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Ni-MH Charging - Help Please!!!

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Allan Bowker01/01/2009 21:25:00
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Summary:

Fusion Elysium LX60B Charger
8.4v Ni-Mh Battery 1000mAh (7x2/3A)
Wild Hawk Plane - 380 Motor (EasyStar copy : http://site.wonderhobby.com/wildhawk.JPG )

Problem:
Battery lasts for 5 minutes and I don't think I'm charging the battery correctly.

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Well Santa, eBay and the local model shop gave me lots of goodies this Christmas and with it a few questions.

For 15 years I have flown Nitro planes and have started to have a dabble in the electric world and need some help with my new "Fusion Elysium LX60B" charger (£80) and a new battery pack.

The charger asks me "C=?" basically what the 'charge current' is for the battery that I am connecting.
Do I put 3.0A? (C=3.0A) as at the moment on this setting the battery charges in 4-5 minutes and only lasts 2-4 mintues in the air on a 380 motor, 2 mini servo's and a Spektrum AR5000 receiver.
Surely I should be getting 10-20 minutes?

Can someone help me out please?

Ultymate01/01/2009 21:32:00
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Allan try charging it at a lower rate say 1 amp sometimes when charging nihms at a high rate the charger senses a false peak and stops the charge prematurely also some packs take a few cycles to form and come to their best. I'm sure someone with more knowledge of the old electrickery will chime in shortly as I'm basically a petrolhead at heart
Tim Mackey01/01/2009 21:57:00
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Pretty well right though old petrol head

Charge at approx 800 - 1000m/a for a 1000m/Ah battery.

Why were you using 3A ?

Allan Bowker01/01/2009 22:50:00
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Thanks Timbo, I knew you could help.

I was charging at 3A for 2 reasons.

1) I don't know what I'm doing

&

2) It said 3A on the side of the battery.

 
So what setting do I set the charger to then? 0.8A ?

How can I work out what charge rate to set my batteries at?
I can't keep asking you now can I Timbo?

I have Ni-Cd / Ni-Mh / Li-Po / Pb batteries.

Frank Skilbeck01/01/2009 23:06:00
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You can fast charge NiCd and NiMh batteries, aim for about 20mins, so that would be 3C, so fast charging a 1000mah battery at 3A is OK for fast charging at the field, but it's probably better to charge them at less than 1C to condition them to begin with. Charging in 5mins at 3A means you are only putting around 250 mah into the battery. NiCd's and NiMh's usually get a bit better after a few cycles.

The cold weather won't help neither and the battery won't give it's best, try running it down at say 1/3rd throttle in the garage and then charging at <0.8A for a few cycles and see if that gives any improvement.

Lipo's should never be charged at more than 1C, i.e. a 1000 mah cell at 1A, 2000 mah at 2A etc.

Pb you should use around 1/10C.

Make sure your charger is set for the correct battery, i.e. Lipo on lipo and correct number of cells, NiCd on Nicd etc.

Tim Mackey02/01/2009 10:07:00
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Can't top what Frank says really ...other than one small caveat....some NiMh cells do NOT tolerate charging at 3C, but these  will usually say so on the label. As Frank said in his earlier post, it was probably the delta peak detection system of the charger which stopped the charging early at 3A.

Delta peak chargers can be a little tricky to get right for every potential type type of nickel cell available.....some cells peak early, some late, and the tiny voltage drop that then occurs is sometimes not detected correctly by the charger. Charge too fast, and it peaks too early, charge to slow and it simply doesnt detect it at all, and continues forcing in the juice.  If you use a very slow trickle rate, then most nickel cells will be OK left on charge for a long time....days or more even. However, if using anything higher than very low trickle current, you MUST either ensure the charger is working correctly and peak detects at the correct time, OR remove the battery from charge.

NiMh exhibit poor peak detect "symptoms" compared to NiCd, which is why a charger specifically designed for NiCd ( such as many wall wart type chargers ) are NOT suitable for NiMh.

Nickel cells do NOT tolerate overcharging and heat will increase proportionally, and could in some situations even lead to cells "venting" - sometimes quite violently and noisely !!

If you feel like a read maybe I can link you to an article I did in the mag recently, about chargers.

Shameless plug over....( 4mm gold of course  )

Allan Bowker02/01/2009 14:02:00
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Thanks to Timbo & Frank

Last night I printed out the articles  "Battery chargers demystified" and "Electrickery demystified" and read all 22 pages. Probably about half went over my head but I will keep revising the pages until over time I understand (probably over 2 years!).

Newbie Tip:
Standardise all your plugs and connectors to 4mm Banana plugs/sockets!
I wish I had earlier and will be doing so soon. 

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So as far as I understand it (please correct me if I am wrong), it's best to charge at 1C for all my batteries (1C being 1000mAh = 1.0A  on my charger setting) whilst I'm getting to grips with it all.

I charged my two 8.4v 1000mAh Mi-Mh last night at 0.8A and they both took about an hour give or take 5 minutes either way. I'm going to try them out today, weather permitting.

