Low battery warning problem

[Robby Mcgee]

Hi. After flying my syma x5sw for a year now all of a sudden when I fly now the low battery warning leds begin flashing shortly after taking off. When I check my batteties they read anywhere from 3.7 volts to 4.0 volts. Does anyone know why this started happening? It does it with multiple batteries. Thanks.

[Cuban8]

Not familiar with that machine so had to Google it!. Two things really. Perhaps your batteries are simply worn out - small lipos don't last very long and it's easy to wind up with several duds. Maybe there's a fault within the model giving a false warning regarding battery voltage. Does the model lose power quickly when the warning lights flash or does it carry on  flying as normal?

 

Edited By Cuban8 on 27/07/2017 18:15:33

[Brian Spearing]

If the batteries have been flown for a year it's possible that they cannot deliver the current without a large voltage drop, so they look fine on the bench but sag when flown.

[Keith Sharples]

Hi Robby. Invest in some new ones they vary in price from £3.50 - £5.00 each it's worth getting 1 and trying it. If your quad is back to normal throw the old batteries out and get new.

[Andy48]

I have the telemetry on my Taranis system to monitor each cell of the lipo. I can get the low battery warning towards the end of a long flight with not-so-new batteries. However, when I get that message on take off with a fully charged battery, I know it is time to bin the battery for the reason Brian states. This is the best indicator I have found to show the state of the battery, far better than checking IR for instance.

[Robby Mcgee]

Thanks for your quick responses guys. My batteries are about 8 or 9 months old. I bought them later on after drone purchase. The quad seems to still keep flying the same although I haven't tried to keep flying long after this happens. I try to land quickly.

[Robby Mcgee]

What is the proven method to test the batteries besides a voltage test?

[Cuban8]

Posted by Robby Mcgee on 27/07/2017 22:19:57:
What is the proven method to test the batteries besides a voltage test?

I think in this case the simplest test would be replacement of the suspect batteries. Thankfully, they're not very expensive so buying a couple of new ones and starting again from scratch will give you an indication as to where the problem is. Just one other thought - are you able to use a different charger from the one you've been using up to now? Might not be charging correctly, bit of a long shot but worth investigating.

[Andrew Cousins]

The best test I found after a similar thing trashed my sons trainer is to load test the battery.

A battery can report a full capacity if it is not under load (even if the battery is faulty) When you put the battery under load you are checking its ability to supply the current with out any significant drop in voltage.

In my case the battery was reporting 4.9 volts on the battery checker all seems good. BUT when i used a volt meter and put a small load on it the voltage dropped to 3.9 Volts. A recently bought battery of the same type voltage and capacity only dropped .3 of a volt.

I now date my batteries and will perform this simple check every few months. A little time checking and a few quid on a new battery saves a lot of Money and time rebuilding a model.

[gangster]

I think that is a good idea Andrew however I would suggest that check for receiver batterys every time you fly. I am however concerned that some of the checkers on the market give misleading results for Nimh batterys. I have seen people say that should be ok I have 50% or worse after a crash say well the battery said 70% maybe that works for the discharge characteristic of a lipo but not sure about nimh

[Andrew Cousins]

Gangster

Yes i do check battery before every flight. The load test i do every few months is a little more aggressive (more load) just to gauge the condition of the battery pack. Its not a long test just a couple of seconds just to see how the battery reacts.

I agree with you on the battery checkers on the market. I might look into making one up that you can switch different loads in and get an actual voltage reading out. I much prefer to see the actual voltage and see how it reacts to the load. You can tell a lot about the condition of the battery this way.

[Engine Doctor]

Flight or RX batteries need to be tested under load conditions to check if voltage drops . I lost a model some years ago through a duff cell that read perfect voltage with a simple tester but switched off under any sort of load.. I made a simple load tester for my NiMh Rx batteries **LINK**

Heath Robinson it may be but it works and shows up the performance of a battery under load and what the voltage drop is under the load . Load is adjustable by fitting a different wattage bulbs in the socket on top then comparing standing voltage and under load voltage . It can also be plugged into the circuit while batteries are in the model working servos etc in the model . Its only suitable for Rx/ servo NiMh flight packs but has saved a model or two from death by dead/Faulty battery. Surely a watt meter could be used for Lipos and check their performance under full power load ?

[Robby Mcgee]

Ok. I have 5 batteries that are aftermarket. After voltage drop test, # 1 dropped 0.2V, # 2 dropped 5.0V, #3, #4, #5 all dropped 1.0 V. So this means all or bad except #1 correct? Cuban8 I do have another charger. What do you guys think?

[Cuban8]

Just to be clear - what capacity are the batteries? Number of cells? What load current did you test them on and for how long? Were they freshly charged before testing?

Edited By Cuban8 on 29/07/2017 18:58:04

[Robby Mcgee]

They were charged. They are one cell 800mah. I don't know what load current is. Explain please. The voltages dropped within about 10 seconds.

[Denis Watkins]

Hi Robby, taking all the lads posts into account, you will see there is more to battery testing than voltage,

And although voltage is useful in diagnostics, the voltage result alone is not the full picture.

