battery change

[ericrw]

 My previous Wot 4 was supplied with a Nicd flight battery and the Futaba T/X  was also powered by Nicd batteries.   The Futaba was supplied with a wall charger but the manual in referring to charging the batteries only refers to Nicd, there is no mention of Nimh batteries.   

 I have recently bought another Wot 4 and the flight battery is a Nimh.  I would like to know whether the Futaba wall charger is ok to be used for charging Nimhs??   Eric

[ericrw]

Found answer in other post!! Eric.

[Tim Mackey]

Hope it was tthe right one

[ericrw]

If I've got it right I can use the Futaba wall-wart (as you call it) to charge my Nimh batteries.  And that Nimh can be left on charge as time duration does not really matter !! Unless you say different !!!  Eric.

[Tim Mackey]

Well yes I am afraid I would say different

Time duration certainly DOES matter with NiMh more so than Nicd TBH - NiMhs do not like to be overcooked, which is perfectly possible even with so called low rate or standby type charge rates. This can allow them to get overheated and then they are toast. The best type of charge system for NiMH is delta peak, where the charger will detect the optimum time ( when the cell "peaks" at around 1.5 - 1.6V or so and then drops a tiny trickle amount ).

If you must use a wall wart style constant current charger then you should certainly time it so that it receives the correct charge...and of course this also requires that the battery be discharged to a normal minimum level ( circa 1V per cell ) before the charge starts. If slow charging like this, then calculate the time along these lines.

Example:

1000 mahr cell ( or battery )

charger pumps out 100m/a

1000/100 = 10 hrs

Allow about 10% extra for inefficiences in the charger etc...so 10 hours +10% =11 hours.

If the battery appears warm at the end of the charge thats fine, but if it starts approaching very warm or hot then STOP.

Edited By Timbo - Administrator on 21/02/2010 13:12:59

[Tim Mackey]

This site has some interesting and pretty reliable info on battery types, but heres an extract form the section on nickel hydride.

 

"Charging nickel-metal-hydride

Nickel-metal-hydride chargers require more complex electronics than nickel-cadmium systems. To begin with, nickel-metal-hydride produces a very small voltage drop at full charge and the NDV is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and degenerating cell match diminish the already minute voltage delta further. This makes full charge detection difficult.

A nickel-metal-hydride charger must respond to a voltage drop of 8-16mV per cell. Making the charger too sensitive may terminate the fast charge halfway through the charge due to voltage fluctuations and electrical noise. Most of today's nickel-metal-hydride chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.

Nickel-metal-hydride should be rapid charged rather than slow charged. Because of poor overcharge absorption, the trickle charge must be lower than that of nickel-cadmium and is usually around 0.05C. This explains why the original nickel-cadmium charger cannot be used nickel-metal-hydride.

It is difficult, if not impossible, to slow-charge a nickel-metal-hydride. At a C?rate of 0.1-0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100% charge. Overcharge could occur even though the battery feels cool to the touch.

Lower-priced chargers may not apply a fully saturated charge. Some will indicate full-charge immediately after a voltage or temperature peak is reached. These chargers are commonly sold on the merit of short charge time and moderate price.

Simple Guidelines:

• Avoid high temperature during charging. Discontinue the use of chargers that cook batteries.
  
• A charger for nickel-metal-hydride can also accommodate nickel-cadmium, but not the other way around. A charger designed for nickel-cadmium would overcharge the nickel-metal-hydride battery.
  
• nickel-based batteries prefer fast-charge. Lingering slow charges cause crystalline formation (memory).
  
• nickel- and lithium-based batteries require different charge algorithms. The two chemistries can normally not be interchanged in the same charger.
  
• If not used immediately, remove the battery from the charger and apply a topping-charge before use. Do not leave nickel-based battery in the charger for more than a few days, even if on trickle charge.

