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Old Jan 27, 2009, 10:14 AM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
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How Much Amp Difference From 2s To 3s

I have a small 16" hull with 2700kv motor, 25A esc & 2s 2500mah 20C lipo, works very well and is very fast. BUT when I use my 3s 2500mah 20C lipo, the esc shut down from over heating, I know this is cause the motor rpm increases from the 2s TO 3s BUT I WANT TO KNOW BY HOW MANY AMPS DOES IT INCREASE. I dont have any meter to verify this my self but just wondering if I could just replace the 25amp esc ith a 30amp esc. I was able to confirm that when in a PLANE using same size prop, the difference between just the going from 2S TO 3S can go around 16amps difference.

I want to know since its only a 1" prop, would the difference be less then 5A and could I get away with using a 30A esc instead of 25A. MY budget is very limites (AKA WIFE) and I can get a 30A ESC for 18$new. This would then also benefit me in that I could use the old 25A esc to replace a 10A esc in my plane.

Basicaly, if the boat works very well with 2700kv motor 25a esc and 2s lipo, what would be the difference in amps be when using the same setup but with 3s lipo. same setup WOULD IT BE MORE OR LESS THEN 5AMPS
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Old Jan 27, 2009, 10:39 AM
Is life for real?
pkboo's Avatar
Almere The Netherlands
Joined Sep 2006
1,320 Posts
Freechip, I believe your rpm increases due to the voltage increase, you're going from 7.4V to 11.1V. What you want to know is probably amp drainage, I'm no scientist in electricity so I only know the basics and in most things you can compare it to water flowing thru pipes (cables). Voltage would be the size of the faucet and amps the flow speed/quantity, I believe! Someone is due to pitch in shortly I think. Boo
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Old Jan 27, 2009, 11:28 AM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
Yes i know that the rpm increases with high cell lipo 2s 7.4v times 2700kv = 19980 unloaded & 3s 11.1v times 2700kv = 29970. But I want to know if anyones knows how much this difference in RPM would be in amps. The 2S setup works fine with 25A esc but then it shuts down from overheating with the 3S lipo. IS IT because I am exceeding the 25amps by only 1 or 2 amps or by 15 or 20 amps. If its just 1 or 2, then I could get away with a 30A esc, if its more then I would need to get alot bigger. LIMITED BUDGET aka wife but I did find a 40A for not to much more.
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Old Jan 27, 2009, 01:55 PM
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difference from 2s-3s

Now a 16" boat on 3s with the increase in rpm would make boat unmangeable as you mentioned ,. it was fast on 2s .
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Last edited by Mikedown; Jan 28, 2009 at 09:35 AM.
Old Jan 27, 2009, 02:36 PM
Submarines, etc.
tsenecal's Avatar
Arvada, Colorado
Joined May 2005
1,570 Posts
freechip,

to answer your question directly:

no-one knows.

you will have to get a meter to check the amperage now, with the 2s battery. you could very well be using 23 amps with the current setup, and with a 3s battery you could end up using 35 amps, or, with the current setup you could be only using 19 amps, and with a 3s, you could be using 28 amps. nobody knows, all that we could do is guess. It is imperative, if you continue to try to increase the speed of the boat that you must do some analysis. the only way you will be able to analyze anything is if you start recording data.

just be glad that your esc's thermal circuit worked!
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Old Jan 27, 2009, 03:51 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
If you click on my name and check out my boat video, you will see what I am talking about. Works very well with the 2S and yes the 3S is a little over kill but thats what I wanted. To see the thing jump and reach high speed compared to stock is crazy. I was just trying to solve my problem after mid way in my run time thet ESC shuts down. I know I am exeeding the amp limit for the ESC or simply because its a air ESC and theres is no air circulation it could just be heat related. WAS just thinking there was easy answer to want the difference would be from a 2S lipo and a 3S lipo. Yes I agree I do need to get a amp meter of sort to determine the real amp draw of this little beast of a boat.

