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Servos Chattering.


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2 hours ago, David Davis said:

Isn't that what cycling does?

 

Yes it is, but Nigel R. also suggested checking whether the servo chattering fault returned when the battery was discharged (after the first half of the cycle) then went away again after the battery was charged again (second half of the cycle). If the chattering never returned after you discharged the battery that would indicate that the initial fault wasn't necessarily down to the low battery.

 

I've looked up the manual for that HobbyKing charger and the coloured squares that you refer to are Red = peak voltage attained during charge, Green = charging current, Orange = mAh that the battery has accepted and Blue (grey on yours perhaps) = battery temperature (which can only be an estimation as there is no temperature sensor). The iMOS that HobbyKing refers to is just their name for the 'operating system' in the charger (ie what you use to programme it for different uses).

 

I hadn't realised until reading your last couple of posts that you were using a 5 cell pack, in which case the 6.1 volts that you initially measured was definitely low, but as your receiver and servos will quite happily work on 4.8V packs I don't see why 6.1V would cause them a problem, unless that 6.1V was dropping substantially under the load of the servos. If that were happening, it could be down to the pack being discharged, or faulty, or a high resistance in one or more of the connectors between the battery and the receiver / servos, or the on/off switch....

 

Also, unless you specifically need to charge the pack in an hour I would set the charge rate rather lower than 2.1A. It's interesting that your charger only appears to have charged at 1.69A (your green square readout) not 2.1A. Also 8.8V is high for 5 cells... are you sure you didn't set the charger to 6 cells in error?

 

Brian.

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Quite possibly you did simply let it get flat. But, no, the suggestion was to try your servos when the RX battery is flat - and see if they chatter. Then charge it up and they should cease their chatter.

 

Assuming they behave this way, this would provide confidence in your suggestion that you simply let the battery become drained.

 

If they battery itself is also demonstrably in good health (by showing good capacity through a discharge/charge cycle as you have done) then I would not look further, or replace anything.

 

Right now you have shown the battery cells are healthy - but still have no proof of what caused the chatter, as you haven't recreated the fault.

 

 

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18 minutes ago, David Davis said:

Just checked. 5 cells

 

Ok, in that case something doesn't look right. The peak voltage of a 2000mAh Eneloop cell is between 1.55 and 1.60V, so five cells maximum peak should be 8.0V. If your charger peak voltage reading of 8.8V was correct then perhaps the 'extra' 0.8V may have been across a poor connection (plug/socket or wires, or within the pack itself). That may also account for the discrepency between the programmed and indicated charging currents (2.1A / 1.69A).

 

It would be a good idea to carry out the same check on your replacement battery, as a comparison.

 

I agree with your previous comments regarding the charger instructions by the way, they aren't the easiest to follow. I have attached a pdf copy in case you find it useful.

 

Brian.

109105740_HobbyKingX120.pdf

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1 hour ago, RottenRow said:

I've looked up the manual for that HobbyKing charger and the coloured squares that you refer to are Red = peak voltage attained during charge, Green = charging current, Orange = mAh that the battery has accepted and Blue (grey on yours perhaps) = battery temperature (which can only be an estimation as there is no temperature sensor). The iMOS that HobbyKing refers to is just their name for the 'operating system' in the charger (ie what you use to programme it for different uses).

 

Indeed. @David Davis, the manual (for what it's worth) is online here. Re: the temperature, unless there is an external temp probe (which some chargers do have) then it is probably the charger internal temperature rather than the battery.

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You are very lucky to get 1900 into an Eneloop at 2.1A. It must have been totally flat to start with which they do not like. By lots of experimenting I have found that 600mA (0.6A) is ideal for these. 1A max. for a quick top up.

26C is the theoretical discharge rate of the pack (really?), i.e. 26A for 1hr (it would melt at that rate) or 2.6A for 10hrs or 0.26A for 100hrs, none of which are likely to occur in real life because your pack is only 2A/hr to start with. The packs are supposedly only 2000mA/hr (2A/hr) anyway so I would buy a more realistic charger if I were you. A supposedly 2000 pack will give you a days flying at 200mA discharge rate which is 1/10thC which is quite high anyway. Thankfully not familiar with your current charger and prefer one which gives actual voltage/discharge/charge capacity such as one of the cheap Overlander range which will cycle a pack through discharge/recharge if you wish.

