A123s and older servos
02-11-2018, 03:27 AM
#1
A123s and older servos
I am converting a jet over to A123s from 5 cell NiMHs that has a mixture of servos: Futaba analogs, JR 8411s and Hitec digitals. I have been running without a regulator with the NiMHs but have been told I may need to run a regulator with the A123s. Is this correct?
02-11-2018, 07:28 AM
#4
There are low voltage and high voltage servos. The low voltage servos typically are designed to not exceed 6.0 VDC. LiFes are 6.6 VDC and even higher on a fresh charge. That being said, many folks claim to be using LiFes on low voltage servos. Some higher end servos do appear to have a bit more margin on the Max end of the voltage spec. Bottom line is; Using high voltage on a low voltage servo adds an additional unnecessary risk. Who is to know when or if one will eventually fail. Manufacturers have specs for a reason.
I came from an industry where nothing is ever operated at its Max spec. So I personally run HV servos on any LiFes. I even regulate all the 2S LiPos I use, even though I run exclusively HV Servos on every giant plane. I suspect some folks flying giants and jets never get out a pencil and/or a current/ammeter to figure out what they are actually running for current and voltage at the endpoints, etc.. If they did they would probably be running some sort of power distribution/regulation devices in their giant planes, especially when you start using digital servos. But to each their own. I personally just figure why take unnecessary risk with a $5K+ plane that is occasionally flying in front of a crowd of pilots and spectators.
From a CD perspective: How does one even declare a plane is safe when the pilot knows the design has intentionally exceed manufacturer's specs? Sounds like a "good in" for a sharp lawyer representing any resulting crash victims. To me personally, flying jets is risky enough w/o intentionally introducing unnecessary risk! But obviously others are less risk adverse than I.
I came from an industry where nothing is ever operated at its Max spec. So I personally run HV servos on any LiFes. I even regulate all the 2S LiPos I use, even though I run exclusively HV Servos on every giant plane. I suspect some folks flying giants and jets never get out a pencil and/or a current/ammeter to figure out what they are actually running for current and voltage at the endpoints, etc.. If they did they would probably be running some sort of power distribution/regulation devices in their giant planes, especially when you start using digital servos. But to each their own. I personally just figure why take unnecessary risk with a $5K+ plane that is occasionally flying in front of a crowd of pilots and spectators.
From a CD perspective: How does one even declare a plane is safe when the pilot knows the design has intentionally exceed manufacturer's specs? Sounds like a "good in" for a sharp lawyer representing any resulting crash victims. To me personally, flying jets is risky enough w/o intentionally introducing unnecessary risk! But obviously others are less risk adverse than I.
02-11-2018, 08:25 AM
#6
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I agree with Len Todd's comments. I had a company from 1967-1983 and we built thousands of servos that were rated at 6volts. I would not recommend 6 volt servos running on 6.6 volt batteries and we would not have honored warranty if someone ran our servos on 6.6 volts. Any time someone has a servo failure I ask and "what battery voltage are your using" and what is your servo rated voltage?
02-11-2018, 11:32 AM
#8
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I would use a Regulator on A123 cells 2 x A123 fully charged works out at 7.2v DS8411 will not take 7,2v for long.
I remember blowing up 2 x Jr 591 servos using A123 without a regulator.
I remember blowing up 2 x Jr 591 servos using A123 without a regulator.
02-11-2018, 12:20 PM
#9
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+1. A fully charged 5 cell Ni pack is pushing 7.0 to 7.2 volts. A LiFe pack quickly falls below 6.6 volts and stays there. In addition anyone running a battery saver with back up pack will typically see .3 to .5 volts drop across battery saver diodes dropping LiFe voltage to around 6.1 to 6.3 volts.
02-11-2018, 09:16 PM
#12
Been running a BVM Bandit MkII (with M140xbl) since 2013 with all the recommended 6v JR servos on 6.6v A123 cells without regulator. In addition Ultra Flash (again M140xbl) with all JR 8411 (6v) on 2 cell A123 cells without regulator. I also have been running 12cell CompArf EDF spark with regular Hitec servos on 6.6v A123 Rx without regulator since 2011. 729 documented flights between all three planes without a single fried servo. If a servo can run on 5 cell NiMh, it can certainly run on 6.6v A123.
Last edited by DrV; 02-11-2018 at 09:19 PM.
02-12-2018, 12:03 AM
#13
Well, Ill put it like this, older servos were rated at 4.8 volts and 6 volts. And for decades guys ran the 4.8 servos on a 4 pack nimh supply, and the 6.0v servos on the 5 pack nimh supply. That was the standard proven setup for DECADES, and is still in use as this post proves. Now take into account that a fully charged nimh batt can achieve 1.5v per cell, meaning after a charge peak voltage could reach 6v on a 4.8 pack and 7.5v on a fully charged 6.0 pack. if your setup was running a 5cell nimh pack, it will handle a Life packs voltage just fine, although they do peak over 7v, they quickly drop to their 3.3v per cell voltage, meaning usually a sustained 6.6 volts. I have run Un-regulated 2s life on 6v servos for years and NEVER a problem, thats just my personal experience.
Last edited by raron455; 02-12-2018 at 03:52 AM.
02-12-2018, 04:15 AM
#14
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The only servos that don't like the slightly higher voltage of a LiFe, over a 5 cell NiMh battery are the early "High Speed" (like tail servos for a heli) or early small digital servos. BUT... these servos generally were not recommended to be used on a 5 cell anyway. (only a 4.8v rating)
My 2 cents... take it for what it's worth.
My 2 cents... take it for what it's worth.
