Discussion
What size Lucas fuses should I be using in my 1971 TVR Vixen?
There are 4 or 5 on the firewall (& 1 under the dash for horn, lighter, & hazards).
Are they all the same size, like the TR6 (35amp) ??
My car has *30A USA* fuses & I know that's too high for a LBC, right?
So, would *35A LUCAS* be appropriate for all fuse locations?
Thanks!!
There are 4 or 5 on the firewall (& 1 under the dash for horn, lighter, & hazards).
Are they all the same size, like the TR6 (35amp) ??
My car has *30A USA* fuses & I know that's too high for a LBC, right?
So, would *35A LUCAS* be appropriate for all fuse locations?
Thanks!!
Exactly.
Altho Amps=Amps on both sides of the pond.......
The British fuses are rated at the "instantaneous blow" rate. A British fuse of 35A will blow at 35A & therefore the wiring design only needs to carry up to that load.
The USA fuses are rated at a "continuous load" rate, & will blow at a much higher amperage (although they will carry the *rated* amps continuously without blowing). A 35A fuse may need something like 45A or more to actually blow.
The TR6 takes all 35A British fuses. The Triumph guys are careful to use British fuses.
My TVR Owners Manual doesn't give the specs on the fuses. So I was going to change them all out to 35A British fuses.
What are you guys running in your older TVRs? I have a '71 Vixen 2500 (non-M era).
Altho Amps=Amps on both sides of the pond.......
The British fuses are rated at the "instantaneous blow" rate. A British fuse of 35A will blow at 35A & therefore the wiring design only needs to carry up to that load.
The USA fuses are rated at a "continuous load" rate, & will blow at a much higher amperage (although they will carry the *rated* amps continuously without blowing). A 35A fuse may need something like 45A or more to actually blow.
The TR6 takes all 35A British fuses. The Triumph guys are careful to use British fuses.
My TVR Owners Manual doesn't give the specs on the fuses. So I was going to change them all out to 35A British fuses.
What are you guys running in your older TVRs? I have a '71 Vixen 2500 (non-M era).
Edited by CapRic on Tuesday 16th January 03:18
Edited by CapRic on Tuesday 16th January 03:19
By removing a fuse, connecting an Ammeter in its place and switching on the component it protects you could measure the current being drawn through that fuse. Once you have a list of current draw for each fuse you can fit the correct fuses, obviously the fuses to be fitted must have a continuous rating above the circuits current draw but be as close as possible to that draw
+1 That sounds like a good idea to measure current drawn.
If one of the devices drawing current has a bad connection will that mean it will draw more current.
If so you will know each device is only drawing the correct amount of current that it should.
Sorry i'm not very good on auto electrics.
Alan
If one of the devices drawing current has a bad connection will that mean it will draw more current.
If so you will know each device is only drawing the correct amount of current that it should.
Sorry i'm not very good on auto electrics.
Alan
Penelope Stopit said:
By removing a fuse, connecting an Ammeter in its place and switching on the component it protects you could measure the current being drawn through that fuse.
Not quite that simple, early TVR's only had about two fuses so you'd either have to know whats on each fuse then switch all on together or individually and add up amps? With this basic set up components obviously don't get fused at the correct amperage but the fuses do offer some protection should a direct earth fault occur (not so likely on a fibreglass car).
It's an English car so a couple or Lucas 35a should be perfect....... imho
OK, thanks for all the info.
Seems like the easy way out would be to use all Lucas 35A fuses.
Actual Amp measurement might be a good tinkering project when the weather warms up.
However, it's more a question of, "What amperage will melt the wires & switches on a 70's TVR?" Then, of course, restrict the Amps (fuse) to something below that, regardless of the actual Amp draw of components.
I would guess that the wiring & switching is a bit more robust than what the components on any circuit actually need. (Probably like the TR6, the TVR electrical design will support up to 35A.)
Seems like the easy way out would be to use all Lucas 35A fuses.
Actual Amp measurement might be a good tinkering project when the weather warms up.
However, it's more a question of, "What amperage will melt the wires & switches on a 70's TVR?" Then, of course, restrict the Amps (fuse) to something below that, regardless of the actual Amp draw of components.
I would guess that the wiring & switching is a bit more robust than what the components on any circuit actually need. (Probably like the TR6, the TVR electrical design will support up to 35A.)
CapRic said:
OK, thanks for all the info.
Seems like the easy way out would be to use all Lucas 35A fuses.
Actual Amp measurement might be a good tinkering project when the weather warms up.
However, it's more a question of, "What amperage will melt the wires & switches on a 70's TVR?" Then, of course, restrict the Amps (fuse) to something below that, regardless of the actual Amp draw of components.
I would guess that the wiring & switching is a bit more robust than what the components on any circuit actually need. (Probably like the TR6, the TVR electrical design will support up to 35A.)
The problem is that older cars were never fused correctly - There are too many circuits on some single fusesSeems like the easy way out would be to use all Lucas 35A fuses.
Actual Amp measurement might be a good tinkering project when the weather warms up.
However, it's more a question of, "What amperage will melt the wires & switches on a 70's TVR?" Then, of course, restrict the Amps (fuse) to something below that, regardless of the actual Amp draw of components.
