How much amps (continuous & peak) will a brushless system draw?
11-24-2007, 10:08 AM
#31
That's the thing...you're never stalled when the car is moving. You can't have it both ways...a 70 MPH sprint from a dead stop at every turn?
The traction is another issue. On a race day, Rev would nearly pull your shoes off. Washed, vacuumed and VHT'd. I highly doubt that your track is superior to what Rev's on-road track was before it got turned into an off-road track. Not saying it's worse, but I really doubt you have something unique there.
My point was that a large track will lower the peak amp draws, not raise them, since the car will almost never be near stall.
The traction is another issue. On a race day, Rev would nearly pull your shoes off. Washed, vacuumed and VHT'd. I highly doubt that your track is superior to what Rev's on-road track was before it got turned into an off-road track. Not saying it's worse, but I really doubt you have something unique there.
My point was that a large track will lower the peak amp draws, not raise them, since the car will almost never be near stall.
So you are saying a large track is just a big oval with no tight turns? We have a huge carpet track up in the NW and while there are some very large straights there are also very tight sections that will def. crank up the amps. I saw more than one mod touring car have its batteries and motor desolder.
Anyone have a data logger?
http://www.rctech.net/forum/attachme...7&d=1194594308
http://www.timezoneracing.com/DSC_0955.JPG
11-24-2007, 10:24 AM
#32
No, I'm saying that a car on a very large track (150-200' straight) will carry more corner speed than would a car on a shorter track, so it will be farther from "stall", thus will generate lower peak amp loads.
I think datalogger would be perfect for this question.
I think datalogger would be perfect for this question.
So you are saying a large track is just a big oval with no tight turns? We have a huge carpet track up in the NW and while there are some very large straights there are also very tight sections that will def. crank up the amps. I saw more than one mod touring car have its batteries and motor desolder.
Anyone have a data logger?
http://www.rctech.net/forum/attachme...7&d=1194594308
http://www.timezoneracing.com/DSC_0955.JPG
Anyone have a data logger?
http://www.rctech.net/forum/attachme...7&d=1194594308
http://www.timezoneracing.com/DSC_0955.JPG
11-24-2007, 10:33 AM
#33
A 3.5r has a rating of 620 watts (from Novak). With that in mind then theoretically at that rpm the motor has gotta be drawing at least ~80 amps at what ever mid to high rpm value that occurs. I read that motors are more efficient (i.e. generating more watts) as the rpms rise (to a certain point then efficiency drops off again... kinda like peak hp and tq relationship figures but in our case inversely proportional as we want more rpm with less amperage draw).
Thinking that I'd expect 45 amps to be on the low side then... perfectly in line with large tracks where you are not under huge amperage draw acceleration and spending more time in the higher rpms near the peak watt efficiency point (or in his case too much power and only going partial throttle to obtain that low 45 amp figure).
Thinking that I'd expect 45 amps to be on the low side then... perfectly in line with large tracks where you are not under huge amperage draw acceleration and spending more time in the higher rpms near the peak watt efficiency point (or in his case too much power and only going partial throttle to obtain that low 45 amp figure).
Last edited by HPI RS4; 11-24-2007 at 10:44 AM.
Sooo...to put it another way, "Whatever I think they said it was going to pull, it must fit whatever I thought it was going to pull in the first place."
11-24-2007, 10:56 AM
#35
I think that to get a mean of 45A on a large track, you would have to see spikes many, many times that to get a mean of 45, because for the majority of a lap, it would be far less than 45A. It's just a math thing.
I'm not saying that his mean isn't 45, just that to get a mean of 45, when you only have a short time at peak draw, that peak better be large.
You guys ARE talking about the mean average..right?
I'm not saying that his mean isn't 45, just that to get a mean of 45, when you only have a short time at peak draw, that peak better be large.
You guys ARE talking about the mean average..right?
11-24-2007, 01:35 PM
#36
Drewdc90 - under high amperage draw I doubt an NiMH is anywhere near 8.4 volts. Doesn't battery labels usually rate cells at ~1.25v @ 30 amps... and guess what voltage drops as amps and heat (unfortuantely) go up. Depending on the need for acceleration I doubt you would be able to stay under 30 amp draws anyway when your always bursting. And at those figures 1.125v * 6 cells = 6.75 volts which is far from 8+ volts. I've speculated that the voltage drop could be dipping into the 5's under high amp draw with NiMH?
Thanks to every body for the helpful knowledge. Let's keep this thread going smoothly to benefit us all.
Thanks to every body for the helpful knowledge. Let's keep this thread going smoothly to benefit us all.
I didn't say that them numbers would 100% right.
Drew.
11-24-2007, 01:52 PM
#37
I think you ment 1.25 * 6 cells = 7.44V which is pretty close (over 7.2 which i used) but as you said thats only 30 amps. When i said 'the real voltage for a nimh battery would be over 8 volts' I didn't mean tha battery would stay at that, I ment that thats where the voltage drop would be from not 7.2.
I didn't say that them numbers would 100% right.
Drew.
I didn't say that them numbers would 100% right.
Drew.
I think I found the problem...my calculator must be broken.
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