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Thread: What size or how many mAh

  1. #31
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    In my sons Stealth we run 8k. Not because we need it but because the boat needs the weight. If we're adding weight we figured we might as well add something that pays back.

    Toms Triton can get away with 4400. It's the absolute perfect spec sport though.

    There's a fine line with this class. You can be too light. Every boat has its own sweet spot. Some fiddling is in order for sure. It's half the fun.
    Noisy person

  2. #32
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    Hmmmm, lead is a lot cheaper than LiPos if all you need is weight. Easier to place too.


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  3. #33
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    True, but I can throw those same packs in my spec offshore, P mono, P sport if I need them.
    Noisy person

  4. #34
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    Quote Originally Posted by T.S.Davis View Post
    True, but I can throw those same packs in my spec offshore, P mono, P sport if I need them.
    This is the direction I like. Going same way. Keeps the voltage up too.
    Nortavlag Bulc

  5. #35
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    Quote Originally Posted by ray schrauwen View Post
    This is the direction I like. Going same way. Keeps the voltage up too.
    Doing things in this 'modular' way is efficient and keeps the costs down.
    Nortavlag Bulc

  6. #36
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    BTW We've run the Stealth on a pair of 4s2200's a bunch of times. Those were the previous generation of cells. Worked fine but they would come in pissed off. Tom is doing it with latest Roaring Top cells. They don't even bat an eye. The newer gen cells from most every manufacturer are much better. If you buy decent cells that is. I can't vouch for the cheapies. I've drawn some of my GP cells down into the 2.5v range. They were not happy but still came back. Came in bloated and hot hot hot. Their days are numbered now but in the old days that would have likely burned inside the boat.

    Also, a pair of 2200's can multitask too if you have the right boats. They fit really nice in most spec riggers too. Extra wires to route down under the canopy but they fit perfectly. Spec rigger amp draw is so reasonable that the wires don't seem to cause problems.
    Noisy person

  7. #37
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    Here is a topic that I have not been able to grasp. How to choose a battery that will give your boat the best performance without them swelling up, disintegrating, damaging your ESC and/or motor. What are all of the factors one needs to calculate and consider? For example: I have an old Kyosho Viper that I've had for years. I started tinkering around with it. I installed a water cooled Leopard LPB2845 motor. It's maximum ratings are 30A, 26V, 800W and 2350KV. I also installed a water cooled Dynamite 3860 ESC. Its specs are 30A constant and 180A peak. Input voltage is 2S-3S (7.4V-11.1V) Li-Po. BEC Output is 6V/1A. I'm using the original Futaba FP-R112 JE receiver.
    One area that gives me the most confusion is the correlation between amps, volts and watts. I am aware that in terms of LiPo batteries, the MAH rating determines the amount of run time and the "S" rating denotes the number of cells and total volt output. The "C" ratings I'm not too keen on. Is there a step by step methodology or calculations that one uses to determine if a particular battery is too much power for a given motor and ESC pairing? Would some of you more senior and experienced hobbyists help me here? Thanks. Boatnik

  8. #38
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    Good questions... Answers are dependent on goals. Do you want to race? Do you sport boat and are looking for longest run time with greatest reliability? Can't get to specific answers without knowing your goals and expectations.

    I can tell you that your ESC, rated for 30A continuous and your motor rated the same leaves no headroom to explore prop options, which most boaters want to do. You should run a 60A ESC on a 30A motor. I understand it has a momentary rating of 180A, but that is so much higher, I wouldn't put much stock in that. Motors can take momentary overrates much better then ESC's.

    So your motor is rated for 800W. Excellent job getting ALL your specs together! So on 2s at max power, the amp draw would be 800/7.4=108A. This is way over the max amp rating of the motor. So this battery/motor combo isn't good at all. At 3s the amp draw is 800/11.1=72A, still way over the motor spec. So with what you listed, you will only get the following safe power out of the motor on 2s, 30*7.4=222W, only about a quarter of the available power. On 3s it's 30*11.1=333W, 42% of available power.

