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P47 - Electric Conversion.

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davegrennan:
Thanks little Keith :-)

Actually I didn't choose the plane, it was given to me by a friend who started to assemble it and never finished it. But if I were to choose a jug would be well up the list anyway. I just love old warbirds, sure I married one:-) (she better not read this)

Yes I got 2x30C 5Ah 6S's. I was looking at the 8Ah ones but they were nearly double the price of the 5Ah ones. Batteries start to get pricy when you go up that end. I made some more progress this evening. Got all the control surfaces hinged up and the tail section installed.  Next trick to install the control rods and wires. The wire that came with the plane look a little flimsy, a can hear the mid air 'ping' followed by expletives so I'll get stronger rudder wire. I also need to get hold of some T connectors as the batteries came with bullet connectors.

I heard that putting a low value power resistor in series can help avoid sparking on these big lipos. Is it necessary?

Cheers
Dave.

Happy Days:

--- Quote from: "davegrennan" ---

I heard that putting a low value power resistor in series can help avoid sparking on these big lipos. Is it necessary?

Cheers
Dave.
--- End quote ---


Interesting point Dave. :D

Firstly let’s clear up a matter of ambiguity. When you refer to ‘T’ connectors I assume you mean these type of connectors.




These are actually called Deans connectors, I use them on all my Li-Po’s including my 6S packs. And yes, they can produce some quite substantial sparks, particularly when you’re trying to connect then together with cold “pingies“. I once received a rather painful burn (all-be-it from a very dramatic spark) whilst connecting my 6S pack.

The second aspect;……..


You may already know this Dave, coming from a technical background, (The angle of incidence equals the angle of outsidence. :oops:  Oopss sorry ,…the angle of refraction.) but it would not be a good idea to leave anything in series with the circuit. It would reduce the circuit voltage and would likely get rather warm unless it’s of extremely low resistance in which case it won’t reduce the sparking anyway.  ( anything that gets warm/hot wastes battery power. :evil: )

It occurs to me that you may have heard of temporarily using a Thermistor, just while connecting the two parts of a connector together. However I couldn’t think of a way of arranging a temporary way of connecting a Thermristor when using my set up of Deans connectors. :!:  So this is how I do it........



It’s a male Deans connector (The female part of the connector should be connected to the battery leads* )

On one of the leads coming from the Deans I’ve fitted a bullet connector (the positive lead in this case although it wouldn’t matter which lead was used) . I’ve fitted some heat shrink insulating covering around the female bullet connector. The insulation is slightly longer than the female connector. The reason being that the male connector has to go inside the insulating sleeve first, so any spark that may occur is shielded by the insulating sleeve. In other words it can't do any damage.
So the procedure is to first make sure that the bullet connectors are ‘open‘. Then, connect the battery Deans, and secondly connect the bullet connector. With practice, if I insert the two parts of the bullet connector quickly, there often isn’t a spark anyway.

There, that wasn’t too painfull was it? Hope it’s been of use. :)

L.K.

* Don’t try to shorten the battery leads from a Li-Po. Some of the multi core leads supplied have an insulating covering on each of the individual strands of the lead and render them extremely difficult to properly solder new connectors to. (Ask me how I know!)

Fred:
Ok, first, I have to say that I have a very limited knowledge on this electric magic things (it's magic right?  :?: )

But here is an article (translated from the French) about this sparking problem (discussed with the author while doing some researches to electrify my P47... One day!  :roll: )

http://www.microsofttranslator.com/bv.aspx?from=&to=en&a=http%3a%2f%2fjivaro-models.org%2fspark%2fpage_spark.html

davegrennan:
Hey Guys, I found where I saw the resistor thing.

http://youtu.be/CJQoUcm7okc

This makes good sense. Watch the vid, its all explained in there.  The trick is to put the resistor in parallel with the negative terminals and then disconnect the wire with the resistor installed when you're powered up. I have so big 7watt 10ohm resistors so I think I'll give this a go. I just dont like the idea of the sparks. I suppose a simpler trick is to wear a pair of rubber gloves to avoid getting burned but that doesn't stop your connectors getting carbonised.

Happy Days:
Good man Dave, go for what feels good! :D

This matter actually epitomises one of the difficulties with aeromodeling. If you ask six pilots the same question, you’ll get six different answers! :lol:

Years ago I met a guy who was responsible for building Atlas rockets. I’ll always remember he told me that, “Precision engineering, is a question of compromise.” :shock:

Keep us up to date with the rest of the build Dave

L.Keith

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