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The 5 amp ESC Problem

Old 11-03-2003, 11:46 PM
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Uncas
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Default The 5 amp ESC Problem

I am using a 5 amp ESC on my Tiger Moth and my Dandy Sport. So this limits the amp draw therefore making it an interesting problem to pick the best EPS. I can raise battery volts to get more watts but it seems that as the voltage increases, the efficiency decreases and in some cases the lower voltage setup is going to produce more thrust, plus I gain a weight and cost advantage from a reduced cell count.

So I think buy a bigger ESC. But maybe I run into another limit - the battery discharge capability.

I am not ready for Li-Ion or brushless motors yet, just trying to make the most of what I have.
Old 11-04-2003, 08:28 AM
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Matt Kirsch
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Default RE: The 5 amp ESC Problem

Actually, the ESC does not physically limit the current to 5 Amps. That's how much it can handle. A motor/prop/battery combination is going to draw what it's going to draw, regardless of what ESC you're using. The problem comes when the motor/prop/battery draws more Amps than the ESC can handle. Then it burns up.

Another thing to consider is that when you raise voltage (increase cell count) without changing anything else, you also automatically raise the current. To keep the current from getting too high, you need to decrease the propeller load on the motor, by either using a smaller propeller, or using a higher gear ratio.

Specifically, what "5 Amp" ESC do you have? The GWS ICS100, which is what I suspect you have, is underrated. As long as you don't push full throttle all the time, it will easily handle 7-8 Amps. This is plenty for both planes you're flying, at up to 8 cells.
Old 11-04-2003, 06:09 PM
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Uncas
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Default RE: The 5 amp ESC Problem

Yes, I have a GWS ICS 100, and a Great Planes C-5 nano. I didn't know that about the ESC rating. Thanks for telling me.
Old 11-04-2003, 10:53 PM
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Dr Kiwi
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Default RE: The 5 amp ESC Problem

Well said, Matt. UIncas IS okay for his current aircraft, but if he wants to move on to an EPS 300C, 350C or 400C powered plane, which might well draw 8-10A or more, I would suggest he get an ICS 400 or, better, a Pixie 20P to be safe.

Cheers, Phil
Old 11-04-2003, 11:05 PM
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Uncas
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Default RE: The 5 amp ESC Problem

Matt,

Thanks again! I love how people post incorrect assumptions right off the bat, DOH! These forums are great.

I recently bought a 9.6 volt battery for my Dandy Sport. I have been using a 7.2v battery. Looking at the GWS charts I could potentially burn up my ESC, so I will use a smaller prop. The only thing is I bought GP AAA battery pack, 700mah nimh. I really don't know if this battery can supply greater than 8 amps. I am struggling a bit with this issue. Certain battery vendors market high current capabilty but GP doesn't really say anything.

Can I burn up my battery by overloading it?
Old 11-05-2003, 08:17 AM
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Matt Kirsch
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Default RE: The 5 amp ESC Problem

Sounds like you're well on your way to becoming an electric expert in your own right

In general, the ~700mAh AAA NiMH cells are good and all, but they're limited to about 7 or 8 Amps, maximum. At that level, the voltage is already starting to drop off under the strain, so you really can't run the battery at full throttle for the whole flight.

Your best bet for finding out the capability of a particular brand/size cell is to check the forums. Manufacturers grossly underrate their cells due to liability concerns, and many vendors don't post the same information for the same reasons. The only way we know, for example, that AAA NiMHs are good for 7-8 Amps is because many generous people are donating their time and money to testing them in very unscientific ways. Sometimes they even ruin a pack. Practical experience is what they call it.

You can definitely burn up your battery by overloading it.

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