    See you got the wrong motor or battery choice. It's a 6s motor, then you control amps by how much load or prop you put on it. Folks are always doing this, running under the voltage spec and pushing the amps way past rating. It's amps that breaks parts, causes heat and puffs batteries. You're going to get all kinds of posts that say they do it all the time. All I know, its way past what the manufacturer states the motor should be used at. For me, I would start with a 14.8V motor, then run these numbers from there. I hope that helps...

  9. #39
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    Oh, on motor specs, each spec is a limiting value. The motor is only supposed to see 30A and not over 26V. The 800W only applies if you apply on-spec volts and amps. The motor will NOT take any amp and volt value that will yield 800W. BTW, I would never get a motor with these specs. It's small, so putting a 6s battery in it doesn't make a lot of sense to the average boater. You didn't mention the ESC's voltage rating...

  10. #40
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    Just an FYI, cold cells will swell underload more often than if ambient or warm.
    Nortavlag Bulc

  11. #41
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    Strange, I got an email with Ray's response, but the second part is not showing up on the post... Anyway he says heating up cells before a run is for professionals only. Yes, that's very risky business. When a battery is heated, it's terminal voltage will rise. So I would think if you're going to do that, then the batteries would be charged to say 4.16V, or whatever testing shows. But if you charge at ambient to max volts then heat it up, you could get yourself a camp fire starter brick there!

  12. #42
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    I edited it for safety reasons.

    I've warmed cell before on 35*F days etc. Very carefully but I avoid it if possible. In Canada by end of September it gets very chilly and the last run for many in my area is an apple butter festival at the end of the month. Last time I ran my Q sport there one cell got a tad puff in it from cold since I was propped way down from normal. These packs have never been more than 130F.
    Running in the cold can kill packs because the chemistry doesn't like high current draw until it's at a decent temp.
    Nortavlag Bulc

  13. #43
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    Yes, that's true. It would be nice to have a heated battery case, something to get and hold them at 85 deg F, like F1 tire warmers. The challenge is to ensure they are at the same temperature, all the way through the battery. Only a good length of time in an enclosed box can do that.

  14. #44
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    Hobbyking sells warming bags and I've half finished a warming case made from hobbyking tire warmers.

    Some use those 12/24vdc beverage, food cooler/warmers.
    Nortavlag Bulc

  15. #45
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    I have the same warming bag and tire warmer :), I also use those disposable hand warmers.


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  16. #46
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    Thanks very much CraigP! Your input helps a lot! My goal is simply sport boating. I have no desire to get involved in competitive racing. I'm looking for the fastest speed, with a decent run time and reliability. In other words, I'd like to get as much speed as I can without burning up motors, ESC's and batteries. Would you elaborate a little more on your equations in the 3rd paragraph? The LiPo I've been using is rated at 3s (11.1v) 30c 2200mah. I've never used a 6s LiPo in this boat. In your 4th paragraph you say my motor is a 6s motor. How did you determine that? I am running a 440 prop on this boat. A few remarks on props would be a tremendous help. How to choose the right prop....What do the numbers mean....If your boat cavatates, how does one address the problem? Thanks again CraigP!

  17. #47
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    What I was showing is the reliable, safe power available using 2 and 3s batteries. The motor spec states that 30A is max, so those equations shows the power (Watts) you can get reliably at those voltages, which are just fractions of the 800W the motor can potentially deliver. I'm also showing just how many amps you would have to run to get 800W, or max power. It's Watts that make the boat go... That motor is rated at 26V but only 30A, so it's not a good fit for lower voltages. What you want is a motor more like a 17V motor with a current rating of 47A.

    This discussion assumes you need or desire the 800W to get some speed out of it, by pushing a bigger prop. I'm not sure on the availability of 3 or 2s motors, I just don't use low voltage setups...

