Higher voltage and efficiency
 

Started this discussion somewhere else, but have wanted input from here on this for awhile. It's my opinion that higher voltage really is only more efficient for higher wattage.

Quote from Slimthelineman. But I have seen others say the same thing, and claim greater gains. I know this example is of different vehicles, just using his #'s as examples. Also there is the probability it's 2-pole to 4-pole motors.
Here's how I see it.

Wattage is wattage, in that example, the 6s setup is making much less wattage then the 2s setup. More then efficiency alone can compensate for, if the motor output was to be equal. The voltage / kv effect on efficiency really shouldn't play into it until the amps the motor is drawing is enough to push it out of it's efficiency range. At the Neu dyno sight, you can see that regardless of voltage, the efficiency is going to run between 85-92% http://neumotors.com/Site/Dyno_data.html But it doesn't really seem dependant on voltage, more so the motor. 600mah of a 6s would have to be 40% more efficient as a 2s setup using 3000mah for the motor output to be the same.

So, Until your wattage needs, takes your amp needs, out of the usable amp range of the system , I don't really buy the higher voltage is going to be that much more efficient. Using , say, a Neu 1412 and MMP, If I was only pulling 100 amp bursts on 2s, then cut the kv in half, and doubled the voltage, so 50amps on 4s, wattage, speed and performance being equal, I don't believe the setups would have a measurable difference in efficiency.

Am I wrong? How much efficiency can trully be gained from higher voltage? I would think for it to be noticeable you would have to see a 10% increase, and I just don't see how you could get that kind of gain, unless your original setup was just way off. What am I missing?

Well good morning sunshine!:lol: your up early lol. We should get some good info and opinions over here. Looking forward to it. I'm not really sure about the efficiency deal as I don't have the equipment to test for it but I have noticed that the current will drop on higher voltage/lower kv setups. That is really the main reason I go that route. The setups quoted were a prime example. The 4.5 vs 6.5 setup runs about 40 degrees cooler on 3s to the 2s. Working in Merced right now and it's been raining so the outdoor tracks are too wet for me right now but when I can I will get some amperage data for comparisons sake. Thinking your right about the efficiency deal but on the other hand with lower currents there would be less heat losses so maybe it's a balancing act between the two? Awaiting mr g to chime in, sure he has some insight on the topic.

For what it's worth, I will present my 2 cents on this subject.

I've often found my train of thought following along the same lines as what you've presented here.

High Voltage versus Low Voltage versus a given wattage of output(load)

This all has to do with resistence. Resistence is the root of all losses of efficiency.

Resistence in the wire, resistence in the fet's that do the switching, resistence in the Lipo Pack itself, and resistence in the motor winding.

Another thing that gets tossed into the equation is voltage drop.

For a given length of wire, you will see a measureable amount of voltage drop for a given load. The greater the load, and the smaller the wire, the greater the voltage drop you will see.

We try to make up for this by using larger wire that has less resistence. There's that word again. :yes:

If resistence makes for more voltage drop with the greater amp load, then it makes sense, by bumping up the overall voltage, we effectively drop the amp load and minimize voltage drop.

By dropping the amp load, we lose less. We lessen voltage drop and we lessen wasted energy spent on heat, because of resistive losses.

The cooler we can make something run, the more efficient it becomes.

But we push the limits. The limits are pushed with the low voltage setups AND the high voltage setups. I think this makes it harder to measure the differences.

I seen a good example with my lithium ion trolling motor setup. By eliminating a 7 foot 10Ga. length of wire, the motor would put out an extra 75 watts of power. This was the only change that was made.

Efficiency was also improved, because that 7 foot length of 10Ga. was noticably warm to the touch. Even though, it was "only" carrying 50 amps.

Well you know what they say,
Early to bed , early to rise,
I was between the sheets, but not her thighs :wink:

So is there really any viable way to test efficiency? Is heat the only effect to look for?

A couple graphs, these are my Rustler with a 1410 MMP , Badland 30 series tires. On 2s SPC 6000mah 30c 45 MPH 25/84 gearing
http://i531.photobucket.com/albums/d...dlandspics.jpg
On a 3s 3300 30c 45mph
http://i531.photobucket.com/albums/d...45mph3spic.jpg

Now if you average the bursts, as there always seems to be 1 or 2 that spike higher, it does seem that it is roughly 1/3 less amps, and the wattage is pretty close. Temps stay about the same also. Even on 2s, nothing is being pushed out of line. Does this mean the overall efficiency is equal?
When you look at the average draw it takes to drain a 2s 3200 mah in 5 minutes, you will almost be guaranteed some very high apm bursts. That would quite probably take that motor out of it's efficiency range, causing a big increase of motor temp. I know the Novak motors are quite bad about that. I would be interested in what kind of amps that pulls, I haven't logged mine yet. What kind of weight is the Jammin, and do you know what kind of speed it ran?

Wire and resistance, whew who's going to cover that ? Is the current all that really matter when figuring a wires resistance? IOW will the losses of 50 amps and 10 volts, be the same as 50 amps and 20 volts, given the same distance and wire?
The smallest wire I have in anything is the Castle 13g . Which I have always felt was a little lacking , though I have been assured from Castle that it is fine for the wattage and lengths we are running. But I've seen some of the new 1410 motors with wires over a foot long, that has to add some resistance. I've seen the 3800 draw 160 amps, take that with 16inches of 13g and you have to be losing something.

I This reminds me of my car stereo days. If I wanted to send a true 50 amps 7 ft I would have wanted at least 4ga. But I know distance has alot to do with it, and for 1 foot, I'm not sure there would be a noticeable difference in using 10g or 4g.

