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Wiring and Batteries - AMPERAGE - Safety Tutorial - Mega Thread

Discussion in 'ESC's, Wiring & Batteries' started by WallacEngineering, Jan 24, 2018.

  1. WallacEngineering

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    Update 12/23/18. Almost no one has replied to this thread. I figure very few people have even read it, so I havent been updating it. RCTech is a far more active RC Forum website, so my updated version is there: https://www.rctech.net/forum/radio-electronics/1009300-warning-lipo-c-discharge-ratings-invalid.html

    The information provided in this thread is very important, but has reached very few enthusiasts in the past year. Now, I would like help to bring this info to Medic's attention. If he were to research this topic using my updated RCTech thread, and then make a tutorial video, Im sure that the majority of RC enthusiasts would be made aware of the information. If you know of a way to bring this thread to Medic's attention, plese let me know.

    The Hobby Grade side of Radio Control vehicles can be dangerous, and NOTHING is more dangerous in this hobby than Lithium-Polymer (LiPo) batteries. Believe me I understand the dangers completely after my Serpent Cobra E-Truggy went up in flames in late 2015 and I very narrowly avoided the immense flames of exploding LiPo batteries. The purpose of this thread is to explain my findings after researching possible causes for the fire. This information can be used to prevent electrical problems and dangerous LiPo situations in the future, so be sure to READ CAREFULLY!

    To understand what happened to my truggy, we must first discuss my technical research. You see I was completely sure that my setup was sound, and according to specifications my setup was sound. In fact, I put 5 charge cycles on the same batteries in bashing sessions with no problem at all, hitting full throttle several times. The irony is that when the fire happened, I was at 30% throttle, testing new City-Block tires in an empty, dirt parking lot. A gentle testing run with no jumps at all was when the RX8 ESC decided to erupt in flames.

    This failure occurred because we, as RC enthusiasts, have been LIED to my manufacturers of RC electrical components for years. Most commonly known information regarding LiPo Amperage Output, ESC Amperage Draw, Connectors used in wiring, and Wire Gauge Capacities are all misconceptions and are INCORRECT! Companies market their products to sell, and companies with integrity suffer because of it. When a company tried to market their LiPo as "TRUE 25C", nobody bought it, as it didn't meet the manufactures suggested requirements for higher end brushless systems. In all actuality though, it was overkill for those systems.

    Lets start with LiPo batteries. Did you know that the discharge rating (shown as C) on ALL LiPo battery packs is actually exaggerated substantially, some being exaggerated by nearly 400%? I too was unaware until I came across an article on the RC-Tech forums from years ago (2010) where an enthusiast decided to use the standard calculation of 1/1000 of mAh rating multiplied by the discharge rate (C) to determine that he could safely load his 5000mAh, 40C LiPo with a current draw of 190 Amps. This amperage load actually caused the LiPo to completely discharge after delivering just 750mAh, and caused irreversible damage to his LiPo, causing it to "puff up" and become too dangerous for further use.

    As an example, lets take a look at he 8200mAh/110C rated battery listed here: https://www.amainhobbies.com/reedy-...se-lipo-battery-7.6v-8200mah-asc27320/p727177

    Now if you use the STANDARD method of calculating amperage, then this battery would be capable of a simply INSANE 902 Amps. But if you loaded 900 Amps onto this battery, it would almost certainly explode, or at the very LEAST it would be irreversibly damaged, and would no longer be safe to use. My full size Volkswagen GTI uses a pretty high-grade lead acid battery for starting. It is rated at 450 Cold-Cranking Amps. Do you really think this tiny 2S LiPo battery is capable of delivering twice that power reliably? No way.

    So how do we determine the SAFE load that we can apply to our LiPo batteries? Well, most people can't. You see, to determine the correct and SAFE amperage load that a LiPo can handle, you need a very high end LiPo charger capable of telling you the Internal Resistance (IR) of your individual LiPo cells (Most "GOOD" LiPos measure between 1.2 and 2.0). Then, you have to determine the Figure of Merit (FOM), which is a very complicated term, described here: http://jj604.com/LiPoTool/ and in even more detail here: https://www.rcgroups.com/forums/showthread.php?1392662-Lipo-C-Ratings-A-Replacement-Overdue

    However, THANKFULLY there is a simple way to determine the APPROXIMATE SAFE amperage for LiPo batteries. To understand, you need to take a look at SMC LiPos. These guys are great, the only company Ive ever seen that actually lists TRUE amperage rating in the title and specifications of their LiPos, not to mention that dozens of YouTube reviews reveal that these batteries are of OUTSTANDING quality and performance, at a price less than even Gens Ace.

    Take a look at his LiPo here, which is actually the LiPo I will be purchasing for my new 1/8th Truggy: https://www.smc-racing.net/index.php?route=product/product&path=67_96&product_id=491

    Now as you can see, the battery is a 4S Lipo rated at 7400mAh/149 Amps/90C. Now if you use the standard 1/1000 mAh X C calculation, then the battery is rated at 666 Amps. So how can it be rated for both 149 Amps and 666 Amps at the same time? Well SMC was actually the company that tried selling the "True 25C" battery and because the company was hurt, just for trying to be honest, they had to find a way to advertise higher C ratings, but wanted to stay honest. So, what the C rating actually is is the MAXIMUM amperage this battery will put out, even if it means less than 10% capacity performance and permanently damaging the battery or causing an explosion. So it is capable of 666 amps, but its a one-hit wonder, and then the battery must be replaced.

