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  1. #1
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    Newbie and batteries baffle me

    Have both a bandit and stampede. When running with the 8.4V 3000mah batteries that came with the cars they run great... Long and fast. So on the advice of local hobby shop i purchased 2 5100mah 8.4V batteries. With the bigger batteries I only get about 5 minutes of run time. Manual says i need to regear for larger batteries hobby shop says no. These are all NiMh not lipos and battery protection is turned off. Before i regear i want to ask... Do i maybe have bad 5100 batteries? Is there a resource somewhere that can explain battery use in RC cars. Maybe someone who wants to take the time to educate a newbie?

  2. #2
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    Welcome to the forums! Everyone here is very friendly and helpful.

    Something tells me those 5100s you bought aren't getting a full charge. What charger did you use? Do you have a voltmeter by any chance? I'd be curious to know what their actual voltage was after charging...
    Last edited by zippogeek; 01-26-2013 at 12:52 PM.
    Make it idiot-proof and along comes a better idiot

  3. #3
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    There's no reason you should have to regear for larger batteries. Higher mah doesn't result in more power (well, maybe slightly) it should definitely be exceeding the run time of the 3000's more than five minutes though. As zippo said I would check with a voltmeter and see what the voltage is after charging, also what brand are the batts?
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  4. #4
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    I'm in the same position, I bought a new Traxxas 5000mah 8.4 volt battery the other week to get more run time than the 3000mah that came with the car. I charged it with the 8hr. Charger that came with my rustler and it worked for a couple days. Now I charge until the green light comes on and I check the voltage (8.4 volts) , OK. Plug into car and the thing barely moves!!!!
    Plug in the 3000mah and the car screams !!!??? I just ordered a new EZ plus2 charger and will charge with that when it gets delivered to see if that's the problem. Not happy with the new battery so far, $54 and two runs before it craps out!!!!

  5. #5
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    The new ones are speedpacks

  6. #6
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    I have charged using the wall charger that came with the car and also with an Onyx 100 peak charger set to 4 amps. Dont have a voltmeter... Gues i will hit up my neighbor for a quick test.

  7. #7
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    When an 8.4v battery is fully charged it should read around 9-9.1v.
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  8. #8
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    Zippo... There is nothing that is idiot proof to a sufficiently talented idiot..

  9. #9
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    Quote Originally Posted by Spidre409 View Post
    Zippo... There is nothing that is idiot proof to a sufficiently talented idiot..
    That's just my signature; I hope you didn't think I was directing it at you! Generally speaking, it's in reference to me. Like when I cut both wires simultaneously on an $80 battery. Boy did the sparks fly! But that's another thread...

    +1 what Liam says...if properly charged, your 8.4v pack should read at least 9V. An inexpensive DC voltmeter from Radio Shack will prove indispensable in this hobby.
    Make it idiot-proof and along comes a better idiot

  10. #10
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    To all of the above I would purchase a good peak charger , then your problems are solved . Those wall chargers aren't that good . JMO
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  11. #11
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    You may need to cycle those packs a few times to get them working well. Fully discharge them, then charge it back. Repeat a few times.
    This is where a good charger with a cycle feature comes in handy.

  12. #12
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    You can see the peak charger i own. Just bought a voltmeter. All the 5100 batteries are between 7.5 and 8.5. Charging now on the peak charger so i can test again. What peak charger do you recommend?

  13. #13
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    Didn't think you were having at me. Just wanted to give you a corollary to the quote in your sig.

  14. #14
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    Quote Originally Posted by Jws1982 View Post
    This is where a good charger with a cycle feature comes in handy.
    Something like this? http://www.airsplat.com/Items/AC-BC-DTXP4100.htm

  15. #15
    RC Turnbuckle Jr. harry697's Avatar
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    Quote Originally Posted by Jws1982 View Post
    You may need to cycle those packs a few times to get them working well. Fully discharge them, then charge it back. Repeat a few times.
    This is where a good charger with a cycle feature comes in handy.

    +1 on cycling the new packs a few times. But DO NOT fully discharge nimh batteries. Charge the pack and run it until you notice it first starts to lose power. Let it set for 10-20 minutes, then throw it back on the charger. Repeat this process at least 10 times before expecting the full potential out of your pack. A good peak detection charger is a good idea too.

    If cycling doesn't work, I would contact the manufacturer because the pack is probably a dud. And no, you shouldn't have to change gearing for a higher mah packs. That statement is meant towards larger voltage (more cells) packs.

  16. #16
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    If they are speed packs. They are junk. I have 6 of them sitting here. I have only had them peek to 5100 once or twice. I even changed chargers to a bigger one still no luck. I do get good run times but not what I paid for. And yes 2 were sent out of warranty by the hobby shop.

  17. #17
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    Quote Originally Posted by Crock View Post
    If they are speed packs. They are junk. I have 6 of them sitting here. I have only had them peek to 5100 once or twice. I even changed chargers to a bigger one still no luck. I do get good run times but not what I paid for. And yes 2 were sent out of warranty by the hobby shop.
    +1
    I have a 3300 and 5100
    I paid 70 bucks for the 5100 it only goes 8 minutes longer
    I coulda bought 2 3000mah traxxas packs instead
    Slash 2wd, Slash 4x4, 30th digger, Rustler VXL

  18. #18
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    Ya the speed packs are not what they used to be they are the low end of the pack now. I was thinking about ordering a onyx dual charger and see if that helps. Won't be wasted money as I have 2 electric and 2 nitro that will be converted when the engines are toast.

