Servo connectors
04-02-2017, 09:56 AM
#1
Servo connectors
I've seen this little tidbit of information pop up every once in a while:
The connectors we use for servos are only rated for 3 amps.
Yes, they are rated for 3 amps. At 250 volts!
Which, doing the math, translates to over 90 amps at 8 volts. (3 amps X 250 volts = 750 watts ÷ 8 volts = 93.75 amps). Even more at lower voltages.
So, nothing to worry about.
They are known as "Dupont" connectors. Here's the specs on them: http://images02.cdn86.net/kps01/M00/...CEYVF0Q563.pdf
Hopefully this puts to rest any concerns anyone has about using modern high power digital servos with these connectors.
...jim
The connectors we use for servos are only rated for 3 amps.
Yes, they are rated for 3 amps. At 250 volts!
Which, doing the math, translates to over 90 amps at 8 volts. (3 amps X 250 volts = 750 watts ÷ 8 volts = 93.75 amps). Even more at lower voltages.
So, nothing to worry about.
They are known as "Dupont" connectors. Here's the specs on them: http://images02.cdn86.net/kps01/M00/...CEYVF0Q563.pdf
Hopefully this puts to rest any concerns anyone has about using modern high power digital servos with these connectors.
...jim
Last edited by JimBrown; 04-02-2017 at 10:41 AM.
04-02-2017, 10:51 AM
#6
Volts times Amps = Watts.
Our servo connectors are capable of 750 watts.
As long as the volts being used times the amps being drawn does not exceed 750 watts, you're good to go.
The next limiting factor is the wire size and its resistance.
...jim
04-02-2017, 10:56 AM
#7
How so?
The spec sheet says 3 amps at 250 volts.
That's 750 watts. (W = V * A)
Good old high school math says that A = W / V.
Plugging in 8 Volts and 750 watts, we get A = 750 / 8, which is 93.25 amps.
This is what it is capable of. Not what we actually use. What we actually use as way below that, generally 5 to 8 amps at full stall. Which, at 8 volts, is 40 to 64 watts. Well within the specs.
Again, it's the wires that are the limiting factor.
...jim
The spec sheet says 3 amps at 250 volts.
That's 750 watts. (W = V * A)
Good old high school math says that A = W / V.
Plugging in 8 Volts and 750 watts, we get A = 750 / 8, which is 93.25 amps.
This is what it is capable of. Not what we actually use. What we actually use as way below that, generally 5 to 8 amps at full stall. Which, at 8 volts, is 40 to 64 watts. Well within the specs.
Again, it's the wires that are the limiting factor.
...jim
Last edited by JimBrown; 04-02-2017 at 10:58 AM.
04-02-2017, 11:02 AM
#8
We typically use 20 or 22 gauge wire for our servos. A bit of research shows that 22 gauge wire can handle 7 amps. And 20 gauge wire can handle 11 amps.
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
04-02-2017, 11:29 AM
#10
My Feedback: (3)
How so?
The spec sheet says 3 amps at 250 volts.
That's 750 watts. (W = V * A)
Good old high school math says that A = W / V.
Plugging in 8 Volts and 750 watts, we get A = 750 / 8, which is 93.25 amps.
This is what it is capable of. Not what we actually use. What we actually use as way below that, generally 5 to 8 amps at full stall. Which, at 8 volts, is 40 to 64 watts. Well within the specs.
Again, it's the wires that are the limiting factor.
...jim
The spec sheet says 3 amps at 250 volts.
That's 750 watts. (W = V * A)
Good old high school math says that A = W / V.
Plugging in 8 Volts and 750 watts, we get A = 750 / 8, which is 93.25 amps.
This is what it is capable of. Not what we actually use. What we actually use as way below that, generally 5 to 8 amps at full stall. Which, at 8 volts, is 40 to 64 watts. Well within the specs.
Again, it's the wires that are the limiting factor.
...jim
3A is the contact current rating
While Power does equal Voltage * Current (ignoring power factor), you can't simply multiply the 2 connector specs ... it doesn't work that way
If you don't believe me try this ...
Take a 1V source and see if the connector can pass 750Amps
According to your math it should since 3*250 is the same as 1*750
04-02-2017, 02:20 PM
#13
We typically use 20 or 22 gauge wire for our servos. A bit of research shows that 22 gauge wire can handle 7 amps. And 20 gauge wire can handle 11 amps.
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
I use a lot of A123 rx's packs and with the little CellPro Multi 4 chargers you can do a node only charge through the balance leads. Basically all of my A123 rx packs are setup with a JR type servo lead charge connector. As someone mentioned; you run 4 amps through that puppy and if the pins are even the least little bit loose or corroded, it melts the plastic housing....
04-02-2017, 04:32 PM
#15
My Feedback: (3)
If you want to understand electrical connector physics, I would highly recommend this course from Dr. Timsit.
If you believe you are correct in your "wattage calculation" for connector ratings, see if you can get Dr.Timsit to agree. I am going to guess he will not.
http://www.timron-inc.com/courses_tact.html
If you believe you are correct in your "wattage calculation" for connector ratings, see if you can get Dr.Timsit to agree. I am going to guess he will not.
http://www.timron-inc.com/courses_tact.html
04-03-2017, 12:16 AM
#17
That would depend entirely on the voltage being used. And it is what is drawing the power that determines the amps being sent. One does not simply send a set amount of amps down a circuit.
Volts times Amps = Watts.
Our servo connectors are capable of 750 watts.
As long as the volts being used times the amps being drawn does not exceed 750 watts, you're good to go.
The next limiting factor is the wire size and its resistance.
