Field charging with a 7s3p

Racing Quads, Self-builds & FPV
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I’ve got this whopper 7s3p lion battery for field changing, but lo and behold, having charged one 6s battery from storage to 99% my Hota D6 pro, just shuts down. Is it the wrong battery, or just cheap and rubbish…?

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What was the mAH on the 6s ?
Did you know how many mAh you put into the 6s via the charger ?
Did you do a slow charge or a quick charge ?

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Is this the battery

https://www.aliexpress.us/item/1005005801160557.html?src=google&aff_fcid=ff9787e376be419f823a2982e194693f-1697372523406-06587-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=ff9787e376be419f823a2982e194693f-1697372523406-06587-UneMJZVf&terminal_id=3b96dc3d59bf4cb2a7a68db9e472242c&afSmartRedirect=y&gatewayAdapt=glo2usa

Was it fully charged

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Yup, thats the battery…
It was fully charged, and i took no more than 800mah out of it when charging the 6s lipo
The big battery’s voltage went from 29.4v to 25ish volts during that one charge. It seemed to stop as the 2 batteries reached equal voltage.

Strange.

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Unless there was a changer in-between stepping up the voltage I would kind of expect that.

Do you use …

7s —> charger —> 6S

Or 7s ----> 6s ?

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Is the hota set to a minimum input voltage? I set an alarm of 11.5 on my chargers to alarm when input gets too low. Not sure on the hotaa

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So yes there’s a charger involved. The 7s 29v whopper is plugged in the input socket (instead of the 240v mains supply) the 6s is in the output socket as normal.

And the minimum input voltage was set at a rather lowly 6.5v.

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Strange then. Yeah 6.5 quite low you don’t want to get that low haha. What amps were you using? I assume 1-2C looking at 2.5 max, should be well easy on that beast for a field charger. Though it’s very cheap for that capacity. Weird! Problem with with hota? Used direct DC input with it much before? I use lead acids at times and have no issues (though I use ISDT not hota). Never an issue like this…

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Can you see the individual mAh of the individual cells and how many are there of them?

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Well, I’ve found the problem… I tore the battery pack apart, tested each 18650, and found a load of duds that were dropping voltage FAR too quickly, so the overall pack voltage dropped below the level that its BMS was happy with - and it cut off.

So I’ll replace the duds, buy a spot welder, rebuild it, and see what happens.

Beware dubious cheap chinese batteries, is the real lesson here I feel!

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@JamesG

Out of interest can you supply the above

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Well the pack itself is rated at 58,000mah.
Its a 21 cell 7s3p. So they’ve laughingly added ALL the mah together AND assumed they averaged around 2700 each, which is at best - generous!
In reality they were around 1000 each with some in the low 100s.

So if there are 3 sets of 7 in parallel, am I right in thinking the average mah per battery is multiplied by 3 to get the effective mah capacity… which in the case is 3000mah at best?

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You’ve been conned

Yes and no,

There are 7 batteries in series, in 3 banks in parallel

The banks have a nominal voltage of 25.2v/2700mAh
as they are connected in parallel the Ampage is tripled

So the pack is 8100 mAh

If I was you, I would take these to the local battery recycling centre and get rid of them as these are the sort of things that burst into flames when charging

and that charger needs binning as well, your home is worth more

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Yup… gonna knock this on the head and rethink!

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