Nominal discharge rate for Ni-Mh testing.

[John Wagg]

I want to test a 4.8 Ni-Mh battery but I have no idea of what discharge rate to set.

I have just guessed at 300mA but is that enough for a 4 channel radio set-up. ? 

Any advice appreciated.

John

 

[Paul De Tourtoulon]

I would set it for at least 600 mah, but then again it depends on the type of battery, AA,  sub C etc, servos, plane weight, size and speed and the type of flying that you do,

this is like how to run an engine in, are you ready for ten pages ?.

Edited September 28, 2022 by Paul De Tourtoulon
another 10 pages

[John Wagg]

Thankyou Paul. 

Battery is AA - 2600 mA. 3 year old.

I could imagine moving 3 servos at the same time and the receiver would also have a current draw.

The other question would be at what voltage do I stop the discharge. At the moment I have set 4.5v as a limit.

[Don Fry]

I assume, (make an ASS of U and ME).

1. That its Wot 4, Pupiteer, even up to a 5 kilo slow thing with standard analogue servos of the 3001 type. 
Then I would be looking at it supporting 300 to 500 mHr for an hour.

Rational, that’s what that sort of servo uses. An hour covers 5 flights. Therefore the setup will fail at some other point.

 

Digital, hi torque, bets off. 
Why are you wanting to test it. Because it’s good practice to test periodically, or not a trusted battery.

[John Wagg]

Thanks Don.

Flying a vintage (3 channel, analogue midi size servos - R,E,Th ) last weekend at Cocklebarrow. I had 4 flights and my Tx reported a low Rx battery of 4.7v so decided to curtail flying for the day. The reading of the battery showed 4.8v but on moving a stick it dropped to 4.7v so decided not to risk a lost model.

I would have expected the battery to have lasted longer so just want to do a check on it's capacity.

i have just put the battery on discharge at 600mA assuming the tester is reasonably accurate.

I'll report back.

John.

 

[Andy Gates]

John,

 

Why not get a receiver pack load tester?

This will do the job of telling you if the pack is OK under simulated load.

Something like this

[Frank Skilbeck]

John, how are you charging the battery, with a standard wall charger or a smart charger. If it's the latter and you set the charge rate too low it can give a false peak which the charger interprets as fully charged.

[Don Fry]

Right, as Paul said, expect 10 pages. If the pack is good, I would expect, from a Junior 60, to a Falcon, that the discharge is no more than 50/70 mAh per flight. I Assume, note the word, deckchair, tranni, beer in other hand.

4 flights, it’s not charged, it’s knackered, your charger is knackered.

One observation, back in the day, aircraft landed, in one piece, same field to takeoff, that was a total success. Now we have telemetry. And I’m not sure, if a momentary drop to 4.7V is bad. I know, I’ve scared myself, operating a hooligan machine with seven digital HV jobbies going end to end, LiPo batteries, when the nice posh lady starts wailing about her lack of volts. Others might say is a momentary drop is bad. 

[John Wagg]

1 hour ago, Andy Gates said:

John,

 

Why not get a receiver pack load tester?

This will do the job of telling you if the pack is OK under simulated load.

Something like this

Hi Andy.  I have one of those but the drawback is it won't tell me how long is left in the battery. 

Because of the general flat discharge curve there is a chance of being near the bottom end of it's capacity.

On a good day I can be up for 20 minutes easily on any flight.

Cheers

John

[John Wagg]

1 hour ago, Frank Skilbeck said:

John, how are you charging the battery, with a standard wall charger or a smart charger. If it's the latter and you set the charge rate too low it can give a false peak which the charger interprets as fully charged.

Hi Frank, I have both a smart charger and an old charger that gives a constant 50mA output. Normally I would use the smart charger.

That is another quandary at what level should the charger be set ?  Charger is currently set at 1.7 Amp.

cheers.

John

 

[John Wagg]

Thanks all for the input. Old days with Ni-cads was just charge at 50mA for 14 hrs and fly all day up on the slope.

Not sure about Ni-Mh cells. Especially when they are said to be 2600mA capacity compared with the old 500mA Ni-cad'.

Still doing some testing but just needed a bit of guidance on real world experience etc.

Regards

John

 

[Andy Gates]

John,

 

Charging AA sized NiMH cells at 1.7A is way too high and will cause the charger to cut off early.

I would cut that by at least 1/3, normally for me I use a dedicated slow charger to charge my buddy box transmitter and receiver pack.

[Paul De Tourtoulon]

I have a couple of these, they are really brilliant, use them to charge or discharge or cycle them and watch the current drain and charge while using it will tell you all you need to know on the state of them, you can pick them up on the cheap.

[Don Fry]

John, capacity, and ability to deliver power are not related. If I wanted a battery to power a radio, a small cell (AA) NiMh would suit very well. 
An aircraft, panic moments, sticks to corner, not too sure.
Fit a C cell pack, same panic, no nice Lady going on about volt shortages.

But even so, your machine will be happy with any pack that is in reasonable condition.

[John Wagg]

1 minute ago, Andy Gates said:

John,

 

Charging AA sized NiMH cells at 1.7A is way too high and will cause the charger to cut off early.

I would cut that by at least 1/3, normally for me I use a dedicated slow charger to charge my buddy box transmitter and receiver pack.

Thanks Andy. I will reduce as per your suggestion and see what happens.

I have other packs and will see if I can do a comparison.

Cheers

John

[Frank Skilbeck]

Yep, I agree with Andy I usually set the charge rate around 1/3rd C, so on a 2300 mah pack that would be 0.7/0.8A. I would also cycle the pack a few times, say set the discharge current to at 0.6A with a 4v cut off then recharge. Do this 2 or 3 times to see what the cells recover to.