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  1. #1
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    Lipo charge time and charger?

    So im brand new to lipo and i bought a new traxxas 7.4v 2s 25c 5000mah lipo and the traxxas 2cell/3cell lipo balance charger #2935. My questions are:
    1. How long should this battery take to charge?
    2. How does this charger work? do i plug in the lipo and leave it till it says fully charged?
    3. Can i leave the battery plugged into this charger and will it tell me when its fully charged and not overcharge the battery?
    4. How do i charge these batteries for storage? do i charge for only half the charge time?

    I have heard all these stories about overcharging and such so im just checking this stuff out cause i know lipos have become a little more safer then 4 years ago, so i just want some newer updated advice. Thanks!

  2. #2
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    1) with the charger you have about 6 1/4 hours.
    2) never used one can't help there,
    3) same as 2,
    4) It will depend on the voltage at the beginning, I'd run the lipo down in the rc and charge for 2.5 hours.
    I'd invest in a new charger.
    Problems.The manual's good starting point. Simple

  3. #3
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    Quote Originally Posted by trax de max View Post
    I'd invest in a new charger.
    Amen to that! Try the Traxxas EZ Peak Plus, or a similar charger in the $80-100 range. It will allow you to charge your LiPos at a 1C rate, which means a charge time of 45-60 min. And always balance charge!
    Make it idiot-proof and along comes a better idiot

  4. #4
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    Quote Originally Posted by bazookal07 View Post
    So im brand new to lipo and i bought a new traxxas 7.4v 2s 25c 5000mah lipo and the traxxas 2cell/3cell lipo balance charger #2935. My questions are:
    1. How long should this battery take to charge?
    2. How does this charger work? do i plug in the lipo and leave it till it says fully charged?
    3. Can i leave the battery plugged into this charger and will it tell me when its fully charged and not overcharge the battery?
    4. How do i charge these batteries for storage? do i charge for only half the charge time?

    I have heard all these stories about overcharging and such so im just checking this stuff out cause i know lipos have become a little more safer then 4 years ago, so i just want some newer updated advice. Thanks!
    Q 2 It charges each cell one at a time Q 3 an yes you can leave it plugged end without over charging & leave it charging till it is fully charged , it well not over charge . But it's best to stay with the battery when charging for safety . Q 4 . You need a LVD with buzzer , storage is 3.85 per cell , I'll charge to full charge an take a auto bulb like a 1157 and discharge till at reaches 3.85 . I set the LVD at 3.9 an watch it from there , till it at 3.85 v per cell . Hope this helps .
    Last edited by rhardy60; 02-17-2013 at 12:08 PM.
    1 Rusty VXL

  5. #5
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    1) 278 minutes from 3.4v/cell, 139 minutes from 3.8v/cell.

    2) Plug and wait. It is automatic, no settings to fuss with.

    3) It will not overcharge the battery. There are LED's on the charger with instructions.

    4) With your charger, there is no storage setting. You are going to have to use a cell checker and monitor the charge to manually stop it at 3.85v/cell. If it is above this, you will have to discharge the battery to 3.85v/cell using some other device.

    I too suggest getting a different charger.
    Whatever it is I just said... I could be wrong.

  6. #6
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    Jimmy Neutron im not sure what your answer for question one means?

    Does each cell hold 7.4v volts so there for around 60% is 3.85v and good for storage?
    As for discharging can i just charge my lipo till it hits 3.85V or do i have to fully charge then discharge to 3.85v?
    What is a good low voltage meter to buy?

    sorry if you guys have answesered these questions before i couldnt find anything.

  7. #7
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    Quote Originally Posted by bazookal07 View Post
    Jimmy Neutron im not sure what your answer for question one means?

    Does each cell hold 7.4v volts so there for around 60% is 3.85v and good for storage?
    As for discharging can i just charge my lipo till it hits 3.85V or do i have to fully charge then discharge to 3.85v?
    What is a good low voltage meter to buy?

    sorry if you guys have answesered these questions before i couldnt find anything.
    Jimmie, I think it's time to copy and paste your famous LiPo battery and charging guide!

    Don't worry, bazookal07 -- this will all make sense eventually!
    Make it idiot-proof and along comes a better idiot

  8. #8
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Quote Originally Posted by bazookal07 View Post
    Jimmy Neutron im not sure what your answer for question one means?

    Does each cell hold 7.4v volts so there for around 60% is 3.85v and good for storage?
    As for discharging can i just charge my lipo till it hits 3.85V or do i have to fully charge then discharge to 3.85v?
    What is a good low voltage meter to buy?

    sorry if you guys have answesered these questions before i couldnt find anything.
    Each cell only holds 4.2 volts max. If it is a 2S pack, there is a system of two cells in series (this is where the "S" comes from in 2S, 3S, ect) to get total pack voltage of 8.4 for a fully charged 2S pack. The 7.4v figure comes from the nominal voltage of 3.7 for a LiPo cell (3.7 x 2 = 7.4).

