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Old Jul 30, 2002, 08:34 PM
LiPo Suction Specialist
JDCochran's Avatar
Atlanta Hartsfield, Georgia, United States
Joined Apr 2002
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Fuse(s) for 3-phase Brushless Motors

Does anyone know how to fuse a 3-phase brushless motor? Single large fuse one lead? 1/3 of anticipated max current in each lead, thus 3 fuses? 1/2?

As I understand the way they work, 2 of the 3 leads at any given time are carrying power to motor, while the 3rd lead is used to measure back EMF as feedback on motor RPM for the ESC. Given this theory, I'm thinking of three 20 amp fuses (1/2 anticipated max current ). Would one suffice? What happens in a jeti 40-3P when one of the motor leads is disconnected and full throttle is called for?

I don't want to fuse the battery side of the ESC with BEC for obvious reasons.

Regards,
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Old Jul 30, 2002, 09:37 PM
Spittin' Sparx forever...
DougB's Avatar
West Vancouver, BC
Joined Mar 2000
482 Posts
With regards to fusing a brushless motor using BEC, it cannot be done safely unless you are lucky enough to have purchased a MaxCim brushless which makes provison for such fusing. No other make has such provision and could actually be dangerous to fuse as the operational safety of your plane could be compromised. Check the Ezone past discussions on this topic for further info.

In Canada, MAAC after much discussion and consideration dropped the fusing of brushless motors when used with a BEC (it was mandatory, but after this issue was raised the rule was removed).

DougB
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Old Jul 30, 2002, 10:37 PM
BEC
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Auburn, Washington USA
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Basically with what you have you can't fuse it safely. For more on that look at the third topic in my June 2000 column here: http://www.ezonemag.com/articles/200.../control.shtml

To use BEC and brushless AND fuse it you must either use a MaxCim controller, or another makers and one of Kool Flight Systems' Universal BECs. This latter option didn't exist when I wrote that column.
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Old Jul 31, 2002, 09:19 AM
jrb
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Edina, MN, USA
Joined Oct 1999
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Switch rather than fuse!

Here are a couple of threads regarding fuses.

I use the fuse not as a fuse; but rather as a high current switch.

Though not advised by most; Iíve been flying a fused (between pack and ESC) BECíd BL system for about 3 years Ė propped @ low 30 with 40 amp fuse. I also on occasion use my mega fuse (jumper) when Iím testing a prop or config will pull near 40 amps.

http://www.rcgroups.com/forums/showt...highlight=fuse

http://www.rcgroups.com/forums/showt...highlight=fuse
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Old Jul 31, 2002, 02:27 PM
Dude, where's My Plane?
JasonJ's Avatar
Green Lane PA USA
Joined Mar 2001
2,167 Posts
You could do it if,,,,,,,,,,

A circuit could be made to fuse a brushless system I think, kind of .
Perhaps an inducitve sensor, such as coil wire around one of the motor leads, the induced voltage could drive a trasistor through a diode rectifier to close a small relay on the Cell pack side that is Normaly Closed (NC) and the Normaly Open side (NO) would loop to hold the realy open and would power the RX through a 5V voltage regulator (Back up BEC) via a spare channel plug to the RX.
The circuit could be made even more fancy fairly easaly to have an adjustable "fuse" value by a variable resistor to adjust the transistor gain and to have a motor time out circuit that opened the realy after X amount of seconds to restore ESC power or even get real snazzy and tie it to the channel of the RX your useing so you can reset the motor from your TX via the flap, or LG switch or what ever.
I suppose for just for the sake of saving $200 dollars or so in Brushless equipment people would pay say $20 for a faily simple plug in system like that????,,,,,,
I dono, just thinking out loud,,,,,, and visualizing schematics,,,,
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Old Aug 01, 2002, 08:11 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
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Re: You could do it if,,,,,,,,,,

Quote:
Originally posted by JasonJ
A circuit could be made to fuse a brushless system I think, kind of .
.....
I dono, just thinking out loud,,,,,, and visualizing schematics,,,,
They already do it. It's called 'overcurrent protection', and most modern ESC's have it already.

A fuse is not needed.
..a
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Old Aug 01, 2002, 03:14 PM
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Atlanta Hartsfield, Georgia, United States
Joined Apr 2002
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OK... here's a likely, yet hypothetical, scenario:

Suppose have a plane that uses a 70 Amp ESC and motor to keep a 10-ish pound airplane airborne. In a high-speed dive, you clap the wings and the "fuse" plummets hundreds of feet and buries itself into the turf. You pick up the peices and notice that the only salvageable parts are the ESC, servos, receiver, etc. The motor is toast -- bent shaft. You add the wings to the collection you've started in your garage.

