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ESC cutting out on one type of battery?

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Ian Whittaker25/08/2020 11:06:14
65 forum posts
1 photos

Hi,

I was at the field yesterday watching some chap with electrical snags. His model would run for approx 4 minutes on a 2100mA, 3 cell pack until the low voltage cut on the ESC kicked in. With a 2900 pack (also 3 cell) it wouldn’t run beyond about 30 seconds before stopping. The battery showed as 80% after. We tried a ground run with a multimeter monitoring the battery voltage and it seemed stable and well above the cut value. This was the case with 2 separate 2900 packs, albeit both from the same manufacturer.
The set up was in an electric C/L model incidentally. There was a device acting in place of the receiver so as to allow him a 30 second delay to energise the model then get to the other end of the lines for flying, and using the low voltage cut of the esc to stop the motor at the end of the flight.

Peter Christy25/08/2020 11:30:23
1901 forum posts

Where were you monitoring the voltage? Before or after the connectors?

If there was a poor joint on the battery-side connector, the battery would still show good voltage, but the drop across the connector might show low voltage on the ESC side and trip the low voltage cut-out.

If you were monitoring across the balance lead (the easy way to do it at the field!), then that is monitoring the battery directly, and not necessarily the voltage at the ESC, the other side of the connectors.

--

Pete

Ian Whittaker25/08/2020 12:21:10
65 forum posts
1 photos

I was monitoring on a make shift lead (Dodge it and Bodge it field improvisation at its finest!) between the battery connection and the ESC. Surely if there was a bad connection on the plane / ESC side (as opposed to the battery) then it’d show up with all three packs though?

Peter Christy25/08/2020 12:35:07
1901 forum posts
Posted by Ian Whittaker on 25/08/2020 12:21:10:

I was monitoring on a make shift lead (Dodge it and Bodge it field improvisation at its finest!) between the battery connection and the ESC. Surely if there was a bad connection on the plane / ESC side (as opposed to the battery) then it’d show up with all three packs though?

Yes, but my point was that if the dodgy connection was on the *battery*, it would only show up on that pack. I was wondering if the pack manufacturer had released some packs with poor connections or soldering, which might have explained the problem.

I thought that in the finest field-bodge way wink you might have been measuring across the balance lead, which wouldn't show up a problem on the esc side of the connector.

--

Pete

Ian Whittaker25/08/2020 12:37:01
65 forum posts
1 photos

Hi Pete,

he has two 2900 packs and the fault is on both. I’m a novice at electrics and Lipos, my learning curve is currently steep!

MattyB25/08/2020 12:39:17
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2305 forum posts
40 photos
Posted by Ian Whittaker on 25/08/2020 11:06:14:

I was at the field yesterday watching some chap with electrical snags. His model would run for approx 4 minutes on a 2100mA, 3 cell pack until the low voltage cut on the ESC kicked in. With a 2900 pack (also 3 cell) it wouldn’t run beyond about 30 seconds before stopping. The battery showed as 80% after. We tried a ground run with a multimeter monitoring the battery voltage and it seemed stable and well above the cut value. This was the case with 2 separate 2900 packs, albeit both from the same manufacturer.

The set up was in an electric C/L model incidentally. There was a device acting in place of the receiver so as to allow him a 30 second delay to energise the model then get to the other end of the lines for flying, and using the low voltage cut of the esc to stop the motor at the end of the flight.

My money would still be on the 2900 packs having been damaged, probably through over discharge (which sounds a distinct possibility based on the way they are being used). Hitting the LV cut-off every time is definitely going to shorten cycle life, decrease capacity and increase IR (internal resisitance) over time.

How many cycles did those batteries have on them, what is their C rating and what was their IR if you have a charger that can measure it? How are they stored - at 50-70%, or fully charged?

Steve J25/08/2020 13:40:44
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2070 forum posts
60 photos

The 2900 is not holding up under load due to age, abuse or inadequate C rating. Recording the voltage during operation (with either a unit on board the model or via a telemetry link would give you an idea what is going on).

Edited By Steve J on 25/08/2020 13:41:26

Geoff S25/08/2020 13:56:09
3814 forum posts
46 photos

Like Matty and SteveJ I'd suspect the the batteries, which it seems may have suffered a lot of abuse if they've been regularly run to exhaustion by reaching the esc voltage limit every time. I don't think I've ever run a LiPo that low.

The only way of checking is to discharge them in the workshop whilst monitoring current and voltage. Measuring the IR might be a good idea, too. If you don't have a suitable instrument or charger that does it you can try this nethod.