A well-designed charger is a reasonably complex device. Taking short cuts will cost the user in the long run. Choosing a well-engineered charger will return the investment in longer lasting and better performing batteries.

[ericrw]

So, if I've been flying with a fully charged Nimh battery and only achieved one, say 5minute flight, for whatever reason, do I have to discharge before  topping-up the battery?

[ericrw]

This happenned to me yesterday.   On returning home, I topped-up my flight Nimh battery for approx 81/2 hours; hoping to fly today but the snow put paid to that !     Does this mean I've "cooked" this new battery ?

[Tim Mackey]

N

Posted by eric loakes on 21/02/2010 15:43:41:

So, if I've been flying with a fully charged Nimh battery and only achieved one, say 5minute flight, for whatever reason, do I have to discharge before  topping-up the battery?

 

Ideally yes, but practically...no.  In reality most folk probably have a 5 minute flight, land, tea and a fag for 20 minutes, - repeat as required. Then we all go home and stick 'em on charge the night before we go flying again. The difference is we probably have around 5 or 6 flights in total, and drain off most of the battery

Edited By Timbo - Administrator on 21/02/2010 17:00:18

[Tim Mackey]

Posted by eric loakes on 21/02/2010 15:51:10:

This happenned to me yesterday.   On returning home, I topped-up my flight Nimh battery for approx 81/2 hours; hoping to fly today but the snow put paid to that !     Does this mean I've "cooked" this new battery ?

 

If you literally only flew for 5 minutes - even allowing for self discharge over an hour or so, you probably drained off only a couple of hundred milliamps. So assuming ( cos you dont say ) the pack is 1500 mahr, then you used just 10 - 15% of it,  which to " top up "  would require just 2 hours at 100ma, or 4 hours at 50 ma - again, you dont state what the charge current of your wall wart is.

What criteria did you use to leave it cooking for 8.5 hours?

[ericrw]

   I used the Futaba Wall charger. The battery is 1600mah.   The charger spec is as follows,  PRI: 230v-50Hz,  SEC: RX4.8v-70mA,  IP40,  ta=40.   The flight may have been less than 5min and very little time to drain off.   Is this what you mean by criteria  used ?    Has the battery gone the same way as my pevious Wot (crashed)    Eric.

[Former Member]

[This posting has been removed]

[Tim Mackey]

Posted by eric loakes on 21/02/2010 17:25:41:

   I used the Futaba Wall charger. The battery is 1600mah.   The charger spec is as follows,  PRI: 230v-50Hz,  SEC: RX4.8v-70mA,  IP40,  ta=40.   The flight may have been less than 5min and very little time to drain off.   Is this what you mean by criteria  used ?    Has the battery gone the same way as my pevious Wot (crashed)    Eric.

 

SEC Rx 70m/a means the secondary winding ( output ) to the receiver battery is 70m/a

Your 1600 mahr battery would need approx 25 hours to fully charge from "flat" at that rate.

To replace the 200 or so m/a you used in your 5 minute flight would need about 3 hours.

These are all guesstimations.

You cooked it for 8.5 hours - my question was  /is how did you decide on the figure of 8.5hours?

 

Is it goosed?  Unlikely, as you are not exactly a serial abuser are you

You really ought to be getting a "proper" multifunction charger that can properly handle NiMHs...after all cheap as chips these days.

[ericrw]

Went to bed ,midnight, up at 8.30, switched off just in case I was overcharging!!   It was for the 4cell r/x pack.

[ken anderson.]

hello eric-in my eye's you are a trojan....to solve all your prob's..i would spend a few more £...on a 'fast charger'...for your nimh batts...you will find that they will charge in 30 min's(give or take a few min's).......the charger's will take care of working out the time and how much to put in for you.......i would think £30.00 will get you what you req..... 

 

     ken anderson........member of young loakesy's fan club...... 

