ESC cutting out on one type of battery?

[Ian Whittaker]

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 Christy]

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 Whittaker]

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 Christy]

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 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 Whittaker]

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!

[MattyB]

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?

[Former Member]

[This posting has been removed]

[Geoff S]

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 Whittaker]

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 Harris - Moderator]

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 Whittaker]

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.

[PatMc]

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

[PatMc]

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 Skilbeck]

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 Walby]

"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 Chaddock]

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.

[Brian Cooper]

Were the batteries Gen Ace?

If so, you've found the problem.

[Geoff S]

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

[PatMc]

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 Whittaker]

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.

[Toni Reynaud]

I have a little gadget that plugs into the balance lead and beeps (VERY loudly) if any cell voltage drops below 3.3V. It has found me a good few batteries on the way out over the years. A battery that flies a plane OK but beeps on opening the throttle part way through the flight is suspect. Search for "LiPo low voltage checker " on ebay.

[Engine Doctor]

I had a similar experience last week. After take off and one circuit the motor suddenly stopped on a large edf powered flying wing. The motor could be restarted to assist landing at low throttle strings. Once landed a meter was plugged into the balance lead to read the cell voltages . All were just under 4v on opening the throttle fully one cell quickly droped below 2v and the ESC cut out whereupon the voltage instantly reset to match the other cells at 3.7v ish . This was a well used 4s 3300 mah battery used in EDF's for 5 years so not unexpected.

The above check was done using a Battery Doctor plugged into the balance lead.

The point I'm getting to is that batteries need to be tested under load condition to get a real idea of their condition and ability to provide the needed current draw. Simply measuring cell voltage and balance is not enough.

The week before this battery was fine so failure although not unexpected with an older battery happen without warning. I try to never discharge my batteries below 25% -20% hence the 5 year life span . On less power hungry models I have batteries that are up to 10 years old ,not used continually and never put into storage voltage ,still going strong.

A quick test underload before recharging should detect a duff cell and if a battery is worth recharging.

[PatMc]

Posted by Chris Walby on 25/08/2020 18:47:11:

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?

Actually I don't think there would be any possibility of the motor restarting.
Last time I ran a battery down to LVC was in the heavy metal nickel cell days but in order to restart the motor the throttle stick had to first be closed then re-opened.
Bearing in mind that this is a C/L model this can only be done deliberately at the model.

[Lawrence Drennan]

Thanks for the interest and thoughts on this matter..

I'm the chap with the model described by Ian. This issue with 3S 2900ma lipos running for a fraction of the time of identical setup using 2200 lipos for a circa 3 and a half minute flight is a puzzle.

Just to clear up a few queries- the control card starts the power run after a 30 second delay, it has a governor to increase power output to sustain airspeed in climbs and aerobatics, and it has a timer to shut motor down after a selected duration. In effect it simply provides a simple automatic throttle and cut off function. This set up is new to me and learning fast, however the plan is not to run lipo's to the ESC cut off but use the timed cutoff- its clear that the ESC cutoff is discharging the 2200ma cell too much. The power train is working to all expected parameters...wattage, rpm etc

Anyway the problem remains that 2 brand new 2900ma lipo's (good brand) are both behaving identically in fraction of time of the brand new 2200ma, and clearly nowhere near the ESC cut off voltage, or the ideal discharge output.

[Ian Whittaker]

I spoke to the chap who's models and batteries are giving him the issue and clarified a couple of points.

All the gear is new - the batteries that are playing up were purchased for this job and haven't seen use elsewhere - equally they've seen no real use I yet either!

The device that switches the esc on is also fitted with a safety device so when the run is finished it needs positive input from him before it will turn the motor back on. It's also fitted with a timer to limit the run length - although I think he uses the LV cut. (He's aware it's not doing his battery any favours and it's set at the highest level.)

The batteries that aren't working are Overlander by the way.

Its stumped me at present!