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Charging, Discharging and other battery care (FAQ)

Section Codes:
NIMH – Q&A applies to NIMH & NICD Batteries
LIPO – Q&A applies to Lithium Polymer batteries
NIMHLIPO – Q&A applies to both chemistries

NIMH – Q. Which is better, NiMH or NiCD?

A. The power-to-weight ratio of NiMH is better than that of NiCD. Additionally, NiMH cells are available with greater capacity (maH). NiMH are also better for the environment whereas NiCDs have the toxic heavy metal Cadmium and MUST be recycled. The benefit of NiCDs is that they are often cheaper than NiMH and some are capable of higher current draw than their NiMH counterparts. This is why NiCDs are often used in cordless power tools. Lastly, NiMH cells are more affected by high temperatures and will degrade more quickly if they get hot. If your vehicle draws a LOT of power and causes your packs to get hot, NiCDs may be a better choice.

NIMH – Q. What is the “Memory” effect I hear about?

A. This is a misleading term used to describe the capacity loss often associated with NiCDs. It has nothing to do with not being discharged completely before recharging and is in fact due to overcharging. It also applies to NiMH batteries just as much!! The reason that the failure to discharge is often blamed is that the use of “dumb” chargers will overcharge a half depleted pack, causing a capacity reduction. The average user can easily assume that this is caused by failure to discharge first and so the cell “remembers” how much it was used. The solution is simple: get a peak charger/discharger and throw your “dumb” chargers out. A battery pack with “memory” can often be revived by repeatedly cycling it on an automatic discharge/peak charge charger.

NIMHLIPO – Q. What is the difference between series & parallel hookup?

A. Wiring batteries in series will result in double the voltage with the capacity of the smallest pack. Wiring batteries in parallel will result in douple the capacity at the voltage of one pack. Some important notes:
Series: Do NOT wire packs of different capacities in series…one will die first and be reversed, possibly damaging the pack or even causing an explosion!! Additionally, be sure to use the same set of packs every time, so that they are all discharged and charged together to avoid cell reversing.
Parallel: You can wire packs of differing capacities in parallel, though it is still best to use identical packs. You MUST use packs of the same voltage!!

NIMH – Q. How should I charge my packs?

A. You should always charge your packs using a computer controlled peak charger. We recommend the AstroFlight 112D which can handle 1-40 cells, allowing you to charge every pack you have! If you have nothing but standard stick packs with no more than 8 cells, we recommend the MRC Super Brain 969, which can charge two packs at the same time. These chargers can be purchased from Tower Hobbies. Both chargers can discharge as well. Some additional tips:
-Always let your packs rest and cool between discharge and recharge.
-Have a fan blow over your batteries while they are being discharged/recharged. The cooler they are, the longer they’ll last. Do NOT let your packs get any more than warm to the touch, especially NiMH cells.
-Charge NiMH at no more than 1x their capacity, and NiCD at no more than 2x their capacity. These are conservative recommendations to help your packs last as long as possible.
-Charging packs faster results in more current capability and lower discharge times. Charging slower results in longer discharge times but without as much “punch”. Overall capacity remains the same.

NIMH – Q. Can I charge multiple packs in series?

A. If you have a charger capable of more than 6 cells, you can charge multiple packs in series. They must be identical packs all in the same state of charge, preferrably discharged to 0.9v per cell in all packs. I’ve charged SIX 6 cell packs in series on my 112D!! The power draw from the 12v source is very high when doing this, so be sure your power supply can handle it. To ROUGHLY calculate the amp draw on the input, take the charge amps times the voltage of all the packs added up and then divide by 12 (or whatever your input is). This estimate does not consider inherent losses during charging and will be slightly low. So in my example, 36 cells x 1.2 x 3 amps = 129.60 watts / 12 = >10.8 amps at 12v…I use Golf Cart batteries to power mine.

NIMHLIPO – Q. I have a 14.4v R/C vehicle…what should I do battery-wise?

A. Buy your batteries in sets and label them as such. This way, the same packs are always used together. When charging, always discharge both and recharge both at the same amp rate to prevent one from discharging before the other. Lastly, stop running your vehicle as soon as it slows down or loses its punch.

NIMHLIPO – Q. Is it better to run two 7.2 motors in series at 14.4v or two 14.4v motors in parallel?

A. This is debatable. Generally, higher voltage is more efficient and running higher voltage motors in parallel would be better, as is the case with the E-Maxx. If you are running a vehicle where one motor powers the left side and the other powers the right, running in series would result in the vehicle acting as if it had a differential…forcing one motor to slow down results in the other running faster, as you’d want for tight cornering. For crawling, running in parallel would be better and the vehicle would operate as if the “axle” were locked.

NIMH – Q. How should I discharge my packs?