[ericrw]

To be honest Ken, I do have a Sigma 11 EQ but apart from being conversent with using it for Lipo, PB; Nimh is another matter.   I hope I'm not guilty of going off thread but I'm sure T, will let me know.   I just cannot get my head around the system for charging Nimh.  On the Sigma you have to choose manual or automatic;mines stuck on manual and no matter what buttons I'm pressing I cannot find automatic.  As to which I need for charging Nimh, I don't know!   I don't find the manual very helpful.  So I've been using my Wall- wart as it is simple in using!  To add to the complexity of it all I'm now using Eneloop batteries.   As I believe you don't have to discharge them and you just top them up if needed!!     Eric.

[Hamish]

Just acquired two old  Algebra gliders an 800 and 1000.  Took the batteries out and one has been dated September 1992.  Checked the voltage and each has just over 4 volts and the models have not been flown for some considerable time.

 

Being a real tight Scot I have put them on charge to see what like just in case there is a delay in the replacement  NiMH's coming from VAPEX .

 

The cost of this hobby!

[Tim Mackey]

Posted by eric loakes on 22/02/2010 11:56:00:

To be honest Ken, I do have a Sigma 11 EQ but apart from being conversent with using it for Lipo, PB; Nimh is another matter.   I hope I'm not guilty of going off thread but I'm sure T, will let me know.   I just cannot get my head around the system for charging Nimh.  On the Sigma you have to choose manual or automatic;mines stuck on manual and no matter what buttons I'm pressing I cannot find automatic.  As to which I need for charging Nimh, I don't know!   I don't find the manual very helpful.  So I've been using my Wall- wart as it is simple in using!  To add to the complexity of it all I'm now using Eneloop batteries.   As I believe you don't have to discharge them and you just top them up if needed!!     Eric.

 

Dont know  ( or like ) the Sigma stuff  - so cant help with its settings, but someone probably can. In manual mode, you usually need to set the cell count and the current that you wish to charge at.  In auto mode, its usually just the maximum current you will permit to be used thats set by you. The charger will decide the rest.

Eneloops are the same as Nimhs in all respects except for having a very low self discharge - they should still be charged / discharged as NiMHs

Edited By Timbo - Administrator on 22/02/2010 12:32:21

[Chris Channon]

Hi Eric L,

Yep use the wall charger as normal, it will be fine.

The reason i know this is that Futaba supply as standard, the same charger on the new 2.4gig stuff fitted with ni-mh as they have always supplied with ni-cd, just give the pack a good 12 to 14 hour ( ish ) charge the night before.

 

The wall charger will NEVER give the packs a full charge, about 95%, but if Futaba supply it then we may as well use it !

 

If and when you can, i would reccommend buying a charger with an LCD , not only does it look flash ! but it also tells you exactly what is going in the battery pack and what you end up with at the end of the charge cycle. ( Ultramat 10 ) is a very good capable first charger.

 

Hope this helps

 

Regards

 

Chris C

[Tim Mackey]

Chris -to just state " it will be fine.... just give it 12 - 14 hours the night before" is over-simplifying things - Eric has already stated that he only used the pack for about 5 minutes, and to simply give it another 14 hours on the charger will not do it any good at all in the long term.

He already has "a charger with an LCD"

Edited By Timbo - Administrator on 22/02/2010 18:36:03

[Chris Channon]

Hi Timbo, i am the first to admit i do not know enough about all things lekky ! which is why i asked the same question to the Futaba rep, i asked if i charge the night before and do not go flying, will it be ok to put the Tx and Rx on charge again the next night to go flying the next day?

 

Hence the reply i gave, if the guy from Futaba says it is ok to charge a pack overnight again without actually using the radio gear then who am i to argue?

 

But i will say, i have been doing just this for a verey long time and had no ill effects at all regarding life of battery packs.

 

We all can be blinded by science but if something works , and is endorsed by the manufacturer, then surely it is ok to carry on doing just that?

 

Regards as always

 

Chris C