Batteries and busbars

[Purple Velvet]

That's probably true of older cars, but has not been the case for many, many years. Modern cars sre fused something like;

That's horrible! I know little about vehicles of this Century, so such abominations have passed me by.

 

[PaulRainbow]

That's horrible! I know little about vehicles of this Century, so such abominations have passed me by.

In what way it it horrible ?

 

[Purple Velvet]

In what way it it horrible ?

How long have you got? ;-)

That sort of setup turns the battery terminal into a makeshift busbar, which is where the problem starts.

You’ve got multiple high-current connections all stacked on one stud, plus the fuse block itself, all relying on one clamping point. Every extra interface adds resistance and another place for heat to build up or for something to loosen off. It only takes one slightly poor connection under load and it’ll start getting warm, then watch out.
Mechanically it’s not great either. The whole lot is hanging off the battery post, carrying the weight of several cables and the fuse assembly. On anything that moves or vibrates, that’s asking for fatigue, loosening or cracked plastic over time.

There’s also the issue of exposure. You’ve effectively got several live feeds right there at the battery. Drop a spanner across that and it won’t end well. A single properly protected feed off the battery is far safer. Thermally it’s all concentrated in one small area as well. High current paths, fuse contacts and terminations all bundled together in plastic isn’t ideal when things start working hard. It also makes fault finding and future additions messy. It encourages just piling more ring terminals on rather than having a proper distribution point. Replacing the battery puts mechanical stress onto all the outgoing feeds too.

My previously stated approach would be one short, heavy cable off the battery to a proper busbar, with a main fuse if you must, as close to the battery as possible and then distribute from there through a proper fuse box. That keeps the battery connection simple, reduces stress and is a lot safer and more maintainable.


It works for the purpose I suppose, but it’s a cost/space shortcut rather than good practice and it's 'ORRIBLE!

 

[PaulRainbow]

How long have you got? ;-)

That sort of setup turns the battery terminal into a makeshift busbar, which is where the problem starts.

You’ve got multiple high-current connections all stacked on one stud, plus the fuse block itself, all relying on one clamping point. Every extra interface adds resistance and another place for heat to build up or for something to loosen off. It only takes one slightly poor connection under load and it’ll start getting warm, then watch out.
Mechanically it’s not great either. The whole lot is hanging off the battery post, carrying the weight of several cables and the fuse assembly. On anything that moves or vibrates, that’s asking for fatigue, loosening or cracked plastic over time.

There’s also the issue of exposure. You’ve effectively got several live feeds right there at the battery. Drop a spanner across that and it won’t end well. A single properly protected feed off the battery is far safer. Thermally it’s all concentrated in one small area as well. High current paths, fuse contacts and terminations all bundled together in plastic isn’t ideal when things start working hard. It also makes fault finding and future additions messy. It encourages just piling more ring terminals on rather than having a proper distribution point. Replacing the battery puts mechanical stress onto all the outgoing feeds too.

My previously stated approach would be one short, heavy cable off the battery to a proper busbar, with a main fuse if you must, as close to the battery as possible and then distribute from there through a proper fuse box. That keeps the battery connection simple, reduces stress and is a lot safer and more maintainable.


It works for the purpose I suppose, but it’s a cost/space shortcut rather than good practice and it's 'ORRIBLE!

Sounds like you know more about battery fusing than every major car manufacturer in the World.

 

[jakew009]

How long have you got? ;-)

That sort of setup turns the battery terminal into a makeshift busbar, which is where the problem starts.

You’ve got multiple high-current connections all stacked on one stud, plus the fuse block itself, all relying on one clamping point. Every extra interface adds resistance and another place for heat to build up or for something to loosen off. It only takes one slightly poor connection under load and it’ll start getting warm, then watch out.
Mechanically it’s not great either. The whole lot is hanging off the battery post, carrying the weight of several cables and the fuse assembly. On anything that moves or vibrates, that’s asking for fatigue, loosening or cracked plastic over time.

There’s also the issue of exposure. You’ve effectively got several live feeds right there at the battery. Drop a spanner across that and it won’t end well. A single properly protected feed off the battery is far safer. Thermally it’s all concentrated in one small area as well. High current paths, fuse contacts and terminations all bundled together in plastic isn’t ideal when things start working hard. It also makes fault finding and future additions messy. It encourages just piling more ring terminals on rather than having a proper distribution point. Replacing the battery puts mechanical stress onto all the outgoing feeds too.

My previously stated approach would be one short, heavy cable off the battery to a proper busbar, with a main fuse if you must, as close to the battery as possible and then distribute from there through a proper fuse box. That keeps the battery connection simple, reduces stress and is a lot safer and more maintainable.


It works for the purpose I suppose, but it’s a cost/space shortcut rather than good practice and it's 'ORRIBLE!

To me it looks almost perfectly optimised for its intended purpose.

 

[Phil_boat]

The reality is most people bodge at that point, sometimes with grand plans to “do it properly” when they have more time but often that time never comes.

Although I will definitely do it when I have more time…

I’ve added main fuses to the batteries so far and will add a small fuse box next to them to move my bilge pump, heater and charger away from the battery terminal.

 

[ylop]

There’s also the issue of exposure. You’ve effectively got several live feeds right there at the battery. Drop a spanner across that and it won’t end well.

You do realise thats a "box" with the lid open don't you?

It also makes fault finding and future additions messy. It encourages just piling more ring terminals on rather than having a proper distribution point.

Not sure why fault finding would be hard. The studs even have nice little dimples to stop your multimeter probe slipping.

I doubt modern car manufacturers are too worried about people wanting to add extra kit direct to the battery. They engineer almost everything you are likely to want into the car for you - but often had a couple of space fuse circuits free at the fuse box (probably so the same fuse box fits many models rather than for consumer upgrades).

Replacing the battery puts mechanical stress onto all the outgoing feeds too.

Doubt it the top of the box provides extra support to the cables, although replacing batteries is far from a common occurrence on modern vehicles.

Modern cars aren't sitting at the side of the road with smoke pouring out of them nor do they breakdown as often with battery gremlins as old cars - despite their greater reliance on electronics.

 

[Alex_Blackwood]

Hopefully a simple question.

I have a yacht with two house batteries and the usual rats nest of direct connections. These include direct loads (bilge pumps, radar, etc) and feeds from solar panels and a wind generator. These seem to be split somewhat randomly between the two batteries.

I would like to simplify these with busbar, but what is the ideal arrangement? I assume that I can rationalise everything to busbar(s) on the positive of battery A and the negative of battery B, but can I put loads and feeds on the same busbar or should they go on separate ones (with each connected directly to the battery or via another short busbar and a single cable to the battery?

Thanks in advance.

I guess you now realise how forlorn that hope is. Or at least the answer