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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 05-10-2014, 12:48 AM   #1
kyleservicetech
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Default Getting Old! (Receiver and Transmitter Batteries that is)

One of my club members recently had a total loss of an expensive giant scale gasoline powered model a few days ago. The model went straight in from 400 feet. It didn't take long to determine what had happened. The transmitter battery had a catastrophic failure, where every one of its 8 cells had failed.

So, I put together this article in our club newsletter describing what happened, and making suggestions for appropriate battery power for the receivers and servos in our model airplanes.

This article is aimed at those modelers that fly giant scale models with separate receiver battery supplies for their model airplanes. There may be some readers of this thread that do use separate batteries rather than a uBEC for receiver power.

As for me, in my giant scale models, they are equipped with a Castle Creations 10 Amp uBEC, along with a backup two cell 2300 Mah A123 pack, with diodes to isolate the A123 pack from the uBEC.

Hope this is useful.

Kyleservicetech


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File Type: pdf Getting Old - - Receiver Batteries.pdf (827.4 KB, 37 views) Getting Old - - Receiver Batteries That Is

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Old 05-10-2014, 04:19 AM   #2
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Hi Denny ...

We can never be too safe when it comes to batterys of all types.

Have problems with downloads at moment ... will get round to read it.

What I am interested in - 8 cells failed at one time ? That you have to agree is very very unusual ... 1 or maybe 2 cells one time but all 8 ? Any ideas what caused that ?

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Old 05-10-2014, 04:22 AM   #3
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We should all do periodic cycle testing of TX and RX batteries...

Electric flight with the RX powered by the ESC's BEC gives a safety margin for the RX and will usually keep the RX powered even if the battery fails to keep the motor going shortly after takeoff.

Part of the issue is the batteries got so reliable that people forget that they need to be tested occasionally, because they will eventually go bad.

EVERY battery eventually goes bad.
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Old 05-10-2014, 04:27 AM   #4
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Originally Posted by solentlife View Post
Hi Denny ...

We can never be too safe when it comes to batterys of all types.

Have problems with downloads at moment ... will get round to read it.

What I am interested in - 8 cells failed at one time ? That you have to agree is very very unusual ... 1 or maybe 2 cells one time but all 8 ? Any ideas what caused that ?

Nigel
Hi Nigel
Yes, I described my opinion on the failure cause in the attachment. Our club member was "Maintaining" that transmitter battery on an expensive battery charger that monitored the batteries voltage. Whenever the voltage dropped to low, it kicks in, topping off the battery.

My suspicion is that charger just overcharged the battery and baked it dry during the winter months. I've seen this before, and normally, when a Nicad cell vents, you see white deposits around the positive terminal of the battery. There were no deposits visible with my microscope in this pack. Maybe that is different for a Nih cell? I don't know.

This charger was configured to fast charge the transmitter battery. Some places indicate that fast charging generic "AA" sized Nih cells in less than an hour is not a good idea.

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Old 05-10-2014, 04:43 AM   #5
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Originally Posted by fhhuber View Post
We should all do periodic cycle testing of TX and RX batteries...

Electric flight with the RX powered by the ESC's BEC gives a safety margin for the RX and will usually keep the RX powered even if the battery fails to keep the motor going shortly after takeoff.

Part of the issue is the batteries got so reliable that people forget that they need to be tested occasionally, because they will eventually go bad.

EVERY battery eventually goes bad.
Yeah

I had to tell my club member that if he'd simply turned on his transmitter for several hours the night before to check it out, he'd still have his $1200 model and its 60 cc engine, plus the receiver and all the $$$$ digital servos. There was nothing salvageable left. Even that engine was in several pieces.

He'd just checked the battery voltage on the transmitter, found it was 10.5 Volts DC, and thought it was OK.

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Old 05-10-2014, 05:22 AM   #6
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Originally Posted by kyleservicetech View Post
Hi Nigel
Yes, I described my opinion on the failure cause in the attachment. Our club member was "Maintaining" that transmitter battery on an expensive battery charger that monitored the batteries voltage. Whenever the voltage dropped to low, it kicks in, topping off the battery.

My suspicion is that charger just overcharged the battery and baked it dry during the winter months. I've seen this before, and normally, when a Nicad cell vents, you see white deposits around the positive terminal of the battery. There were no deposits visible with my microscope in this pack. Maybe that is different for a Nih cell? I don't know.

This charger was configured to fast charge the transmitter battery. Some places indicate that fast charging generic "AA" sized Nih cells in less than an hour is not a good idea.
Having spent a lot of time racing electric cars and the fast charging of packs .. we were charging packs in 15mins with fans and all sorts trying to keep them cool. I have an aversion to over-stressing any NiXX pack.
For anything other than the race cars - I adamantly refuse to fast charge. As you say Denny - Venting is start of death bell for any NiXX.

