Grounding to chasis, is there any need for additional one if leisure battery is linked to starter battery?

[QPiepelr65]

Ok so grounding has been tying me in knots mentally these past couple of weeks.

When I initially installed my basic 12v system with only a single 100ah battery from what I read online grounding to chasis was not essential due to the small loads.

I am speaking here only about for safety in malfunction cases, not the other idea of using chasis ground as the 'return' route of the negative. Although the former may also necessarily imply the latter that is not what I want to do it for but due to 'best practices' that people keep telling me of online.

The only issue I can think of might be the wire sizing but the size I have currently from starter to leisure is 110a rating and the leisure battery is only 105ah. The only questionable bit of wire will be from the starter battery to the chasis ground which looks maybe 16mm2 but might be thinner. Certainly rather worn and rusted. That would only take a load for a couple of seconds in case of a malfunction though wouldn't it? It is really awkward to get to that with other stuff I would have to remove to access it probably so don't fancy changing it if can be avoided. I can see about updating that but for now it is fine no? Any I may want to update that but the main question is whether just using that as ground alone for everything is fine from a theory (and practice) perspective.

Now up until now my leisure battery wasn't linked to the chasis at all and rather 'free floating' as I have seen it termed. No issues but would often get the comments of 'you should really ground to chasis' if it came up.

I have recently bought a dc-dc charger, sterling's bb1260. I was again told I really want to ground to chasis now more than ever due to the rather large amp that will be flowing through the wires.

Apart from a brief test, I have not connected it up properly yet.

Having read much more on the subject and received advice both on and offline I am wondering, if the starter battery will be linked to a negative busbar and all other leisure negatives are linked to that busbar, including the leisure battery, and given that the starter battery is ground to the chasis under the van hood, is there any point it making yet another chasis ground in the habitation space?

The dc-dc connection, as per the sterling instructions which expressly state to make a full wiring connection, and not use ground as negative, will be: starter positive to charger input positive, starter negative to negative busbar. Charger negative to negative busbar and charger positive out to leisure battery out. Also as stated all other habitation negatives to negative busbar.

So, as such, can I just forget about any more grounding to chasis since everything should be grounded to chasis via the starter battery's existing chasis ground right? No point making things more complicated than they are already right and the ford's own ground is going to be the best isn't it? Ok it isn't that clean which may be something to think about but still better to work with what I have already eh rather than reinvent the wheel?

Also another side question. When people discuss using the chasis as a negative return instead of a dedicated negative wire to complete the circuit how is than not a shock risk if current is flowing all through naked metal rather than insulated wire?

 

[drinfinity]

Ford?

Nevertheless, your starter battery -ve will be connected to the chassis. Any other return is best to go to the nearest available earth point.

Don’t connect anything directly to the starter -ve as you are bypassing the shunt that tells the van how much current is flowing through the starter battery.

Yes there might be current flowing through the van chassis, but it’s a very big conductor, so minimal potential difference between any points on it.

 

[QPiepelr65]

Ford?

Yes how did you know?

Nevertheless, your starter battery -ve will be connected to the chassis. Any other return is best to go to the nearest available earth point.

Why is that? I thought since I already have a cable run for negative which will connect starter battery to habitation area for the purposes of the dc-dc charger then why reinvent the wheel and have to do more drilling if the chasis if it is not necessary? It is probably only milliseconds difference anyway in terms of the current flow difference isn't it?

Don’t connect anything directly to the starter -ve as you are bypassing the shunt that tells the van how much current is flowing through the starter battery.

I have had mention of this on other replies on a different forum and I think I don't have that since my ford (transit connect) is from 2007 and they stated that that was only introduced in 2012.

Yes there might be current flowing through the van chassis, but it’s a very big conductor, so minimal potential difference between any points on it.

Can you explain what that means for someone who does not know the jargon?

 

[Salty Spuds]

Yes how did you know?

Why is that? I thought since I already have a cable run for negative which will connect starter battery to habitation area for the purposes of the dc-dc charger then why reinvent the wheel and have to do more drilling if the chasis if it is not necessary? It is probably only milliseconds difference anyway in terms of the current flow difference isn't it?

I have had mention of this on other replies on a different forum and I think I don't have that since my ford (transit connect) is from 2007 and they stated that that was only introduced in 2012.

Can you explain what that means for someone who does not know the jargon?

Well then, Just do what you think is best.

 

[drinfinity]

Can you explain what that means for someone who does not know the jargon?

Imagine trying to squeeze 50A down a long thin wire. It will get very hot, and resist the current going through it. You might have 12V at one end, and 6V in the middle. That’s a potential difference of 6V.