1: Measure the battery off load voltage.

2: Apply a load and note the current and on load battery voltage.

The IR (internal resistance) in ohms is given by. Off-load V - On-load V/ current in amps. Anything greater than 10 milliohms per cell makes the battery well on its way but usable up to a point. A good battery will be below 5 milliohms per cell.

Geoff

Ian Whittaker25/08/2020 15:53:16
65 forum posts
1 photos

I measured the internal resistance of all the packs - the 2900 packs do have a higher IR than the other one and also much higher than my 6 cell 5200 pack...

Martin Harris25/08/2020 16:26:25
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9532 forum posts
258 photos

I'm wondering if the ESC measures voltage more quickly than the response time of the meter? Perhaps cutting the power before the meter responds therefore keeping the displayed voltage looking good?

Ian Whittaker25/08/2020 16:27:45
65 forum posts
1 photos

I think 6 milli ohm was the highest my charger registered on his 2900 packs - for reference my 6 cell 500/5200 packs were in the region of 1 to 2 milli ohm per cell, his 2100 pack was about 3.

PatMc25/08/2020 17:00:51
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4481 forum posts
548 photos

Remember that the IR should be considered as inversely proportional to the cell capacity,

PatMc25/08/2020 17:10:27
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4481 forum posts
548 photos

Is the ESC set to sense the type of cell (i.e. chemistry) automatically ? Has the cut of voltage also been set automatically ?

I've seen similar problems to that described in the OP because the ESC apparently sensed a part discharged nickel battery instead of a freshly charged lipo then triggered the cut off soon after power up. The problem was established by programming for specific count of lipo.

OTOH I think high IR is more likely, especially since the batteries seem to be regularly run down to cut off voltage.

Edited By PatMc on 25/08/2020 17:13:35

Frank Skilbeck25/08/2020 17:24:25
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4843 forum posts
107 photos

We saw something similar on a friends plane, it lost power on take off. On checking on this battery by connecting up a battery checker to the balance lead we were able to see that the voltage across one cell collapsed under load. Check the battery off load and all was well.

One thing to watch is that not all balance port battery checkers are the same, my friends recorded the battery as it was connected and remembered those values until it was disconnected whereas mine gave live readings.

Is the 2900 pack a NanoTech ?

Chris Walby25/08/2020 18:47:11
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1345 forum posts
338 photos

"There was a device acting in place of the receiver so as to allow him a 30 second delay to energise the model then get to the other end of the lines for flying, and using the low voltage cut of the esc to stop the motor at the end of the flight"

Am I missing the point here....run the lipo until the ESC cuts out (good way of knackering a lipo IMHO) then go and retrieve model.....if the Lipo voltage recovers is there not a possibility of the ESC restarting the motor?

Has safety gone out of the same window as battery care?

PS my money is on one cell voltage collapsing under load.

Simon Chaddock25/08/2020 18:58:09
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5791 forum posts
3063 photos

I would have to agree using the LVC to limit the flight time is not what it is intended for but only to allow a plane to land in the event of an accidental over long flight.

The thread title is quite correct "ESC cutting out on one type of battery". The "one type of battery" is any that is worn out. wink 2

Brian Cooper25/08/2020 20:14:18
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602 forum posts
27 photos

Were the batteries Gen Ace? sad

If so, you've found the problem. wink

Geoff S25/08/2020 21:11:32
3814 forum posts
46 photos

Good point about the LVC recovering once the load has been removed and restarting the motor. Rather like my hearing aid battery which has to be removed to stop its restarting and shutting down rhythmically

Geoff

PatMc25/08/2020 21:47:22
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4481 forum posts
548 photos

Actually it wouldn't be normal for the motor to run until the LVC. The device that drives the ESC is usually also a timer that can be set for the desired flight time, meaning that LVC is merely an override from the ESC in the same way as it is in RC models.

Perhaps the set time simply hadn't been reached when the LVC operated or Ian misunderstood the full operation.

Ian Whittaker25/08/2020 23:21:48
65 forum posts
1 photos

I'm not an expert on Lipos - with that out of the way....

i got the impression that his packs were new (ish). I don't think either of the 2900 had ever performed as the 2100 did though, even from new (but I could be wrong on this). As a matter of interest I think his Lipo knowledge was a little short - as the low voltage cut off was set as a level where the pack was somewhat low. He has since amended his settings on the esc.

for what it's worth his 2100 pack showed as 3 milliohms per cell, his 2900 battery 6 per cell. As a reference my 5200 and 5000 packs are about 2 per cell.

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