  19. #19
    RC Turnbuckle Jr. harry697's Avatar
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    Quote Originally Posted by Crock View Post
    Ya the speed packs are not what they used to be they are the low end of the pack now. I was thinking about ordering a onyx dual charger and see if that helps. Won't be wasted money as I have 2 electric and 2 nitro that will be converted when the engines are toast.
    Makes me wonder how long these packs have been sitting on a shelf in the LHS and/or warehouse. Nimh batteries aren't very popular these days, so I have my doubts as to how "fresh" they are.

  20. #20
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    The last 2 that I got were down to 2 volts. Took 5 cycles to get them up to voltage

  21. #21
    RC Turnbuckle Jr. harry697's Avatar
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    Quote Originally Posted by Crock View Post
    The last 2 that I got were down to 2 volts. Took 5 cycles to get them up to voltage
    Makes sense. Considering the self-drain rate of nimh cells, it's pretty safe to say those packs had done their fair share of shelf sitting.

  22. #22
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    Went to the hobby store and bought a venom charger. Am in the process of cycling that the volt meter said was the lowest. Let ya'll know tomorrow how it went. Thanks to everyone for the help!!!

  23. #23
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    Checked the voltage on the battery today and it shows 9.4 volts, but still won't power the car?????.

  24. #24
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    Well folks looks like cycling the batteries did the trick. Word of warning though... Keep checking the battery temperature while cycling. After 2 cycles the battery is HOT.

  25. #25
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    Glad to hear it. If the packs are getting hot during cycling, you may want to turn down the amperage!
    Make it idiot-proof and along comes a better idiot

  26. #26
    RC Turnbuckle Jr. rag6's Avatar
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    How hot did they get? Most budget and midrange chargers discharge at 1 amp, You should be charging nimh at no more than 1c, which in your case is 5.1a. Does your charger have a peak sensitivity setting? Should be no more than +/- 5mv. Do you have a temp gun? Would be good to know how hot, "hot" actually was...
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  27. #27
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    Also your charger should have a setting that gives you a pause between cycles to let the battery cool down. U can specify the time.

  28. #28
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    Quote Originally Posted by rag6 View Post
    How hot did they get?...
    Not so hot that i could not keep them in my hands. Maybe a bit hotter than after a hard run in a car. I was cycling at 5amps

  29. #29
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    Quote Originally Posted by Crock View Post
    Also your charger should have a setting that gives you a pause between cycles to let the battery cool down. U can specify the time.
    This charger does not have that option. Figure if i keep it to 1 or 2 cycles at a time i m good. That and i keep an eye on the batteries when i cycle.

  30. #30
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    I have a quick question on lipo batteries. When you run your car, do you run until the Low-Voltage Detection turn on or to you stop before the LVD turns on?

  31. #31
    RC Turnbuckle Jr. rag6's Avatar
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    If you feel the packs are getting too hot, and your charger has limited options, you could just manually cycle them and monitor the temps by hand. Its a pain, but may prolong the life of the battery.
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  32. #32
    RC Turnbuckle Jr. rag6's Avatar
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    Quote Originally Posted by HoosierGuy View Post
    I have a quick question on lipo batteries. When you run your car, do you run until the Low-Voltage Detection turn on or to you stop before the LVD turns on?
    The way I look at it is that the lvc is there as a last resort. I dont like to hit lvd. After running the packs after a while, I can feel the pack getting slightly weaker near the end of the charge and just kinda know when to stop. My packs are usually between 3.6-3.7v/cell (resting voltage) when I throw them back on the charger after a cycle. Some esc's will let you adjust the lvd,s votage, and you can set it higher, and then depend on the lvc to kick in. I just dont like my packs getting below 3.5v/cell.
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  33. #33
    RC Turnbuckle Jr. harry697's Avatar
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    Quote Originally Posted by rag6 View Post
    The way I look at it is that the lvc is there as a last resort. I dont like to hit lvd. After running the packs after a while, I can feel the pack getting slightly weaker near the end of the charge and just kinda know when to stop. My packs are usually between 3.6-3.7v/cell (resting voltage) when I throw them back on the charger after a cycle. Some esc's will let you adjust the lvd,s votage, and you can set it higher, and then depend on the lvc to kick in. I just dont like my packs getting below 3.5v/cell.
    Same here. When I start having trouble clearing the big double on our track, I usually stop. Cells are around 3.6-3.7 each. I think it's funny when people say that lipo has full power for the whole cycle. 3.7 is nominal voltage and that's when we usually see a noticeable loss of power.

  34. #34
    RC Turnbuckle Jr. rag6's Avatar
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    Yea. It just seems like full power because the lipos only lose a 1/2 v/cell when they get 75% discharged, which is a lot less than nimh voltage drop(per pack) when they are depleted the same percentage.
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