Amp Draw Question

[mschaffer66]

Ok, so I have ran my Supercat with two different props. Once on 4S, 2200KV through a 45:66 gear drive on the stock UL1 3 blade prop and it pulled 74A. Then I ran it with an X442 prop and it hit 111A. I was using one of those watt meters that stores peak current.

All of those are well within spec of my ESC and batteries so I have no concern there.

My real question is that those are peak current, which to me would be the second you nail the throttle to get up on plane, after that it seems like the current should drop off a bit when you are cruising on plane. Is this true? If so what kind of drop off typically would occur?

I'm not really looking to drive my ESC right to the edge, but if this 111A is just a 2 second peak and its running constant at like 80A(for example) I know I've got plenty more room to play with.

Thanks :)

[Jesse J]

You might want to get an EagleTree or one that actually logs the data. It is good to see where the peaks are and where the average is. Here is an example of a plot you can make. You will probably be able to answer many questions with this cool interface that lets you plot many different things.

On the first, I plotted amperage vs. time. You can see the turns - the spikes, then the drop as it gets back up. The main spikes I attribute to wave jumping and re-entry, but not totally certain.
the second is Watts and the red line is the cumulative mah or capacity of the battery being used.

[mschaffer66]

That is some awesome software/device... I want one now :)

But I'm kinda seeing from there your peak was like 110ish Amps and your average was around more like 35A... That is actually a much larger difference than I had expected.

I'm not going to assume anything until I have data to prove it, but It looks to me that if my cat is even remotely similar in trend the constant draw is considerably less than that peak of 111 that I saw.

I know that safety factors are always a good thing to have, but based on your data what amperage ESC are you running? To me it seems like in that config 60-80A continuous would be plenty safe.

God I'm sooo getting one of those EagleTrees :)

[Jesse J]

yep pretty sweet! software comes with it and they have great service. I had them re-solder some wires and it cost me $10.

I was using a 200A ESC to be safe, but this gives you the data to help choose just how much extra room you want. Based on this data, I would not go lower than a 150A ESC. The extra room helps things not get hot and helps manage the spikes and their stress on the electronics.

[mschaffer66]

What kind of boat were those numbers from?

After seeing that I guess I'm kinda rethinking how big of a an ESC traxxas actually had to make for the new Titan...