Cable size crimp size for prismatic cell links?

[Scooterman]

I was planning on using 8awg silicone for the cell links and controller power (120A r-net), but the only 8mm^ 6mm terminals I can find are RNB series and only rated to 62A.

So are most people using 7awg silicone with a 10mm^ 6mm crimp/solder terminal?

Is 7awg much thicker/stiffer than 8awg silicone? I've not got any to compare.

NB: I won't be using the supplied bus bars.

[Burgerman]

I use 10 sq mm cable. And solder ring terminals.

Silicone is bigger as its insulation is weaker and thicker. And SWG AWG all means nothing much to me!

[Scooterman]

Thanks

And I do agree about awg cable sizing being confusing. It only seems to be used for silicone cable and some automotive cable. All mains rated cable is square mm.

[Scooterman]

Also for the charging lead.

If the 0v and 24v balance terminals are common'd (aka linked) with the +ve and -ve power terminals inside the d-sub connector then you only need 7 balance wires and 2 power wires in the charging cable.

Previously I've always had 9 balance and 2 power in charging cable. But 0v and 24v balanced cables are common'd with power cables at battery terminal so might as well just common them in the d-sub instead?

Yes/No?

[Burgerman]

You need 9.
We are balancing to a couple of mV (a 2000th of a volt...).

The resistance of a main charge cable allows much more than that between charger and chair. So it makes the balance LOOK incorrect at the charger while charging on cells 1 and 8....

[Scooterman]

Thanks BM I was hoping you were around to answer.

Something like that did occur to me after I'd asked the question, and I see what you say and totally agree.

It was just a thought I had.

I will definitely go with 9 balance cables of same csa and length.

[swalker]

I live in the US, where it is hard to find cables in metric sizes.

I am pretty much compelled to use AWG. This is what I used for my build:

For the cable, 6 AWG. Yes, 7 AWG is a better match for 10mm and is what I calculated would be sufficient, but 7AWG is not readily available. Here is the product I used: https://www.amazon.com/dp/B01MZH9C65?re ... in_title_3

For the terminals, I used https://www.amazon.com/dp/B072KBVS4N?re ... tle_1&th=1. Note that these are 8 AWG terminals. That is because the manufacturer (Selterm) recommends 8 AWG terminals for 6 AWG stranded cables. I first tried to use the 6 AWG Selterm terminals and they were too large.

I crimped my connections using this: https://www.amazon.com/dp/B00MVE48Z6?re ... tle_2&th=1

I am aware that Burgerman prefers soldered connections. I prefer properly crimped connections. If you don't know what a properly crimped connection is or how to reliably make one, then I think you are better off using soldered connections.

My battery pack has been going strong for over 6 years now.

Steve

[Scooterman]

Understood Steve thanks

Back in the day on mains electrical panels with either solid cores or stranded cable. With solid cores they'd bend the end of the cable into something like shepherd's crook, (for stranded cores they'd do the same but solder it). Back then the terminals were all brass and they'd slide a cup washer with a side cutout over the stud. Then they'd put the shepherd's crook in the cup washer, with the cable shank sitting in the side cut out. Then they'd put a flat washer on top and then a nut and crank away, voila! It made for a good connection both mechanically and electrically. The nuts and washers were all brass as well as the stud.

NB: Stranded cables have a lot less strands than silicone cables. Cables with a squillion strands (like silicone) are called flexible cores by the IEE wiring regs in the UK. And usually insulated with butyl rubber rather than silicone. I'd never seen or even heard of silicone cable until joining this forum.

Learning all the time!

[Burgerman]

SILICONE Cables were not really a thing for many years. They started to happen first in the hobby world, just like the LiPo battery thing. The reason is that we fly helis and planes that take maybe 150A at times. Copper is heavy and bulky. So we use smaller thinner lighter cables and just let them get hot! This is possible because the insulation no longer melts and causes a fire. So with silicone cables you can use far more Amps for a given size. And save weight and make it easy to work with.

[Scooterman]

Yep, I totally get that. Not only does PVC melt easily but it also goes stiff and is harder to strip at low temperatures, i.e. outdoors in british winter.

And if I remember correctly the current carrying capacity of a conductor is dependant on how efficiently it can shed it's heat before melting the insulation or the conductor itself melting. Aren't super conductors something like that, or am I getting muddled? Don't they cool them in liquid nitrogen or something?

