A123 4s battery in my T-Rex  
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All Forums >> RC Helicopters >> Electric RC Helis >> T-Rex heli >> A123 4s battery in my T-Rex
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A123 4s battery in my T-Rex - 4/19/2008 5:09:03 PM   
BeavenX5



Posts: 133
Joined: 3/27/2007
From: Montreal, QC, CANADA
Status: offline 		Well, as promised, I buit some 4S A123 batteries for my P-38 and tried them on the T-Rex. I am new at flying helis with only about 20 flights on my T-Rex 450SE v2. I am still only hoovering and doing small circuits. I crashed Monday practicing my first nose in hovering... Obviously I am not doing any 3D yet.
- At 13.2v they give the T-Rex a very good head speed.
- You can get easily 10 minutes flight with this battey. Takes only 15 minutes to charge it back to full charge so you can fly all day with only 2 batteries.
- They are quite heavy at 345grams. The extra weigh did not matter for my flying. It migh even help with stability.
- They are quite bulky so I needed to build them in two packs of 2cells. One goes at the normal location, the second goes under the belly between the skids. You need to do this in order to keep the center of gravity where it shoould be.

Overall, I think A123 4S packs are great for sport flying as they are relatively cheap (out of a Dewalt pack), will last for 1000 flights, are extremely safe, can be discharged lower than lipo without consequences and will allow you to fly all day on 2 batteries. The negative side of it is their weight and bulkiness that might not be as good for hard 3D flying. Current draw is not a concern here at they can easily handle constant 30C discharge.

There is a great thread on them at: helifreak here

Here are a few pics of my installation.


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< Message edited by BeavenX5 -- 4/19/2008 5:21:27 PM >

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       Post #: 1

RE: A123 4s battery in my T-Rex - 5/5/2008 6:29:39 PM   
BeavenX5



Posts: 133
Joined: 3/27/2007
From: Montreal, QC, CANADA
Status: offline 		Here is an update:
After only 3 flights with the A123 4s packs, my ESC got "smarter" all of a sudden. I don't understand why this changed but my ESC now recognizes the batteries as being 4s and engage the low voltage lipo protection after 1 minute of flight . A123 batteries are only 3.3v per cell and they can get to 2.9v easily under load. The low voltage lipo protection engage at that point.
To make it harder to work around, the latest versions of the 35X ESC won't allow you to set the lipo protection to Low. Only medium and high are available

I changed the pignon to 12T (from 13T) and hope that it may fix my problem. I did not have a chance to test this yet as the weather has been bad over the week-end. Other solution would be to get a better programable ESC that would recognize the batteries as being 4s A123 at 13.2v and with a low cut-of of 8.5v not 11.6v like now.

_____________________________

I am in R/C Cars/Trucks/Boat/Airplanes/Heli
Please visit my Garage/Hangar/Marina to view all my toys.

(in reply to BeavenX5)
       Post #: 2

RE: A123 4s battery in my T-Rex - 5/5/2008 7:19:27 PM   
BryFlyGuy67



Posts: 1499
Joined: 8/27/2007
From: Grand Rapids, MI, USA
Status: offline 		I have a CC35 ESC in one of my Helis. As you say, it has a PC programming interface that allows you to set a custom voltage level for the battery cutoff.

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Flying may not be all plain sailing, but the fun of it is worth the price. -Amelia Earhart
2 CX2s, Walkera 4, TREX SE V

(in reply to BeavenX5)
       Post #: 3

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