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EssexBOF

A Tattu, 1300, 3 cell li po that suddenly decided to behave like nothing I have experience before It charges up to 12.6 V, with all cells balanced out. But under load it runs down very quickly. Checking it out shows it has lost little in voltage approx 12.25 V and all the cells still show them balanced, re the slight loss of voltage. I was expecting a cell to be gone, but that is not the case. Obviously under load is he problem, answers from the experts on electrics appreciated.

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Dick Whitehead

More information required - e.g.

What exactly do you mean by "it runs down very quickly"?

What is the load (in amps)?    What voltage does it drop to under that load?    Where are you measuring that voltage?   What mAh are you putting back in on recharge?

Dick

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thermaldoctor

Sounds like it has gone to high internal resistance Brian...

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simon_t

Or something is high resistance in the feed from battery to motor - have you got a slack or high resistance battery connector? (May work fine at low charge currents but not at high discharge currents), or any dry or poor older joints - check all those before ditching the battery.  How old is the battery?  Has it been storage charged or kept full?  When did you last use it and it was fine?

Simon

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Phil.Taylor

Maybe the ESC - not the battery? Have you tried it with a different battery?

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mikef

Come on EssexBOF!  I'm on the edge of my seat - tell us more - exactly what we’re you doing/seeing…

 Too high a cut-off set on ESC?  Check ESC settings.

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tonym

Wixy and myself had this happen, in both cases it was the internal resistance of one cell that under load caused a dramatic loss of power, only getting the models to 40 or so meters from a full charge. My Turnigy charger has a setting to test IR, John H has a meter of some sort that does it.

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EssexBOF
1 hour ago, tonym said:

Wixy and myself had this happen, in both cases it was the internal resistance of one cell that under load caused a dramatic loss of power, only getting the models to 40 or so meters from a full charge. My Turnigy charger has a setting to test IR, John H has a meter of some sort that does it.

This matches the problem I had. It did exactly that. So charged it up, but ground ran it where it followed the same pattern. No problem with other batterys, of the same size, or smaller 850's. Battery is approx 3 years old and always store them in a storage condition. 

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DaveH

For our use, where we tend to push batteries nearer to their limits, the sudden collapse of a cell is almost common. A good ground testing regime helps to avoid the loss of airframes.       The collapse of a cell can be so sudden that there is insufficient power for the radio.   This is why many use backup power systems, be they single cell devices or a little more.        Confusingly, a cell failing under load in this way can recover its cell voltage when checked only minutes later.  Relying solely on cell voltage to indicate battery condition is unreliable.  

 

    

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SteveH

Checking internal cell resistance periodically can be useful. I use ISDT chargers that have this function and will certainly weed out a high resistance cell in the pack.

 

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simon_t

3 years is a long life for an F5J launch battery - they have a hard life.  I reckon one year is good and after 2 years they are end of life.  When they start to go high resistance, they are at their most dangerous and liable to swell/burst when charged, so I don’t risk old batteries any more.  I have had good results generally with the Tattu batteries though.

Simon

PS - it probably means yu need to build/buy a battery heater!

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EssexBOF

Some pictures of the offending battery. it has a sligh swelling but have had battery's worse than that, which still performed OK. Looking back, when there was a small comp at Bartletts, last September, had it happen on a couple flights which, was a no no. Now I check the model under power for a dry run on the ground/hand. if it is going to go down it shows up pretty much straight away. If OK, can get two launches from a charge.  I always use a Ubec & tap off the battery terminals, with standard servo connector, so as the airborne set up is powered aside from the ESC.

Anyway for interest,some pictures of the battery causing the problem. These were taken after the faulty run, which was static. So it shows capacity , then the readings of the cell count & has not been re charged.

Apologies for the images of the Smart Meter images being on their side, but for some reason they load upside down, when attaching them, even if turning them upside down to start with20210611_112352.thumb.jpg.e46c2a68ba4376919a413c8edafef245.jpg20210611_112409.thumb.jpg.27d246c03a8186059452b1aec14f54eb.jpg

Brian

 

20210611_112532.thumb.jpg.d4de6edfb97bc3942fb900bed1af8251.jpg

20210611_112443.jpg

20210611_112453.jpg

20210611_112521.jpg

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oipigface

If in doubt, chuck it out!

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13 hours ago, oipigface said:

If in doubt, chuck it out!

Yes, that is the right way to go, but is interesting as to what the problem might be. Tony & Wi's experience seems to mirror what happened with me.

 

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