    The 149 Amps rating on the other hand is the TRUE SAFE amperage limit for continuous discharge. It was determined at the factory using the TRUE IR and FOM methodology. So how is this useful for determining SAFE amperage for other batteries? Well simple, just use the tool: http://jj604.com/LiPoTool/ and enter 2.0 as the "Measured Cell IR" for a conservative, safe calculation, and then just enter the capacity. The FOM will be auto-calculated and will be incorrect but only slightly. If you calculated the 5000mAh 40C battery from the earlier example you will see exactly why his LiPo failed. It is ACTUALLY only capable of handling 122 continuous amps, ouch. To calculate the Insanely claimed 900 Amp battery above, enter 1 for IR (as it is a very expensive, high-end battery and therefore should have very low IR) and then its 8200mAh capacity. You will see a REAL approximate rating of 222 Amps, just over 1/4 of the manufactures claimed C rating. If you get a lemon pack with a lesser 2 IR rating, even that massively expensive LiPo is only capable of 157 Amps. If you went with the manufacturers rating and loaded anywhere near 900 amps on this battery, this thing would explode FOR SURE! (Thread Continues in post #4...)
     
    #1 WallacEngineering, Jan 24, 2018
    Last edited: Dec 23, 2018
    Lobe77 and Antho11 like this.
  2. Antho11

    Antho11 Studio Forums Elite
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    That’s a great write up! Thanks for the info!
     
  3. WallacEngineering

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    Thanks! Unfortunately the tutorial is not complete yet. The second post was posted right after the first, but for some reason it is still awaiting moderation. Weird, the first post didn't require any moderation...
     
  4. WallacEngineering

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    Now, lets talk about ESC's and Brushless motors. We will be using the Tekin RX8 Gen 3 and T8 Gen 2 motor combo as an example. If you head to Tekin's website and look at the specifications tab of the RX8 Gen 3 product information page, you will see that Tekin Claims it can draw up to 300 Amps per phase (continuous, basically), and can burst at up to 1000 amps. Pffffft, no lol. 1000 Amps is the kind of power you would see from a full size Tesla electric sports car, or some of the worlds largest, most powerful industrial welders. If you took 1000 amps and pumped it into the RX8, it would instantly melt the circuit board into a puddle of molten plastic and solder. So how do we determine the correct draw made by ESC's? Simple, ignore the ESC ratings. So long as it is rated to handle your choice of motor, then run it, because the motor is what determines ESC load, so lets take a look at those next.

    Brushless motors, insane technological achievements capable of propelling a 1/10 RC faster to 60 MPH than a full size, heavily modified 1000 HP Twin-Turbo Chevrolet Corvette (look it up on YouTube, it is astounding)! So just how powerful are they? Well, testing shows that the Tekin T8 Gen 2 series of 1/8th scale motors typically draws in 3 different amp rates. The Burst rate is only found under INITIAL ACCELERATION circumstances.

    To explain, lets say your RC is at a standstill, and you are about to punch full 100% throttle and launch as hard as you can. When a brushless motor has to go from 0 to 100% throttle and it has to get the weight of the RC moving, the burst is that instant moment when you first hit the throttle, otherwise known as the "Punch". To achieve the highest amp draw on an Brushless motor wired to an ESC with programmable "Punch" or "Launch" Power settings, you must set this setting to MAXIMUM. So yea, most of us will never get to actually see the effect of burst amperage as it lasts for less than one half of a second in most cases and would also almost certainly damage the drive train on your RC vehicle, but it is very important regardless. Bursts can happen under certain circumstances, like say landing from a jump while at 100% throttle and all drive tires achieve good traction and "Hook Up" or "Launch" the vehicle. So its rare, but it is necessary that you prepare your electronics for this occasion. When amperage bursts, it puts a TREMENDOUS amount of electrical stress on the motor, ESC, battery, and all wiring and connectors. Its times like these when an electrical failure or fire is MOST LIKELY to happen. In the case of the Tekin T8 motors, bursts have been recorded as high as 200 Amps, but typically hit around 120 Amps. No worries about this stage. Your LiPos and ESCs are built with burst amperage in mind, and so as long as the ESC and battery are rated to handle the motor's continuous amperage, then they will also handle its bursts with no issues.

    The next stage of amperage is the "Under Acceleration" Stage. This stage is something all RC owners will see every single day, and quite often. Its the amperage pull caused during acceleration, just after the burst stage. In this stage, the T8 motors tend to draw 90-100 amps at 100% throttle depending on your configuration (the larger truggy motors tend to draw a few more amps) and how much traction is achieved. This is also what you will draw during mud bogging as the resistance to spinning the tires increases the amperage load on the motor. The more resistance, the more amperage required.

