Techniques > Radios
RX batteries...
Fred:
Ok, I'm back with my batteries stories !
In my howm town in France, we are lucky enough (well, for us, modelers!) to have one of the biggest battery manufacturer in the World (use to be at the time...), the SAFT. They use to make batteries for Sanyo, Philipps, Panasonic etc etc (yep, Sanyo were at some stage, mostly "made in France", 3km from my house :D ).
We knew a few people working in these factories, so we always had on the field the latest batteries (I still have some!), all for free ! This is also when I saw my first Lipo battery pack, at the time, they costed an arm and a leg, but they assured us that was the future... :roll: ... Yeah right, it's like computers, that will never take of :mrgreen:
Ok, so, anyway, called a friend who is an engineer in the SAFT, and also fly models (handy :D ) and told him about my issue.
For him, this is a Delta Peak issue, that's all... Asked him about the charging of batteries, what the pro are doing basically... So, here we go.
All the batteries are tested at 1/10 of their capacity for charge. They call that the normal charge for a battery, whatever type you are using, and they use that to make the charts etc etc for the specs.
The good thing, is that you put more capacity in a battery this way, and will, therefore gives you back more than the number written on the cell.
Fast charge for the company, is 1C. Only issue is that you can't fill the cell at 100% with a fast charge, and life expectancy is also slightly reduced. Overcharge, that can hurt the cells badly at this rate, is hard to get as the delta peak is more easier to detect by chargers (for whatever reason... It seems that there is some really boring scientific explanations for that...).
Also, the faster you charge your batteries, the more "trained" to deliver high current they get... Which would be great if you power your motor with NiMh cells, but for a TX/RX battery who need to deliver "slowly", and if possible for as long as possible...
Soooo... At the end, what he said is : charge at 1/10C if you have time. Your cells will leave longer, deliver more, but be careful of the memory effect (cycle from time to time).
In a hurry, do it at 1C, (or even 2C, but you need fans to cool the cells down...), but not all the time to keep your cells healthy.
Best compromise is 0.5C :P
Another important thing, is to check the value of your delta peak, as this is the thing that will keep your batteries from overcharging etc etc... There is some math to be done to find the DP of your batteries, but it seems that for NiMh, 0.8mv is a good rough value.
So, that's what I remember from our conversation on Friday.
In my experience now, I never charge batteries at a fast rate, never! Must come from the good old days, where we did not had all that technology in our chargers I guess (still have my Robbe Ladder5!). But I have some packs that are more than 12 years old, still performing relatively good.
Now, the issue seems to be with the chargers, not really designed for nimh / RX batteries anymore, but it seems that is another story (in my case, old charger, works great, brand new one with all the gizmos, troubles!).
Anyway, more food for the brain, or more information to get even more confused! :lol: :P
Happy Days:
Thanks for that Fred. :clap:
Regarding finding good chargers, yes that is a problem and begs the question , How good are any chargers? (It's a bit like buying a torque spanner for tightening bolts on your car. How do you know how well calibrated it is?)
I guess the ‘belt & braces’ approach would be to find a charger that senses both Delta Voltage and Delta Temperature on a battery. Although there could still be a potential problem with a pack of cells as one cell could become weaker than the others. i.e. there is no balancing sensors for these type of batteries on any chargers that I’ve ever seen.
All interesting stuff,……thanks again for posting.
Keith
Fred:
To conclude (for me) the subject on RX batteries, finally found some numbers to concure with what I see for the past 2 years now !
My 5 euros packs are even slightly better than the Eneloop it seems (see the charts/graphs down the page) :D
http://www.candlepowerforums.com/vb/showthread.php?t=252408
I'll try to re-stock those cells next week :D
Aidan:
--- Quote from: "Fred" ---To conclude (for me) the subject on RX batteries, finally found some numbers to concure with what I see for the past 2 years now !
My 5 euros packs are even slightly better than the Eneloop it seems (see the charts/graphs down the page) :D
http://www.candlepowerforums.com/vb/showthread.php?t=252408
I'll try to re-stock those cells next week :D
--- End quote ---
Hi Fred
I just got a second hand Multiplex Royal EVO that I'm converting to Jeti Duplex. It arrived with a dead TX battery. I was debating whether to replace it with another standard Multiplex NiMH pack or solder up an Eneloop pack for it. I think I'll drop into Aldi and see if I can get a few of these to make up a pack. Low self discharge, slightly better capacity and cheaper!
Did you solder yours - any problems or do you remember?
Aidan
IceWind:
Why not go for a LiPo?
Just remember to add a diode to reduce the tension and make the radio warn properly on low power.
I had the same problem on my FF9 and went that way... now I can't even remember the last time I charged it. :)
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