Also back to silicone, it stays super flexible even at cold temperatures and must be great at absorbing vibrations in model aircraft and getting bounced about in a powerchair. I think prismatics linked together with copper bus bars in a powerchair is a definite no no. I don't know if anyone in this forum has tried and with any success?

[Scooterman]

I not fully watched the video but it looked interesting so thought I'd share it.

https://dronelab.se/siliconewire.html

[Burgerman]

Yes. That vid is good. It shows exactly why we use it on hobby stuff.

Its not needed on a powechair other than on a charge cable.

And as you can see, that silicon cable can take a lot of amps!

With the PVC stuff I use a rule of thumb, that just multiplies cross section by 10.

So a 4mm2 cable is good for 4 x 10 or 40A continuous. Maybe a little less if its in a bit of twin or has more layers, or in a place where no free air.

So 10sq mm is 100A and double that for a couple of secs. Works fine in a chair even used for sport or my mentalist programming. Anything more is overkill. Its already bigger than any stock chair.

As for crimping thise weedy thin plated soft copper ring terminals well I just do not think thats good! Dip one in some road salt for half an hour and leave it outside for a year. Then use an impedance meter across the joint. It will be terrible.
And the thin copper is so soft that no matter what you crimp it with you could pull it off the end. Especially if you wiggle it side to side as the strands walk... Not enouh strength in those terminals.

If you really cant be bothered to solder, then use much heavier crimps.

Heres an example. The 2 on the left are too flimsy to crimp alone. The one of the right is heavy walled, that can be crimped permanantly! But hydralic crimpers and dies needed.

[Burgerman]

Heres some that are heavy enough to solder, and some that are just weak...

See the wall thickness differences. The ones that are just made from flattened copper tube are great if SOLDERED. But far too weak if only crimped.

The cast ones with thicker walls CAN be safely and pernanantly crimped with the right tools.
If you can find any...

[ex-Gooserider]

Wire is a fairly complicated subject because there are a lot of different variables...

The guage or size - Metric tends to be in Sq mm, and BM likes 10mm^2 for his chairs, which translates to (about) AWG 7. However while there are defined sizes for the odd numbered AWG sizes, the only ones that are generally available are the even numbers, so we are stuck w/ choosing between AWG 6 and AWG 8. I've never seen a chair w/ AWG 6, from the factory, but have found some w/ AWG 8.... Back when there was a lot of discussion about power soccer chairs and similar high demand uses AWG 6 was recommended, but for 'normal' use, AWG 8 was said to be fine...

Stranding - The standard home wiring or many automotive wire tends to have fewer strands which is cheaper to manufacture but makes a stiffer wire. You can get 'super-flex' wiring that has more strands (each strand is thinner) with pretty much any sort of insulation... However it is more commonly available with silicone insulation. In larger sizes, I've had good luck with "Welding" cable that is flexible and has a heavy duty (thiick) plastic / rubber insulation that is very heat and damage resistant. I've also seen mention of "marine" wiring that is similar with the addition of plating on the strands.

Insulation - most common is the usual PVC / plastic stuff, fairly rugged , resists moderate heat, etc. Silcone will handle high temperature better, but is more delicate and easily damaged so may need better protection. Teflon is extremely high temperature rated, and heavier duty but can be harder to work with (especially hard to strip)

There is a lot more, but that is some of the more common variables...

I still have a lot of AWG 6 welding wire, so likely will use that, but if starting from scratch, I'd go with AWG 8 welding wire or similar...

ex-Gooserider

[Scooterman]

I remember trying to crimp the thick walled anderson pins. Couldn't do it, they just wouldn't squeeze down sufficiently.

Re cable sizing, I was looking at the stranded copper pvc cable that Sunrise use for the power connector on 120A r-net. And it says it's 10awg. I was originally going to use 8awg silicone for the links (which are very short). But if the r-net power lead is only 10awg (and a longer cable) then I can't see the point of using 8awg silicone.

But the 10awg Sunrise use for the power doesn't seem very thick considering I think BM has said r-net can deliver 120A per channel. So theoretically controller could draw 240A from the batteries? But I'm dubious whether the controller spade terminals could carry that current for long. IMHO it's usually connections/terminals that fail (burn) under excess load rather than the cable insulation itself melting. Although I have seen this happen with an extension lead where the person didn't fully unwind the lead before plugging in a 3kw electric fire.

