super gripper 419 Posted September 11, 2012 I have been reading a lot on this web site about people being unsure about swtiching to lipo batteries. It is all very safe as long as you use the 'C' rating formula. the formula is this battery capacity x 'C' rating = esc amp draw (using mine as an example) 4.000 x 25 = 100 you need to put a decimal point after the first number of you batteries capacity. 4.0 x 25 = 100 if your esc current drain is greater than what your lipo battery can give you are risking a big 'BANG' as long as you follow this simple formula then all will be ok, for those of you out there that are going to say well mine is fine! well its on your head then think of a lipo battery as a bag (cos it is) when it charges it swells, when it discharges it contracts. ESC's with lipo cut off as you know detects the batteries low voltage point. If the battery is taken past its low voltage point it can be damaged, charge it back up again and after a couple of cycles 'BANG' by using an esc that has a higher current drain than your lipo can give this then in effect is taking too much out of the lipo during its 'burst' (the point when you ask for full power) anyway I hope this all helps and settles a few minds. thanks guys, enjoy. Share this post Link to post Share on other sites
Percymon 2184 Posted September 11, 2012 Sorry to be pedantic but battery capacity (in amps) multiplied by C rating gives the max current deliverable by the battery pack So 4.000 X 25 = 100 Its a useful reminder though, especially with so many lower capacity (1800-2200mAh ) battery packs available cheaply - if in the market for these smaller /lighter packs its advisable to go for 30C or higher rating, especially if you intend running them in various vehicles with varying motors and current demands. 1.8 x 20C = 36 amps - OK for 1/16th scale 1.8 x 30C = 54amps - OK for general touring/buggy runners on hard ground 1.8 x 40C = 72 amps - nice bit of safety margin if you really want a small capacity battery 2.2 x 40C = 88 Amps These days unless the dimensions of a battery compartment are very restrictive its barely worth buying a 1800mAh lipo pack. I do have a 1300mAH 3S pack, but thats purely because of the limited battery space on the mini erevo. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 yes sorry my fault, your right. changing it now. thanx Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 To be honest, I don't get the point. If the battery can not deliver enough current to satisfy the demand coming from the motor, won't the battery just limit the availabe current instead of blowing up? Just as NiMHs won't blow up as well when being used with very powerful brushless setups (they'll only limit the power and may produce cogging as being the inferior part of the electronics). As long as you don't shortcut the battery leads, of course. However, I've just used LiPos with a minimum rating of 30C in conjunction with LiPo-capable speed controllers so far. Share this post Link to post Share on other sites
Percymon 2184 Posted September 11, 2012 To be honest, I don't get the point. If the battery can not deliver enough current to satisfy the demand coming from the motor, won't the battery just limit the availabe current instead of blowing up? Just as NiMHs won't blow up as well when being used with very powerful brushless setups. As long as you don't shortcut the battery leads, of course. However, I've just used LiPos with a minimum rating of 30C in conjunction with LiPo-capable speed controllers so far. Insufficent current demand will lead to stuttering of the motor, which will probably annoy you so much you'll sort the issue long before the battery decides enough is enough. Also remember to fit suitable electrical connectors capable of the current flow, Tamiyas are something like 7.5A rated. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 Thanks, I've edited the cogging issue into my previous post while you were writing yours. I agree with you, advanced connectors (like Deans) are a must for such a setup. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 the demand isn't coming from the motor, its coming from the esc. Lipo's are different to NIMH's thats the point. The internal construction of the battery as in a lipo and a nimh's is completely different. The battery can give more than its 'C' rating. The rating on the battery is there for your safety. ignore it and blow yourself up if you wish. its like a rubber band for example, keep stretching it to its limit and it will break. and you should only be using Hard Case packs in cars. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 Thanks, I assume I will be on the safe side with my 30C 5000mAh hardcase LiPo in a 12T brushless 1/10 scale buggy? Must be 5 x 30 = 150A then if I do the math right. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 Thanks, I assume I will be on the safe side with my 30C 5000mAh hardcase LiPo in a 12T brushless 1/10 scale buggy? Must be 5 x 30 = 150A then if I do the math right. whats the current rating of the esc chap ?? Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 The ESC has a rating of 100 A (120 A peak), the 3380 kV motor has a demand of 40 A (60 A peak), 210 W output. And holy cow, that DT-02 Sand Viper is pretty fast with this setup, I wouldn't go faster for the sake of motor temp on rough ground and handling. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 The ESC has a rating of 100 A (120 A peak), the 3380 kV motor has a demand of 40 A (60 A peak), 210 W output. And holy cow, that DT-02 Sand Viper is pretty fast with this setup, I wouldn't go faster for the sake of motor temp on rough ground and handling. yes thats fine, the esc current rating is lower than the batteries output, thats the way it should be. I find my motors get hot in my DT-02's. very poor air flow over the motor. best make sure your esc has thermal cut off. Share this post Link to post Share on other sites