Because it was your last plane, you decide to build another one. This time, you go with a 4-5 lb. model. Your wife is monitoring your purchases and you convince her that you're finished with the big planes and that you don't need another $100-ish speed controller... only a new motor for the smaller plane. You give her the $100 savings; she buys some new shoes; and you're safe for another month.

You buy a brushless motor that needs only 40-ish amps and you pair it with the 70-amp ESC and place them both in the 5-lb plane. All is well. You put this ESC it in the plane expecting to upgrade to a peppier motor in a few months when your wife needs more shoes.

Now, some say that you should not fuse any of the wires -- motor side or ESC side. Fusing the battery side on most ESC setups creates an unsafe (in-flight) condition -- when the fuse blows, the receiver/servos are rendered useless. Fusing the motor side is not reccomended, because you tinker with one of the phases/timing/etc.... It's unnecessary, they say, because most ESCs have overcurrent protection circuitry. Ahhh, but you need protection above 40 amps - the max operating range of the motor. If the motor sees anything between 40 and 70 amps, something is wrong, probably unsafe, and should be fused.

So, you decide to put a fuse in for high-current protection... but where? If you fuse on the battery side, while on the ground, this might be OK. There could be a scenario where somehow you blip the motor while leaning over to pick up the plane that is lying on the ground (sans landing gear). The folding prop becomes a lawn mower and starts making divots. Without a fuse, won't the 70-amp ESC continue to do damage, possibly ruining a prop or twisting the plane into unwanted contortions? Will the overcurrent features at 70 amps be quick enough? Personally, I'd trust a 30/40-Amp fuse before I'd trust any TTL electronics or current-limiting device.

My point is that a fuse is designed to protect anything downstream of it from overcurrent scenarios. I plan on continuing to fuse my electric planes... for safety considerations. If my motors/ESCs are potentially damaged in-flight from some anomaly, if I must choose, I'd rather protect them than the airframe. They're more expensive than CA and balsa.

So.. bottom line: I'll fuse all my planes. Brushed motors on the motor side and brushless motors on the battery side.

Of course, it would be better to protect both. It's a shame that the bulk of the ESC manufacturers do not provide for simple high-current FUSE-ing... and solve this dilemna.

It also amazes me that most ESC manufacturers don't provide a power-interrupt device. The "arm" switch is not a safety switch. All my planes are equipped with a safety on/off switch that interrupts DC power. This is added weight that I always design for. I get mine from Radio shack (illuminated, 12 VDC, 25 A).

I will admit, however, that my next ESC will probably be a MaxCim or I'll look at the UBEC.

Thanks all for your input.
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Old Aug 01, 2002, 03:27 PM
jrb
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If you had a chance to look at the links I posted or some others here ( http://www.rcgroups.com/forums/searc...der=descending ), I have a diagram showing a UBEC off the battery and a fuse between there and my BL ESC.

Oh I happen to use a 40 amp fuse with my 40 amp motor and 70 amp ESC.
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Old Aug 02, 2002, 08:48 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
I for one am very glad that most ESC manufacturers don't provide for a fuse. I also try to buy ESC's that don't have "arm" switches. I don't want an additional point of failure in my models, and in many applications, don't want to carry the additional weight. When a battery is installed, the model is armed - I have a power-interupt system - it's called removing the battery. I've also never had a damaged ESC or motor because I didn't have a fuse. I HAVE had fuses rated for far more current than I was drawing fail on me, both in very critical situations (powering up pulling out of a loop, and another time on takeoff as I was attempting to climb out over the trees at our field).
To each their own.
..a

Oh yes, my airframes are often much more expensive than the motors that power them..
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Old Aug 02, 2002, 09:14 AM
jrb
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Wonder how many folks with 12+ cell planes have removable packs?

I don't remove the packs in my 21 cell Cub or 15 cell FreeStyle; between flights or at home.

Use a fan to cool the packs post flight; pulling air through my aft cooling hole, past the motor and packs just like in flight (I hope).

My wiring set up allows me to charge the cells, or check out the radio, or carry the plane to and from the flight line with maximum safety. On the line a flick of a 2 switches (TX then RX), and then pluging in the fuse (or mega link) and then its armed and dangerous.
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Old Aug 02, 2002, 05:20 PM
(Batteries not included.)
Dave Wenzlick / Slickraft's Avatar
Mesa AZ
Joined Jun 2001
655 Posts
Quote:
Originally posted by jrb
Wonder how many folks with 12+ cell planes have removable packs?
I'm one I guess.

