Power question

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lee5593555
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Power question

Post by lee5593555 »

I just had a quick question about providing power to the arm:

The rules say we must use *commercial* batteries where the voltage does not exceed 14.4 V across two points. Or we can use laptop/tablet connection as long as they aren't plugged into the wall.

I assume this means we can't plug directly into the wall outlet?


Also, can we use something like a power bank with an AC outlet on it to power the arm? Something like https://www.amazon.com/Nature-Power-800 ... B00BGP2MPO

I have one and would rather power my arm that way, but I feel like I'm overthinking the rules maybe? Using the powerbank would be just like plugging into a laptop anyways (sort of).
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Re: Power question

Post by jander14indoor »

Not official, etc.

Seems to me that 120V AC (the output of that power supply) certainly violates "...does not exceed 14.4 V across any two points...".
Now, get rid of the AC outlet side and associated circuitry of that battery pack (that's all that thing is) and show me that its internal voltages do not exceed 14.4V and I don't see any problem. External battery packs are allowed, they just have to meet that 14.4V rule and become part of the larger 'device'.

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Re: Power question

Post by lee5593555 »

What do you mean by "get rid of the AC outlet side..."?

Trying to figure out how I can construct my own power supply with the proper type of plug. I thought I've seen a "battery pack" where you just plug in your own batteries, but the cord is one of those 5.5x2.5mm male plugs.
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Re: Power question

Post by windu34 »

lee5593555 wrote:What do you mean by "get rid of the AC outlet side..."?

Trying to figure out how I can construct my own power supply with the proper type of plug. I thought I've seen a "battery pack" where you just plug in your own batteries, but the cord is one of those 5.5x2.5mm male plugs.
You are seriously overthinking this. Most commercially available LIPO and NIMH battery packs will prove more than sufficient for almost any application. What makes you think you need so much power?
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lee5593555
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Re: Power question

Post by lee5593555 »

I AM overthinking it.

I went ahead and made a small battery pack with 8 AA batteries and a snap connector. It seems to work just fine.

The rules are just not super clear. They say we can use a laptop/tablet to power the device, but they cannot be connected to a wall outlet. I assume the internal voltage of the laptop/tablet is going to be greater than 14.4V, but the rules say it won't be checked so it doesn't matter. I was making the assumption that an external battery pack with an AC outlet would be the same, but it's the AC outlet part that is probably breaking the rules.
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Re: Power question

Post by Northridge »

lee5593555 wrote:I AM overthinking it.

I went ahead and made a small battery pack with 8 AA batteries and a snap connector. It seems to work just fine.

The rules are just not super clear. They say we can use a laptop/tablet to power the device, but they cannot be connected to a wall outlet. I assume the internal voltage of the laptop/tablet is going to be greater than 14.4V, but the rules say it won't be checked so it doesn't matter. I was making the assumption that an external battery pack with an AC outlet would be the same, but it's the AC outlet part that is probably breaking the rules.
Nothing Official, but just a thought. While it is true that many laptops run on around 19 V, most of the out puts (USB, etc) are significantly less then that. Rules like the "must not be connected to a wall outlet," are put in place to make sure the students are bringing charged laptops to competitions if they intend to use a laptop to power their robot. Having ran Robot Arm several times over the years, many times I was placed somewhere were there was no available wall outlets only to have teams show up with Robots that needed to be ran with a laptop that was not charged. By having this rule in place, I have not had this issue this year as everyone has showed up with a charged laptop.
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Re: Power question

Post by jander14indoor »

Voltage limits are considered a safety issue. Yes you can hurt yourself seriously with 14.4 V, but it takes a lot more work. It is easy to hurt yourself with 120VAC.

Some computers can't be opened to check battery voltage (I used to do that, which competitors hated as they had to reboot their computer, till I hit the first sealed one!). Laptops are carefully designed to make sure they are safe and certified so by regulatory agencies. So, we excluded checking them from a practical POV. And as stated previously by another poster, all normal outputs are acceptable voltages and acceptable current levels for safety.

Of course if I saw a laptop with a 120VAC outlet, that would be another story. Wouldn't be a matter of internal voltage then. Simple inspection would show a circuit with more than 14.4V

Oh, and by taken out the circuit I mostly meant you bought one without it.

On constructing your own battery pack, you can buy almost any connector type on line and with wire and batteries string it together in a way that meets the rule and mates to your robot. I've seen everything from commercial to home made, er, messes. The only problem with home made messes (example, wires taped to the ends of batteries) is that they tend to fail often. Well made home built power supplies can be as good as commercial.

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Re: Power question

Post by lee5593555 »

I found a battery "pack" that I had where you can fit 8-12 AA batteries and it has a multi-use connector so I'm going to put a 2.1mm plug onto it and cross fingers. I don't see why it wouldn't work power-wise. Just hoping the wiring doesn't need to be checked.
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