    The final stage is the "Running" or "Continuous Amperage" Stage. This stage is after you reach your desired speed and are keeping the vehicle at that speed or accelerating with very little throttle. The T8 motors typically draw about 50-60 continuous amps depending on your configuration.

    So finally, its time to talk about wiring and connectors. Most RC enthusiasts think that 12 AWG wire and Deans Ultra Connectors will handle any setup up to 1/8th scale. Nope, while 12 AWG will run 1/10 scale motors just fine as well as SOME 1/8th scale, it will not be able to handle higher grade 1/8th scale electronics such as Tekin, Castle, LRP, or Orion ESC/Motor combos. Because our hobby deals with short lengths of wire, we can get away with running higher amperage than what 12AWG is actually, technically rated for. However, even with our short wires, 12AWG is only good for 50-60 continuous amps and 100-110 burst. Now while this is okay for "Lower End" 1/8th brushless motors such as Hobbywings or Leopards because they draw less amperage, once you have a Tekin or other "Higher End" 1/8th motor, you will be completely maxing out your 12AWG wire. Now while its technically rated for it, do you really want to be at the absolute ragged edge of what your wiring is capable of? No, definitely not, that is how fires happen. So if you have a "Lower End" 1/8th brushless system then you should be fine with 12AWG wire, but once you have a "Higher End" setup, 10AWG will be required to be SAFE. As a general rule of thumb, I would just wire ALL 1/8th electronics with 10AWG or larger wire. This includes the battery itself as well, which may be an issue in some cases. It is VERY DANGEROUS to have different size wiring between the battery, ESC, and motor. If you have 10AWG battery wire headed into 12AWG ESC wire, you are at VERY HIGH RISK of fire as the downsizing creates a choke point that causes extreme heat and resistance!

    As for connectors, the Deans Ultra plug is rated for about the same as 12AWG wire - 50-60 continuous/100-110 burst. Also, connectors are the choke point of any electrical system. Its where the most heat and resistance occurs in a wiring setup. I had a deans on my Serpent Truggy and it has now been identified as the most probable cause of my fire since I was running 10AWG wire, so yea, choose something else for 1/8th scale electronics. The XT90 (90 Continuous Amps rated) is a good choice, or if you want to be bulletproof as Im being on my next build, then get these RCProPlus Supra S6 connectors (S5 Supras will work as well): https://www.amainhobbies.com/rcprop...ector-4-sets-810awg-rppreb6808pros6p8/p492923 or the XT150 connectors. These use gigantic 6mm bullets in completely isolated housings, and are made for 8-10AWG wire and will handle up to 200 Amps without a sweat. They are even NEARLY powerful enough to handle 1/5th scale brushless systems, just to give you an idea. Watch the video in the link and you will also see an EXCELLENT feature of these connectors: Thanks to the positive and negative lead not being attached to one another, you can plug the positive into the negative of another LiPo and create a much more SAFE series connection without an adapter! Traditional series adapters add more wire length and connectors to the electrical system, which adds electrical resistance and more heat to the system. Therefore, getting rid of the need for series connectors and adapters is a VERY GOOD THING! The XT150s are also capable of this.

    So what will I be running next? RX8 Gen 3, T8 1700Kv Truggy motor, ProTek 170SBL Servo (450 oz-in at 0.08 sec on 6V, thats insane, why do people love Savox so much, no Savox servo can hold a torch to this thing, especially at the same price!), the 4S SMC LiPo in this discussion, 10AWG wire (as thats what the SMC LiPo comes with from the factory), and RCProPlus S6 Connectors. Since the LiPo can deliver 149 continuous amps while the highest continuous draw from the T8 wil be around 100 amps under acceleration, this setup should be 100% bullet-proof and safe from electrical issues, so long as my soldering is nice!

    Well, I know this has been a novel of sorts, but I genuinely hope it has helped someone out. If I have another fire like the Serpent Truggy this time around, I might be done with this hobby permanently.

    If you need more info on fake battery amp ratings, just type "LiPo Fake C Rating" into google, there are hundreds of discussions on this subject and people are trying their hardest to have the system changed.
     
  5. WallacEngineering

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    There we go, just copy-paste to a new post, that other post is still frozen so I made it a blank message lol
     
  6. william dobrovolny

    william dobrovolny Active Member

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    thanks this is very helpful
     
  7. WallacEngineering

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    So I know that I created this thread quite long ago, but it seems the information has reached almost no people. I ahve the same thread up over on the RCTech Forums as they are a far more active forum: https://www.rctech.net/forum/radio-electronics/1009300-warning-lipo-c-discharge-ratings-invalid.html

    However, I feel as if this information, being as it is so important, should be spread to more than a few doezen enthusiasts on a couple Forums. If anyone could get ahold of Medic, I think it would be perfect if he could make a tutorial video on it.
     
  8. WallacEngineering

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    @RCSparks You should make a video on this information for the YouTube Channel.

    Too many people select the wrong batteries for their vehicles far too often and then wonder why it doesn't run properly.
     

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