djmcnz

Not quite on the money. The higher the resistance, the high the heat - heat isn't directly related to current. Resistance is proportionate to length and inversely proportionate to the cross-sectional area of a cable.

A "better" (lower gauge) cable will take more more current without overheating not because it dissipates heat any better (in fact it would be worse - surface area/mass) but because it generates less heat because it has lower resistance (for a given length).

#1
Quick answer is "if nothing's getting hot, cables/wires are okay". There's no point in "increasing" the cable gauge (thinning the cables out) you will get no benefit (okay a few gm's of weigh), only loss. I may not have understood the question?

Motor -> ESC = 18AWG & ESC -> Battery < 18AGW and you would like to swap out the ESC -> battery cables with smaller ones?

Nope. Can't think of a reason for wanting to do that unless it's for aesthetics but then you wouldn't mention laps times in the same sentence...

Don't swap in thinner cables. If you want to reduce overall resistance use shorter cables (of the same or lower gauge).

Either way, given the low loads of a Mini it will make no appreciable difference to your lap times assuming the car is basically maintained, and I assume that's not an issue for you.

#2
Quick answer is "when they're loose" which translates to "before you run the car". But this may not be an option. If you are required to use Tamiya connectors you need to be aware that:

They are very high resistance and only get worse. This can be measured with a Ohmmeter pretty easily. You'll also see resistance rise over the course of a single pack (albeit marginally).

So, you're starting from a poor position but if everybody is using them then you're relatively fine. So the objective with Tamiya connectors is to simply keep them with as low resistance as possible. They will never be Super Conductors...

Rule of thumb: If they're never warm they're making no difference to your lap times! So don't bother changing them.

However, if they do start to get hot then you should replace them. If they're always hot (i.e. from new) then you're overloading them and need alternative connectors or shorter wires or shorter runs or less motor.

You can do a quick inspection:

• Wire near connector going brown - replace connector
• Connector discolours, deforms, melts - replace connector
• Corrosion visible inside female socket or outside male socket - replace connector
• More then a few mm play when wiggling the wires when connected - replace connector
• Fire - replace connector

Other than that there's little value in replacing them like-for-like. And even in a worse case scenario, with a silver can you're probably talking 10ths of a second over a 25 second lap, not full seconds.

Hope that helps, if not I'm happy to try and clarify.

niznai

Ahem. The higher the resistance the lower the current, the lower the heat. Anyone who has ever charged a battery knows that. Heat is directly proportional with current, my dear. The dissipated power of a resistor is not the same as the electrical power (i.e. consumed power). That's one reason you have power ratings on resistors.

What you say about cross section and length is true, but you got it wrong as soon as you tried to apply it, because a wire with the same cross section area, but a higher strand count ( i.e. a smaller strand cross section) increases the surface area per unit of length which is what helps disperse heat more efficiently and faster (that's why heatsinks are large surface aluminium things). Ergo, a better wire does carry higher currents which generate more heat, but a better wire (higher purity vesicle free copper for instance) is efficient at dispersing it to the point of a steady state, at a lower temperature than a poorer wire which not being able to disperse the heat as effectively, will reach a steady state (if at all) at a higher temperature with potentially adverse consequences.

You know the basics, but applying them was completely arse-about.

Granpa

Thanks for the replies. This is what I understood from your posts. The wire to the motor is the limiting or determining factor. That as long as the wires to the battery and esc are larger in X-section than the ones to the motor, it should be okay. It also leads me to believe then that using 12 gauge wire isn't of significant advantage over 18 providing that the motor leads are smaller. Is this correct????????

Wanted to use the smaller gauge wire cause it's so much easier to work with and, yes, cause it just looks better to me. Having these huge, clunky looking wires hanging all over my car ------. Painting and wiring are just not my favorite things to do.

mariob62

iTrader: (2)

The motor leads are 16 gauge. You will lose a little punch with 18 gauge, since a silver can will draw 70 amps or more on start up.

I've done dyno tests with diiferent gauges & 18 gives less torque than 16, but it evens out once the amp draw is below 10A. The major drawback to 18 is that it is more fragile when using the plugs; don't have to break too many strands to get into problems. If you hard wire the motor 18 is adequate, if you keep the leads short.

The plugs are OK with a little care. Solder the joint after crimping on the plug. Squeeze the female end of the plug to tighten it & put a little silicon dielectric (AE ball diff grease will do) on the plug to prevent oxidation.

djmcnz

Perhaps it wasn't intended but your reply sounds condescending, and a little insulting. Nevertheless I thought a reply was justified, however off-topic, because I really do think almost everything you said in that post was factually and scientifically inaccurate. Perhaps I've misinterpreted it?

Your theory: "The higher the resistance the lower the current, the lower the heat." Do you really believe this?

The science: the higher the resistance (R) in a cable, the less current (I) it can carry without increasing the heat (H) generated - which you'll see doesn't match yours.

Illustrative examples:
1. A Superconductor has "0" resistance and generates "0" temperature change along it's length (likely in a circle) when suitable current is applied (e.g. A MRI machine can operate in a hospital forever without melting).
- By your logic a Superconductor will generate ~infinite heat? (Lower R = Higher I = Higher H)?

2. A toaster or light bulb demonstrate the opposite. Apply sufficient current to a sufficient resistance wire/cable and you will generate Joule heat and other outputs (like noise). "Sufficient" here means rel.Ohms > rel.Mhos.
- By your logic a toaster and light bulb run cold? (Higher R = Lower I = Lower H)?

For discussion's sake, voltage can remain constant.

