high kv & less cells VS low kv & more cells
06-24-2011, 08:03 AM
#16
Tech Champion
Thread Starter
I had a 5s 1400 and a 4s 1900 setup and loved them both. I think the 1400 was a little smoother.
Normal you reach 25900rpm with the 1400 one and 28120 with the 1900
. The difference in torque given by the lower kv motor is compensated by the lower rpm
Depending on if I was racing with nitros and running 15-20 min mains I would us the 5s 1400 system as it would go 22 min at Revalations. 25+ at TA and run ALOT cooler than the 4s system, the 4s system was lighter but would only go 12-14 min tops and run hotter so when racing in a 115 deg weather it got cookin.
The heat is definitely a difference, but was the 1400 5S enough for the top end? I know lower kv motors don't like to have bigger pinions..
Another thing to look at is you can use 5s 5000 20-30c batts (or 6s) with absolutly no issues. the 4s needs alot higher C rated batts
Why?
Normal you reach 25900rpm with the 1400 one and 28120 with the 1900
. The difference in torque given by the lower kv motor is compensated by the lower rpmDepending on if I was racing with nitros and running 15-20 min mains I would us the 5s 1400 system as it would go 22 min at Revalations. 25+ at TA and run ALOT cooler than the 4s system, the 4s system was lighter but would only go 12-14 min tops and run hotter so when racing in a 115 deg weather it got cookin.
The heat is definitely a difference, but was the 1400 5S enough for the top end? I know lower kv motors don't like to have bigger pinions..
Another thing to look at is you can use 5s 5000 20-30c batts (or 6s) with absolutly no issues. the 4s needs alot higher C rated batts
Why?
06-24-2011, 08:51 AM
#17
Now you are talking about voltage drop. That is a separate issue. I really doubt over the 6 inches of wire that a voltage drop will be anything significant here. Don't forget this is a non continuous load on conductors exposed to air. Also this a DC system so you won't have to deal with Power factor and reactive losses in the motor.
For a simple system (which this isn't of course, but still provides valuable and useful insight) the power loss due to current is related to the square of the current times the resistance. But current also causes voltage drops, it's simply a different way to look at the same thing, either approach will result in the same power loss and thus reduced efficiency. My apologies if I jump around a little due to familiarity with the subject. Note in these beasts currents can be well over 100 amps, since it's a square function that can be significant, even with fairly low resistances.
As far as a non continuous load, well how can that be DC? There is a lot of switching going on, hardly a DC system (after the battery to speedo portion anyway). However power factors, phase lags, etc, are another topic.
06-24-2011, 09:13 AM
#18
Just something to say here:
Last year I ran 2050kv on 4s 5200mah 30C. With my Tekin 2050kv and MMM ESC, with punch control at 100% and lowest timing, it could easily wheelie in the street. With my now 6s 3600mah 30c and 1400kv motor, and the same settings, it can not. I would say it is a little smoother and not quite as ballistic on the top end. Plus the run times are better and it runs much cooler.
Another valuable tuning options people forget about is the throttle curves (at least with castle ESCs). It's a great way to limit the power down low, which is where brushless can have issues, and then once you get into an open section let it rip. Radio expo and epa are also good to use, if you'll notice most of the pros have their epa limited.
Last year I ran 2050kv on 4s 5200mah 30C. With my Tekin 2050kv and MMM ESC, with punch control at 100% and lowest timing, it could easily wheelie in the street. With my now 6s 3600mah 30c and 1400kv motor, and the same settings, it can not. I would say it is a little smoother and not quite as ballistic on the top end. Plus the run times are better and it runs much cooler.
Another valuable tuning options people forget about is the throttle curves (at least with castle ESCs). It's a great way to limit the power down low, which is where brushless can have issues, and then once you get into an open section let it rip. Radio expo and epa are also good to use, if you'll notice most of the pros have their epa limited.
06-24-2011, 09:23 AM
#19
I'm talking about voltage drop because that is directly related to current losses, a significant source of inefficiency in any electrical power system, save the special case of superconductors. Not just in the few inches of wire, but in the several feet of wire in the motor windings, the transistor circuitry in the speed control, connectors, solder joints, and the batteries, they all contribute.
For a simple system (which this isn't of course, but still provides valuable and useful insight) the power loss due to current is related to the square of the current times the resistance. But current also causes voltage drops, it's simply a different way to look at the same thing, either approach will result in the same power loss and thus reduced efficiency. My apologies if I jump around a little due to familiarity with the subject. Note in these beasts currents can be well over 100 amps, since it's a square function that can be significant, even with fairly low resistances.
