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  1. #1
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    Question A few questions on c and mah ratings

    I was looking into getting a 3 cell lipo (as my first lipo ever ) and I'm having a bit of trouble understanding c and mah ratings. This is what I think I have: The c rating is how quickly the battery can discharge. Does it change the max charging speed? For a not super fancy motor, is 30c enough? I would assume so, but if that was enough, then why would people buy 150c batteries? As for mah, I heard an analogy that it's like the size of a fuel tank, so the more mah(s?), the longer I can run it. What if I have a larger motor? Would a 5000 mah 3s lipo on a brushless motor give me a similar runtime to a 3000mah 7s nimh?

    Sorry for the wall of bad questions, but I'm pretty confused! Thanks for reading this!

  2. #2
    Marshal Double G's Avatar
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    Mah is the gas tank of the battery. The listed C rating is the max it can push. Both are used to determine the amount of amps it can supply. So a 3s 5000mah 50C battery will be able to push 250 amps (5000mah/1000 * 50c = 5 * 50 = 250). If you have an ESC that will pull a max of 125 amps then this battery will handle it with ease. Even a 5000mah, 30C battery will (150 amps); just don't buy a battery that is not able to supply the amps (such as a 5000mah, 10C which will give 50 amps) as the battery will heat up and puff.

    For charging, take the mah and divide by 1000 and that is the amps you can charge which is coined as "1C." Take the battery above with 5000mah and divide by 1000 and you'll get a 1C charge of 5 amps. If the battery says max charge of 2C, then multiply it by 2 and you'll get 10 amps. A 7500mah battery can be charged at 7.5 amps for 1C and 15 amps for 2C. The standard is to charge at 1C for longevity, but if the battery allows you to charge at 2C it'll charge in half the time but at the expense of overall battery life.

    A 5000mah battery (regardless of nimh or lipo) will give more run time than a 3000mah. A 7-cell battery may have a max charge of 10.5v but as soon as it is used that voltage drops and you'll notice performance slows the entire charge of the battery. Lipo have a max voltage of 4.2v per cell so your 3s will be at 12.6 and will drop but you'll see consistent performance of the battery until it is dead (at a recommended low-voltage cutoff of around 3.5v/cell).
    The Super Derecho

  3. #3
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    Agreed, people will spend a lot of money for 150 c rating lipos just for racing and stuff. You NEED a lipo charger to charge lipos and if you don't use one, bad things will happen... I recently switched to lipo and am very happy with the results. I have 2s lipos, but will switch to 3s soon.
    3000 mah lipo = charge at 3 volts
    5000 mah lipo = charge a 5 volts
    Lipos generally take about an hour to charge at this rate.
    c rating does not effect charging speed. Lipos need to be stored at 3.85 volt per cell. Here is my old lipo thread with my questions that I had. I hope this helps. https://forums.traxxas.com/showthrea...po-please-help!

  4. #4
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    Quote Originally Posted by Double G View Post
    Mah is the gas tank of the battery. The listed C rating is the max it can push. Both are used to determine the amount of amps it can supply. So a 3s 5000mah 50C battery will be able to push 250 amps (5000mah/1000 * 50c = 5 * 50 = 250). If you have an ESC that will pull a max of 125 amps then this battery will handle it with ease. Even a 5000mah, 30C battery will (150 amps); just don't buy a battery that is not able to supply the amps (such as a 5000mah, 10C which will give 50 amps) as the battery will heat up and puff.

    For charging, take the mah and divide by 1000 and that is the amps you can charge which is coined as "1C." Take the battery above with 5000mah and divide by 1000 and you'll get a 1C charge of 5 amps. If the battery says max charge of 2C, then multiply it by 2 and you'll get 10 amps. A 7500mah battery can be charged at 7.5 amps for 1C and 15 amps for 2C. The standard is to charge at 1C for longevity, but if the battery allows you to charge at 2C it'll charge in half the time but at the expense of overall battery life.

    A 5000mah battery (regardless of nimh or lipo) will give more run time than a 3000mah. A 7-cell battery may have a max charge of 10.5v but as soon as it is used that voltage drops and you'll notice performance slows the entire charge of the battery. Lipo have a max voltage of 4.2v per cell so your 3s will be at 12.6 and will drop but you'll see consistent performance of the battery until it is dead (at a recommended low-voltage cutoff of around 3.5v/cell).
    This great info thank you. My daughter just bought a Slash 2WD at the local hobby shop and it with came with the NiMH, but she got a 5000mah 50C lipo.

    Looking on Traxxas' site the XL-5 (if I'm reading this correctly) has a peak forward pull of 100A so the most it'll pull is 100A. So if she got another battery a 30C would be sufficient correct? Is there any benefit of having a 50C over 30C if the ESC can't pull that much?

    Thanks
    Last edited by kantonburg; 08-04-2020 at 09:08 PM.

  5. #5
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    What are some good brands? The iD batteries look good, but they seem expensive for what they do. Spektrum smart batteries seem like a good option, since they have a popular connecter already attached. Also, their chargers seem a lot fancier compared to traxxas chargers. Would I have to not use my 7c nimh with an iD connector if I got ec5 connectors? I found this adapter:

    https://www.amazon.com/OliYin-Traxxa...ustomerReviews

    It doesn't look like it'll handle high current, but a 7c nimh isn't really high current so I guess it'd work?

  6. #6
    RC Qualifier Calebs0615's Avatar
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    SMC makes awesome batteries for great prices. Thats what i use. And what a lot of people on this forums use.

    Sent from my LGL722DL using Tapatalk

  7. #7
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    I've checked out smc, but they're just too expensive for what I'd use them for. I get that they're good batteries, but 85 for a charger? Am I missing something? (Plus, I like how easy iD and spektrum batteries are to use.)

