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General RC Heli Discussion Discuss general topics on rotary wing aircraft, including construction, Servo's, Gryo's and Stabilizer discussions. Heli Pro Shop

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Old 01-08-2007, 02:54 PM   #11
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I dont think you will be close to 35amps i ahve a T-rex and the most i have pulled is 26 and that with Full throttel and full +10 pitch.
What do you mean , I can land upside down
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Old 01-08-2007, 08:52 PM   #12
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Can 773,

The other way around, although it is subtle with such a small pack.

When you hear the head bog under load, the battery voltage is usually dropping and hte current rising to meet the increased power demand from the motor.

Having 2 packs in parallel will help keep the voltage higher under load.
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Old 01-08-2007, 11:49 PM   #13
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Originally Posted by tech1
Can 773,

The other way around, although it is subtle with such a small pack.

When you hear the head bog under load, the battery voltage is usually dropping and hte current rising to meet the increased power demand from the motor.

Having 2 packs in parallel will help keep the voltage higher under load.

Its all watts, more voltage gives more rpm...which takes more power (watts). You wont get the watt increase only from increase in voltage (wouldn't that be nice, but it doesnt happen), it will work out that both your voltage and current draw are going up. Regardless whether you are bogging the head or just hovering if your headspeed is higher in all those cases because of the higher voltage, you watts will be higher and therefore both your current and voltage will have increased.

If you maintain the same headspeed your system will run slightly (but probably not measurably) more efficient due to the slightly higher input voltage.

Every time a manufacturer comes out with a pack that can hold better voltage under load my current draw goes up (all other things being equal) not down...which is what will happen with two packs in parallel.
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Old 01-09-2007, 12:51 PM   #14
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Using a battery that is not capable of putting out enough voltage to the motor will result in higher amperage pull as the motor chokes during pitch changes (or using a motor that isn't exactly up to the task of what you're doing), thus consuming more amperage in order to try and make up the difference in dropped voltage.

It's almost always better (performance and electronics wise) to use higher voltage if the option is available to you as it will result in lower amperage draw.

This is one of the big problems with Aligns new T-rex 600, when they advertise it to fly on 6S lipos. Sure it flies well on 6S, but it peaks near 90 amps in heavy pitch changes which will pretty much destroy most lithium batteries out there! Meanwhile, going to 8 or 10S on a lower kV motor with adjusted gearing will see your amperage stay in the sub-50 area even during pitch pumping.

Because micro helis typically operate on lower voltage, this is why we often see the need to have 35 amp speed controllers on them and sometimes it's barely enough during aggressive flying. Meanwhile, a helicopter 4 times the size will get by on nearly the same amp speed controller if the voltage is considerably higher. I've seen guys fly .50 size birds using 8 or 10S on a 45 amp ESC (CC45HV).

You can't go by watts alone. If your voltage increases but your amperage pull decreases, then it's entirely possible that your output wattage stays roughly the same, but your system efficiency goes up.

Let's assume a 12 volt system that pulls 30 amps. This gives you 360 watts. Now we take the same system and increase voltage to 18 volts with some gearing changes. Now after this voltage and gear change, lets say amperage pull goes down to 20 amps, by these numbers our output power is still at 360 watts but the system is running much more efficiently. (This is just the general idea, obviously you won't get a perfect step down like that, but it gets my point across).

EDIT: I forgot to mention that assuming RESISTANCE stays the same, increasing voltage WILL increase current, so in this regard you are correct. I didn't read your post properly the first time around Chad.

If you use the same motor and speed controller and SAME GEARING (most important) but increase voltage then amperage will (usually) go up as you said.
My whole post is based on the idea of setting up your power system before having the parts available (so this usually means picking a lower kV motor with adjusted gearing) in which case my previous paragraph applies, as higher voltage will give you lower current consumption with the same output wattage.

It's all very confusing stuff, trying to figure out what you need to fly your model. In this regard, nitro is just oh so much simpler..
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