understanding power supplies & piggy back fuses

[franka]

There appears to be some confusion about power supplies and add on fuses.
I will try to clarify some points.

The enclosedimage shows schematics of a "piggy back" fuse holder.
This is in reality a dual fuseholder made to be inserted into a position vacated by removing one of the fuses in your vehcle fuse box. The removed fuse is reinserted into the piggy back holderin the inside slot. Into thje other slot you insert a suitable fuse to protect your PSU, or any other device that you may wnt yo install.
For correct operation with single dashcam, the fuse removed should be in a slot feeding a device from the "acc" supply. The acc supply is a voltage that is only present when the cars ignition is turned on.
A suitable fuse is one that is fed to the cigarette lighter socket[usually].

You can see from the enclosed schematics it is possible to insert the piggy back holder in the fuse box in two ways by r4otating the holder through 180 degrees. The schematics show the effect o0f rotyating the holder,

In the upper schematic both fuses are shown connected to the acc supply. This places the two fuses in parrallel giving independant fusing to the two connected devices.
In the lower schematic the fuses are connected together at the opposite ends thus the fuses are connected in series. In this case the original fuse has the current to both devices flowing through it,

The upper configuration is deemed to be the correct way but it not always possible to achieve this, for example if you have to piggy back holders you want to place adjacent to each other, they will not fit in. So does that rule out the second way?

Not at all. If the rating of tha additional fuse is small relative to the initial fuse the additional load imposed on the original fuse will affect its integrity.
In this case the original fuse will be 20A or higher with extra fuse for the camera being 2 or 3A.

It is interesting to note that if the supplied PSU is plugged into the cigarette lighter holder the above connection senario is followed.

Now what PSU to use.

All cameras are shipped with the manufacturers own power supply, usually it fits into the cigarette lighter socket.
If like me you do not like cables draped all over the dashboard, eventually arriving at the camera, there are other solutions. The most co9mmon being the hardwire kit. For me that has an aspect that i do not like. The output cable of these devices is usually permanently connected to the PSU. I prefer a PSU with a USB connector on the output in which to connect a cable of my own choice and importantly, the correct length.
Such PSUs are widely available from Amazon, Ebay etc.

They are almost exclusively made in China, are very cheap and of excellent quality and reliability.
They cabe tucked away under the dash with the cable running up inside the A pillar and under the headlining to the camera.

Under NO circumstances should this cable cross or infringe the side air bag if fitted, as if you nlucky enough to trip the air bag it will fly out bringing the cable with it and possibly wrapping it round your neck.

If you do remove the A pillar trim and an air bag is fitted, the trim will be fitted with a restraining clip to stop the A pillar also flying through the air if the air bag trips.
One last point, if you decide to run the cable up th outside of the pillar, do not cro0ss any part of the pillar for the same reasons.

If you do not follow this advice and the insurance company find out, in all probability they will void your insurance.

The last thing to say is, another reason to choose your own USB cable is to choose one that is to supply power and not just for signals. In these cables the wires are quit thin an over a long length the volt drop within the cable may be excessive and possibly cause problems supplying a high enough voltage to satisfy the camera.

 

[Ralph2]

Your first sentence and heading are correct.. your second.... the first part.. not bad, the second not so much.

Part two... where you delve into "Now what PSU to use." Acronyms are not standard or known to many.. what does PSU stand for? I am guessing Power Supply U(something). Then.. "I prefer a PSU with a USB connector" (a more common acronym) is a function of what your camera needs.. whether they are commonly available means squat if the camera you purchased uses a 12 volt supply.

My 2 cents.. and I am sure you will have more. There is a lot of confusion.. and it seems everyone tries to help, but.. We.. You.. are dealing with an audience of variable intellect on the subject.. it seems trying to clarify invariable confuses the issue more.

 

[franka]

Your first sentence and heading are correct.. your second.... the first part.. not bad, the second not so much.

Part two... where you delve into "Now what PSU to use." Acronyms are not standard or known to many.. what does PSU stand for? I am guessing Power Supply U(something). Then.. "I prefer a PSU with a USB connector" (a more common acronym) is a function of what your camera needs.. whether they are commonly available means squat if the camera you purchased uses a 12 volt supply.

My 2 cents.. and I am sure you will have more. There is a lot of confusion.. and it seems everyone tries to help, but.. We.. You.. are dealing with an audience of variable intellect on the subject.. it seems trying to clarify invariable confuses the issue more.