A. Do NOT use a bulb discharger. You are at risk of overdischaring which will result in cell reversal and damage to that cell. Instead, use a computer controlled charger such as the AstroFlight 112D or the MRC SuperBrain 969. If you insist on manually discharging using bulbs or motors, do not bring an individual cell below 0.9 volts.

NIMHLIPO – Q. Can I take cells from old packs to repair or augment other packs?

A. Short answer: NO. Chances are that an older cell will have a different capacity or electrical characteristics and will be reversed if it dies first. If a cell is reversed, it RAPIDLY heats up and is will no longer hold a charge. It may also explode violently from internal pressure due to the heat.

NIMH – Q. Why doesn’t everyone use D cells in their packs?

A. D cells may seem like a good idea, however statistically speaking, they have a higher internal resistance than Sub-Cs and are not capable of as much current draw. In other words, your vehicle will have less “punch”. If you are going for LOOOOONG runtimes, however, D cells can work very well. Since they are larger, though, the heat will be harder to get rid of.

NIMH – Q. How should I store unused packs?

A. If you are not going to use the pack for a long time, charge it and let it sit for a day. Then place it in your refrigerator. When you are ready to use it again, let it warm up to room temperature, discharge it, and then recharge it at a rate of half its capacity.

NIMHLIPO – Q. Where do I recycle my old batteries?

A. First, ensure that the old batteries are completely discharged before disposal. Hook up a motor or light bulb to the pack and let it go until it stops. Take them to any Home Depot in your area and chances are that there is a battery drop-off point near the entrance.

LIPO – Q. What is Lithium Polymer?
A. Lithium Polymer (LiPo) is the latest battery technology, even newer and better than Li-Ion. It’s still a technology in its infancy and is improving in leaps and bounds. LiPo’s main advantage is its power to weight ratio. A LiPo pack can produce TWICE the power of a NiMH pack at only 2/3s the weight!! In R/C, every gram dropped means better performance and longer runtimes. Additionally, LiPos keep a more constant voltage during discharge, meaning almost full power until the end. The main disadvantage at this time is expense and current draw capability, though things are improving in this area as well.

LIPO – <>Q. Can I use them in my E-Maxx?

A. YES!! Though caution must be used. The best way to explain how it’s done is to look at the PolyMaxx, my custom built LiPo powered Emaxx. It has a 24v electrical system, dual 775 motors, battery monitor, BEC and more. The page explains the wiring methods and safety measures used.

LIPO – Q. How do I charge and discharge LiPo batteries?

A. LiPo battery can NOT be charged on your standard NiMH charger. The Superbrain 969 is NOT a LiPo charger as advertised and is a fire hazard if used and will damage your batteries. A proper LiPo charger will slowly reduce the charge current as the battery reaches capacity and then pulse the pack towards the end of the charge cycle to reach full capacity. The Astro Flight 109 is the perfect LiPo charger, capable of 9 cells at 8 amps. This charger can be obtained from astroflight.com. LiPos must not be charged at any higher than 1C rate…so a 3400mah LiPo pack can not be charged at a rate higher than 3.4 amps to avoid damage. LiPos do not EVER have to be discharged. A fully charged LiPo cell will be 4.20 volts. The minimum voltage after discharge is 3.0 volts per cell.

LIPO – Q. How do I care for and store LiPo batteries?

A. LiPos have a VERY long shelf life, on the order of 10 years. If you intend to store the packs for a long time without use, drain them to about 50% capacity. They do not need to be refrigerated. LiPos are expected to provide full power for roughly 500 cycles, possibly longer provided that they are charged and used properly. LiPos are also very delicate and do not have the heavy metal can to protect them. Caution must be exercised so that the cells are not smashed, puntured, bent, etc. LiPos must not be over-discharged. Minimum voltage per cell varies amongst manufacturers, however 3v per cell is recommended. A device such as the BattSignal is recommended for each of your LiPo projects to give you a visual and audible battery status. I also recommend a fuse or circuit breaker to prevent overloading of the batteries. The fuse should be at a value just below the maximum amp draw specified by the manufacturer.

LIPO – Q. I’ve heard LiPos are fire hazards…

A. LiPos WILL catch fire if charged on a Non-LiPo charger, are charged at too high a rate, are discharged too quickly or are physically damaged. Every pack is different as far as current capabilities are concerned. Follow the manufacturer’s instructions provided with your packs to avoid problems.

LIPO – Q. Where can I get LiPo batteries?

A. You can get LiPos from the following reputable sources:
http://www.allerc.com/
http://www.starluckrc.com/catalog/index.php?cPath=40&osCsid=d216598b049a56284cce6f4932eeba08
http://www.botparts.com/marketplace_lipoly-pq.html
http://www.finedesignrc.com/lipobatteries.asp
http://www.unipros.com/cbpsite/fpacks.asp?session_id=240627