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titan74
08-29-2005, 01:54 PM
yesterday I saw an energizer AAA nimh battery with 850mah. (this is the common battery we use for cameras and the like..) I made a 6 cell batt pack to make 7.2v.. recharged it and tested how long a 850 mah lasts with my ducted fan motor (i think size 150)..

It went down for only 15 seconds!!!!:( .. what is the matter?.. is it normal for this kind of battery?.. theres only one hobby store here and they are not selling batt packs for rc plane.. only the sub c cells for r/c cars so I tried to resort to this type of batteries.

By the way, it is worth mentioning that while I was preparing the pack, I accidentally short circuited it.. the batteries then were new, I have not recharged yet, but there was a light spark.

So, is it that I damaged the batteries due to that incident?.. or is it because AAA's cannot be used for the r/c plane as batt pack?

U2Steve
08-29-2005, 07:24 PM
If the batteries were only shorted for a few seconds or less, there's likely no damage.
The problem is that most RC plane motors draw current faster than cells like this can supply, so their voltage drops too low too fast. Keep trying, and the batteries will cook!
Stick your batteries in a flashlight or a Discman or something, and go on-line for some "real" packs. Plane motors don't sip power, they chug it- we need battery packs that can take that sort of hard use.

Steve

GeraldRosebery
08-29-2005, 10:17 PM
The problem is one of internal resistance. When you try to pump too much out it just heats up. These cells were nver designed for high current draw. I tried the same thing with the 2500 mah 15 minute (4C) charge AA cells (Energizer) I wasted $35 on 16 cells for two 8 cell packs. They also couldn't cut it.

titan74
08-30-2005, 07:13 AM
Last night I tried AA cells with 2100mah.. the motor went for 3 minutes.. then got toasted.. ahahaha!

Now I got to order batt pack and new motor on the net.. oh boy!..

By the way UDsteve, your right, the AAAs were not damaged.

Thanks for the replies.

Warden
08-30-2005, 04:41 PM
GWS sells a great AAA pack. The packs I'm using are eight cell 750mah and come with a JST connector. The plane I'm using them in is a Soarstar (like the Wingo) and it has a geared 380 motor with an 8/4 prop. I get waaaaaaay better performance with the AAA Nimh than I did with the stock 650 Nicd. More power AND longer run time. Current draw is probably at the high end of the pack capability but so far I'm not seeing any signs of problems.

And the really good news is that they're cheap! This is my first post so I don't know if I can name retailers or not but I can get these packs on line for $11.50 each including shipping!

Smash
09-01-2005, 03:07 PM
Hy!

I want to bulid an electric sailplane with a Speed 400 + 3.5:1 gear. What do You think, 7 cells of Sanyo AAA 800maH will be good for power supply? Warden, what do You think could be a big difference between a GWS pack and this?

Andrew

Warden
09-01-2005, 04:34 PM
Don't know. GWS may be Sanyo's for all I know. The discharge rate would be the big thing I'd be concerned about. Obviously, the GWS can handle it.

Twmaster
09-01-2005, 05:07 PM
The AAA GWS packs I have are a either Sanyo or Panasonic cells. I have to agree with the poster said GWS sells a great pack.

Twmaster
09-01-2005, 05:13 PM
yesterday I saw an energizer AAA nimh battery with 850mah. (this is the common battery we use for cameras and the like..) I made a 6 cell batt pack to make 7.2v.. recharged it and tested how long a 850 mah lasts with my ducted fan motor (i think size 150)..

It went down for only 15 seconds!!!!:( .. what is the matter?.. is it normal for this kind of battery?.. theres only one hobby store here and they are not selling batt packs for rc plane.. only the sub c cells for r/c cars so I tried to resort to this type of batteries.

By the way, it is worth mentioning that while I was preparing the pack, I accidentally short circuited it.. the batteries then were new, I have not recharged yet, but there was a light spark.

So, is it that I damaged the batteries due to that incident?.. or is it because AAA's cannot be used for the r/c plane as batt pack?

That is a little surprising that the pack only lasted 15 seconds. One thing I have noticed with NiMH packs is that it usually takes a few slow charges from new to 'wake' NiMH cells up.

I'm sure others will be chiming in here if I am mistaken but new NiMH cells should be slow charged (1/2C?) for their first few charge/use cycles. What rate did you charge them at?

--
Mike N

titan74
09-04-2005, 12:46 PM
That is a little surprising that the pack only lasted 15 seconds. One thing I have noticed with NiMH packs is that it usually takes a few slow charges from new to 'wake' NiMH cells up.

I'm sure others will be chiming in here if I am mistaken but new NiMH cells should be slow charged (1/2C?) for their first few charge/use cycles. What rate did you charge them at?

--
Mike N

I think I got it. I slow charged the same energizer AAA pack I mentioned above and made remarkable performance on a GWS EDF55 300H fan..

On the otherhand, I charged a new GWS 7.2v panasonic AAA 500mah pack using the greatplanes DC peak charger.. it peaks at less than 5 minutes, but when tested with the GWS EDF55, it lasted less than a minute.

The point is, now I know I can use these rechargeable AAAs you can buy on most stores.

debhicks
09-04-2005, 01:16 PM
You can get the GWS batteries here too www.willshobbies.com (http://www.willshobbies.com)

titan74
09-04-2005, 03:21 PM
That is a little surprising that the pack only lasted 15 seconds. One thing I have noticed with NiMH packs is that it usually takes a few slow charges from new to 'wake' NiMH cells up.

I'm sure others will be chiming in here if I am mistaken but new NiMH cells should be slow charged (1/2C?) for their first few charge/use cycles. What rate did you charge them at?

--
Mike N

How many slow charges does it take to "wake" NiMH cells up?.. after several slow charges, you think I can now use the DC peak charger, then it would work fine?

Twmaster
09-04-2005, 04:08 PM
How many slow charges does it take to "wake" NiMH cells up?.. after several slow charges, you think I can now use the DC peak charger, then it would work fine?

I like to cycle my packs three times before using a higher charge rate. I am wondering if your charger is part of the problem. Some chargers while they claim to work with NiMH cells fail to charge smaller NiMH packs correctly. I had this issue with a Super Nova 250S charger. It never would do the right thing on any NiMH packs I owned. I currently use an E-Flight Pinnacle peak charger for both my NiMH and Nicad battery packs. It has an adjustable charge rate setting as well as trickle charge mode.

I'd try to trickle charge that GWS pack a couple cycles and see what happens there.

titan74
09-06-2005, 03:13 PM
the greatplanes DC peak charger has 200mah charge rate for 330mah or less batt pack and 600mah charge rate for bigger batt capacity.

Ill try to charge the GWS 7.2v 500mah batt pack on a 200mah charge rate instead of the 600mah. will try these for several cycle and check if the performance improves...

mwhitman
09-06-2005, 06:21 PM
Hy!

I want to bulid an electric sailplane with a Speed 400 + 3.5:1 gear. What do You think, 7 cells of Sanyo AAA 800maH will be good for power supply? Warden, what do You think could be a big difference between a GWS pack and this?

Andrew

Smash-
I just installed a Wattage 8 cell 1100 mAh NiMH 2/3A pack in my Cermark Newtimer which has a Speed 480 motor and it works well. I thought about using a lighter pack but needed the extra weight to ballast the plane and set the CG properly; this way, I didn't need to add lead weight.

Mike