Correct fusing for basic setup with fans

Thread Starter

youradds

Joined Jul 3, 2018
15
Hi,

I'm glad I found this forum :) Hopefully you can help!

I've started a little project that is going to have:

1 x 12v computer fan (0.3amp, 3.6w)
1 x 12 v computer fan (smaller, 0.16A)
1 x Raspberry Pi W 1.2 ( https://shop.pimoroni.com/products/...pc&utm_source=googlepla&variant=3147218944010 )
2 x 9 volt motors ( https://www.ebay.co.uk/itm/SZUK-2PC...cro-Motor-for-CD-DVD-Player-Y2O1/173341885199 )

The problem I'm having is 2 fold:

1) I am going to be running this all off a 12V (12V 7Ah /20 HR) battery.
2) The Raspberry Pi I've been told will not run from that - it needs to be stepped down to a lower voltage
3) The wires on some of the parts are quite thin - my dad has suggested a 500Ah fuse to protect it. Or would it be better to put a fuse on each section?

I'm still a bit new to all of this (I'm a web programmer by job, but I've started playing with the Raspberry Pi and wanted to build myself a little project =)), so please be gentle ;)

FWIW: I just came across this, and it seems like it would work for the Pi bit:

https://www.ebay.co.uk/itm/12V-to-5...635284?hash=item3d5cd78d14:g:RtkAAOSwLopaqh9b

Thanks!

Andy
 
Last edited:

Thread Starter

youradds

Joined Jul 3, 2018
15
The adapter looks like it will work.
Max.
Thanks for the reply. Yeah, the adapter looks good :)

The main issue I can see now is:

1) How to drop the voltage of the 12v down to something my 9v motors can take (without frying the board: https://www.ebay.co.uk/itm/Adafruit-TB6612-1-2A-DC-Stepper-Motor-Driver-Breakout-Board/263487356583 , which was suggested on this post: https://howchoo.com/g/mjg5ytzmnjh/controlling-dc-motors-using-your-raspberry-pi )
2) How to protect the fans with small enough fuses. I've found some spade inline fuses, but the smallest I can find is 2amp. My dad is concerned the thin wires would burn well before that tripped out in the case of s short circuit.

Thanks!

Andy
 

Thread Starter

youradds

Joined Jul 3, 2018
15
It won't matter if you run the motor/controller with 12v and just restrict the max RPM.
The controller is good for 13v.
Max.
Ah sweet - so that sorts that issue then. Those motors are literally just going to be pointing upwards, with a rotating disk attached to it (a product). Rotation speed will be very minimal as I want to show the products off =))

How about for the fans? Currently its going to be going into a chock strip (+ and -), then the wires coming out going to each individual item. I'm a bit concerned that the low ampage fans are sharing the higher ones, and that they could over heat with a short. I'm really struggling to find any inline fuses that will take such a small amp (i.e 500mA)

Thanks!

Andy
 

MaxHeadRoom

Joined Jul 18, 2013
25,019
You can get the glass 3AG fuse down to a few Ma.
You can get the inline quick disconnect for them. Try auto supplies.
Or the smaller version (#??).
Max.
 

Thread Starter

youradds

Joined Jul 3, 2018
15
You can get the glass 3AG fuse down to a few Ma.
You can get the inline quick disconnect for them. Try auto supplies.
Or the smaller version (#??).
Max.
Thanks. That sounds interesting. I assume you are talking about these?

https://www.ebay.co.uk/itm/10pcs-Sc...594228?hash=item3621a37434:g:W1wAAOSwVuNbKzeL

...then with some small fuses like:

http://uk.farnell.com/eaton-bussmann-series/tdc10-500ma/fuse-quick-blow-500ma/dp/534900 (for the 0.3amp fan)
http://uk.farnell.com/littelfuse/0313-187hxp/fuse-cartridge-187-5ma-6-3x32mm/dp/1149704 (for the 0.16amp fan)

Thanks! :)

Andy
 

Sensacell

Joined Jun 19, 2012
2,985
Consider that fuses are really about preventing fires, they don't really protect the loads.

Size the fuses to protect the wiring, don't base the rating so much on the loads, you will under-rate the fuse by a large margin.

A 500 ma fuse will "nuisance blow" and annoy the hell out of you.

Just use a single 5A fuse right at the battery, that way if you get a short, the wires will not melt and burst into flames.
(which can happen with batteries quite easily)
 

Thread Starter

youradds

Joined Jul 3, 2018
15
Consider that fuses are really about preventing fires, they don't really protect the loads.

Size the fuses to protect the wiring, don't base the rating so much on the loads, you will under-rate the fuse by a large margin.

A 500 ma fuse will "nuisance blow" and annoy the hell out of you.

Just use a single 5A fuse right at the battery, that way if you get a short, the wires will not melt and burst into flames.
(which can happen with batteries quite easily)
Thanks. Will that not cause issues running the 0.5amp between the 2 fans, 1amp for the Raspberry Pi, and then the 2 motors? I'm all for simple - I just don't want my hard work going up in smoke =) haha
 

Thread Starter

youradds

Joined Jul 3, 2018
15
That 6000 Rpm motor will not like going slow.
I would choose a different motor, maybe with gear reduction.
Would a small stepper motor be better? I did wonder when I re-read the 6000 rpm bit on the motor (after paying), but thought I'd wait and just see how it went. The idea of the project is to have 2 discs on top of a wooden box. These will then have a motor underneath each of them, rotating them slowly to show off the products sitting on top

Thanks!

Andy
 

Thread Starter

youradds

Joined Jul 3, 2018
15
Thanks - I've just ordered a couple :) I'm sure I can find something else to use the other motors on, so not a major loss :) Just hope it arrives in time now (as its coming from China)
 

Thread Starter

youradds

Joined Jul 3, 2018
15

Thread Starter

youradds

Joined Jul 3, 2018
15
The motor has now arrived. I'm just trying to work out how I can connect it to my metal bar rod. This is what the end looks like (attached).

2018-07-16 12.14.12.jpg 2018-07-16 12.14.24.jpg

I'm struggling to find a way to have a metal rod that will go from that to a rotating disc (in the center of it, glued into place I guess)

Maybe I'm not searching for the right phrase. Any ideas? :)

Thanks!

Andy
 

DNA Robotics

Joined Jun 13, 2014
624
Isn't the hole in the shaft threaded for a screw? If that shaft isn't long enough to poke through the box and screw the disk to it, you could use a long screw and nut as the axle for the disk. Poke it through a hole in the box and screw it into the motor shaft.
 

Thread Starter

youradds

Joined Jul 3, 2018
15
Isn't the hole in the shaft threaded for a screw? If that shaft isn't long enough to poke through the box and screw the disk to it, you could use a long screw and nut as the axle for the disk. Poke it through a hole in the box and screw it into the motor shaft.
Ah man - not sure how I missed that!!! Looking at it at an angle, you are indeed correct! I'll try and source a bolt that is the correct size (seems to be 2mm wide), and see if that fits the thread. Then I just need to find a way to attach the other part :)

Thanks
 
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