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[chingdevil]

I am having a problem with fuses blowing on the battery side of my Esc. The set up is as follows:-

Mtronics Viper Marine 15 with reverse
Johnson 540 Motor direct drive onto a 40mm 3 bladed prop

The set up works alright out of water but in water its blows 7.5amp fuses. The motor only pulls 2.5 amps when running on its own and the prop is not tight. I am at a loss, any ideas anyone?

The other Brian

[HS93 (RIP)]

By running on its own do you mean out of the water?  is it a motor with a fan in it?

Peter

[chingdevil]

Hi Peter

I meant if I run the motor not connected to the prop shaft, no it does not have a fan in it.


The other Brian

[John W E]

Hi there chingdevil

According to a graph I have, a 540 motor on 6 volts, driving a 40mm prop, pulls approximately 15 amps - unless of course it is a low drain type it should drop between 9 and 10 amps.

aye
john e
bluebird

[chingdevil]

Hi Bluebird

Blimey I did not think it would pull that much, sounds like I might need a new ESC as well as a fuse.

The other Brian

[malcolmfrary]

Try with a 10A fuse first - this should be well within the limits of a Viper 15 if I read the instructions on mine right.  It might be as well to measure the resistance of the motor while turning it by hand - a DC resistance reading is not a totally accurate guide for current consumption of a motor in service, but an unexpectedly fluctuating reading can indicate a problem with the motor.

[chingdevil]

Hi Guys

Thanks for the info, brought a new esc. The motor was pulling 12 amps when connected to the prop and in water, decided to get a bigger esc so I could put the appropriate fuse inline.


The other Brian

[FullLeatherJacket]

Guys
I've been updating the drawings for ACTion units and I sent Craig Talbot an example for his approval. This showed fuses in the positive wires between the ESCs and batteries. Here is his reply, word for word:

"Hi Dave,
    Just read your P40 Mixer Drawings/Instructions. The thing I picked up on is the mention of fuses in speed controller ciruits. A 20 AMP FUSE will run for EVER with a current of 20 AMPS. A Standard time fuse will run at twice its indicated current for two seconds. A delay fuse will run for ten seconds at twice the indicated current. You will judge from this that fuses are a nightmare component to use, they don't protect electronics (they are a thousand times too slow) they just protect wiring from fires. This is the reason I never suggested fuses in any of my instructions.
Ok buddy"

I've always followed this advice, which Craig first gave me a long time ago. I use decent quality, high-current, silicon-covered multi-strand cable; gold-plated bullet connectors, and I NEVER use "choc-blocks" with twisted-wire connections. Maybe it's just coincidence that I've never blown an ESC and never had a wire get even warm. It's cheaper on fuses, too!!

Works for me. Suit yourselves.

FLJ

[chingdevil]

Thanks for that FLJ

That is interesting, most information I have ever seen on ESC's always says that a fuse should be fitted. Now I know that fuses in mains electrics are only there to protect the cables not the components, did not think it was the same in electronics.

Food for thought.

The other Brian

[Doc]

Interesting philosophy about fuses.  Certainly not the 'standard' one, and can't say that I would agree with it, but interesting.  A standard 'fast acting' fuse of the proper size should be plenty of protection for an ESC, motor, whatever.  It will be subject to surges as is typical for any fuse, and should handle those surges just fine (so will the electronic devices).  A 'slow acting' fuse is a different thingy all together, and is intended for circuits where there are huge or prolonged surges.  I don't think R/C systems need a 'slow acting' fuse, the 'fast acting' ones would be more suitable.  To know the right size of fuse to use you have to know what the 'average' current demand of the system is.  A size that's just ~slightly~ higher than the average current draw should work fine.  If done correctly, fuses really are a nice thing to have.  Fuses are not just to protect the wiring.  If that's all that they protect, then they are the wrong size for that particular application.
 - 'Doc

[kendalboatsman]

Hi all,

I work in the electric motor rewinding trade and one of the earliest things I learned was that a fuse will never ever protect a motor, all a fuse really helps against are sudden surges of current. I never use fuses, but I do use "choc" block connectors occasionally and the only ESC I blew was way back in my early days of buggy racing. I shorted the battery leads :-[

Mostly I use some Thomas and Betts connectors i buy from RS components, they are designed for using in multipole plugs but I just use them loose with heatshrink for insulation.

To avoid overheating cables you need to use the correct size cable for the current drawn. I just found this on Google. http://www.unlimited-power.co.uk/Cable_sizing_chart.html Cable run doesn't normally apply to us model boaters as the boats are too short.

The best form of motor protection is a thermal trip (Tamiya used to produce one in the late seventies/early eighties for their SRB range) and these can be purchased in different ratings from people like RS components or any decent electronics shop.

