Modify shunt resistors on a LiPo-Charger (E5 from EV-PEAK) - Page 1
Forum section: electronics / beginners

author: Bunkerotter
author_rank: Newbie
timestamp: November 10, 2017, 04:19:09 pm
content: Hi @all,I hope that's the right subforum i'm posting (:I have recently bought a "unintelligent" 4 Channel charger, namely EV-PEAK e5(product website)."unintelligent" because it can only do one thing: Balance Charge. And it can do that really great and accuratly, the charged batteries are balanced at 4.195V per cell. It's a great field charger for RC stuff.It also looks really great constructed (PCB pictures included), the plastic case is good. Not bad but okay.Anyhow: I have one issue with it, the charge current is a bit to high (selectable 2A, 3A or 5A). I mainly charge 4S 1.3Ah or 4S 1.5Ah LiPo's with it. I know some of these LiPo's could be charged at 5C or what ever, but I don't have to pound my batteries if I don't have to (you also don't drive your car always in the red zone if you don't have to right?).I was thinking about to modify the shunt resistors for the current feedback of the MCU's on the board. As far as I can see and understand, there are a maximum of 9 shunt resistors on the board (blue, white and green circles).The Blue one (R001, 0.001Ohm) looks like it is used to calculate the input power (the charger throttles down if the power of the whole charger exceeds 200W). That's not really interesting.The White shunt resistors (R010, 0.01Ohm one for each channel) looks like it is for monitoring the input power of each indiviual channel (each channel can give a maximum output of 100W) and also not interesting for my modification (I hope so).The green shunt resistors (R010, 0.01Ohm) near the JST output connectors look like the actual shunts that the MCU of each channel use to determine the charge current of the batteries. And these I have to exchange. If my understanding of Ohm's law and shunt measuring technics are correct, I have to increase the shunt resistor to decrease the charge current (because higher resistance increases the sense voltage or in other words the voltage drop across the shunt).Am I right to assume if my three selectable ranges are 2A, 3A and 5A with a shunt of 0.01Ohm, and I double the shunt to 0.02Ohm I should have charge currents of 1A, 1.5A and 2,5A?And am I right that the actual dissapated energy in the shunts also halves? (5A with 0.01Ohm = 0.25W, 2.5A with 0.02Ohm = 0.125W)?That's the things that I found out, calculated or researched etc.My actual questions are:Are my assumptions correct? And can I do that modification?What are the specs of these resistors, like the power rating actual name of the resistor size? (I measured ~3x6.5mm)What are the specs of the resistors that I should use to replace them? (power rating, accuracy, size)Thanks for any input on this topic,Cheers!- BunkerotterEDIT: Wow... this forum can't display the omega majuscle? Replaced it with "Ohm". Fix the Character set in the forum Dave! :P

author: Bunkerotter
author_rank: Newbie
timestamp: November 11, 2017, 04:12:18 pm
content: I did some searching, and it looks like these shunt resistors could be 2512 resistors. But I don't really have any experience with smd parts :/

author: Rendeverance
author_rank: Newbie
timestamp: November 11, 2017, 07:34:59 pm
content: Quote from: Bunkerotter on November 10, 2017, 04:19:09 pmMe tooQuote from: Bunkerotter on November 10, 2017, 04:19:09 pmSame here, though what I will say at this point is for a 1300mAh 4S, you are charging at about 1.5C, which should be fine...Quote from: Bunkerotter on November 10, 2017, 04:19:09 pmOk, so to answer your questions:Are my assumptions correct? And can I do that modification? -I cannot say with 100% certainty but I would say you would appear to be correct from what I can seeWhat are the specs of these resistors, like the power rating actual name of the resistor size? (I measured ~3x6.5mm)I have not looked them up, someone on here with more SMD knowledge might be able to identify the exact series, however for testing you you could just attack one leg with any suitable shunt resistor and calculate the maximum power likely to be dissipated,- i.e. A current shunt whose resistance is 0.01 Ohms having a max current of 5 Amps flowing through it will produce a voltage of 0.01 × 5 = 0.05 Volts, therefore 0.05*5 = 0.25W, therefore safe to assume with some headroom, a 0.5W shunt resistor should do the trick - however I DO agree with your assessment of 2512, and they have specified 1W, which is loads of headroom, see:http://uk.rs-online.com/web/p/surface-mount-fixed-resistors/0565920/(these should do the trick) (anyone else feel free to chime in) ).What are the specs of the resistors that I should use to replace them? (power rating, accuracy, size) -See aboveI am interested in potentially doing this to one or two of my legs so I get the best of both worlds... mega busy atm with work so may take a while to reply but will be keeping an eye on this

author: Bunkerotter
author_rank: Newbie
timestamp: November 17, 2017, 07:49:39 pm
content: Well, my lovely small, crowdy electronic shop didn't have SMD powerresistors... And order it from some bigger companies isn't worth it to pay ~14$ postal for something 2$ worth. I have to order it from far east :/ and that will take some time. I think I will use 0.015 Ohm resistors. That should give me 1.3A/2A/3.3A. Which is a nice range. But I will also buy some 0.02 Ohm resistors and maybe but them on two of the channels.Stay tuned for updates.- Bunkerotter

author: Bunkerotter
author_rank: Newbie
timestamp: January 29, 2018, 05:19:39 pm
content: Quote from: Rendeverance on November 11, 2017, 07:34:59 pmWell... the shunt resistors finally arrived and I got the time to change them. As expected the charge currents are now in the above mentioned ranges (slightly of ~100mA) I'm at the moment testing the charger if the cutoff voltages are still okay (should be, but you never know...)It's a quite easy modification to do, I have now two Channels with 1A/1.5A/2.5A and two channels with 1.3A/2A/3.3A. Thats really a good range and should cover almost all "standard" batterypacks to charge with 1C.About why I charge them only with 1C?I rather charge LiPo's with maximum of 1C to increase their lifetime a bit. I know some folks who charge their packs just seconds after the flight with 3-5C so they can keep airborne all the time. But that stresses the LiPos additionaly to their abuse in flight. I rather have more LiPos with me and charge them slowly