I appreciate your comments, although the text of them leaves me in some confusion about what you are saying. Foe example what does "squat" mean?
I thought every one knows that PSU is a power supply unit, but obviously i am wrong.
My background is having worked as a consultant engineer for most of my life, designing and commissioning test and production equipment for a major Electronics company, these phrases and acronyms come naturally to me. In future i will think more carefully before i write.

 

[cctrader77]

Thank you for this write up. I understand everything that you have written however, I still have some questions that I can't seem to find anywhere and was wondering if you knew.

I am trying to hardwire a battery pack(cellink neo) with the add-a-fuse. This new device(cellink neo) I am adding is rated to draw around 9 amps and I am using a 20 amp fuse (what was supplied, feel like it is kind of high). I can only use allocated fuse slots, no empty ones are ignition powered.

My question is 1) Which allocated fuse slot should I piggy back off of in terms of amp rating? One that has a device with low rated fuse(7.5 amp) or one that has a high rated fuse(20 amp)?
From my research it seems that if the fuses and piggy back module is inserted correctly, there shouldn't be any issues with shorting the fuses. However, I am afraid that there might be too much load on the fuse buss(wires leading to the fuse, not sure if that is the right term).

For example, if I piggyback off of a fuse slot that has a 7.5amp fuse, could the wire leading to the fuse be only rated for 10 amps? Would adding an additional 9 amps(cellink is rated) to that wire overload it?
Or could all the wires that lead to the fuses be rated for 30 amps, so 30-7.5 amps means that that I can add an additional 22.5 amps to that circuit?

My main question is, does anyone know how much the wires leading to the fuse box are rated for? are they all the same? does a low fuse rating mean a low rating for the wire? does this not matter at all as they are rated for 100 amps?
Any insight is helpful, thanks!

 

[Nigel]

For example, if I piggyback off of a fuse slot that has a 7.5amp fuse, could the wire leading to the fuse be only rated for 10 amps? Would adding an additional 9 amps(cellink is rated) to that wire overload it?

It will depend on the vehicle and fuse. Unless you can confirm that the wiring is capable of more than 7.5 amps then you should assume that it is only 7.5 amps rated and adding another 9 amps is going to cause a fire and reduce your vehicle to a steel shell, or having watched the last episode of Top Gear where they had an aluminium bodied vehicle, 4 wheels, a pool of molten aluminium and a pile of ash!

Also, if you are provided with a 20 amp fuse, you should assume that your device will consume nearly 20 amps for a short period when you first turn it on, so adding it to a 20 amp circuit that is already using 15 amps is quite likely to blow the fuse.

You should find a fuse that has a spare 20 amps of capacity available, or run a wire from the battery with a 20 amp inline fuse near the start. Adding 9 amps is not like adding a dashcam, which typically only takes 0.2 amps from the 12 volt supply - a small percentage extra, not double the amount.

 

[Ralph2]

Also, if you are provided with a 20 amp fuse, you should assume that your device will consume nearly 20 amps for a short period when you first turn it on, so adding it to a 20 amp circuit that is already using 15 amps is quite likely to blow the fuse.

That.. depends on how the Add-a-Fuse thing is installed. A subject of much debate.

 

[Nigel]

That.. depends on how the Add-a-Fuse thing is installed. A subject of much debate.

True, when you are taking more than 100 watts of extra power you had better put the fuse tap the correct way around!

 

[franka]

There are a number of things that you should be aware of when adding electrical devices to your car. Especially high curent devices.
The first thing is fuse boxes/fuse blocks etc. These are simply power distribution devices, much the same as a fuse box in your house.

In a car the various electrical devices are sorted into groups, each group usually originating from the battery and supplied via a high power fuse, which can be 250A if supplying the starter circuit.

These groups of fuses are connected in their fuse boxes to a common bus bar, which is capable of carrying the current dictated by the fuse at its origin, usually about 100A. Each of the circuits in the group are connected to the bus bar via local fuses.

These fuses do NOT protect any thing before the fuse and its primary purpose is to protect the cable following it. If the device connected to this cable requires protection is should be supplied locally.

A piggy back fuse will parallel a further fuse with an existing fuse. If the piggy back fuse is inserted the wrong way round it means that the two fuses will not be in parrallel but in series. This will not cause catastropic damage but it will mean that the original fuse will be carrying increased current and could[most probably will] fail prematurely.