Correct voltage for corona servo

[Rob43]

I have some corona DS339HV servos. On the side of the box ot says that they are rated at 7.4 volts. No minimum operating volts is written on the box. I had intended to run them off of a 2s lipo but this fully charged will be at 8.4 volts. Are they designed to be run this way or should i be using an sbec, although the ones i have been looking at seem to have either 5 or 6 volt output. Can anyone say from experience if i should be running them through an sbec off the 2s lipo or am i able to run from the 2s lipo directly?
Thanks all

[Martin Harris - Moderator]

I would suspect that they are rated at the nominal voltage for a 2S LiPo (7.4V)

[cymaz]

You could email them to find out.....that's if they reply. The website states 7.4v so that should be ok.

[Rob43]

Good idea i think, i will give them an email in the morning. Got thier email from the website. There is no rush to use them now, im just planning ahead for a build i will do in a couple of months time.

[Andy Meade]

I use these servos quite a bit. I buy them from Hobbyking, and they state 7.4v in the spec.

[Rob43]

Hi Andy
So how are you powering these servos,are you doing it directly from a lipo or are you using a voltage regulator and if do what voltage do you use?

[Andy Meade]

Sorry, I should have mentioned that! 2 cell LiFe usually, but I do have one or two models using them on 5 cell NiMh. Hope that helps.

[Rob43]

Sojust to update.
I did email corona, three days have passed and not had any reply so far.
Oh well im not in a hurry i suppose lol

[Peter Beeney]

Rob,

If I were using these servos I would be more than happy to connect them to a 2S lipo, the letters HV after the number indicates that it it would be quite safe to do so; and to be quite honest, it’s the only way you are going to be able to supply them with 7.4 volts anyway. Other than using other higher voltage multi-cell batteries, of course. If Corona were slightly more pedantic they would have indicated the voltage range as 6 to 8.4 volts.

All these electrical items have a nominal, or name plate, value. Take for instance the common or garden car headlamp bulb. The nominal value of a car battery is 12 volts, so the bulb will be a 12V 55W (say). But because the bulb is mostly on when the engine is running the bulb’s input voltage will be around 14.4. because the battery voltage will be 14.4 volts. So there always has to be a bit of leeway built in, but the driver doesn’t worry or care about this.

The nominal voltage of a 2S pack is 7.4 volts and there is a valid reason for this.

I’d be slightly concerned about the receiver, though, I’d check this first, but I’m sure most if not all 2.4 receivers are HV. The Frsky ones that I’ve seen can be up to 16 volts. Also if I connected a 2S lipo to the rx I’d make sure that all the servo were HV, hanging a standard servo on as well would result in it quickly showing some displeasure; such as noticeably twitching and then possibly bursting into flames. It has happened.

Good Luck…

PB

[Rob43]

Hi Peter and thanks for the reply

You make some sensible points here, very well presented!

I had intended to use all the same servos so as not to have a voltage mismatch and I had looked previously too at the rx voltage too as I had noted that the orange 9ch rx i am intending to use is rated from 3.7 to 9.6 volts so i always knew I would be operating that well within its safe range.

This sets my mind at rest anyways and Im happy to go ahead this way.

Thanks again for the input

[Frank Skilbeck]

As I have a couple of corona hv servos I emailed them earlier this week and they've replied and advised that 8.4v is fine.

 

Edited By Frank Skilbeck on 14/05/2016 09:26:40

[Rob43]

Frank, thats yet more reassuring to know. I still havnt heard back from corona yet but i have all the info i need now.Many thanks

Edited By Rob43 on 14/05/2016 17:23:24

[Peter Beeney]

Thanks for the reply, Rob, and apologies for adding one last post. I also forgot to mention that in this case HV = High Voltage - although that is pretty obvious, I suppose…

It’s always going to be logical to label any electrical component with the working voltage that it’s designed for, but it will also be able to accept the range of voltage that it’s supply can cover. In the case of the lipo that about as simple as it gets, 3 to 4.2 volts per cell.

The nominal voltage of 3.7 volts/cell was originally 3.6, the mid point between 3 and 4.2, this will be the average voltage of the cell as it discharges from fully charged down to completely discharged. Then someone thought they might be able to claim a bit more performance over the opposition by upping to 3.7. Everyone else then naturally enough followed suit and it stuck.

The capacity of a cell is usually quoted in ampere hours, Ah, but there is an alternative way which is watt hours, Wh, (or maybe minutes, or seconds,); but to do this we need a voltage as watts are amps multiplied by volts. We can only sensibly use the average voltage because anything would give us an incorrect value.

Looking at a single cell, say, a 1000mAh 3.7 would be 1Ah x 3.7V = 3.7 watt hours, 2S would equal 7.4 watt hours. This is useful if we want to compare it with a different type of cell, let’s say a NiMH. Again the capacity is 1Ah but the average voltage is only 1.2 so the Wh capacity is only 1.2 watt hours. So we need 3 NiMHs to 1 lipo. for the same amount of Wh capacity.

It’s also another means of checking the flying time of electric models. Our model has 100 watts reading on the wattmeter and we are using a 2200mAh 3s pack. So 2.2Ah x 11.1V = 24.42Wh. Divide by 100 = 0.2442 hours. Multiply by 60 to convert to minutes = 14.652, and 0.652 by 60 again for seconds = 40. So a total flying time of 14 minutes 40 seconds on a constant full throttle. It doesn’t really matter much how you do this little calculation either, but it’s necessary at some point to make the units the same value to give the answer conveniently in minutes. And this is only very much an approximation anyway, trial and error using the throttle will soon prove to be more accurate.

Hope this might of some interest and assistance to someone…

PB

[Steve Hargreaves - Moderator]

I have a few Corona servos & run them direct on a 2S LiPo no problems at all.....my Rx is rated up to 10V so I just plug the Lipo in as "normal".

Worth bearing in mind that the HV servos will be a litle sluggish & lack power if you use them on a low voltage battery......