Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Davenotdone on January 26, 2013, 09:15:35 pm
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Hello gents. My setup is as follows. Small tug ( 24inch in length ) 6v 4.5amp gel cel battery, MFA 385 motor turning a scale 30mm brass 3 blade prop and a Mtroniks 15amp plug and play speed controller. Everything works fine but on my last sailing the one of the two motor mount screws came undone and jammed against the prop shaft coupler and stalling the motor. My son did'nt really know what was the problem and kept the transmitter stick on full throttle. Hence the release of the dreaded ' black smoke ' one duff motor and it even melted the motor mount!! The model at this stage is not fused and i notice that Mtroniks suggest a 10 amp fuse between the battery and speed controller but i was thinking of putting it between the speed controller an the motor. I can understand Mtroniks view so that the battery wires are not crossed to the speed controller but as i am using Tamiya type connectors this is not a problem. So if you gents can give me an idea of a spade type fuse and where to put it i would be most obliged. Regards, Dave.
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Good practice is to have one fuse close to the battery, conventionally on the positive lead, and another between the speed controller and motor. The first one protects the entire electrical installation against short circuits and the latter protects the speed controller from problems with the motor. Fuse ratings should be just above the normal on load running current taken by the motor(s) as anything above this is likely to represent a short circuit or stall condition. Fuses cost just pence, new motors/speed controllers cost a lot more as you have discovered.
Colin
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One fuse in the positive side of the battery to esc, nothing else is required, any fault current regardless of its cause has to pass through this wire.
Nick
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Question now deleted as I've figured it out myself! :embarrassed:
Dave.
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Dave....my electrical or electronic knowledge is limited :embarrassed: ....however in questions such as these I try to consider the electrical circuit as a hydraulic fluid circuit
So from this I see two areas of concern
1. we need a relief valve on the discharge side of the pump O0
2. we also could use to our advantage a second relief valve on the input side of the componet that could suffer an overload >>:-(
This is why British, American & Australian naval forces utilize ETS [electrical trades] people to look after hydraulic systems.....
I rest my case %) .....Derek
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Thank you all for your help in this matter, I think i will go over the top and fit 2, one from battery to speed controller and one from speed controller to motor. If and when i finish my model i hope to post finished pictures. Regards, Dave ( not ever done )
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If there is more than one fuse in the chain, they should never be the same value. If they are, they tend to take it in turn to blow. The battery fuse needs to be between the maximum motor current and the current rating of the ESC. A motor fuse is really redundant on a single motor setup, but should be of a lower value than the battery side fuse. With a single ESC and multiple motors, fuses make sense because a problem causing one fuse to blow will leave the remainder working and give a chance to drive the boat back. In a single motor setup, in the event of a fuse blow, you are left with the model safely drifting away into the distance. Just something extra to go wrong, and best avoided.
Most modern ESCs have current limiting which provides enough safety, there have been stories of ESCs burning, but that was invariably due to an internal fault within the ESC and no battery fuse.
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Thanks for that, so are you saying that i should fit one fuse between the battery and the speed controller and let the speed controller deal with any problems with stalled motor / weeds around the prop etc? IE the speed controller will cut out the power to the motor? I don't have a problem with a model drifting away as i usually run my son's two boats at the same time and at Stanley Park ( Blackpool ) there are usually helpful people rowing around on it anyway who could retrieve it ( hopefully ) Regards, Dave.
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Thank you all for your help in this matter, I think i will go over the top and fit 2, one from battery to speed controller and one from speed controller to motor. If and when i finish my model i hope to post finished pictures. Regards, Dave ( not ever done )
You won,t be going over the top. I fuse all my models like that.
Better safe than sorry. O0
john
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Thanks for that, so are you saying that i should fit one fuse between the battery and the speed controller and let the speed controller deal with any problems with stalled motor / weeds around the prop etc? IE the speed controller will cut out the power to the motor?
The ESC won't cut out if the motor stalls, it will carry on until the battery fuse blows.
Although coming from a model aircraft background where we don't fit fuses, as it's highly unlikely an aircraft would ever need a fuse.
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Usually, the ESC senses when it is getting a bit too warm for comfort and reduces power delivery. Blowing a fuse does leave the boat drifting, but without a motor fuse, using a bit of good sense and gentle reversing can unwind what has been picked up, entirely if you are lucky, enough to limp in if not quite as lucky. Of course, if its a bit of discarded fishing line thats been snagged, the boat might be effectively anchored.
The purpose of the battery fuse is to protect the boat from misbehavior in the ESC.
On Stanley Park, you do need another boat for rescue - it is surprisingly deep in places, and much of the bank is inaccessible. A mate of mine once claimed to have cured some warts on his hand after trailing said hand in the water while his girl friend was rowing him. Down at Fairhaven, we have been pretty much weed free the last few years, its a "no fishing" lake so relatively few lines left, just feathers at moulting time of year.
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In all my models I use only one fuse, fitted between battery and ESC. What is really important is the fuse RATING. For example, for an ESC rated at 15 Amps, I use a 10 Amp fuse. For an ESC rated at 20 Amps, I use a 15 Amp fuse. Using the auto-type spade fuses, I have not had any problems. (Touch wood). Pete
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Thanks for that, so are you saying that i should fit one fuse between the battery and the speed controller and let the speed controller deal with any problems with stalled motor / weeds around the prop etc? IE the speed controller will cut out the power to the motor? I don't have a problem with a model drifting away as i usually run my son's two boats at the same time and at Stanley Park ( Blackpool ) there are usually helpful people rowing around on it anyway who could retrieve it ( hopefully ) Regards, Dave.