As far as a non continuous load, well how can that be DC? There is a lot of switching going on, hardly a DC system (after the battery to speedo portion anyway). However power factors, phase lags, etc, are another topic.
For a simple system (which this isn't of course, but still provides valuable and useful insight) the power loss due to current is related to the square of the current times the resistance. But current also causes voltage drops, it's simply a different way to look at the same thing, either approach will result in the same power loss and thus reduced efficiency. My apologies if I jump around a little due to familiarity with the subject. Note in these beasts currents can be well over 100 amps, since it's a square function that can be significant, even with fairly low resistances.
As far as a non continuous load, well how can that be DC? There is a lot of switching going on, hardly a DC system (after the battery to speedo portion anyway). However power factors, phase lags, etc, are another topic.
Even if it is 100 amps, Its not 100 amps for 3 hours. contiunous load is a load that runs 3 hours or more. This is to account for the heating of the conductors.
You are wrong current does not cause voltage drops. Resistance cause voltage drops. The wire, conductors, solder joints etc all act as a resistor and provide resistance to the circuit. In any dc circuit, you will have a voltage drop over a resistor as long as there is a current flow.
We are also talking about .005 ohms here of resistance throughout the entire circuit between conductors and esc circuitry.
So lets say in fact that there was 100 amps flowing throw the entire circuit.
100amps * .005 ohms = .5 volts.
so out of the 22.2 volts you are losing half a volt. Really not all that much to worry about.
It would be more worried about the efficiency of the MOSFET more than anything as that is really the key to any good ESC.
06-24-2011, 09:56 AM
#20
these are dc motors, you can't get AC from a battery unless you use a power inverter which would be useless in this case. Yes, there are MOSFET transistors inside the speed control that do some switching. But this is far from an Alternating current waverform. This is a basic DC motor controlled via pulse width modulation(PWM). Then of course you have a basic PID control sysem in the case of a sensored system.
Assuming brushless, the only thing being discussed by anyone else here, the speed control acts as an inverter of sorts with its switching. The power going to the brushless motor has a significant AC component to it (not a pure sine wave, but certainly not just DC). Try connecting the DC of the battery directly (and briefly!) to a brushless motor and see what happens. PID doesn't really apply, this isn't a servo system in the traditional sense. Control yes, but mostly just timing-rotor location, it's not a PID feedback loop in the sense that term suggests.
Even if it is 100 amps, Its not 100 amps for 3 hours. contiunous load is a load that runs 3 hours or more. This is to account for the heating of the conductors.
If it takes 3 hours to see power losses, why does the motor and speedo heat up in a 5 minute race? I do agree it's not a continuous load.
You are wrong current does not cause voltage drops. Resistance cause voltage drops. The wire, conductors, solder joints etc all act as a resistor and provide resistance to the circuit. In any dc circuit, you will have a voltage drop over a resistor as long as there is a current flow.
Voltage drop is a combination of current and resistance, those parameters multiplied. And yes, there is a voltage drop over the various resistances, that is where the efficiency losses come from. Ever notice that resistors tend to heat up? That's the power loss we are discussing. Including that in the motor windings, where a lot of it occurs.
We are also talking about .005 ohms here of resistance throughout the entire circuit between conductors and esc circuitry.
So lets say in fact that there was 100 amps flowing throw the entire circuit.
100amps * .005 ohms = .5 volts.
so out of the 22.2 volts you are losing half a volt. Really not all that much to worry about.
Then please explain where all of the heat comes from. (Do you have any experience with these electric 1/8 beasts?)
It would be more worried about the efficiency of the MOSFET more than anything as that is really the key to any good ESC.
Agreed its important. Reduced current will make that somewhat less of an issue, well assuming enough voltage breakdown capability.
Assuming brushless, the only thing being discussed by anyone else here, the speed control acts as an inverter of sorts with its switching. The power going to the brushless motor has a significant AC component to it (not a pure sine wave, but certainly not just DC). Try connecting the DC of the battery directly (and briefly!) to a brushless motor and see what happens. PID doesn't really apply, this isn't a servo system in the traditional sense. Control yes, but mostly just timing-rotor location, it's not a PID feedback loop in the sense that term suggests.
Even if it is 100 amps, Its not 100 amps for 3 hours. contiunous load is a load that runs 3 hours or more. This is to account for the heating of the conductors.
