Common +ve & -ve via busbar

[Mr Meenah]

I'm starting a van conversion and am wondering whether I can have a common negative for all my wiring via a busbar and a common positive ( apart from the +ve from the starter battery that goes to the b2b charger ).
Sterling Charger/inverter
Sterling B2B charge
Leisure batteries
12 way fuse connector
Negative from the starter battery for the b2b unit uses a 16mm² cable, negatives for the charger/inverter and the leisure batteries use 60mm² cable..

 

[autorouter]

Yes it's a good idea. If you have more than one leisure battery, you can make sure that the wires from batteries to fuse are exactly equal length. Then wire in an isolator switch, then the positive busbar.

Are you fitting a shunt by the batteries, in the negative lead? Connect the batteries to one side of the shunt, and the negative busbar to the other side. The chassis connection is made to the busbar.

 

[Mr Meenah]

This is the busbar I have bought

albeit with 8mm studs.
'Re the +ve, will this work..
B2B out >100A fuse > Busbar > leisure batts.
Charger/inverter out 200A fuse > busbar

What do you mean by shunt on the negative?

If both the leisure batts and starter batt are connected to the busbar I wouldnt need to ground the busbar to chassis surely

 

[mitzimad]

a shunt is for an amp meter

 

[Mr Meenah]

Something like this?
MICTUNING Digital Multimeter, DC 6.5-100V 0-100A LCD Amperage Power Energy Meter DC Volt Amp Testing Gauge Monitor LCD Blue Backlight Digital Display with 100A/75mV External Shunt Amazon product ASIN B01JOUZELG

^{_{Subscribers  do not see these advertisements}}

 

[autorouter]

What do you mean by shunt on the negative?

If both the leisure batts and starter batt are connected to the busbar I wouldnt need to ground the busbar to chassis surely

I mentioned the chassis connection because if it's there, it can be connected on the wrong side of the shunt. If you don't have a shunt (for a battery monitor) then just connect everything to the negative busbar.

The starter battery negative is always connected to the chassis, because that's the return path to the alternator. The leisure battery also needs a return connection so that it can charge from the alternator. On many MHs the leisure battery is some distance from the starter battery, and the negative connection from leisure battery to starter battery/alternator is made through the chassis.

As you say, if you already have the starter negative on the busbar there's no need of a chassis connection.

 

[Mr Meenah]

https://photos.app.goo.gl/E7WSHjJmA4GSRprp9
This is as far as i got today, hopefully the link works

 

[Mr Meenah]

 

[autorouter]

Looks OK so far - just two comments:

Is that a second leisure battery to be connected? If so, it's a good idea to equalise the voltage drop on the wires that go to the batteries. There are a number of ways to do this, but since you have pos and neg busbars, one way is to make the wires from fuse to each battery exactly equal in length. Looking at the wires, I'd say that if you wired the second battery, the wires would have to be longer. You could make the two positive wires the same, ie both longer, but then you'd have to scrap the wires you just made. Then do the same (equalise the lengths) for the negatives to the neg busbar.

Also if it was my MH I'd want an isolator switch between the fuse and the pos busbar. You can get away without one, I suppose.

 

[Mr Meenah]

This is the sort of help and advice I was after. I plan to put a dc isolator in.
1. Does it go between the fuse an battery?
2. Does an ammeter ( like the one shown above in the comments ) go between -ve battery terminal and -ve busbar?
3.Equal cable lengths from bat to bat as well as to fuse or to busbar ( not taking fuse into consideration?
My next step is to wire up the b2b unit.
Can I run the +ve out via a fuse straight to the +ve busbar?

^{_{Subscribers  do not see these advertisements}}

 

[DBK]

Based on my experience wiring up a B2B it needs a bit of thought to get your battery monitor (ammeter) to reflect the B2B charging current.

Essentially the cable linking the starter battery negative to the leisure battery negative needs to connect not directly to the leisure battery negative but to the shunt terminal furtherest from the battery. If that makes sense! Or with your planned setup if the shunt is between the negative busbar and the leisure batteries then connect the linking cable to the busbar. The shunt should then report what the B2B is up to.

 

[Mr Meenah]

Based on my experience wiring up a B2B it needs a bit of thought to get your battery monitor (ammeter) to reflect the B2B charging current.

Essentially the cable linking the starter battery negative to the leisure battery negative needs to connect not directly to the leisure battery negative but to the shunt terminal furtherest from the battery. If that makes sense! Or with your planned setup if the shunt is between the negative busbar and the leisure batteries then connect the linking cable to the busbar. The shunt should then report what the B2B is up to.

Does this apply if I want to wire the ammeter to tell me how many amps I'm using as opposed to the charging status of the B2B?

 

[autorouter]

3.Equal cable lengths from bat to bat as well as to fuse or to busbar ( not taking fuse into consideration?

The most popular way to equalise the voltages, which only works for two batteries (but not three or more) is,
positive wire to battery 1 positive, link wire between the two positives.
negative wire to battery 2 negative, link wire between the two negatives.

The other way, which works for any number of batteries, is
separate positive wires of equal length from each battery positive to the fuse.
separate negative wires of equal length from each battery negative to the shunt (or busbar if no shunt used)

 

[autorouter]

Does this apply if I want to wire the ammeter to tell me how many amps I'm using as opposed to the charging status of the B2B?

Wired this way it will show all amps into or out of the batteries, wherever they come from or go to. Basically, batteries to one side of the shunt, everything else to the other side, including the busbar.

 

[autorouter]

Basically, batteries to one side of the shunt, everything else to the other side, including the busbar.

To be clear, I should have said leisure batteries to one side of the shunt, everything else to the other side - including the busbar, starter battery negative, chassis or whatever else there is.

^{_{Subscribers  do not see these advertisements}}

 

[DBK]

Does this apply if I want to wire the ammeter to tell me how many amps I'm using as opposed to the charging status of the B2B?

If you wire it the way I suggested you should see both. However, mine isn't wired that way and the battery monitor only shows charging from the solar and usage by the various loads. Its a long story how this happened but it all stems from my inability to understand how the B2B works. For example, there is very little current runs in the common negative going to the B2B. The main current flows in the positive wires going to the B2B (but in opposite directions) and in the cable linking the two battery negatives together.

I may get round to sorting it at some point. We are on our first long trip with it at the moment and I'll see how we get on.

 

[Mr Meenah]

For example, there is very little current runs in the common negative going to the B2B. The main current flows in the positive wires going to the B2B (but in opposite directions) and in the cable linking the two battery negatives together.

Thanks for that, I'm even more confused now

 

[DBK]

The lightbulb moment for me was realising polarity has nothing to do with the direction the current is flowing. So current flows out from the positive terminal of the starter battery even if it is coming directly from the alternator. This flows to the B2B which increases the voltage and uses this to charge the leisure batteries, meaning current flows into them through the positive terminal.

So you now have two batteries with current flowing out of one and into the other. The only way the circuit can be complete is by linking the negative terminals together, which is what you do.

The B2B needs a circuit too so its electronics can work which is why it has a common negative. That's all it does.

And can no one please ask me if the current flow is electrons moving in one direction or holes moving the other way? My brain is of limited capacity. It melts when over stressed.

 

[autorouter]

And can no one please ask me if the current flow is electrons moving in one direction or holes moving the other way? My brain is of limited capacity. It melts when over stressed.

In copper, like almost all metals, it's electrons. They carry negative charge and go from negative to positive. In electronic devices, the current is a mixture of negative electrons and positive holes. And in superconductors? You definitely do. not. want. to. know.