# Running 12s motor with 6s batteries

Hey. I’m new to all of this but I’ve done tons of reading and already bought the components I need, specifically:

• Turnigy Aerodrove SK3 - 6374 149 kv Brushless Outrunner Motor (12s)
• 2 Turnigy Multistar 6s 8000 mAh Lipo Batteries
• VESC
• 14:27 ratio

According to several online calculators I should be getting a weighted top speed of roughly 20mph.

I’m wondering if it’s possible to run the motor at 6s… that way I can link my batteries in parallel instead and double my range. It seems like I can configure my VESC (via the BLDC tool) to limit the voltage and current input to the motor. I would configure it to simulate a 6s setup. Is this possible? Will this harm the motor or the VESC? I realize my motor will be going half as fast, but cruising at 10mph is fine with me.

Thanks!

parallel will not double your range. Energy inside your pack will stay the same. Actually in series you might see higher range because the efficiency is better at higher voltages.

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Say what now? Doubling your capacity and keeping your max speed the same doesn’t give you double range? Paint my fart green while you’re at it.

Going faster increases the energy used / kilometer and if you were to travel at 50% speed with the 12S you are operating on the worst possible duty cycle if you’re going for efficiency, AKA 50% duty cycle.

@Pafrican I have a very similiar setup to you voltage, motor and gear ratio wise with 6S, SK3 149KV and 15:30 ratio and my board cruises at 100% duty cycle at ~15 mph on flat with 80 mm diameter wheels. Here’s some pics in case you’re interested http://imgur.com/a/Mjodj

20V10Ah=200Wh which is the same as 10V20Ah=200Wh so you don’t magically get double the range just because you rewire your batteries (which he was suggesting).

Plus higher current draw at lower voltages will decrease efficiency as higher current generates more heat. Higher voltage is always favorable in terms of efficiency.

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I’ll agree in the case that he also limits his speed to the same maximum as with the 6S setup.

And here’s my point on the efficiency with the VESC at 50% duty cycle, which you would have to do if you want to run the motor at 6S speeds with 12S battery. You get much more heat dissipation in the capacitors, because of the large ripple current, which is at it’s maximum at 50% duty

Do you really think the ripple current are the main factor here? I’m not so sure. The power loss in the FETs is proportional to the current, not to the total power. By going for 12s instead of 6s will cut your resistive loss per output power in half for basically any component of your electronics. Also it will be much better for the LiPos to drain only half the current. This will increase their lifetime and reduce the voltage sag. I don’t see any advantage in staying under the maximum voltage that your esc can do.

The old story: half the voltage, double the current is just as good is only true in context of motor windings/KV. Lower voltage is worse for any other electrical components of your system. Or am I missing something here?

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You are nitpicking. He never said he actually WANTS to lower his speed. He just said that he wants to rewire because he would get double the range - that is wrong and what you should be correcting.

I simply said that the energy will stay the same and rewiring will not make a difference.

If you start making assumptions to calculate the exact effects the rewiring has on his range you would need a lot more data. We are simplifying here and in this case higher voltage is more favorable than higher current (plus having the ability to choose higher speeds)

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The LiPos also drain at half the current each when parallel, because your capacity is doubled and each of them is supplying half the current. The resistive losses in the FETs is dependent on the battery & motor current, with less than 100% duty causing extra losses in the lower FETs.

I guess the best thing would be say to the OP @Pafrican , if you’re really not sure then try each configuration and if you’re not getting the range you want, go slower. And in the end, it maybe just easier to wire for the 12S.

And the point I was trying to make (rather poorly I guess) that speed impacts range more than anything else. if he were to go full speed with the 12S and 6S, the 6S would go double the range. And I actually did some practical tests to test the effect of the traveling speed on your energy consumption / distance. Link to the thread.

The 6S just would just limit his max speed lower, so he would get more range out of the pack without feathering the throttle with 12S to travel the same speed. I mean it’s just hard to go slower than what the board can do right

You actually think he will see a difference in range? The effects will be so small that wind and temperature differences between the days would have larger effects.

On the level you are taking this to you would also have to check his solder joints and cable thickness for weak spots. What about his anti spark or loop key - they will heat up with more current going through. What about his fuse? Will he need a new and bigger one at his “new” current levels? Just stop overcomplicating this!

Edit: just read your new post about higher speeds. Sure wind resistance at higher speeds will eat his battery. But what if he only rides with tail wind?

Going half the speed actually decreases your range in most scenerio’s.

Air resistance isn’t that important at normal e-board speeds and these motors normally gain efficiency near top speed.

Cars do suffer from air resistance and are the most efficient arround 80 km/h. Without air resistance the most efficient speed would be near topspeed. Just like E-boards.

And both ways I guess

With some people on this forum going for 50-60kmh what are normal eboard speeds to you? Above 30kmh the wind resistance will have an effect

I’ll refer to my thread on the effect of speed on energy consumption / distance

Also cars are most efficient at a certain motor RPM. As you increase speed your aerodynamic drag increases exponentially as a factor of speed. Cars are just optimized for highway travel at 80 km/h with their gears, so the motor is closest to it’s optimum RPM.

About 10-22 mph (16-35 km/h) is normal I guess.

The gears of the car tuned for highway speed is a valid point though.

I am still right though You will lose range by going half the topspeed on the same motor/battery setup on an e-bourd that doesn’t go too fast.

Can’t technically back this up though, do we have a captain over here?

It’s pretty linear from what I concluded from my own tests with a limited amount of different travel speeds, as I only had 2. but the Wh/km increases very linearly with the travel speed, for example, if you’re using 8 Wh/km at 15 km/h then you would be using about 16 Wh/km at 30 km/h. Why is the Wh/km number linear and not exponential? Well when doubling your speed you quadruple the average power needed to travel due to aero drag, but you’re also spending only half of the time doing a kilometer for example and that’s where the linearity comes from.

So I might be wrong here

My practical test proves the opposite… WITH PROOF!

And what you mean with “an e-board that doesn’t go too fast”? The aerodynamic drag is always present at low speeds as it is at high speeds.

EDIT: Ok, you read the thread. Thank you. I just thought it was an interesting experiment with useful results to share with the community.

Without looking at your data (I am on mobile right now): I just doubt that you could actually maintain all conditions the same when doing your tests. You did not ride on a treadmill in a temperature controlled room so all “effects” that you observed in your limited data set might come from something else. I agree that higher speeds will need more energy - but as to what degree and if the dependency is actually linear I have no idea.

But this is all offtopic anyway. The main point was if he will double the range if he rewires and the answer to that is no.

I have also stated how my tests were performed. I use a quiet road, where there is no need to slow down unnecessarily. The route is also a forth-and-back route, so it averages the terrain to flat plane and what ever head- or tailwind I had traveling to my turning point, becomes the opposite on the way back. And the results were very even across all runs.