# Discharged servo batteries



## lvst4evr (Feb 28, 2008)

My IDA's throttle & reverser servo batteries get discharged after only a few minutes of operation? The "pack" I made up is five new 2700mAh "AA" batteries. I retained the orig. Acc. reverser assy. & disabled the spring loaded detent & hooked up the servo linkage to the arm. With the T/X lever pushed all the way in either direction, I've got the linkage adjusted so the servo doesn't bottom the reverser out but I can hear a slight "buzzing" at the servo! If I back the T/X lever off a bit, the buzzing will stop, but I shouldn't have to do this, right? I've tried adjusting the "trimmer" with no success? Any help would be greatly appreciated! Jim Spanier


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## seadawg (Jan 2, 2008)

I don't know the actual term (hunting or seeking) but the buzzing is the servo trying to position the output arm a tiny bit, then it can't, so it trys it again and again. I've had that problem in the past and it seem as if there was a slight bit of drag on the object I was trying to move. The buzzing is annoying and does put extra wear and tear on the servo, but it shouldn't drain 2700 mAh too quickly.


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## Michael Glavin (Jan 2, 2009)

What type of 2700mAh cells, NiMh? These cells require form charging; typically it was recommended to fully charge/discharge cycle these cells three to four times prior to use to bring them to life. 

Sounds like the linkage needs some work, you should be able to deflect the TX joystick without binding the servo up. Some adjust the TX travel volume setting to limit servo travel arcs, BEST case is to match the required degrees of rotation of the throttle needle and reverse mechanism mechanically with linkage, and this is easy to do with different control arm lengths. The extra effort here is well worth the trouble! 

Michael


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## lvst4evr (Feb 28, 2008)

Hi Michael. Thanks for the advice. All my rechargeable batteries are NiMH. As far as the linkage, I always use the proper holes in the servo's control arm that give me "full throw" on whatever I'm activating, without bottoming it out (i.e.: when the T/X lever is pushed all the way forward & the reverser lever moves to it's forward position, there's still a little "wiggle room"! Likewise in reverse. 
Since my batteries have now been in service, do you think it will still do any good to discharge them all the way down & re-charge them as they probably should have been in the beginning? Is it recommended to give the batteries a short fast charge with almost twice the voltage as the pack or a slow charge with maybe a volt more than the pack, for a few hours? I've got a neat little Radio Shack bat. charger (no longer available) that has 5 stepped settings from 3v. to 9v. From past automotive experience, I'm a firm believer against "fast charges"!!! When I got my Aristo mike lv. steamer I charged the bat. pack overnite & when I shut the charger off it was really hot! Hooked up my VOM to it & it was putting out 17 volts. Thats a bit much for a 7.2 v pack! Nothing was mentioned in the inst. book about dangers with long term charging? It wasn't too long after that I had to make up another pack as that overnite charge definitely shortened the orig. pack's life! Jim Spanier


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## Dick413 (Jan 7, 2008)

hello
sounds like you have one bad aa that is drawing the pack down .did you match the bat. up when you made the pack?
richard


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## Michael Glavin (Jan 2, 2009)

Jim, 

Sounds like you got the servo/linkage thing down and need to adjust the linkage slighty to backoff a few degrees of travel. 

Does your charger have a specific auto-charge regimen for NiMH cells; this is paramount to properly charging NiMH. Is there a cycling routine available? 

The minimum voltage you need to get a full charge varies with temperature in all scenarios. The charging efficiency of NiMH cells around 65% if I recall. That means you need to charge/provide about 50% more potential into the battery than it’s rated to deliver… A 2700mAH battery will require from full state of discharge around 4000mAH to reach full charge. Best and simplest case is to charge at C/10 (capacity divided by 10 or 10% of the rated capacity per hour) for 15 hours MAXIMIUM. Some battery warming maybe noted near the end of the charge cycle; at this charge rate and time interval its expected and safe. 

An automatic properly configured NiMH FAST charger will work, but I don’t believe it’s recommended; at least not with new unconditioned cells, thereafter it’s not uncommon and cell life is compromised. 

