esc melt down

[mark burrows 1Participant @markburrows1]

hi models.i have built 39″ply motor cruiser,fitted johonson 600 motor direct drive,12v-4.5 amp acid battery,and el 110amp esc,no fuse fitted in line,run in my fish pond ,back and forth,5minutes then i see smoke coming out boat ,tried to motor it back but no drive,so fished it out diconnected battery and see melted esc,it  was smokin.  -where have i gone wrong anyone?

[mark burrows 1Participant @markburrows1]

help needed

[Paul TParticipant @pault84577]

Hello Mark.

 

A few questions:

 

How hot was the battery?

Was there any weed around the prop?

How did you wire the system and could you post a photo of your setup?

 

Paul

[ashley needhamParticipant @ashleyneedham69188]

Mark. I hope thye motor was 12v capable !     also, how big is your prop? as too large a prop would overload the motor causing it to draw lots of amps and fry…things.

 

Hot tip…always fit a fuse !!! (but you knew that already)

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Hi Mark

 

O dear. As with most things, you only get what you pay for – and it sound like you’ve bought a whole load of trouble here.

If the motor is the one I’m thinking of then it’s only suitable for highly-geared applications like power drills; I’d never recommend using one direct-drive in a model except maybe a Club 500-type on 7.2v, with a smallish prop. For a 39″ plywood cruiser you’re pushing the limit with any type of 600-size motor unless it’s geared down.

 

Those “110A” ESCs from China are also trouble, with practical experience showing that the claimed 110A continuous rating is more like 20A in reality. The Johnson 600 motor draws silly Amps even on a moderate load, so you’ve the perfect ESC/motor/model combination for a disaster. I’ve a dozen customers or more who’ve found this out the hard way. Add one?

As the ESC is now toast then there’s no option – it will have to be replaced. There are any number of decent ones around, but I’d advise you to buy one from a UK supplier eg ACTion, MTroniks, Electronize.  At least return or repair is possible in the event of a mishap.

 

As regards a suitable motor then the MMB900 is a versatile unit and can swing a 45-50mm 3-blade prop with little effort on 12v. See the thread on Paul Godfrey’s Sir Lancelot build. A 12v Speed 700 Turbo might also do, as long as you keep the prop down to about 40mm diameter. Avoid 2-blade “racing” props unless you have loads of power and you want a ballistic performance – in which case you should also avoid SLA batteries (the L stands for Lead, which doesn’t encourage an already-heavy boat to plane).

 

Finally, do put a fuse between the ESC and the battery  – it will prevent a fire if nothing else!

 

PM me for further info if required.

 

Dave M

 

[Mike DavidsonParticipant @mikedavidson22772]

I absolutely love that HOT TIP Ashley……………………………Mike D  and sound words from Dave too What I have done in the past is to put the speed control output to the base of several 2N3055 transistors wired in parallel they will handle the currentas long asthey are wired correctlyI think it is best to remember that the speed control introduces resistance into the motor circuit to slow the motor down, and if it has too big a job to do, the current flowing through that resistance is bound to generate heat. If you read transistor manuals, they tell you to use a heat sink in power applications and the addition of an efficient heat sink considerably increases the power handling characteristics if a transistorwhich iswhat the output stage of your ESC is you will see black fins on the unit, and they are to increase the surface area of metal in contact with the air to transfer heat away. In the electronics trade, we use a substance called thermopath a sticky white substance in tubes like toothpaste. We put this in between a transistor and a heat sink to aid the transfer of heat from one to the other. Essential in some caseslike CB radio outputs. I hope you sort this problem out, as it spoils the fun if you are worried all the time………………………..Mike Davidson

Edited By Mike Davidson on 10/09/2009 18:01:16

Edited By Mike Davidson on 10/09/2009 18:03:47

[ashley needhamParticipant @ashleyneedham69188]

It strikes me as very few modellers appear to posess an AMMETER. This is a very useful device, useful for calculating life of motor and battery before imminent destruction, or even BOAT destruction come to that.