Backlash 481 Posted September 11, 2012 Super Gripper... Sorry, I must disagree with you.. The current drawn from the battery is determined by the motor... The ESC of course MUST be able to handle the current drawn by the motor, as does the battery.. Using the same, no motor limit ESC, a 27 turn motor (eg kit silver can 540) will draw LESS current from the battery than what a 12 turn motor will.. This works the same for Brushed and Brushless ESC's.. Same for NiMh and LiPo.. If what you are saying was true, i.e., your ESC will continuously draw its maximum rated current from the battery, then you would get the same runtime from a 12 turn motor as you would from a 540 silver can kit motor... (Which is not the case) You are correct in that the ESC does have some bearing on the current drawn from the battery, just not quite in the way you describe.. A high quality, no motor limit (race, if you like) ESC will enable the motor to draw more current from the battery than what a cheap (read Tamiya TEU101BK) ESC will, but that has to do with the internal resistance of the ESC, and the subsequent voltage drop accross the ESC when on load.. You are also correct in your advice for buying LiPo's with sufficient "C" rating to suit the requirements of the vehicle, and Motor / ESC combo that you are using.. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 Mr backlash, you are correct in some of what you are saying yes. if the esc is rated at 120 amps, it can only handle 120amps therfor will only supply 120amps. If the motor is asking for more it won't get it. if you are using a 'silver can' for example. a 120amp esc will make the motor go faster than a 60amp esc. so as you see the internal resistance of the esc is the factor in all of this. an expensive esc as you say will give you longer run times than a cheap esc as you say but thats because its not cheap and nasty. and the esc will not always draw its maximum current rating unless of course you only have an on and off button on your transmitter. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 I doubt a silvercan motor would ever ask for 60A, thus leaving the advantage in maximum possible current draw of an 120A rated ESC useless? Well, maybe only if you power the poor can with 3s LiPo or more. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 I doubt a silvercan motor would ever ask for 60A, thus leaving the advantage in maximum possible current draw of an 120 A ESC useless? yes your right, the 'silver can' was really only meant to be a example in all of this. and if you are using lipo you really want to be brushless anyway with all the safety features of a good quality ESC. I will only ever use an esc that has no limit (brushed) and a very low turn for brushless. its false economy to buy a non limit esc (this has been argued before on another thread) Share this post Link to post Share on other sites
Backlash 481 Posted September 11, 2012 No mate, that is where you are wrong.. The current rating of an ESC is only the current rating of the individual Mosfets used to build it at a given temperature, typically 25 degrees celcius.. A 120 Amp rated ESC is quite capeable of delivering much more current than 120 Amps, but it will overheat, and if there is no thermal protection, it will burn itself out due to overtemperature.. This is basically what many of the TC members are doing when they connect a Tamiya 23 turn TZ or BZ motor to the TEU 101BK that has a current rating designed to suit the Kit 540 silver can and Sports tuned motors only.. Basically, if you short circuit the motor leads of a 120Amp ESC, or connect a motor with a much lower turns than the motor rating on the ESC, then you will overload the ESC (exceed the current rating of the ESC), and potentially burn it out.. Obviously electricity must work differently in the UK than it does in here Australia.. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 See this is why when one posts useful helpful information on the internet, someone always thinks they know better. Another reason why tamiyaclub is not a friendly place to be. One reason why I do not post on the forums one of the reason's why i was away from this web site for 2 years. and why I will not subscribe next year. thank you for confirming what I always knew about this web site. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 I apologise. There was no offense intended by me. EDIT: Again, I want to thank you for explaining the math behind LiPo battery C-rating, which is something I wasn't aware of before. However, please don't feel offended if somebody corrects some points of your statement. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 I apologise. Please don't feel offended, there was no offense intended by me. no chap it wasn't you. I just hope my info is of some use to somebody. Share this post Link to post Share on other sites
wolfdogstinkus 1876 Posted September 11, 2012 @Supergripper I spent two minutes with you at the Tamiyaclub meet and learned more than I have in 5years on this website. OK so I have learned loads about Tamiyas from here but you gave me some tips that I shall never forget. Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 thank you wolfdogstinkus, you were a really nice person and we had a good old chin wag. I was nice to meet you. I will contact a moderator and have this thread removed. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 From my point of view, there's no need to remove this thread or even to leave TC. You don't have to feel embarassed about this discussion, I'm totally honest to you. Share this post Link to post Share on other sites
Backlash 481 Posted September 11, 2012 Well that's an over reaction if I ever saw one.. Tamiyaclub is one of the most friendly forums on the net... Obviously you are not a member of RC Tech.. I dont have a problem with you posting "helpful" information on the net, but if you are going to do so, then please try to make that information as accurate as possible.. ESC's come with instruction sheets, dig one out and have a look at the specs for the ESC.. may I draw your attention to the notice that will often be written near the current rating of the ESC... It will read " Current rating of the Mosfets @ 25 degrees C".. If an ESC's rated current was the maximum current that could be drawn from that ESC (i.e. the ESC had some type of maximum current limiter) then effectively there would be no need for motor limits on ESC's, as any ESC could run any motor, irrespective of the wind, due to one only being able to draw the maximum current rating from the ESC..... Doesnt sound right does it...? But that is what you appear to be saying..? Share this post Link to post Share on other sites
super gripper 419 Posted September 11, 2012 From my point of view, there's no need to remove this thread. You don't have to feel embarassed about this discussion, I'm honest. I am not embarassed my friend, just completely fed up with it all. i am a racer and have done for over 25 years now. I stand by my guns at races as I race a Tamiya and am proud of it. And I get one badword of a ribbing I can tell you. Share this post Link to post Share on other sites
GregM 1109 Posted September 11, 2012 But that is what you appear to be saying..? Well, I think it is just more of a slight misunderstanding on both sides. Share this post Link to post Share on other sites