[Burgerman]

I remember trying to crimp the thick walled anderson pins. Couldn't do it, they just wouldn't squeeze down sufficiently.

Wrong size cable or weak crimper...

Re cable sizing, I was looking at the stranded copper pvc cable that Sunrise use for the power connector on 120A r-net. And it says it's 10awg. I was originally going to use 8awg silicone for the links (which are very short). But if the r-net power lead is only 10awg (and a longer cable) then I can't see the point of using 8awg silicone.

There isnt any.

But the 10awg Sunrise use for the power doesn't seem very thick considering I think BM has said r-net can deliver 120A per channel. So theoretically controller could draw 240A from the batteries? But I'm dubious whether the controller spade terminals could carry that current for long.

Thats a theoretical max. I can achieve that. Just! And I have to try. It does so for 3 to 4 seconds as I accelerate up a steep slope only. It does this only at a certain speed where 120A per motor corrosponds to a full pulsewidth, meaning motor current = battery current. So most of the time its a lot less. And enen in extreme circumstances the R-net system can only do 120A per sde for 10 seconds before rollback.

IMHO it's usually connections/terminals that fail (burn) under excess load rather than the cable insulation itself melting. Although I have seen this happen with an extension lead where the person didn't fully unwind the lead before plugging in a 3kw electric fire.

I did that! Smelled bad, popped a breaker and ruined my extension lead.

[Scooterman]

Thanks BM I totally agree with your answers.

I think I vaguely remember you posting a video of a clamp amp meter showing the current draw. I've got a clamp meter and I think I tried it too and the current draw for me (lightweight user in lightweight powerchair) wasn't particularly high. But is obviously a lot higher ( as you say for short period) when climbing steep ramp, or trying to get chair out of being stuck in a rut! You obviously have to be sensible and not totally abuse the system. Just as you shouldn't abuse a car starter motor and battery by repeatedly cranking it when there's a fault that needs fixing first.

[Scooterman]

I remember trying to crimp the thick walled anderson pins. Couldn't do it, they just wouldn't squeeze down sufficiently.

Wrong size cable or weak crimper...

You forgot to mention the weak and feeble user of said crimper!

[Burgerman]

What type do you use?
Mines a cheap hydraulic one, and its really easy to crimp even the very heavy solid terminals in my images.

[Scooterman]

Do we need a fuse between cell pack and controller?

[Burgerman]

Yes. Why? IF nything bad happens inside the controller such as a lot of mosfets failed shorted, then it will directly short the battery. Will try and flow thousands of amps and melt and burn the cables and chair. So 150A midi fuse near battery is perfect.

[Scooterman]

Then a 150A midi fuse it is.

Thanks BM

[Burgerman]

Needs 2 ring terminals, 2 short M5 nuts bolts, crimp/solder and a bit of heatshrink...

[Scooterman]

[LROBBINS]

If you put that fuse in an SB50 & mount another SB50 connected to the battery in an easy to reach place, it can serve as a disconnect link when, for example, traveling by airline or wanting to work on the chair with assurance that power is disconnected.

[Scooterman]

If you put that fuse in an SB50 & mount another SB50 connected to the battery in an easy to reach place, it can serve as a disconnect link when, for example, traveling by airline or wanting to work on the chair with assurance that power is disconnected.

Yep that is a fair point. My mobility scooter has that exact set up and I disconnect the SB50 for long winter storage otherwise cells discharge through s-drive controller.

With my powerchair a sunrise salsa/jive R2 the r-net controller is easily accessible by removing one thumb screw and rear plastic cover. Can then just unplug power lead from cell pack to controller. It's a lot easier than trying access battery compartment which is difficult on my chair with lithium cells with lots of wires.

[Burgerman]

Mount an anderson where you can add a loop. Many of my chairs have this as I only use 1 at a time. It can house the fuse, or not. Your choice.

[Scooterman]

I see, you mean an Anderson and loop in just the +ve cable. Basically a switch. That’s a good idea

[Burgerman]

Yes mines just a "switch" lenny went one further and used the thing with his fuse in it too. Easy swap!

[Scooterman]

Ah! Apologies to Lenny I misunderstood him.