The one fuse will blow if there is a problem with a stalled motor or ESC, the ESC is a switch for the motor current, an analogy is the circuit for your light in a house, the fuse is located at the source of power, the switch only controls the current to the switch, (a light dimmer is the same principal as an ESC), there is no fuse after the switch. A fault anywhere in the circuit will cause the fuse to blow. There are certain circumstances where a second fuse is prudent as has been mentioned but not necessary in this case ;)
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Thanks to you all again for your advice in this matter, it has all just become clear ( a light bulb has just come on in my brain...hmmmmm? i wonder if i should fuse that as well?)
Regards, Dave.
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There was a boat on ebay recently that must have had a a dozen 'car blade' type fuses in it all on a neat board, made up with 1/4" spade connectors.
( Rather annoyingly, I can't find a pictures of it now! ) >:-o
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These are handy .......
http://www.ebay.co.uk/itm/1-x-SELF-STRIPPING-INLINE-STANDARD-BLADE-FUSE-HOLDER-SCOTCHLOCK-TYPE-ATO-SPLICE-/200682858628?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2eb9a16884 (http://www.ebay.co.uk/itm/1-x-SELF-STRIPPING-INLINE-STANDARD-BLADE-FUSE-HOLDER-SCOTCHLOCK-TYPE-ATO-SPLICE-/200682858628?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2eb9a16884)
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I have gone for the ' mini ' ( small ) type car spade fuses complete with leads. I will just fit one 10amp between the battery and the speed controller. Thanks again for all your help, regards , Dave.
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Hi Dave, could you post a photo of your fuse set up please when it's done. It's something I need to do and a picture paints a thousand words as they say.
Ta, Chris M
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I would like to join in this debate having just taken my model out of the bath where it is blowing all but 15 amp fuses.
I am using a 6volt 4.5 amp battery running a 600 motor through a Viper15 ESC. As the recommendation is for a fuse 5 amp less than the ESC I am concerned.
I am using spade type fuses in those neat little clips and have one very close to the ESC
Any help would be appreciated.
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A little more info would help us help you.
Are they blowing as soon as the system is switched on?
Or as soon as a motor is turned?
Or when run at full power for a while?
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If it is one of the cheap Johnson motors it could well draw that sort of current.
Ned
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Hi Guys,
Thanks for your quick replies, the motor is a Venti 600 and it appears to blow after it has run within a minute. The power leads from the ESC to the motor feel quite warm.
The system in this model worked fine with this ESC with a Futaba 40 system, however I have now changed to a 2.4 GHZ and the problems seem to have arisen since then.
Thanks for your questions
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Nothing to do at all with changing to a 2.4 set up.
WOA hang a Mo just looked up the specs on this motor and Boy oh boy that is one heck of a currentr HUNGRY motor.
Right then for starters it is rated as a 12amp draw so if you have been putting in a 10 amp fuse I am NOT at all surprised that you are blowing them and if the cables are getting hot Maybee they are far to thin.
Another thing that really concerns me is that the esc you are using is to small and you are on the edge most definatly of the dreaded acrid BLACK SMOKE and If I was you I would either change the esc and the cables as BOTH in my humble opinion as to small
Dave
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Thanks Stavros
The boat is a Fairey Huntsman (wooden variety 36" long). The prop is a 2 blade x35.
The motor is of dubious origin and at least 10 years old. If you think that's the problem then I have no hesitation in changing it to perhaps a Graupner 500 or similar. She's a heavy beast and I just want to get her up on the plane. :-)
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This depends on the exact type of fuse in use, but your description sounds like they are 'general purpose'.
In which case at 12A a 10A fuse would last a long time - probably many hours. If it's a 10A lasting a minute I'd think you were pulling well over 15A and maybe nearer 20A. A 15A fuse could well handle 20A for several minutes at a time, and given you would probably slow down every so often while on the lake you might never blow it.
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Chris I wouldnt borther with a 500 as it is far to small for that boat Personally I would as Alan Debsnall's advise and go brushless I wouldnt hessitate as they are far more efficient and draw a lot less currecnt than a ordinary motor and TBH with you you are going to need a bigger speed controller with a larger motor anyway.Alan will put you right on a motor and speed controller....just Pm him
Dave
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Chris
on my huntsman I use a suppo brushless A2814/6T 1400kv outrunner
on a 70 amp boat esc with a 2 blade 40mm x type prop and a 30 amp fuse
in-between batt & esc.
It flies on 8.4v( I dare not try it on 12v) you have to be gentle on the turns
It replaced a Graupner speed 700BB
john
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Thanks John/Dave - suggestions sound great - too much vino tonight to get my head around this so will have to wait until after church tomorrow morning ;) but just the sought of advice/expertise I was hoping for, I really appreciate it.
My thoughts are that I get a larger ESC and see how she performs.........
Cheers - Chris
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A bit late coming in again, but Stavros has got it right. There are many types of 600 motor and most of them are very current hungry. As other members have advised, either go for a higher rated ESC and fuse, or go brushless. Pete
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Thank you for the advice I just cannot understand what has changed. It all worked last year, same motor same battery same ESC and 10 amp fuse. The only 2 changes are prop size and R/C.
Never mind I will start by changing up to a 25 amp ESC, would seem a cheaper and simpler option. Never seen her on the plane, can't wait.
Thanks again Chris G
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You changed the prop? That just might be the problem then. What was the previous prop?
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Hello Mike
In my ignorance I thought a bigger prop made the boat faster. It had a big 3 blade job around a 40 I think. I was advised that a with the boat configeration a 34 2 blade would be best.
Thanks Chris G
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If you want a boat to go forward fast, you need the water being shoved backwards by the prop to move fast. A bigger prop moves a wider stream of water, but, given the same power, more slowly. A smaller prop spinning a lot faster will produce the faster water stream, but at the cost of reduced acceleration. A bit like sticking a bike in a high gear and trying to pedal away from a stop.