cable gauge

[Tim MoodyParticipant @timmoody76107]

[Tim MoodyParticipant @timmoody76107]

I have a speed 400 motor that I need to solder the cables onto so that I can connect it to the speed controller. My question is what gauge cable do I need for this?

[Dave Cooper 6Participant @davecooper6]

Hi Tim,

Assuming you've already got an ESC that is suitable for your motor, I would go with the wire gauge on the ESC inputs and outputs, These are likely to be on the 'conservative' side and should be fine. If in doubt, go up a little in gauge.

Rig up a bench test with motor, battery and ESC and check if things seem OK. A little warmth is to be expected but nothing should be getting too hot to touch.

There are mathematical formulae for all this, but, good 'old-fashioned' common-sense will surely prevail.

Come back if things don't seem right…..

Cheers,

Dave

[Ray Wood 3Participant @raywood3]

Hi Tim,

Normal domestic flex cable will do for a 400, but I would tin the ends with soft solder.

Regards Ray

[David Marks 2Participant @davidmarks2]

Tim – On the main MB website under "Features" there is an excellent article entitled "but I don't understand Electronics" by the late Dave Milbourn. I am pretty sure that within that article you will find what you are looking for. Dave was a well respected authority on many aspects of Model Boats including electronics.

[Richard SimpsonParticipant @richardsimpson88330]

Tim ideally you should know what the stall current is for your motor. Easy to say but not always easy to determine.  You need to hold the motor rotor still while applying voltage and measure the current drawn, not something many of us like to do.  If you do then it should be very brief but that will give you the stall current.  You can also measure the current on normal load with a meter and multiply it by a significant amount, starting current is usually seven times full load current and stall current even higher, or speak to the motor manufacturer if that is possible.

As Dave suggests useful guidance is to go by the speed controller cable. To give you a bit more of an idea if you refer to the silicone cable specifications available from Component Shop you should be able to get a good idea. I'm sure a chat with them will also lead you in the right direction. I tend to go for silicone covered cable as it is nice and flexible and so easy to fit so I keep a couple of coils of it in my box.

At the end of the day a Speed 400 motor is not a high current draw so as long as you are generous I'm sure you will meet the needs easily. As Ray suggests domestic flex should be way over what you need and easy to get your hands on a piece. It doesn't need to be kettle flex though!

This is worth having in stock:

Silicone Cable

Edited By Richard Simpson on 16/02/2023 09:22:16

[Chris EParticipant @chrise]

Buy several different colours & use them. It is much easier to sort out any problems if where each wire goes is obvious – & I speak as the guy who many years ago rewired an whole motorcycle with old British electricals in black cable and only black cable.

Edited By Chris E on 16/02/2023 11:00:17

[ashley needhamParticipant @ashleyneedham69188]

With Ray here. Domestic lighting flex good enough for a 400. Cheap, found in most garages, pretty colours….

Ashley (fit a fuse….top tip)

[Ray Wood 3Participant @raywood3]

Hi All,

As Richard says Silicone cable is the business, I wouldn't use anything else in my aeroplanes which are brushless with big Lipo's , I have not yet used a brushless motor in a boat yet !!

Electric flying is expensive my 62" Hawker Hurricane has just cost £320 for the power train !! I may go back to 4-Strokes of which I have plenty

Regards Ray

[Tim MoodyParticipant @timmoody76107]

Thanks for the help, flex it is then. I am aware that people use car fuses with spade connectors but what size fuse would I need for the 400 motor and a 2S battery? One last question is it best put in the battery circuit or the motor?

[Chris EParticipant @chrise]

You are going to get very divergent opinions about this. In the past several people have said that they don't use fuses at all but I always do.

How many fuses depends on the model. If it is simple – one battery one esc and one motor and nothing else then I would put it next to the battery. If the model is more complex – multi motors etc then I would add a fuse between each esc and its motor.