Michael


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## lvst4evr (Feb 28, 2008)

Michael, my 5 step Radio Shack charger doesn't distinguish between NiCad & NiMH batteries, but I've had no problems charging both types in the past with it. I've got another Radio Shack charger that you have to physically put the 1.5v. batteries into "IN PAIRS" for it to work! With a VOM hooked to the batteries being charged "in series" they're getting 10.80v. "in series"! Of course my loco battery packs aren't accessible without taking covers off. I charge thru R.C. cable/receptacle assy's mounted under the bodies. 
So you're saying it's o.k. to charge any battery pack with 1-1/2 times it's base voltage for around 15 hrs. after it's been completely discharged, right? This is to be done only when the batteries are brand new, also, & only for a few times? Once this proccess is completed i& the batteries are not run down much below their normal voltage, is it acceptable to charge them for a couple of hours or so with a voltage no more than about 1-1/2 volts above their normal static voltage? Jim


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## steveciambrone (Jan 2, 2008)

NiCad and NiMH battery packs should only be charge in a current control mode and not by varying the voltage. This is normally done with a C10 rate or one tenth of the rated capacity of the cell, 2700ma + charge rate 270ma, unless you use a fast charge charger that is designed for NIMD or NICAD batteries. 

Steve


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## Michael Glavin (Jan 2, 2009)

Jim, 

Your charger is probably inadequate for routine NiMH charging if it’s not specifically designed for same, end of story…. More likely than not you’re having issue with charging due to your NiCD chargers inability to recognize the diminutive negative delta V bump (-delta V) realized of NiMH cell chemistry, a proper NiMH charger will use a different charge termination criteria, such as -dV/dt or preferably dT/dt. (I’m assuming you have NiCD only charger, these use –delta V scenarios) 

negative delta V = Batteries are charged at a specified constant current. The battery voltage rises as charging progresses to a peak when fully charged then subsequently falls. This voltage drop or - delta V bump that is indicative of end-of-charge is harder to see or detect in NiMH than NiCad, and as I noted it is temperature dependent too. 

dT/dt = Measures the temperature rise during a timed capped charge interval. After the battery is fully charged a chemical reaction generating and recombining oxygen is realized. This process heats the battery. This sudden increase in temperature rise can be used to terminate the charge. 

NiMH cells can be damaged by prolonged trickle charge. 

I suggested NiMH cells can be charged at C/10 for up to 15 hours. Other cell chemistries have different coulometric charging efficiency numbers! 2700mAH/10=270mA; voltage is not a factor in this calculation. 

C/10 is acceptable for continued charging and or normal use without detrimental damage to the cells, provided they are discharged to some extent IMO. At C/10 the cells can absorb some overcharge due to the inherent oxygen recycling catalyst which mitigates damage to the cells during overcharge, charge rates above C/10 overwhelm the aforementioned oxygen recycling and heat builds quickly and exposes the cells to chemical breakdown and shorter life expectancy. 

Voltage required to get a full charge varies with temperature at least 1.4V per cell at 70*F is the minimum. 

Michael


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## lvst4evr (Feb 28, 2008)

Michael; when you refer to "trickle charge" I think of "low amps" but fairly constant voltage (maybe only a couple of volts more than the rating of the battery being charged) sent to a given battery? I'm not up on all the techical terminology of these re-chargeable miniature batteries, just an old retired diesel truck mechanic, so you'll have to forgive me! 
Where's a good source for compatable chargers? Does one have to have a different charger for every size (voltage-wise) battery pack or does the charger recognize the voltage & regulate the voltage & amperage accordingly? Jim


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## Michael Glavin (Jan 2, 2009)

Jim 

There are many offerings out there for smart multi chemistry battery chargers and I believe there are MLS site sponsors that have chargers available too. 

Smart chargers are able to charge multiple cell technologies, typically NiCD, NiMH, PB, Gel, Lead cells, Lithium and more. You select the cell type, confirm cell count, enter battery capacity and the charger configures voltage and charge algorithm, charge/discharge cycles and more. 

This is basic for NiCD/NiMH. 
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWTE0&P=ML 

Smart auto charger: 
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVRS6&P=ML 

I use this charger EOS 0615i DUO3, more bells and whistles but then I again play with battery powered trains and airplanes with Lithium cells predominantly and find the cell balancing features important afforded this type of charger. 
http://media.hyperion.hk/dn/eos/ 

I also have several other smart chargers I have used for many years, cost runs the gamut and is relative to feature sets it really depends on what your needs are. Internet searches will bring up literally hundreds of chargers for RC Car-Boat-Airplane and then there are offerings for laptops and much-much more….. 

Michael


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## HMeinhold (Jan 2, 2008)

Jim, 
why do you use 5 cell packs? This gives you more than 6V with fully charged cells. Usually R/C receivers/servos are operated off 4 cells = nominal 4.8V. This might also explain the hunting of your servos. 
Regards


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## TonyWalsham (Jan 2, 2008)

I can't speak for all brands of R/C , but I know for sure some 2.4 GHz RX's do not like 5 cell battery packs for power. 
The Planet Twister R6M RX for one, will simply not work with a freshly charged 5 cell pack. 
I have tried using diodes to drop that voltage down but it does not work reliably. 
I eventually removed one cell from the pack and now all is well.


