PDA

View Full Version : Stupid question of the day


Mike Freas
12-22-2005, 06:20 PM
I just bought an X-peak 3 plus charger from Dymond (2nd hand). This charger will fill all of my current e-flight needs but one is seems. I was planing on getting a 5S2P 8000 mah pack for my STM but the charger only goes to 5000 mah capicity. Does this mean I need to get two 4000 mah 5S packs and charge them seperate?

RC-Tester
12-22-2005, 07:16 PM
Does this mean I need to get two 4000 mah 5S packs and charge them seperate?
In principle yes.

Please check the total power that can be delivered by the charger: it is quite common for the smaller chargers to not be able to charge at maximum current for a 5S pack - although it *will* charge just slightly slower.

Rod

Mike Freas
12-22-2005, 07:36 PM
If I'm not mistaken it's set at 1c for lipo packs but can be adjusted for other types. Maybe I don't understand charging of lipos fully but if the charger is set at 5000 mah it should cut at that point right? That would leave 3000 mah "empty"? Set me stright on this. It's really not a big deal to order two packs.

RC-Tester
12-22-2005, 07:48 PM
If I'm not mistaken it's set at 1c for lipo packs but can be adjusted for other types. Maybe I don't understand charging of lipos fully but if the charger is set at 5000 mah it should cut at that point right? That would leave 3000 mah "empty"? Set me stright on this. It's really not a big deal to order two packs.

It *will* charge your pack correctly to the capacity.

I believe that the maximum charge power is 120W (someone may confirm) which on 5S should mean that the maximum charge current is (120/20 =6A) .... which is greater than 5A and will be fine for you!

... forget the technical bit:
The answer is yes! you can charge two 5S 4000 mAh quite happily separately!
Rod

ForestCam
12-22-2005, 08:20 PM
If I'm not mistaken it's set at 1c for lipo packs but can be adjusted for other types. Maybe I don't understand charging of lipos fully but if the charger is set at 5000 mah it should cut at that point right? That would leave 3000 mah "empty"? Set me stright on this. It's really not a big deal to order two packs.
Look at it this way, the battery in your car puts out anywhere from 650 to 800 amps but I've never seen a battery charger that charges at that rate, most charge at 10 to 50 amps and after an overnight charge your car battery is at the full capacity.
I've seen it said that quite a few people don't charge their lipos at a full 1c even though they can. Quite often low and slow is much better then hot and fast, unless you're in a hurry to get back up.:)

Mike Freas
12-22-2005, 08:26 PM
I think the light just went on for me. The settings on the charger of charge rate and pack capicity are used to figure how many amps the charger will put out. So setting the charge rate at 1C and 5000 mah capicity means a 5 A charge rate. I was thinking the charger would shut off at 5000 mah. Am I correct in my thinking? So a single 5s2p 8000 mah pack would charge full just take longer because it would charge at less than 1C.

everydayflyer
12-22-2005, 08:33 PM
Some LiPoly chargers can be set fot he number of cells and any charge rate less than 1C suchas as 11.1V and .7A (700 mA) for a 3S 1000 - 4000 mAh battery and it will fully charge tha pack . It would ytake between approx. 1 3/4 for the 1000 and perhaps 6 hours for the 4000 mah one.
Some chargers you set the number of cells (volts / 11.1) and the capacity (1000 mAh) and the charger sets the rate (1A / 1000 mAh) and it will timeout / shut down if a LiPoly of greater capacity is connected before the charge is complete.



Charles

Mike Freas
12-22-2005, 08:35 PM
Yes my charger can charge between 1-5 cells and has to be set. I'm confused again.

Rugar
12-22-2005, 08:41 PM
I think the light just went on for me. The settings on the charger of charge rate and pack capicity are used to figure how many amps the charger will put out. So setting the charge rate at 1C and 5000 mah capicity means a 5 A charge rate. I was thinking the charger would shut off at 5000 mah. Am I correct in my thinking? So a single 5s2p 8000 mah pack would charge full just take longer because it would charge at less than 1C.

Don't be confused.
Your above understanding is 100% correct.

Mike Freas
12-23-2005, 05:21 PM
Alright folks. I need someone with one of these chargers to help me. This thing is easy enough to use but it doesn't seem to be charging my pack all the way. I cycled one of my TX packs (9.6V 1650 ma) on the discharge to charge cycle. Because I didn't think it was charging all the way I put the same pack on my hobbico charger and hit the discharge button and only got 746 mah out of it before the charge cycle started. So is my charger AFU or am I AFU? I'm charging the pack at 1.5 A because that is what the pack says for fast charge.

