Fuse size

Albynsw

Well-Known Member
I have wired in some permanently powered charging points in the cabin for phones and iPad that could have two phones and an iPad all charging at the same time.
My issue is what size fuse to put on this supply, the cable is rated at 7.5 amps so I can rate a fuse to protect that but the USB and USC charge points have lighter wire
I note the factory usb and lighter plug outlets are on a single 10 amp fuse

what does ya think!
 

smitty_r51

Well-Known Member
you not got an amp meter in that fancy new rig of yours?

google pixel 6 draws 669mah

samsung tablet 8" draws 183mah

HardKorr headlamp draws 291mah

GoalZero mini lantern draws 207mah

that is reading my built in meter when using the twin hardwired USB port marked 2.4A @ 5v

So even with two things in and charging i am lucky to pull an amp per double socket
 

Albynsw

Well-Known Member
no fancy amp meter doodah here. Sounds like it draws even less than what it is capable of. Sounds like a 5 amp should do the trick
 

boobook

Well-Known Member
Well I think you should replace the 7.5a wire and put in something like 15a to 20a wire, or similar, with a 15A fuse

In the good ol days USB was 5v at 0.5 or 1 amp. But now phones and tablets can charge at 50 or even 100w. There are 2 new standards QC3 or 4, or PD 3 that most new phones or tablets use. USB can get to several amps at 28v, or 6 to 10a at 12v.

Two new uncharged phones will blow a 5a fuse all the time if you have the right quick charger.
 

boobook

Well-Known Member
One of my charge points is QC3 and the other two are 2.1 amp each usb points

Potentially that's about 7 amps full bore Alby. I have one of those sockets from eBay It works well and shoves charge up the phone's bum at a great rate.
 

Albynsw

Well-Known Member
Potentially that's about 7 amps full bore Alby. I have one of those sockets from eBay It works well and shoves charge up the phone's bum at a great rate.
Ok , I might put that one on a separate circuit, that one is for my iPad running Hema
 

Ron0z

Active Member
The fuse is to protect the wiring. The fuse should blow before the wire gets hot. You don't want the wire getting hot. It should run cold. If you're likely to draw a lot of current then use a suitably rated cable and fuse. Electronics gadgets generally use very little power - very low current.
 

typhoeus

Well-Known Member
Here's a rough guide
 

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Ron0z

Active Member
Love the auto alert fuse.

Though, the irony of this is that it happens, and I'm not joking. The last two houses I bought had fuses in the meter box, rather than circuit breakers. In both properties, I found copper wire had been used rather than fuse wire. No doubt a temporary thing that had been subsequently forgotten. If your house has fuses and you haven't checked, you might be well advised to have a look.
 

dabbler

Active Member
Love the auto alert fuse.

Though, the irony of this is that it happens, and I'm not joking. The last two houses I bought had fuses in the meter box, rather than circuit breakers. In both properties, I found copper wire had been used rather than fuse wire. No doubt a temporary thing that had been subsequently forgotten. If your house has fuses and you haven't checked, you might be well advised to have a look.
Probably a permanent fix because fuses were constantly blowing. Another common thing was multiple strands of the correct fuse wire were used in the belief it safely prolonged the time before a fuse blew.
 

Triton14

Well-Known Member
I have 1x 2A USB factory socket in the Triton then I just added an additional double USB 1A & 2A cup holder style charger that runs via the cigi lighter port which is similar to this-


They come in all shapes & sizes, no extra wiring needed so not sure why you have to have add a hard wired solution for such low amp consumption??

If these modern phones/tech have much higher draws as @boobook is describing then Id like to see the specs.

Unless they have some huge screen like a laptop then most mobile devices as you describe are still pretty low in draw/consumption which can be taken off the cigi outlet.

The only issue I ever had was with an add on double cigi outlet running through the factory cigi outlet that was running a 75W Lightforce spotlight.
But I guess that was just inviting trouble with running such a high draw item out of it :oops: , it burnt out the add on $15 double cigi unit after a few hours & before the cars factory outlet.

Lesson learnt there, big draw items now straight to the battery or a higher rated outlet.

Happy to be proven wrong ;)
 
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discomatt

Well-Known Member
If these modern phones/tech have much higher draws as @boobook is describing then Id like to see the specs.
The charge draw of devices is never over about 2.4 amp , look at any charger details and a battery will only ever draw what it can not what is pumped into it
 

boobook

Well-Known Member
The charge draw of devices is never over about 2.4 amp , look at any charger details and a battery will only ever draw what it can not what is pumped into it

Well 101 electrics will tell you that amps are never pumped into any load. LOL. But tons of devices can draw much more than 2.4A. Infact it's pretty standard for any decent Phone with USB C.

Using amps alone for USB charging is not the whole picture and means nothing these days. You need to refer to watts, not amps to understand how it works. You will never see any phone spec refer to charging amps, it makes no sense and all will specify watts. Alby's charger supports both USB PD, and QC 3. These are completely different to 5v USB. Both PD and QC 3 start with 5v, then they ask the device being charged what is the highest volts and power that it can handle. Some charged devices can take 20v. For example my Dell laptop has a USB c charger and takes 100w at 20v. That's about 5A at that charge rate and voltage. And a massive 9a at 12v if the charger Alby has could deliver that. The voltage and current ramp up to what the device let's it do.
The charger has an internal inverter so the watts are constant but amps at 12v will change depending on the device. Getting back to Albys need, the several devices he is charging can easily exceed 5a in total.
I have that same charger an regularly see over 3A at 12v just with my tablet charging.

If these modern phones/tech have much higher draws as @boobook is describing then Id like to see the specs

Dell laptop is 100w, Samsung s21s are 25w, Samsung Tab s is 45w, oppos and some other Chinese phones are 65w, I think new ipads are 45w and iMac airs are 50w USB.

With PD and QC, becoming the new standards we will soon see most tablets and many phones with charging rates of 40w or more.



Bringing it back to amps for the fuse and wires, (at 12v not on the USB) 45 w for the Samsung tablet, plus a 25w phone plus a 15w phone plus 2 other devices at 10w is 105w Divide each power draw by 12v to get their current at 12v. About 8a in total for what Alby could easily use.

Look up how QC 3 and PD work, it will surprise most about how the old 5v usb has changed for fast and super fast charging in most new phones.

If people want to learn what is going on with USB charging, I suggest getting something like this. This one goes up to 32v and 5A. It's an eye opener.


Little knowledge is a dangerous thing.
 
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Albynsw

Well-Known Member
This should be straight forward but these new outlets seem to have changed that. I am thinking that I will run each one separately and individually fuse them
I just looked up a QC3 and it says 3-4 amps @ 12v which is surprisingly high
 

boobook

Well-Known Member
This should be straight forward but these new outlets seem to have changed that. I am thinking that I will run each one separately and individually fuse them
I just looked up a QC3 and it says 3-4 amps @ 12v which is surprisingly high

Yep either run seperate 5a fused lines or one with a 10a fuse and appropriate wiring. You will thank yourself. Especially if you get new phones or tablets that are 45w or more each.

And always get QC or PD chargers depending on which one your phone supports for fast charging. Some support both but most phones like Apple and Samsung are moving to PD so they don't have to pay licence fees to Qualcomm.

The new PD USB coming out will support 48v at 5 Amps or 240w . That's 20a at 12v and will fully charge a tablet or phone in about 8 mins.
 
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