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Amp draw on a four channel w/standard servos

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Old 01-03-2017, 02:12 PM
  #1
Yasbush
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Default Amp draw on a four channel w/standard servos

Just bought a hanger 9 load volt meter to test my 4pk nicad 600mah receiver Battery packs for load testing? What amp draw should I set it at? .5, 1A or 2A for realistic measurements. Thanks.

Last edited by Yasbush; 01-03-2017 at 04:20 PM.
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Old 01-03-2017, 03:35 PM
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Desertlakesflying
 
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Just make sure you aren't using that battery with a Spektrum radio... at least 5 cell or 6.0v Personally I wouldn't use a 4pk nicad in anything these days.
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Old 01-03-2017, 04:10 PM
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Yasbush
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Futaba 6J radio. Plan to purchase 4pk nimh 2000mah batteries but the original question remains.

Last edited by Yasbush; 01-03-2017 at 04:24 PM.
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Old 01-03-2017, 04:39 PM
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Hmmm..... I am ASSUMING that you are using low end servos, and not much of them. Those don't draw much current, but still, I would do the 2 amp, as that is what I did when I still used nimh. You always want to check if your battery is performing properly. I am also pretty sure that even 4 servos might be able to peak at over 2 amps, as I have tested this with 2 servos, and was able to get one peak at 1.6 amps. I will try to test a few futaba s3003s today to make sure. And yes, a upgrade to life or atleast nimh is recommended, as 3 flights on that battery is pushing it.

Desertlakesfying, I tested my spektrum tuff, and it brownsout at 3.1 ish volts. If your battery is at 3.1 volts, well um, your servos will move very slow, at the least.

Hubert
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Old 01-03-2017, 05:09 PM
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jester_s1
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A momentary peak isn't the same as sustained amp draw. All the battery meter does is tell you if the battery is ok. The .5 amp load is appropriate for that size battery. It's another question entirely if the battery is appropriate to the model, which depends on the servos you are using and the flight loads on them. My rule of thumb has been to size the battery for 8-10 flights based on the average amp draw. That lets me fly 5 and still have safe voltage at the end.
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Old 01-03-2017, 05:14 PM
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Hydro Junkie
 
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I have to agree with Jester, set it at .5 and see what happens. My battery charger/cycler discharges and recharges at 50ma, IIRC. To me, it doesn't make sense to run them that much higher than the .5 since pulling a lot of amps can damage the pack

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Old 01-03-2017, 05:26 PM
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I underastand that .5 amps probably makes the most sense, because it will check that the pack is good, but 2 amps shouldn't damage the pack. Of course, a momentary peak isn't the same, but when I tested my packs, I didn't hold the 5 amp setting for longer than 2 seconds. 5 amps might be much for that pack, since it is a 600 mah nicad.

The reason I recommended 2 amps, is because a pack may show little voltage drop on .5, but alot more on 2 amps. I guess if the pack shows no drop on .5, then you are ok. If it drops a bit more than you think it should, then test at 1 amp, to make sure that the voltage doesn't drop too much.


Hubert
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Old 01-03-2017, 06:51 PM
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You need to cycle it on a discharger to check its capacity.. The NiMh chemistry/construction has been modified a lot over the last few years and you may not be able to tell the health by the voltage as well as in the past. as far as usage per flight My 1/3 cub with the old standard brick futaba servos would use 500-600mah total at a flyin with 7-8 15-20 min flights all flying hard and flying formation touch and goes so always on the sticks.... standard servos wont pull that much current 1-2 amps max then they will fry.. my 44% yak will use 200mah getting the motor started the first flight of the day...and then 500 per flight with 14 digital servos humming away...
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Old 01-03-2017, 07:08 PM
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Battery health of nicad is best determined with battery cycling equipment
I fly on nicad for 23,years without any battery issues ever

600-700 nicad will have no problem flying four std servos for a days flying at the field ( 3 -15 minute flights )
You need - an expanded volt meter- then you can check the batteries condition before each flight if you like ( a good idea )
The genneral rule is 100mah for each servo and 100 for the receive

I went to 1000 mah and 6v and never looked back
The 1000 holds up better than the 6or 700 packs for the long haul
That increses the flying time (great ) and increases the servo speed which is no problem as most all servos have a 4.8 and 6v rating for speed
The higher mah reading will cause you batttery cycling time take longer which is a little down side
i alway cycle my batteries when i remove a plane from my wall and plan on taking it to the field

It is important to use a good percentage of the battery after a days flying so that you keep the battery pack in a good state of health ( discharge and recharge cycles )
For that reason i would not go much more than 1000 mah or so
i do think 2000 Mah is not a good idea
Keep Nicad in a high state of charge prevents internal shorts from happeing

I buy my brand nicads Tenergy at American batteries.com mostly single cells
i build my own battery packs for the past 10 years

I greatly dislike NIMH batteries way to sensative to handle for me

Flying two cycle glo is my RC passion

Rock on
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Old 01-04-2017, 03:46 PM
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Yasbush I believe you missed the point that the gentleman was trying to make in post #2 and that is with a 2.4 system of any brand it is not such a good idea to use any Nicd or Nimh with only four cells. Regardless of the capacity. I believe only five cell packs should be considered when using Nimh, Nicd.

For 72 MHz systems yes four cell packs were fine but not with the 2.4, there is simply not enough voltage safety margin.