If it takes 3 hours to see power losses, why does the motor and speedo heat up in a 5 minute race? I do agree it's not a continuous load.
You are wrong current does not cause voltage drops. Resistance cause voltage drops. The wire, conductors, solder joints etc all act as a resistor and provide resistance to the circuit. In any dc circuit, you will have a voltage drop over a resistor as long as there is a current flow.
Voltage drop is a combination of current and resistance, those parameters multiplied. And yes, there is a voltage drop over the various resistances, that is where the efficiency losses come from. Ever notice that resistors tend to heat up? That's the power loss we are discussing. Including that in the motor windings, where a lot of it occurs.
We are also talking about .005 ohms here of resistance throughout the entire circuit between conductors and esc circuitry.
So lets say in fact that there was 100 amps flowing throw the entire circuit.
100amps * .005 ohms = .5 volts.
so out of the 22.2 volts you are losing half a volt. Really not all that much to worry about.
Then please explain where all of the heat comes from. (Do you have any experience with these electric 1/8 beasts?)
It would be more worried about the efficiency of the MOSFET more than anything as that is really the key to any good ESC.
Agreed its important. Reduced current will make that somewhat less of an issue, well assuming enough voltage breakdown capability.
Last edited by Dave H; 06-24-2011 at 10:11 AM.
06-24-2011, 11:34 AM
#21
Hello,
I would like to know what would be the difference between a setup with high v and less kv and low voltage with high kv for comparable setups (same max RPM)
Let's compare these two setups, they both reach 31080rpm:
- 6S 1400kv
- 4S 2100kv
How would they theorically compare in:
- heat
- torque
- smoothness
- the way the power is delivered
....
I have my own ideas about the question but need to complete some foggy aspects of it.
I would like to know what would be the difference between a setup with high v and less kv and low voltage with high kv for comparable setups (same max RPM)
Let's compare these two setups, they both reach 31080rpm:
- 6S 1400kv
- 4S 2100kv
How would they theorically compare in:
- heat
- torque
- smoothness
- the way the power is delivered
....
I have my own ideas about the question but need to complete some foggy aspects of it.
Your esc and lipo's will have less of a work out on 6s if that is important to you.. reduced amp draw = lower temps and more effecient on the mAH use but keep in mind to get the extra voltage you need more cells so the total weight of a 6s pack will stay very simliar to the 4s pack at a higher mAH so there is no weight savings going from 4s to 6s w/ similar run times. The biggest thing really is you dont have to rely on fans to keep with in temp on the esc, especially on bigger vehicles like truggies (smaller vehicles may not matter much). You lipo's may get more cycles due to reduced amp draw as well.. you can also have a slightly reduced "C" rating on your lipo at 6s but that only goes so far. EX. A 90c 4s 6500 setup would most likely hold out longer before LVC vs a 20c 6s 4400mah setup if they were true ratings. The amp demands are greater on the 4s setup yes but that 4s setup noted can take a ton more amps (585amps vs 88amps) and would hold voltage longer than the 6s setup.. both packs would be of similar weight.
06-24-2011, 09:29 PM
#22
these are dc motors, you can't get AC from a battery unless you use a power inverter which would be useless in this case. Yes, there are MOSFET transistors inside the speed control that do some switching. But this is far from an Alternating current waverform. This is a basic DC motor controlled via pulse width modulation(PWM). Then of course you have a basic PID control sysem in the case of a sensored system.
Even if it is 100 amps, Its not 100 amps for 3 hours. contiunous load is a load that runs 3 hours or more. This is to account for the heating of the conductors.
You are wrong current does not cause voltage drops. Resistance cause voltage drops. The wire, conductors, solder joints etc all act as a resistor and provide resistance to the circuit. In any dc circuit, you will have a voltage drop over a resistor as long as there is a current flow.
We are also talking about .005 ohms here of resistance throughout the entire circuit between conductors and esc circuitry.
So lets say in fact that there was 100 amps flowing throw the entire circuit.
100amps * .005 ohms = .5 volts.
so out of the 22.2 volts you are losing half a volt. Really not all that much to worry about.
It would be more worried about the efficiency of the MOSFET more than anything as that is really the key to any good ESC.
Even if it is 100 amps, Its not 100 amps for 3 hours. contiunous load is a load that runs 3 hours or more. This is to account for the heating of the conductors.
You are wrong current does not cause voltage drops. Resistance cause voltage drops. The wire, conductors, solder joints etc all act as a resistor and provide resistance to the circuit. In any dc circuit, you will have a voltage drop over a resistor as long as there is a current flow.