Jerry Porter
12-23-2005, 07:01 PM
I have an old Astro Flight charger that was made for nicad pack up to 18 cells, it will adjust rate of charge from .1amp to 5.0amps, can I use to safely charge these lipo packs ??
If so what is the best rate of charge to set it at ?


Was looking on tower and found a astro flight #109 lithiun charger that looks a lot like
mine but with a cooling fan and rated 1-9 cell 7.5 amps

Rugar
12-23-2005, 07:09 PM
I have an old Astro Flyte charger that was made for nicad pack up to 18 cells, it will adjust rate of charge from .1amp to 5.0amps, can I use to safely charge these lipo packs ??
If so what is the best rate of charge to set it at ?

NO!
Lipos can only be charged on a charger specifically designed for their use!

Please, Please, Please, read up on Lipo safety Before attempting to either charge or use a Lipo pack.

*****Now that thats out of the way, Welcome to WattFlyer!***** :D

Will Hicks
12-23-2005, 07:15 PM
Do not use a NiCd charger to charge a Lipo!

If your new to Lipoly batteries, do the research to learn all you can.

Jerry Porter
12-23-2005, 07:38 PM
Thanks Guys,
Have been reading about lipo's and cannot see what the diference is in chargers.
You just apply a DC voltage higher than it's max charge and then limit the charge rate,
just like any other battery, so what is the difference ??


I am not trying to be a smart a$$, I started working in electronics in the 60's
I understand the cell balance thing but this is another circiut,
not part of any charger that I have looked at.

ForestCam
12-23-2005, 08:14 PM
Lipos don't peak and that's how a nicad charger knows that the pack is charged and to switch to trickle mode. A lipo will just keep taking it untill BOOM.

Jerry Porter
12-23-2005, 08:27 PM
Thanks ForestCam,
I had not seen in what in any of the articles I have read.
How does the lipoly charger know when to stop charging ?

rcers
12-23-2005, 08:40 PM
Thanks ForestCam,
I had not seen in what in any of the articles I have read.
How does the lipoly charger know when to stop charging ?

They stop charging at a fixed voltage somewhere around 4.2v. The second reason that Nicad/NiMh chargers won't work as the charge rate needs to drop as they near full charge.

Mike

Jerry Porter
12-23-2005, 09:02 PM
Thanks Mile

Now if they would put this kind of pratical info in the articles rather than all the power output vs weight, etc it would be more helpfull.

rcers
12-24-2005, 03:24 AM
Jerry - ask away we can help. The power output and weight are important things too, just a lot to learn. In fact we are all still learning or we would be bored!

Mike

RC-Tester
12-24-2005, 04:29 AM
Maybe this thread should be titled '(not so) stupid question of the day' - it might just become one of the most popular threads on WattFlyer!

After all there is so much information that is not obvious to someone new to electric flight that i'm not sure that a 'stupid' question is possible.I like to think that most people will help someone out here, and help avoid costly mistakes, and that often it is better to ask if you are unsure.

Just my $0.02

Rod

Jerry Porter
12-27-2005, 04:18 PM
Hi Guys,
My son is thinking of upgrading my old long wing Kadet senior that is powered with a Astor flight 40 geared motor and a 18 cell nicad pack that is good for about 6 min at full power or 15 at 1/2 power.

What lipo pack would you guys recomend to get some more flight time?? Jerry

rcers
12-27-2005, 04:26 PM
Jerry at 18 round cells youare looking at 6s LiPoly. What amp draw were you getting?

Jerry if the budget will take it here are a couple of options that I would look at. That is if your amperage is in target:

Two 3s of these 3700 mAh packs in series should do it. New cells but I have the 1200's and am very impressed so far....

http://www.aircraft-world.com/shopexd.asp?id=3765

I am also a big fan of Tanic:

http://www.tanicpacks.com/catalog/product_info.php?cPath=61_65&products_id=509

Save your $$$ they are not cheap.....

Nice to have these high capacity packs now.

Mike

electron
12-27-2005, 05:04 PM
Hi, I am a new member to this post though I have doing electric for about four years now. My 'stupid' question is can one charge Lipos using a power supply with a current limiter? I have a shultze 330d but it is rather heavy on the current draw when I charge anything above six cells. A power supply working off the mains would be quite convenient as we do have mains supply at our site.

rcers
12-27-2005, 05:57 PM
Hi, I am a new member to this post though I have doing electric for about four years now. My 'stupid' question is can one charge Lipos using a power supply with a current limiter? I have a shultze 330d but it is rather heavy on the current draw when I charge anything above six cells. A power supply working off the mains would be quite convenient as we do have mains supply at our site.

