Author Topic: Decision: 4S or 5S (Read 1073 times)

Allan Perret · « **on:** February 16, 2012, 11:58:50 AM »

If everything else is a wash, which is better a 4s or 5s system ?
What I mean is suppose the motor and batteries you are considering are available in both of the following combinations for a theoretical 50oz plane:
1. 900kv motor and 4s3000mah
2. 750kv motor and 5s2400mah

Motor is available in both KV's (or real close), and both batteries are about the same cost, weight, and size.

Will the 5s system run cooler because of the lower amps ?

Any other advantages either way ?

phil c · « **Reply #1 on:** February 16, 2012, 03:47:03 PM »

Everything in the system will run cooler, wasting less energy. Using the basic equation V=I*R figures the current and power loss will be about 20% less with the higher voltage. So the battery can be somewhat smaller, saving a significant amount of weight. Heck, go with 6 cells if you can.

Igor Burger · « **Reply #2 on:** February 16, 2012, 04:13:47 PM »

It is exactly the same, if both motors differs only in KV, then loses in iron are also the same, and since internal resistance changes with power of 2 then also loses in copper are the same.

for example if you have motor with kv=1000 on 10 turns of winding, running with 4 cells at 20A and Ir=0.1 then loses in copper are 20^2 * 0.1 = 40W

if you go to motor with kv =500, it will need 20 turns, what leads to Ir= 0.4 and current 10A on 8 cells (makes the same input power) and loses in copper are 10^2 * 0.4 what is the same 40W

The difference can be in ESC, but if you need ESC for higher voltage, it will have also higher Ir and also switching loses will be aproximately the same.

The key tis to use proper number of cells to keep proper head room in foltage for keeping rpm loaded and with discharged battery at as much as possible "open choke"

Keith Renecle · « **Reply #3 on:** February 16, 2012, 10:28:14 PM »

Hi Allan,
The simple answer is that 5 cells will save you around 7 to 8 amps in current, and if the price, size and weight of 5 cells is the same........go for the 5 cell setup. Just make sure that the esc can work with 5 cells. The lower current is a better bet in all the wiring connections, and the esc can be a little smaller as well, so if all things are equal as you said, the 5 cell setup is good.

Just as a matter of interest what exactly are the components that you have in mind? Thanks.

Keith R

Allan Perret · « **Reply #4 on:** February 17, 2012, 07:19:41 AM »

Quote from: Keith Renecle on February 16, 2012, 10:28:14 PM

Hi Allan,
The simple answer is that 5 cells will save you around 7 to 8 amps in current, and if the price, size and weight of 5 cells is the same........go for the 5 cell setup. Just make sure that the esc can work with 5 cells. The lower current is a better bet in all the wiring connections, and the esc can be a little smaller as well, so if all things are equal as you said, the 5 cell setup is good.

Just as a matter of interest what exactly are the components that you have in mind? Thanks.

Keith R

40 size profile, hope to keep weight around 46 oz.
Cobra 2826, KR governor (you know anything about those?

), ZTW esc.

John Rist · « **Reply #5 on:** February 17, 2012, 08:17:39 AM »

Quote from: Allan Perret on February 17, 2012, 07:19:41 AM

40 size profile, hope to keep weight around 46 oz.
Cobra 2826, KR governor (you know anything about those? ), ZTW esc.

Not sure about the Cobra motor but the KR is being discussed a couple posts below this one. Titled: KR Governor with switch

Within that post is web site:

http://www.keithrenecle.co.za/Electric%20CL.htm

Haven't tried one yet. In fact I haven't flown an electric stunt yet but based on what I read it looks like the way
to go.

Andrew Borgogna · « **Reply #6 on:** February 17, 2012, 10:32:13 AM »

I agree with Igor there is very little difference. I learned from Dennis Adamisin you want to start with the prop. What size prop and how fast do you want to spin it. Once you have determined that you size the motor (Kv) and battery to deliver what's required. This has worked well for me. I tend toward larger diameter with pitch in the 4 to 5 range and lower Kv motors and 4 cell batteries for my larger planes. I could just as easy bring up the Kv and lower the cell count, but I tend to stay with way works.

