bobmarkert

bobmarkert

Well Known Member
Electrical is not my strong suite but??..
I?m installing two USB port chargers in my -8. The install directions say the units can pump out 5 amps yet they are protected by a 2 amp breaker!!

How can a 5 amp unit be protected by a 2 amp breaker without continuously tripping the breaker?

From the install manual: ?Unit MUST be connected to a 2 Amp circuit breaker or fuse, Klixon 7274-11-2 or similar. The unit is a conservative design. The voltage charge pump converter is a 5 A unit but don't push it to its limit.?

Product Info http://www.commitlift.com/usbchargers.html

Install manual http://www.commitlift.com/USBASinstructions.pdf

Thanks for the education I?m about to get??
 
What you have there is a 12V to 5V converter... think about power, P = I x V. In round numbers and making simplistic assumptions about efficiency, (2A x 12V) = 24W ~= (5A x 5V). Not knowing any more about the device, that's all I can say!

mcb
 
It is a function of total power in and power out. Power is equal to voltage times current.

Power input = current X voltage or in this case 13V X 2A= 26 watts

Power output = 5V X 5A = 25 watts.


But they really say it is a 4 amp output total between 2 ports, typically 2.1 on a fast charge port and about 1.1 or so on the other. I think an Ipad on brightness full needs the 2.1 to maintain the battery charge. One of their models provides 2 amps to each point for a total of 4. That's a total of 20 watts, so your input voltage could drop as low as 20/2= 10. Roughly.... Things don't always add up perfectly because there are heat losses (power losses).



Don
 
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I believe this could be a design item. The unit has a 100 percent duty cycle at a bit less than 2 amps at a certain voltage probably around 5 volts, however the components within the USB device could be rated for 5 amps or more.Which means it would be loafing along at any normal output for an IPAD etc. which is around 1 amp and phones being less than 500 ma.
Just food for thought.
 
Two USB outlets

Thanks all.... that makes sense 12v- 5 volts.

Now my next dilemma; I will have two of these units on the same circuit/breaker. Do I double the 2 amp breaker to 4 amps and size the wire appropriately or stay with the two amp breaker?

Can I PLEASE go back to riveting something.... anything.... I understand that!

Thanks
Forrest Gump
 
bobmarkert said:
I will have two of these units on the same circuit/breaker. Do I double the 2 amp breaker to 4 amps and size the wire appropriately or stay with the two amp breaker?
Click to expand...

A single 4 amp breaker and separate wire runs to each unit, or a single wire run that feeds both units????

Remember the breaker is to protect the wire. And the wire is sized to the load.
 
Even though "standard practice" is the CB is to protect the wire, in this case you have a non-enclosed unit that that could be a potential hazard or fire/high heat source.
You should run seperate circuits with a 2A breaker/fuse for each, or let them both use the 2 amp fuse but only use one at a time.

Installing electrical equipment per 43-13 requires installing the "appropriate" size CB, this is the size called out by the equipment manufacturer and is not dictated by the size wire you installed.

43-13, chapter 11-48

DETERMINATION OF CIRCUIT
BREAKER RATINGS. Circuit protection
devices must be sized to supply open circuit
capability. A circuit breaker must be rated so
that it will open before the current rating of the
wire attached to it is exceeded, or before the
cumulative rating of all loads connected to it
are exceeded, whichever is lowest.
 
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Walt is correct, but remember the CB protects the wire, not the unit. Even with a 2 amp breaker there is no guarantee that the unit will not turn into a toaster.
 
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