Zenoahphobic

I was reading a very interesting closed post (RE: My aquacrat 1800KV toasted) where the poster was villified for suggesting that a bad connection caused his motor to overheat and fail- other peoplesview was it was the motor that caused it's own overheating because it was overloaded.
This appears true but not all sources of the overload were thought about; in particular the THERMAL load directly received through the electrical wires into the motor!. (melted solder 2 inches from the motor would certainly heat the motor to it not being able to handle the extra heat produced be passing electricity through it)
I have raised this thread because I am new to FE boats, that is new to Lipos, and the control and use of Brushless motors, and I seek views about the adequacy of the wires and connections used. I have a problem where these are getting very hot (yes solder melting) but motor and batteries are only warm but ESC hot but not failing!
As a newbie but not unknowledgable about electricity, it immediately struck me that the wiring and connections if used in other worlds are grossly too small - in other words I can understand with the currents used (100Amp upwards) why they are getting very hot and will eventually of themselves destroy everything within the boat including the boat. When I investigated the ratings of the components that I see used, the manufactures ratings are actually exceeded!
There is no power authority or wiring regulationthat would approve the wiring because clearly it would be regarded as a FIRE HAZARD!!!
So why is inferior wiring used in boats - because of weight and space I suspect.
Added to the problem is that the confined small space within a RC boat has to also be sealed to stop electrics getting wet, and to stop boat filling up with water.

So I ask how have people addressed this problem with wiring clearly on the edge of thermal limits. I.E have people used other wire, other connections, have they actually cooled them, not used solder (as I see solder as a thermal problem because of high resistance and low melting point, weak physical stability)? This surely must become increasingly a problem as technology increases , e.g. now have 400Amp ESC's

sundogz

There is no question that too small connectors can cause heat failures as well as robbing you of top speed. I use 8mm connectors on any 5000mah and above lipos, and am changing (from inefficient Deans) to xl60 for smaller batteries. If your connectors are getting hot, you're not getting all the power available.

Von Ohain

Wiring is typically not inadequate in my opinion.
Of course that is a can of worm in itself, so my opinion is based on that "fire hazard" question.
Wires used in hobby applications is typically silicon insulated wires, while wires for permanent installation in your house is typically PVC insulated.
Silicon can handle a lot more heat that PVC.
Another aspect is that your hobby application has very little time in use, most of the time is just standing on the shelf.
Your household wires is in use 24/7. Thermal breakdown of the insulation doesn't have to be catastrophic at a given temperature.
It can also degrade slowly over time at a lower temperature which is acceptable for our hobby boats, but not acceptable in a permanent electrical installation.

And another thing to remember about household installations is that wire lengths is much longer. Therefor cables need to be thicker or the voltage drop over the cable would be unacceptable.
In out hobby applications we typically has just a few centimeters of wire, which means we can have a much greater voltage drop per meter than household installations, without having a problem.

sundogz

I agree. It's usually not a problem of wire gauge or insulation, it is undersized connectors which have a higher resistance than the larger connectors. The connectors heat up the wires and motor, sometimes causing the solder in the connectors to melt and the connection to fail completely. I have seen where some people are using silver solder (higher melting point) to remedy the situation(!), but the correct fix is to size your connector accordingly. A properly sized connector may look over-sized on the wire, but keep in mind that 'adequate to over-sized' is good, undersized is bad. No gray area there!

Von Ohain

Yes, that, or bad solders.
Tin solder has a lot more resistance than the wires themselves, and this is a problem with connectors that is tricky to solder with a good contact between wire and connector (deans, for example).
The deans connector itself might be taken way past 100A without any problems, if you got a good solder.
But actually getting a good solder on a deans style T is easier said than done.
Having a higher cross section on the connector than on the wires themselves makes little sense.
Which in fact means that you can go quite extreme with just a humble 3.5mm bullett connector. And it works, as long as toe solder is good.
Putting in 8mm bullets, which I see someone do makes no sense unless you are pulling 1000A. My tip to those using that is just: learn to solder.

Old Sloppy

larger connectors can reduce resistance in the circuit.
larger guage wires allso reduce resistance.
If you are melting solder your wiring needs upgraded.

Harry

sundogz

1000A on 8mm connectors? Last time I checked, 8mm was good for up to 250A. And I wouldn't recommend Deans connectors be used over 60A. We simply have not had the same experiences.


Harry, I totally agree - if by upgrading you mean larger connectors! LOL

srt10

My Feedback: (20)

that makes no sense to me if the wires are cool to the touch...
the biggest issue I think and have woeked with is bad solder connections..
I clean up all my connections even on my battery packs to make sure the solder job is nice an clean, and it dones make a big difference IMO

Zenoahphobic

It seems 60/40 lead tin solder and soldering to bullet connectors the weakest link. The bullet connectors I have seen require in effect the wire to be loosely fitting susspended in solder. Additional solder is required for larger and looser connectors, adding to the affect of additional resistance in the joint.
Does anyone know of any other system used to tightly screw or crimp etc in R/C boats?
Another thought, has anyone actually simulated and tested a setup . say applying many amps on a bench and checked with thermometer various sizes etc. (i.e a bit more scientifically)?.

*delete M i k e u p delete*

Message gotten.

