Bi11ybuck

I would like to plug in 2 6v 2700mah batteries into my 921 RXwith my9503. Can I do this without a regulator and is it better to run 2 batteries instead of one? I'm concerned with voltage drop with the 6 large Hitec digital servos if I load them up durring manuvers.

Thanks for your help.

snuts

Absolutly! I was introduced to redundant power in 1992. Dual packs, and dual switches. No honest glitches since. I firmly beleive most glitches are intermittent opens in the supply. 2.4 has also brought out voltage drop to the receiver buss. I too fly my 1221's and 921's with dual power supplies. Most are still Ni-Mh, with only 1 upgraded to Li-Fe. I will be leaning more that way as new airframes come along.
Hope this helps.
-Snuts-


Also a firm beleiver in battery management, cycle and log. at least on the pack or inside the airframe (1/4ly)

Bi11ybuck

Thanks for the fast reply. You guys help alot and rest assured it is appreciated.

Thanks!

electricpete

Hi

Can you suggest a budjet suitable system, that is not too large.

Peter

snuts

The simplest, the one I use most is your normal battery pack and HEAVY DUTY switch duplicated and pluged into any unused channel port. Never plug both together, into a Y harness and then into your receiver. This simple step negates the purpose. This will be the week link in the redundancy. All it takes is a intermittant connection into the receiver buss for a brown-out, or open in your supply voltage. If you have run out of open ports, place a Y harness into your Rudder (or any other ch) and supply voltage into the buss (supplimental). I usually choose the Rudder as it may have one of the largest servo's on it.
I do like J.R's Heavy duty switch harness. But most of my airframes have the MPI heavy duty switch with the charge port in it. Hope this makes sense, and is helpfull to those interested.
-Snuts-

As a note of interest, several of the senior pilots in the area have addopted this style of supply over the past 2 decades.

airbusdrvr

snuts, not having a wiring diagram to look at, how is plugging the extra batt/sw into an unused receiver slot different than a y connection? Would not the batteries be connected in parallel by both being connected to the receiver bus?

snuts

You are right. But the catch is, if the one connection to the buss (which will be carrying the full current of the sum of the loads) gets loose, or warm and becomes a resistive connection THAT will be the week link.
Now if this same connection is duplicated. The intermittent open, or resistive (High voltage drop) connection is paralleled. The receiver buss will be carried by the second power source for the duration of this occurance. Now that 2.4Ghz has brought forth the dependance on a stable voltage supply AT THE BUSS! A lot of brown outs may be aleviated (spelling?) this way.

In a rural situation, when the well pump starts, and the lights dimm, up sizing the powerhouse will not help a darn. It's all about dependable, adiquatly sized distribution that will carry the VOLTAGE through the start-up of the pump. Scratching your head yet? This should make all the sense in the world, That inrush to start the pump, is that big rudder flipping into a heavy knifedge.

I beleived in this so much that all my factory light switches I would use with the factory 600mah packs in my 40 size ships all through the 90's. Not a hick-up, Tree's ponds dumb-ass thumbs etc. But never a glitch. It could all be explained, say 150 different models over 19 yrs, this last run at the hobby (started 1973). And there are a lot of modellers using this it's not at all new, and very popular in western Canada.

-Snuts-

Zeeb

My Feedback: (41)

Well a couple of thoughts here;

1. The R921 already has two separate battery input ports, the Batt/Bind and the Batt/Data and two inputs are usually fine for up to 50cc size models. I run my 50cc with one 2300mah A123 using two outputs through two switches and have outside access to the Bind and Data ports.

2. The point on not running the two batteries together on a Y is correct in that even good quality servo lead connectors are limited to about 4 amps max continous throughput so Y-ing them would cause that issue as well as the lack of redundancy which the OP seems to be after.

3. Be very careful selecting your NiMH batteries for high current servos. There can be a large variation in the cell impedence (resistance) and if you get cells with that issue, they won't be able to supply the necessary amperage when needed. The old idea of having a higher than necessary mah rating should yield the necessary continous and burst amperage output doesn't necessarily apply anymore.

4. IMHO, either the original A123's or the copycat LiFEPO4's are the only way to go for rx packs anymore. They're not difficult to use but do require some differences in how they're handled i.e. you cannot volt check 'em to determine charge state and you must have a charger with A123 software.