High Power Connectors: Which Ones?

Hello Everyone,

I'm currently going through the process of sourcing all the little hardware for my build, and right now I'm searching for the best compromizes in tems of power connectors.

A little reminder of my config should help:
2 batteries in parrallel. Each battery is 72V and 40AH, so 80AH in total. I need those to be able to push around 600 Amps continous.

So I need the connectors that can withstand that kind of current. Basically, what I need is:
-One connector for each battery, each being able to reach 300A continous without melting.
-One connector to link both paralleled batteries to the controller, able to withstand the total amperage of both, so 600A continous.

I thought about using Anderson connectors, but they are big and bulky.
Is there anything better you could recommend?

Any suggestion is very welcomed!
Thanks in advance,

If you have a 40Ah, and a 80Ah battery, each connector is not likely to be carrying 300A

It's more likely to be 200A and 400A respectively due to the internal resistance of the packs. (In reality, it'll be off from that, as there is both conductor and and connector resistance, but it definitely won't be an even split. Also possible that your 40Ah packs are higher quality/power density and it's closer to half half, or even split the other way.)

If you use SBE 700s for all connectors, twin 4/0 AWG for the pre-parallel connectors and 250kcmil for the main connector, you should be safe.

I have serious doubts that you could get anything smaller than an SBE 700, as you need to accommodate the cable. While you may be choosing to undersize the cable for a short run/well ventilated, anything designed for 600A, would be using at least 1000kcmil, or 2 x 4/0 AWG, which takes up space.

Big current stuff ends up at bus bars and bus bar connectors, or bolted ring terminals (or ring terminal arrays).

Sunder said:

If you have a 40Ah, and a 80Ah battery, each connector is not likely to be carrying 300A

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It's 2x40AH in total, so two batteries of 40Ah each, equals 80AH.

Sunder said:

If you use SBE 700s for all connectors, twin 4/0 AWG for the pre-parallel connectors and 250kcmil for the main connector, you should be safe.

Click to expand...

Those things look super massive... Even bigger than the Anderson Connectors I've found...



For the wires, I'll use 2/0 AWG wires, I think that should be ok since the distance will be short and they will be very well ventilated. I'll try that and see if it turns out to heat too much.

liveforphysics said:

Big current stuff ends up at bus bars and bus bar connectors, or bolted ring terminals (or ring terminal arrays).

Click to expand...

I'd like to avoid this since It would not be super convenient to use for me, having to unbolt stuff anytime I'd want to take out one battery... But to be fair that might be the best solution if I cannot get a compact enough connector.

Just to hopefully make things a bit cleared, here is a hideous paint drawing of what I'd like to do:

Sorry, my bad, misread your post.

The SBE 700s ARE Andersons. they're the right size Andersons for your stated application (Which I think you've over-estimated. At 110km/h on the flat, I use 8kw on a 220kg, upright seating position maxi scooter. For a sports bike to use 42kw+ "continuous" that must be one hell of a hill).

Which Andersons are you thinking of using? You can undersize cables for short runs and good cooling, but under-rate a connector by too much, and it'll have a pretty short life at best, and potentially an electrical fire at worst.

At the end of the day, you have the limits on physics. You need big contact area to avoid the contact points from overheating. You can't cheat physics. Either you make the contact area bigger, cool it, or lower the current either by using less or raising the voltage. That will be the limit to the size of your connector.

Sunder said:

Sorry, my bad, misread your post.

The SBE 700s ARE Andersons. they're the right size Andersons for your stated application (Which I think you've over-estimated. At 110km/h on the flat, I use 8kw on a 220kg, upright seating position maxi scooter. For a sports bike to use 42kw+ "continuous" that must be one hell of a hill).

Click to expand...

Well, continous doesn't necessarly means that it will be used at this level of power all the time during a ride. In my case I ride in a huge city, so there are stops and starts all the time, it's not some kind of long empty road where I could ride smoothly at a given speed.
So it wouldn't be continuous in that way, but it would be accelerations and decelerations all the time.
Currently I'm using a Sabvoton rated at 200A continuous, and from what I can see on my dasboard with the current meter, it is actually pumping that current most of the time (except, indeed, when speed stabilizes, At max speed for instance it sits around 70-100A depending on my flux weakening settings). I tend to go heavy on the throttle all the time, so things get hot...

Sunder said:

Which Andersons are you thinking of using? You can undersize cables for short runs and good cooling, but under-rate a connector by too much, and it'll have a pretty short life at best, and potentially an electrical fire at worst.

Click to expand...