    If the LiPo is below the 3.85 mark, you can just charge it up to this voltage. There is no need to bring it up to full and then back down. LiPo has ZERO memory.

    I use a variety of LiPo cell checkers... they are so much simpler than using a multimeter on a LiPo pack.
    Here is one: http://www.ebay.com/itm/2in1-Lipo-Ba...item3a6576622f
    Here is another: http://www.ebay.com/itm/2S-6S-2-6-ce...item56513ae038
    Yet another, this one in USA: http://www.ebay.com/itm/2-in1-1-8S-L...item4abece6914

    Charging from 3.4 volts is a decent example of charging from when your ESC shuts down due to low voltage detection. Charging from 3.8 volts would be the example for charging from storage voltage.
    This is why my answer to #1 is phrased as it is.
    Last edited by Jimmie Neutron; 02-17-2013 at 01:24 PM.
    Whatever it is I just said... I could be wrong.

  9. #9
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    I wrote this a while back... but most of it applies here too:

    I apologize in advance for the length of this write up. However, I feel that it is important to have as much factual LiPo information as possible and to have it all in one location. Try not to get overwhelmed... just take it in bit by bit.
    That being said...

    LiPo 101
    now in session


    Rules
    1) NEVER discharge below 3v/cell
    2) NEVER charge above 4.2v/cell
    3) NEVER puncture your pack
    4) NEVER short out your pack
    5) NEVER use a pack that has puffed
    6) NEVER charge unattended
    7) NEVER charge at a higher C rate than recommended
    8) NEVER use a pack that has been over charged/discharged
    9) ALWAYS check cell voltage before connecting your pack to anything
    10) ALWAYS keep your LiPo pack well balanced

    To calculate the charge rate of your pack
    mAh x charge C rate / 1000 = charge amps
    For example:
    A 2200mah 20-40C pack that states a 2C charge rate.
    2,200 x 2 / 1000 = 4.4
    This battery pack can be charged at 4.4 amps.
    - Please note that if no charge C rate is stated, 1C is standard.

    To calculate the constant discharge rate of your pack
    mAh x minimum discharge C rate / 1,000 = available amps
    For example:
    The same 2200mah 20-40C pack.
    2,200 x 20 / 1000 = 44
    This battery pack can consistently provide up to 44 amps.

    To calculate the peak/burst discharge rate of your pack
    mAh x maximum discharge C rate / 1,000 = available amps
    For example:
    Again, the same 2200mah 20-40C pack.
    2,200 x 40 / 1000 = 88
    This battery pack can provide a peak discharge rate of up to 88 amps.
    Peak rates are limited in time... unfortunately, this amount of time does not have an industry standard. This is how a lot of inflated discharge ratings can be claimed. In my experience, honest retailers/manufactures of packs will list the constant discharge rating along with the burst discharge rating and not only the burst rating.

    Ratings
    When setting up your power system for your RC, make sure that the lower discharge C rate matches or beats the continuous amperage rating of the ESC. I try to beat it by at least 10%. This practice will provide you the most out of your system and it will also keep your batteries from working too hard. A LiPo should NEVER be warm... during use or charging. If it is, you are abusing the pack. Also, the less your pack has to work the longer it will last.


    Parallel
    Running two LiPo's in parallel will double run time and also your available amperage... which is handy for high demand systems. Some misinformation I have read about the discharge C rating of packs in parallel is that the rating of the pack doubles. This is not the case. The C-rating of a battery pack is a fixed parameter of that pack; well actually it is the cells within the pack that have the C rating. Connecting two packs in parallel does not change either pack as they still have the same specifications, however it does create a battery "system" with twice the effective C rating. The packs are the same, but the parallel system is now theoretically capable of discharging at twice the Amp rate. This is much like the cumulative capacity available when connecting two packs in parallel.
    The packs ran in parallel MUST be of the same cell count and should be the same age, capacity, and brand.

    Series
    Running two LiPo's in series will double voltage, therefore nearly doubling the speed of your RC. Capacity remains the same. The two packs ran in series MUST have the same capacity and discharge rate. Also, they should be of the same age and brand.
    Be prepared to gear down when increasing voltage on your power system.

    Charging
    There are many charging options out there... it can get really confusing really fast. The best advise I can give is to get the absolute best charger you can afford and to ask before you purchase. Your charge system is the backbone of your electric RC hobby, treat it as such. RC's will come and go, but your charge system will remain.

    The following features are what I consider to be the absolute bare minimum for a charger... balance charging and a storage charge/discharge feature. If the charger cannot perform these tasks, look for another charger. If you are going to be charging multiple LiPo's at the same time or 10th scale or larger packs, I recommend getting a charger that is capable of at least 10 amps or more. Also, ANY half-decent charger can charge multiple LiPo's at a time. It does not require a dual or multi-charger to perform such a task. It only requires the right support equipment... such as a ParaBoard, which I use.

