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How to keep Batteries Healthy?

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  • FTC12676
    replied
    Is there any reason LiPo or Li ion batteries not allowed? They are quick charge and can have more AH rating.

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  • Alec
    replied
    The 3Ah NiMH Tetrix battery was specced out when the only motors and servos that were legal were the Tetrix motors and servos. The legal motors and servos have been amped up over the years plus two iterations of a new control system have been rolled out, each with different specs concerning the quality of the power source. Also, battery technologies have improved and battery prices have gone down since the Tetrix battery was specced out.

    With the increased demands on the robot battery I suggest it is time for FTC to switch to the newer, better, and cheaper batteries that are readily available to teams. Teams could have the option of using their legacy Tetrix batteries if they choose.

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  • FLARE
    replied
    Originally posted by FLARE View Post


    - Do not discharge to less than about 5 volts. Usually it will not run the robot at this level anyhow, but we weren't even watching for it.
    I don't know why sometimes you and edit a post & sometimes you can't...

    Should have said "... about 8 volts"

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  • FLARE
    replied
    Originally posted by RoyM View Post
    there's a $200 charger and a $600 charger discussed.
    I'm absolutely no battery expert, but have learned a lot of info while researching this issue. I believe the $600 charger mentioned (Hitec X4 Plus) is an older model of the $200 one (Hitec X4 Pro). It probably has a higher price because they are not making them any more?

    I have ordered the X4 Pro, but not received it yet. Don't rely solely on my word, but for my 2cents here are some things I learned that we have been doing wrong.

    - Batteries should cool 30-60 minutes before charging & after charging. At competitions especially we would often take from robot directly to charger & then right back into robot.
    - They may need to be charged & discharged up to 5 times before a battery is able to hold it's full rated capacity. The X4 Pro will do this.
    - Do not discharge to less than about 5 volts. Usually it will not run the robot at this level anyhow, but we weren't even watching for it.
    - For maintenance it is recommended to fully discharge & recharge monthly
    - Charging on higher amperage can shorten battery life & possibly not allow it to reach full charge
    - Batteries will likely need to be replaced after about 2 years.

    It would be great if an expert in this area could created a document with suggested procedures on this important topic.

    Leave a comment:


  • 5294-jjkd
    replied
    Well, we use the Hitec X4 at $200. That's $200 to charge four batteries at once, so $50/battery. If you don't need to do four, there's an X2 two battery version for $100. The 'not so smart' single battery chargers appear to be around $25 to $32 each. So, unless you ever only charge a single battery at a time, I am not seeing that much of a cost difference. Of course, if you don't have the option to skip buying the single battery chargers in the first place, then the cost is more replacement rather than incremental, so that is indeed a factor.

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  • RoyM
    replied
    Excuse me, in the above thread, there's a $200 charger and a $600 charger discussed. And of the $600 charger it was said "I see a lot of teams using this one", which I doubt due to the cost. It would be a real service to the FTC community if we can identify the most economical charger that treats the batteries well. Besides crowd-sourced recommendations, do the folks at FIRST (like Tom Eng or Phil Malone) have any experience with chargers?

    --Roy Mead
    Team 9915 Robo Thunder

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  • mikets
    replied
    Originally posted by FLARE View Post
    How did you determine that there was one bad cell? And is there anything you can do about it?
    NiMH cells are about 1.2V each. So 10 cells in series gives you about 12V. If you have one cell shorted, you lose 1.2V. So that's quite easy to tell. If you have a smart charger, it will probably tell you since you will never be able to charge to the full 12V. If you don't have a smart charger, you can just charge the battery and check its terminal voltage. If it is below 12V after charging for a long time, it's bad. There isn't really anything you can do to save the battery once it's bad.

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  • RollerCoaster45
    replied
    We have that charger. It is amazing for quick charging and checking battery health.

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  • FLARE
    replied
    Originally posted by 5294-jjkd View Post
    Note that internal resistance by itself doesn't tell the whole story. Last night we were testing more batteries, and found one that had a good internal resistance reading, but low terminal voltage. In this case, one cell was shorted in a relatively new battery (about a year old). This battery could have been left charging on a 'stock' charger at some risk of a meltdown, but the new charger helped us find the problem.
    I know this is an old thread, but...

    How did you determine that there was one bad cell? And is there anything you can do about it?

    We have 2 batteries that don't seem to be lasting as long as they should, 1 in particular that won't run more than about 15 minutes. We use the Matrix batteries & all are less than 5 months old. We are using on a robot with 8 motors, but I still wouldn't have expected them to "go bad" this quickly"

    We are thinking about getting this https://www.servocity.com/x4-pro-ac-dc-charger , but is it worth the $ to help diagnose the problem and maybe help to protect future batteries?

    Leave a comment:


  • Inventer bots
    replied
    Another charger that I think would work quite well would be the Hitec X4 pro http://hitecrcd.com/products/charger...harger/product but any Hitec charger will work fine. The X4 pro is the new and improved X4+, I don't have ether one but I plan to get an X4 pro.
    Note Hitec is the biggest brand in servos and chargers.

    Leave a comment:


  • 5294-jjkd
    replied
    Note that internal resistance by itself doesn't tell the whole story. Last night we were testing more batteries, and found one that had a good internal resistance reading, but low terminal voltage. In this case, one cell was shorted in a relatively new battery (about a year old). This battery could have been left charging on a 'stock' charger at some risk of a meltdown, but the new charger helped us find the problem.

    Leave a comment:


  • RollerCoaster45
    replied
    Interesting. We found a couple of Modern Robotics batteries that we have and are at .068 ohms. We also had an adapter from xt-30 to power poles for our Rev batteries. We believe that this increased the resistance because when we removed the adapter and crimped the power poles directly onto the wire coming out of the battery, the resistance was lowered.

    Leave a comment:


  • 5294-jjkd
    replied
    I see a lot of teams using this one: https://www.amazon.com/HiTec-44167-P.../dp/B005MW0WZO

    We did just get one, but don't have that much experience using it yet.

    Note also that I have heard the Rev batteries do tend to read higher than the 'fat' Tetrix/Matrix batteries, so starting out higher might not be that bad an indication. The resistance going up, however, is not a positive thing. I recently measured some brand new Tetrix/Matrix style batteries, and the best was at 0.078 ohms.

    Leave a comment:


  • RollerCoaster45
    replied
    What is considered a better charger? Could you share a link? This is our second year competing and last year our robot didn't really require the battery to be very high in order for our robot to perform well so we didn't require a better charger.

    Leave a comment:


  • 5294-jjkd
    replied
    NiMH batteries require some care to manage well. Some chargers will treat the batteries better than others, the 'official' charger isn't particularly smart. Increasing internal resistance and loss of capacity are the two major ways in which they show they are deteriorating. Generally, keep batteries cool, don't leave them on charge after they are 'full', don't allow the state-of-charge to get too low (don't discharge too much). Getting a better charger than the stock charger (if you don't have a better charger already) is probably a good first step.

    Leave a comment:

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