I was thinking of using stuff like that:
https://item.taobao.com/item.htm?spm=a230r.1.14.1.19dc5208KZuAX2&id=558372569858&ns=1&abbucket=6#detail

I'm using those on my scooter (a smaller version, rated at 175A) and never had any problem, but they are not super convenient to disconnect (need to pull real hard) and they are not water resistant either. And those 300A version are quite bigger.

Sunder said:

At the end of the day, you have the limits on physics. You need big contact area to avoid the contact points from overheating. You can't cheat physics. Either you make the contact area bigger, cool it, or lower the current either by using less or raising the voltage. That will be the limit to the size of your connector.

Click to expand...

Well yeah, I know . But contacting surface can vary a lot depending on shape. On a typical Anderson connector, you just have 2 flat shapes touching each other, which is indeed quite a small surface. But you could imagine having a tube and rod connection style, giving you way more surface for the same volume. Kind of same stuff like the bullet connectors. I assumed those kind of stuff existed in higher power versions too.

Dui said:

But contacting surface can vary a lot depending on shape. On a typical Anderson connector, you just have 2 flat shapes touching each other, which is indeed quite a small surface. But you could imagine having a tube and rod connection style, giving you way more surface for the same volume. Kind of same stuff like the bullet connectors. I assumed those kind of stuff existed in higher power versions too.

Click to expand...

I'm no mechanical engineer, but I expect that those things rely on spring force both for retention and contact. The thing is about two perfectly curved concentric circles, is that in theory, there should only be one "point" (mathematically), or one molecule (physically) of contact.

How bullets work is that plug is made of very thin, sprung metal, so that when it is pushed in, there is some level of deformation increasing contact. Perhaps that's just not feasible with thicker guage metal, or doesn't scale so well?

I'm speculating entirely, but I do know that when something that should have a high demand doesn't exist, it's because people smarter than me have found a good reason as to why it won't work.

Sunder said:

I'm no mechanical engineer, but I expect that those things rely on spring force both for retention and contact. The thing is about two perfectly curved concentric circles, is that in theory, there should only be one "point" (mathematically), or one molecule (physically) of contact.

How bullets work is that plug is made of very thin, sprung metal, so that when it is pushed in, there is some level of deformation increasing contact. Perhaps that's just not feasible with thicker guage metal, or doesn't scale so well?

I'm speculating entirely, but I do know that when something that should have a high demand doesn't exist, it's because people smarter than me have found a good reason as to why it won't work.

Click to expand...

Ok so the only solution seems to be the Anderson connectors or bus bars. That kinda sucks.
I wonder why there isn't more choice, really. I get your points, but it seems very easy to get around these issues. Like building some kind of connector using a similar system as the collet chucks of CNC milling machines. (stuff like that: https://www.grainger.com/product/35YG66?cm_mmc=PPC:+Google+PLA&s_kwcid=AL!2966!3!50916767037!!!s!71846391319!&ef_id=WvUxUQAAAHEvPmjc:20180516014734:s )

In which case you would plug the stuff, turn a knob to tighten the collet and it should be almost as good as a wire (provided the material would be a good conductor of course).

LFP has your answer ! His deathbike will make your mind twist just to watch.
Aka liveforphysics.
Need vid of first test ride.

If you don't have space for the right anderson (SB175 cabled heavy would work fine for you), this bullet connector is about as high of current density per size short of bus bar finger mating connectors.

10mm diameter gold bullet connector:

https://www.amazon.com/ProgressiveRC-AC-10MM-10mm-Bullet-Connectors/dp/B00CDAPJ74/ref=sr_1_fkmr0_1?s=industrial&ie=UTF8&qid=1526454694&sr=8-1-fkmr0&keywords=10mm+bullet+connector+gold

If you ran say 2-3 in parallel per polarity, each cabled with perhaps 4~2awg, you will have low R loss without the hassle of a ring terminal or bus bar. If you did make a bus bar mating joint, connectors like this are amazing for currents in the kA range. This model is 500A continuous, and has low mating insertion force and is blind-mate friendly and packages very tight, but it's not weather robust as it ships (you could make seals if you felt ambitious, or just pack it with dielectric grease).

http://www.te.com/usa-en/product-2204273-1.html

liveforphysics said:

If you don't have space for the right anderson (SB175 cabled heavy would work fine for you), this bullet connector is about as high of

[...]

, but it's not weather robust as it ships (you could make seals if you felt ambitious, or just pack it with dielectric grease).

Click to expand...

Thanks!

Unfortunately for me, they don't seem to have those here in China... Well I'll just go with the Anderson Connectors, no big deal.
Thank you guys for your help, appreciate it