We are also talking about .005 ohms here of resistance throughout the entire circuit between conductors and esc circuitry.
So lets say in fact that there was 100 amps flowing throw the entire circuit.
100amps * .005 ohms = .5 volts.
so out of the 22.2 volts you are losing half a volt. Really not all that much to worry about.
It would be more worried about the efficiency of the MOSFET more than anything as that is really the key to any good ESC.
6S: 22.2V x 100A = 2220 watts
4S, requires 150 amps for the same battery power: 14.8V x 150A = 2220W
Voltage drops (using your fairly low resistance number, but any number will illustrate the trend):
6S: 100A x 0.005 Ohm = 0.5V
4S: 150A x 0.005 Ohm = 0.75V
Power losses:
6S: 100A * 0.5V = 50W
4S: 150A * 0.75 = 112.5W
A 125% increase in power loss, which goes to heat. In at least some cases, granted not all, this would be considered a significant, possibly even problematic, increase.
Suspect the actual numbers will be larger, don’t believe these systems are 95%+ efficient.
Just something to say here:
Last year I ran 2050kv on 4s 5200mah 30C. With my Tekin 2050kv and MMM ESC, with punch control at 100% and lowest timing, it could easily wheelie in the street. With my now 6s 3600mah 30c and 1400kv motor, and the same settings, it can not. I would say it is a little smoother and not quite as ballistic on the top end. Plus the run times are better and it runs much cooler.
Another valuable tuning options people forget about is the throttle curves (at least with castle ESCs). It's a great way to limit the power down low, which is where brushless can have issues, and then once you get into an open section let it rip. Radio expo and epa are also good to use, if you'll notice most of the pros have their epa limited.
Last year I ran 2050kv on 4s 5200mah 30C. With my Tekin 2050kv and MMM ESC, with punch control at 100% and lowest timing, it could easily wheelie in the street. With my now 6s 3600mah 30c and 1400kv motor, and the same settings, it can not. I would say it is a little smoother and not quite as ballistic on the top end. Plus the run times are better and it runs much cooler.
Another valuable tuning options people forget about is the throttle curves (at least with castle ESCs). It's a great way to limit the power down low, which is where brushless can have issues, and then once you get into an open section let it rip. Radio expo and epa are also good to use, if you'll notice most of the pros have their epa limited.
06-24-2011, 10:23 PM
#23
Efficiency. If you run a 6s system that arrives at the same power output it will require less battery capacity.
BUT the weight will be the same...
Don't know what you mean by this. I was pointing out that the poster got long run times despite the extra weight of his truggy. That said, usually a 6s/3300mah pack is lighter than a 4s/5500
This is how the other poster achieves 20-25 minute runs with a heavy truggy.
Just considering this question for the same weight. Would a 1400kv 6S with a 3300mah lipo have more range than a 2100kv 4S lsetup with 5000mah lipo? I doubt it, but could be wrong..
That is wrong. The 6s/3300mah with 1400kv will run longer than 4s/5000mah/2100kv by a significant amount.
A downside to running 6s is that the chargers become more power hungry which can be problematic at tracks with limited or no power.
BUT you will be able to charge your battery at 4 or 5C with a charger with less Amps. 3300mah in 6S needs 16.5A to be charged at 5C, 5000mah in 4S will need 25A (!)
Why would you want to charge @ 5c?
BUT the weight will be the same...
Don't know what you mean by this. I was pointing out that the poster got long run times despite the extra weight of his truggy. That said, usually a 6s/3300mah pack is lighter than a 4s/5500
This is how the other poster achieves 20-25 minute runs with a heavy truggy.
Just considering this question for the same weight. Would a 1400kv 6S with a 3300mah lipo have more range than a 2100kv 4S lsetup with 5000mah lipo? I doubt it, but could be wrong..
That is wrong. The 6s/3300mah with 1400kv will run longer than 4s/5000mah/2100kv by a significant amount.
A downside to running 6s is that the chargers become more power hungry which can be problematic at tracks with limited or no power.
BUT you will be able to charge your battery at 4 or 5C with a charger with less Amps. 3300mah in 6S needs 16.5A to be charged at 5C, 5000mah in 4S will need 25A (!)
Why would you want to charge @ 5c?
