Higher voltage and efficiency

[slimthelineman]

It is hard to fathom runtimes like posted above, but with lower current draw the same packs will run much longer. Not sure how long my rigs run. Typically get six minutes with a warm up and the five minute heat but using some numbers (600-700mah for the ebuggy) should be able to run hard for around 15-20 minutes on a 6s 2650 40c with my 1400 kv motor.

Nothing is simple but it's easy to remember that the less current you are using be it spikes or avg. The longer yo can run for a given capacity compared to a lv high current setup. By the way, great discussion so far. Lots of good stuff.

[x-y]

all depends of the scale of you use...... but if you use the correct config all this setups are perfect for race and win:

1/10 1500-2500gr .................... 2-3s
1/8 2500-4000gr ......................3-4s
big monsters 4000-6000gr .......... 3-6s
big scales 6000-10000gr .............4-10s

of course all depends of the circuit and the top speeds ...... if the top speed of your track is 25-30mph you dont need much voltaje because is innecesary ....... but if you need big top speeds is better if you use more voltaje........and

+voltaje and -mah = +speed and -temperature = same run time

[Thomas]

Originally Posted by x-y

all depends of the scale of you use...... but if you use the correct config all this setups are perfect for race and win:

1/10 1500-2500gr .................... 2-3s
1/8 2500-4000gr ......................3-4s
big monsters 4000-6000gr .......... 3-6s
big scales 6000-10000gr .............4-10s

What exactly is your point against a 1/10 with 4s or a 1/8 with 6s? There are small car ESCs for 6s, there are appropriately-sized motors with <2000 kV and there are 30C LiPos with <3000 mAh.

I would recommend running the highest voltage which makes sense with the available components.

Is the overall query based on, "why all the hype over hv?" when your lv setups work fine?

More so how much is hype, so I was shooting for proof of a real world difference, and at what point does it really start to help. I'm a firm believer in once your wattage needs gets to a certain point then Higher voltage is the way to go. 8-12s in a Baja, the way to go, 6s in a Rustler running 40mph, probably not going to matter over a 3s setup. In my Rustler, MMP 3800, temps are roughly the same on 2 or 3s, the system could care less. I know that's not a big jump, and maybe the kv of the motor must be changed for it to be accurate, but a 50% increase in voltage should give some notceable result, IMO. Here's an example
25/84 on 2s got me
speed= 45.8
Motor= 131
esc=112
ambient = 86


on 3s
Speed = 48.6
motor= 135
ESC= 115
Ambient = 86

Once you average the power used, the wattage was actually pretty close in the 2 setups.

I would love to see some examples like that comparing a true HV setup, if anyone has them.


This is a battery testing place, currently in the works, but he lists some wire and connector resistance specs, http://www.rclipotesting.com/Performance_Tips.php

[crazyjr]

I might be racing this year and plan to run the 4s powered T4 against the nitro ST's, if any show up. I got the ok from my local track to try it, he's cool, his answer to it was, "It would be like being told how much gas (nitro) to bring for a heat." The reason I tryed this was to see how much of the hype, was hype. I seen claims to and wanted to try it, got what i was after.

Hopefully in the next year i will try something more ambitious, I want to build the first 5-6s powered Mini e-revo with possibly an outrunner for a motor. Now that i'm running lowerkv and loving it, I want to explore outrunners and see if there is more efficiency to come

[snellemin]

HV is good to have as long as the required amount of wattage is met for your setup. However you can only go so far as weight becomes an issue and throws out your gained efficiency.

[sikeston34m]

Originally Posted by snellemin

HV is good to have as long as the required amount of wattage is met for your setup. However you can only go so far as weight becomes an issue and throws out your gained efficiency.

One point here is, with the higher voltage setup, the amp load demand is less.

This allows you to consider smaller mah cells that make up the HV packs.

Instead of going from a 4S 5000mah pack and just adding 2 more cells, for a 6S 5000mah pack.

Perhaps going with a 6S 3000mah pack would help offset the weight penalty.

[crazyjr]

Originally Posted by sikeston34m

One point here is, with the higher voltage setup, the amp load demand is less.

This allows you to consider smaller mah cells that make up the HV packs.

Instead of going from a 4S 5000mah pack and just adding 2 more cells, for a 6S 5000mah pack.

Perhaps going with a 6S 3000mah pack would help offset the weight penalty.

My point exactly, with higher C-ratings, smaller packs can be used, Which adds to the efficiency thing. I have room to grow on this 1/10 project, The Lehner is good for 60,000 RPM, so 8s+ is possible with this setup. I figure two 1500 mah 4s packs will fit in a T4 tray, Just need an 8s capable esc small enough

This is good, something i can contribute to with experience.