I would guess that the wiring & switching is a bit more robust than what the components on any circuit actually need. (Probably like the TR6, the TVR electrical design will support up to 35A.)
The problem with the above scenario is that the circuits aren't protected very well, obviously some circuits take more current than others, all the fuses are doing is covering the total possible current that might be drawn through them if all those circuits are switched on at the same time
The solution for this problem is to split the circuits and add more fuse holders/fuses so as to be able to fuse all the circuits seperately, if you do upgrade the the fusing I suggest that you choose the new type blade fuses due to them being far more accurate, blade fuses do blow easier than glass fuses or ceramic fuses and they blow very close to their ratings
Below is a cropped image of fusing I am working on at present that will give you something to think over, I do appreciate that your TVR doesn't have all the included circuits
Penelope Stopit said:
The chances are that your TVR is mostly wired with 14/0.30 8.75 Amp and 28/0.30 17.5 Amp cable
The fuses are of a higher rating than the cable which means that the cable can begin to melt before blowing the fuse that protects it
If that's the case, then the 35 [instantaneous blow] Amp fuses originally designed into the system, basically do *nothing* (since the wire will melt/burn up, before the 35A fuse will melt/burn up/"blow"). That's as good as NO fuses at all.The fuses are of a higher rating than the cable which means that the cable can begin to melt before blowing the fuse that protects it
In 46 years, my TVR has survived with, effectively, no fuse protection?
To put it another way, .....No fuse has ever blown on an original TVR? (Since, for *that* to happen, one would have to draw a level of amps across the fuse from wires that won't support that level of amperage!)
I'm not disputing anything here, I'm just trying to understand this.
What about other LBCs with the 35A British fuse design? The TR6 has more fuses than the TVR, but they're all 35A British. Did Triumph also use wires capable of only 8.75A & 17.5A ??
CapRic said:
Penelope Stopit said:
The chances are that your TVR is mostly wired with 14/0.30 8.75 Amp and 28/0.30 17.5 Amp cable
The fuses are of a higher rating than the cable which means that the cable can begin to melt before blowing the fuse that protects it
If that's the case, then the 35 [instantaneous blow] Amp fuses originally designed into the system, basically do *nothing* (since the wire will melt/burn up, before the 35A fuse will melt/burn up/"blow"). That's as good as NO fuses at all.The fuses are of a higher rating than the cable which means that the cable can begin to melt before blowing the fuse that protects it
In 46 years, my TVR has survived with, effectively, no fuse protection?
To put it another way, .....No fuse has ever blown on an original TVR? (Since, for *that* to happen, one would have to draw a level of amps across the fuse from wires that won't support that level of amperage!)
I'm not disputing anything here, I'm just trying to understand this.
What about other LBCs with the 35A British fuse design? The TR6 has more fuses than the TVR, but they're all 35A British. Did Triumph also use wires capable of only 8.75A & 17.5A ??
The whole idea of building a good wiring harness is to use cable that is sufficient to carry the current of its particular circuit allowing for volt drops that are dependant upon length, there is no point in using cable that is bigger than needed as it will be adding weight to the vehicle
A thinnish wire with an over-rated fuse will heat up, the longer the wire the more chance of it heating up and melting due to it acting in a similar fashion to a mains fire element, many older cars suffer from their rear looms burning out due to the over-rated fuses/long cables scenario
A short cable has more chance of blowing an over-rated fuse before melting
Bear in mind that cable current ratings are for continuous current flow and they will stand up to carrying a higher current for a short while and that this will help to possibly blow a fuse, its the possibly not blowing fuses that cause the damage
Also bear in mind that when a cable rubs through and shorts to earth, there are no guarantees that all of the cables strands are shorting at the same time which means that there is more chance of burning than blowing
None of this information I am posting for you is new in any way, this is common knowledge amongst many
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, the cost of rewiring vehicles under warranty eats up much of the profit
I hope you now understand why/that there are lots of older incorrectly fused vehicles on the road
Edited by Penelope Stopit on Friday 19th January 20:36
Penelope Stopit said:
The whole idea of building a good wiring harness is to use cable that is sufficient to carry the current of its particular circuit allowing for volt drops that are dependant upon length, there is no point in using cable that is bigger than needed as it will be adding weight to the vehicle
<snip>
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, <snip>
That makes sense. I get it now. <snip>
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, <snip>
The problem isn't insufficient size cable, ....it's fuses that are too large (I suppose due to the *few* number of fuses/circuits used).
The solution, as pointed out above: Design a greater number of fused circuits, with the appropriate [lower amp] fuses.
Ah, another project on the drawing board!
CapRic said:
Penelope Stopit said:
The whole idea of building a good wiring harness is to use cable that is sufficient to carry the current of its particular circuit allowing for volt drops that are dependant upon length, there is no point in using cable that is bigger than needed as it will be adding weight to the vehicle
<snip>
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, <snip>
That makes sense. I get it now. <snip>
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, <snip>
The problem isn't insufficient size cable, ....it's fuses that are too large (I suppose due to the *few* number of fuses/circuits used).
The solution, as pointed out above: Design a greater number of fused circuits, with the appropriate [lower amp] fuses.
Ah, another project on the drawing board!
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