Regarding the KR timer/governor about the only thing you need to know with the ZTW ESC is make sure it has the default setting for governor mode. That is "Governor Off". That's true with any ESC that has governor mode. You don't want the governor in the ESC fighting the governor in the timer. This is one of the reasons I like inexpensive ESCs that don't have a governor mode option. Other than that the ZTW ESC will work great with the KR timer/governor, I have used a couple of them and find they work quite well.
Andy

Dennis Toth · « **Reply #7 on:** February 17, 2012, 01:57:00 PM »

Andrew,
Since you have the choice look at the battery weight. The 5 cell setup will generally be lighter for the same headroom on the motor run. If you can find light packs in the mah range you need this is one big area to save weight. The downside is the 5 cell is generally more expensive.

Best, DennisT

Dean Pappas · « **Reply #8 on:** February 17, 2012, 03:19:39 PM »

Hello Allan,
At that size, I'd go 4S only because great 4S chargers are available nice and cheap (FMA).
Up to 64 ounces, 4S is just fine as well, and much of the recent excitement about 5S setups has to do with flyers seeing the value of having lots of voltage overhead above that which runs the correct RPM under load at the end of the flight.
In general this has been because "low" Kv motors have been combined with low pitch props. A 900 or 100 Kv motor with more than 4-1/2 inches of pitch will work beautifully. In the 46 ounce neighborhood, you will likely run a motor weighing 5-1/2 to 6 ounces. It will take effort to find motors with 5S-like Kv's (750 ~ 800) unless you go to nearly 7 ounces.
What's the Kv for the Cobra 2826?

All that said, there is no reason not to run 5S! If I were building 60 ounces and above exclusively, then I'd gear up for 5S.

RRegards,
Dean P.

Allan Perret · « **Reply #9 on:** February 17, 2012, 04:03:18 PM »

Quote from: Dean Pappas on February 17, 2012, 03:19:39 PM

Hello Allan,
At that size, I'd go 4S only because great 4S chargers are available nice and cheap (FMA).
Up to 64 ounces, 4S is just fine as well, and much of the recent excitement about 5S setups has to do with flyers seeing the value of having lots of voltage overhead above that which runs the correct RPM under load at the end of the flight.
In general this has been because "low" Kv motors have been combined with low pitch props. A 900 or 100 Kv motor with more than 4-1/2 inches of pitch will work beautifully. In the 46 ounce neighborhood, you will likely run a motor weighing 5-1/2 to 6 ounces. It will take effort to find motors with 5S-like Kv's (750 ~ 800) unless you go to nearly 7 ounces.
What's the Kv for the Cobra 2826?

All that said, there is no reason not to run 5S! If I were building 60 ounces and above exclusively, then I'd gear up for 5S.

RRegards,
Dean P.

The charger is not an issue, I already have one that will handle up to 6s.
The Cobra 2826 (weight 6oz) is available with KV's of 760 & 930.
But I have decided that the Cobra 2820 (weight 5oz) will be big enought to handle a 45oz profile.
The 2820 is available with KV's of 840 & 970.

Dean Pappas · « **Reply #10 on:** February 18, 2012, 12:10:37 PM »

Hello Allan,
Agreed, and I'd go for the 4S and 970 combo with one of the many 4" and 4-1/2" pitch pushers available, possibly clipped to 11" or 11+".
Enjoy,
Dean

Allan Perret · « **Reply #11 on:** February 18, 2012, 02:51:05 PM »

Quote from: Dean Pappas on February 18, 2012, 12:10:37 PM

Hello Allan,
Agreed, and I'd go for the 4S and 970 combo with one of the many 4" and 4-1/2" pitch pushers available, possibly clipped to 11" or 11+".

Oops; I already ordered the 840kv.

Keith Renecle · « **Reply #12 on:** February 20, 2012, 09:53:35 PM »

Quote from: Allan Perret on February 17, 2012, 07:19:41 AM

40 size profile, hope to keep weight around 46 oz.
Cobra 2826, KR governor (you know anything about those? ), ZTW esc.

Hi Allan.............sorry.......I missed that one!

Yeah.....I do know a little bit about them!

Keith R

Author Topic: Decision: 4S or 5S (Read 1073 times)

Allan Perret

Decision: 4S or 5S

phil c

Re: Decision: 4S or 5S

Igor Burger

Re: Decision: 4S or 5S

Keith Renecle

Re: Decision: 4S or 5S

Allan Perret

Re: Decision: 4S or 5S

John Rist

Re: Decision: 4S or 5S

Andrew Borgogna

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Dennis Toth

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Dean Pappas

Re: Decision: 4S or 5S

Allan Perret

Re: Decision: 4S or 5S

Dean Pappas

Re: Decision: 4S or 5S

Allan Perret

Re: Decision: 4S or 5S

Keith Renecle

Re: Decision: 4S or 5S