Therefore:
Pb             12v   7000mAh     = Charge at 0.7A (one tenth 1C)
Li-Po       7.4v      800mAh     = Charge at 0.8A (1C)
Ni-Cd      8.4v      600mAh     = Charge at 0.6A (1C although can be charged at 2C)
Ni-Mh      8.4v    1000mAh     = Charge at 1.0A (1C although can be charged at 2C)

Obviously I would set the correct battery type on my charger & connect the balance leads where appropriate. Is this OK? Should I be let loose yet?

Tim Mackey02/01/2009 14:57:00
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Full marks sir - get off the naughty step and go play!

( although of course when you charged your 1000 mAh nickels last night at 800 ma that was bit below 1C )

Charging lower than 1c will not harm them, so long as the charger correctly detects the delta peak voltage drop-off. There is much talk that charging any cell at lower rates is generally kinder to them as less heat builds up for one thing.

Watch out for an upcoming imminent article or two on "everything batteries" in the mag

Allan Bowker02/01/2009 15:01:00
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Thanks Timbo.

I subscribed a few weeks ago by Direct Debit, so will look forward to your article in the mag.

Tim Mackey02/01/2009 15:27:00
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I never said it was by me
Allan Bowker02/01/2009 22:27:00
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Well I had a successful flight today with the Wild Hawk.

It was a bit blustery for the lightweight and underpowered foamy but it all ended with good landings and all on one battery (with power to spare!).

So it looks like the charging is going well now, thanks again for your help guys.

 

I'm all charged up now for all batteries except for one, the Sealed Lead Acid battery (Pb)
It's a Yuasa NP7-12 (12v 7Ah)


Pb is selected on the charger,  set to 0.7A and it charges for 1-3 minutes and then finishes, sometimes with the message "Open Circuit". The manual explains that the battery has become disconnected but the connections are 100% and contacts are clean and checked with a multi-meter. Tried about 8 times to charge it now.

The wall wart charger is rated at 12v 0.9A output (I have tried these settings on the charger) and it still only lasts for 5mins max.

The only conclusion I can come to is that the battery is charged, although it was used last month for a good days Nitro/IC flying. The battery is new, purchased in July. Comments welcome.

http://www.mdsbattery.co.uk/images/products/Fullsize/NP7-12.jpg

Tim Mackey02/01/2009 23:53:00
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What open circuit ( unloaded ) voltage do you read across the battery terminals?

Full, it should show around 2.4 per cell ( so 6 cells = 14v+ )

It could be full, or simply goosed.

I find that these SLA batteries dont last too long, especially if they have been abused through overcharging, fast charging, or allowed to drop to low and left "empty"

Eric Bray03/01/2009 00:19:00
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I suspect they are burglar alarm type batteries, and while supposedly capable of delivering 7 amps, can only do so for a short while, because the gel electrolyte begins to boil, and then it dies!

My purpose-made motorbike wallwart charger delivers a mere 300 milliamperes, switchable between 6 or 12 volts, and the lead-acid battery is a 7ah thing.

Allan Bowker03/01/2009 14:02:00
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I'm reading 12.5v at the moment on my meter and the battery charger reads 13.8v

I think I will have to play it by ear and see how it goes with the battery.
What flight box battery would you recommend guys?

Tim Mackey03/01/2009 14:58:00
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Off load and disconnected what does it read?

Lithium

Frank Skilbeck03/01/2009 16:54:00
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I use one of these for my flight box battery and it's been fairly good, had it about 4-5 years now. I charge it off a standard wall trickle charger and it seems to work OK.

I've even used it to recharge my 3200 mah 4s lipo's at trhe field but I can't quite get two batteries fully charged before the charger warns of low input voltage.

But it drives my IC power panel and starter fine (max engine is a 90FS)

Frank Skilbeck03/01/2009 16:58:00
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On a separte topic of Nimh charging, I have 3 chargers a couple of propeaks and a turnigy. The Turnigy always cuts off soon when charging Nimh cells (even when doing a discharge/charge cycle) whereas both propeaks seem to put a lot more in.

I can only guess this is to do with the peak volt detection, this is adjustable on the Turnigy, are there any guidelines for setting this?

Tim Mackey03/01/2009 18:57:00
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Frank.... I usually set it at around 8mV for NiCD, and 4mV for NiMH.

Can you disable / set a delay peak detect action on your charger?

My rather clever 1010B+ allows you to set a delay of up to 30 minutes on the nickel charge programs, to avoid these false detects, which can exhibit themselves in packs which have been left standing discharged too long, or were very deeply discharged in use. As long as the charge current is not set too high, even 30 minutes without peak detect is safe, and allows the charger to pump in sufficient juice to get the packs back up to "normal" levels.

Frank Skilbeck03/01/2009 19:31:00
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The Turnigy is not that clever, but I'll try changing the setting and see what that does.
Bert03/01/2009 20:38:00
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In my experience those SLA batteries will die if allowed to go flat for too long. They also don't like being overcharged because the electrolyte boils away and topping up is not straightforward.

They can be topped up by prising the plastic cover off the top with a screwdriver

They aren't 'gel' cells by the way, if you prise the top off you will find that it is conventional water and acid, they don't leak because the top of the cell has a spigot with a rubber 'helmet' on it. When the cell needs to vent the rubber helmet allows the gas to go by but not the acid - so long as you don't have the battery on its' side  or upside down

Bert

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