Hello everyone, i have 6 HK15298B servos and i want to power them with a RAVPower 22000mAh Portable Charger it has 3 usb port (2.4 Amp each) i want to power the servos directly from the battery, i will connect 2 servos to each usb port.
Will it work and how much time will it last ?
Hi,
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Can you post spec/data on the RAVPower 22000mAh Portable Charger please?
If it has a mAh rating it has to be a battery.
Can you post spec/data on the HK15298B servos please?
Thanks.. Tom.. 
this are the specs for the servo
Spec.
Torque: 18kg @ 6v, 20kg @ 7.4v
Weight: 66g
Speed: 0.18 / 60deg @ 6v, 0.16 / 60deg @ 7.4v
Voltage: 4.8v~7.4v
Motor type: Coreless
Plug: JR Style
and the battery :
22000mAh
5.8A Output 3-Port Battery Pack
2.4A Input
Li-polymer Battery Banks)
To estimate battery lifetime in hours, divide the battery capacity in Ah or mAh by the average current draw of the entire system, in A or mA.
This means the you will need to run the servos under realistic conditions, while measuring the current draw.
Normally you would divide the resulting number of hous by two, because batteries age and battery manufacturers exaggerate.
Those battery-based chargers tend to have an automatic switch off function. I had this problem even when trying to run a small air pump off a USB battery. Not sure how to tell the battery to keep it's power on, it probably expects a feedback signal or so.
maybe this could help
Based on your specs, and assuming you wire it up correctly, then yeah, it should work. Do investigate the "keep it on" circuit, cause that is the main problem with charger devices.
5.8A maximum output is probably not going to be enough for those servos if you're going to want them all to start moving at the same time. Based on the servo specs I'd expect the startup current to be anything up to 2.5A each servo so you're in danger of tripping the over-current protection. But if only a few of them are running at once you may be o.k.
Since those are HV (High Voltage) servos not really intended to run on 5V it might be better to just run them direct from a 2S 7.4V lipo battery. That will get rid of all the fancy protection circuitry that causes so much trouble though then you will need a proper Lipo charger for the battery.
Steve
slipstick:
5.8A maximum output is probably not going to be enough for those servos if you're going to want them all to start moving at the same time. Based on the servo specs I'd expect the startup current to be anything up to 2.5A each servo so you're in danger of tripping the over-current protection. But if only a few of them are running at once you may be o.k.Since those are HV (High Voltage) servos not really intended to run on 5V it might be better to just run them direct from a 2S 7.4V lipo battery. That will get rid of all the fancy protection circuitry that causes so much trouble though then you will need a proper Lipo charger for the battery.
Steve
The spec sez 4.8 - 7.4 volts. Sure they will run better at 7.4, but they will work with 5 volts. And it seems the op has the 5 volt supply.
Slipstick is right about the amps - servos can use about an amp to start moving, each.
Even small servos like the almost ubiquitous SG90s can get close to 1A on startup. Large digital 20Kg-cm servos can go way past that.
And I must admit I was guessing that the reason the OP is using relatively expensive fast high-voltage high-torque aluminium digital servos was because of a need for speed, torque etc. Running them on a low voltage turns them into slower, lower torque servos. But that may be all that's needed I suppose since we have no idea what they're being used for.
Steve
Hi,
It worries me when places like HobbyKing cannot spec their own servos correctly
Torque: 14kg @ 6v, 15kg @ 7.4v
When I went to school, Torque was N-m.
Okay it will lift 14kg, but on what length arm.
14 kg-m sounds better which is 137.3 N-m, but way too high.
The SI derived unit for torque is the newton meter.
1 kilogram meter is equal to 9.80665 newton meter.
This spec quotes some sort of understandable torque figures;
It's extremely common for hobby servos to quote torque in kg-cm (so common that I didn't even notice that HK had missed the "-cm" off).
SI units are indeed international standards but some of them suffer from the problem that almost no-one understands them in any instinctive way. I know what a kilogram and a centimetre are and even an ounce and an inch for those Americans who still insist on using oz-in for torque. I have no feel for how much Newton weighed.
When I went to school torque was measured in foot-pounds so I guess I may be older than you.
Steve
slipstick:
It's extremely common for hobby servos to quote torque in kg-cm (so common that I didn't even notice that HK had missed the "-cm" off).SI units are indeed international standards but some of them suffer from the problem that almost no-one understands them in any instinctive way. I know what a kilogram and a centimetre are and even an ounce and an inch for those Americans who still insist on using oz-in for torque. I have no feel for how much Newton weighed.
When I went to school torque was measured in foot-pounds so I guess I may be older than you.
Steve
Hi Steve, it was feet, inches and pounds and hundredweight when I went to school to.
You would think if they can measure the torque they could quote some sort of current for producing that torque.
Merry Christamas mate.
