Voltage, Amps, and Heat - RC-Monster Forums

z1nonly · **Voltage, Amps, and Heat -** 11.11.2007, 01:44 AM

I have some questions that I hope you guys can help me with.

I've read that running more voltage helps with decreasing heat and increasing runtimes. Since the motor doesn't draw much amps, it will generate less heat.

Which set-up would be more ideal for less heat and more runtime:

Set-up A:
-4s 6000mah
-higher kv motor
-gearing to match battery and motor set-up

Set-up B:
-6s 4000mah
-lower kv motor
-gearing to match battery and motor set-up

I also read that with more voltage, there would be more cogging; hard to start off or run at slow speeds. Is this true?

jnev · 11.11.2007, 01:45 AM

Low KV and high voltage will always be more efficient and run cooler... so set-up B will be what you want.

aqwut · 11.11.2007, 01:56 AM

Quote:

Originally Posted by jnev

Low KV and high voltage will always be more efficient and run cooler... so set-up B will be what you want.

Yes.. I totally Agree, that's why I've moved up to Higher voltage setups...
and there's less cogging with higher voltage setups.. Lower Kv motor, more startup torque... That's my opinion of it anyways...

So "B" get's my vote...

z1nonly · 11.11.2007, 03:06 AM

Would "B" be too much for racing?

sleebus.jones · 11.11.2007, 03:20 AM

Not if it's set up properly. You just have to pick the proper kv/gearing and it'll be fine. I'd say B would be better for racing if anything.

zeropointbug · 11.11.2007, 03:33 AM

Yeah, I have heard lower voltage setups being better than higher voltage ones FAR to many times on this forum.... can those people explain to me why you say that?!

Just go Play · 11.11.2007, 04:09 AM

The other bonus to the high voltage setup (in this example) is that the 6s1p pack will weigh less then the 4s2p by @ 45grams depending on mfgr.

starscream · 11.11.2007, 05:16 AM

Lower voltage setups are unfortunately much cheaper as finding a good HV ESC for a car is EXPENSIVE.

I don't run anything less than 5S

6S Lipo was my standard but I'm now running a min of 8S A123

Those NEU energy Lipo's are looking interesting though.

Finnster · 11.12.2007, 09:53 AM

Quote:

Originally Posted by z1nonly

I have some questions that I hope you guys can help me with.

I've read that running more voltage helps with decreasing heat and increasing runtimes. Since the motor doesn't draw much amps, it will generate less heat.

Which set-up would be more ideal for less heat and more runtime:

Set-up A:
-4s 6000mah
-higher kv motor
-gearing to match battery and motor set-up

Set-up B:
-6s 4000mah
-lower kv motor
-gearing to match battery and motor set-up

I also read that with more voltage, there would be more cogging; hard to start off or run at slow speeds. Is this true?

Who said that? That's not been my experience at all....It would seem more dependent on the esc programming more than anything.

The only complication I've seen w/ this is that w/ high turn motors you can run alot lower FDR. Every ESC has limits to how slow it can run the motor, say ~120rpm, so that min spd is higher w/ a low FDR.

Other than that the setup is very smooth. It would be too much for racing only if you choose too hot a motor, but this is true of any system. If you run a 2000kv motor on 6S, you will be flying off the track. Just choose the motor for the final desired spds and you are good.

Also, the battery choices you have have exactly the same amt of energy, so runtime won't be greatly improved, but will be a bit better w/ B as you are losing less to heat.

Serum · 11.13.2007, 02:41 AM

I'd like to know who said that too, Zero; from my understanding this forum is preaching it the other way around. High voltage setups will draw less amps, and the higher the voltage of a setup, the less the total internal resistance of the setup becomes an issue (runs more efficient) Unless you use the same gearing and same motor on 4/6S that would increase the current flow.

aqwut · 07:06 AM

Maybe it's just a matter of preference...
We can obviously agree that the Higher voltage setup are more efficient.. but speed wise and heat issue... really depends on the setup, gearing, driving condition and habits...
Of course you'd have to use different gearings with different voltage setups...
Maybe it's like comparing Apples to Bananas..

Finn is right too... same of total battery power (88.8 Watts) so run time would almost be identical...

z1nonly · 11.13.2007, 07:19 AM

I read it on another forum. I've been looking for the right set-up to use when I build an E-Revo for racing.

I came across a thread where a guy was using 6s and his gearing was high. It mentioned about the great speed, but had problems starting off a dead stop or going slow. I may have probably been something to do with the esc. I didn't ask though. From what I read, it sounded as if the high voltage was causing it.

But, thank you guys for clearing that up.

aqwut · 11.13.2007, 11:48 AM

maybe it was geared too high, did you remember what kind of ESC it was...
or maybe the motor he used was a weak motor ?.. I dunno..

sleebus.jones · 11.13.2007, 12:56 PM

I think many folks want to gear too high, then blame the wrong thing. I usually gear lower, so I get better acceleration. It certainly is not the high voltage being the problem....I think it's more that guy doesn't know what he's doing. :)

aqwut, i hear you on the weak motor. My 10L cogged bad on my 1/8th buggy. The 10XL in there now is smooth as glass. I think lots of people try to get the cheaper setups to perform as well as the more expensive ones. A high Kv S can ain't gonna work in a MT, but some people want to do that so they can get a cheaper motor and not have to spend big bucks on a high cell count lipo packs. It just don't work that way.

Sleeb

DrKnow65 · 11.13.2007, 03:08 PM

Another motor question for you guys,

I have a XXXT I'm running a MM esc, and a cs325700 (5700KV) motor, I'm geared as small as I can get and the motor temps are just acceptable (150') after a good hard run. (2S lipo now, 3S later this month)

I want to step up to a NEU motor (thinking 1509/1.5Y) 2400kv, use 4S lipo's and have a cool running setup.

The question I have is,
I also have a HYPER7 I'm wanting to run brushless, I would like to use the MM/NEU in both setups, what is the smallest NEU I should use in it on 4S? I'd like to have one motor/esc that would work in both (xxxt-hyper) untill the MMM comes out for the hyper7...

The MM esc, is modded with heatsinks on both sides of the fet board (wind tunnel dual fan setup) and runs cooler than ambient in the XXXT no matter what gearing or how hard I drive it, so I'm not worried about the esc.

One NEU, not WAY too big for the xxxt, not WAY too small for the hyper7, 4S in both cars... will a 1509 series be ok? need a 1512 series? will the xxxt steer with a 1515 hanging off the back?