The number of cells determines voltage start point, then the capacity is important

That they are stored around 1/2C, charged at 1C, and field charged now and again at 2C

A fully charged battery can look the part, but can then fall off rapidly underload.

Even without sophisticated test equipment, a recommended pack should keep you airborne for about 5 minutes

This is a good test to try, and if your flight lasts a couple of minutes, then replace the pack

[iqon]

Do you normally fly until battery is flat ??

[Dwain Dibley.]

Assuming the one that dropped 5 Volts was a typo, I would still just renew the lot mate. I don't fly Multi rotors but they all do a lot of whizzing and to me that requires a lot of amps, a single cell lipo won't last long under that kind of duress. Also the after market jobbies, I have loads of 1s 180Mah ones for my 4site bipe, can be a bit hit and miss.

Get new and carry on having fun dood...

D.D.

[Cuban8]

Posted by Robby Mcgee on 29/07/2017 20:02:36:
They were charged. They are one cell 800mah. I don't know what load current is. Explain please. The voltages dropped within about 10 seconds.

Putting it simply, load current is the amount of electricity being extracted from the battery at a particular moment. I suppose it's a bit like the amount of petrol flowing out of the tank in your car at a particular throttle setting i.e foot to the floor, lots of petrol flowing, sitting idling then hardly anything being used.

To test a battery on load then knowing how much current (amps) is flowing out of it is vital. Your 800 ma battery will be designed to supply a maximum current (amps) and still maintain its voltage (what the detection circuitry in your model is monitoring). Your 800ma battery will have a C rating which will indicate how good at supplying current it is. That rating can vary a lot depending on battery size and quality, but usually ranges between 10 and 40.

If your 800 ma battery has a C rating of 10, then in theory it should be capable of supplying and maintaining a current of 8 Amps without its voltage reducing too much when fully charged, because 800 ma X 10 = 8A. If it only has a C rating of 5 then the maximum from it will be 4A. It should be noted that manufacturers published C ratings are often notoriously optimistic.

So, you can appreciate how important it is to know how much current (amps) is being extracted from the battery when you test it by connecting it up to a bulb, motor, resitor or something similar whilst  measuring its voltage at the same time.

Were you actually measuring the test current with an ammeter?

 

 

Edited By Cuban8 on 30/07/2017 09:50:09

[Robby Mcgee]

I have 2 original OEM batteries that came with the quad. They are 500 mah. I corecttly put them away and don't use them. The test I did means nothing because I did it wrong. I did not use an ammeter. I tested the 2 OEM batteries and got a drop of 1.0V. So I will perform a new test and report. Thanks for all your advice guys.

[Robby Mcgee]

Cuban8 my batteries are 25c so is my math correct it should maintain 16 amps. And can I test with 2 multimeters at same time?

[Cuban8]

In theory, a 500 ma battery rated at 25C should be able to source 12.5A (0.5 X 25). In the real world, tests that I've made on my own batteries of a similar size to yours had the voltage collapsing at nowhere near 25C and I'd say my batteries were realistically at best something like half the claimed C rating. This hasn't been a problem because the model that used them (a small heli) only draws a small amount of current.

To do a meaningful test you will indeed need a meter to measure battery voltage and another meter to measure current (volts in parallel, current in series) or a Watt meter that does both jobs in one and gives volts, amps and watts (an essential bit of kit really).

A single lipo is regarded as fully charged at 4.2V and discharged at 3.0V, so on-load at the desired test C figure, the closer to 4.2V the battery remains, the better it is. The nearer it runs to 3V the worse it is performing. A very bad or damaged cell may collapse to near or under 3V as soon as any demand is made of it. Without getting too carried away, how a cell performs is a function of its internal resistance and this can vary with a number of factors. Plenty on the web about all this and is worth mugging up on.

Edited By Cuban8 on 30/07/2017 19:48:15

[MattyB]

Posted by Robby Mcgee on 30/07/2017 15:45:20:
Cuban8 my batteries are 25c so is my math correct it should maintain 16 amps. And can I test with 2 multimeters at same time?

If the C-rating they gave the pack were true it could provide 12.5A, but as has been observed above achieving the rated C value is almost never possible nor recommended - most advertised C-ratings are wildly optimistic. On a pack of that capacity I would be surprised if a real world C-rating of more than 10 were achievable.

I know I am known here for nannying my batteries and analysing facts and data about them to ensure they perform at their best for the longest period of time, but when it comes to tiny single cell lipos I've come to the conclusion they are simply disposable items. No amount of care seems to help - many seem to die early despite being treated within their C ratings, in-line with the instructions and not over-discharged. I can only assume it is harder to make these small packs to the desired levels of QC because of their small physical size, hence their high levels of failure.

Whatever it is though, I wouldn't get too bogged down in analysis at this point - just buy some more batteries and I am certain it will fix your problem.

Edited By MattyB on 31/07/2017 10:27:59

[Robby Mcgee]

Well I don't what I did to change it but after test flying today my flight time is back to normal. Maybe a loose connection. I did take the quad apart to look for any but didn't see any. Thanks for all your help guys.