Model Boat Mayhem
Technical, Techniques, Hints, and Tips => DC Motors (Brushed) and Speed Controllers => Topic started by: Buster22 on May 19, 2015, 11:01:24 pm
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i have 2 new mfa 6/1 motors just put in my tug hooked to p94 with 12v battery thru actionp102
ran the motors on workbench for like a minit testing and one of the capasitors or noise suppressors started smoking there is three pre installed on the motor the bottom one did it but the others on the other motor r fine had the same issue with the 2/5/1 motors i had in there before the new ones i just installed any ideas what would cause this thanks for any help
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Buster
Check that the leads from the capacitors aren't shorting against the motor case or each other. MFA don't fit insulating sleeving.
DM
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the 2 top ones are soldered to the can and the third one ties to the others dont see anything wrong other than the one that the capaciter blew on seems slower now can i get by with the 2 on the one motor or is there something wrong with the p94
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If you think there is something wrong with the speed controller then send it back, but first check the appearance of the two black diodes fitted between the green screw-terminals. It's possible that something you did earlier has blown one or both of these and that's now causing your problems.
It will be pretty obvious if they have blown as the cylindrical black case of the diode will be split from top to bottom. If you have a digital multimeter there may be a diode test function on it. The voltage for a working diode should read around 0.5 in one direction and open-circuit the other way. A dead diode will read the same in both directions. If you turn the board over then one or both of the soldered joints between the diodes and the copper track will appear brown and burned.
Meantime I would change all of the suppressor capacitors on the motors. They only cost pennies and replacing them would eliminate them as the source of the problem.
DM
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A capacitor is essentially a wire with a very carefully constructed disconnection inside the case. The only way one would start smoking is if it was passing current, and a healthy one wont, so a smoking one is a dud. No ESC for model use running on 12 volts can produce a high enough voltage to kill a suppression capacitor - if its internal insulation was broken down by excessive voltage, the only source is back emf from the motor. If the internal insulation has broken down due to either excessive heating on installation or from the motor arcing, it is now probably shorted, and won't be doing the motor efficiency any favours. It probably won't have done the ESC much good, either.
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Thanks, Malcolm; that puts the technical icing on the cake far better than I could.
As I said, best now to change the motor capacitors and check the diodes on the P94. The MFA 500 motors aren't the very best quality but I've never known any of them behave like that. Strange, though, that all of the ones I've had were only fitted with one capacitor (across the terminals) out of the box. Recommended capacitors are 0.1 -0.22uF across the terminals and 0.01-0.1uF from terminals to case. In both cases use ceramic disc types.
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I bought a couple of suppressor packs from Action a few years ago for a pair of mfas. Two discs and a small cylinder per motor, the latter to go across the motor terminals, and the discs terminal to case.
On first power up and motor test one of the cylinders produced a fair bit of light and a lot of smoke, for not very long. The one on the other motor was OK. The esc and motor were fine once I replaced the capacitor.
So I'd say they are sometimes just duff out of the box. C'est la vie :-)
Edit: No criticism of Action is implied here. I mention them solely to show that these caps were correctly sourced for the job and not some random bits I'd acquired.
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The ACTion capacitors in question were sourced from Farnell, one of the largest and most reliable suppliers of electronic components in the UK. These days practically all of the passive components we use here are made either in the Far East or Central America, where QC is sometimes of a secondary consideration to cost. That said, it's impossible to test every single capacitor that comes off the line - they're made in thousands per minute! Like the man says, c'est la vie.
DM
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thanks guys i will will replace the caps on the one motor and check the p94 and report back
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capacitor QC has been known to be a problem in the past... it was a MAJOR problem for computer manufacturers a few years ago...
http://en.wikipedia.org/wiki/Capacitor_plague
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capacitor QC has been known to be a problem in the past... it was a MAJOR problem for computer manufacturers a few years ago...
http://en.wikipedia.org/wiki/Capacitor_plague (http://en.wikipedia.org/wiki/Capacitor_plague)
True enough, but those were electrolytics with a liquid on the inside, not dry like the ceramic discs here. Electrolytic types don't have a place in suppressing reversible DC motors, since one certain way to let the magic smoke out is to reverse connect them. Been there, got the tee shirt with the holes in it. Disc ceramics, provided that they don't see volts above their rating, and I haven't seen any below 50 volts, are usually immensely reliable. Then again, they are man made and a dud batch is always possible.
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inertia on the p94 i see 2 small black barrel caps in front of the relays dont see any splits but on the terminal blocks for the motors i see browning on the board and i see the solder looks weird
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Dead diodes for sure.
I can fix them for a few bucks but the postage will cost plenty. If you do it yourself you will need to strip back the two copper tracks where the diodes are soldered until you reach track which is intact, then use the legs of the diodes underneath the board to bridge the gap. The diodes are 1N4007 type - I pay almost 1 penny each for them.