Now imagine the same current going down a massive fat wire the size of a transit van. Hardly any resistance, the van is not going to get hot, and you will have virtually no potential difference between the various points of the van.

I thought since I already have a cable run for negative which will connect starter battery to habitation area for the purposes of the dc-dc charger

Unless your Transit is a boat, this is an unusual approach.

Remember V=IR. Lots of information here

Electrical Circuit Basics | 12 Volt Planet

Electricity is a key part of most vehicle systems and this section explains the basic principles to help you with your auto or marine electrical projects. 12 Volt Planet Knowledge Centre

www.12voltplanet.co.uk

 

[QPiepelr65]

Imagine trying to squeeze 50A down a long thin wire. It will get very hot, and resist the current going through it. You might have 12V at one end, and 6V in the middle. That’s a potential difference of 6V.

Ok but if the wire is rated higher than the maximum amps the battery can put out then what is the problem? The wire is 110a and the battery is 105ah.

Unless your Transit is a boat, this is an unusual approach.

Unusual yes, but that doesn't mean wrong does it?

 

[Alster]

It’s not wrong-just pointless!

 

[Skyliner33]

Ok but if the wire is rated higher than the maximum amps the battery can put out then what is the problem? The wire is 110a and the battery is 105ah.

Unusual yes, but that doesn't mean wrong does it?

110A and 105Ah are two totally different things/ units.

 

[drinfinity]

The wire is 110a and the battery is 105ah.

105Ah is the total charge the battery holds. It doesn’t mean that’s the maximum current it can supply.

The size of wire you need is based on the current your load is going to draw, and how long the circuit is. Your circuit is twice as long as it needs to be.

Please read the 12Vplanet knowledge base articles, they are very useful, and help you to avoid mistakes that might set your van on fire.

 

[Alster]

@Skyliner33 and @drinfinity good point- I must read things more carefully!

 

[Sim60]

Ok but if the wire is rated higher than the maximum amps the battery can put out then what is the problem? The wire is 110a and the battery is 105ah.

Unusual yes, but that doesn't mean wrong does it?

You are confusing Amps( current) with Amphours( battery capacity) - these are 2 entirely different things. The current that your battery can supply is only limited by its internal resistance and can supply way more than 100A which is why you must put a fuse immediately next to the battery to avoid melting your wiring in the event of a short.

 

[CJW]

In the case of the T6, we ground to chassis so we don’t bypass the shunt attached to the starter battery negative. The shunt is necessary for smart alternator function (amongst other things). The chassis is a very low resistance pathway.

Don’t know about Ford Transits - you may have a more fruitful response on Ford Transit Forum?

 

[Salty Spuds]

Imagine trying to squeeze 50A down a long thin wire. It will get very hot, and resist the current going through it. You might have 12V at one end, and 6V in the middle. That’s a potential difference of 6V.

I didn't say that, you're getting even more confused.

 

[Stay Frosty]

Ok but if the wire is rated higher than the maximum amps the battery can put out then what is the problem? The wire is 110a and the battery is 105ah.

Unusual yes, but that doesn't mean wrong does it?

Potentially if the battery was dead short through that wire and the main fuse was a 300A maxi then that crusty starter battery earth lead you mentioned earlier will probably let go, bear in mind fuses will blow at some point past their indicated amperage rating.
Not familiar with the Sterling unit you've got but there's a lot to be said for KISS and treating the leisure battery side separately from the starter charging side after the B2B has provided an input for the leisure battery.

 

[QPiepelr65]

110A and 105Ah are two totally different things/ units.

Ok it was not my words but something another respected member on another forum stated to me. Maybe they were wrong or I misunderstood but they told me my specific battery cannot discharge more than 100a. Here is the battery: Lithium Leisure Battery - Fogstar Drift 12v 105Ah

There is also a tech sheet on that page with more data. Could you tell me what the maximum discharge rate could be at once, if indeed that person that stated 100a is wrong?

I see here on the site it says: Max Cont. Discharge 100A

So is it just that it is a coincidence that it is 105ah and it has no relation to the discharge rate but it just so happens to be 100a?

 

[QPiepelr65]

In the case of the T6, we ground to chassis so we don’t bypass the shunt attached to the starter battery negative. The shunt is necessary for smart alternator function (amongst other things). The chassis is a very low resistance pathway.

Don’t know about Ford Transits - you may have a more fruitful response on Ford Transit Forum?

Ok but this forum also deals with other vans so I was just asking here due to that and more active than the ford transit forum, at least for van building related stuff.

I don't think mine has a shunt since it is from 2007 and don't see anything by the ground chasis terminal, which is where it would be isn't it?