Von Ohain

SRT10 is right, resistance is highest where the heat develops.
If the soldering is whats getting hot, the wires isn't your problem.
And neither is the connectors.
Its the solder itself.

If you haven't had the same experiences sundog, then just do some proper solders and test again.
Or just do the maths.

srt10

My Feedback: (20)

I know in my UL-1 I have the stock 3.5mm connectors on the motor and they don't get all that hot after I took them all apart and did my own solder job
now my boat runs 52-53mph with those little connectors..
anyone ever seen the gauge size on a UL-1 esc?
they are small....... and the wires do not get hot.......

sundogz

I don't have overheating connector problems since I went to larger connectors. But I can tell your mind is made up on this subject. Happy boating to you!

Von Ohain

Yes my mind is set because the reasoning here behind how to solve heat problems in connectors doesn't add up with science.

Heat develops where resistance is greatest, as per (Where P = power, I = current and R = Resistance):
P = I^2 * R

Resistance is greatest where either cross sectional area is small, or resistivity is great, as per (Where R = resistance, � (rho) = specific resistivity of the material in question, L = Length of the unit in question in meters, and A = area of unit in question, in square meters) :
R = � * ( L / A )

Substituting R in the power equation yields:
P = I^2 * � * ( L / A )

And as you see, for a given current and length of conductor, the only factors dedicating heat loss is resistivity and cross sectional area.
The connector itself is made of copper or aluminium, which has very low resistivity. The cross sectional area of the connector is larger than the wire.
Hence, the connector has less resistance per length than the wire itself. No problem there.

However, the tin used to solder the wire to the connector both has less cross sectional area than the connector (come on, how much thin do you use?).
And the resistivity of tin is much higher than for both aluminium and copper.

And bobs your uncle, mathematics tells you that you need to do proper soldering, not swapping to larger connectors

Goldenduff

Unless swapping to larger connectors enable you to solder better and increase the area of the solder....!?!

Von Ohain

Sure, Goldenduff, and thats what I was saying in my first post: Learn to solder.

Higher contact area (cross section) between wire and connector pin is better.
Smaller distance from wire to connector pin is better.

You can make Deans style T work incredibly well if you simply can make a good solder.
But Deans style T has a rectangular pin, joining to a round wire.
That doesn't automatically make good joints unless the solderer is giving this a thought.
And thats also why so many people has trouble with Deans style T.

Zenoahphobic

It's suggested using a plug with greater (surface) area than the wire being connected to it senseless.

I looked at some specifications of different bullits and the Amp increase capabilityis not proportional to the apparent increase in diameter (surface area increases by the ^ 2 of diameter) - changing from 6mm to 8mm only a 30 Amp increase in one example! .
I guess going to "oversize" bullits is advantageous to have surplus capacity because no doubt overtime, with the plugs being taken apart and reconnected, warpage and cleanliness will gradually deteriorate the available "surface" of the connection.

Not mentioned is the importance of the tension or the pressure of the physical connection, which overtime will also deteriorate.

I am leaning towards using a soft silver solder (lead tin silver alloy)as silver is more conductive, 10 AWG wire and 6MM plugs for a 200 Amp system.
I'll try to measure resistance, however multimeters ohm not low sensitive, need to setup a large current and measure voltages across and perhaps extrapolate to calculate actual power consumed (wasted) - to determine if acceptable

sundogz

LOL, are you suggesting that? Consider that stranded wire has a very large 'surface area'. 6mm bullet connectors are not rated for 160A use. If you are that concerned, just solder the wires together, you don't need connectors. You know, 8mm is only about the size of a pencil eraser. Is that too big? I think not. But of course, you can do whatever you want (silver solder, 10AWG wire, etc) if it makes you feel more comfortable. I'm just not sure if you are looking for advise, or just want to stir up some excrement. BTW, you're welcome.

Von Ohain

Well, as proven by common sense, and now also by maths, having connectors with a cross section larger than the wire itself doesn't make much sense.
So unless you got 50.26mm² (that is 1 AWG) wires, then 8mm bullett is overkill.

sundogz

So Von Ohain is saying that using a connector that is larger than the wire is overkill? Don't try to sell that to someone that races boats or pushes them to the edge of failure. LOL, you haven't proven anything to me. It is easy to sway the ignorant and gullible. This would all be hilarious, except that some newbies will now have to find out for themselves the hard way. Nice work there, Von Ohain

Von Ohain

Maths is always wrong, sundogs is correct.

Goldenduff

No don't go in a huff Von Bain!

Old Sloppy

This is true IF all conections are clean and properly soldered or grease ( residue from your flexcable you just lubed) contamination is not present.

This does not happen at all times, sometimes fingerprint oils can be existant on said connectors.

Many times connector prongs have low tension, microscopic corrosion (fretting) or carbon build up resulting in a 8mm connector acting like a 5.5mm connector.

To compsenate for "real life conditions" does make sense.


Harry
from Atlanta

siberianhusky

Von Ohain question,
What ever happened to the 20$ 50000amp home brew esc's you were claiming you could build? You went on about them enough what happened to them?

Von Ohain

It finished as a B. Sc. thesis at school. You'll find it on the online bachelor database of my university college, http://www.hekta.org/~hpe1116/
It ended up being built up from scratch, also with homebrew firmware for the µC, written on behalf of an external customer.