    Storage
    Storage voltage is 3.85v/cell. This voltage is the only voltage that is not super critical for LiPo. Anywhere between 3.5-4v/cell is considered to be acceptable for storage.
    I suggest putting a full pack to storage voltage if it is not going to be used within 30 hours or so. The longer a pack is at full capacity, the shorter its lifespan will be.
    I also suggest bringing a pack up to storage voltage after a run. When a LiPo's voltage lowers to a certain point, they begin to loose their voltage quickly. I would hate to see you loose a pack (or more) due to not charging up within a few hours after a run.
    For long term storage; I bring my packs to storage voltage, seal them in an airtight container, and stick them in the refrigerator. As I type this, I have had my "speed" set of 3S packs in the fridge for over 8 months at storage voltage... I check them monthly and they are still at 3.85v/cell. Almost makes me regret buying them. lol

    Making your LiPo's last
    I will just give an example of how much a small change in how a pack is taken care of can dramatically change how the pack behaves.
    Two identical packs were both charged and discharged in the exact same matter.... except one pack was charged to 4.20v/cell and the other to 4.10v/cell. This was done in a very controlled environment... NOT in an RC.
    After 500 cycles, the pack that was charged to 4.20v/cell had reached its life expectancy... it would not take more than 65% of its original capacity; meaning the LiPo was no longer able to be used safely.
    The pack that was charged to 4.10v/cell was still at 70% capacity after 1,000 cycles... so the .10v/cell difference more than doubled the life expectancy.



    Here is what I have done...
    this information might help with your decision

    I use inexpensive batteries.
    I have found them to be very reliable, extremely cost effective, and they have been proven to be under-rated; usually providing more mAh and a higher discharge C rate than stated on the pack. SPC is a great brand that under promises and over delivers. There are others that claim extreme discharge ratings that are simply impossible with the technology that is available.

    I use an iCharger 206B.
    When I purchased the charger, I thought I would never use all 20 amps of its capability. Well, now I rarely charge at anything less than 20 amps lol. I have even considered selling it to get more amperage! I have performed hundreds of charge cycles with this charger and it handles the task without a single issue.
    I highly recommend any charger in the iCharger line.

    I built my own power supply.
    I have ~$30 into my 24v 75a 1800watt power supply.
    Sounds complicated, but it really is not that difficult. If you go this route, you are going to want a server power supply as they do not drop voltage when you are pulling amperage like a standard ATX PC power supply.
    You can also purchase these pre-built at a very reasonable price.

    I hope this information helps!!

    Here are some links to some more:
    http://traxxas.com/forums/showthread...rger-vs-cooker
    http://traxxas.com/forums/showthread...charging-setup
    http://traxxas.com/forums/showthread...ply-Conversion
    Whatever it is I just said... I could be wrong.

  10. #10
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    ok i think that helped alot
    So when my esc cuts me off it should be around 3.4v and your saying it will take 278 mins to charge to full.
    When im ready to store my lipo i throw it on the charger and keep checking the voltage till it hits 3.85v.
    Correct me if im still not getting it?

  11. #11
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    You got it!

    Two things I will add:
    1) The voltage that the ESC shuts down at might not be 3.4 volts per cell.
    2) If the battery is above 3.8 volts per cell, it will not discharge them.
    Whatever it is I just said... I could be wrong.

  12. #12
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    Im confused with what you said in number two? Are you saying that once the cells hit 3.8v it will never discharge by itself?

  13. #13
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Your charger will not discharge the pack. So if you put it on the charger when the pack is above 3.8v/cell it will just charge the pack up, not bring it down.

    Smart chargers usually have a discharge function as well. This means when you attach the pack to the charger and tell it to storage charge the pack, the charger will either charge it up to 3.8v/cell or bring it down to 3.8v/cell.

    All batteries self discharge. Some slower than others.
    Whatever it is I just said... I could be wrong.

  14. #14
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    cool ok thanks guys this was helpfull

  15. #15
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    I was reading the Traxxas Battery Basics (article #76387) and it says "The Traxxas EZ-Peak Plus makes it easy to store LiPos properly; just recharge the pack using Storage mode and it will charge the pack to 50% capacity." If that's the case will is charge to 3.7v instead of the standard 3.85v or am I missing something?

  16. #16
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    If it does, 3.7v/cell is fine.
    Whatever it is I just said... I could be wrong.

  17. #17
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    Thanks Jimmie. I'm actually going the opposite direction because I won't be using the batteries for a while (Traxxas 2-cell). Discharge is now down to 3.80v and am expecting it to stop at 3.7v.

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