The size of fuse again depends on the model but it should never exceed the safe max load of the esc. Whether you want it to blow if the motor is stalled is up to you.

Edited By Chris E on 16/02/2023 12:36:28

[Colin BishopModerator @colinbishop34627]

I go along with Chris E on this. I size my fuses between the motor full load and stall current. Weed round the prop can slow the motor down and it can still get hot despite not being fully stalled.

My thinking is that if the normal full load current is being exceeded then there is something wrong that needs to be sorted. (the speed controller should of course be sized to substantially exceed the full load current and ideally the stall current)

But, as Chris says, there are different views…

Colin

[ashley needhamParticipant @ashleyneedham69188]

Female flat connectors and car blade fuses, so easy.

I would fit a fuse the same rating as the esc, or a bit less. A 400 won’t take much current. A bunch of fuses is cheap.fit a 10A one and thrash the boat by the jetty, if it blows, try a 15A one etc etc.

A wattmeter is a handy thing and cheap. Tells you all sorts of stuff and in the case of our air-prop devices, can tell you what prop is best regarding current draw against speed out on the water.

Ashley

[Chris EParticipant @chrise]

If you own a multimeter then they usually have a setting for up to 10A which should be great for a 400 and you can measure the voltage under load. A wattmeter is obviously better but if you own a multimeter it will do the job.

[Richard SimpsonParticipant @richardsimpson88330]

It's the current you want to know Chris. I agree with you that the fuse should be rated somewhere between the full load current and the stall current. I would rather have a fuse blow than have stall current go through the system for any length of time. Usually when something is wrapped round the propeller. I also tend to have the fuse lower than the rating of the sped controller, although some ESCs nowadays also include cut out functions.

I know many don't bother but I've always had a good quality multi-meter. I use it for domestic fault finding, model railway use, vehicles and model boats. Fluke is recommended by many electrical engineers and while seeming expensive at first, should last you a lifetime. The trouble is a standard multi-meter frequently will not measure current so you will need to buy a multi-meter and a clamp meter. For model boat use though you can now get simple cheap in line ammeters that remember peak current so are perfect for checking out what a motor is drawing.

[Chris EParticipant @chrise]

Posted by Richard Simpson on 16/02/2023 13:42:13:

It's the current you want to know Chris………

I agree and that is what the 10 amp capacity that I referred to will measure but I also like to know how my batteries are doing (both as a pack & individual cells) which the voltage under load helps with.

Edited By Chris E on 16/02/2023 14:53:43

[ashley needhamParticipant @ashleyneedham69188]

£18 from component shop, a ‘up to’ 150A wattmeter. No guessing. A must have. How I managed for so long without one I don’t know. My life has been transformed etc etc.

Ashley

[Richard SimpsonParticipant @richardsimpson88330]

Posted by Chris E on 16/02/2023 14:49:13:

Posted by Richard Simpson on 16/02/2023 13:42:13:

It's the current you want to know Chris………

I agree and that is what the 10 amp capacity that I referred to will measure but I also like to know how my batteries are doing (both as a pack & individual cells) which the voltage under load helps with.

Edited By Chris E on 16/02/2023 14:53:43

I once had a lengthy argument with an old chap in a model shop who had sold me a battery from a bargain bin but it wouldn't hold charge when I got it home. He stuck a cheap voltmeter across it and tried to tell me that because the voltage was fine the battery must be fine. I told him you have to measure the voltage under load to get a more accurate idea of the condition. He wasn't having it. Eventually he starts shouting at me until his wife comes out and asks what is going on. He got dragged off by his ear and I got my money back.

[Dave ReedParticipant @davereed72029]

Richard,

I guess the clue was in "bargain BIN"

Dave

[Richard SimpsonParticipant @richardsimpson88330]

Posted by Sinking Feeling on 16/02/2023 23:19:00:

Richard,

I guess the clue was in "bargain BIN"

Dave

He obviously didn't explain it properly!

[Author]

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