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Author Topic: How long should it last?  (Read 3177 times)

Purgatory

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How long should it last?
« on: August 11, 2011, 12:10:22 pm »

Hi Guys
I have a humble Futaba T2ER TX (40Mz) complete with 8X new 2500 batteries. This will be for my boat (currently under construction)

 For test purposes this has been fully charged - but if left for (say 2 weeks) has seemingly drained to the extent that when used it is only a short period before the low battery warning appears. The question is - is this 'drain' normal OR am I getting a premature warning when the voltage/capacity is still available?

My difficulty is that I cannot run the set-up until it is genuinely exhausted under true operating conditions at the moment. I seem to recall that there is a way to adjust/alter the time when the warning light appears?
Your thoughts would be appreciated
Cheers :-))
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Colin Bishop

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Re: How long should it last?
« Reply #1 on: August 11, 2011, 01:02:59 pm »

Standard NiMH batteries do tend to have a high self discharge rate so they will drain significantly over a two week period depending on their quality. So you do need to charge them shortly befor useing them, i.e. the night before.

You can buy low self discharge versions which will hold most of their charge for six months or more but typically the capacity is a bit less and they may cost a little more. I use these in my R/C gear for convenience.

R/C gear is usually designed to work with both alkaline non rechargeable cells and NiMH ones. The former are rated at 1.5v per cell and the latter 1.2v which means that the NiMHs have less voltage in reserve before the low voltage warning comes on.

So your experience sounds quite normal to me! Just charge before using.

Colin
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Martin (Admin)

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Re: How long should it last?
« Reply #2 on: August 11, 2011, 01:51:23 pm »


Also, try spinning the batteries in the Tx ( clean all the contacts ).
 My camera often gives low battery warning, I clean the contacts and get another 2-300 shots off before it actually shuts down!

 Also, watch for green corrosion!
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Purgatory

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Re: How long should it last?
« Reply #3 on: August 11, 2011, 02:48:37 pm »

Thanks for the info Guys
should have mentioned that the Attack T2ER is as new - never been used before this month! - hence a non corrosive unit.

 Useful to know that NiMH batteries have a high self discharge rate, this therefore makes  the whole picture more understandable.
Thanks again
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Tug-Kenny RIP

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Re: How long should it last?
« Reply #4 on: August 11, 2011, 03:16:12 pm »


Very informative.  If I may continue the thread a bit, here's a query from me.

I recently purchased a new T/X which has a voltage read out and fitted 4 new NimH at 1.2 volts each. The meter read 4.8 volts, which agrees with your statement Colin. A week or so later the meter had dropped to 4.6 so I charged them  'in situ'  with my Ripmax Delta pro Charger unit for a few hours. When I refitted them to the R/X the meter read 5.6 volts ????

I was a bit alarmed at this and suspected they were overcharged. The set still works OK and it's been a month now and they read 4.4 volts at the moment.

Any ideas before the next charge please.

ken


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Colin Bishop

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Re: How long should it last?
« Reply #5 on: August 11, 2011, 04:57:16 pm »

Don't worry Ken! When you charge them the voltage does rise over the nominal amount but soon falls back either when you switch the T/X on or leave it for a few hours. Same thing with lead acids, a 12v cell can go up to 14 volts or so under charge but will soon settle back. I think LiPos are similar but haven't used them myself. A decent charger will not allow the cells to overcharge. When you charge a battery by shoving a current up it's terminals, it tends to get a little excited - it will soon calm down....

The only thing to watch out for is inside the boat where some speed controllers and other gear don't like overvoltage and using more than the recommended number of cells can damage them. An example of this is ACTion's P82 Micro Mixer which is intended for use in miniature models where both the RX and motors are supplied from a single 4.8v pack. It can tolerate the overvoltage charge on 4.8v but will become unhappy, as will Dave, if you use it with a 5 cell pack or 6v SLA.

It's always best to read the instructions and be sure you understand them before connecting up. It's not like buying a TV where you take it out of the box, switch it on, fiddle with the buttons and then think about looking at the instruction booklet.

Colin
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Subculture

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Re: How long should it last?
« Reply #6 on: August 11, 2011, 05:49:08 pm »

Hobbyking sell the low self-discharge NiMH batteries in AAA and AA size, and they're very reasonably priced. e.g.

http://www.hobbyking.com/hobbyking/store/__10456__Turnigy_AA_LSD_2200mah_Low_Self_Discharge_ready_to_use.html

In my (Robbe FC16) radio set I use three Lithium ion cells. These are rated at 1700mAH, can be left for weeks on end, and keep the tx going for quite some hours. I keep two packs, and they cost me nowt as they're recycled from redundant pocket PC's. :-)
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Netleyned

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Re: How long should it last?
« Reply #7 on: August 11, 2011, 06:13:31 pm »

 redundant pocket PC's.
Police cuts are a help to the hobby  %% %% %%

Ned
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malcolmfrary

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Re: How long should it last?
« Reply #8 on: August 12, 2011, 11:54:32 am »

A meter is a wonderful thing to have.  It can check the individual cells, and spot if there is one in there that is less good than the rest.  Being brand new means little.  It might only have been minutes between the shop shelf and being used - there is no saying how long it was between being made and sold, and waggling the cells about a bit (tech term) is as good a way of breaking down any insulating film as any.  Of course, the meter is also good for measuring the actual voltage that the battery has charged to.
As Colin says, all batteries have their nominal rated voltage, will legitimately show a higher voltage when fully charged, and a lower voltage when in need of a recharge.  Early NiMH cells did have a high rate of self discharge, current ones less so, but most batteries do better after they have been cycled a few times, avoiding either overcharging or over discharging.  While the chemistry in rechargable cells gives a lower voltage than non rechargable types, the rechargables are generally capable of delivering more current.
Long life alkalines would typically have a capacity vastly more than Nicads, but could only deliver a fraction of the current, albeit for much, much longer.  This was fine for transmitters, until the accident that everybody does, which is to leave it switched on.  With rechargables, it means recharging, with alkalines, a new set.
With hindsight, higher capacity cells do take longer to fully charge.  They may show a healthy voltage quite early on in the proceedings, but might need several more hours to be brimmed up.
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Tug-Kenny RIP

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Re: How long should it last?
« Reply #9 on: August 12, 2011, 12:07:42 pm »


Thanks for putting my mind to rest.   :-))


ken



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