Charger setting for Futaba Tx NiMH

[Alan]

Hi All i have just purched a new radio (futaba 8fg) but it has no wall charger and my old one is no good.

 

But i have a sigmaEQ charger and was wondering what would be the best setting to charger the battery 1700Mah NiMh.

 

Alan

[David Ashby - Moderator]

Hi Alan

 

1C or 1.7 amps will be fine on a fast charge and opinions seem to converge that NiMHs like a fast charge. I've got an 8FG and that's how I charge my 1700mAh pack. Lasts for ages too.

[Yobyid]

Hi Alan

My 8FG 'Wall Wart' is marked as 7.2V / 170mA and the Tx Futaba Battery as needing 170mA for 12 hours.

So it looks like 170mA (C/10) for starters - though you might be able to push the charge rate if the battery is removed from the Tx

Les

[David Ashby - Moderator]

Yes that's true I do charge the pack direct, not through the TX.

[Alan]

How long does it take to charge at 1C.

 

Alan

[PatMc]

Posted by Alan on 24/01/2011 21:47:34:

How long does it take to charge at 1C.

 

Alan

Just over an hour from fully discharged. Less if the battery's part charged already.

[Alan]

Got new radio today, tried battery in my Fusion battery checker completely dead, put it on charg at 1C(1.7amps) it charged for 7mins and took about 200Mamps.

Used radio it started beeping for low battery after 20mins put battery back in charger and it took the same length of time again 20mins about 200Mamps.

 

Am i doing something wrong or is the battery nackered or even my charger, charger works fine on LiPo's andNiCd

[Peter Beeney]

Alan,
If I may, this is the way I would see it. I’ve seen your sort of problem a number of times and in some extreme (and rare) cases it’s resulted in a crashed model due to a flat battery a short time after it started flying. There is certainly every chance you are not doing anything particularly wrong, quite often it seems that new Ni-MH cells can confuse fast chargers. And even the wall-socket types, too.

I’m afraid I don’t know anything about your charger so this may be a bit of a wild-goose chase in any case. To get 1.7Ah out you first have to put it in, so a full charge must consist of at least 1,700mAh. Is it possible you can set the charger to charge at say 100mA? And disable the automatic peak detection? Although at this low charge rate it’s it’s quite likely the detection circuit would be inoperative anyway. If so, then start it going and leave it for 24 hours. That’s around 2,400mAh. Then let it stand for a while, a day is good, two are better, and then do a test discharge. If possible at 1.7A, but I know many chargers have a max 1 amp discharge rate, if this is the case then it should run for 1.7 hours, or 1 hour, 42 minutes before reaching the end voltage of 8 volts. You should get fairly close to 1,700mAh returned, anything less than 1,530mAh, 10% down, and you should be at least asking questions, to say nothing of querying it with the supplier.

My charger, a Schulze, is always running in one form or another, there are always packs of some sort to check. I’m pretty familiar with it now and I know that even this can occasionally get cocked up, usually with new or dormant packs. The manufacturer states this can happen, and has built in a time delay to try and stop premature peak detect. One trick that I’ve found sometimes works, I stop the charge after a few minutes and start again. It then carries on and hopefully completes the charge but it’s by no means always successful. You have to keep an eye on what’s happening.

Is any of this any good for a start?

PB

[Alan]

just wondering what would be a good discharge setting for this battery and also cut off voltage.

 

also how often would you cycle your battery.

 

Alan

[Allan Bennett]

Although 1C charge rate (i.e. 1.7 amps for a 1700mAh battery, taking about 1 hour) is normal for high capacity power batteries, my understanding is that for AA size cells it's much better to charge them at 1/10C (i.e. 170mA for a 1700mAh battery) for a duration of about 14 hours. The slow charge rate doesn't harm the cells even if it continues after they're fully charged and, if any cell is lagging behind the others, it gives it the chance to catch up with the others at the end of the charge. So, a better-balanced pack results.

 

As for a new pack not taking anywhere near a full charge, with NiMh you sometimes have to slow-charge the pack (1/10C) a couple of times initially to "condition" it and to get it charging fully. Either that, or the pack was already nearly fully charged, so won't accept any more.

[Chris Bott - Moderator]

This is a very confusing area.

Last time I looked into this there was tons of conflicting information.

The general consensus however was that 1/10C charging, and especially continuing past full, is BAD for NiMh's. Virtually all the rechargeable AA's available now are NiMh's.

 

1/10C was perfect for NiCads. They could absorb any overcharge at this rate so if one cell was lower than the rest, they would automatically balance while the full cells just dissipated the extra as heat.

 

But apparently this overcharging can damage NiMh's.

So bear this in mind when using a slow charge, especially if the cells get warm at the end.

As I understand it, a 1C charge with the battery out of the transmitter is MUCH better to keep NiMh's in good condition for a long life.

 

[Alan]

I understand that 1C charge is good for them. But what about when you cycle them what would be a good value for discharge and also voltage setting.

