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Old Aug 22, 2003, 02:59 AM
Little Bo's Lab
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Refilling LiPos (Discharge???)

I have several ETEC 3S 1200mAH LiPos that I fly in my 15oz MM Switchback with the Astro Motor (4.43:1 geared with 10x8 prop)...get 45 minutes of flight time!!!

After the 45 min flight the pack still has power...I have a Triton Charger do I need to discharge the pack and then recharge or can I just recharge the pack after each flight?

Thanks,

Mike
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Old Aug 22, 2003, 05:02 AM
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lipos don't need (and it is also risky to) discharging.

Cool hey :-)
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Old Aug 22, 2003, 09:47 AM
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You don't need to discharge LiPolys. There is no "memory" effect.
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Old Aug 22, 2003, 10:17 AM
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If you are asking questions like that I would suggest that you do some serious reading about safe handeling of lithium batteries before you use them again.

Steve
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Old Aug 22, 2003, 10:24 AM
luc
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good advice, steve...

people go into deep technology without taking the time to learn the minimum....sad
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Old Aug 22, 2003, 03:47 PM
Little Bo's Lab
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I asked for help and get....

Quote:
Originally posted by luc
good advice, steve...

people go into deep technology without taking the time to learn the minimum....sad
I've read allot about NEVER OVERCHARGE LITHIUM BATTERIES but what about discharge???...

I have done research on LiPOs... but my Triton charger states: for discharging Lithium Polymer or Lithium Ion batteries...."Discharge cutoff voltage: set "Li-ion discharge" voltage to 3 multiplied by the number of cells in the battery. For quick discharges set discharge current to no higher than 2C max."

This implies you can discharge the pack!!! I've not read that you should not discharge...or cycle but this is new technolgy and we are all in the learning mode.

Also I have read that Li Po cell can be left at room temperature as they have much lower self discharge (about 5% in six months).

I'm asking for advice??? So whats the verdict ...and where is the reference for the above statements?
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Old Aug 22, 2003, 04:26 PM
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I can see why you're confused if the instructions with the Triton charger suggest that it can be used to discharge lithium cells. I'm not sure why they included those instructions, as all of the data posted here by various lithium cell manufacturers and distributors suggests that there is no reason to discharge lithium cells with your charger.

You are correct that lithium cells have very low self-discharge rates, and can be allowed to sit for months without losing much charge.

There is a lot of sensitivity right now about inexperienced people using Li-poly packs because there have been several accidents where cars and houses have caught on fire due to pack malfunctions. There is a concern that those who don't have a lot of knowledge about the potential problems with Li-poly are more likely to have an accident. So the tone of some of these posts is due to the fact that no one wants to see you have an accident due to lack of knowledge about these cells.
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Old Aug 23, 2003, 05:09 AM
Little Bo's Lab
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Thanks DAVE!!!!!!!!!

Quote:
Originally posted by Dave Hederich
[B]I can see why you're confused if the instructions with the Triton charger suggest that it can be used to discharge lithium cells. I'm not sure why they included those instructions, as all of the data posted here by various lithium cell manufacturers and distributors suggests that there is no reason to discharge lithium cells with your charger.

/B]
Dave...Thanks for setting the record straight...Even with the right charger you can have mistakes/problems and it appears that we must be very careful with the LiPos unless other developments tell us otherwise. I've followed the Triton's charging recommendations (1C max) and have no problems...I like the Triton but its slow but dependable.

If discharging is not necessary then Great Planes needs to clarify in their Triton manual..this may be an oversight on their part???.

Mike
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Old Aug 23, 2003, 08:32 AM
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I'd imagine that Triton provide the discharge function so that you can perform the occasional battery capacity check to keep tabs on the health of your batteries.

If you analyse the instruction you quoted (set cutoff to 3x no of lipo cells - it should say no of series-connected cells), Triton is telling you not to discharge the pack below 3V per cell, which is accepted as the minimum voltage below which you should not discharge Lipo cells, otherwise you risk shortening their operational life.

Gordon

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Old Aug 23, 2003, 08:34 AM
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I use the discharge function for testing the cells. Got a question about the health of your battery? Run the discharge test - only negative thing about it is the current is limited to 2.5A.
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Old Aug 23, 2003, 03:01 PM
Little Bo's Lab
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Not Sure What This Tells You???

Quote:
Originally posted by hoppy
I use the discharge function for testing the cells. Got a question about the health of your battery? Run the discharge test - only negative thing about it is the current is limited to 2.5A.
hoppy
Hoppy,

If I run the discharge test...what should be the end result??? Min voltage reading at end of tests...and since I have 3 cells in series I assume we have an additive response???

Mike
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Old Aug 23, 2003, 03:09 PM
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Mike,
Just this morning I had a question whether my battery was holding up under a 3A draw....Since I had a 2s pack I set the final V for 6V (3V x 2 cells). The Triton was set to 6V shutoff and a 2.5A draw. The discharge showed 1175mah from a 1200mah pack so the battery was given a clean bill of health.

So with a 3s setup, the cutoff would be 9V. You don't want to go below that just for a test although you will probably run lower than that during real time flying at the end of a battery run.
hoppy
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Old Aug 23, 2003, 07:08 PM
pfm
Patrick Mahoney
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I use the discharge function to check mine as well. I charge the pack all the way up and then discharge it back down and see how much current it supplies before it hits the cut-off voltage.
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Old Aug 23, 2003, 09:45 PM
Little Bo's Lab
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Ah Ha!!! Now thats how we can check!

Quote:
Originally posted by hoppy
Mike,
Just this morning I had a question whether my battery was holding up under a 3A draw....Since I had a 2s pack I set the final V for 6V (3V x 2 cells). The Triton was set to 6V shutoff and a 2.5A draw. The discharge showed 1175mah from a 1200mah pack so the battery was given a clean bill of health.

So with a 3s setup, the cutoff would be 9V. You don't want to go below that just for a test although you will probably run lower than that during real time flying at the end of a battery run.
hoppy
Thanks guys...now I understand why we use the discharge function and how it can be used to check the fill and refill degredation effects of the cells over time!!!!!!!!!

Does any one have any figures on number of cycle lifes of Thunder Power versus ETEC versus KoKams???


Thanks again!!!

Mike
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Old Aug 24, 2003, 07:57 AM
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Life cycles of different brands of cells are hard to calculate outside of a laboratory. In flying use, it's virtually impossible to duplicate the same conditions for the life of each set of cells. In a lab, you could program discharge patterns into computerized equipment, maintain consistent atmospheric conditions, etc.
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