Blixsim

Hi Guys

Can anyone give me some advise on how to connect a separate battery to a large servo.

I have a large 16kg (I think) servo which I will be using on the rudder of my 28% Cap232 (my 1st biggish bird). I want to connect a separate battery to this servo in such a way that it is powered separately and not from the receiver &other 5kg servos. I'm concerned that this large servo will place a huge drain on my battery which may cause an excessive voltage drop and which may lead to a dead receiver. Is it possible to have one battery for receiver and other (5kg) servo and another separate battery for my giant servo. If so how do I connect it such that the servo still receives signal from receiver but power from the additional battery.

I plan to use a 6V 1800ma NiMH battery to power this but looking at the other threads I'm now concerned that NiMH may not be a good idea for such a large servo. Also is it safe to run a 1800ma battery thru the receiver or will it roast the circuitry.

thanks & regards
Hedley

CL215FAN

My Feedback: (13)

Hedley
I use 2 batteries and 2 switches,and a y-harness.I use batteries of same m.a. to keep it simple when charging.Hook first battery as you normally would Hook second battery up the same way.Just plug it into any open channel using the y-harness,plug other end of y-harness into jumbo servo.Another advantage is if one switch or one battery fails every thing will still work.Two batteries connected this way will not hurt your system.Its still only 6 volts.
BOB

Captain351

Check out this link for the I4C Isolator.

http://www.i4cproducts.com/the_isolator.htm

Blixsim

Thanks for the info guys. I had an idea that possibly I could split the cable and send signal from receiver to servo and the power lines from battery to servo. Dont know much about electronics tho but would like my plane home in one piece and not in a garbage bag

Hedley

Rodney

Yes, you can connect a seperate battery to your servo. Just break the positive lead between the servo and the reciever (leave the negative and signal lead connected between the reciever and servo). Now connect the seperate battery between the positive and negative leads of the servo. note that the negative lead from both the reciever and from the added battery both go to the servo. Put a switch in the positive lead from the added battery to the servo so you can turn it off/on as required. Doing this will often cure servo jitters caused by long leads.

sfaust

My Feedback: (11)

On a 28% airplane, you are trying to solve a problem that doesn't exist. Even on airplanes as large as 40%, driving 12 or more servos, all high power, high torque, the voltage problem doesn't show itself if you adhere to a few rules.

Use 22ga wire. Use 5cell packs. Minimize the number of connectors in the system, Keep all your leads at the right length (ie, do not bundle up 6' of excess wire). Use two batteries and two switches plugged into the receiver.

If you do the above, you can run 10 or 12 digital servos in airplane up to 40% without any isolators, separate power busses, and so on. And by using an isolator or power buss, you lower your reliability of the whole system because you have more components, more wires and connections, and instead of having two batteries and two switches of which either can provide power giving you redundancy, you have two batteries and two switches of which either one can kill all power to your system . Kind of redundancy for failures, and not redundancy for reliability .

Before you do this, spend a little bit of time doing some research on this. If you want to increase your reliability, using a separate power system is traveling in the wrong direction.

The 1800 NiMh packs won't cause you any problems roasting the receivers. In fact, you can't roast the circuits with 5 3000mah NiMh packs plugged into one receiver. Most people flying the larger airplanes 35%, 40%, and 42% typically run two 3000mah NiCd, NiMh or Lithium packs and either one or two receivers. You are definitely on the safe side with your setup and one or two 1800mah NiMh packs. In fact, I would have recommended two 2150's 5cell packs for redundancy, added flight time, and the extra headroom against voltage depression.

mulligan

Steve, this has to be the ump-teenth time you've posted on this topic. Kudos for your stamina and you are hereby branded "Redundancy Man"

- George

sfaust

My Feedback: (11)

Sorry bout that... I just hate to see someone that is obviously concerned with reliability take such a big hit in reliability trying to solve another problem that doesn't exist in his installation.

Just trying to help.

I'll be quiet now.. (he says as he slumbers back to his corner)

mulligan

???

Why apologetic?... I was thanking you!!!

sfaust

My Feedback: (11)

Cool! (he says as he bounds out of his corner, looking for his keyboard)

Blixsim

Thanks guys

Will keep it simple and just plug two 1800ma packs into the receiver, or maybe one via a y-harness to the servo The jumbo servo idles at 800ma hence my concern.

Stephen pls keep the comments coming. Your fellow modellers rely on contributions from experienced flyers

Regards
Hedley

sfaust

My Feedback: (11)

Ok, I am concerned here to. 800ma at idle? That seems like a lot, or my memory of what I have measured in the past is off a lot. Whose servo are you using? Did you get this number from measuring it yourself, or from the manufacturer? Let me know what the manuf/model is, and I'll do some checking. 800ma just seems high.

Do you know what it pulls when you move it, or the max draw?

Blixsim

Hi Stephen

It is a Hitec Jumbo which I bought from a fellow modeller. I'll check the model number when I get home tonight (morning on your side of the world).

The little spec sheet which comes with the servo claims 800ma at idle and recommends a minimum 1200ma as a power source.

I'm a bit concerned that under airload it will suck the juice from the system and leave the receiver without power especially since I want to use NiMHC

I'm beginning to wonder if maybe this servo is not maybe more trouble than its worth. I couldnt resist the bargain but then again which modeller can.

thanks
Hedley

Rodney

Not only is 800 ma a little high, it is outrageously high. something is wrong, idle current should be well below 20 ma. Peak draw at max load will most probably exceed one ampere but for a short time only.

Blixsim

ok, here are the specs

its a hitec HS-805BB 224oz Mega quarter scale servo,

I had ma rating incorrect. It is idle 8ma, 800ma zero loaded,
minimum 1200ma source supply required,
connect via y-harness to servo for BEC receiver (What is BEC, is the JR 9channel PPm receiver a BEC type receiver)

I would assume then its ok to run on two 1800ma NIMH

thanks for advise


regards
Hedley

mglavin

My Feedback: (31)

OK, you've provided enough info to make an educated guess for a sound NO fat system....

The 805 has been around almost as long as dirt, blow the dust of it, it's a very good servo. Might be more than you need for a 28% Cap, but what the heck. Where is it going, belly in pull-pull? Is this the known location for the rudder servo? Balance plays a keen factor with rudder servo size, type, number and location...

The wye is not required plug the the beast right into the rudder channel.

Battery Eliminator Circuit [BEC]. Not needed for aircraft generally. Typical application is a car or boat with small RX with a large capacity 6-cell 7.2v battery used for motor power and RX power... The wye is not a bad idea for use in the rear of the model, you can locate the battery nearby. Hopefully you need the weight in this location.

Go with the dual switch/battery scenario Stephen recommended. Simple, trouble free, light-weight, redundant and reliable.


A much wiser man once said:
It is important to differentiate between unforeseen failures, and avoidable failures. Now you feel the need to lump both into the same category?

Wise-man, me thinks :idea: