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HelicopterMain Discussion › Cycling NiCd/MH Battery Packs
03-19-2009 05:52 PM  8 years agoPost 1
nnonname

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Great Lake State

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I'm cycling a 4.8v 2700 mA NiCd/MH battery pack in my Raptor 30. The Accu Cycle Elite charger defaults to a discharge cut-off of 1.1v per cell, then begins a cool-down cycle, then charges to full capacity after that. Is the 1.1v default low enough for proper cycling, or should it be lower than that for a more thorough cycle?

Thanks

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03-19-2009 06:22 PM  8 years agoPost 2
Four Stroker

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Atlanta

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The 1.1V per cell is correct. Most of the capacity is gone by then. With only 4 cells you could go a little lower but to no avail. What are you cycling them at charge ? discharge ?

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03-19-2009 06:40 PM  8 years agoPost 3
nnonname

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Great Lake State

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I'm quite sure I have it set at 1.1A on both. The problem is that it only discharges 638mA, then cools down, then recharges 755mA. With a rated capacity of 2700 mA, it says I should recharge around 70% of that. So I would think I should be discharging & recharging somewhere around 1890 mA. So, I'm wondering if my pack is shot.

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03-19-2009 06:42 PM  8 years agoPost 4
Four Stroker

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Your battery is probably toast but try a lower setting, say 300 mA. If this is a 2700 NiMH A cell pack, they have a very large internal resistance which translates to a big voltage drop at higher currents.

You do have it set to the correct number of cells ?

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03-19-2009 09:45 PM  8 years agoPost 5
steve69

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Berkshire, UK.

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As I understand 0.9v per cell is the norm for discharge cylcling of Nicd, 1.1 is a little high.


Steve.

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03-19-2009 10:14 PM  8 years agoPost 6
Four Stroker

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Atlanta

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0.9v per cell is the death of many 8 cell transmitter backs.

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03-20-2009 04:24 PM  8 years agoPost 7
nnonname

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Great Lake State

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Thanks for all the info. I cycled it again, this time down to .9v per cell. As before, it still only took back a charge of around 700 mA. I have a local "Batteries Unlimited of Michigan" making me a new pack for around $20. Anxious to see how that goes. They said maybe mine has a cell that's cooked (I would suspect 2 cooked cells considering the amount of mA it would handle). Thanks again.

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03-20-2009 04:28 PM  8 years agoPost 8
nivlek

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Norfolk England

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Manufacturers usually quote capacity using a five hour discharge rate . So , for a 2700mAh battery , it's rated capacity would be at a discharge rate of 2700/5 = 540mA . However , I doubt that that is your problem , it does look like your battery has had it .

At the end of the day , it gets dark .

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03-20-2009 04:39 PM  8 years agoPost 9
nnonname

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Great Lake State

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Ya know, maybe that 1.1A discharge & charge rate is extreme. That translates to 1100 mA, I believe, and it's possible I'm not getting as good of results as if I would slow it down a little. nivlek, you're suggesting .54A, or about 1/2 of what I'm doing, correct?

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03-20-2009 04:44 PM  8 years agoPost 10
chris6414

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Sneads Ferry, NC USA

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NIMH

I had some AA 2200 and 2700 brand new and put them in a square rec shell for loose cells. I cycled them on slow charge for 5 cycles and discharged them twice in the charger and 3 times in a plane under normal receiver servo load (5 servos). To this day neither will discharge to the rated capacity. one reached over 1000 MAH (the 2700) the 2200 never gets above 850-950 MAH. NiCad Sub Cs are great packs and keep solid voltage over their range where AA, NiMh drop almost a volt when put on the discharger. Under load the NiCad seem to hold a slightly higher voltage and has a broader range throughout the discharge whereas NiMh has a tighter range and voltage falls off rapidly when nearing the end of it's curve.

I made a automotive dual element(blinker) light, discharger with a pig tail to monitor voltage. This is an extreme duty discharger and can sometimes revive NiCad packs that haven't seen action in awhile. If you use one, be sure to monitor the pack for temp. NiMh batts need to "exercised" to reach their rated capacity.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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03-20-2009 04:58 PM  8 years agoPost 11
cdrking

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Seattle

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0.9v per cell is the death of many 8 cell transmitter backs.
I just purchased a new transmitter battery pack for my DX7. I bought the new pre-charged eneloop Ni-Mh cells, they are 2000 mah.

What is recommended is a conditioning cycle, this consists of three discharge/charge cycles. They (BatteriesAmerica) say to discharge to approximately 0.8v per cell. I have one more charge cycle to complete the conditioning cycle.

So 0.8v per cell will not kill your transmitter pack.

I also did the voltage regulator mod to the transmitter so this should reap some long run times with these new packs. They will also hold their charge much longer.

Jeff

To hover is divine, the alternative is rather PLANE.

