GordDavey
Senior Member
- Joined
- Jan 2, 2019
- Posts
- 218
- Reaction score
- 108
- Location
- Toronto, Ontario
- Ram Year
- 2015
- Engine
- Hemi 5.7
Pacofortacos,"1000 watt heating pads at 8.3 amps each"
Not possible on 12 volts. P=VxA so 8.3A x 14 v = 116.2 watts
Are those being fed 120V or are they rated for 120V?
"So, 3 amps for one, means to me 6 amps for 2, I would think it would require a bit more power in than you get out thanks to converting down to 5v, so 6 amps min, even though there is no startup load, would it still be a good idea to use the 125% as a safety net... especially when the input is unknown? If so, then 6 becomes 7.5 amps"
Are you going to run 2 of the dual usb adapters? Or are you just considering the one dual unit?
They are rated at an output of 3A @ 5 V EACH port, but the input isn't 6A due to the input being 12/14V. That why you go for the wattage and convert from there.
So if you run 2 separate adapters @ 36 watts (still a guess that there is 6 watt loss) that will equal 72 watts of power needed at 12-14V. P=V*I so P/V=I so 72/12=6A input just like you figured I would 10A fuse it and call it a day.
Many things will actually have the input voltage and current needed as well as the output voltage and current when converting. On most things it is printed on them if not in the specs.
Thanks. I have two of these dual usb’s and the only power use indication is they say 36watts output 12v/24v. No other specs and nothing I’m the box or even printed on them. So it’s a bit of a guess. The choice I have is to run one by replacing an existing power outlet and one on a new wire. Or I can run one wire to power them both. Understanding how to choose the right wire and how to fuse them properly is what I’m trying to learn. That way I can make the right decisions later.
The 1000watts for the heating pads is the value KC said in his post. I should look up what I bought and try to get something more accurate. Both pads come with wiring that has a 10amp fuse on the main wire and a 5amp fuse for the On wire, relay and switches. At a guess the 8.3 amps KC said is I would imagine pretty close to wait they would draw. So again understanding which wire and how to fuse it all properly is what I’m trying to learn that way I can make the right decisions when I want to do something else. Like bed lighting or adding a light to the lower glove box etc.
Between you and KC I understand now how to work out how much power each unit draws and pick a wire based on that. I think there is no difference if doing 2 units as you just double the values and choose the correct wire for that. Having a chart that shows the ampacity down to 22ga really helps.
I still need to understand how to fuse it properly. I know I need to put a fuse on the wire by the battery that is just lower than the max the wire can carry. I imagine I need to keep the fuses close to the equipment to protect the equipment, but the statement “the fuse is there to protect the wire and nothing more” makes me question that.