Forming a recent NiMH purchase on the Hitec X4 and other computerized chargers.

Ed writes me about properly forming a recent NiMH purchase.

Hi Dave,

I recently bought one of the FDK Twicell 6.0V 5-cell 2000mah NiMH AA Flat Pack and would like to try it in one of my airplanes . I read all your comments about this battery pack and I have the HiTec Multi-Charger X-4 and not sure what is the best way to charge it. The charger is fairly new in my collection and I am still learning the best way to use it any thoughts?

Thanks,

Ed

Ed,

The best way to do it on most computerized chargers is:

General procedure,

1. Go into setup, make sure the mah limiter and time limiter are both off.

2. Put charger in PB mode, yes for Lead acid.

3. Set charge rate to 100mah, any more will ruin the battery eventually.

4. Set voltage of battery to 8V

5. Start charger.

If it refuses to start, set voltage to 6V and let it run a minute or two, the go back and restart with setting at 8V

“Generally” Eneloop’s (Twicell’s) come to you about 1/2 charged. So, the hole your filling is about 1000mah. (Hole * 1.4) / charge rate in mah = time in hours. 14 hours in this case.

What we are doing with the procedure above is tricking the charger into functioning like a dumb wall wart where it will just plod along indefinitely until we disconnect the battery.

The best practice would be to connect the cells to a dumb charger that charges at 50mah for about 30 to 40 hours and is the ONLY method for which I would ever consider warranting a pack. People try to break in new batteries in peak detection modes all the time which is the cause of my slightly “acidic” warnings against such acts on my website. One issue is there are no makers of chargers like that that I know of in the hobby world today. The last one (Sirius) seems to have become inactive. The best chargers to own for this forming purpose at this time are an ACE DDVC, ACE Digipulse or Sirius Pro-Former. Should you run across one at a swap meet or on Ebay, snap it up.

Dave

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Forming Charge On Peak Charger Email Question

Question:
Hi Dave;
Firstly- thank you for your quality battery packs. I received my recent purchase- your 1650mah NiMH 8 cell 9.6 tx pack, plugged it in to my tx just to see what it was at, it started at 8.9 but quickly went to 8.5 where I pulled it out. So on to the first break in charge at 0.1A- on a Triton 2 with a thermal probe connected. The pack temp was at 79 degrees, so I set the cutoff temp at 88 (about 10 degrees higher) The charge lasted 16 hours with a delivery of 1670ma- terminated by the temp sensor. I had anticipated a longer charge time but am happy with the results- My question is: should I expect even higher mA delivery?
Thanks.
Matt K.

Matt,

Your charge time at 100mah would be a bit short for a completely empty 1650 pack. I’d suspect it might not cycle as full but it could. I’ve never checked a Triton to see how accurate that number might be at low charge rates. Normally you have to put in 140% at low charge rates to get a full pack. A NiCad or NiMH has a lot of resistance to accepting a charge.

I would never expect the chosen procedure to work properly and consistently. There is not enough temp rise. The peak in a first charge is more of a “several peaks” along they to the final peak. One of those peaks is often large enough to trick the charger into declaring the pack full. On virgin packs, it will happen about 60% of the time when you use normal rates like Cx.5 to Cx2 (C=capacity). I’ve never run a study on doing it at 1/8th the minimum peak charge rate but I’d expect the results to be very poor. The temp will fluctuate with room temp also. All this is not to say you should have charged the pack faster as an initial peak charge. It is to say never use peak detection on an initial charge, never on a pack coming out of storage. There is no way to have the screen of your charger (or any other) showing NiMH or NiCad mode and not be in peak detection mode.

The best way to form (initial break in charge to complete manufacturing of the cells) on a computerized charger; Put the charger in PB (lead acid) mode, set the rate to .1, the voltage or cell count to a 12v pack (6 PB cells). Make sure all time limits and capacity input limits are turned off. This will get the charger to plod along slavishly well past when the first couple of cells fill. The point is to fill all the cells (which are initially of unequal charge) to overflowing at a very slow rate with gentle overcharge at the end. Peak detection will not get in the way by reacting to any false peaks. Peak detection is not reliable unless the charge rate is about 1/2 pack capacity or more. A new battery might have several peaks before it gets full. Calculating charge time when forming or slow charging (not using peak detection) is; (Capacity (or empty hole in the battery) x 1.4) / Charger output = hours to full. Let it run that long. Rates should never be above 10% of cells capacity. If it’s a AA cell above 1700mah, the rate should never be above 100mah, 50mah is even better.

What I’m going for here is a system that works 100% of the time. Every other kind of form charge is just fraught with problems. Using a peak type charger in PB mode (not in peak detection mode) is the only way to make them work reliably as a forming charger.

Once the pack is broken in, and it’s in regular use, I wouldn’t Peak charge it slower than .8 amps. The slower you go below this the slower it heats up after it’s full, the slower the peak detection happens, the more you hold the pack in an overcharge condition. Heating up is what happens when it can no longer store the energy your putting in it. This causes a slight voltage reduction. The charger knows the pack is full because the voltage is dropping, there for it has detected that it must have “peaked”. Peak charging is a form of detecting heat indirectly by watching for the voltage to drop which can only because the pack is full and heating up. (The exception is virgin packs which may reduce in voltage very slightly during the first charge.)

Never peak a pack that’s been in storage. This kind of charging is only for packs in regular use. After it’s set in storage a few months, the cells could contain unequal states of charge. As the fullest (best cell) is peaking (heating up and dropping in voltage), the others may still be rising (as they do as they are filling). This can mask the peak and apply a damaging overcharge current to the first cell(s) to fill.

I know these steps will prove to get your pack into most reliable service for you.
Dave

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RadicalCast #005

Bob’s Lucky 13 Kadet Senior and my flight predictions. A photo of the model and it’s owner was posted on June 1st. The High Voltage Paradigm Shift. Form Charging NiCad and NiMH packs. Important Considerations and general information on how peak charging works. Post flight commentary on Bob’s Lucky 13 and the importance of understanding what you want from a power system. The test flight video is available in the June 3rd post.

Show Notes:
Stick 400 Kit
GWEDP-300(A,B,C)

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