Both if these examples disprove your logic. Yes, higher resistance will lower current and separately (i.e. in a separate formula) lower current will generate less heat (at a fixed resistance) but they do not have the causative relationship you claim them to. The mistake you've made here is that you're not factoring in how the current is reduced when resistance is applied and where that (excess current) energy goes. It doesn't stay in the battery as you apparently assume, and it can't get to the motor... so it gets dissipated as heat. "Ergo" in the application we're talking about resistance = heat. Less current draw can mean less potential heat sure, but we can't feel, see, recognise or shouldn't even care about potential heat. It needs to be actual heat for it to matter and it's resistance that turns that energy into actual heat. And in RC we always want more current, not less so that's not a lever we get to pull. Resistance is.

So this (abridged) statement doesn't change:

And I'm sorry but to believe that cable wouldn't get as hot simply because it's bigger and can therefore dissipate heat quicker is really a little naive. Contrary to your expressed opinion a thick piece of copper cable will cool slower than a thin piece at a constant ambient. Get some 22AWG copper wire and some 12AWG copper wire or cable and put them both in the oven at the same time at say 180 degrees C. Take them both out after 20 mins, wait for the 22AWG wire to cool just enough to touch and then pick them both up at the same time. Post back here and tell us how big the burn is on your hand from the 12AGW cable which will still be very hot. Your heat sink logic is invalid because in a wound copper cable the total cooling surface area != the sum of all of the surface areas of the individual strands... some are touching each other remember!

---------

Most importantly, that was ultimately a departure from topic and, however it was arrived at, my original conclusion and advice was accurate with respect to what was asked.

djmcnz

Yep, totally correct assuming you're only running servos and a motor (which you are). The logic changes a little if you hang more stuff off (like lights, MFC's, extra servo's etc) but that's not relevant in this application.

As a rule of thumb I use singe gauge all through but if I were to change them up a little I'd do so only by small margins, i.e. 18+16 or 12+14 but not 12+18.

rccartips

iTrader: (3)

Hi, been running the same stock tamiya battery and motor plugs for about 40 battery packs. To me no noticeable difference vs deans/hardwire/thick cable on the track. Occasionally need to crimp the motor connectors to keep them snug. This is with Tamiya 2400 nicad and 28T motor.

djmcnz

I couldn't agree more. A Tamiya connector will work fine on a 1.5kg touring car down to about 15x2. And although they have more resistance than other connectors it would be very marginal on lap times in a Mini, if anything at all.

Having said this, if you have a soldering iron and it's allowed then Deans (brand) connectors are far more reliable for the piece of mind, especially if you have expensive electronics.

djmcnz

So anyway, now that I have sufficient posts I can actually show you my Mini's. I'm very proud of them although there's nothing particularly special about these ones! I'm just enamored with the scale look of them and I quite liked the different builds and the various differences.

All are build with bearings and socket screws, the silver and gold wheels are real alloy and the M-05 is a blue 'Pro' with almost every conceivable Hop Up.

These ones have actually been built for a special display project but since I've pretty much fallen in love with them I'm going to get one to run (somewhere and with somebody I hope lol).

The British Icon
M-01 chassis with M-03 "Racing" body with incomplete decals and real alloy wheels (gold anodised)



The Italian Job
M-03 chassis with fog lights, extra decals and real alloy wheels



The Full Monty
M-05 Pro chassis with almost every conceivable Hop-Up and M-03 Monte Carlo body



Complete Set





Hope you like them.

SirSwiftAlot

iTrader: (11)

HOLY JESUS !!! Someone please start a thread on wiring resistance to horsepower loss and heat index control PLEASE. This is absurd. How about this!!!! Run the damn wires that came with the speed control. Or better yet run consistently enough to tell the difference between 18 gauge and 10 gauge and I will personally fly to where you live and buy you a cocktail and a lapdance for your intense research and results. Grandpa you damn shit starter Ok anyone looking to sell a KO controller?

djmcnz

I do live in Amsterdam, so the offer seems somewhat appropriate.

tony gray

iTrader: (7)

Brandon...Thank You.... for a while there I thought I'd subscribed to an electronics message board instead of an r/c one...

superspeed

iTrader: (5)

nice minis

lots of blue parts on the m05

niznai

That's OK. I thought your answer was condescending too.

Here you go. Run this test.

Plug in your powerpoint at home your favourite heater. Read then the resistance on the appliance, or work it out of the power rating given on the appliance.

Plug in another heater of lower power. Read/calculate the resistance of the appliance.

Compare the two. Relate with which delivers more heat. My money says it is the heater with the lower resistance.

Done.

You still think about the whole thing arse about because you start from superconductors. We don't have those, and Ohm's law does not apply there. That makes your example irrelevant.

You can not apply current to anything. You can apply voltage. The current will be chosen by the consumer according to Ohm's law (which you apparently don't know exactly how it applies). If you want more current, you need to increase the voltage. That will indeed generate more heat, but we have strayed already from the conditions imposed by a battery in a R/C car where you can not have more than whatever the battery gives you.

If you ever measured a toaster and or a bulb you would notice they have a very low resistance (actually, a 100W bulb rated at 240V would have to have about 0.4 Ohm resistance. That's very low by any standard). You really need to get your science right man, but start with the facts first, if you want to keep any semblance of credibility.

I take your point though about the effective cooling area of a larger cross section of a multistrand wire. You might be right there, but I think some constructive desings are better than others at avoiding that (i.e there are wires with more than one core).

Your idea of experiment though is wrong. I would run that experiment not by heating the wires from an external source, because if you remember I said the wires will reach a steady state and I guessed the thicker wire will reach it sooner and at a lower temperature. What you are proposing is to forcibly bring the wires at the same temperature with an external source of heat (your oven). I am betting that in real life, (i.e. wires building up heat only under their current load) the thicker wire will not heat as much at the same current.

monkeyracing

iTrader: (10)

DUCK! Swifty's gonna blow!!!