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-   -   Wall Charger Question... (https://www.rcuniverse.com/forum/questions-answers-154/5441050-wall-charger-question.html)

alqwad 02-19-2007 11:09 AM

Wall Charger Question...
 
Hey guys-

I have a starter for my glow planes that I rigged up with two 7.2 volt battery packs in a series configuration giving me 14.4 volts of power. Here's my question. I have a wall charger that puts out 600 mah at 12 volts. Is this simple charger adequate to charge my setup or should I go with a wall charger that puts out 14.4 volts? Thanks.

-RME

bob_nj 02-19-2007 11:17 AM

RE: Wall Charger Question...
 
What is the capacity of the batteries?

alqwad 02-19-2007 11:25 AM

RE: Wall Charger Question...
 
3300 mah at 14.4 volts. Thanks.

firstplaceaviator 02-19-2007 01:41 PM

RE: Wall Charger Question...
 
In order to charge a 14.4 V pack, you will need a charger that puts puts out 16.0-18.0 volts, otherwise the batteries will not receive a full charge. Since you have 3300 Mah packs, you can charge them with a 1200 Mah charger in about eight hours or quick charge them at 5 amps. There are several wall chargers that would do the job. Personally, I would charge them individually with an R/C car battery charger. They are not very expensive (Tower Hobbies model 420 is only $30.00) and you could charge both packs in about three hours.
Doug

firstplaceaviator 02-19-2007 01:43 PM

RE: Wall Charger Question...
 
[8D]

alqwad 02-19-2007 01:48 PM

RE: Wall Charger Question...
 
Hey, thanks. Originally I had them in series with the connections/plugs outside the case and I could charge the two packs separately with my Accu-Cycle. I now have all of the connections inside the case for a cleaner install and appearance. Because of that, I have only one connection coming outside to have access to. Basically, now I'm looking at a 12 cell pack and my charger will only do up to 10 cells at a max of two amps. Oh well, maybe function will win over form and I'll go back to my old setup. Thanks for the replies.

Rodney 02-20-2007 11:04 AM

RE: Wall Charger Question...
 
Most wall warts put out an "open circuit " voltage much higher than the batteries being charged depending on the internal resistance of the charger to limit the current. The only way to know for sure if your wall wart will charge the batteries is to put an ammeter in the circuit with the charger leads. If you get a current higher than the self discharge current, the battery will eventually become charged. You can determing the time required by dividing the battery capacity by the measured current and multiply the result by 1.6 to see how long it would take to charge a nearly discharged battery.

alqwad 02-21-2007 12:42 AM

RE: Wall Charger Question...
 
Rodney-

Thanks a bunch... I spoke with another very experienced gentleman in the local area and he said the exact same thing so it must be true!! Thanks.

-RME

Matthew007 01-02-2008 05:19 PM

RE: Wall Charger Question...
 
sorry for bringing this back up but why multiply by1.6?
For example, I have an old red nikko 9.6v charger that says 12v 300ma output, but when I put an ammeter on the leads it says around 1.6 amps.
So If I want to charge say a 3000mah battery, isn't charge time 3/1.6? Where you get that other constant from?

Jazzy 01-02-2008 08:28 PM

RE: Wall Charger Question...
 
1 Attachment(s)
An Ammeter is placed in-line with either the pos or neg lead while connected to a load.
A Voltmeter is placed accross the positive and negative leads open circuit or closed (with a load).

The 1.6, (many use 1.5), multiplier is used when charging at rates close to the capacity divided by ten. It is there to compensate for innefficiencies during charging. I personally have found that as charge rates increase the multiplier decreases. For instance: A standard 500 mAH pack charged at 50 mA will take (500mAH/50mA)*1.6 = 16hrs.

Matt, you likely found the max current the charger can supply to ground by placing the Ammeter across the leads without any load. (Load meaning a battery to charge.) Connected to an 8 cell pack it may yield the rated voltage and current. Since I don't know what it was designed for this is just a guess.

Matthew007 01-02-2008 11:46 PM

RE: Wall Charger Question...
 
My ammeter sucks. Just a small portable one that reads to 10A for 15 seconds safely.
Yea I was detecting max amps, I'll do it in series but it's sort of a pain with the leads.

When checking amps per say on a 2700mah AA battery I have, it gives me 10+ amperes (no load on battery) and if i leave the leads on the +/- the battery gets warm fast. So I assume the ammeter itself is a kind of load when connected that way.
Thus, I believe the 1.6a given was max current.

Thanks for the info.

scratchonly 01-03-2008 02:41 PM

RE: Wall Charger Question...
 
Yere is a low resistance shunt in the ammeter circuit. DONT put an ammeter across the battery; Use only in SERIES as shown in the drawings. I hope you didn't destroy your battery, melt the test leads or start a fire!

Matthew007 01-03-2008 07:09 PM

RE: Wall Charger Question...
 
LOL I tested it on a 2700mah AA, dont worry.
I'm going to post on using a 100A shunt


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