    You can hook up low voltage to that motor and put a big prop on it, but it will run very hot or burn up. I too do not race and want a fast, reliable boat. To accomplish that goal, I drop my working amps by using HV packs such as 6-8s. These electrical designs need to be taken from a starting point, then worked through. Many just put parts in boats and see what they get. Often they end up letting all the magic smoke out! Don't be one of those guys....

  18. #48
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    Boatnik, that is not a 6s motor, the max of 26v just means that is just the maximum the bearings are rated for. Please Ignore CraigP and dont run it on 6s. You have a decent mild 3s setup there, more powerfull and eficient than what it came with from the factory, I would guess you are along the right lines with a 40mm prop too. What brand and type of 40mm prop are you running? Surface drive props are prone to cavitating when running submerged, switching to a differnt prop the same size may help that. increasing diameter will help too, but that increases amp draw and heat too, so if you go bigger just run for 30 second then bring it in and check temps, if things are cool go a minute and check again, carry on, continuing to slowly add runtime to your testing untill you are getting a full run.

    CraigP, advising a newbie to run 6s on a 28mm 2350KV motor is totaly irresponsible. That is someone asking for a reliable sport setup, and you are telling them to run 60,000rpm unloaded on 30A electrics! there isnt a prop that size available, and even if there was it would be a SAWs setup with a risk of smoke on every run, for a specialist lightweight boat not a plastic submerged drive RTR.
    Paul Upton-Taylor, Greased Weasel Racing.

  19. #49
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    Paul, you are out of line! I did not tell him to run it on 6s. He wants his boat to scoot, so he's going to need 800W to do that. As my equations clearly show, he cannot do that on that motor without seriously over amping it. I recommended a 17v, 50A motor as a better way to make the wattage he needs to hit his speed expectations. That motor has a 30A MAX rate. So your advice is to put 11.1v in it, prop it up and let him burn his electronics up. What a freaking idiot! So who is the unresponsible one now! I was telling him he needs another motor, and trying to give him the math as to why. I also told him it's not a good motor choice, the kv is not in line with the voltage rating. You almost have to overamp it to get 800W out of it. It's a weak motor choice for any boat!

    Boat, make up your own mind. I showed you the equations. Use or ignore, it's your choice. There is a Leopard 2845 rated at 18v, 45A and 3300kv that would be a nice fit to 11.1v I'm done with this post.... Paul, say hello to the Queen for me...

  20. #50
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    This is not boatniks thread and things are beginning to unravel.

    Boatnik needs his own thread.

    Mods need to take care of this.
    Nortavlag Bulc

  21. #51
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    Quote Originally Posted by Buoyhunter View Post
    Its a ProBoat stock 1050 kV motor and a ABC 1817
    I think the problem started with this typo of 1050kv when it was supposed to be 1500kv.

    Craig jumped in because he is familiar with this kv in his setup.
    Nortavlag Bulc

  22. #52
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    It seems obvious that I am a new member and a newcomer to rc boating. I'm trying my best to learn how to navigate this blog. Ray Schrauwen's suggestion that I should start my own thread is spot on. How do I do that? I haven't seen any instructions on how to start a new thread. Thank you everyone for your patience.

  23. #53
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    Hit the "Forum" tab, then go to the rc boating folder. Under that, there should be "+Post New Thread" on the upper-right side of the screen. Put in a Title that is appropriate and makes sense to people seeing it. Then, type away!

  24. #54
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    Thanks CraigP

  25. #55
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    Thanks for all the info. Do the MMEU guys have a different website or club related meetings? I know Rochester Hills is this weekend but is somebody typically out at the pond on weekends?

  26. #56
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    We try to keep everyone informed here but sometimes we get lazy. It's worse as the season starts to wind down.

    Typically we are out every Wed evening about 5:00. Then every Saturday at 10:00am until about 2:00pm or so. This weekend is an exception. None of us will be there as we have two club members getting married. How cool is that!
    Noisy person

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