Well not really and for sure not safely. The LiPoly batteries are just not something to mess around with.

The issue with LiPoly is they have to have constant current, until they approach full and then you need to decrease the output amperage as you go.

Most of the chargers also do safety checks on cell counts before they crank out the power to the battery.

LiPoly charger is the only safe way.

Mike

Jerry Porter
12-27-2005, 06:50 PM
Mike, on the bench, with a 12/8 prop it draws 26 amps full power 21volts, with throttle at about 1/2 power it pulls 12 amps.
the pack is made up of 18 sanyo 1800va C-cells and weighs 3lb 2oz
the plane weighs 13lbs with a 140" wingspan, it will lift off in about 30' from grass and clime quite well, it will slo-fly level at about 1/3 throttle for 20 min.
I see what you mean $$$, 3 of those packs and a charger would be more than I have in the whole setup. Jerry

rcers
12-27-2005, 07:09 PM
Jerry - at 26 amps you might get by with smaller less expensive cells.

You could use these instead.....

http://www.aircraft-world.com/shopexd.asp?id=3763

Two of those 3s Packs will be $200, not cheap, but much ligher than the 16 big round guys......

Then you could use them for smaller planes since they will be 3s 2500 packs. You might even get away with the 2100 cells for $80 each.

But then your flight time might come into play.

It's only money - and you can't take it with you!

Sounds like a fun plane.

MIke

Fred Marks
12-27-2005, 08:00 PM
Thanks Guys,
Have been reading about lipo's and cannot see what the diference is in chargers.
You just apply a DC voltage higher than it's max charge and then limit the charge rate,
just like any other battery, so what is the difference ??


I am not trying to be a smart a$$, I started working in electronics in the 60's
I understand the cell balance thing but this is another circiut,
not part of any charger that I have looked at.


Please take a few minutes to read the section on charging in the Li Po Handbook at

(http://www.fmadirect.com/support_docs/item_1197.pdf)

Your basic reasoning is OK; however, the voltage must be controlled with extreme accuracy. One notorious charger callewd Suprtbrain that carries a Sticky by Red Scholefield tries to do that and has a history of ruining packs. To clarify: When I was trying to see if one could use the old reliable Supernova Ni Cd/Ni MH charger to charge Li Po based on charging, watching, and checking voltages in a way that a microprocesor add-on might do. It took a lapse of just a few minutes ( as I was lured away by a neat item on PBS TV) to ruin a brand new 4S pack of KOK 1020 cells. Luckily, I heard the first one go Hissssssss and knew there was not a snake in my shop! The problem is that Ni Cd chargers try to hold costant current by forcing voltage up very gradually and Li Pos are not tolerant of that.

electron
12-27-2005, 11:16 PM
OK Mike, maybe this is not the general recomended way to charge Lipos, but a good power supply is more accurate than any charger and setting the voltage and limiting the current will in effect do the same thing a charger tries to do with software. But yes I have to agree that setting the voltage manually is not for everyone.

electriconly
12-28-2005, 12:30 AM
OK Mike, maybe this is not the general recomended way to charge Lipos, but a good power supply is more accurate than any charger and setting the voltage and limiting the current will in effect do the same thing a charger tries to do with software. But yes I have to agree that setting the voltage manually is not for everyone.
Sure a good quality regulated power supply can make for a very good Lipo charger... in fact some of the long time Lipo flyers swear by it.....of course you must have the dicipline to always have the settings correct every time and give your total attention to the process or you will find you are swearing at it. :)

Brad

Jerry Porter
12-28-2005, 12:43 AM
Thanks All.

I now think if I am going to get up-to-date I will start out with a new plane kit designed for these lypo packs, a brushless motor, etc.

What is your thoughts on a good modern kit to start with ??
At least 5ft wingspan, also I like to build not these ARF's.

Fred Marks
12-28-2005, 01:48 AM
You are obviously a builder. Good for you. With the power and efficiency we now have with Li Pos and brushless, it is a snap to do conversion of many glow models to electric. A favorite of mine is to build and convert a Goldberg Falcon 56 or Senior Falcon to electric. I think the next issue of Fly RC will have an RC conversion of the Sr Falcon. You can locate a DIY kit instead of buying the ARF, build it and convert as you go. Check out the FMA Direct web site, Li PO Gallery to see some of the neat things done by a number of electric flyers.

electron
12-28-2005, 05:09 PM
Thank you Brad for your contribution. Maybe we can start a new tread on this subject as I have had some costly experiences when charging at 4.2 V on a purpose made charger.