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  1. #1
    RC poster
    Join Date
    Jan 2010
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    14

    7,2v-pack + 8,4v pack

    Hi there!

    I have ended up with odd battery packs. Now Im wondering if it is okay to run the car with one 7,2v-pack and one 8,4v-pack at the same time?

  2. #2
    RC Champion
    Join Date
    Oct 2007
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    1,394
    As long as they have the same capacity (mah rating), you'll be just fine.
    Two Rusty VXLs, M2Ks 18/83 - Tag! You're it!

  3. #3
    RC Champion
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    Jan 2009
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    New Jersey
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    T-timeout. in parallel or series....
    what was that? what was what..oh that. thats mine.

  4. #4
    RC Champion
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    Oct 2007
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    Good point. I assumed that no-one would try to run a Summit on single-digit voltage...

    As long as you are running in series, and the batteries are the same mah rating, you'll be good to go.

    But don't run mismatched voltages in parallel - bad idea.
    Two Rusty VXLs, M2Ks 18/83 - Tag! You're it!

  5. #5
    RC Champion
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    Aug 2009
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    Spruce Grove, Alberta
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    Quote Originally Posted by jolynsbass
    Good point. I assumed that no-one would try to run a Summit on single-digit voltage...

    As long as you are running in series, and the batteries are the same mah rating, you'll be good to go.

    But don't run mismatched voltages in parallel - bad idea.
    I guess instead of running 14.4 v or 16.8 v he would be running 15.6 v? So then would it be best to run the higher voltage on the BEC side? or the lower voltage on the BEC side?

    Personally I would go out and get yourself another matching 8.4 volt pack. You will benefit from more speed and power and longer run time. IMO.
    http://traxxas.com/forums/showthread.php?536733

  6. #6
    RC poster
    Join Date
    Jan 2010
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    14
    OK. Thanx for input. Guess I will get another 8,4v-pack instead...

    :-)

  7. #7
    RC Qualifier
    Join Date
    Jul 2009
    Posts
    727

    Mixing batteries?

    Hi, I had a battery burst (970 revolver conversion,wish I'd been told about that )So I soldered it up.it runs fine wherever I put the battery.I take it they're nimhs? You CAN'T run unequal lipos! they can catch fire!! .

  8. #8
    RC Racer
    Join Date
    May 2009
    Posts
    132
    C/p

    You will need to choose the correct voltage(2S-6S) and size(physical dimensions) to fit in your vehicle, but how do you know if the pack can actually keep up with the power that the motor requires?

    We make it easy for customers to choose the correct battery pack for their motor by rating our batteries based on surge watts.

    The “surge watts” of your battery must be higher than the “surge watts” of your motor. The motor’s “surge watts” should be found in the instruction manual or on the motor manufacturer’s website. If you can not find the surge watt rating of your motor, our sales department also has a list of motor surge watt ratings from the manufacturers. Call us toll free at 888-654-4450 and we can give you the rating of your motor.

    Our batteries are rated with the same system used for RC motors. Most motor manufacturers including Castle Creations and Novak rate their motors by maximum “surge watts”.

    How does MaxAmps test a battery pack’s “surge watts”?

    Using a data logger and an actual RC motor and speed control, we test the “surge watts” by applying a load to the pack(not an individual cell) and confirming that it will maintain well over 3.2V per cell during this load. By using this method, we are confident that your MaxAmps pack will deliver the rated “surge watt” load without hitting the low voltage cutoff or damaging your pack.

    Why don’t you rate your packs by constant amp draw?

    Most lipo retailers rate their packs based on the individual cell’s performance(C rate) rather than the actual pack’s performance. We no longer use this method because of resistance and heat build-up in the welds, shrink wrap, wire and the plug. This makes the cell’s individual “C” rate irrelevant. The “C” rate of a pack will always be lower than the “C” rate of the individual cells in that pack.

    The constant “C” rate of an individual lipo cell is just an arbitrary number without a standard for testing it. There is no standard “C” rate test. A manufacturer or retailer can rate a battery at virtually any “C” rate since there is no required voltage or temperature range for the test.

    For example, if you actually run any 5000mah lipo “pack” at 40C constant(200 amps) the following would happen even if the individual cells could handle the load:

    Your entire run time would be less than 90 seconds.
    You would melt the RC plug attached to the pack(Deans, Traxxas, Tamiya, etc).
    The bullet connectors on a hard case pack would melt out of the casing.
    Even 12awg noodle wire would get too hot to touch.
    *

    The “surge watts” are a much more accurate way of rating an RC battery pack due to the fact that in a real world RC setting, you would never have a “constant” amp draw from the start of the cycle to the end.

    Why Watts and not Amps?

    Since amps x volts = watts(power), a rating means nothing without both the amp draw and the voltage under load.

    Amp draw only gives you half of the information required to determine the performance of the pack. For example, if a pack can handle 100 amps for one cycle but goes down to 2.5V per cell under that load, it is useless at 100 amps since the low voltage cutoff would kick in at 3.2V-3V per cell. It is the combination of amps and volts that create a higher performing pack.

    *

    Lithium Polymer Charging/Discharging Instructions & Safety Information

    Connection: You must be sure that the correct polarity is observed when connecting battery packs to charger or ESC.

    RED = POSITIVE (+)
    BLACK = NEGATIVE (-)

    Charging/Discharging: Charge your lipo battery pack at 5C or less on a lipo approved charger only.* If you choose to charge at any rate higher than 1C, you must use a balance charging system similar to the Hyperion chargers offered here at MaxAmps.* Otherwise you risk your pack becoming severely out of balance over time, which in turn will significantly decrease the lifespan.

    Ex: If charging a 4000mah lipo pack at 1C, you would be charging it at 4 Amps.
    Ex: If balance charging a 4000mah lipo pack at 5C, you would be charging it at 20 Amps.