06-25-2011, 05:59 AM
#25
Tech Initiate
Perhaps I can explain better with numbers:
6S: 22.2V x 100A = 2220 watts
4S, requires 150 amps for the same battery power: 14.8V x 150A = 2220W
Voltage drops (using your fairly low resistance number, but any number will illustrate the trend):
6S: 100A x 0.005 Ohm = 0.5V
4S: 150A x 0.005 Ohm = 0.75V
Power losses:
6S: 100A * 0.5V = 50W
4S: 150A * 0.75 = 112.5W
A 125% increase in power loss, which goes to heat. In at least some cases, granted not all, this would be considered a significant, possibly even problematic, increase.
6S: 22.2V x 100A = 2220 watts
4S, requires 150 amps for the same battery power: 14.8V x 150A = 2220W
Voltage drops (using your fairly low resistance number, but any number will illustrate the trend):
6S: 100A x 0.005 Ohm = 0.5V
4S: 150A x 0.005 Ohm = 0.75V
Power losses:
6S: 100A * 0.5V = 50W
4S: 150A * 0.75 = 112.5W
A 125% increase in power loss, which goes to heat. In at least some cases, granted not all, this would be considered a significant, possibly even problematic, increase.
Here's the problem with this, those are purely burst figures, that happen for fractions of a second. In reality, most are only going to average 15-20 amps, so the average is going to be closer to a 12w difference, pretty insignificant when you are looking at systems averaging 400+ watts.
That is wrong. The 6s/3300mah with 1400kv will run longer than 4s/5000mah/2100kv by a significant amount.
The difference in torque given by the lower kv motor is compensated by the lower rpm
06-25-2011, 07:21 AM
#27
Tech Initiate
I can prove that, sorta. My 3600mah 6s 30c 1400kv setup can make a 20 minute main, and run cool. So could my 4s 5200mah 30c 2050kv, but it ran hotter, and was heavier.
The 6s is pretty snappy, but not as much as the 2050kv 4s.
The 6s is pretty snappy, but not as much as the 2050kv 4s.
Those are the kind of things that always seem to be missing, for a totally fair comparison. Either they are different kinds of motors, different sizes, different speeds, different vehicles, different capacity of batteries, ect.
06-25-2011, 07:39 AM
#28
It's common knowledge that a higher voltage system is more efficient. Numerous racers have changed from 4s to 6s and all have had the same results (less heat, longer run times on lower mah batteries). For data, the evidence presented on this thread alone should be sufficient enough.
06-25-2011, 08:20 AM
#29
Tech Champion
Thread Starter
All in all what kind of motor/lipo setup would you choose for a 10h endurance race?
My needs:
- the less heat possible
- the less stress on the ESC
- as much range as possible of course
- has to be smooth and efficient, easy to drive
The buggy will be light (JQ The Car converted to brushless), the track is fast & the traction level is high with almost no jumps. It's hard packed with few dust (racing line clearly visible).
As someone said before I first want to choose a motor that suits my needs (kv, power, size etc..) before I begin to mess up with the radio, ESC curves etc.. First the motor
Do you have any suggestions?
My needs:
- the less heat possible
- the less stress on the ESC
- as much range as possible of course
- has to be smooth and efficient, easy to drive
The buggy will be light (JQ The Car converted to brushless), the track is fast & the traction level is high with almost no jumps. It's hard packed with few dust (racing line clearly visible).
As someone said before I first want to choose a motor that suits my needs (kv, power, size etc..) before I begin to mess up with the radio, ESC curves etc.. First the motor
Do you have any suggestions?
06-25-2011, 09:29 AM
#30
Tech Initiate
It's common knowledge that a higher voltage system is more efficient. Numerous racers have changed from 4s to 6s and all have had the same results (less heat, longer run times on lower mah batteries). For data, the evidence presented on this thread alone should be sufficient enough.
I can prove that, sorta. My 3600mah 6s 30c 1400kv setup can make a 20 minute main, and run cool. So could my 4s 5200mah 30c 2050kv, but it ran hotter, and was heavier.
So the 4s was heavier, and we don't know what speed they were going, but it was hotter then cool The 6s is pretty snappy, but not as much as the 2050kv 4s.
If performance is not equal, then wouldn't the expectation be for the more peppy system to run hotter?
So the 4s was heavier, and we don't know what speed they were going, but it was hotter then cool
The 6s is pretty snappy, but not as much as the 2050kv 4s.If performance is not equal, then wouldn't the expectation be for the more peppy system to run hotter?
It's something I will be putting some effort into testing soon. I just need to find exactly the right batteries, to keep them even.