Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: BarryM on April 28, 2013, 12:13:07 pm
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This should be a simple problem but this simple soul has failed to come up with an answer and thus I throw it open for somebody else to tell me I’m missing the obvious.
A single SLA battery supplies two ESC plus an independent BEC feeding the Rx. Each ESC feeds a brushed motor. The ESCs do not have internal BEC and each motor has a maximum running current of 4A.
An On/Off switch is inserted in the battery positive supply to the ESCs. Another On/Off switch is fitted in the battery supply to the BEC. Fuses are fitted in the battery positive feeds to each ESC.
My usual routine is to switch on the Tx, then the Rx and then the battery supply.
Here’s the problem: When I switch on the battery power, there is a power surge that blows any fuse of less than 20A rating; sometimes, even a 25A fuse will blow. After I replace the fuse, normal service is resumed. However, obviously I do not regard the fitting of larger and larger fuses as a safe means of operation. That route leads to fried circuits and expense I can do without.
There is no sign of wiring shorting or other defect and once the original power surge is dealt with by changing the fuse, I can cruise around to the limit of battery endurance.
All suggestions of what is going on and how to solve it (capacitors? earthing?) will be gratefully received.
Barry M
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I would say that the inrush to the capacitors on the ESC's is blowing the fuse. You could try putting a switch with a resistor in series with it (say 20 ohms) in parallel with your main ESC power switch activate that first to charge the caps.
HTH
Steve
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Try removing the main battery switch and touching the wires together.
Is the main switch shorting?
What is the equipment installed?
Bob
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An On/Off switch is inserted in the battery positive supply to the ESCs. Another On/Off switch is fitted in the battery supply to the BEC. Fuses are fitted in the battery positive feeds to each ESC.
My usual routine is to switch on the Tx, then the Rx and then the battery supply.
I'm not sure exactly what you mean by the last statement - unless you mean turn on the BEC followed by the ESC supply {:-{
Are both ESCs switched together or separately??
The only thing I can suggest is to remove one ESC and try your 'power up', if no problem then repeat using the other ESC and report back your findings :-))
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I'm not sure exactly what you mean by the last statement - unless you mean turn on the BEC followed by the ESC supply {:-{
Are both ESCs switched together or separately??
The only thing I can suggest is to remove one ESC and try your 'power up', if no problem then repeat using the other ESC and report back your findings :-))
Just as I wrote "An On/Off switch is inserted in the battery positive supply to the ESCs. Another On/Off switch is fitted in the battery supply to the BEC. " I switch on the Tx followed by operating the switch to power up the Rx via the BEC and then throw the other switch to send power to both ESCs simultaneously.
Steve - I can see where you are coming from but this is the same set-up that I have in two other models and doubtless many others have the same configuration but this one doesn't conform to the norm.
Bob - I don't follow you. Whenever the switch is closed then it is effectively shorted. However, the switch has been checked and is working normally.
If it helps, the ESC are both Fleet Speedmaster FPS-24B and the motors are Monoperm Super. Not exactly the cutting edge of technology but very well proven. As mentioned, once the initial surge is dissipated, the system works normally.
Barry M
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As Mark says do a bit of faultfinding by the
process of elimination by disconnecting
each ESC in turn.
It seems that one of the escs has a capacitor
problem,which, once charged behaves and
no more fuse blowing.
Ned
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The only way you will find the problem is to remove/replace components unless you can check each piese of equipment electrically.
What Radio set are you using?
Bob
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Thanks for all replies. I will start swopping and substituting this week and see what happens.
A few years back I had a similar problem: different model, different ESC manufacturer, different motors. In that case the circuit board in one of the ESC blew. An expensive learning curve.
Regards,
Barry M
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Are you using a 2.4 Radio Set?
Bob
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OP mentions fuses supplying ESCs. I assume one fuse per ESC. Is it one fuse at every time, either fuse as it feels like it, or both together? Capacitors don't normally grow extra capacitance - a shorting capacitor should not only blow the initial fuse, but should discharge enough to blow the replacement as well. Silly question - you haven't accidentally got a supply of quick blow fuses?
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Bob,
No, One of my oldie but goodie 40MHz Fleet Tx/Rx sets
Malcolm,
Now you've got me thinking. Yes, one fuse per ESC in the +ve line which currently are automotive 25A Blade fuses. However, at one time I tried glass fuses which also blew. It can be either fuse that blows but not both together.
I have a couple of 10A self-resetting thermal cutouts which may be worth trying in place of fuses?
Regards,
Barry M
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The thermal cutouts sound good, moreso if they can have an indicator wired across them to show their state.
Does the blowing happen with the motors disconnected? I am a bit dubious about the capacitor fail - a capacitor has to be a real big 'un before it will blow a fuse, and if it was a dud, it should only show on one side. Two together with the same problem is less likely. Should be less likely. If that ESC has a power smoothing capacitor fitted.
The excess current has to go somewhere, either through the motor, which implies something switched on at power-up, or, if not through the motor, the output stages must be switched in both forward and reverse at the same time, offering a short to the power. In an ESC with no BEC, there really isn't anywhere else for the main power to go.
Another silly question. Is the main, heavy, neg circuit good all the way to the ESCs? I have had weird sh stuff happen with the ground line connection entering ESCs not via the big thick wire, but via the RX lead. Usually results in a fried RX lead, but when protected by a fuse elsewhere - ? Presenting the input end of the ESC with strange and unlikely voltages can give odd effects.
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Malcolm,
Thanks for those comments; they have given me a lot to think about. I will not be able to start waving the AVO around for a couple of days but when I can I shall go back to basics and start working through the wiring.
The only other thing I can throw into the pot is that one of the ESC is quite twitchy around the dead spot between ahead and astern and needs very careful setting up. A rheostat problem, I assume, and probably not relevent. On the other hand................it occurs to me now that that is the one which usually blows the fuse.........but on the other, other, hand everything works fine after the fuse is replaced.
Regards,
Barry M
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It may be easier to say than do, but have you tried substituting the suspect ESC with another? Pete
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Pete,
It is! I can only swop them over unless you have a Fleet Speedmaster FPS-24B tucked away?
Regards,
Barry M
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It may be easier to say than do, but have you tried substituting the suspect ESC with another? Pete
Needs swapping with a known good one - the problem migrates itself and doesn't restrict itself to one ESC. This means either two ESCs with the same fault, or something common. One thing - it will be perfectly obvious once the answer is known.
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the on / off switches are they identical - also is there any possibility they are somehow shorting out the circuit at part of the switch movement, are they make before break type or break before make, I am wondering if they may be creating a problem as you throw the switch? or if there is a surgeback between esc's when you throw the switch, maybe seperate switches for each esc so they can be fired up seperately?
Grendel
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The switches are standard toggle switches appropriate to the current draw. Without cutting them open, I cannot confirm the internal action.
Barry M