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Old Aug 12, 2005, 08:40 AM
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Hobbico Quick Field Charger MKII - *how* do you know when a battery is charged ?

Good morning guys ! and happy Friday !

I have a good question, and I have read the manual a few times last
night while watching BigBrother 6 ( on CBS ) hehe, and didn't find the
info anywhere.

- How does one know *when* any type of battery is really fully charged ?

For example, I got my charger going for the first time last night, and put on a 1400 mAH battery pack ( NiCAD) 7.2 on for a charge.

Nice I thought, this is a nice charger... so I get it going and set it to just less than 1 amp of charge......

The thing charged my battery for some time, then beeped... I read in the manual this means it has finished charging, and is now gone to a "trickle" charge....

ok fine I thought, but is the battery fully charged ? .... does the charger somehow determine that the battery is charged fully ?

They don't explain this at all in the book....
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Old Aug 12, 2005, 09:16 AM
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I'll start with charging a single NiCd/NiMH cell. It's important to keep in mind that I'm talking about one cell only.

While charging a NiCd/NiMH cell, the voltage increases. When the cell reaches full charge the voltage stops to increase and then starts to decrease - this shows that the cell is fully charged (in fact almost - 95-98%). That voltage peak is detected by the "peak" chargers (as the Triton and others) and they switch to trickle charge.

Now I'll be talking about charging battery packs - consisting of more than one cell.

The purpose of the trickle charging is to top off the single fully charged cell but also to fully charge all cells in a multi cell pack. During a fast charge the cells in a pack do not reach full charge simultaneously. One cell reaches full charge first and its voltage peak is detected by the charger which stops charging. But the rest of the cells in the pack are not fully charged yet. Here trickle charge comes handy - trickle charging is done at currents below 0.1C (C/10) - usually around C/32 to C/50. This low current tops off the cells in the pack so they are fully charged. The packs should be trickle charged after a full charge for at least 20 minutes and up to 8-10 hours max. Prolonged trickle charging is not recommended by manufacturers - they claim that the cells start to lose capacity after trickle charging them longer than 12 hours - I cannot remember the exact term used for the phenomenon - it was something like "voltage depression".

I hope this was helpful.
Ivan
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Old Aug 12, 2005, 04:29 PM
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With that charger (I have one and am content with it for now) when it beeps it's done.

That's it. It's pretty simple. One of the things that I always do is monitor the charge process with a volt meter as well (especially my lithiums) and it has become pretty predictible based on the info from the volt meter.

I've charged NiCds, Nmhis and lithiums and only killed one NiMh pack which was because I had been charging it at a higher amperage than it could handle. I would suggest you not do that with NiMh and especially not with Lithiums (we all know that right?). With nicds it's not a big deal - they can take the abuse but when switching between the three be careful to set your amps correctly on the charge rate, It's easy to forget. I charge my nicds at 2amps regardless of their amp rating and have had no problems yet. I also cycle them pretty often to make sure they stay good. I just cycled all my tx/rx packs last week. Charging them at higher rates does reduce their life but I typically replace them within 2 years as a rule anyway. I don't do nimhs for my tx/rx packs because I don't like waiting for them to charge when I can quick charge a nicd pack and it takes at least an hour with a nimh pack.

I am considering trying a lithium pack in my next plane for the rx because it will have 7 servos (tri gear retracts and two ailerons) but I haven't researched the battery circuitry to get the 2cell lithium down to 6 volts.
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Old Aug 12, 2005, 04:45 PM
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NiMHs should never be charged at currents higher than 1C - that might damage them.
All I use for Tx/Rx packs is 2300-2500mAh NiMH. I don't cycle them - just add charge after 2-3 days of flying. It takes approximately an hour to recharge them and I normally leave them overnight on trickle charge. Occasionally I'd fully discharge a pack just to check its capacity. So far no problems. Currently I have 10 planes all ready to fly. Two are electrics, so in all 8 glow planes I have a total of 8 Rx packs and 3 Tx ones - one for each tranny I have.

The only NiCds I have are the flight packs for my SuperStar EP. I had a total of 4, 2 went dead, one is on its way to die (or maybe already dead as I haven't used and cycled it for several months). I'm tired of having to take constant care of NiCds, so I might replace these with Li-Pos or sell the plane.
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Old Aug 12, 2005, 05:36 PM
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I like Nicds and Lithiums but have had the worst luck with Nimhs; it was certainly my own mistakes though.
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Old Aug 15, 2005, 10:27 AM
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Hi guys,

Thanks much for the info above, I appreciate that.

By the way, I took my brand new boat to the lake on Saturday, it's an electric boat... made by Traxxas, it's the model called "Blast"
you can see it here: http://www.traxxas.com/products/mari.../trx_blast.htm

Anyway, I used a metal (NiMH) 3000 mAh battery in it..... ( 7.2 volts ), I could only get the boat
to run about 45 seconds to 1 minute maxium at full throttle. The boat would then just stop in the water.

After leaving the boat for about an hour, the boat came back to life, and I was able to run it again. It must be overheating.

Now, with that in mind, would the battery I'm using have anything to do with this ?

I was under the assumption that a 3000 mAh metal battery, and a NiCAD 1400 mAh
7.2 volt battery would put out exactly the same "power" ... but the 3000 mAH would just last longer.....

Now I'm not so sure.... ? ... is it possible that the battery I used is just pushing too much current and is over heating the boat ? .... in reality the boat should be lasting much longer than 45 seconds to a minute at full throttle.... ... so there must be something causing the overheating..... so would it be the battery ?

I'm totally confused...
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Old Aug 15, 2005, 11:15 AM
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A battery does not push current, the load pulls it. It is entirely possible (that's the norm actually) that a stronger battery will suffer less voltage drop than a weaker one (we're talking mainly higher capacity batteries here, 20 amps is easier to provide by a 3300mah pack than by an 1100) so the net result is indeed that the motor will operate at more amps.

The MKII beeps a number of times when the charging is completed. I have found it excellent for regular 7 and 8 cells pack. I does not work well with one cell, and 4cells rx pack are suffering from early detects too, especially so, it seems, if the cells are unequal from the start.
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Old Aug 24, 2005, 09:23 AM
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Hi guys,

I just got 2 batteries from my hobby shop: 7.2 volts, and these ones are NiCads.

they are 2000 mAH models.

At what amperage do you suggest I charge these at ? ..... I'm thinking 1 amp is NOT a good rate, it's a bit much ? ..... what do you suggest ?

thanks in advance
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Old Aug 24, 2005, 10:45 AM
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You can charge them at 1C without any trouble. Oh, that would be 2.0A current.
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