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Too much voltage?

Old 10-13-2003, 10:55 PM
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scudrunner77
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Default Too much voltage?

I have an older Futaba receiver with built in electronic speed control: MCR-4A.
It is rated for 280-540 class motors and 7.2V or 8.4volts. I have been interested in some kits out there using 9.6volts. Does anyone know if I will fry this setup using 9.6V with a speed 400 motor or similar. An extra 1.2 volts doesn't sound like a lot to me...but I don't know how fragile this stuff is.
Also, I have a House of Balsa T-6 I would like to convert to electric. I was told a speed 500 geared with 12 volts would do....wouldn't 12 volts fry the receiver? Does a ESC regulate voltage to the receiver when using two separate units?

Thanks
Old 10-14-2003, 08:08 AM
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Matt Kirsch
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Default RE: Too much voltage?

Unfortunately, it's not a simple yes/no answer. There are a lot of factors at work here. The best anyone can say is it MIGHT work with an extra cell, especially if you're not using it to its full Amps capacity. Personally, I wouldn't chance it, but that's me.

Yes, 12 Volts will fry the receiver. In fact, anything above ~6.5 Volts will fry the receiver! That's why most ESCs have battery eliminator circuits, BECs. A BEC is a voltage regulator that will reduce the voltage from whatever the main battery is down to 5 Volts. Most built-in BECs are good for batteries up to 10 cells (12 Volts). After that, you need to get a separate receive pack or an Ultimate BEC.
Old 10-14-2003, 08:24 AM
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Default RE: Too much voltage?

Thanks for the info on BECs.....

So the extra voltage might damage the Futaba receiver/ESC.

I was reading more of the fine print about the Futaba receiver/ESC, and it is rated at 100amps continuous and 450amps momentary. Don't most speed 400/9.6v
setups use a 20amp ESC? So maybe I will be ok with current draw....
Old 10-15-2003, 10:59 PM
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Dr Kiwi
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Default RE: Too much voltage?

I simply cannot believe that extraordinary amp rating for an ESC! Few ESC's are rated as high as 100A, and surely nothing known to man will survive 450A?

I wouldn't risk any of my planes to such an outmoded system - I'd just go out and spend $50-60 for a Castle Creations Pixie 20P and a decent modern receiver.


Cheers, Phil
Old 10-15-2003, 11:12 PM
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Default RE: Too much voltage?

I was waiting of someone to say something. I have read it ten times, but that what's in the print 100amp-450 momentary....I have a feeling they mean 10.0 and 45.0???
Old 10-16-2003, 06:56 AM
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Default RE: Too much voltage?

No. That's an ESC for an R/C car. R/C car ESCs use a different rating system. The ESC can't really handle 450 Amps or even 100 Amps. An R/C car works differently from an airplane; the typical mode of operation is, "accelerate, coast coast coast coast coast." There's a momentary burst of very high current to get the car up to speed, but it only takes a tiny amount of current to maintain speed.

Nah, that 100 Amp rating is actually the true momentary rating, and 450 Amp is the really momentary dead-short rating. It's still got plenty of chutzpah to run a Speed 400, but...

Another major problem is that the receiver is most likely on an R/C car frequency. Forget flying it at an AMA club-operated flying field. They won't let you because it's against FCC regulations, and breaking FCC regulations voids AMA liability coverage for you and the landowner AFAIK. I'd also be worried about the range of the radio. R/C cars don't get nearly as far away as R/C airplanes, and the radios don't have the same amount of range.
Old 10-16-2003, 08:22 AM
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Default RE: Too much voltage?

Maybe your right about the guts of the ESC being borrowed from a rc car tech...but it's an electric airplane receiver with built in ESC. I've got the box, owners manual, everything that came with it. Family member of mine bought it some time ago and only used if for a while. It's AM, 72Mhz, channel 54. Don't know how old it is...transponder has the gold sticker on it. I have been using it just fine in my Gentle Lady(unpowered) until I get an electric. Think I will buy all new gear so I can have more airplane choices, but sounds like it would be fine for anything up to 8.4 volts, slowflyer or foamy.



Thanks
Old 10-16-2003, 08:24 AM
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Default RE: Too much voltage?

nice....transponder...Gentle lady squawk VFR right?!?!?

I meant transmitter!

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