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01-16-2013, 09:05 AM   #1
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## 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.

01-16-2013, 09:24 AM   #2
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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.

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 01-16-2013, 09:30 AM #3 Newbie   Join Date: Jan 2013 Posts: 2 Rewards Points: 10 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.

 01-16-2013, 09:39 AM #4 Member   Join Date: Jan 2009 Location: WV Posts: 3,471 Rewards Points: 3,130 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).
 01-16-2013, 10:13 AM #5 A "Handy Husband"     Join Date: Feb 2007 Location: South Carolina Low Country Posts: 7,292 Rewards Points: 4,142 2 of these would work http://www.amazon.com/Tripp-Lite-PS3.../dp/B00005115S Half way between Myrtle Beach and Charleston. Supposed to be mid 70's today. __________________ Location: Coastal South Carolina
 01-16-2013, 11:01 AM #6 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,761 Rewards Points: 1,872 School safety inspectors HATE plug strips, even thought they are mostly all self protected. Circuit wise you can do pretty much whatever you want. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
 01-16-2013, 12:33 PM #7 Special User   Join Date: Jul 2012 Location: Idaho, US Posts: 917 Rewards Points: 1,230 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. __________________ The above post is for entertainment purposes only. Its contents may, and probably will, lead to legal liability and damage or loss of property, life, or limb. Use at your own risk.
01-16-2013, 01:22 PM   #8
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Quote:
 Originally Posted by tylernt 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.
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01-16-2013, 01:24 PM   #9
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Quote:
 Originally Posted by mpoulton 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.
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01-16-2013, 02:25 PM   #10
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Quote:
 Originally Posted by tylernt 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.

01-16-2013, 02:30 PM   #11
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Quote:
 Originally Posted by jeffnc 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.
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01-16-2013, 02:37 PM   #12
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Quote:
 Originally Posted by tylernt 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.
I understand.

01-16-2013, 07:20 PM   #13
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Quote:
 Originally Posted by tylernt 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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