  8. #8
    RC Qualifier Calebs0615's Avatar
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    Quote Originally Posted by EclipseMantis View Post
    I've checked out smc, but they're just too expensive for what I'd use them for. I get that they're good batteries, but 85 for a charger? Am I missing something? (Plus, I like how easy iD and spektrum batteries are to use.)
    Lipo chargers aren't cheap. I bought the traxxas ezpeak plus. Its a great charger with the settings you need. Other people may give you ideas on other chargers you could use but i don't know about going with a cheap charger. If anything your charger and battery should be one of the most expensive things for your truck. Cheap chargers im sure ruin batteries sooner than later.

    The traxxas first gen plug they give you an option for, is compatible with the traxxas id plug by the way.

    Sent from my LGL722DL using Tapatalk

  9. #9
    Marshal Double G's Avatar
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    Quote Originally Posted by kantonburg View Post
    This great info thank you. My daughter just bought a Slash 2WD at the local hobby shop and it with came with the NiMH, but she got a 5000mah 50C lipo.

    Looking on Traxxas' site the XL-5 (if I'm reading this correctly) has a peak forward pull of 100A so the most it'll pull is 100A. So if she got another battery a 30C would be sufficient correct? Is there any benefit of having a 50C over 30C if the ESC can't pull that much?

    Thanks
    If the 30C is over 3500mah then it would be okay but it never hurts to have a little cushion of reserve. Nothing wrong with going to a 30C 5000mah vs a 50C 5000mah rated battery but you'll see no more punch if the ESC won't pull more than 150 amps.

    Quote Originally Posted by EclipseMantis View Post
    What are some good brands? The iD batteries look good, but they seem expensive for what they do. Spektrum smart batteries seem like a good option, since they have a popular connecter already attached. Also, their chargers seem a lot fancier compared to traxxas chargers. Would I have to not use my 7c nimh with an iD connector if I got ec5 connectors? I found this adapter:

    https://www.amazon.com/OliYin-Traxxa...ustomerReviews

    It doesn't look like it'll handle high current, but a 7c nimh isn't really high current so I guess it'd work?
    SMC are very good batteries. I've ran them and the late SPC batteries and have nothing but good things to say. Best to steer clear of any adapter as they become a bottleneck of power. Solder the connectors of choice to the battery and ESC.

    Quote Originally Posted by EclipseMantis View Post
    I've checked out smc, but they're just too expensive for what I'd use them for. I get that they're good batteries, but 85 for a charger? Am I missing something? (Plus, I like how easy iD and spektrum batteries are to use.)
    $85 for a charger is an okay price but is not going to be that powerful. Traxxas chargers and iD batteries take some of the complexity out of the charging process. If you plan on just occasional playing around then Traxxas is the way to go. If you are in the hobby and have multiple batteries with higher capacities then you'll need to get a more powerful charger. I went with a Hitec dual charger with a DC power supply which didn't break my bank but some of the other systems our fellow board members have will astound you.
    The Super Derecho

  10. #10
    RC Turnbuckle Jr. olds97_lss's Avatar
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    Quote Originally Posted by Double G View Post
    I went with a Hitec dual charger with a DC power supply which didn't break my bank but some of the other systems our fellow board members have will astound you.
    You are not kidding! Some of these guys are really hardcore with hundreds/thousands of $ worth of charging equipment.

    I bash alone, I typically take 2 trucks with me. I spend very little time not driving the RC. I'm either driving to the bash site, or I'm driving an RC. So I tend to want to have at least 2 sets of batteries for both trucks. Since I have an ERBEv2, that means 2 packs for 1 run, 4 packs for 2 runs, etc. With my smaller 1/10th trucks, they require just one pack.

    I have 3 6S trucks and instead of having 6S packs that fit only one of them, I use dual packs in all 3. So when I take 2 of my 6S trucks, I like to take 8 charged packs with me. So 8 3S 5000mah+ packs need charged before I leave. To avoid having to get up at 5am to get to my bash area at 8-9am, I had enough "charger" to charge up all 8 packs at once in under an hour.

    I started electric with the ERBEv1 4 years or so ago. I also started with the traxxas dual charger and 4 of the 2S SMC 9000mah lipo's. The traxxas charger would time out on me during one cycle of charging, so it would take 1.5 cycles to fully charge 2 of them. That would end up being 3+ hours of charging to charge up 4 packs... it got old, fast. After a month of that, I got a 4x100W/4x10A charger, then I could charge all 4 packs in a bit under an hour. So, I spent $100 on the trx charger and $210 on the new charger.

    That was when I ran 4S. Now that I run 6S, I find that my 4x100w charger is just capable enough to charge at about 1.2C for a 5000mah pack as it hits the 100W limit. Which is fine, still only takes 35-40 minutes to charge up 4 packs.

    Then I got a hitec D7 charger which was 2x200w/2x20A so I could then parallel charge 4 packs at a similar rate. After a year or so, it started dying on me and not balancing properly. I got it used for a good price, so I got my moneys worth out of it. If I paid retail, I would have been more annoyed at $270 for the charger.

    Then instead of getting a big expensive AC charger, I decided to try DC. Got a 72A 24V DC PSU and a couple revolectrix GT500 chargers that can both do 1x20A/1x500W. Beings they were $75 a piece and the PSU was $100, now if a part of it dies, I'm not out as much. Getting 40amps/1000watts of charging power for $250 isn't too bad of a deal.

    Sadly the GT series of chargers appear to be getting discontinued, so if my 4x100 dies on me, not sure what I'll get to replace it.

    TLDR: Buy chargers that will be capable for future needs to avoid buying twice... or 3 times.
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