02-12-2018, 02:52 PM
#15
My Feedback: (360)
Older JR servos
Older JR servos do NOT like a fully charged A123, long term. (ask me how I know...)
Unless all servos are fairly new, run a 5.9 regulator. The problem is that they will work fine for a while before they burn out-not worth the risk.
My 2 cents...
Unless all servos are fairly new, run a 5.9 regulator. The problem is that they will work fine for a while before they burn out-not worth the risk.
My 2 cents...
02-12-2018, 04:01 PM
#17
I've run unregulated A123s with 8411,8611,9411,8711 for years and NEVER had a problem of any kind. We make this way harder than it needs to be. Regulators, Power boxes, gyros, fancy switches and other crap which make so many failure points we don' have a clue what causes a failure.
Last edited by tp777fo; 02-12-2018 at 04:04 PM.
02-13-2018, 10:49 AM
#18
The only issue I have ever had with A123’s is with Eflight electric retracts.. I put a voltage regulator on the gear down to 5 volts and it works.. I have also used Jeti inline regulators on some of the older small 5v servos..otherwise no issues
02-13-2018, 01:47 PM
#19
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I've run unregulated A123s with 8411,8611,9411,8711 for years and NEVER had a problem of any kind. We make this way harder than it needs to be. Regulators, Power boxes, gyros, fancy switches and other crap which make so many failure points we don' have a clue what causes a failure.
Amen to that. Likewise no issues since I started using them about 6 years ago.
02-13-2018, 05:11 PM
#21
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GR,
Especially if just using the smaller servos as air valve controls etc you could always solder diodes in line with the + lead to the servos observing the polarity direction. A diode inherently drops voltage by 0.7 and 2 in line will get you 1.4 v etc. I have however seem some equipment that cautioned to not use diodes as regulators. There is a momentary very very short period of full voltage and even reverse current if on an ac circuit until the diode saturates. They have amp ratings so just pick a diode above your max expected amps. But they will have that drop continually no matter what the input voltage until you get very close to that voltage. They are not really regulators just v droppers.
I saw an article on heavy use servos rated for 5 amps but during high load reversals aka 3D they were seeing 35amp micro spikes. This was probably causing micro damage to the circuits which may explain why some sponsored flyers would dump their very high dollar servos each season.
Cheers
Charles
PS i have vet to run it but my weatronic with 30 servo control accommodates v regulation to each port
Like our old servos some of the now unsupported "junk" from 5 years ago can still be fun to fly.
Especially if just using the smaller servos as air valve controls etc you could always solder diodes in line with the + lead to the servos observing the polarity direction. A diode inherently drops voltage by 0.7 and 2 in line will get you 1.4 v etc. I have however seem some equipment that cautioned to not use diodes as regulators. There is a momentary very very short period of full voltage and even reverse current if on an ac circuit until the diode saturates. They have amp ratings so just pick a diode above your max expected amps. But they will have that drop continually no matter what the input voltage until you get very close to that voltage. They are not really regulators just v droppers.
I saw an article on heavy use servos rated for 5 amps but during high load reversals aka 3D they were seeing 35amp micro spikes. This was probably causing micro damage to the circuits which may explain why some sponsored flyers would dump their very high dollar servos each season.
Cheers
Charles
PS i have vet to run it but my weatronic with 30 servo control accommodates v regulation to each port
Like our old servos some of the now unsupported "junk" from 5 years ago can still be fun to fly.
02-13-2018, 05:38 PM
#22
I run regulators with my A123's on non HV servo airplanes. I can also say I have NEVER had a problem I have been flying several of my jets that way since 2002 with the same servos and regulators. When people bring up the KISS princible, or additional failure point arguement, I always counter with thats why I run two batteries, two regulators, two switches. If anything fails, I still fly. Also, and biggest benefit, by having two, neither component is working very hard which greatly reduces the chance of failure in the first place. Good example in real life of this in action would be a Cessna magneto. They have two for a reason, well several reasons( redundancy and more power). That sure would be a bummer to crash everytime a 10 dollar magneto failed. How bout a skydiver with a spare chute? I dont buy into the kiss princible or additional failure point argument....I think I fall into more of a lets not make it overly complicated but complicated enough to have power redundancy and a constant voltage...lol Just my .02
02-14-2018, 08:05 AM
#23
It's really simple, if you've been using 5cell NiCd/NiMh packs without regulators then you can use 2S A123s without regulators. The fully charged voltage, etc are nearly identical. If your servos are rated for 4.8V (4 cell NiCd/NiMh) only, then don't use A123s.
02-14-2018, 08:57 AM
#24
I run regulators with my A123's on non HV servo airplanes. I can also say I have NEVER had a problem I have been flying several of my jets that way since 2002 with the same servos and regulators. When people bring up the KISS princible, or additional failure point arguement, I always counter with thats why I run two batteries, two regulators, two switches. If anything fails, I still fly. Also, and biggest benefit, by having two, neither component is working very hard which greatly reduces the chance of failure in the first place. Good example in real life of this in action would be a Cessna magneto. They have two for a reason, well several reasons( redundancy and more power). That sure would be a bummer to crash everytime a 10 dollar magneto failed. How bout a skydiver with a spare chute? I dont buy into the kiss princible or additional failure point argument....I think I fall into more of a lets not make it overly complicated but complicated enough to have power redundancy and a constant voltage...lol Just my .02
02-14-2018, 11:32 AM
#25
Like I said in my post Andy, been working since 2002. And my transmitter does have two batteries........
Heck, come to think of it, my diesel truck that pulls my trailer to the field even has two batteries....cant ever be too prepared...LOL
Heck, come to think of it, my diesel truck that pulls my trailer to the field even has two batteries....cant ever be too prepared...LOL