 

Alan

[Martin Harris - Moderator]

Don't know if it's best practice but I usually discharge at 1/3 C and cut off at 1V per cell

[Tim Mackey]

I'm with Chris Bott on this one

And, Martin has it right on the cycling thing, although the discharge rate is not that critical, I use anything from around .25C up to 1 C

[Allan Bennett]

Posted by Chris Bott on 02/04/2011 09:41:58:

This is a very confusing area.

Last time I looked into this there was tons of conflicting information.

The general consensus however was that 1/10C charging, and especially continuing past full, is BAD for NiMh's. Virtually all the rechargeable AA's available now are NiMh's.

 

1/10C was perfect for NiCads. They could absorb any overcharge at this rate so if one cell was lower than the rest, they would automatically balance while the full cells just dissipated the extra as heat.

 

But apparently this overcharging can damage NiMh's.

So bear this in mind when using a slow charge, especially if the cells get warm at the end.

As I understand it, a 1C charge with the battery out of the transmitter is MUCH better to keep NiMh's in good condition for a long life.

 

 

Interesting. It seems to depend on which forum you read. But, the common factor on which we seem to be agreed is that overheating is bad for NiMh -- as it is for any battery. I believe the distinction between AAA, AA, and larger cells is that the larger ones are able to dissipate heat better, so can handle a higher charge current without warming up.

 

My understanding is that NiMh cells can take a small current passing through them after they're full, just as you've described for NiCd and, after many years of charging my Tx and Rx packs overnight at 1/10C or less, I have never experienced any warming. Indeed, with my larger cells (sub-C size, 3300mAh), which I usually charge at 1C, I have sometimes slow charged them to bring them back into balance and restore, to a certain extent, their oomph.

[Tim Mackey]

Here is a source of pretty reliable info, and despite the slightly corny "company name" the info is generally regarded as sound.

 

Heres an a extract from their take on charging NiMHs.

"NiMH cannot absorb overcharge well and the trickle charge is set to around 0.05C. In comparison, the older NiCd charger trickle charges at 0.1C, double that rate. Differences in trickle charge and the need for a more sensitive full-charge detection render the original NiCd charger unsuitable for NiMH batteries. A NiMH in a NiCd charger would overheat, but a NiCd in a NiMH charger does well because the lower trickle charge is also sufficient for NiCd.

It is difficult, if not impossible, to slow-charge a NiMH battery. At a C‑rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer. Harmful overcharge will occur if a fixed timer controls the charge. This is especially apparent when charging partially or fully charged batteries".

 

Hope that's of interest /help

[Peter Beeney]

If I might join the general melee for a moment can I say that I’ve never seen any evidence of harm done to hydride cells by slow charging, and that includes wall socket chargers, or yet read about about it, other than in aeromodelling literature. Strictly speaking, I think the term, - trickle charging, - is something else. A standard charge, from flat, would be C/10 for 15 hours, that’s 150% of Capacity; but this of course may well depend on having the right equipment to be able to do this. Likewise, a standard discharge would be a C/10 rate, down to an end voltage of 1V/cell; the same caveats applying. This would be the de facto charge/discharge test, if a pack failed at this rate it would fail any test! When I sparred about with this stuff for real, the standard charge set by the Company was 160% of capacity. To ensure the battery was fully charged to start with.

Ni-MH cells can be difficult, they sometimes seem to have an artificially raised internal resistance, which can seriously confuse the issue. Also the quality can vary greatly, as I’ve said before, from excellent down to packs that would be considered useless as second grade rubbish at the local tip…. … Well, perhaps that’s a little bit of an exaggeration, but you get my drift.. And to complicate things further, this often includes new packs, too.

More or less any reasonable discharge rate will do, as long as you get the requisite of milliamp hours out. If it’s less than about 10% down on capacity, carry on flying! At 10 - 15% down, carry on but you need to remember your pack is slightly reduced. More than 15%, and you have to consider what to do. Personally I would go lower than that, but I would always be well aware of the circumstances. The battery won’t suddenly completely fail, it only appears to do this sometimes because no one is aware that it’s faulty anyway.
Concerning discharge rates, the faster you discharge it, the less, proportionally, you get out. A Law of Diminishing Returns. But that’s a subject all on it’s own.

Cycling the packs. Again, for me, it’s just a personal thing, I never do it, I consider it just wears the packs out, but many people seem to swear by it, so you take your pick. In all the experiments, years ago, I was unable to get any results on cycling cells.

All in all, I reckon a sound battery will stand quite a lot of ‘varied treatment’ so within reason you can do what you like and get away with it. Modellers do tend to do that.

Tim, I have read Isidor Buchmann, of Cadex, before, long ago. I believe his book, Batteries in a Portable World, is quite expensive. It was back then, anyway! If you also read other authorities though, you tend to get a different picture. Again, really a case of just taking your pick.

Putting my ever-ready cynical hat on, I’ve said many times before I’m convinced the Trade in general is not fussed about a little bit of confusion here and there. So if in fact the odd perfectly sound pack or three are occasionally thrown away by mistake not too much sleep is lost.