...jim
Volts times Amps = Watts.
Our servo connectors are capable of 750 watts.
As long as the volts being used times the amps being drawn does not exceed 750 watts, you're good to go.
The next limiting factor is the wire size and its resistance.
...jim
04-03-2017, 07:21 AM
#18
My Feedback: (21)
I have tested these connectors and the voltage drop exceeds 1 volt once you go above 3 amps. It continues to rise until the connector melts at about 5 amps. The 250 volt rating is an arc over rating only.
The contact area of the pins is too small to carry much current
The contact area of the pins is too small to carry much current
04-03-2017, 11:53 AM
#19
I stand corrected.
Apparently I misunderstood the specifications. Not to mention misunderstanding the rest of the amp/volt thing. Not my area of expertise, obviously. Guess I'll stick to computers. ;-)
...jim
Apparently I misunderstood the specifications. Not to mention misunderstanding the rest of the amp/volt thing. Not my area of expertise, obviously. Guess I'll stick to computers. ;-)
...jim
Last edited by JimBrown; 04-03-2017 at 12:08 PM.
04-03-2017, 08:11 PM
#20
My Feedback: (1)
In my Micro 3D planes I set out to see what' s possible in current draw of a servo style plug by using it on the 2s battery as a main lead that acts as a balance lead thus elimination additional wire and plug weight. By plugging it in to a 12amp esc. The setup is 8-9 amps continuous wide open throttle. This over 5 years no issues, I'm convinced they are more than capable beyond 3a.
The 4S Cellpro on A123 2s is an interesting reply because I have that exact setup and it gets warmer on servo style plug as a balance lead than does the Motor/ESC setup of which I never felt any heat as a 60 watt setup. I contribute it to the wire gauge as not proper as compared to the motor setup which is the larger 18g versus 22g.
As a side note what I do religiously is not to intermix mating plugs from different manufacture brands. The pins are a rolled U shape design and not all U shapes or oriented the same to mate up by OEM design for most contact surface, You can actually get a worst case scenario going across the thinnest profile of the U.
The 4S Cellpro on A123 2s is an interesting reply because I have that exact setup and it gets warmer on servo style plug as a balance lead than does the Motor/ESC setup of which I never felt any heat as a 60 watt setup. I contribute it to the wire gauge as not proper as compared to the motor setup which is the larger 18g versus 22g.
As a side note what I do religiously is not to intermix mating plugs from different manufacture brands. The pins are a rolled U shape design and not all U shapes or oriented the same to mate up by OEM design for most contact surface, You can actually get a worst case scenario going across the thinnest profile of the U.
04-04-2017, 03:44 PM
#21
We typically use 20 or 22 gauge wire for our servos. A bit of research shows that 22 gauge wire can handle 7 amps. And 20 gauge wire can handle 11 amps.
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
My point is that the servo connector itself is just fine for our application. The "3 amp" thing is a red herring.
Regards,
...jim
I think your message got lost in the noise of the mathematics. In a sense you are right, as an RC connector, they rarely see 3 amps, and then only in short bursts.
The 3 amp limit is set by heating, and that heating is a result of the I2R losses in the connector. The higher the current (the "I" term) the more power is dissipated inside the connector at the connection point.
Over time, the resistance (the "R" term) can go up (dirty connector, many insertion/extraction cycles etc) and the I2R losses can go up. The voltage losses through the connector will increase as well.
So the engineers figure what will the heating be if you have worse case connector resistance, with a continuous current level. 3 amps is what they came up with apparently
As someone said on this thread, if you run 4+ amps through them continuous, like in a charger, they can get hot.
On one of my planes, I am running 2 batteries, with 11 servos I think. I charge about 300 mah into each battery after 2 flights. So maybe 1.2 amp/hour drain average, continuous, shared by the 2 batteries. Far below the 3 amp spec. And the average current on the worst case servo connector might be 0.2 amps continuous with 5-7 amp spikes (msec long)?
So yes these connectors are fine, IMHO. Plug and unplug one a zillion times things go bad so I just clip them and replace them periodically.
04-05-2017, 03:28 AM
#22
Max voltage is driven by the capacitor effect of the isolating plastic between the pins.
Anything above 250 V and you start transforming your plug into a capacitor...
high frequency=capacitor is passing current.
low frequency=capacitor is blocking current.
In other words, one pins will start leaking its potential to the next pin or to a conducting object outside of the plug with a high frequency signal beyond 250V. Obviously, in this case, there is also a safety risk of electrical discharge to operators...
3A is heat limit for these plugs as mentioned by many people above.
250V is a signal leak limit for signal processing.
The two shall not be combined.
Anything above 250 V and you start transforming your plug into a capacitor...
high frequency=capacitor is passing current.
low frequency=capacitor is blocking current.
In other words, one pins will start leaking its potential to the next pin or to a conducting object outside of the plug with a high frequency signal beyond 250V. Obviously, in this case, there is also a safety risk of electrical discharge to operators...
3A is heat limit for these plugs as mentioned by many people above.
250V is a signal leak limit for signal processing.
The two shall not be combined.
04-05-2017, 05:26 AM
#23
My Feedback: (2)
from an electrical stand watts has nothing to do with wire size and connector size, the current is what dictates those (amps). take welding machine a little more watts going in do to inefficiency then going out but wire in on a standard buzz box is 10 gauge wire out Is 3/0 wire fine strand (smaller strands equal more amp capacity due to the fact electricity is carried out on the od of the strand) it's up to 225 amps out but only 24 volts as where input is 240v 30amps. more amps = bigger wire more volts equals thicker insulation or more distance.
