Higher voltage and efficiency

[_paralyzed_]

Originally Posted by asheck

So according to this claim, if I was to run the same time , even at my lower speed, I would need 3 packs , or 18000mah on 2s the equivilant to a 9000mah 4s, or around 2.5 times more battery.

These are the kind of claims that confuse me. I just can't see where that kind of difference can really be had. I could see maybe the extra 5mph coming from the added efficiency of the voltage, but 5 mph and 2.5 times the runtime....

Too many variables to deduce anything. Is the overall query based on, "why all the hype over hv?" when your lv setups work fine?

IMO low voltage setups only work as well as they do now because all of the esc manufacturers have had time to work the bugs out. A simple oversight in gearing or maintenance can highlight the shortcomings in these setups and make them go poof.

Whether they are really more efficient or not in terms of usable mah, I believe, in the end will be negligible. However, the power flowing is used more efficiently as evidenced by component temperatures. The peace of mind of having cool components is enough reason for me to go hv. Ambient temp is way better than, "within acceptable temp range".

[sikeston34m]

Originally Posted by _paralyzed_

Too many variables to deduce anything. Is the overall query based on, "why all the hype over hv?" when your lv setups work fine?

IMO low voltage setups only work as well as they do now because all of the esc manufacturers have had time to work the bugs out. A simple oversight in gearing or maintenance can highlight the shortcomings in these setups and make them go poof.

Whether they are really more efficient or not in terms of usable mah, I believe, in the end will be negligible. However, the power flowing is used more efficiently as evidenced by component temperatures. The peace of mind of having cool components is enough reason for me to go hv. Ambient temp is way better than, "within acceptable temp range".

VERY Well Said Harold!

I aggree.

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.

[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.

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.

[slimthelineman]

In my experience using the same kv motor on low and high voltages has negligable gains in anything but speed. To fully embrace it you must go down in kv and up in voltage at the same time. This is the only way I've found it to be worthwhile to use higer voltages. Not to beat a dead horse but the 4.5 ballistic is 5000kv and a amp hog I might add. The 6.5 ballistic is 3400kv and much better on three cells and makes the same rpm and power on the track but runs 30-40 degrees cooler iirc. That's the easiest comparison for now but my rc8 runs about the same temp margin cooler on 6s 1400kv vs. 4s 2050kv. Plus the 3&6s packs are smaller in capacity and weigh the same or less than a 2&4s pack of higher capacity. Hope this helps. Might be able to produce some data this weekend but we will see what I can come up with, I have a plan and a few rigs to try stuff with so maybe I can offer more than just my experiance.

[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

Not to beat a dead horse but the 4.5 ballistic is 5000kv and a amp hog I might add.

They earn their nickname of spinning toaster of death for good reason BUT, Honestly, I must have a special one, it's the old version HV4.5 before the 5mm shaft, but has the good rotor and endbell. I can run it 45mph on 4s in my E-revo, no problem unless you go for 50 ;) , or drop it in my Slash 4x4, on 2,3 or 4s, and never have it even start to get hot, above 140. People are going to want to shoot me for this, but speed for speed , voltage to voltage, in my Slash 4x4, I think my Novak runs cooler then my Castle 2400. I have much love for my 4.5, it's been around along time, in alot of vehicles, pushed beyond what it's little size should have allowed, and my toaster still spins up a mean piece of toasted ground.

But let's face it, with Novak's latest system being 4s limited, they have no business being talked about in a high voltage thread.

[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?????