What Power input for fuse box/multiple loads?

Nic_A31
Getting to know the place
Posts: 14
Joined: November 19th, 2017, 12:41 pm

What Power input for fuse box/multiple loads?

Unread post by Nic_A31 » April 19th, 2018, 6:26 pm

I'm setting up an extra fuse box in my bay to power high and low beam amps, UHF CB, and down the track spotties and LED bar...the relay box has 6 slots all up, I'm immediately going to be using 3 and at least 2 more down the track. I'm using 15A wiring and fuses for all circuits (I'll install a lower rated fuse if needed for the UHF CB or whatever else, if necessary, when I install them).

All of these slots are being powered via a distribution block.
Do I need to run 90A (6x 15) into the block to effectively power all the circuits at the same time? ...this seems excessive.

Don't really know auto electrics that well...on factory looms I see they run a single wire that splits once or more to power multiple devices of the same amperage...
I feel that running a 90A cable into the distribution block is excessive, even if I were to run all 6 relays at the same time.....

Peter Aawen
Admin
Posts: 20807
Joined: June 17th, 2005, 8:01 pm

Re: What Power input for fuse box/multiple loads?

Unread post by Peter Aawen » April 21st, 2018, 7:40 pm

Hi Nic, if you are ever likely to be pulling 15 amps down each of the 6 circuits powered by that fuse block at the same given moment, then yeah, you really WILL need to run wires & power to the fuse block at that level of output - to do anything less means something is probably gonna give when you hit that level, or shortly there-after.... and that could mean the insulation on the wires leading to the fuse block burst into flames, or any lesser fuses or wires between the fuse block & the battery give up explosively!! :eek: Btw, you do realise that fires in your car's wiring loom can bloody hard to put out once the insulation's started burning, don't you?? (Do you really need to ask me how I know that!! :o )
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

Nic_A31
Getting to know the place
Posts: 14
Joined: November 19th, 2017, 12:41 pm

Re: What Power input for fuse box/multiple loads?

Unread post by Nic_A31 » May 5th, 2018, 5:13 pm

Cheers for the reply Peter.
Any idea how I can neatly fuse 75A or 90A?

I found a 60A fuse holder at SCA, but still not enough...It'll do for now since I won't be using 60A.

I'm new to the 4x4 scene so I've got no idea what kind of power I need to run for UHF, LED spotties, LED light bar....would 15A be enough for each of those? could I get away with less ?

Peter Aawen
Admin
Posts: 20807
Joined: June 17th, 2005, 8:01 pm

Re: What Power input for fuse box/multiple loads?

Unread post by Peter Aawen » May 5th, 2018, 5:34 pm

Rather than trying to find a fuse big enough for all that, why not try a quick acting re-settable Circuit Breaker? Same protection, only no need to replace the entire unit if it trips; just sort out the cause, fix that, then reset the Circuit Breaker! :thumb:

And to work out how big a fuse or breaker you need, you hafta find & add up all the current draws for each of those devices & total them, then make sure that circuit breaker & wires to the fuse block are suitable, and that their individual circuits have sufficient capacity to carry their load with a reasonable safety margin in the wires & fuse/breaker. Your UHF shouldn't be too much greater than 5W, and the LED's are more likely to be in the vicinity of 35W rather than the 200W from a pair of 100W Halogen globes! So your power needs might be somewhat smaller than you expect!!


Still better yet than running heavy leads & fuses for anything, if you run a heavy power lead direct from the battery with a big enough circuit breaker to each individual unit thru a relay under the bonnet that's activated by your switching device and protected by the fuse block, you can probably use a tiny current draw via the switch & fuse block! With that triggering each of the individual relays & their much larger power draws that are protected by each circuit breaker, you lessen the fuse block load & the in-cab risk, AND you get better & cleaner power direct from the battery to the device! Relays & circuit breakers are great for looking after devices with big power needs - the switching side of the relay can use the minimal power draw required so that you don't have a whole bucket load of power running all the way into the cab & then out again to reach the device, & posing a shorting & fire risk for the entire length of the wiring; while the relay & big power lines can be breaker protected & kept under the bonnet, well away from your precious cargo! ;)
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

Return to “12v and Electrical”