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Martin,

 

David (the original poster) didn't say that the 26C figure was the theoretical discharge rate, it's 26 degrees C and is the pack temperature, though as I mentioned earlier (as did Matty B) there is no temperature probe for the cells so it must be calculated using some algorithm and guesswork, combined perhaps with a thermistor inside the charger. Anyway the temperature can even be used as a cut-off limit if required, according to the manual (a pdf of which I included a few posts back).

 

David's charger does do the things you mention but the instructions are very poor and confusing. At the end of the charge it provides the usual data and a multicoloured line graph showing voltage, current, temperature and mAh on a timebase.

 

The wording in the manual is typical chino-English and raised a few smiles when I read it.

 

Brian.

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Sorry, it occurred to me after posting that it must refer to temperature, not capacity. Strange to use a probe on a NiMh though.

Does not solve the original problem of servo chatter although digital ones will do this because of the weight of the control surfaces which they constantly try  to keep at neutral; this is perfectly normal. If they continue to do so with the surfaces disconnected then there may be a problem.

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As there is no temperature probe I can't see any way that the temperature relates to the battery. Is it more likely to be the internal charger temperature? If by some magical means it does relate to the battery temperature then there wouldn't have been a fire when charging a Lipo. 

 

In my mind something does not add up.

 

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Early Bird

 

2 hours ago, EarlyBird said:

In my mind something does not add up.

 

Yes I quite agree. The charger instructions are pretty useless; they say the following (with regard to Cut-Off Temperature):  "Range of setting 40-80 degrees C, cut-off temperature, charger will stop charging / discharging when temp of batteries is lower than setting value" which is clearly wrong however (and wherever) the temperature is measured.

 

The charger "knows" how much energy it is supplying to the battery during a charge (volts x amps x time) so it could be using an algorithm to calculate the battery temperature. I can't see how it can be very accurate though, as it would depend on the state of charge of the battery, cooling etc. Anyway, there's no point in guessing here.

 

One must wonder how accurate these chargers are when it comes to other measurements. Not just the HK chargers, many others have poorly written instructions.

 

Brian.

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43 minutes ago, RottenRow said:

Not just the HK chargers, many others have poorly written instructions.

 

I can't write Chinese; wouldn't stop me producing something that worked though.

 

29 minutes ago, EarlyBird said:

The 8.8 volts reading is another issue especially when compared to 6.9 volt reading with a battery meter.

 

No, it isn't. DD took the 6.9V measurements whilst the pack was idle; they are irrelevant to our discussion here. Voltage during charge is always higher than when disconnected.

 

The fact that we expect close to 8V during charge is a concern, however, we do not know if there is a systemic error introduced by the charger (possible, if not particularly likely given the size of error). Hence my suggestion to benchmark the charger with a known good battery. Then we can establish whether the high voltage on charge is likely to be due to poor wiring in the pack.

 

3 hours ago, EarlyBird said:

 Is it more likely to be the internal charger temperature?

 

This.

 

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22 minutes ago, Nigel R said:

No, it isn't. DD took the 6.9V measurements whilst the pack was idle; they are irrelevant to our discussion here. Voltage during charge is always higher than when disconnected.

Yes I know that voltage is higher when charging but the voltage drops off slowly not immediately from 8.8 volts to 6.9 volts or have I got that wrong as well?

 

27 minutes ago, Nigel R said:

This.

 

?

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13 minutes ago, EarlyBird said:

Yes I know that voltage is higher when charging but the voltage drops off slowly not immediately from 8.8 volts to 6.9 volts or have I got that wrong as well?

 

 

?

 

I don't believe DD obtained the 6.9V figure immediately after charging completed. Happy to be corrected.

 

Cell voltage does actually drop very quickly, within a few seconds normally, to something close to its "resting" figure, which is 1.4V (ish) for nimh, and 5 cells x 1.4V per cell = 7V total.

 

1.2V (i.e nominal voltage) times 5 cells = 6V, will be measured when the cell is "resting" (i.e. no load) and fully discharged.

 

 

 

as for "this" - I agree, the 26C is most likely ambient temperature inside charger. Maybe if you connect a probe you get the probe reading instead.

Edited by Nigel R
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21 hours ago, David Davis said:

Thankyou for all of your advice gentlemen. Having cycled the model's battery, the chattering servos have stopped. I feel that I may have unwittingly allowed the battery to discharge too much and that was the cause of the problem.

 

DD, have you done any checks since you performed that first cycle?

 

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