Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => DC Motors (Brushed) and Speed Controllers => Topic started by: dan on June 28, 2008, 08:23:12 PM

Title: electrical fault
Post by: dan on June 28, 2008, 08:23:12 PM
hi guys,
i was testing my latest build  today for the second time, it was going extremely well until about half an hour of running, when it stalled an what looked like steam started to appear. i thought a little bit of water had splashed on the the motor and had started to evaporate (as it is a open toped speed boat) but then i began to realise it wasn't steam because of two factors. one being th steam was now pouring out of the hull fasted and thicker, and the fact there were flames coming out of the top :'(. after getting very wet and taking the boat out of the water, i discovered that it was not the motor, but the speed controller. Does anyone know how this could have happened, i have had the boat on the water once before and had no problems with it. could it just be a technical fault with the speed controller or is something else to blame???

cheers,
Dan
Title: Re: electrical fault
Post by: Shipmate60 on June 28, 2008, 08:25:58 PM
Dan,
What motor and speed controller is it?

Bob
Title: Re: electrical fault
Post by: dan on June 28, 2008, 08:35:16 PM
hi,
its a torpedo 850 which pulls 11 a, and a mtronkis 15a speed controller
Title: Re: electrical fault
Post by: dougal99 on June 28, 2008, 09:02:10 PM
According to MFA the 850 has a typical current draw of 11 Amps, would be considerably higher if there was any large resistance, such as weed on the prop. I use a 20 amp ESC with mine. No probs to date (fingers crossed).

Doug
Title: Re: electrical fault
Post by: Shipmate60 on June 28, 2008, 09:02:49 PM
Well there is your answer, the speed controller, was it fused?
The MFA 850 is capable of pulling far in excess of 11 amps at times.

Bob
Title: Re: electrical fault
Post by: dan on June 28, 2008, 09:24:12 PM
there wasn't any obstructions such as weed on the pond. and no it wasn't fused, but it will be once i replace it. where would you suggest the fuse is put because i am not 100% sure.

cheers guys

Dan
Title: Re: electrical fault
Post by: banjo on June 28, 2008, 10:00:25 PM
Hi,

On the Mitroniks Instruction sheet it recommends fitting an in line fuse in the positive wire between the cells and the ESC. ( Usually 5A lower than the ESC's stated limit)

When you get your new one be sure to read the instruction sheet.  Check out ALL the wiring when you are fitting the new one.

 ;)
Title: Re: electrical fault
Post by: Colin Bishop on June 28, 2008, 10:04:53 PM
I wouldn't care to think just how many instances we have had reported on Mayhem of ESCs immolating themselves due to the lack of a fuse. Cost of fuse - 5p. Cost of new ESC?? ?

No contest really is it?

Colin
Title: Re: electrical fault
Post by: Shipmate60 on June 28, 2008, 10:05:40 PM
For an in-line fuse fit the car type blade fuse NOT the plastic cylindrical split fuse holder.

Bob
Title: Re: electrical fault
Post by: banjo on June 28, 2008, 10:15:15 PM
 O0

Halfords
Title: Re: electrical fault
Post by: DickyD on June 28, 2008, 10:18:47 PM
30 amp Fuseholder Redbank Models.  O0

http://quantrum.co.uk/redbankmodels/advanced_search_result.php?keywords=fuse+holder&x=13&y=6
Title: Re: electrical fault
Post by: banjo on June 28, 2008, 10:21:24 PM
 {-)

The Halfords item is rated at 40 amp

The Redbank is only 20amp

hhhhhmmmmm
Title: Re: electrical fault
Post by: HS93 (RIP) on June 28, 2008, 10:32:41 PM
What I want to know is why the manufacturers all say that there should be one fitted, then Why don't they build one in to the case so there is no extra wiring, all it would need is a pair of pcb spade connectors and a slot in the lid and the potted ones could have it on the edge, they could then mark them max fuse size to be fitted and then modelers who do not like wires wont have to worry.and minimal cost,I'm shore marine modelers would not mind paying the extra 20p for the parts.

Hs93
Title: Re: electrical fault
Post by: Colin Bishop on June 28, 2008, 10:36:13 PM
Good point. Although a fuse in the positive line from the main battery also provides general protection to the power circuitry so you would still need one there too.
Title: Re: electrical fault
Post by: Stavros on June 28, 2008, 11:38:57 PM
Right I have used this particular motor in quite a few boats and I will not use an ESC of less than 25 amps as I dont trust what MFA say.This motor I have seen 20amps pulled at full chat with a 3 bladed 65mm brass prop and as far as a fuse goes 25amp same as ESC


Stavros
Title: Re: electrical fault
Post by: Martin [Admin] on June 28, 2008, 11:46:22 PM
"why the manufacturers all say that there should be one fitted, then Why don't they build one in to the case so there is no extra wiring" - Here! Here!
Title: Re: electrical fault
Post by: Peterm on June 29, 2008, 10:18:45 AM
I have always used the relevant value of fuse in the positive supply line, using the principle of fuse rating being 75% of the ESC rating.   I started off using Halfords blade fuses and holders, but have now moved on to ACTion P95 fuse units which can carry up to 25 Amp fuses.   Pete M