AND P.S : The budget AKA wife was just to make sure some readers understood that I did want them to tell me to buy a 60 or 100 amp esc. I do and want to stick to my budget because I do agree with my wife that between my truck, 2 boats, heli and now PLANE. I have been spending to much money & time on my toys and not her. BUT I TELL HER THAT I HAVE MORE FUN PLAYING WITH HER. LOL

Thanks every one for trying to help. I will do the right thing and invest in a amp or watt meter of sort but there is no need to get this done right away since my water bashing is under 3 feet of ice for a couple of months, DAM CANADIAN WINTERS.
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Old Jan 27, 2009, 04:47 PM
Registered User
Davenport Iowa
Joined Jan 2006
173 Posts
Amp draw problems

Hi We used to get into this problem with the brushed car motors in boats .With more volts came more amp draw. If you didn't do something you usually burned up motors. The most obvious (and not mentioned )answer, is to use a smaller or less pitch prop. What prop do you use now? A smaller prop will reduce amp draw and still produce more speed at the higher rpms that you get with the higher voltage.
n.h.schmidt
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Old Jan 27, 2009, 05:23 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
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Its the stock prop its 1.00" dia. X 1.58" pitch. I did not want to under prop. I simply wanted to get proper ESC. 30A esc was 18$ and the 40A is 25$ or so. I will wait until I can check the amp draw under load with proper meter and then get the ESC I need. THANKS FOR ALL THE HELP
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Old Jan 27, 2009, 06:09 PM
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cyberhoops's Avatar
Seattle
Joined Feb 2006
928 Posts
While the general answer to the question of amp draw is just a guess... I ran some numbers through FeCalc, and the amp draw seems to just about double.

I checked it with a couple different motors since I don't exactly know what motor is used in the Villian. Typical numbers came back like this with the same motor/esc/prop and just changing the battery voltage.

2s - 19.9 amps
3s - 37.1 amps

In other cases it jumps from 14amps to 27, or 21amps to 41amps. The results seem pretty typical so I would imagine you are seeing about the same thing. The power levels are jumping from numbers like 105 watts to 400 watts - so I don't doubt you are seeing a huge change in performance.
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Old Jan 27, 2009, 07:22 PM
A piece of sublime engineering
Malaysia
Joined Nov 2008
67 Posts
Correct me if i'm wrong. Basic principle would be P=IV.
In your case i think the esc shut off is due to its voltage limits.
The current is drawn by your motor depending on your voltage and rated power.
Yes.. since the voltage is increased.. so does your current. Check your motor rated power and you will know your current drawn with the increase voltage.
Change your esc that can accept 3s would be a solution.. and expect wild ride.. ehehe. Enjoy!
-z9-
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Old Jan 27, 2009, 09:50 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
The motor is rated at 28amp cont. and peaks at 50amps and the ESC is 25A and its 2 & 3s rated. Everything works and yes its fast, heres the proof
Reef Racer 2 Brushless Project (3 min 11 sec)


Thanks for the MATH on the difference between 2s and 3s with same motor/esc/prop. thats what I was looking for. I know I am well within the spec wehn running 2s cause I can run WOT for the full runtime about 15 to 20 mins and everything motor/esc/lipo are just warm, but with the 3s I can still run for 10 to 15 min before it shuts down. I think I mite just try to reroute the motor water cooling to cooled the esc and try that.
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Old Jan 28, 2009, 05:47 AM
Closed Account
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difference of 2s-3s

Trim tabs for that unit!
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Old Jan 28, 2009, 05:55 AM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
Quote:
Originally Posted by retoabcr
Trim tabs for that unit!
LOL not quite the answer I am looking for . the last portion of the video just before it dives under. I am at 90-95% full throttle, for the most of the video where its jumping out, doing this by applying full throttle at startup for the making of the video. BUT THANKS, I did consider them.
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Old Jan 28, 2009, 06:50 AM
Tom
Huntingdon UK
Joined Apr 2007
21 Posts
Hi Useing a simplistic approach, if you go from 2s to 3s you are increasing the input voltage by 50% this will raise the RPM by 50% (from about 20,000 rpm to 30,000). A simply (if not stricty true) approach says the current will rise by 50%. But what is the original current? A very crude way to find out, is to time how long you can run at full speed on your 2s battery,
If you run (for example ) 6min with the 2.500 mAh battery
6min =0.1Hr and 2500mA =2.5 A hence 2.5/0.1 =25A load. or if you run for 15 min =.25Hr hence 2.5/.25 = 10A load.
based on this a 50% increase would give about 38A or 15A, I would guess your somewhere in between.
This is only a rough estimation, but may help
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Old Jan 28, 2009, 08:07 AM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
23,098 Posts
yes, as you can see in post #9 using same motor esc & prop the difference between 2s & 3s is almost double. I mite just try to put it in the tub and check that actual amp draw on the 2s setup and then get the amp draw on the 3s setup. This will give me better idea if I can get away with simply adding water cooling or need to get bigger ESC.
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Last edited by freechip; Mar 04, 2009 at 12:09 PM.
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