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5.5v too high for MKS servo?

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David Hall 905/08/2020 11:09:28
286 forum posts
16 photos

I have fitted a 5.5v SBEC/ESC to my F5J glider. This has several MKS DS6100 servos fitted. It seems to work well except for a later model servo recently fitted to replace a faulty servo. It can behave oddly near the centre when the stick is centered from full movement quickly.

In a separate job on the same plane, I was planning to add a battery backup system and had to look up the low voltage limit for theses servos. I was surprised that the specified higher voltage limit is 5v.

Am I risking a failure of the MKS DS6100 by running at 5.5v?

 

 

Edited By David Hall 9 on 05/08/2020 11:09:43

flight105/08/2020 12:05:56
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738 forum posts
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a short answer is yes you are risking it. The manufactures states

NOTE: Use with 4 cell Nicd/NiMH battery or use UBEC (4.8V~5.0V)

as quoted from MKS site

 

it's all red type How??

 

 

 

 

Edited By flight1 on 05/08/2020 12:07:13

David Hall 905/08/2020 12:41:15
286 forum posts
16 photos
Posted by flight1 on 05/08/2020 12:05:56:

a short answer is yes you are risking it. The manufactures states

NOTE: Use with 4 cell Nicd/NiMH battery or use UBEC (4.8V~5.0V)

as quoted from MKS site

it's all red type How??

Edited By flight1 on 05/08/2020 12:07:13

Thanks for repeating the spec to me.

I run another glider on 5.5v (most budget integrated BEC/UBECs over 40A rating have a 5.5v output), this has had no issue.

I wondered if anyone has actually blown a DS6100 on 5.5v?

On the other hand, this will facilitate my future plan to add a diode in the output to allow the use of a backup battery.

Richard Wills 205/08/2020 13:16:49
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249 forum posts
7 photos

If a 4 cell nimh is ok, 5.5v should be fine. Fully charged a 4 cell nimh is a tad over 6v.

Martin Harris05/08/2020 13:37:53
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9491 forum posts
256 photos

Won't that voltage drop very rapidly under load? The regulator will continue to supply 5.5v under load, effectively indefinitely.

flight105/08/2020 14:18:07
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738 forum posts
37 photos

Well if a electronic circuit is designed to run at a said voltage it should do so , anything above that will generate excessive heat that the either the circuit can cope with or not, but will shorted it's service life.

Running at more than 5v is a chance you either take or don't, fit a diode to drop voltage and then don't worry

as for me parroting the specs the MKS designers put it there for a reason but Hay hoindecision

John Wagg05/08/2020 14:45:40
115 forum posts
20 photos

A fully charged Ni-cad will be 5.6v, but not for long. As suggested above, fitting a diode in series on the output of the voltage regulator will reduce it by 0.6v. (5.5v will then be 4.9v approximately). You will need to make sure the diode will withstand, at least, the current drawn by the servos etc.

Edited By John Wagg on 05/08/2020 14:46:11

Denis Watkins05/08/2020 15:45:34
4621 forum posts
129 photos
Posted by David Hall 9 on 05/08/2020 11:09:28:

In a separate job on the same plane, I was planning to add a battery backup system and had to look up the low voltage limit for theses servos. I was surprised that the specified higher voltage limit is 5v.

Am I risking a failure of the MKS DS6100 by running at 5.5v?

From another angle David,

Most " microchips " as we call them, encapsulated in black plastic, are integrated circuits.

In our case are commonly used circuits that are manufactured within a black box with often 2 rows of evenly spaced

legs to mount them with. More recently they have become surface mount, but are much the same circuitry.

Most of these are rated at 5v

So the voltage limit of 5v was not just plucked from the air; just that the internal components are rated 5v.

Is in large why 4.8v was adopted in the begining by manufactures as rechargeable cells fell nicely at 1.2v

David Hall 905/08/2020 16:43:23
286 forum posts
16 photos

The spec is a little contradictory, rated at 4.8v NIMH battery or 5v BEC, where the NIMH battery will be significantly higher than 5v at times. What limit to apply?

As I had the parts in hand, I have added a diode in series with the supply to the RX. I used a diode rated at 15A (still physically small). I had measured the forwards voltage drop as near to 400mV, so may work well here, giving a supply voltage of around 5.1V.

I have tried it, it works.

I was surprised find that the servo that had odd behaviour is now as near perfect as it could be.

For info... when the stick (aileron in this case) was moved from its end stop to the centre, as fast as I could, it sometimes overshot the centre by a noticeable amount, hesitated for a fraction of a second, then centred. All slower movements over the full range were fine. I cannot make it do this, now the voltage is lower.

Thanks to those that suggested that the spec should be adhered to.

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