My jammin scrt10 iirc is about 6.5 lbs rtr. With a 2s 5000 40c and a 550 4.5 motor after a five minute heat is about 160 degrees. The 550 6.5 on 3s 3200 40c is about 110-120 after a five minute heat. Geared for the same 38-40 mph and both with the same rpm output (within about 1000 rpm of each other). Heat is a good measure of heat losses but idk if you could literaly equate it to efficiency. As soon as I get a chance I will log some amp draw from both setups on the track and see exactly how much less current the 3s 6.5 setup uses compared to the 2s 4.5 setup.

IMO, Heat is the main indication of efficiency losses.

It takes power to create that heat, so there goes some of your battery pack's power. It was used to make heat, not motor power.

Resistence isn't only found in the wiring, but also the other things that I mentioned.

Those others also produce heat as a result of losses, even your Lipo Pack.

If it gets hot, it is using energy to become heated.

Heat is energy.

I was thinking the same thing, the battteries can play a part in it too. If you are light on the trigger then there may be little difference but if you have a demanding track or a basher that like's showing brute power then there will be a lot of standing starts and out of control full throttling. That's when the system is under most stress and where a higher voltage system would show cooler temps (if not, then more grunt). So both systems are highly reliant on the batteries where you are heavy on the trigger and no punch control is used.

That's my understanding anyway:tongue:

I have been wondering when this conversation was going to start here, I got a few things to add. I'm not all that scientific, I go by feel and temps. I have played with higher voltage and lower kv for a few years now, I see the efficiency both in temps and runtime. I started with a full FLM'ed stampede, with a lehner basic XL1200/1200kv motor, a Quark 80 esc

[IMG]http://i187.photobucket.com/albums/x...icture2004.jpg[/IMG]

[IMG]http://i187.photobucket.com/albums/x...icture2003.jpg[/IMG]

I forgot what the weight was, but heavier than most Stadium trucks. I could run 60+ minutes running a 4s 3700 mah 20C flightpower lipo. Not sure exactly what the gearing was, but it did 45 on radar runs with masher 2k tires. Temps always at around air temps

Next i put the motor and esc into my RC10 gt conversion with 20/66 gearing on stadium truck tires. This time on a 5s 2500 25c flightpower lipo. It was nothing fancy, just a good basher. I could run as long as my mamba 4600 (CM36) powered T4 8000mah MA pack, roughly 30 minutes. Temps never above air temp geared to 35 mph, only problem was it spread the diff outputs to the point of the dogbones slipping

[IMG]http://i187.photobucket.com/albums/x...ture2002-3.jpg[/IMG]

The latest setup is using my associated T4 and running 4s lipo running a 23/87 gearing on ST tires, I expect to run over an hour on the same pack as the stampede, The 3700 4s 20C. will post pics when i really test it out.

Glad to see others looking at this

This whole discussion is rather simple. For a given performance, it takes X amount of power. If using higher voltage along with the right kv motor, and geared appropriately, less current will be drawn.

As far as efficiency, that's simple too. Efficiency as a percent can be determined by (input_power/output_power) * 100. So, obviously, the closer the input and output power are, the more efficient a system is. Unfortunately, wires, FETs, etc all have resistance. That resistance * current = voltage drop. Then, that voltage drop * current = power lost. So, reduce the current to reduce voltage drop, and therefore power lost. There are other losses (ESC FET switching, Motor magnetic flux, etc) that are going to happen no matter what setup you use, but reducing current, using a high quality motor (even a few % points in eff can make a BIG difference), and making sure the vehicle is in proper working order (no drivetrain drag, bearings ok, etc) are the main things we can do to make the efficiency as high as possible.

If you are moving up from a 2S to 3S setup, I doubt you are going to see much of a gain, maybe a couple percent, especially if the 2S setup is running with descent size wire to handle the amps that are being pulled. I think you would have to move up to a much higher voltage to see a 10 percent gain.
I've run stadium trucks and the temp differences between 2S and 3S geared for the same speed are night and day. Run the same setup on 4S and it can stay ice cold. I still dont think you would see a 10 percent difference even there, but thats my 2 cents.

Sure, simple :)
Brian, can I have your opinion on how much the overall system efficiency would change going from a 1000 watt setup on 3s to a 1000 watt setup on 6s, using a MMP 1512 type combo, adjusting kv for max motor efficiency. Also dropping the Mah of the battery in half.


Ha ha, crazy, I'm running one of those Quark 80's now. I have it in a Slash 2x with Jato arms. I run it with a Tacon 3930kv 3650 motor on a 2s 6000mah. Temps will normally be around 30-40 above ambient. This is a graph of it running 40mph, with Badland 30 series. I kill the battery in around 20 minutes. It's probably pretty close to the same weight as the above Pede.
http://i531.photobucket.com/albums/d.../slato3650.jpg
So here's what I don't get, I'm running 20 minutes on 6000mah going 40mph, you say
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....

Shore! It's simple! :whistle: LOL

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.

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

I am comparing my Mamba Max 4600 CM36 verses a 1200kv Lehner basic XL

You need a noticable jump in voltage for the efficiency to really show, I did the 2s to 3s/same motor and saw not too much improvement. When i doubled and 2.5 times the voltage and lowered the kv, i saw mediate gains in efficiency and lower temps. I also gained by going bigger in motor, The Lehner XL basic motor was considered a MT motor when brushless rc was sorting itself out. At 1200kv, it's only pushing 22,000 RPM's on 5s lipo. I know that the motor is capable of 60,000 rpm, but why do you need ti run it like that? Runs fine and cool and like a 4 stroke nitro, torque out the wazoo