My Tx batts (NiMH 2300 AA's) stay on a 50mA trickle constant charge when not in use .. When I leave for assignment - they are unplugged. Those cells are now years old and still deliver similar to first day they were installed. I also have a faster 1A auto-detect charger but that clicks out to 50mA once full charged and will not resume 1A without unplugging and connecting again IF the pack is down.
I do not like auto resume chargers except on my Lawn Tractor !! On that I can top up the water in the cells !!

NiXX may be easy to look after .. but still need to have respect when charging. Some say .. go ahead and bang it in. Sorry - not me. Standard charge for me is STILL 1/10th rate and maximum 1A. I only exceed that rule of mine IF absolutely necessary.

On the subject of cycling ? I never do it ... all I do is do a run down check to the LVA timing it to make sure I am still using good cells.
My Tx's should give me about 9hrs to LVA. My 4.8 Rx packs should give me about 4hrs ...

It sounds like your pal - 'cooked' his cells ...

Nigel

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Old 05-10-2014, 05:29 AM   #7
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Originally Posted by solentlife View Post
Having spent a lot of time racing electric cars and the fast charging of packs .. we were charging packs in 15mins with fans and all sorts trying to keep them cool. I have an aversion to over-stressing any NiXX pack.
For anything other than the race cars - I adamantly refuse to fast charge. As you say Denny - Venting is start of death bell for any NiXX.

My Tx batts (NiMH 2300 AA's) stay on a 50mA trickle constant charge when not in use .. When I leave for assignment - they are unplugged. Those cells are now years old and still deliver similar to first day they were installed. I also have a faster 1A auto-detect charger but that clicks out to 50mA once full charged and will not resume 1A without unplugging and connecting again IF the pack is down.
I do not like auto resume chargers except on my Lawn Tractor !! On that I can top up the water in the cells !!

NiXX may be easy to look after .. but still need to have respect when charging. Some say .. go ahead and bang it in. Sorry - not me. Standard charge for me is STILL 1/10th rate and maximum 1A. I only exceed that rule of mine IF absolutely necessary.

On the subject of cycling ? I never do it ... all I do is do a run down check to the LVA timing it to make sure I am still using good cells.
My Tx's should give me about 9hrs to LVA. My 4.8 Rx packs should give me about 4hrs ...

It sounds like your pal - 'cooked' his cells ...

Nigel
Yeah

For transmitter charging, there is nothing wrong with those wall chargers that charge up in 12 hours.

I designed my own high powered Nicad Battery charger back in the late 1990's. That charger charged an 38 cell Sanyo RC2400 Nicad battery pack at 5 Amps. I rewound an automotive alternator to put out up to 50 Volts DC at a current limited five Amps, regardless of the Nicads battery voltage. It was controlled by a microcontroller control box that monitored voltage to two decimal places, adjusted the alternator for that 5 Amp current limited output, and when the voltage dropped off about 1% at full charge, shut down the gasoline engine. Nih cells drop off even less than that 1% at full charge. Still got that control box and the alternator.

Those Nicad cells were DESIGNED for high charge rates. I'm not at all certain that these transmitter packs are.

With these Lithium and A123 packs, its little more than an old memory piece of junk.

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Old 05-10-2014, 05:43 AM   #8
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I think some people tend to forget - particularly now we have chargers that can thump out incredible rates - that Tx's cannot take high rates through the sockets. The battery pack maybe can - but the socket and wiring / diode / voltage regulator etc. cannot. It used to recc'd that the older NiCD powered radios in 80's with their 500mAh packs were not charged at higher than about 300mA .. and is why the standard charger was a 50mA item - based on the 1/10th rule.
Now we have 2300 and even more sized NiMH AA cells and people think .. no problem - we can now thump 2.3A in ... sorry - but don't include me in THAT school of thought. I prefer to a) not ruin my radio and b) not overstress my cells.

I suggest that todays Tx is not suitable to have a rate of more than 1A on a regular basis through the charge socket. And certainly not for significant time. A quick charge top-up OK .. but not left connected.

I prefer to be kind and have good service.

Nigel

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Old 05-10-2014, 12:28 PM   #9
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No expert here, but for the most part, anytime we charge battery at a higher rate than recommended we arent doing the the batteries much good.....its an ohms law thing. I have never fast charged my transmitter batteries, and never will, and always my charge aircraft batteries At at the lowest recommended rate per the manufacturer...i dont mind waiting......!
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Old 05-10-2014, 02:12 PM   #10
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If you time how long it takes your TX battery to hit the low voltage alarm... you are doing a cycle test.

A test to see if the pack has lost capacity.
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Old 05-10-2014, 03:21 PM   #11
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Originally Posted by fhhuber View Post
If you time how long it takes your TX battery to hit the low voltage alarm... you are doing a cycle test.

A test to see if the pack has lost capacity.
True - but some put forward the Cycling regime as a Gospel .. and it's not just as I do every 6 months or so to check time to LVA .. they talk about multiple cycles ..

As Mallory guy said to me - why waste life cycles ?

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