David Hall 9 Posted August 5, 2020 Share Posted August 5, 2020 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 Quote Link to comment Share on other sites More sharing options...
flight1 Posted August 5, 2020 Share Posted August 5, 2020 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 Quote Link to comment Share on other sites More sharing options...
David Hall 9 Posted August 5, 2020 Author Share Posted August 5, 2020 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. Quote Link to comment Share on other sites More sharing options...
Richard Wills 2 Posted August 5, 2020 Share Posted August 5, 2020 If a 4 cell nimh is ok, 5.5v should be fine. Fully charged a 4 cell nimh is a tad over 6v. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted August 5, 2020 Share Posted August 5, 2020 Won't that voltage drop very rapidly under load? The regulator will continue to supply 5.5v under load, effectively indefinitely. Quote Link to comment Share on other sites More sharing options...
flight1 Posted August 5, 2020 Share Posted August 5, 2020 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 ho Quote Link to comment Share on other sites More sharing options...
John Wagg Posted August 5, 2020 Share Posted August 5, 2020 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 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted August 5, 2020 Share Posted August 5, 2020 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 Quote Link to comment Share on other sites More sharing options...
David Hall 9 Posted August 5, 2020 Author Share Posted August 5, 2020 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. Quote Link to comment Share on other sites More sharing options...
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