another Mini Vapor board issue - RC Groups
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Nov 09, 2017, 04:16 PM
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micro_builder's Avatar
Discussion

another Mini Vapor board issue


Last time I put the Mini Vapor away everything worked fine, went to try it today seeing as outdoor season has ended, and I had no throttle, though the servos work fine.

I took the board off the plane to take a closer look and none of the components appear damaged under magnification. I resoldered the motor, but still nothing, tested the motor directly with a lipo and it does run just fine. I soldered a different motor on, and the motor will spin up for just a split second when plugging in the battery, but no response after that. Put a voltmeter to the motor outputs on the board itself, and theres nothing but a momentary spike.

Tried different batteries, reflowing the solder, different TX, but still no power to the motor other than that little blip at first. Bad FET? I know they can sometimes sort of half burn out, kind of works, but not really, but not sure how I could test that other than replacing it. Feels like I'm just missing something obvious...

Nick
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Nov 09, 2017, 04:46 PM
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cybermike's Avatar
Battery connector? On my oldest UMX's (2+ years), the connectors are getting corrosion and getting intermittent. The servos may work fine, but with any significant current draw, the voltage drop over the bad connection is enough to trigger the low-voltage cutoff. Same thing can happen with the batteries too.

A little tuner cleaner (you're old enough to remember "TV tuners" ), 320 grit sandpaper, scraping with a knife blade, etc. on the Rx battery connector might help. Not much you can do with the battery-side connector other than junk it and get a new one.

I've also had one board where the negative battery wire mostly broke from wiggling back and forth, and the remaining couple of strands weren't enough for a reliable connection.
Nov 10, 2017, 05:39 AM
Registered User
You've probably already checked this, but could it just be the battery is failing? Yes, I know, just too obvious, but worth asking.

Pete
Nov 10, 2017, 09:03 AM
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funwithplanes's Avatar
Try a newer battery. Sometimes it happens to me, but normally if i switch batteries it seems to work.
Nov 10, 2017, 09:29 AM
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CorvetteC5's Avatar
I have 2 MV bricks that behaved the same way. Go to throttle up the motor and it pulses once then dies. The servos remain fine. Using a stronger Lipo, that holds voltage longer during the current spike, helps for a time, but then the throttle finally fails completely. My fix so far has been to replace the bricks with a new one.

If you find that replacing the SMD SOT FET fixes it for you then please share the part number of the component.
Last edited by CorvetteC5; Nov 12, 2017 at 08:17 PM.
Nov 10, 2017, 11:39 AM
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micro_builder's Avatar
Thanks for the suggestions guys

I did try a few different batteries, charged up a 100mah that I know works well, but still no dice. I'll resolder the battery leads and connectors though and see if that does it. If that doesnt work I'll try replacing the FET (I'll post the part number when I find it, CorvetteC5).

Nick
Nov 10, 2017, 03:47 PM
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cybermike's Avatar
Corvette - a burned MOSFET usually manifests as no motor (burned open), full motor (short circuit) or partial motor (leakage through the MOSFET) regardless of throttle - it happens as soon as you plug in the battery. What you guys are describing really sounds like a weak/dirty battery contact. The high resistance doesn't matter until you throttle up, at which point the voltage drop is high enough to cause an LVC.

BTW-I tried to find the MOSFET part for the built-in ESC. All my google-fu turned up nothing on RCGroups or the interwebs (surprising - no one has identified this part before???). All my Mini-Vapor and AR6400 bricks have the same FET, marked AG?X 1H (the ? character varies per unit - presumably a lot or date code). The format matches what Vishay Siliconix has used in the past to mark SOT-23 MOSFETs, but I couldn't find any current N-Channel MOSFETs that use "AG" as the marking code. So, it's likely it's an older, discontinued part.

Any decent low-resistance/high current N-Channel MOSFET should do. I would drop in a DMN2041L or IRLML6244 because I have them on hand, and they have worked well for me in 1-cell brushless ESCs.

Keep in mind I haven't actually done this on any of my bricks, so I disclaim any liability for any damage that may be caused
Nov 10, 2017, 08:36 PM
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CorvetteC5's Avatar
Thanks, cybermike. I hope you are correct and the throttle issue with the MV bricks is the battery connector/harness. I happen to have spares handy and will try a replacement and report.
Nov 11, 2017, 09:08 AM
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CorvetteC5's Avatar
Quote:
Originally Posted by CorvetteC5
Thanks, cybermike. I hope you are correct and the throttle issue with the MV bricks is the battery connector/harness. I happen to have spares handy and will try a replacement and report.
No help this morning messing with the harness on a MV brick. Motor still pulses-once immediately after throttle is applied.

What I did witness is:
1) Slowly advance throttle and motor spins normally at the very lowest setting.
2) Let motor and prop spin, at this throttle, for maybe 1 seconds before ESC pulses once and motor shuts off and stays off.
3) During motor pulse the battery voltage sags and returns after pulse finishes and motor is stopped. As witnessed by LED turning off then back on from circuit board.


During normal functioning the MV ESC will surge the speed of the motor when LVC is reached. The observed one-shot pulse is different than that, but likely related.

The problem could simply be a failing motor, as one of the failure methods is pulling higher amps before dying. Easy enough to check after I get a replacement one.
Nov 11, 2017, 01:10 PM
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micro_builder's Avatar
I resoldered my battery leads, but no change. I'll pull a FET off a broken board and see how that goes.

Corvette, could very well be a motor on its way out, could try using a multimeter and reading the resistance to see if anything looks off.
Nov 11, 2017, 04:41 PM
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cybermike's Avatar
Quote:
Originally Posted by CorvetteC5
During normal functioning the MV ESC will surge the speed of the motor when LVC is reached. The observed one-shot pulse is different than that, but likely related.
Hard cutoff is normal if the voltage drops too low. A fun way to wreck your batteries is to tool around at very low throttle until you hit the hard cutoff . My g/f does it all the time with her Sport Cub S, leading to the inevitable walk of shame when she can't taxi it back to home plate. Good thing the batteries are cheap
Nov 12, 2017, 09:03 AM
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CorvetteC5's Avatar
Quote:
Originally Posted by cybermike
Hard cutoff is normal if the voltage drops too low. A fun way to wreck your batteries is to tool around at very low throttle until you hit the hard cutoff . My g/f does it all the time with her Sport Cub S, leading to the inevitable walk of shame when she can't taxi it back to home plate. Good thing the batteries are cheap
Nov 12, 2017, 09:36 AM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by micro_builder
I resoldered my battery leads, but no change. I'll pull a FET off a broken board and see how that goes.
Did you resolder the leads on the board? Because that might not be where the problem is.

Either replace the battery lead with a new one, or beef up the connector by pulling out the pins and add a tiny bit of solder where the lead connects to the pin.

I've seen this many times on micro quads and other boards using the small 1.25mm connectors, particularly if they've been sitting unused for a number of months.
Nov 12, 2017, 07:33 PM
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micro_builder's Avatar
Quote:
Originally Posted by Pouncer
Did you resolder the leads on the board? Because that might not be where the problem is.

Either replace the battery lead with a new one, or beef up the connector by pulling out the pins and add a tiny bit of solder where the lead connects to the pin.

I've seen this many times on micro quads and other boards using the small 1.25mm connectors, particularly if they've been sitting unused for a number of months.
Yeah, resoldered the connector and board ends, just to be on the safe side. The connector I'm using I have used on nearly every micro I've built, so I'm assuming its good, but I'll try swapping it out for the heck of it...much easier fix than replacing the FET, which I havent gotten around to yet...I havent done SMD soldering in quite a while
Nov 13, 2017, 02:26 PM
Registered User
Petefoss's Avatar
The other thing I run into is battery connectors damaged by the Hitec 4x charger when used without the pigtails.


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