 

Something along these lines…
A short while ago a pilot was cursing eBay. A new battery, which he’d just bought thereabouts, was showing completely empty on his brand new model with a battery monitor. He was about to bin it. So I took it home. It’s a 4 cell, AA size pack, standard green heatshrink and a very basic computer printer written label, Power Zone 2000. That’s it. No wrapper or instructions. Compare that to Lipos! I assume it’s meant to be 2000mAh capacity, I found his charger had partially charged it but a definitive bashing yielded a steady 1400mAh. So, not by any means in the excellent bracket, but not a rubbish tip reject either. No signs of any faulty single cells, so eminently serviceable, now with a known capacity of 1400mAh; plenty for a 46 size sport model; and so I notified him to this effect. I had an email from him this very morning saying that he’d tried another pack and now he’s going to throw the monitor away, except that he’s sealed it under the canopy!?!* My reply will be ‘Hang on a minute, lets prove that for sure.‘ I’ve met double coincidences before.

When I get a couple of minutes I’ll post a photo of a recent tx pack discharge curve, which is quite interesting. Also I’m sure there are cases of cells being ‘trickle charged’, but that might be a separate debate.

PB

[Chris Bott - Moderator]

There certainly is a lot of rubbish spouted by modellers about batteries Peter.

 

Some years ago I witnessed a club examiner talking about his models on board battery montor. You know the type, cheap little thing with a few green and a few Red LED's in a row. His comment - "These battery monitors are rubbish, every time I move a servo it dips right down to the bottom red. I know this battery is fine 'cos I just charged it".

[PatMc]

Posted by Alan on 01/04/2011 23:25:32:

just wondering what would be a good discharge setting for this battery and also cut off voltage.

 

also how often would you cycle your battery.

 

Alan

Don't bother about the discharge setting let the Tx do it at the current that the battery will be working at.

Best way to cycle a Tx battery is to first fully charge the battery. Next switch the Tx on, zero the timer & be prepared to wait several hours until you hear the low batt alarm - watch TV build a model or whatever.

Instead of the battery capacity in mAH you will now have something more useful i.e. the actual time you can expect from the battery doing it's job. Recharge at either a max of 1A (700 - 800mA would be better) with the battery in the Tx or at 1C outside the Tx. Personally I do it 700-800mA in the Tx.

How often ?

Only ever if the Tx hasn't been used for a while or if the duration seems down. The low batt alarm gives plenty of warning if there's a problem so it's not as critical as an Rx battery. Contrary to some tales nimh's don't die to nowt within seconds of the alarm. I've tested this on FF7 & FF8's & found that I could still do a full range check for 20 minutes from the alarm sounding before I got bored.

[Alan]

Thanks for all your replies.... got alot of usefull info.

 

Alan

[Allan Bennett]

Thanks for the link to The Battery University, Tim.

 

So, it seems like the chargers we get with our radios may be a compromise between getting an overnight charge, and prolonging battery life, since all the ones I have are rated for 1/10C. Since I never run my packs down beyond about 70% remaining, an overnight charge at 1/10C is far too long, and may be damaging my packs, according to The Battery University. Maybe I should start using my old 50mA charger, which came with my original Futaba when battery capacity was 500mAh, instead of the 150mA one which came with the 1500mAh packs in my latest radio.

 

Or perhaps I'll just not worry, and live with having to replace my packs after 300 cycles instead of 350-400 In fact, I do monitor my packs, and discard them when their capacity and/or charge-holding capability are reduced, so cycle-counting is a waste of time too!

I agree, Chris, it is confusing. I just hope that Alan is not put off.

[Former Member]

[This posting has been removed]

[Lazygit]

Posted by Chris Bott on 02/04/2011 14:53:09:

Some years ago I witnessed a club examiner talking about his models on board battery montor. You know the type, cheap little thing with a few green and a few Red LED's in a row. His comment - "These battery monitors are rubbish, every time I move a servo it dips right down to the bottom red. I know this battery is fine 'cos I just charged it".

I had a similar thing happen. I changed the switch. Problem solved.

[Alan]

I agree with Allan thanks for the link to the to The Battery University, Tim.

 

also Allan definitely not put off just so much to learn in this hobby.

 

[Peter Beeney]

Those battery monitors can sometimes be a bit tricky to understand, I think the scale can be a little bit over expanded. Calibrating with a voltmeter does help. They can also go faulty, I’ve seen one or two. A good mate once said, “Have a look at my battery Pete, it won’t go flat!” I replied that I would rather look at his monitor. Sure enough, it was stuck on the top green, whatever voltage was applied. He was a lucky lad, no harm done. That just about sums it all up really, a device designed with some safety aspects in mind defaults to a Safe condition on a fault! At the very least it should default to an Alarm condition, the bottom red led. However, this may help to justify my previous cynical complex! I think my same line of reasoning may apply in this case, too.

I think my advice, just for what it’s worth, might be to check your battery from new, new packs can definitely contain problem cells, I know this for a definite fact, and then inspect it from time to time thereafter. By which ever way you choose. Same with charging, provided it’s not constantly undercharged it’s possible more or less anything goes within reason, I’ve found them to be quite hardy. Mine, for whatever reason, seem to last quite a long time. Maybe I’m just lucky.

Think I’d better put the 2V on charge, looks like a good day tomorrow……

PB