 

[QPiepelr65]

Potentially if the battery was dead short through that wire and the main fuse was a 300A maxi then that crusty starter battery earth lead you mentioned earlier will probably let go, bear in mind fuses will blow at some point past their indicated amperage rating.
Not familiar with the Sterling unit you've got but there's a lot to be said for KISS and treating the leisure battery side separately from the starter charging side after the B2B has provided an input for the leisure battery.

Could you explain it again please as that first paragraph was hard to understand so I was unable to get what you meant clearly due to the grammatical structure. Why would I be using a 300a maxi fuse on 110a wire? Lol. Not sure where that came into it. I fuse for the wire size, I have 100a fuse, as recommended by the sterling manual for 110a wire, also recommended by the manual. Now the chasis ground cable I am unable to speak on that and so there is merit in considering that.

Well the manual specifically states you should NOT ground directly to chasis and they advise a common negative linking all 3, the 2 batteries and the charger. As such this is the 'simple' method for this device. You can find the manual on 12 volt planet: Sterling BB1260 'Pro Batt Ultra' Battery-To-Battery Charger - 12V/12V 60A

So, as such, if the device itself is saying a direct link to the battery is mandatory I am asking why not use that for all grounding now, since I haven't made one in habitation space.

I am just asking for the logical reasons why I should favor drilling another hole and running more wire if this was is going to be in use anyway with the charger link up. You say KISS well this seems to be more KISS because there is perfectly good wire running to a ground point on the chasis already.

Maybe one has been intimated above that it would be better to have one I made myself in hab space simply because I can control that in terms of wire size. For the starter battery I can't be sure what type of cable it is to know what its tolerance it is. So probably easier to just ground to chasis on a short run in hab space with wire I know is good!

So, indeed I may have teased out a good reason to do it.

Anyway I got my busbars installed yesterday. Soooo much better and cleaner now that trying to cram everything on the battery posts! So I should just sand down a point near the battery and drill a hole with a battery thickness wire and attach it to busbar?

 

[drinfinity]

So I should just sand down a point near the battery and drill a hole

On a VW there are multiple earth points all over the van, no need to build your own.

I see Sterling’s manual thinks that chassis earth points are poor conductors. This is not true.

On an unrelated note, someone at Stirling needs to Select All, Font Arial, colour black. The manual looks like it has been written by an enthusiastic 8 year old trying out every button in MS Publisher 91.

 

[Stay Frosty]

Could you explain it again please as that first paragraph was hard to understand so I was unable to get what you meant clearly due to the grammatical structure. Why would I be using a 300a maxi fuse on 110a wire? Lol. Not sure where that came into it. I fuse for the wire size, I have 100a fuse, as recommended by the sterling manual for 110a wire, also recommended by the manual. Now the chasis ground cable I am unable to speak on that and so there is merit in considering that.

Well the manual specifically states you should NOT ground directly to chasis and they advise a common negative linking all 3, the 2 batteries and the charger. As such this is the 'simple' method for this device. You can find the manual on 12 volt planet: Sterling BB1260 'Pro Batt Ultra' Battery-To-Battery Charger - 12V/12V 60A

So, as such, if the device itself is saying a direct link to the battery is mandatory I am asking why not use that for all grounding now, since I haven't made one in habitation space.

I am just asking for the logical reasons why I should favor drilling another hole and running more wire if this was is going to be in use anyway with the charger link up. You say KISS well this seems to be more KISS because there is perfectly good wire running to a ground point on the chasis already.

Maybe one has been intimated above that it would be better to have one I made myself in hab space simply because I can control that in terms of wire size. For the starter battery I can't be sure what type of cable it is to know what its tolerance it is. So probably easier to just ground to chasis on a short run in hab space with wire I know is good!

So, indeed I may have teased out a good reason to do it.

Anyway I got my busbars installed yesterday. Soooo much better and cleaner now that trying to cram everything on the battery posts! So I should just sand down a point near the battery and drill a hole with a battery thickness wire and attach it to busbar?

Not being funny but if you release relevant information retrospectively then it's quite difficult to offer an alternative choice to what was posted.
The point I was trying to make was that both your leisure battery and starter battery were relying on a crusty battery ground lead Ford installed 17 yrs ago.
Regarding the 300A Maxi fuse that's what I've got on my leisure battery output incase I go to a 3kw inverter.

 

[CJW]

I wonder if the Sterling install sheet is referring to avoiding the kind of ‘self-tapper chassis earthing bodge’ approach rather than the sanctioned and provided earth points that are shown in the T6 manual under heading ‘earthing concept’?

As @mmi showed in a thread somewhere, the T6 chassis (cannot speak for the Transit) has less than one milliohm resistance.