Clive

[malcolmfrary]

Back in the elder days when I had a proper job, it was said that "Any electronic device will protect any fuse". 
The semiconductors, if presented with an out of limits condition would usually die long before the fuse. 
The fuse really is there to prevent the wiring from starting a fire due to a component failure, be it in the control circuit or the load, or any of the other wiring on the way there.  With most present day ESCs the current limiting that is built in will stop too much damage, but this still doesn't rule out the possibility of an internal component giving an unprotected short.
I had plenty of times where either a stuck magnet or a stalled motor would cheerfully sit there cooking itself without blowing its fuse - the protection in these cases was either a release alarm intended to attract attention rapidly before the smell of hot electric filled the room, or a "slow blow" fuse which would blow after several seconds.

[Shipmate60]

I do hear what you are saying about fuses, but on this speed controller I let the thermal overload protect the unit.
Due to an internal short, if I had a fuse I could have saved the deck of the model.

Bob

[Peterm]

Obviously everyone has their own opinion.   In my lifeboat, which I built several years ago, I have a watercooled esc and a fuse in the power line between battery and esc/rx.   The fuse is well below the current rating of the esc, and as the fuse has blown about four times over the years and no damage to the electronics has occurred, I must assume that the fuse is doing its job.   Pete M

[justboatonic]

We currently run 3700Mah NiMh 6 cell packs in 2 RC cars. We've used MTronik, MSonic, VRT and other ESC's. ESC's have only been upgraded as the standard and competition of driving has improved. We've never used fuses with the ESC's and never had one go pop.

I dont believe ordinary boats ie not racing electric boats, take anywhere near the current that RC racing cars do. If you melt an ESC in an ordinary boat you're doing something wrong imo. Oh and we've had siezed wheel bearsing in the cars and still the ESC hasnt blown!

[DickyD]

One wonders if a lot of the problems with ESCs are caused by buying the wrong ones for the boats set up ie too small amperage.

Richard

[Shipmate60]

justboatonic ,
Just for info about the "blown" ESC.
The ESC was replaced with the same unit, the model is exactly the same and has been running now for over a year with no problems.
I ALWAYS check the current consumption of the motors and use cable well in excess of the voltage/current capacity of the speed controller.

Bob

[malcolmfrary]

A fuse might not have saved that ESC from whatever happened, but it would have limited the collateral damage by stopping the supply of energy that was converted into heat. 
The rule was that fuses were always picked to protect the wiring against a failed component - the components were picked to survive in the conditions expected.  If a fuse ruptured, it was good practice to have a look at the blown one to try to guess if it had died of old age or been taken out by some other cause, then it was normal to try another, and test whatever it was feeding.

[Shipmate60]

As an aside to the original question.
Mtroniks have had a very small number of ESC's returned with the same symptoms that mine had.
The only point I was trying to make is that with a fuse in the battery line the excessive current consumption in a dead short circuit would have saved a lot of damage to my model.
Personally not impressed being told that if I over-rate the wiring it will save a short circuit in the ESC!!

Bob

[BobF]

Hi all,

I've been having problems with my ESC's of late,  and have had a few burn out. I won't say the manufacturer unless Martin says I can.  These have all burnt out when only on stand by and not due too battery incorrect polarity connection. Talking to other boaters at Skipsea week and my local club, there appears to be a common link, not heavy amp loading or long run times. The common denominator appears to be using them on 8 . 4 volts. The last one that went up in smoke, still worked on rudder, just the speed control stopped working.
Any one else have this ring a bell. This is not a swipe at the manufacturer, as I still use their controllers, to exclusion of all others, and if there is a problem at manufacturing stage, it is in all our interests to advise them of this.

Bob

[chingdevil]

I think my problem has been that as a novice I underestimated how much power the motors we use pull when under load. I was quite surprised when told how much a Johnson 540 will pull under load, so I ended up buying another ESC so as not to fry the original one in the middle of the lake, the difference between the motor current and the ESC was too close to put a fuse in line.

The other Brian

[cbr900]

I have been out to my shed and counted the ESC unit I have and there are 27 in total, I have never on any literature that come with the ESC that a fuse was necessary, and I have to admit that I have not had an ESC failure or any other problem that causes fires or damage to other parts, I have over the years sold about twenty boats and at this time have 29, so in that case could the problem be the ESC in your country cannot stand the temp changes, yours are far more drastic than ours, ans I have never used a fuse in any boat, and cannot remember seeing one in anyone else's over here.............


Roy

[Welsh_Druid]

OK - my experience.

Running a Mersey lifeboat with props in tunnels, in very shallow water I picked up a small stone which jammed one prop against the wall of the tunnel. The controller virtually melted and looked just like the photo that shipmat60 posted.

Replaced the controller but put a fuse in the circuit. Two weeks later the same thing happened (picked up a stone and jammed the prop) but this time the fuse blew and no damage to the controller or my pocket.

Fuses for me every time now.

Don B