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rx battery levels and check

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Phil 913/08/2017 06:54:30
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I have one 2600mAh NiMH 4 cell battery in my acro wot to power the rx and servos.

I have two testers

one a good day I can get in 10 or more 1o min flights and I worry about the battery getting to low, although these give me an indication I don't know what is a reasonable level to stop at.

trebor13/08/2017 08:32:15
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Watching with interest, I tend to install a voltage meter inside the plane then operate as many servos as I can at one time and check the voltage stays above Rx low voltage level.

Not sure what else to do, some of my mates install a charge socket on the fuselage that makes top up charging possible without taking plane to bits between flights.

Denis Watkins13/08/2017 08:44:53
2120 forum posts
108 photos

Phil, I never fly on when the green drops two increments, it is then the field charger comes out and tops up back to full.

Your Lipo checker on the right of the picture, is totally unreliable with the Nimhs

The load tester on the left is the one to use, and approximately every 3 flights, check for a drop, and at two lights field charge back to full.

This is just a safe margin, and not anywhere near flying to destruction

Brian Spearing13/08/2017 08:55:37
32 forum posts

The Fusion checker is way out on %age, but mine is accurate for voltage. I used to use the red button jobbie but nowadays get voltage info and warnings by voice while flying. Voltage is logged, so battery behaviour can be checked if needed. 

 

 

 

 

Edited By Brian Spearing on 13/08/2017 08:59:49

John Lee13/08/2017 09:21:52
441 forum posts
31 photos

There is steep drop off at about 4.6v so don't approach that. I find the best way is to measure what you put back in after a day's flying with a decent charger. We used to fly all day on 500mah NiCds so with 5 times that capacity you should be OK.

Phil 913/08/2017 09:47:03
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Posted by John Lee on 13/08/2017 09:21:52:

There is steep drop off at about 4.6v so don't approach that. I find the best way is to measure what you put back in after a day's flying with a decent charger. We used to fly all day on 500mah NiCds so with 5 times that capacity you should be OK.

but did you have mini digital servos? using the button checker I seem to be in the yellow after only 3 flights hence my worries. the battery is new and a replacement as i worried it may be a battery fault but similar results with two different and new batteries would suggest not

John Lee13/08/2017 09:55:19
441 forum posts
31 photos

If you are using the majority of 2600MAh in 30 mins it suggests that either you are pulling the best part of 5amps so something is wrong with the setup or there is a battery/charger/checker fault.

No, we did not have mini digital servos in the Acrowot at the time but our Futaba 128 servos did the same work.

Ben B13/08/2017 10:25:02
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Voltage at rest is a terrible indicator of capacity because there are so many unknowns (capacity, current draw). The usual trick is wiggle the servos and if it goes "low" then stop flying but as you've said define "low"- how lucky/unlucky do you feel? A safe voltage and voltage drop will depend on servos, flying style, battery pack etc.

Thankfully generally speaking all these things will be consistent for a given plane.

When a plane is new I usually tend to do a few flights each day, gradually increasing as I get used to the plane. At the end of each flying day I measure the voltage (at rest and with stick wiggling) and then check to see how many mAh I put back into the battery with the charger.

It would of course be possible to do all this using a chargers discharge function before the first flight.

You can then work out an approximate chart of volts (at rest and with wiggling) for given capacity.

Another thing to consider is that you need to worry not only about running out of capacity but also volts dropping under load to below brown-out voltage (less of a problem with modern receivers).

In cold weather you need to be a lot more cautious.

I tend to just put a charging port on my planes and fast charge between flights with an occasional volt check for peace of mind if I worry I've been flying more than usual.

Chris Bott - Moderator13/08/2017 10:36:26
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Are these 2600mAh batteries AA types by any chance? If so, then that may be the issue.
The higher capacity AA nihms are generally only any good for use in low current applications.

To get the capacity in such a small can, they have to use really thin materials which has quite an affect on things like internal resistance.
Engine Doctor13/08/2017 11:15:50
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1812 forum posts
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I never use NiMh AA batteries over 2200 may  due to voltage drop they suffer under load . I have also found that the higher capacity AA are more fragile and likely to fail if dropped or used in harsh environment . I f extra power or duration is needs then I use either sub C cells or two 5 cell packs with a diode in circuit . Always test under load as simple voltage check is no indicator of state of charge .

trebor13/08/2017 11:22:01
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1293 forum posts
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Posted by Phil 9 on 13/08/2017 09:47:03

but did you have mini digital servos? using the button checker I seem to be in the yellow after only 3 flights hence my worries. the battery is new and a replacement as i worried it may be a battery fault but similar results with two different and new batteries would suggest not

Are you running a stabalized Rx or any of your servos buzzing at the end of servo arm movements ?

Peter Jenkins13/08/2017 14:31:22
944 forum posts
32 photos

I have checked this on several occasions with checking the charge going back into my Rx battery which is a 2 cell LiPo of 800 mah capacity run through a voltage rectifier to give either 5.9 or 6.1 v to the Rx and servos.. I fly F3A and the current FAI P schedule results in a consumption of 85 mAh per 8 min flight. I used to fly 3 flights and change the Rx battery but I am now confident enough to fly 4 (occasionally 5 flights if not flying a schedule) with the same Rx battery. That equates to around half the available capacity of the pack.

