Power consumption with 2S/3S

[MuntyScruntfundle]

Hi there.

 

If you imagine the following 2 setups:

 

ESC+Motor+2S battery

ESC+Motor+3S battery

 

If I dial down the power 30% (which I can do on my transmitter), I would assume I'm going to get the same power output as the 2S setup but have a lot longer running time, is that correct or am I missing some strange electrical calculation?

 

Reason for asking, I have one car that is running longer with a 2S than the 3S and I'm not pushing the car harder on the 3S.  So either I'm miss understanding something or I've buggered up a bunch of Lipos!

 

Thank you.

[Kpowell911]

What mah are the lipos?

 

I wouldnt know for sure but id imagine dialing the power down  (EPA im guessing?) would have zero effect on run time?

Edited May 1, 2018 by Guns

[Tug]

In theory, yes, but you might start heating up your ESC because it's working harder to reign in the motor that's seeing 3S on offer and will get greedy for the extra voltage. 

 

Not exactly a scientific explanation, but it's tricky to explain. Basically, the ESC controls speed by switching the offered voltage on and off at lightning speeds. Slow speeds mean the power is off more than on, high speeds mean the power is on more than off and mid range is where the hard work happens. That's what I've been told and it does make sense, just hard to explain. 

 

Someone more knowledgeable is welcome to correct that if I'm off. 

[dazp1976]

I don't think EPA makes a huge difference. You'll still be pulling the same amount of amps on both with same gearing.

Technically you should get a bit more but the key things I've found myself for this are:

1: Higher voltage, lower pinion = same top speed as 2s pulling less amps (monitor temps due to higher rpm)

2: Higher voltage, lower kv motor = same top speed as 2s again uses more of the voltage and less of the amps.

Using less amps is the key imo to increasing running.

 

Similar scenario for my 1/8th.

Using a 4s with 2200kv gave me 7-8 mins on tough ground with a 16T pinion. Top end = 40mph. Amp hungry, 70C on motor.

Using 6s with a 1600kv gives me 12-14mins on the same ground same pinion. Top end = 42mph. A bit cooler.

I've gone with a 1700kv. Gives similar time as the 1600.

 

I think if you want to keep the same top speed on the 3s as the 2 then a lower kv motor will be beneficial to you.

Or try a smaller pinion and leave the EPA.

 

This calculator helps you work out the kv that will give you a similar top speed if you fancy trying it out.

Remember it's unloaded so expect about 5 mph or so discrepancy to actual.

http://scriptasylum.com/rc_speed/top_speed.html

Edited May 1, 2018 by dazp1976

[Tug]

Good comparison that! ^

 

I've also got a 1/8 Truggy, tried it on a 2200 Neu motor and got less than ten minutes on 4S. Switched to a 1480 on 5S and the difference is night and day, double runtimes and cooler temps. Speed is roughly equal. 

[MuntyScruntfundle]

Aha ok.  I think I have a motor I can swap out pretty easily for this one.

 

I think I've fallen into the trap of thinking a higher KV is better all round.

[Fly In My Soup]

10 hours ago, MuntyScruntfundle said:

Aha ok.  I think I have a motor I can swap out pretty easily for this one.

 

I think I've fallen into the trap of thinking a higher KV is better all round.

 

As a general rule, for me anyway, the smaller the motor and the lower the voltage.... the higher kV I need.

 

Think of it like gearing up or down.....if your using a low kV motor, you'll need higher voltage to spin the motor fast enough to get good top speed...... And as you lower voltage, you compensate the lack of voltage by upping the kv

[Nickarla]

I get nearly double the run time on my Ripmax Husky by sailing the EPA down to 0. 

[MuntyScruntfundle]

EPA?

 

I think my problem is I'm not testing anything all that scientifically.  All I'm after at the moment is a decent run time with enough power.

 

Another thing confusing me, which you may be able to help with;

 

I have an SC5M (2wd) which runs on two saddle packs, 5000mah and 50c, with a Hobbywing Max8 and 3652 3800kv motor.  This truck will give me 20+ minutes of run time before I notice any power drop.

My Losi SCTE (4wd) is currently running a very similar battery setup, a competition Max10 Pro SCT with a G2 v3 10.5 turn motor (kv escapes me at the mo) and I get 7 minutes.  I've tried a 15 turn motor, I don't get any longer running time but the performance is way down.  (I only had one other pinion that fitted which was only 2 teeth more)

So, is the lower amperage of the Max8 helping here, or is the Pro motor sucking huge amounts of power?

 

Would I be better, in general, going for 3660 motors with more torque and gearing up?

[Fly In My Soup]

14 hours ago, MuntyScruntfundle said:

EPA?

 

I think my problem is I'm not testing anything all that scientifically.  All I'm after at the moment is a decent run time with enough power.

 

Another thing confusing me, which you may be able to help with;

 

I have an SC5M (2wd) which runs on two saddle packs, 5000mah and 50c, with a Hobbywing Max8 and 3652 3800kv motor.  This truck will give me 20+ minutes of run time before I notice any power drop.

My Losi SCTE (4wd) is currently running a very similar battery setup, a competition Max10 Pro SCT with a G2 v3 10.5 turn motor (kv escapes me at the mo) and I get 7 minutes.  I've tried a 15 turn motor, I don't get any longer running time but the performance is way down.  (I only had one other pinion that fitted which was only 2 teeth more)

So, is the lower amperage of the Max8 helping here, or is the Pro motor sucking huge amounts of power?

 

Would I be better, in general, going for 3660 motors with more torque and gearing up?

 

Go get yourself one of those cheap in line watt/amp/ power meters.

 

You can get them cheaper, but here's what you want

https://www.ebay.co.uk/p/High-Precision-GT-Power-LCD-RC-130a-Watt-Meter-Power-Analyzer-Ver-2-for-Heli-DVZ/2126495670?iid=121615918865&chn=ps&adgroupid=59254216728&rlsatarget=pla-432963209475&abcId=1134056&adtype=pla&merchantid=113739244&poi=&googleloc=9050382&device=t&campaignid=1340839189&crdt=0&ul_ref=https%3A%2F%2Frover.ebay.com%2Frover%2F1%2F710-134428-41853-0%2F2%3Fmpre%3Dhttps%253A%252F%252Fwww.ebay.co.uk%252Fp%252FHigh-Precision-GT-Power-LCD-RC-130a-Watt-Meter-Power-Analyzer-Ver-2-for-Heli-DVZ%252F2126495670%253Fiid%253D121615918865%2526chn%253Dps%26itemid%3D121615918865%26targetid%3D432963209475%26device%3Dt%26adtype%3Dpla%26googleloc%3D9050382%26poi%3D%26campaignid%3D1340839189%26adgroupid%3D59254216728%26rlsatarget%3Dpla-432963209475%26abcId%3D1134056%26merchantid%3D113739244%26gclid%3DCj0KCQjw28_XBRDhARIsAEk21FjleFfOsctk42Hp2p2oyW-Dz_Rf35Pc0A-jiZBKASSBmbmKISYojDEaAmfjEALw_wcB%26srcrot%3D710-134428-41853-0%26rvr_id%3D1525824440227%26rvr_ts%3D491839f81630ac892f536ba3fff3b3cb

 

It will help you pin point any power system issues

 

Edited May 10, 2018 by Fly In My Soup