Two Electronics Questions

[JZH]

1. How would you calculate the maximum amperage rating of a multi-pole connector if you're using multiple poles for the same current? In other words, a connector has eight pins, each of which is rated 5A, if you connect all eight pins to the same wire, the resulting current carrying capacity is certainly more then 5A, but it is also likely less than 40A. There must be a formula for this!

(Why? Because I want to use some really cool connectors I already have (Lumberg IP68 DIN) in a high power application, e.g., for a heated clothing controller, which is rated at 15A.)

2. Shared grounds and ground loops... I'm putting together a bunch of electronics components, each of which is powered by 12v DC from the bike's battery (through a common fuse block). Unusually, only one of these wired components has audio (Valentine One radar detector); the rest are things like wheel and temperature sensors, gear shift indicators, voltmeters, 5v transformers and a Touratech IMO. I suppose there is no substitute for simply hooking everything up and testing it, but I'm wondering how the various ground connections used by each of these different devices will (or won't) work together. I'm particularly worried about the V1 and the IMO. The IMO control box sends a ground out to a remote control unit (a wired switch and diode array), which ground I need to use as the (shared) ground for a voltmeter, as well as the V1 remote display (due to a limited number of poles available on the connector I'm using). Apart from the fact that the voltmeter is not wired directly to the battery as it should be, sharing the ground should work, shouldn't it? Or should I simply connect all of the grounds together to eliminate any potential loop issues?

Any EE's out there?

Cheers,

[Switchblade]

?

And 5A @ 250VAC. Your safe.

250VAC x .707(RMS) = 176.5 Vdc

[Switchblade]

And I like the idea of a single point ground .

But here's a great article on the subject .

http://www.ridermagazine.com/gear/adding-electrical-accessories-to-your-motorcycle.htm/

[Switchblade]

Another thing I have read a couple times is to locate the multi grounding point as close the battery as possible.

[Nobody]

1. How would you calculate the maximum amperage rating of a multi-pole connector if you're using multiple poles for the same current? In other words, a connector has eight pins, each of which is rated 5A, if you connect all eight pins to the same wire, the resulting current carrying capacity is certainly more then 5A, but it is also likely less than 40A. There must be a formula for this!

(Why? Because I want to use some really cool connectors I already have (Lumberg IP68 DIN) in a high power application, e.g., for a heated clothing controller, which is rated at 15A.)

It is as simply as 8x5A = 40A

[JZH]

Thanks, Switchblade, yes those are the connectors. I used them on the previous version of my electronic tank-thing, and they have been excellent. Yes, I have a weakness for IP-rated electronic hardware--there ought to be a 12-step program for that!

I'll read that article.

And Nobody, I know I've read somewhere that doubling (or tripling, etc.) the contacts in a connector or wires in a cable is not a straight multiplication, due to factors such as heat and the surface area of the contacts/strands of wire, but I cannot seem to find it. I'm planning to use an 8-pole connector as a main power connector, which means that I will use four of the poles for 12v and four for ground, with a direct battery connection (and a suitable in-line fuse). I'd like to think that this would give me a full 20A capacity, but I'm not sure. I'm confident I would get 15A, which is enough for the Heat-Troller, but I would also like to have a Powerlet/BMW outlet for emergencies, which socket is rated 20A. Of course, I wouldn't be using the outlet constantly, so I might be able to get away with it.

Cheers,

[Nobody]

Well, as i was taught it is straight multiplication. If one wire can take 5A considering heat/contacts and so on, then 4 wires can take 20A. And i think heat is not important here as wire designed for 5A shouldn't be noticeably heating at that current (if only contacts are good).

Formulas can get complicated when there are several phases or high frequencies, but in DC it's mainly very simple.

It just came to me, that there can be problem, if contacts are not reliable. If 2 contacts noticeably lose connectivity, then other 2 wires will have to take 10A each and that can lead to overheating. But if contacts are good, then there's no problem.

[JZH]

Thanks.

Ciao,

[NorthernVFRDave]

There is a derating you have to use for parallel feeders. Been a while since I've done it but I believe you have to derate the current capacity of your wires by 20%

This is in the AC world, where your using parallel feeders for thousands of amps at 440vac and higher.

But there is a heating issue in the DC world as well. 5a@12v doesn't make a lot of heat, but 40a@12v across 5 wires all bunched together inside that connector just might.

We use those connectors at work all the time on 90vdc actuators and they hold up well to every day usage. But we are only pushing 1 or 2 amps on a single line.

[JZH]

There's also peak current versus normal, I would expect. Not much heat would be generated from a momentary surge up to maximum. I think I'm good to go with the theoretical 20A rating for four + and four - pins. The Powelet/BMW connector would only be for tyre inflators or the like, and the modern ones don't draw anything near that. So long as I can cover the heated clothing load, I should be fine.

Cheers,