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## Semper Vaporo (Jan 2, 2008)

Hmmm... ??? I know of no R/C receiver that will work well on just Four NiCads. Four alkyline work okay, but not NiCads. When I bought my R/C set for my Mikes, the hobbyshop sold me a 4-cell penlight battery holder, but when I wanted to get rechargables, they insisted I had to use a 5-cell pack. I tried 4 individual NiMH rechargables in the 4-cell holder and they operated for only about 5 minutes and then the receiver became very intermittant and quit shortly thereafter. Replaced the NiMH with Alkylines and it worked again for a couple of hours before the batteries were too low to keep it running. When I use the fullly charged NiCad 5-pack it will run for about 3 or 4 hours, depending on how much I change the servo settings while running.

I had a problem with the R/C losing signal when the batteries in the transmitter ran down so the hobby shop sold me a device that fits between the receiver and the servo that senses loss of signal from the transmitter and moves the servo to a pre-determined point . I put the device in the Reverser servo circuit so it goes to "neutral" if the train gets too far away for the power of the transmitter (saves from having the engine run away if it gets out of range with the throttle wide open!... not good on an elevated system with loopbacks on each end... Don't wanna to highball the curves!).

This device also senses the voltage from the receiver and if it is low it does the same thing as when the signal is lost. I cannot use this device when using alkyline batteries because the voltage drops too too low in about 10 or 15 minutes. It also shortens the run time to about 2 hours when using the NiCads, because the voltage drops just enough to cause it to trip its function trigger.


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## TonyWalsham (Jan 2, 2008)

Freshly charged 5 cell NiCd or NiMh batteries provide much too much voltage for some brands of RX's. The Planet Twister R6m is one of them. It simply shuts down from over voltage. 
Take the extra cell out and it works just fine.


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## Michael Glavin (Jan 2, 2009)

Yep battery pack voltage is a factor for RX's and servos..... There are many that must be ran on 4.8V only.... Seen issues with this for many a year in my airplane days. 

Good stuff on the Alkaline and NiCads-NiMH voltage info; simple consideration herein solves most problems thereof..... 

Michael


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## HMeinhold (Jan 2, 2008)

Posted By Semper Vaporo on 10 Nov 2010 04:21 PM 
Hmmm... ??? I know of no R/C receiver that will work well on just Four NiCads. Four alkyline work okay, but not NiCads..... .

All my locos (5 x Spektrum R/C system) run on 4 cell NiCd's. I charge them 2..3 times/season, so no problem with capacity. I chose the antiquated NiCds, as they are less vulnerable to "emergency makeshift chargers".

Regards


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## lvst4evr (Feb 28, 2008)

Mike; thanks for the info on the"automatic chargers"! I'll check them out. Maybe I should consider changing over to "LITHIUM" in the future?
Henner; I added the 5th. battery because the 4 orig. Nicads were not holding the charge? Maybe the buzzing at the servo was pulling them down? I've now installed Sanyo 2700 mAh NiMH batteries & "fine tuned" the servo linkage adjustments! Thanks to everybody for all your advice!!! Jim


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## lvst4evr (Feb 28, 2008)

Finally found the "CULPRIT" that has been running my Spektrum DX5-E receiver/servo battery pack down! By process of elimination I worked my way back from the servos, all the way thru the wiring to the receiver! With only the receiver hooked up to the battery pack thru the off/on switch I lose .01 of a volt every 1 to 1-1/2 second! As soon as I turn the switch off the batteries start to recover on their own! I've been fighting this since early 2009! I probably went thru 5 different sets of batteries & now have Sanyo 2700mAh batteries in there! That's what I get for not getting the VOM out & staying with it until it was uncovered! I talked to "TECH" at Horizon & the guy agreed with me that the receiver needed attention! Thankfully the owner of my local hobby shop, where I bought the system, is going to replace the receiver with a new one. It's well out of warranty, but he knows what has been going on! Looking forward to some decent runs with my IDA, since it's been awhile with this battery problem! I would never have thought the receiver would cause this kind of problem! Jim Spanier


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## HMeinhold (Jan 2, 2008)

Jim, 
don't forget: 4 cells only! 
Regards


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## lvst4evr (Feb 28, 2008)

Thanks Henner. Now you know why I added the 5th. battery in the 1st place! Of course it only gave me a slightly longer run than I would have had with only 4 batteries! Jim


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