RCU Forums

RCU Forums (http://www.rcuniverse.com/forum/)
-   Questions and Answers (http://www.rcuniverse.com/forum/questions-answers-154/)
-   -   Standard switch with lipo and regulator (http://www.rcuniverse.com/forum/questions-answers-154/11232848-standard-switch-lipo-regulator.html)

KitBuilder 09-18-2012 03:45 PM

Standard switch with lipo and regulator
I have moved from NIMH 4.8 to Lipo 11.1 for my glow planes using a regulator set at 5v. Can I use the standard switch that comes with most radios in between the lipo and the regulator. The regulator has wires on the input side as thin as the switch wires. At the moment... i'm unplugging battery from regulator.

What I have been trying to understand is.... does the volts coming out of the battery depend on the pull from the downstream device. For example.. it's not like the pressure behind a dam.. where a small hole and the water will come out with brute force due to hte pressure behind the wall.

Since receivers can't be plugged directly into a lipo I assume the volts coming out is 7.4 or 11.1 based on cells. Would I need a heavy duty switch I can mount on the exterior?

I moved to 11.1 rather than 7.4 in case i lose a cell I sitll have the volts needed.


scale only 4 me 09-18-2012 03:53 PM

RE: Standard switch with lipo and regulator
Yes, your theory is correct,, Amps are what the servos and RX demand,, not what the battery can deliver.

So the question is, does your amp draw exceed the max your switch/wires can handle?

jester_s1 09-18-2012 06:41 PM

RE: Standard switch with lipo and regulator
And my question is "Why?" If you're really worried about losing a cell, then buy a 6v NiCd made from Sanyo cells with welded construction and stop worrying about it. Of all the things to happen to our planes, this is the least likely scenario unless you're in the habit of using 7 year old receiver batteries. Don't get me wrong, I'm all for redundancy and making things as failsafe as possible, but you're far more likely to have a regulator go kaput on you or to plug in a defective (used up) Lipo than you are to lose a cell in flight from a NiCd.

scale only 4 me 09-19-2012 01:42 AM

RE: Standard switch with lipo and regulator
I tend to agree with jester on this one,

The one time I had a pack go bad, lost a cell that is, it was a 5 cell Nicd pack, the cell shorted and I found the pack had dropped the voltage to 3 volts after I clean up wreckage and tested it,, I started to loose elevator power, I knew what was happening, but it was to late to save the plane. A cell goes bad in you pack, chances are good the pack will go dead quick.

If you want true redundancy against battery failure, you're better off with a Bat Share, Wolverine or Powerexpander type switches and use two smaller batteries instead of one large one. Of course the chance the switch can go bad always exists too.

There's no way to prevent component failure 100%, but keeping an eye on things and cycle testing your packs many times will alert you to a component or battery that's going bad.. Many times your plane gives you a warning that you must not ignore.

Good luck

jester_s1 09-19-2012 04:50 AM

RE: Standard switch with lipo and regulator
A pilot can even get the same effect just mounting two standard switches with two batteries and running them to the receiver. If you don't have an extra channel to plug the second battery into you can Y harness them into one. FWIW, a regulated Lipo isn't about redundancy or safety. If anything, it's less reliable and far more prone to being damaged than a standard NiCd is. Using Lipos with a regulator is about feeding large numbers of power hungry servos in a big plane that pulls too many amps for a NiCd to keep up, or either where using a NiCd or Nimh would be heavier than a Lipo with a regulator due to the capacity required.

KW_Counter 09-19-2012 06:25 AM

RE: Standard switch with lipo and regulator
Kit Builder,

You are on the right track.
Voltage is like water pressure.
Current is the amount of water.
Your receiver will take the amount of water it needs.

Good Luck,

rlipsett 09-19-2012 12:53 PM

RE: Standard switch with lipo and regulator
One small correction on the receiver taking only what it needs. Internaly to the receiver circuits it takes what it needs but the receivers power buses take all the current that the receiver needs and also the servos too. I do not know what the amp ratings of the buss is for receivers but under most circumstances that is not a problem

jester_s1 09-19-2012 02:33 PM

RE: Standard switch with lipo and regulator
On the original topic, there's a general tendency for modelers to want to do things "better" than the stock way or the regular way. "Better" usually means more expensive and more complicated. We strengthen landing gear plates, beef up firewalls, use digital servos on non-aerobatic planes, go to monster size batteries, add extra hinges, use some kind of stickum when we cover, and on and on. Most of the time, all that our efforts get us is a little extra weight and a lot of extra time spent for no change in performance or reliability.
For planes that don't require a power expander or draw unreal amounts of current, the only actual "better" that is needed or even helpful in the battery department is to spend the extra $5 on top quality switches, the extra $20 on top quality batteries, and invest the time and effort to do cycle testing and store the batteries in a non-abusive environment (not out in a shed where they burn in the summer and freeze in the winter). For very power hungry planes in the smaller sizes, redundant packs and switches can give some peace of mind, but even that's generally overkill.

KitBuilder 09-19-2012 07:47 PM

RE: Standard switch with lipo and regulator
My goal wasn;t for redundancy and I wasn't overly concerned about losing a cell. I just figured at 7.4, if I did Llose one I was screwed using 2.4.

I moved to lipo for the convenience...namely quick charging and the volt depletion curve. Using a 5 cell NIMH still requires a regulator for the majority of my servos so lipo still makes sense to me. I realize I'm adding connections - regulator and switch and thus more poitns of failure... but I became nervous about hearing of brownouts and such with 2.4 and the receiver rebooting etc. I wanted to be sure I had 5 volts for the days flying. I'm using a castle creations regulator so it should be of good quality and lipos of generally 1500 mah on a typical 5 servo model

So for the switch... I assume it would need to handle the full 11.1+ coming from the battery. I'm thinking of trying one of the arming switches I saw advertised. http://www.rcaccessory.com/armingswitch.aspx

or a heavy duty swtich

jester_s1 09-19-2012 09:13 PM

RE: Standard switch with lipo and regulator
You're using servos that can't handle 6v? How old are they? If you'd consider 6v compatible servos, a 2 cell LiFe will give you all of those conveniences with no regulator needed. Even if you do go ahead with your plan, a 3 cell pack isn't going to do anything for you. If you do get a bad cell, the first thing that normally happens is its internal impedance rises. That causes a drop in voltage under load for the whole pack, so you're under the threshold anyway. Use a 2 cell pack and always balance it, then do a cycle test every few months to make sure both cells are maintaining capacity.

To answer your question though, voltage is not much of a worry with wiring or switches. All it does is increase the distance that sparks can occur, but that's not a concern when you're only talking about doubling the voltage. Current is your problem because that's what makes heat. You haven't said what servos you are using or how many, but for most sport models you won't come anywhere near 5 amps. So either of those switches should be fine.

KitBuilder 09-20-2012 05:59 PM

RE: Standard switch with lipo and regulator
I thought I mentioned 5 servos but didnt realize about the cell loss and internal impedance, etc.. You're right.. min are rated for 4.8 or 6. I didnt want to move to life batteries at 30 bucks each as I had several right sized lipos and fully charged I thought they approached 3.6 per cell or 7.2 and figured that would be to much for the servo. I realize a 6 v pack is more than that but thought 7.2 was to much. Life does sound like the way to go and my charger does handle Life...... so I guess I'll need to start moving over to them for my glow models

All times are GMT -8. The time now is 12:40 PM.