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 pstowe 01-16-2013 08:05 AM

Max load on a standard outlet.

I am trying to figure out the best way to charge 20 tablets daily. I use them for a class I teach and will need to charge them every night after class. A transit case will hold 20 tablets and I would like to develop a system so I can charge them while they are stored in the case. I am trying to figure out what is the maximum number of tablets I can plug into a single wall outlet. Each tablet charger has an output of 12V/1.5A. Does anyone have any guidance. Thanks in advance for your help.

 rjniles 01-16-2013 08:24 AM

1.5 amps at 12 volts is approx. 0.15 amps at 120 volts. Call it 0.2 amps to account for transfomer losses. 20 tablets at 0.2 amps is 4.0 amps. One 15 amp circuit is plenty.

 pstowe 01-16-2013 08:30 AM

So I should be able to daisy chain power strips, then plug them all into one outlet? I know that isn't quite OSHA standard, but would it work? If you're around Charleston, hope you're enjoying the warm weather. That's where I am from. Thanks for the help.

 md2lgyk 01-16-2013 08:39 AM

12 volts at 1.5 amps is a power output of 18 watts. I have no idea what the efficiency of the chargers might be, but even if it was as low as 50%, each one would only draw about 0.3 amps at 120 VAC. So plugging in all 20 would only draw around 6 amps. Since wall receptacles are at least on a 15-amp circuit, you could certainly charge all 20 tablets at the same time (assuming there's not a lot of other loads on the circuit).

 rjniles 01-16-2013 09:13 AM

2 of these would work

http://ecx.images-amazon.com/images/...500_AA300_.jpg

http://www.amazon.com/Tripp-Lite-PS3.../dp/B00005115S

Half way between Myrtle Beach and Charleston. Supposed to be mid 70's today.

 Speedy Petey 01-16-2013 10:01 AM

School safety inspectors HATE plug strips, even thought they are mostly all self protected.
Circuit wise you can do pretty much whatever you want.

 tylernt 01-16-2013 11:33 AM

You don't want to plug plug strips into plug strips. Each plug strip should plug directly into a wall receptacle. There is resistance in each plug connection. Plugging strips into strips increases the resistance, which causes heating of the connections.

But as long as each plug strip is plugged directly into a wall receptacle, you could hang 30 tablets off one 15A circuit no problem.

 mpoulton 01-16-2013 12:22 PM

Quote:
 Originally Posted by tylernt (Post 1094871) You don't want to plug plug strips into plug strips. Each plug strip should plug directly into a wall receptacle. There is resistance in each plug connection. Plugging strips into strips increases the resistance, which causes heating of the connections. But as long as each plug strip is plugged directly into a wall receptacle, you could hang 30 tablets off one 15A circuit no problem.
As long as the total current draw is less than the power strip rating, there's no conceivable way that daisy chaining power strips could cause a problem. The total current draw for all the tablets is so low that it's a non-issue.

 tylernt 01-16-2013 12:24 PM

Quote:
 Originally Posted by mpoulton (Post 1094910) As long as the total current draw is less than the power strip rating, there's no conceivable way that daisy chaining power strips could cause a problem. The total current draw for all the tablets is so low that it's a non-issue.
My workplace has strict rules against daisy-chaining plug strips, using the above reasoning. Maybe they're being overly cautious, but even so, to avoid disciplinary action, I don't do it. :eek:

 jeffnc 01-16-2013 01:25 PM

Quote:
 Originally Posted by tylernt (Post 1094871) You don't want to plug plug strips into plug strips. Each plug strip should plug directly into a wall receptacle. There is resistance in each plug connection. Plugging strips into strips increases the resistance, which causes heating of the connections.
Bah, negligible. If this were an issue, you'd never sleep at night worrying about all the wire nut connections hidden in your house. Not to mention all the connections in the main panel, electronics and appliances, etc.

 tylernt 01-16-2013 01:30 PM

Quote:
 Originally Posted by jeffnc (Post 1094959) Bah, negligible. If this were an issue, you'd never sleep at night worrying about all the wire nut connections hidden in your house. Not to mention all the connections in the main panel, electronics and appliances, etc.
Connections torqued into intimate contact with wire nuts or clamps have a lot less resistance than the little leaf springs in receptacles just kissing the plug blades...

Anyway, as I mentioned, it's an issue for my employer. Maybe it's an OSHA thing, who knows. I may or may not have daisy-chained plug strips in my house. :whistling2:

 jeffnc 01-16-2013 01:37 PM

Quote:
 Originally Posted by tylernt (Post 1094964) Connections torqued into intimate contact with wire nuts or clamps have a lot less resistance than the little leaf springs in receptacles just kissing the plug blades... Anyway, as I mentioned, it's an issue for my employer. Maybe it's an OSHA thing, who knows. I may or may not have daisy-chained plug strips in my house. :whistling2:
I understand.

 mpoulton 01-16-2013 06:20 PM

Quote:
 Originally Posted by tylernt (Post 1094964) Connections torqued into intimate contact with wire nuts or clamps have a lot less resistance than the little leaf springs in receptacles just kissing the plug blades...
So? The load either exceeds the ratings or it doesn't. The power strips don't "know" whether there's a space ehater plugged into them or a dozen more power strips. As long as the total load is less than the rating of the first power strip, it makes no difference. Current is current. OSHA doesn't like chaining power strips, but I have never seen a logical explanation of why it's supposedly a problem.

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