General dumper wiring question

[Richard Hunton]

Morning all, im going to wire up my own heater plug supply for my 7ton Thwaites.

Im going to go:
battery to dash
Push switch to
Heater plug buzz bar.

My question is this im going to put a 50amp fuse in , just in case.

Would you put it before or after the switch or would it not matter ?

Thanks guys

 

[Shovelhands]

I’d put it in before any switching. But to be honest I think it wants to be wired in via a relay or a solenoid. Take the load away from the switch.

 

[Gecko]

To be useful, the fuse needs to be rated higher than the load as its function is to protect the wiring.
The closer to the battery, the more wiring is protected.

Your plan is fine and will work well. Personally I'd probably sex it up a bit with a relay. Main power line to the battery and pick up the trigger power from the 'run' position of the start switch (if it's got one).

 

[Mick-the-fitter]

Yep use a relay, fuse the battery supply to and from the relay when switched, switching current and earth only need to be 10/15 amp fuse.

 

[Richard Hunton]

@Mick-the-fitter @Gecko if thats the case i might aswell use the existing relay its the rest of the wiring thats letting the job down

 

[Russell]

You need to know what the wattage or current of the load is before choosing the cable size and fuse.
You could measure the resistance of the bus bar to ground and work it from that . The resistance will increase as it heats up but that doesn't matter. Or you could measure the current when you stick 14.4.v or whatever it charges at.
If it ends up requiring an unrealistic cable size you could use the adiabatic equation although that might only work for AC I'm not sure.

 

[V8Druid]

when you say heater plug .... are you talking glow plugs in the cylinders, or a diesel fired, 'flame thrower' in the inlet manifold? ..... I assume glow plugs as you mention bus bar.
as said either will need feeding via a relay unless you have a seeeeerious switch in charge of delivering the substantial current draw.
does the exiting relay have a timer circuit or is it simply a make/break type?

 

[Richard Hunton]

when you say heater plug .... are you talking glow plugs in the cylinders, or a diesel fired, 'flame thrower' in the inlet manifold? ..... I assume glow plugs as you mention bus bar.
as said either will need feeding via a relay unless you have a seeeeerious switch in charge of delivering the substantial current draw.
does the exiting relay have a timer circuit or is it simply a make/break type?

Glow plugs to confirm,

Currently there are 2 fuses and 2 relays, relays work, but the rest of the rats nest doest
The current fuses are 50 amd 30amp.
I was intending on using a 50amp fuse and 50amp push switch with 6mm cable

Im currently using a spare jump lead, from battery to buzz bar atm to get it going.

 

[Mick-the-fitter]

You need to know what the wattage or current of the load is before choosing the cable size and fuse.
You could measure the resistance of the bus bar to ground and work it from that . The resistance will increase as it heats up but that doesn't matter. Or you could measure the current when you stick 14.4.v or whatever it charges at.
It the ends up requiring an unrealistic cable size you could use the adiabatic equation although that might only work for AC I'm not sure.

don’t think I remember any old dumpers with jump leads bolted to the preheat system, some chunky cable to a 50 amp fuse and 75 amp relay would probably do!

 

[Russell]

Hence why I mentioned the adiabatic equation.
It tells you how long you can run X amps through x mm2 conductor before the cable reaches x°c.
So theirfor you could work out how small a cable you could use if you want to only use it for a few seconds.
That is if I remember correctly
As I said, that particular equation is for AC and could be different for a DC circuit.

 

[JD450A]

FYI the prestart thermoplug on my MF65 is no greater than 1mm wire...

 

[V8Druid]

FYI the prestart thermoplug on my MF65 is no greater than 1mm wire...

which melts if it's on too long

 

[JD450A]

which melts if it's on too long

It's grand tbh.

 

[Mick-the-fitter]

FYI the prestart thermoplug on my MF65 is no greater than 1mm wire...

Weren’t they 1 mm solid copper wire!

 

[Smiffy]

Weren’t they 1 mm solid copper wire!

I thought solid wire Caries less amps than the same diameter multistrand?? Hence welding cables being how they are

 

[V8Druid]

Weren’t they 1 mm solid copper wire!

quite probably ... was my thoughts too ... can't beat a single core for carrying ..... none o' this flexi sh1t

 

[V8Druid]

I thought solid wire Caries less amps than the same diameter multistrand?? Hence welding cables being how they are

would like to see you coil up a solid 50mm2

 

[Gecko]

I thought solid wire Caries less amps than the same diameter multistrand?? Hence welding cables being how they are

Solid is only suitable for fixed installation with no vibration (just because MF thought something was a good idea in the 1960's, doesn't mean it was!). Look at the lightening conductor from a church spire for high current, single conductor.
The current carrying capacity of a wire (DC or low frq. AC) is all about cross-section area of the conductor and it's ability to loose heat.
In exotic situations you can use copper pipe and run refrigerant though it. (probably overkill for a starter circuit).

 

[Russell]

You sound like you know your onions.
I was I told switch gear/ isolators on DC circuits (pv) needs to be rated at twice the amp rating.
Why's that?

 

[Vinpetrol]

You need to know what the wattage or current of the load is before choosing the cable size and fuse.
You could measure the resistance of the bus bar to ground and work it from that . The resistance will increase as it heats up but that doesn't matter. Or you could measure the current when you stick 14.4.v or whatever it charges at.
If it ends up requiring an unrealistic cable size you could use the adiabatic equation although that might only work for AC I'm not sure.

Or you could use a bit of wire that looked the same thickness