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Old Nov 17, 2001, 05:09 PM
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Peter W's Avatar
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Is charging flight packs off a car battery charger bad?

Hi
i have a car battery charger to charge my flight packs using my hitec 315? charger. is this a bad idea? if so, WHY?!
also, if i connected the charger to a car battery and left a pack on charge, after it has been peak detected, would the charger stop current to the batt and sit there i.e. not get hot and melt.
if no complete circuit then what can damage it right?

Thanks to anyone who can help

Peter
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Old Nov 17, 2001, 06:53 PM
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I connect my car battery charger to an old car battery first then connect the charger to that, and it has worked fine for ages, I heard that the output from the car battery charger wasn't reliable enough, it might produce a false peak, by hooking it up to the battery the output is regulated. A more reliable source is an old PC power supply.
Grant
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Old Nov 18, 2001, 11:10 AM
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okay will do, have a small 12v 3.2ah sealed lead acid. that do the trick in terms of requlating?
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Old Nov 18, 2001, 08:27 PM
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Yeah that should be fine, it's just like putting a big capacitor across the terminals
Grant
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Old Nov 19, 2001, 07:08 AM
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Peter W, I'd be careful with the size of battery you mention a typical car battery charger will probably over charge it - if its sealed it could explode. I also use a car battery charger but also use a car battery - this has the advantage that you can take it to the field and also recharge there.

Brian
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Old Nov 19, 2001, 07:19 AM
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What Brian said - do not connect a sealed battery that small to a basic car battery charger!

Your best bet is probably a PC power supply (as posted), personally I use a 75 Ah lead/acid battery for charging both at home and on the field ... and just use the charger (one intended for leisure & sealed batteries) to periodically recharge the wet battery. I also have a 7 Ah gel battery for my IC flight box (and indoor e-flight sessions).
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Old Nov 19, 2001, 12:05 PM
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forgot to mention that the charger is the Hlafords fully automatic one that has a switvh for charging small sealed lead acid batteries as well as car batteries. still be okay to do it now?
anyone know where you can get leisure batteries and/or 12aH + sealed batts for cheap? want to use something as a field battery that ain't tooheavy but will charge my twinstar 7 2000 packs a couple of times.

Thanks

Peter
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Old Nov 19, 2001, 12:16 PM
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Mmmm still not sure about chaging the little sealed lead acid from the car charger, do you know what the charge rate is?

You can get leisure batteries from Halfords, Caravan suppliers, boat shops etc, should be able to get small sealed lead acids from Maplins.

Brian
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Old Nov 19, 2001, 01:57 PM
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Yes, Maplins for sealed cells (I got a replacement one from them only last week!). Some of the big DIY shops stock them too (backup batteries for alarm systems) and of course model shops! I got a Yuasa 12V 7Ah which was about 24, they had bigger ones (15 or 18 Ah I think) for the same price.

Halfords is probably your best bet for a leisure battery.

Check the instructions with your charger, mine is a Gunson one that only cost 19.99 from Argos ... sadly they don't sell it any more. Most car chargers are too agressive for small sealed batteries, but if yours had a specific setting for them it may be fine.
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Old Nov 19, 2001, 03:12 PM
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the instructions state that it is defininately made to charge small sealed lead acids as WELL as car batteries.
can someone help me with another problem please.
i fly my twinstar until i can not semm to climb at all under full power. this is with stock motors but graupner 5.5x4.3's with a 7 cell 200o pack. so i land and charge it up. but it only seems to need five to ten minutes charge. what's going on? am i not discharging them completely cos i land early or what?
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Old Nov 20, 2001, 04:41 AM
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Are you using Nicd or Nimh flight packs? What flight duration are you getting? With 2000s I would expect a run time of maybe 7-8 mins. The Twin Star is not exactly a ball of fire on 7 cells ... even fresh off the charger - I suspect you're landing with quite a lot left in the packs. What rate are you charging at? My Hitec 335 puts out about 5.5A with my 2400s and they typically take around 25 mins to recharge. so your 5-10 mins is probably putting in up to 50% of a full charge.

5.5x4.3s may be OK on 7 cells, but on 8 (my setup) they were not good. They pull a lot more curent than Gunthers and are too high-pitched for a relatively slow flying plane. 6x3 folders were excellent for duration and just stooging around (but lowish level speed, so not good for aerobatics etc.), these might be a bit marginal on 7 cells though. Most of the time the Gunthers are hard to beat (despite their appearance!).
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Old Nov 20, 2001, 08:52 AM
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Peter,

Urrrgh! Looks to me like you are attempting two 'bad' things!

1) The output of car battery chargers have a extremely large ripple (just generally being full-wave rectified AC). This is fine for car batteries (in fact, it can 'shock' the lead plates in the battery and help break up any suphates that have become deposited). For the Hitec, this is bad news! At the very minimum you should put a large value electrolytic capacitor across the output (with the polarity correct)to 'smooth' out the voltage.

2) Having said 1) above, it is still bad news to use a car charger, because the output voltage is not regulated. To charge a car battery to 14v-plus the charger output voltage has to be somewhat higher, and can be close to the Hitec input voltage limit.

3) If the 'sealed lead acid battery' is a gel-cell then you shouldn't use the car battery charger to charge it. A gel-cell can be wrecked by the heavy ripple and unlimited current being pushed into it.

Overall, keep the car battery charger for charging car batteries!

Cheers,
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Old Nov 20, 2001, 12:08 PM
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not to fear, my battery is not gel cell.
but i've found a pc powersupply thingy that outputs 5A 12v dc so i'm using that now.
maplin do 'cheap' lead acid field batteries. an 18 ah is 38
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