John

Last edited by JohnBuckner; 01-04-2017 at 03:49 PM.
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Old 01-04-2017, 04:43 PM
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To be honest, lot's of people use 4 cell nimh on 2.4 at my club, without any problems. This is only on 4-5 channel planes, so the voltage drop will be minimal, and a nimh stays over 5 volts (I usually recharge after it's at 5.2) for quite a few flights. Not sure about nicd. A 4 channel trainer is really the only thing tha a 4 cell can sort of handle, but you have to be really careful to not have a brownout.

That said, you should definately switch to something better. I recently switched to life, and have not looked back. To me, 3 flights is not enough, especially since the last one is too close to the battery being flat. I aim for not draining over half of a batteries capacity. Since I use life, I can easily top it off after a few flights very quickly.

Hubert
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Old 01-04-2017, 07:44 PM
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Yes I also use sometimes four cell packs however only on a lightly loaded system and one with a limited number of servos perhaps just two or three. In addition I also use four cell packs in my controlline airplanes where only one small servo is used.

I use for the vast majority however five cell Nimh and have been for at least eighteen years now when I abandoned the use of Nicd types. Even am currently using a mix of Nimh, Life in my three turbines.

There is nothing wrong with using Nimh nor are they obsolete. In addition when Life's are suggested to new folks seldom is the fact that they will require a capable charger which most new folks do not have mentioned. The worst part is the fact that the Life' will required two leads to be hooked up every single time it is charged not one as with Nicd and Nimh. This of course requires the battery to be removed each time or worse and extra extension be cobbled up.

No there are likely more folks using Nimh than you are willing to believe and agine folks who would like to use Nicd or Nimh you would be wise to use a five cell type. It only takes one hung surface or even more likely a hung retract to cause a brown out if you are using only four cells with a 2.4 system.

John
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Old 01-05-2017, 07:31 AM
  #13
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I'd use the 1/2 amp setting. You should get 3 or 4 flights out of a 600 mAh pack
consider the pack completely discharged at 4.4v unloaded.
A 2000 mAh pack is a bit of over kill, instead I'd go with a 6V 1000 mAh pack
do you have a charger that will charge a 6 V?
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Old 01-05-2017, 06:50 PM
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I'm going to go with John on this one. There is nothing wrong with Nicad packs or running 4.8 volts in a plane using 5 servos. I run the Futaba NR-4J 4.8 volt 600mah pack to handle the receiver and servos in a 1/8th scale hydroplane. At a race, we run three to four heats of no less than 5 minutes, one or two more "consolation" heats and a final. I have run the same pack for an entire day, some events for two days, without recharging or changing packs and I'm sure my rudder servo, an S9156 high torque digital, takes some serious power when under load which unfortunately, is all the time. My throttle servo, a standard digital, probably takes a decent amount of power as well, just due to being digital. If the plane in question is using standard servos, there's no reason to have to buy a high power battery pack. Someone mentioned LiFe packs. I have one in my boat's 2.4 FHSS transmitter and, after two years, have never had to recharge it. That kind of charge life tells me that, unless you're flying a very big plane with lots of digital hi-torque servos, a LiFe pack is overkill for the average hobby flier
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Old 01-06-2017, 04:40 AM
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IMHO 6V on 2.4 systems. But it's your plane
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Old 01-06-2017, 08:50 PM
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jester_s1
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Spektrum is the only brand that has a problem with 4.8v batteries. Everybody else designed their receivers to work properly with the batteries most of us prefer to use.
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Old 01-07-2017, 07:43 AM
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I agree with John, that a stalled servo will almost certianly cause a brownout on a 4 cell. It might also cause a brownout on a 5 cell, especially on a higher torque servo. I'm pretty sure that a short circuit servo will cause a brownout on almost any battery, unless you can land really fast, without that servo.

I use spektrum, and am now using life, but used to use 4 cell nimh with no problems. This was on a 7 servo plane so nothing special. As I mentioned earlier, the rx brownsout at 3.2 ish volts. I wonder how low other systems can go? I also wonder if a 4 cell goes to 3.2 volts, can it stil be ok? I'm assuming that you would need lots of current to drop the voltage that low, unless the battery is close to being completly discharged.

Hubert
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Old 01-07-2017, 08:58 AM
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If you are drawing a 4.8v battery pack down past 4 volts, you are using too small a battery pack for the plane you are flying.

There is no excuse for having a stalled servo in your plane. Proper setup is meant to prevent that, and is definitely one of the things you have to check for. Between that and a good preflight routine, stalled servos are a practical impossibility.

Catastrophic servo failures that result in high amp draws are certainly possible, but aren't really anything you can plan for or mitigate against. The vast majority of non-crash related servo failures result in the servo just stopping, which won't kill your battery but will wreck your plane. You can guard against that by rebuilding or replacing old servos periodically.

So in short, if your battery is in good condition and sized properly for your plane, if you set up your plane correctly and do good preflights, and you don't have some act of God that takes out your electrical system, you'll be fine. The conventional wisdom of checking batteries with a 1C load holds up very well, and the recommendation from Spektrum to stick with 6v battery packs will prevent you from having any problems.
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Old 01-11-2017, 10:03 AM
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Just trying to get a realistic voltage reading on my meter before flying again when checking. I learned quite a bit. Thanks everyone.
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