I don't have a single plane without removable packs ranging anywhere from 6-30 cells systems. I can't think of anyone I fly with here who doesn't pull the packs out after a flight to pop in another and we do a lot of 12, 14 and 16 cell planes at the CASL field. I also share many packs between planes and need to get them out at the field so I can go fly again quickly or use them in the next bird to go up. No fuses for me and no BEC on anything that pulls serious current. Not worth the risk IMHO...

Dave
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Old Aug 02, 2002, 05:26 PM
LiPo Suction Specialist
JDCochran's Avatar
Atlanta Hartsfield, Georgia, United States
Joined Apr 2002
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To fuse or not to fuse. It's a great debate. There's really some good discussion on this subject. The manufacturer's should take note. I'd LOVE to see a(nother) technical article on the state of fusing. In my experience, unfused high-current devices almost always BURNS the insulation off the wiring when max current is exceeded. In my 12 years of building and flying electrics, I've exceeded max current of the wiring MANY times.... Here's a subtle point: when I've burned the insulation off the wiring... it's ALWAYS occurred while I'm on the ground... usually in the shop and never at the field (either in the air or preparing to be in the air). For the simple fact that I don't want to burn my house, car, or flying field down... I'll fuse. I've done some bonehead things in my quest to get airborn with a new plane. The latest: leaving my soldering iron on all night and resting near the tail feathers of my Electrostreak. (did I admit to that in public?).

As for expensive electronics and motors downstream of the battery... where or whether to fuse based on brushless or brushed is also an interesting debacle. Based on my experience as a control systems engineer where I design panels with many dc-powered devices feeding electronic controls (plant-floor computers), I ALWAYS FUSE TO PROTECT THE FIELD DEVICES... This is because the computers have internal safeguards against overcurrent (usually opto or inductive isolation). The analogy here would be the motor as a field device and the ESC as the electronic control. For those who understand this: fusing the power supply ckt to a PLC is not only redundant... it's redundant.

Many use the fuse as a safety switch and mount it in a holder for easy access outside the plane. This is a great idea. Although I mount mine inside, I use an automotive-type fuse and holder I get at Radio Shack (RS 27-1231).

http://www.radioshack.com/product.as...5Fid=27%2D1231

Thanks, all, for the fuse discussion.

Regards,
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Old Aug 02, 2002, 05:29 PM
LiPo Suction Specialist
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Atlanta Hartsfield, Georgia, United States
Joined Apr 2002
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Andy, two months ago, when I buried my Goldberg Mirage that I purchased in 1989 for $60, I sure was glad the $200 in jeti motor and ESC survived. I can re-bild the "fuse"-lage for $10.00 in balsa/ply.

I'm a newlywed and don't have my wife calibrated to the notion of expensive airframes.

Also, Andy -- was it you that flew my Partenavia at the tail-end of SEFF.. when everyone was packing up on Sunday?

If so, I've added the Aeronaut props you suggested and also adjusted the thrust angle of the motors slightly upwards. I also added wing struts (guy wires) to keep the flimsy wings from deflecting in dives.

I've flown her myself 20+ times. I've been having a competition with myself to see how long I can stay airborne. Latest record is 24 minutes (I ride thermals at 25% throttle) on 7 cells.

Regards,
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Old Aug 03, 2002, 08:24 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
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I don't think that was me. I don't recall flying anyone's model later that day, and I was there until most were packed up and gone..

Ok, jrb, if you don't remove the pack, then unplugging it works too (see how Jim Bourke does it with his SpaceWalker).
..a
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Old Aug 03, 2002, 02:02 PM
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N. Staffs, UK
Joined Jan 1997
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As far as fusing BEC equippped planes between the battery and ESC goes I personally would regard that as an almost criminally dangerous thing to do.

Fuses can and do blow unexpectedly, sometimes simply from "wear" (heat cycles). If that happens you've now lost all control and have a plane about to crash. I don't mind you breaking the plane but I mind very much that your now uncontrolled missile might crash into someone, possibly even me.

Like Andy I don't like fuses or arming switches and I certainly wouldn't put any mechanical switch in a high current power line. The connectors are plenty for me. Deliberately adding multiple additional failure points into a system is not in my view a safe or even sensible thing to do.

Steve
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