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03-20-2009 05:50 PM  8 years agoPost 12
nivlek

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Norfolk England

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nivlek, you're suggesting .54A, or about 1/2 of what I'm doing, correct?
Correct .

The only reason to terminate the discharge at 0.9V , is to ensure that no cell is completely discharged .
In fact , it is OK to completely flatten a single cell . However , in a pack , it is possible that one cell reaches 0V while the other cells still have some charge . If the discharge then continuse , the flat cell becomes 'reversed charged' as the current continues to flow out of the pack . Terminating the discharge at 0.9v per cell , ie 7.2V for an 8 cell pack , should ensure that no one cell drops to 0V .

At the end of the day , it gets dark .

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03-20-2009 05:54 PM  8 years agoPost 13
nivlek

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Norfolk England

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It is also worth knowing that your transmitter probably only draws about 250mA , so as long as you use a discharge rate of 250mA or more , it should be representative of the useable capacity that you really have .

At the end of the day , it gets dark .

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03-20-2009 06:03 PM  8 years agoPost 14
Leif

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USA

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I'm cycling a 4.8v 2700 mA NiCd/MH battery pack
Well, which is it? NiCd or NiMH? Those are very different cell chemistries and the charge/discharge behaviors are different. Your charger needs to know what type of cell it is seeing in order to properly detect the discharge/full-charge points. I suspect that you have the charger set to the wrong cell type, which is why it is cutting off early in the charge cycle.

Leif

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03-20-2009 06:43 PM  8 years agoPost 15
nnonname

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Great Lake State

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My charger only has the ability to differentiate between these two battery Types:

1) NiCd/MH
2) Li-Ion/Po

Apparently the charger makes no discerning difference between the two in option one above. However, my pack is the NiMH.

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03-20-2009 06:48 PM  8 years agoPost 16
Four Stroker

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Atlanta

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Well is it a AA 2700 NiMH pack or a A 2700 NiMH pack ?

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03-20-2009 07:32 PM  8 years agoPost 17
nnonname

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Great Lake State

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I think it's what they call a sub-C sized cell. They're about the diameter of a Quarter and probably 2-1/4" lg. There are 4 in the pack. 4.8v & 2700 mAh.

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03-21-2009 01:39 PM  8 years agoPost 18
Leif

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USA

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Sub-C only tells you the physical size of the cell. You need to know what the CHEMISTRY in the battery is.

I strongly believe that the problem is your charger. The fact that you don't know whether the pack is Nickel-Cadmium (NiCd) or Nickel Metal Hydride (NiMH) means that you can't be choosing the right charge/discharge settings for the cells. I don't know of ANY charger that can automatically detect whether a cell is NiCd or NiMH, and there is a difference in the charge behavior with these two types of cells.

The problem lies in the attempt by Hobbico to build a charger with the peak sensitivity set to a value that is safe for both NiCd and NiMH cells, but not optimum for either. If those cells are NiCd, the peak sensitivity value is set too low. This is causing the charger to cut off the charge too early, which is resulting in the cell not being fully charged. Here's the pertinent section of the manual:
Press DOWN to find the PEAK SENSITIVITY screen. This value determines the sensitivity/accuracy of the peak detection circuit. The factory default value of 8mV is acceptable for NiCd and NiMH batteries. Adjustment of this value can help match the characteristics of your battery to the charger for better peak charges. The recommended settings are 5-15mV for NiCd batteries, and 3-10mV for NiMH batteries. A lower number means the cycler will try to be more precise in finding peak charge, but in certain situations could cause the cycler to errantly stop peak charge too quickly, in which case it may be necessary to increase this number to 8mV or greater (especially if using AC input power). Press CHANGE, then UP or DOWN to find the desired peak sensitivity value. Press CHANGE to confirm selection.
Before doing anything, find out if the cells are Nickel-Cadmium or Nickel Metal Hydride. If they are NiCd cells, then increase the peak sensitivity value to a number between 12-14. If the cells are NiMH, set the peak sensitivity up to 9-10. Since these are Sub-C cells, you don't need the charger to be so sensitive for the charge cut-off. The default value set on the charger makes it safe for smaller NiMH cells, but at the expense of cutting off too early for high-capacity cells.

Leif

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03-21-2009 03:43 PM  8 years agoPost 19
nivlek

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Norfolk England

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So , which part of
my pack is the NiMH.
can't you blokes read ?

At the end of the day , it gets dark .

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03-21-2009 04:30 PM  8 years agoPost 20
Four Stroker

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Atlanta

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So we have finally narrowed it down to a 2700 mAh Sub C NiMH 4.8 V or 4 cell pack.

1.1 A is fine for such a pack. So either your pack is toast or the charge is terminating prematurely as Leif suggested. Change the peak delta and see what happens. You are sure as hell not going to find a lot or extra capacity between 1.1V and 0.8V when discharging at < C/2.

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HelicopterMain Discussion › Cycling NiCd/MH Battery Packs
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