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Topic: Powering a 7.4V servo with a wall wart (Read 264 times) previous topic - next topic

konidias

Hi, so I'm using this guy:

HS-7940TH Servo

Which has an operating voltage of 4.8V - 7.4V

I want to run it at maximum voltage to get maximum torque out of it... which would be 7.4V

The problem is that I want to use a dc adapter/wall wart to power it, instead of batteries... I can't seem to find an adapter that is 7.4V. I have one that is 9V but I'm afraid that is going to destroy the servo... I can't seem to find a maximum voltage number anywhere for this servo.

Would it be okay running 9V to this or would it just burn up the servo?

If that won't work, how can I properly step down the voltage from 9V to 7.4V? I've never done anything like that so I'm really unsure of the best method to go about it.

Could the servo handle 9V from an adapter? The servo is rather expensive so I'd rather not just plug it in and find out...

Thanks

Southpark

A power supply should usually be linked to power ratings.... like ...if it operates at a particular voltage (RMS voltage), then they need to have some kind of specified value of RMS current for which the device is able to happily operate on a continual basis - under normal operating conditions.

So if you know what sort of current levels your motor requires (including maximum current requirement)..... then you can work toward getting or building a power supply to meet the requirement.

There are step-down (buck) converters that can be purchased online (or elsewhere). Just got to make sure that power output capabilities are adequate. The converters usually have specifications that tell you what voltage range is needed for input voltage...and what output voltage range it is capable of (if the converter has an adjustment dial for you to set the output voltage).

Robin2

#2
Jul 14, 2017, 09:39 am Last Edit: Jul 14, 2017, 09:40 am by Robin2
The servo will probably draw a significant current when under load and if so you will need a high-amperage wall-wart.

Have you considered using re-chargeable batteries with a wall-wart as a trickle charger for the batteries. The batteries will handle any short term high current demands.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

konidias

I have a 6V 5A wall wart and that does okay but I need that extra 1.4A to get the maximum torque out of it... I would think 3A would probably be sufficient enough...

Are you saying I should get lithium batteries that equal up to 7.4V and just have them recharging with a wall wart at the same time??? Is that going to be efficient?

slipstick

If the servo is specified for 7.4V that really mean 2 lipo cells, 7.4V nominal. Fully charged they will be at around 8.4V and you can bet that won't kill the servo.

So my guess is that it will be o.k. running on 9V particularly if it has fairly intermittent use and a relatively light load. But it is only a guess and if it's going to be in continuous heavy use and/or stalled a lot then all bets are off.

Steve

Robin2

Are you saying I should get lithium batteries that equal up to 7.4V and just have them recharging with a wall wart at the same time??? Is that going to be efficient?
That's what I had in mind?

Does efficiency matter? It's only going to be a tiny amount of energy anyway.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

konidias

Well the problem with running it from charging batteries is that batteries have a lifespan of like 400-500 charges... Which means I'm going to have to keep replacing batteries over time... which isn't ideal.

I'm going to try and contact the company and see if 9v is doable... Thanks for the help!

Robin2

#7
Jul 15, 2017, 09:24 am Last Edit: Jul 15, 2017, 09:24 am by Robin2
Well the problem with running it from charging batteries is that batteries have a lifespan of like 400-500 charges... Which means I'm going to have to keep replacing batteries over time... which isn't ideal.
I think you have the wrong end of the stick :)  With what I have in mind the batteries will never be discharged completely so they should last a very long time. Just make sure that you have a charger that does not over-charge them.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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