I use 5 digital servos in the model which is a 2 mtr class model weighing 5 Kg. There is very little stick banging but a lot of small movements most of the time during manoeuvres. There are 17 manoeuvres plus landing and take off per flight.

On a petrol model I have now standardised on using 2500 mAh LiFe batteries for Rx (and servos) and the ignition. I feed this directly to the Rx and to my JR servos which are perfectly happy with the top voltage of, usually, 6.6. The JR servos are not happy with a 5 cell NiMh as their voltage fully charged takes them over 7 v.

Hope that helps.

John Stainforth13/08/2017 15:00:30
98 forum posts
30 photos

I have charger/sockets on all my i.c. planes and check the voltage of the Rx batteries (all NiMH) before every flight, with a load-testing voltmeter. Takes all of five seconds! When fully charged, the batteries are way above their nominal voltage; I seldom run them down below their nominal voltage. I check the batteries in this regular way, not just to see whether they have enough charge for the next flight, but to get to know their behaviour as the charge is withdrawn.

I have never had a plane fail through lack of battery charge.

Phil 913/08/2017 15:27:51
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4109 forum posts
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Posted by John Lee on 13/08/2017 09:55:19:

If you are using the majority of 2600MAh in 30 mins it suggests that either you are pulling the best part of 5amps so something is wrong with the setup or there is a battery/charger/checker fault.

No, we did not have mini digital servos in the Acrowot at the time but our Futaba 128 servos did the same work.

the only reason I mentioned mini digital servos was because I read that they can use more power than a standard analogue servo.

so today I got 4 good flight is before the battery checker went out of the green (according to the manual this indicated a recharge is needed) the voltage sill said 5.3v

it is a 4 cell AA pack

Phil 913/08/2017 15:35:05
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4109 forum posts
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some great posts and lots of info here. gathering from above I either have a faulty servo somewhere or this type of large capacity AA pack is just nor suitable for my use.

I did do one flight using a 1100mAh LiFe pack and my B6 charger showed 86 was needed to charged back to full. If this means 86 mAh that would indicate about 10 flights worth of capacity and shows my NiMH is not suppying it potential? (Maybe)

Phil 913/08/2017 15:39:11
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4109 forum posts
194 photos
Posted by Peter Jenkins on 13/08/2017 14:31:22:

I have checked this on several occasions with checking the charge going back into my Rx battery which is a 2 cell LiPo of 800 mah capacity run through a voltage rectifier to give either 5.9 or 6.1 v to the Rx and servos.. I fly F3A and the current FAI P schedule results in a consumption of 85 mAh per 8 min flight. I used to fly 3 flights and change the Rx battery but I am now confident enough to fly 4 (occasionally 5 flights if not flying a schedule) with the same Rx battery. That equates to around half the available capacity of the pack.

I use 5 digital servos in the model which is a 2 mtr class model weighing 5 Kg. There is very little stick banging but a lot of small movements most of the time during manoeuvres. There are 17 manoeuvres plus landing and take off per flight.

On a petrol model I have now standardised on using 2500 mAh LiFe batteries for Rx (and servos) and the ignition. I feed this directly to the Rx and to my JR servos which are perfectly happy with the top voltage of, usually, 6.6. The JR servos are not happy with a 5 cell NiMh as their voltage fully charged takes them over 7 v.

Hope that helps.

your 86mAh from the lipo seems to match the power I drew from my LiFe pack today. Do you estimate the same usage from your LiFe pack

Phil 913/08/2017 16:13:08
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4109 forum posts
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my battery woes started a while back **LINK** the 2600 pack was recommended to me to replace my 2000mAh eneloop pack.

I guess I have a few options. continue with the batteries I have and charge at the field every 3 or 4 flights.

use LiFe packs and estimate the number of flights for each pack.

or use lipo's that I can measure the capacity left with relative confidence but I would need a voltage regulator.

The fact I can measure the lipos for me would be a big bonus and I think I will go down this route.

trebor13/08/2017 17:37:29
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1293 forum posts
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That's ok if you can take the lipos out easily, most of my batteries are buried where the sun don't shine and very rarely come out.

gangster13/08/2017 18:00:48
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703 forum posts
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So many things that give a digital readout are taken as absolute gospel. Those meters that give a % readout are no use for the discharge characteristics of a nimh. It's akin to someone feeding you sweets out of a tin. They all taste the same right to the end but you have no idea how many are left. Most batterys must be tested on load. Probably the simplest way is to fit a cheap and cheerful monitor e.g. Tower and waggle all the sticks for a few moments Once it is getting tired those leds will start going into the yellow. I do not trust so called high capacity  nimh batterys. As have been mentioned on this and similar threads we were better off with 500mA/hr nimh AA cells. 2500 mA/hr from an Aa cell well quarts and pint pots come to mind Also I don't know what the figures are for NI MH cells but A/hr ain't what it says on the tin in practice i.e. Don't expect to draw 100 amps for an hour from a 100Ah lead acid half that is more like it in practice

 

Edited By gangster on 13/08/2017 18:05:21

Phil 913/08/2017 18:34:48
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4109 forum posts
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ganster do you mean one of these?

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