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a few battery questions

Old 07-23-2013, 09:56 AM
  #1  
carl24bpool
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Default a few battery questions

I'm in using the bog standard batteries in my tx and rx. Ni-mh i think they are but i always thought they were called nicads.

anyway i know that unlike lipo you cant just keep topping up so at what point should i charge my rx battery? After each trip out or check the voltage and use that as a guide?

its just if i have half battery left but i want to fly for the duration of a full battery the next day what should i do? Can i top it up? Do i have to run it flat? If so how as id rather not do it in the air for abvious reasons.

Thanks again guys.
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Old 07-23-2013, 10:41 AM
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bigedmustafa
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Default RE: a few battery questions

Newer NiCd and NiMH batteries aren't prone to "charging memory" issues like in the past. You can top up your transmitter and receiver batteries before every flying session without fear of shortening their life span, so long as you recharge at the recommended rates.
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Old 07-23-2013, 10:43 AM
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Rodney
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Default RE: a few battery questions

You can learn a lot if you take a look at www.rcbatteryclinic.com/
With either NiCad or NiMh you can just put them back on the charger, no matter what the current state of charge is. If you are using the wall wart (the charger that is usually packaged with a transmitter) you can just charge all night before you go out to fly. At the low rates that the wall warts put out, no harm will be done if you do a few hours of overcharge and you will be assured of a full charge for the start of the day. If using a smart charger and you set it for the proper battery type (NiMh and NiCad have slightly different peak voltage drops which is what the typical smart charger uses to terminate a charge) you can charge a partially discharged battery as well as a fully discharged one. The charger will detect when the battery is full. Do not forget, you will benefit from looking at Red's site referenced above.
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Old 07-23-2013, 10:49 AM
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Default RE: a few battery questions

OK, first, NiMh (Nickle Metal Hydryde) is different from Nicads (NiCd or Nickle Cadmium). I'm more familiar with NiCd that NiMh, so I can't really tell you the difference. The best way to use your batteries is to check the voltage each time. There is a limit which if the voltage is below, don't fly! You can top off the battery after you are below this limit. Anything below 9.6v on a transmitter and you are asking for trouble, and 4.8v on the rx. If you are charging at the field, go ahead and top it off when you are close or below these limits. It is a good idea to get yourself a battery cycle device. This will discharge the battery and then charge it. It is also called conditioning the battery.

One of the problems with some rechargeable batteries is that they can develop a "memory". This happens when a battery is reduced in voltage to a set limit and then recharged over and over again. The battery will get "use" to this and the charge life will be reduced. By occasionally cycling the battery (fully discharging it before charging) the chances of the battery getting a memory are reduced.
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Old 07-23-2013, 12:56 PM
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Rodney
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Default RE: a few battery questions

I have to disagree with BobFE. I've dealt in instrumentation where batteries are often the life line for some 40 years or more. Both NiCad and NiMh will work well down to 1 volt per cell so dropping down to 1.1 volt per cell is perfectly safe and gives you some margin of error. Thus your 4 cell Nixx batteries can be safely used down 4.4 volts and your 8 cell batteries down to 8.8 volts with a safe margin of error. Also, as to memory; a big myth that refuses to die. The way these cells are used in RC makes memory nearly an impossibility. Now, there is a thing described as voltage depression but that effects both NiCad and NiMh and this can most often be corrected with a forming charge. A forming charge is defined as charging at a current of 0.1c for 16 hours. If you want some honest and factual info on batteries, check out www.rcbatteryclinic.com/
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Old 07-23-2013, 04:53 PM
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Default RE: a few battery questions

If you're using a wall wart charger then charge all night before you fly. 15 to 17 hours.
I would not fly below 1.1V a cell, that gives you a cushion
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Old 07-23-2013, 05:00 PM
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Default RE: a few battery questions

I would also add that after a year I would get a charger capable of cycling the battery. I try and cycle nimh and NiCad at the start of the season. This helps in 2 ways. It exercises the battery all the way to bottom and top a few times and when it done properly gives you the faith that your battery is good. If you notice a lack in time you should be able to use the battery it starts getting shorter and shorter then a good round of cycling may be the fix. After a few years of this then its time to replace them. These are my practices I would rather spend 20 dollars every 3 years than risk an airplane.
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Old 07-23-2013, 06:13 PM
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Default RE: a few battery questions

If I recall correctly, nicad generally has a longer life in terms of charge/discharge cycles, where nimh generally has higher energy density (more milliamp hour capacity for the weight).

Anyway, newer ones seem much less effected by memory- damage from repeated shallow discharge/recharge cycles.

I would just charge it when you see fit, though it wouldn't hurt to run a charge/discharge cycle a couple times a year on a smart charger. Mainly so the smart charger will give you the pack's capacity. If the milliamp hour capacity the battery produced is way under what the pack is rated for, that would be a good indicator the pack's condition/performance is going down hill.
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