :

  1. Using a High or VERY high thick copper PCB (4oz to 20oz) probably the most expensive and not available anywhere

  2. Copper bus bars welded or screwed into PCB

  3. Copper wires soldered into PCB

  4. Solder wick/Braid , this is my favorite since it doesnot required the amount of heat that the previous methods used which leads to permenant PCB bend.

very compact High current ESC

bus bar pcb stiffeners

copper bars

Wire

screwed bus bar

MY Preferred Solution :

solder braid

EDIT: Added PCB termination

Wurth Electronics power elements

wurth power elements

or lugsdirect PCB Wire Connectors

lugsdirect

ElectronS
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  • JOOI, if *you* soldered those copper bus-bars, did you pre-heat them in an oven or such? – Andrew Morton Sep 05 '16 at 18:32
  • i personally donot know how the correct process – ElectronS Sep 06 '16 at 07:48
  • Thanks for this practical answer about layers. I've used a braid in my current Perfboard, and I can confirm that it is both easy to implement and doesn't bend (too much) the circuit. However, my original question was about how to connect the power cables to the PCB. I've seen in one of your photos that you use a bolt and screw plus a cable lug. Could you give me some insight? – jmgonet Sep 06 '16 at 13:26
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    @jmgonet , make a big pad lets say for m6 screw the pad should be (hole:6-6.5mm and outer ring about 12-14mm) then use a brass screw and a nut to lock the screw , if you can use solder on both to lock them in place. then you put the wire lug and tighten it with a second nut. there are some ready products that i will add in my answer that also solve this problem – ElectronS Sep 07 '16 at 09:11
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It looks like the power cables are soldered to a metallic area reinforced with small dots. Someone knows what it is?

It looks like those are vias-in-pad. My guess is that they are stitching the top metal layer all the way through to the bottom for both good electrical conductivity and structural integrity. I would suggest to use all metal layers in the pad.

Daniel V
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