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brightspark
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no point in fusing the negative on a negative earthed vehicle always the positive
premmington
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+1 for the above
Tinbasherdan
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I always fuse positive, put a battery cutoff in negative
julianf
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I know you're an electrician, but I can't understand why, on a dc circuit, that should make any difference.
Current will be identical at the positive pole as it will be at the negative. Indeed the flow of electrons go from negative to positive, and it's only historical convention that states that "current" flows from positive to negative.
Again, current at the negative would be the same as at the positive. Assuming you're not shorting prior to the fuse at either pole I can't see why it would make any difference at all which pole the fuse was on.
pedrobedro
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Where is the fuse going ? You don't fuse between batteries.
All true.
The problem is the entire car body is the earth. Any short from the power in your bit of bolted on equipment will earth to the body and the fuse in it's own earth lead will do not a lot. But one in the positive lead should blow, assuming its rated correctly, before things get too exciting.
To add an edit - on older, positive earth vehicles, the opposite applies.
brightspark
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as above all the neutrals are conected to earth. through the chassis the lives are through fuses at different amperage to the various switches and whatever they controll
Moose McAlpine
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It's not just a matter of current flow from consumers, but if the wiring were to be damaged and short to ground, you want the fuse as close to the battery as possible on the live side to protect the wiring.
If you fuse the negative near the battery and the wiring shorts to ground the fuse won't blow as it's now not part of the "circuit".
Barking Mat
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If this is a leisure battery, have you got it on the same charging circuit as the starter battery ?
If so watch out for them both discharging.
If so watch out for them both discharging.
sako243
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But if the setup is negative terminal of the battery -> fuse -> chassis then when the fuse blows everything is at the same potential as the positive terminal.
The car chassis is just a conductor it only becomes an earth when it is connected to the negative terminal of the battery. If that negative connection is removed then the whole chassis will float up to 12V which is irrelevant because there is no reference point to provide a potential difference to.
The difference may be with modern vehicles there may be a lot of capacitance in ECUs so they will still maintain a potential.
julianf
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The OP said "fuse" not "fuses" -
In light of that, I took that to be a single fuse, probably on one of the terminals. (to clarify that assumption, I said, in my prior post -
"Assuming you're not shorting prior to the fuse at either pole")
I still can not see why it should make any difference what else is in the circuit, what it's connected to, or how it's configured (what potential the chassis is at) - if the fuse is on the battery terminal, the current at either terminal is identical.
I see no reason why any of the rest of it is in any way relevant?
In light of that, I took that to be a single fuse, probably on one of the terminals. (to clarify that assumption, I said, in my prior post -
"Assuming you're not shorting prior to the fuse at either pole")
I still can not see why it should make any difference what else is in the circuit, what it's connected to, or how it's configured (what potential the chassis is at) - if the fuse is on the battery terminal, the current at either terminal is identical.
I see no reason why any of the rest of it is in any way relevant?
Not sure any of my vehicles, registered 1979 through to 2016, have a fuse in either battery lead until the positive lead makes its way to the main fuse box - where each circuit is protected by a fuse. Other fuses are dotted around (especially in the Lancia!) for individual item.
Never had any hassle, so see need to re-invent the wheel, or indeed argue about it, given the explanations above.
Never had any hassle, so see need to re-invent the wheel, or indeed argue about it, given the explanations above.
julianf
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Not sure any of my vehicles, registered 1979 through to 2016, have a fuse in either battery lead until the positive lead makes its way to the main fuse box - where each circuit is protected by a fuse. Other fuses are dotted around (especially in the Lancia!) for individual item.
Never had any hassle, so see need to re-invent the wheel, or indeed argue about it, given the explanations above.
The chap is adding a second battery, to be wired in parallel, to an existing battery, in a camper van.
I mean, if he has a 50/50 choice, why not go with convention, but, so far as I can see, based on what he actually said, and my (stated) assumptions, there is no reason, based in science, as to why one side is better than the other.
It's fine to say "convention is (X) - go with convention"
But to say physics is different from what it is shouldn't be encouraged on an engineering forum.
pedrobedro
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Are you adding the second leisure battery to an existing leisure battery or to your vehicle charging system ? Do you have a split charge system installed ?
Perhaps I should have explained more details?
First battery is fused via feed from solar panel,then supply cable to fridge,is also fused,both on positive side.
Does that detail change anything,part of the problem is ,I just forgot how I connected them in the first place,I’m 60 now so keep forgetting
.
@Barking Mat ,learnt that the hard way! In the dark at Le tranche sur mer,had to ask locals for a push,lucky it’s an easy starter.lol.
First battery is fused via feed from solar panel,then supply cable to fridge,is also fused,both on positive side.
Does that detail change anything,part of the problem is ,I just forgot how I connected them in the first place,I’m 60 now so keep forgetting
.@Barking Mat ,learnt that the hard way! In the dark at Le tranche sur mer,had to ask locals for a push,lucky it’s an easy starter.lol.
Bobupndown
What could possibly go wrong?
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My 1963 mini is positive earth. Not hard to change them to negative but its still running with an original dynamo and I like it's originality. Always have to think a bit harder when doing anything electrical, positive being earth is just counter intuitive, to me anyway. Being a child of the 70's I remember warning stickers in car engine bays advising "Warning this vehicle is negative earth" when a few years earlier the opposite was the norm. Saw one only yesterday at a car show on a beautiful Mk1 Escort RS2000.
pedrobedro
Man at Matalan
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Perhaps I should have explained more details?
First battery is fused via feed from solar panel,then supply cable to fridge,is also fused,both on positive side.
Does that detail change anything,part of the problem is ,I just forgot how I connected them in the first place,I’m 60 now so keep forgetting
@Barking Mat ,learnt that the hard way! In the dark at Le tranche sur mer,had to ask locals for a push,lucky it’s an easy starter.lol.
Have a read on 12 volt planet and see if there's anything useful you can pick up. The leisure circuit should be isolated from the vehicle circuit to prevent drain on the start battery and leisure batteries do not like rapid charge or discharge and can be damaged by such activity.