    Set your speed control to hard cut-off at 3V/cell or higher-3.2V per cell is best.* If your ESC does not have this feature, you will need an external cutoff or alarm. (Ex. Novak Smart-Stop or LVA)

    Do NOT charge your lipo packs on a NIMH/NICD charger. Your charger must be designed for lipo cells. Do not charge above 4.2V per cell, over discharge under 3V per cell. Never leave lipo packs unattended during charging or after a crash in your vehicle. Don’t leave the battery pack plugged into a vehicle while not in use. The pack can still discharge to an unsafe level and damage the pack even if all components are turned off.

    It is dangerous to draw more power than what the pack is rated for. *This will void any warranty on the pack and can also cause your battery pack to ignite into flames.* The temperature of the pack should never exceed 140 degrees.* If it does, you may need a pack that can handle more surge watts.

    Storage: If you don’t plan on using your lipo pack for longer than a week, store it at 50-60% of the pack’s rated capacity.* Make sure to cycle and/or balance your packs at least once per month since leaving them on the shelf for a prolonged period of time can cause the packs to get severely out of balance or even go dead.

    Taps on Lipo Packs: All MaxAmps lipo packs come standard with Hyperion style balancing taps (white connector).* This tap can be used with our Method Balancer, Hyperion LBA10 Balancer and all Hyperion balance chargers. Always balance your pack before each use to prevent the possibility of over-charging or over-discharging.* This also “matches” the voltage of each cell to give you the highest performance and longest life.

    Lithium Polymer Safety Tips: Lithium Polymer cells are a tremendous advance in battery technology for RC use. However, due to the chemistry of lithium cells, there is a possibility of fire if charging is not properly done. It is unavoidable due to the nature of lithium itself. This is no different from many things we use in daily life – knives, kitchen cleaners, automobiles, for a few examples – which are inherently dangerous, but which can be used safely by adhering to simple rules and precautions.

    Be absolutely sure that the Lithium Polymer charger settings are correct for the battery pack being charged – both voltage and current settings.
    Lithium Polymer must be CHARGED and STORED in a fire-safe container like a Lipo Sack.
    Do not charge batteries near flammable items or liquids.
    Keep a dry fire extinguisher nearby or a large bucket of dry sand, which is a cheap and effective extinguisher.
    Never charge inside an automobile even when parked.
    Batteries should NEVER be left unattended while charging.
    KEEP BATTERIES AWAY from children and pets at ALL times.
    *

    Handling Cautions:

    Never leave batteries inside a car on a hot day or any other place where temperature may exceed 140F / 60C.
    Although environmentally friendly, lithium polymer cells must be FULLY discharged before disposal. Use a resistor setup (light bulbs, for example) to accomplish this, to avoid the possibility of a short-induced fire after disposal.
    Immediately discharge damaged batteries at 1/2 C rate and dispose.
    Do not put the loose cells in a pocket, bag, or drawer where they could short-circuit against other items, or the battery tabs could be pressed against each other.
    Do not place the loose cells on any conductive surface, such as a metal-topped table.
    We recommend purchasing pre-assembled packs rather than assembling packs from loose cells.
    Take care that the cells are not punctured, especially by metallic objects like hobby knives.
    If the electrolyte in the cells should get on your skin, thoroughly wash with soap and water. If in the eyes, rinse thoroughly with cool water. Immediately seek medical attention for this, or for burns.
    Although our batteries are now water sealed, we do not recommend submerging our batteries for extended periods of time. The battery packs will be protected during normal rc conditions.
    *

    All Lithium Polymer Batteries we carry are only approved for rc use, and may not be used in any other application. Battery discharging, charging, electric motors, spinning propellers, and flying models all have the potential for serious injury to persons and damage to property. In purchasing these products, the user agrees to accept responsibility for all such risks, and not to hold the battery manufacturer, distributors, or retailers - (all including owners and employees) -responsible for any accident, injury to persons, or damage to property.

    The use of Lithium Polymer batteries in radio-controlled models is to be considered experimental, and there is no warranty, expressed or implied, by the manufacturer, distributors, or retailers with respect to the capacity, life in cycles, storage, or discharge characteristics of lithium cells in RC use, nor any other use nor aspect unless otherwise stated.

    Lipo Battery Warming Devices/”Bumping” Lipo Packs:

    Do not, under any circumstances, attempt to “heat up” your batteries or increase the voltage of a pack above 4.2V per cell using these devices or techniques. Some insidious lithium polymer retailers/distributors have suggested using these devices and techniques to increase the performance of your lithium polymer packs. THIS IS NOT SAFE AND IS LITERALLY PLAYING WITH FIRE!

    Devices on the market that heat up lithium polymer batteries can increase the risk of a fire. Lithium polymer cell manufacturers suggest that exceeding 140 degrees is NOT a safe temperature for a lithium polymer cell. At 140 degrees, the pack can become unstable and very dangerous. The small increase in performance is not worth the risk of a fire. PLEASE STAY SMART AND SAFE BY NOT USING THESE PRODUCTS!*

    Some retailers/distributors of other brands of lithium polymer batteries have suggested that their customers and racers “bump” the voltage of their packs using settings other than the lithium polymer setting on their charger. The manufacturers of lithium polymer cells suggest a voltage range of 3V-4.2V. Increasing voltage above 4.2V per cell is not safe. You should never attempt to charge your packs beyond the voltage set for lithium polymer packs on your lithium polymer charger. Using other battery settings to “bump” the voltage beyond 4.2V per cell can cause fire and injury. The small increase in performance is not worth the risk of fire. PLEASE DO NOT USE THESE METHODS!
    2-REVo 3.3
    1 summit
    2-XMAXX
    And many others

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