Arming switch

[Tim Mackey]

sounds OK to me, and many people use a similar setup using deans plugs /sockets

[Former Member]

[This posting has been removed]

[Chris Card]

Sorry for the thread revival but I'm just revisiting this thread as I'm putting together my biggest electric model so far (a Hangar 9 corsair electric conversion) .  Hence I will need to use an arming plug arrangement and since I will be using A123 cells I want to charge with the batteries in situ within the plane.

 

I assume that in Chris Bott's scheme described above, the 2mm connector is wired to the negative at the ESC (not the negative at the arming socket), since if it were the latter this would be no different to plugging your charger into the arming plug and the ESC would remain in circult?

[Chris Card]

This is my interpretation of Chris's method:

 

 

This loom is for my Hangar 9 Corsair conversion, the series connections for three 4S packs are on the left, on the right hand side of the loom, to be positioned at the front of the plane are connections for the ESC (top connection) and the arming socket which doubles as a charging socket.



The arming socket will be positioned at the underside of the cowl and a shorting plug will be inserted to provide power the ESC and motor only when I'm ready to fly. 

Since I want to charge the batteries with them still in the plane I also need a way to hook up my charger safely and without the ESC in circuit.  This is achieved using a small fly lead from the negative side of the ESC connection (with a 2mm socket on the end) in combination with the arming socket.



An adapter lead shown above can be connected to the fly lead and arming socket and then plugged into the charger, meaning it charges the batteries while the ESC is out of the circuit.  Thanks for the idea Chris!

[Simon UK]

Hi Peevie

 

Excellent work and thanks for taking the time to post pictures of your wiring loom, my only question is in the bottom picture, the way i figure the circut the bottom deans (male) should be flipped over in the picture, is this correct? 

 

I need to make a loom up for my H9 Cub as i'm using A123's and your pictures have saved me a major headache

 

Cheers

Simon

[Martin Harris - Moderator]

Aren't you concerned with the length of the cables?  It's generally held to be a bad thing to extend the battery cables to any significant degree as it can cause damage to the speed controller.  Normal advice is to extend the motor wires if you need the extra length.

[Simon UK]

No Martin not really, i had read that it was bad practise to lengthen the battery cables, but to be honest i can see no other way of running 2 packs in parrallel with a seperate charging socket. Maybe you can enlighten me?

 

Also i fail to see how it could damage the ESC surely the current having to travel a little further cannot make That much of a difference?

 

[Tim Mackey]

Its not the current travelling  further thats the issue - its the fact that having the battery "close" to the ESC helps to dampen out any back EMF spikes that may be present in the cabling. If you lengthen the cables a lot, then these spikes can damage the input capacitors as they are no longer effectively damped by the battery.

[Simon UK]

Well Timbo i'm afraid that went way over my head :P

 

And in Laymans terms? Also a solution?, how did you wire up your Sopwith Camel that could be of help?

 

Thanks

Simon

[Tim Mackey]

Laymans term?

A) Dont lengthen the battery to ESC leads if possible.

B) Lengthen the ESC to motors instead

C) The camel had the batteries and the ESC and the motor all inside the cowl!

 

I used a Deans connector as a charging socket /battery isolator.

Ill try and dig out a picture.

[Tim Mackey]

Pics.

The multicore cable is the balance lead hard wired to the pack and would be used occasionaly ( not required much with A123s )

You can just make out a length of yellow nylon fishing line -  on the end is a deans plug with soldered bridge acrss the terminals - plugged into "arm" socket.  This forms a simple single pole isolator in the positive lead from battery to ESC.

Top deans socket is wired across the main battery terminals and is the charge socket.

The nylon line was later cut and repositioned to a position which prevented the arming plug from reaching the charge socket should I have a dumb moment

 

close up of panel.

 

 

 

And the rear of panel - heavy guage copper single wire used to wire it up.

Edited By Timbo - Administrator on 10/02/2010 20:10:34

[Chris Card]

Posted by Simon UK on 05/02/2010 14:00:59:

Hi Peevie

 

Excellent work and thanks for taking the time to post pictures of your wiring loom, my only question is in the bottom picture, the way i figure the circut the bottom deans (male) should be flipped over in the picture, is this correct? 

 

I need to make a loom up for my H9 Cub as i'm using A123's and your pictures have saved me a major headache

 Hi Simon, sorry I missed your post until now.

 

Firstly, yes you're correct, the male deans should flip over, it's just the way it was laying when the photo was taken.  Secondly, as a general rule it is correct that you shouldn't extend the cables from the battery to the ESC too much.  The question is - how much is too much?

 

 

In electrical terms the reason for not extending cables is that you are increasing the inductance of the circuit.  Inductance is like the opposite of capacitance.  Wheras a capacitor allows quick fluctuations in current to pass, an inductor acts in opposition and an opposing voltage forms to oppose the change in current (the "back EMF").  If the sum of the induced voltage and the normal circuit voltage (battery voltage in a plane) is too much for the input capacitors on the ESC, that's when you get into trouble.

 

So I'm basically saying I did the wrong thing, right?  Wrong!  I only said you shouldn't extend the cables "too much" and using my Mk 1 ready reckoner of "I think that'll work" I decided that I could get away with that length of wiring loom.  I didn't have a lot of choice actually as the batteries needed to be back in the middle of the fuselage and the ESC needed to be in the airflow, so the length of the wiring loom was a fait a complis.   But the key thing is this, I'm only drawing about 27A at full throttle and the back EMF created by rapid switching is proportional to the square of the current.  I'm also using nice thick wire which will have a lower inductance than thin wire.   My ESC is rated for 12S lipos and I'm only running 12S A123s so I have some spare voltage "headroom" on the capacitors in the ESC (which are rated to 50V).  I'm confident that I'm well inside safe margins and reserve the right to go on believing that at least until I blow up my ESC

 

Now if I was running my ESC at its limits and using wire that was only just thick enough for the current then I might start measuring my wiring loom to make sure it's not too long, but as with many things in the model plane world, the fact that under certain circumstances something is inadvisable gets a little lost in translation and leads to over cautious advice being given.  Like people saying lipos can explode at any second and need to be treated like an unexploded bomb.  Actually, a little knowledge and staying within sensible parameters is all that's needed to stay safe. 

 

 

So tell us some more about the plane you're putting together and we can all confuse you with some contradictory advice

 

[Simon UK]

Thanks for taking the time to answer guys, Peevie i am just looking a way to easily recharge my A123's in situ, the plane is a H9 Cub 40 and it's quite an old kit so no nice battery hatch like the new model has - and to be honest i don't think the new model would take a 6s a123 pack anyway. So mine will sit where the fuel tank should go, i have allready made the hatch in the top of the fuz, alas there is no way of easily opening and closing the hatch due to the windscreen having to be attached aswell.

 

Hmmph! I reckon i can keep my wiring very short for a seperate charging plug, so i am going to go for it.

 

Thanks for the advice