Canada
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Batteries

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Hi all,

As I read through the forum I notice a few people having concerns about batteries, that said,

I have found a solution for powering all my bots including a 19 servo, wireless camera, fan cooled, MCU controlled servo board, wireless PS2 controlled , Xbee wireless serial ,six legged Hexapod....that's a mouthfull...

I use Lipoly batteries 7.4V to be exact and a Castle Creations BEC or 2

The Bec can be programmed to output anywhere from 4.8 volts to 9 volts and can have an input voltage of 5 volts to 25.2 volts

It can supply up to 10amp Peak and give a constant 7amp output!!!

Canadian price from my only hobbies shop in town is $39.00

The lipo battery I use is a 5000 Ma. at 7.4 volts

Just a thought for batteries.

:)


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Australia
#2  

Hi People,

I also use Lithium Polymer (LiPo)(3.7volts per cell) batteries in all my toys and are probably one of the best power sources available today. Lithium Ion batteries are good and much safer than LiPo's but be careful in buying off eBay as many are not what they say they are and the Chinese sellers love to tell you the capacity of there batteries is much higher than it actually is, same goes for NiMh cells and packs. With the Lipo packs many are what are called "B-GRADE" which are good for about 10 charges and that's about it. Lipo batteries need to be balance charged with a good quality Lipo balance charger( some cheap copies of chargers are just not good enough and after time will destroy your batteries). This is extremely important as a Lipo pack is made up of a number of 3.7volt cells and all the cells in the pack have to stay very close to the same voltage while charging and should never go below 3volts and never over 4.2volts. If your electrics/electronics doesn't have an auto cut-off installed it is wise to use a Lipo alarm or some other Lipo indicator there are many to choose from. as Lipo's will explode and catch fire if not treated correctly. For some more info on See The Bottom Text taken from Hobby King as it give a good understanding of Lipo batteries.

Example: I just purchased a lot of what I thought to be average NiMh sub-c cells to replace some cordless dill packs, the cells were rated at 2900mAh but the most after many cycles was about 1600mAh,( I would have expected to get at least 2000mAh in them as they weren't the cheapest cells, ended up getting 60% refund on them as I asked the seller many questions before making the purchase. I have purchased many AA NiMh cells from wholesalers and eBay over the last 4 years and same goes with them, bought some very cheap ones rated at 2600mAh and the very most I could get into them was about 400mAh(pretty much good for nothing).

If you wan't the best NiMh batteries buy brand name ones and if you wan't the very best money can buy get yourself some GENUINE(because there are Chinese copies) SANYO ENELOOP CELLS(NiMh battries that are ready to use straight from the pack), they don't have huge mAh ratings(AA=2000mAh and AAA=900mAh) but last longer than standard higher rated cells even branded ones and they also don't self discharge like standard NiMH cells, Check out the Sanyo Eneloop Site HERE for further info.

A123's high-performance Nanophosphate lithium iron phosphate (LiFePO4) batteries come in round cell shapes simmilar to ordenary batteries and come in only a few differant sizes and are all 3.3volts and 20amps each. Same goes with these cells they must be GENUINE as the Chinese get the reject cells and sell them off as genuine ones(way to tell is a no genuine cell will have a black stripe (permanent marker) under the thin shrink wrapped covering(which you can see through the wrap), but there are also copies of these as well. You can make up awesome packs with these cells and the beauty with these is they are heaps safer than LIPO's and can take quite a lot of abuse. The drawback is the cost of these cells they are very expensive. Once again don't forget that these cells are 3.3volts and need to be charged with the correct charger. For more info on these cells go HERE. More general info about Lithium-ion batteries can be found at Wikipedia, HERE.

As for Lead Acid batteries or Sealed Gell cells I reckon they are to older technology and are slow to charge, fast to discharge and just to big and heavy, after all you are using the most up to date High Tech computers, controllers, servos and other peripherals. why add such old tech batteries to drive them.

Rich

The Following text has been taken from the Hobby King web site as I think it gives a good understanding of Lipo batteries.

Lithium Polymer (LiPo) Basics

It can sometimes be difficult to know which battery is best for your application. For R/C aircraft there is a huge variety of batteries available and while many may suit your application your ultimate goal is to purchase a battery pack that will; -be within your budget -have a long cycle life -have the correct size and weight -give you the longest flight times -be able to deliver the correct voltage/amp (Power) We hope this simple guide helps you understand the different types of LiPoly (Lithium Polymer) batteries and which is right for your model.

You may have noticed by now that batteries have different ratings, sizes, plugs, wire, charge rates and chemical makeup. Lets decipher;

Capacity (mAh). This is usually the biggest number shown on the pack and is measured in mAh (Milliamp/hour) or Ah (Amp/hour). The capacity is the first indicator of the batteries size. To keep things simple, think of capacity (mAh) as the amount of fuel in your cars gas tank. A higher capacity tank will run your car for longer. A 4,000mAh battery will run for twice as long as a 2,000mAh battery. A 2,000mah battery will (in theory) run for 1hr if drained at a constant 2,000 Milliamps.

Discharge (C) Discharge is the amount of power the battery can 'push' out and the number shown '20C' is an multiplication of the capacity. For example; A 20C battery can discharge at 20 x 2,000mAh which is 40,000mAh or 40Amps. This is an important number if you know your motor requires a certain power level. In addition to this, batteries have a 'Burst' rate, which is the amount of power the battery can discharge for a short period, usually 10-20 seconds. A typical battery label may show 20-30C, this would mean a 1,000mAh battery can discharge 20,000mAh constantly or give a sudden and short 10-20 second 30,000mAh (30A) burst of power. Tip: A higher 'C' rated battery will last longer if run at a lower 'C' rate. Example: a 30C battery run at 20C maximum will have a longer cycle life than a 20C run at 20C each flight.

Voltage (S) All lithium Polymer cells in any industry have a nominal voltage of 3.7v per cell. When fully charged a LiPoly cell should be 4.2v and when discharged it should never be below 3v. You will notice that LiPoly RC packs are made up of layers of multiple cells. If the battery's rating is 3S this means it is 3 x 3.7v which is 11.1v. It has 3 layers of 3.7v each. In other words, its a '3 cell pack'.

Weight/Size For a battery to be right for your model it must fit within the models battery compartment and also balance the plane correctly. It's temping to choose the biggest and most powerful battery your model can handle, but this will sacrafice flight performance and if your packs voltage is too high; destroy the ESC or Motor. Check with your ESC and Motor specification to ensure you have the right voltage pack then check the models CG (Center of Gravity) to decide on the right battery weight.

LiPoly Charging Always use a lithium Polymer battery charger and never charge the battery above 4.2v per cell. (example: 2S, never above 8.4v) Never leave a charging battery unattended. Never allow the battery's voltage to fall below 3v per cell. (example: 3S, never below 9v)

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