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hobbico mkII and li-poly?

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hobbico mkII and li-poly?

Old 01-01-2004, 06:52 PM
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tbucket
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Default hobbico mkII and li-poly?

I have a IFO with a pixie-20p speed control powered by an thunder 860mah 7.4v li-poly, the speed control is set for a 6v cutoff, when the controller cuts the motor off (low batt) I put the li-poly on the charger at 400mah (or any charge rate) and with in about a minute the charger show complete.
The battery has about 8v on it before I charge it? I put a meter on the battery and ran the motor, voltage droped to about 6.2v than the motor shut off, with the motor off the voltage will jump back up? is the charger bad or do I need to turn off the cutoff feature and let the battery discharge more before I charge it.

Thanks Kevin
Old 01-02-2004, 01:21 AM
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shams42
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Default RE: hobbico mkII and li-poly?

I am really interested in this reply. I am a newbie and I bought a Li-Poly pack and a Hobbico Quick Field Charger Mk II because people on this site reported that it is capable of charging Ni-Cad, NiMH, and LiPoly batteries. In the instructions that accompany the charger, it descibes how to charge Lithium Ion batteries and it says specifically not to try to charge other types of lithium batteries with this charger. My understanding is that many people here at RCU use this charger with LiPoly batteries with good results. So where is the error? Can I use this charger with my LiPoly battery or not?

Thanks,
Matt
Old 01-02-2004, 08:06 PM
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sethml
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Default RE: hobbico mkII and li-poly?

When you charge the battery, the charger should slowly increase the voltage up to 4.235 volts per cell, and then stay at that voltage for a while. So, in your case, if the charger isn't reaching about 8.5 volts before cutting off, there's something wrong with the charger, or maybe the battery. If the charger seems to be doing the right thing but the battery still doesn't hold a charge, maybe the battery is damaged.

For details of how LiPoly batteris are charged, see [link=https://www.fmadirect.com/support_docs/item_1080.pdf]FMA direct's LiPoly app manual[/link], and go to the "Charging" section. There's a whole lot of useful stuff about LiPoly packs in [link=https://www.fmadirect.com/support_docs/item_1115.pdf]FMA's other LiPoly manual[/link].

I have a Hobbico Mk II charger, and have charged 340 mAh and 1200 mAh 2-3 cell Kokam and E-Tec LiPoly packs, with no problem. LiPoly batteries charge the same ways as LiIon - the Hobbico manual is just poorly written, and doesn't say this.
Old 01-03-2004, 06:24 PM
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Default RE: hobbico mkII and li-poly?

My battery only reaches about 8.25v at full charge. It was also only the 2nd time the battery had ever been charged. Is this indicative of a problem? The pack is a 2-cell 1500 mAh [link=http://www.balsapr.com/catalog/battNCharge/lithView.asp?ProductId=T231537]pack[/link] from Balsa Products.



Matt
Old 01-03-2004, 08:01 PM
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Default RE: hobbico mkII and li-poly?

To start, the Hobbico MKII field charger does not give a full charge on LiPos. It was designed to charge old generation Li Ion cells and packs which are charged @ 4.1v per cell. Hence a 2S LiPo pack reading 8.2v fresh off the charger. Today's LiPos are fully charged from 4.2-4.235v per cell.

No worries - this doesnt mean the MKII will not charge LiPos. It does an excellent job, but only charges your packs to about 85-90%. More modern LiPo chargers will give 95-100% charges. The good news is, this isnt a huge drop in flight time and power, and its hard to beat the $50 price tag on the MKI!!

Kevin -

What motor do you have on your IFO? Anything bigger than 280 would be a problem. The TP860 cells can handle 5C max current - that is around 4.3 amps max continuous, with short 5-15 second bursts to 6.8 amps.

If your motor is pulling more than 4-7 amps, the cells are dropping in voltage under load to a point of 3V per cell (where your ESC cuts in). This is typical anywhere people use cells that are too small for a given motor.

The newest Thunder Power 830s can handle 8-10C continuous. I fly them in GWS powered models pulling 7-10 amps at full throttle and the packs work excellent. However, if I put one of my older 860 packs in, the ESC will also shut the motor off after a minute or so.

Let us know what motor, gearing and prop youve got. That way we'll know if youre pulling too much current from those cells and causing the premature shut down. Dont set the cut off any lower - it will work if you do this, but you will be killing the cells pretty quickly.

Also, is the battery cold when you are flying? If your motor isnt pulling too much current, then a cold battery might be the problem. Anything under 70 degrees and I notice packs put out much less voltage. To remedy this, I'll keep my packs in the car or warm while they charge.
Old 01-03-2004, 11:31 PM
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Default RE: hobbico mkII and li-poly?

Thanks. Sorry for hijacking your thread, Kevin.

Matt
Old 01-04-2004, 10:11 PM
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Default RE: hobbico mkII and li-poly?

The motor is a gws A with a 1047 gws prop, the tempture has been about 60, it is pulling about 1.7 amps.

Thanks Kevin
Old 01-05-2004, 01:29 AM
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Default RE: hobbico mkII and li-poly?

Based on your motor and current, I dont see a clear problem. I used the A drive w/10x4.7 for hundreds of flights on the 2S 730 and 860 TP packs with no troubles. However, when I check my notes, the voltage was around 7.2v under load with the 860s on this motor @ around 2.0 amps.

I think you might want to try getting the pack warmer before using it. Try charging and checking current in the house. Also, try running the motor at full throttle for 60-90 seconds to help "warm up" the pack.

Today in 45 degrees temps in Las Vegas, my ESC prematurely cut out on a 1320 mAh pack about 3 minutes in. The same pack on days 50 degrees and above would fly for an easy 15 minutes before cut off. When I checked the battery temp, it was still around 50 dergees. I took the meter out, checked it again and sure enough, the cold battery was delivering less than 6v under load (2s pack). I took the pack inside the shop, warmed it up to 72 and ran the motor inside for 6 minutes straight with no cut off.

If warming the pack up doesnt help, let us know!
Old 02-13-2004, 09:17 PM
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Default RE: hobbico mkII and li-poly?

Here's some news. I've got a brand new Hobbico Quick Field Charger Mk II that I've been using to effectively charge Nimh for the past 2 weeks. I just charged my first Lipo pack Etec 2s2P 2400 and it came off the charger with 8.62 V! I waited 30 mins. and it's now reading 8.61V. It seems that maybe Hobbico has bumped up the voltage a bit to match the newer Lipos! I've got two no-load meters and they're both reading 8.6-8.61 V on this pack.
Old 02-15-2004, 04:04 PM
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Default RE: hobbico mkII and li-poly?

I saw your thread and I sell Lithium batteries and chargers at www.AtomicMods.com I also have lithium Ion/Poly chargers for as low as $14.95.

I even sell some that you can adjust the voltage that the cells are charged to. I usually set the to 8.5, but you can go higher if you have the guts.

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