Here's a picture of one which I did earlier:
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mine looks worse than that do u have a repaired one i can purchas from u
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PM sent. Don't forget this one is shown after being repaired! If you look carefully you can see that the copper tracks have been cut away and the epoxy-glass scraped clean of burn marks. The legs of the diodes have been used to replace the tracks. It's a ten minute job.
DM
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Thats what I like about this page,loads of advice and help,and freely given. DM (inertia) is a credit to the page as is Malcolm Frary,always helpful,and note Dave was NOT trying to gain any financial reward,telling Buster 22 not to send something he could repair himself.
Now come on,how many people in the trade (or retired!) would do that?
Well done to ALL who offer good advice on here.
Mick F
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That's what I like about this page,loads of advice and help,and freely given. DM (inertia) is a credit to the page as is Malcolm Frary,always helpful,and note Dave was NOT trying to gain any financial reward,telling Buster 22 not to send something he could repair himself.
Now come on,how many people in the trade (or retired!) would do that?
Well done to ALL who offer good advice on here.
Mick F
:-)) :-)) I most heartily concur O0 O0 having been on the receiving end of such good advice and commentary, even though we are on the opposite side of the planet.
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thanks alot for the help guys ive ordered the new diodes will install and let you know how it goes
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When you fit them, make sure that they are the right way round. Diodes are picky about that. I am fairly sure that there is a diagram on Dave's site showing their orientation.
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http://www.componentshop.co.uk/p94-dual-esc-and-mixer-2-x-20-amps.html (http://www.componentshop.co.uk/p94-dual-esc-and-mixer-2-x-20-amps.html)
Click on "P94 Data Sheet" (PDF icon) and scroll to Page 9 for diagram and Page 13 for photo (Picture 5). Diodes fit into the outer holes, with the silver band at the top.
You'll need some desolder braid to soak up the solder from the unburned ends - the burned solder won't melt so you'll need to cut it off along with the burned copper track. I understand that a damaged P94 is in the post to me from a CompShop customer. If that needs the diodes replacing then I'll do a photo blog of the job for you (and for any others who might have a similar accident).
DM
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well p94 replaced new caps on new motors and still having a lot of motor arcing and when im running in steer mode like turning on its own length thats when i have the issues ahead and reverse work normal very wierd motors r twitching very bad when i try to turn left or right may try disconnecting servo to see if it is causing the interferiance
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These motors do spark quite a lot under normal conditions. Are you using a digital servo for the rudder? They can create havoc.
DM
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A small amount of arcing is quite common, but heavy arcing is a bad sign. If they are new motors, they might need the brushes bedding in, if not new, worn brushes will give arcing. Either way, if heavy arcing has taken place, the commutator surface will have suffered damage and at least need cleaning. The arc does damage, the damage creates the condition for more arcing, arcing is a sign that the motor is generating a lot of back EMF. The current flow resulting from that voltage is what gives rise to interference, either by radiating from the motor leads and being picked up by low power wiring (aerial, servo leads etc) or by dumping the unwanted voltage into the power leads. To minimize that sort of thing, motor leads are best twisted so that the unwanted signals cancel out.
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the servo is a futaba s3003 the wires to the motors is 2 conductor and is sheilded
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S3003 is a bog-standard non-digital servo and should cause no problems at all. P94 was behaving perfectly when it was tested before sending - just like a new one, in fact! Motors are still the clear favourite as the cause, but which radio are you using - there may be a compatibility issue here?
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im using a multiplex europa nautic radio
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so i switched to tank mode not having any issues with glitching now
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so tried the boat out yesterday and the one motor blew the capacitor again
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so tried the boat out yesterday and the one motor blew the capacitor again
If that motor is the one arcing a lot then it sounds like it may be faulty and the emfs produced are breaking down the capacitor. If I was going to persist with it I'd replace the suppressor cap (again) but also add a much higher value, say 1 microF (but not a polarity sensitive type like an electrolytic), capacitor in parallel to try and swamp some of the arcing.
Ideally I'd try a different motor though.
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If that motor is the one arcing a lot then it sounds like it may be faulty and the emfs produced are breaking down the capacitor. If I was going to persist with it I'd replace the suppressor cap (again) but also add a much higher value, say 1 microF (but not a polarity sensitive type like an electrolytic), capacitor in parallel to try and swamp some of the arcing.
Ideally I'd try a different motor though.
I would give the commutator a really good clean and check the brushes before doing anything else at all, then check it on raw battery to see if the sparking gets cured. If not, mend it with a new one, you will never be able to trust it.
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Check the flywheel diodes on the (new) P94. Sounds like you may have two of them to fix now. No known compatibility problem with that radio, but it is a pretty unusual one - at least in these parts.
As has been said, a motor transplant would probably save further heartache and expense.
DM
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well i put the p94 in mode 4 not having any issues now
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If the motor is still sparking, it is a problem lying in wait for the future. Minor sparking is fairly common. heavy sparking is damage being done.