 

It lasts a lifetime, and can be moderately useful in matching hulls/props/motors to get optimum current consumption and optimum motor performance, saves all that theorising.

 

Especially useful to suss out those “a.n.other” manufacturers motors. Useful on hovercraft motors to see the effect of doubling up on propellers to see if this overloads the speed 400 engine,   and that sort of thing.

 

Looks clever on the pond.

 

Invaluable

 

Ashley

[mark burrows 2Participant @markburrows2]

hi ashley,i have tried my multimeter to measure motor amps but meter only goes up to 10amp,so i will have a look for a car one that should have higher rating,i have now got 7.2 battery and 20 amp viper marine esc.thankyou.

[Mike DavidsonParticipant @mikedavidson22772]

  If we have any modellers who would like to measure currentin their system but can’t, I have a tip which is to use ohm’s law to fiddle the system, what I do is to get a one ohm resistor rated at 12 watts and accurate to one per cent if you can get it, note this might be a bit pricey. If you put this resistor in place of the fuse in the positive wire coming from the batteryyou can then run the systembut at this point, there will be a volts drop across the resistor, but not much more than 2, so all the boat’s facilities should run as normal. Now I mentioned Ohm’s law, this works out that with a one ohm resistor, each amp that flows will generate a volts drop of one volt, so at this point, you need a voltmeter. At this point, I must tell you that the resistor will get hot, very hot, enough to turn your skin beige brown if you touch it. Now for a little maths, and a cautionary taleIf your battery is twelve volts, and ten amps is demanded by your motorsas I said , each amp will generate a one volt drop across the resistorso maths time, ten amps means a drop of ten volts across the resistor  thus  the supplied voltage from the twelve volt battery will drop ten volts leaving only two for the poor old motorwhich will grind round exceeding slow

            Here I have explained the major down point of using a shunt in a meter, if you could get such a thing, a nought point one ohm resistor would be much better, and only lose one volt when tem amps is flowing. This is all a fundamental part of electrical theory and is in use in all branches of electronics, just ask the electricity generating board how much they lose in those great long overhead cables

                 A straw for the drowning man to clutch,  if you have a meter, even if it is a cheapie you might be able to buy and fit a shunt resistor to extend its range, it might be worth contacting the makers and asking.    

                    A last word of warning,A meter switched to an amps range has quite a low resistance, and I have seen one explode when the operator connected it to the mains And it exploded, so feel free to ONLY WORK THIS WAY WITH BATTERY POWERED DEVICES, TOUCH THE MAINS AT YOUR PERIL.               Happy modelling……..Mike Davidson.

 

  

Edited By Mike Davidson on 24/09/2009 20:06:58

[AridlandsParticipant @aridlands]

The one ohm resistor approach is not a good idea if the current is more than about one Amp as the voltage drop affects the current delivered to the motor.

Also the example of 10V drop = 10A is correct but the resisitor would be fried/burning at this point and in a 12V system the motor would only be getting 2V so the calculated result is meaningless!

Ammeters must only be connected in series with the battery lead, never connect it across a battery.  Even at the low voltages used in model batteries you can get large currents to flow…

[ashley needhamParticipant @ashleyneedham69188]

The easiest way to go is buy a proper little ammeter like the sort of thimng that was fitted to cars years ago. i bought mine only a few years ago from a fairly large supplier of model type elctricals (name forgotten now) and it was very cheap.

 

O.K, its not going to give an exact figure, but unless you are racing and need the ultimate prformance, I think a “ballpark” figure is adequate. To know your setup is drawing slightly less than 10A, be it 9 or even 8, is all you need to know if you only have a 15A speed controller, for instance.

 

In any event, a static pondside current measurement is not going to be the same as the current ACTUALLY drawn when the boat is moving, at least I assume so?

 

Ashley

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