More Voltage = Less Amp Draw?
 

Is this true? I know the guy that got the 160+mph run in RCCA was running only a CC Pheonix HV85, which is rated at 85amps continuous, in his car running 8S on a Neu.

The motor I plan to use is a 1530, and BK-electronics.com says its rated like 55amps continuous. If I run something like 6S or more, is ok to run an CC Pheonix HV45 (45 amps continuous?).

And damn...my third thread in like 2 days...I think I'm starting get annoyed LOL

With the same power output, a higher voltage setup with the appropriate motor will have a current draw that is less than half of a lower voltage setup with an appropriate motor. With higher voltage comes higher efficiency, so for the same power input, a slower motor with a higher voltage will put out more power than a faster motor/lower voltage setup.

It's annoying when you visit the forum without posting new threads and share information.

???? That makes no sense whatsoever. I've been on the forum quite a while and do contribute as much as I can whenever I can, but compared to a majority of guys I know very little about brushless.

I said that as a joke...not to get flamed. :028:

I think he was talking about people in general, not you.

Hi,

From my dim memory :

P=IV where P is power & I is current & V is Voltage

where heat is wasted power probably using this formula P=IsquaredR (R is internal resistance of the system)

Of course efficiency comes in somewhere too.

From this, one can say that higher voltage X lower current gives a similar result to higher current X lower voltage. However, in the process, less energy is wasted using a higher voltage.

Does this make sense ? I hope I'm right here. Feel free to correct me if I'm leading everyone down the garden path.:o

I'm in the process working on something based on the above thinking. I am seriously thinking of using a higher voltage esc like the BK36120 or BK3695 with 8S & a 12XL motor instead of a 4S with 7XL motor.

Regards,
Joe Ling

I hope so...cause if that was directed to me... :012:

joeling - that was exactly what I was looking for - thanks. I think 8S should be plenty to overcome the 10 amp difference in continous draw, though I may just get the Pheonix HV85 and forget about it. Also depends on the packs...dropping ~200 bucks for 1 set of packs is pretty hard for a smaller truck lol... Your explanation also seems quite logical and reasonable. It must be pretty accurate.

Seeing the top pics of the CRT .5, I really have no idea how you'd be able to fit a 6S pack in there unless they're small capacity. This thing ain't exactly got an abundance of real estate:
http://www.jamminproducts.com/CRT5images/Large3Qtr.jpg

Oh, I don't know. I just looked at that pic and the chassis is at least 14" long.

Of course, that was on my 21" monitor. :005: ;)

Power is watts and watts is power.... pure horsepower. :)

No doubt the best way to build power is with high voltage/low current.

The key is to resist the urge to strap in more motor than the formula requires. That will only lead back to higher amps and the heat that comes with it.

Nothing's free... it's too bad we can't just take the same motor that works well on 4s... and run it on 6s or 8s and get less current. ;) But it doesn't work that way unfortunately.

More voltage equals higher amps (and heat) if everything else remains the same. So we have to change everything....

Wheelbase is ~220mm according to Tower, which means that the chassis plate area itself must be at LEAST 150mm, probably more. The only thing the lipo's must be short enough to clear is the steering servo, which can't be more than 25mm or so.

However, I am using smaller packs which are only 35mm wide and 98mm long. These will be used in 8S configuration. The higher voltage should reduce the current requirements. I did some simple calculations and even factoring ~25% more watts than the motor's continuous rating is, I only came out to 35 amps continuous. The cells are capable of 42amps, and my ESC will be capable of 45 (and has a programmable cutoff which protects against over-drawing). Again, this is all preliminary, but as of now, I am assuming it should work pretty well. My planned motor is a LMT1530 by the way.

My system is pulling 60A at 15V (4s) on a typical full throttle accleration... 60 x 15 = 900 watts.

So to get the same 1.2 or whatever, horsepower (900 watts) using an 8s setup would only need to pull 30 amps. Which also means less heat, more efficiency. Also, because of the lower amps... the battery voltage will not drop as much, so you need even less motor to make that 900 watts... or you get a little bonus... maybe the battery holds at 31.5V instead of the 30v... that's 945watts.

Hey that's 45 watts for free... so I was wrong about the nothing for free thing. :)

I think you're a little off on your servo length. Most standard steering servos are around 1.6" long (40.64mm). Even a mini servo like a Hitec HS-81MG is 30mm long.

The packs sound like they should fit ok. They sound like the same size as I use in my 18th scale vehicles.

Yay! Free power! Thats gotta be the best thing I heard all day.

Hmm, so 60A at full throttle on 15V. I'm running 30V (to be safe) and my motor is rated 770 (say 800 to be safe). 800/30 = 26.7 - which is alot less than the battery and speed controls rating. Sweet! This is gonna be a fun project (but does anyone think this may be too much motor?)

Well, off or not with the servo lengths, the packs should fit with room to spare.

all i have to say is, bp ur a psyco!!!!!!!!!! 8s in a flippin crt.5!!!!!!! DAM!!!!!!!! LOL