[crazyjr]

Originally Posted by snellemin

HV is good to have as long as the required amount of wattage is met for your setup. However you can only go so far as weight becomes an issue and throws out your gained efficiency.

The cool part is, with all the talk of going up in voltage, I haven't gained weight on the setup. My 4s 3700 flightpower is still lighter than the 6 cell NIMH i used to run

Yeah IMO for a comparison to be accurate, the batteries need have the same punch. IOW a 5000mah 2s would have to be compared to a 2500mah 4s, because if it's a 3000mah battery, how could it be determined what's coming from voltage, and what's coming from it just being a more powerful battery.

Tacon has a 2230 KV motor ,that is like my 3930kv motor I'm running in my Slash . I also have a pair of 5000mah 2s 20c batteries. So I'm thinking about picking one up, gearing for the same speed and testing it. Using the batteries as a 10000mah 2s setup, or a 5000mah 4s setup.
Does anyone think the KV's are far enough off to skew the results?
By data logging, radaring and temping, this setup, do you think some results can be had?
Is there a better way to test for results?

Thomas, I think his point, which is something I also want to know, is how much does the amp draw play into the need for high voltage. I think we all know that if you need 3000watts then a 2s is not going to cut it, but if you need 200, what is trully the advantage to 6s? Please if you have any input on this, state your case, hopefully with some hard data, but personal experience works also.

[Thomas]

Originally Posted by asheck

... IOW a 5000mah 2s would have to be compared to a 2500mah 4s, ...

I totally agree. Further, to be completely fair, you would have to use different ESCs for the different voltages. The setup with lower voltage could do with FETs for lower voltage, but needs more of them (or higher current rating). However, it's not very practical. But I would argue that a 1/8 buggy on 3s probably needs an MMM, while it works with a smaller and lighter MMP at 6s.

I have not tested or measured different setups, but try to look at it from a scientific point of view:
Batteries: When going from 3s2p to 6s1p with the same cells, the amount of cells and the required power are constant. So the losses in the cells should be the same, both setups should see the same battery temperature. But in the wires and connectors, losses are higher because of P = R * I^2
Please tell me if you find a mistake in my calculations

ESC: More current through the FETs, wires etc. equals more losses. HV setup -> cooler ESC.

Motor: Double the voltage -> half the kV. Let's compare a 1509/2Y (1820 kV, 0.018 Ohm) to a 1509/1Y (3600 kV, 0.004 Ohm). From the specs, they should have roughly the same ohmic losses. This is because they have the same amount of copper, just different winding configuration (very much similar to the battery example above).

When theoretically comparing two setups, I assume both carry the same amount of energy (Wh), motor RPM is the same and the performance (W) is the same.

I'm afraid with this simple math, I can only explain the difference concerning wires, connectors and ESCs, not motors and batteries. I'm pretty sure the simplification holds true for the batteries, but not the motors (impedance etc. not taken into account).

[nuz69]

Totally true Thomas, a HV setup makes the ESC cooler for sure, but theoritically it's the same for the motor and the battery (with the same runtime). For a low Kv motor, the windings wires are thinner (more turns in the same space). But it's maybe easier to package thinner wires (low Kv) in the motor than larger wires (high Kv)...
Some people noticed the some change on motor temp using low and high voltage setup, I didn't (Castle 2200Kv 4S versus leopard 1400Kv 6S with heat sink). But my ESC now operates at cooler temp.

I don't get it guys? The higher voltage setups run cooler, right? So to me and my simple brain just the absence of heat means that setup is more efficient. After all isn't heat just wasted energy that isn't turned into motion by the motor????? Doesn't that dictate that cooler HV setups are more efficient?????

[_paralyzed_]

Originally Posted by BIG-block

I don't get it guys? The higher voltage setups run cooler, right? So to me and my simple brain just the absence of heat means that setup is more efficient. After all isn't heat just wasted energy that isn't turned into motion by the motor????? Doesn't that dictate that cooler HV setups are more efficient?????

yes, and yes. But we are into details, we want to know how much more efficient. And we want to weigh the benefits of increased efficiency against the cost of hv setups. We want data and hard numbers!!

If cost is a factor than hv goes out the window for many. It cost me 2x as much for my mamba xl in my e-maxx compared to the previous MMM.

I feel cool when I tell people it runs on 30 volts!

[nuz69]

Originally Posted by BIG-block

I don't get it guys? The higher voltage setups run cooler, right? So to me and my simple brain just the absence of heat means that setup is more efficient. After all isn't heat just wasted energy that isn't turned into motion by the motor????? Doesn't that dictate that cooler HV setups are more efficient?????

You are taking the problem from the wrong side.
The point is that HV voltage runs not necessarily cooler... For the motor it's pretty much the same, although the ESC is a little cooler with HV setup. So the gain in efficiency can sometimes be negligible...