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2x12v dc circuits use common return busbar?


reg

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Is there any problem with this idea which would make my wiring addition much easier. Could I use the existing return bus bar from my 6 gang panel for my newly added additional 3 gang panel? 

Set up

2 banks of domestic batteries 4x105 and reserve Bank of 3x110ah

Alternator charging via 1, 2 both rotary switch of which only 1 or 2 will be used I. E will not be charging both banks together as of mixed types. Important point here is that no services or loads will be taken from this switch. I'm happy with this part

Bank 1 has own battery switch which serves 6 gang panel and inverter. I'm happy with this part

Question now arises 

My new 2nd bank will service a completely separate 3 gang panel I  can physically run the live Red wire to this panel with no problem. Ideally I would then install a separate return bus bar for this panel and connect that to the second bank through its own wire however, and this is where the problem lies

In order to return the negative wire, due to exiting through Hull fitting being full, I would need to create a new through Hull Hole just to run this wire. In order to achieve that it would take a lot of work involving both unwiring and rewiring  240v and 12v circuits within existing cabinet. 

My question is can I use the existing return bus bar for both panels even though they have separate live feed wires? 

I can't think of a reason not to as both battery banks have a common ground but slightly afraid I may of missed something obvious. 

Thanks

 

Edited by reg
Add word physicaly
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6 minutes ago, Jess-- said:

as long as the wiring is strong enough to handle the current returning from both systems you shouldn't have a problem.

Should be as I oversized the spec when I built it and also since then I have replaced all of lighting with led so happy existing return wire will have capacity for both panels. 

Was looking at quite a big job until the thought came to me that this might be possible I was just slightly afraid that I had missed something as  it seemed to simple to be true:)

Edited by reg
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I think you would struggle to truly seperate the negatives any way since they would each need to connect to an alternator on the engine eventually and doing that would bond them there regardless of what you had done elsewhere

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No problem as Sam/Jess say but this sounds quite complex for charging. You dont say what you are going to take from each bank or if you have any solar but if say you take 70 Ahr out of one bank  and 30Ahr out of the other overnight, how are you going to put the charge back in? The final 10-20 Ahrs needed to fully charge the first set is going to take hours of alternator running during which time your other bank is sitting there discharged. Towards the end, the first bank will be taking 8A charge (2% tail current) whereas if you charge both togther you will get 14A in. Far more efficient. You say you have differnt types. What types are they?

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2 minutes ago, Jess-- said:

I think you would struggle to truly seperate the negatives any way since they would each need to connect to an alternator on the engine eventually and doing that would bond them there regardless of what you had done elsewhere

That was my thinking but I had some nagging doubts as it isn't a standard 2 domestic bank setup

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39 minutes ago, Dr Bob said:

No problem as Sam/Jess say but this sounds quite complex for charging. You dont say what you are going to take from each bank or if you have any solar but if say you take 70 Ahr out of one bank  and 30Ahr out of the other overnight, how are you going to put the charge back in? The final 10-20 Ahrs needed to fully charge the first set is going to take hours of alternator running during which time your other bank is sitting there discharged. Towards the end, the first bank will be taking 8A charge (2% tail current) whereas if you charge both togther you will get 14A in. Far more efficient. You say you have differnt types. What types are they?

Was hoping not to get into this:)

Started out with a simple idea the grew into a less simple idea. 

Old 5 year old lead acid Bank of batteries just prematurely replaced with 4 x Numax calcium 105s. However once the old batteries were taken out I decided that they still had maybe 2 or 3 years light use in them so I wired them up as a seperate bank and dedicated 2 solar panels (240w total) to charging them up. They seem to of took and held the charge well so I thought why not retain them as a separate bank and have a separate  reserve circuit powered by solar only. ok so far but then having done that I thought I may as well have a 1 2 both bank switch so that I have the ability to either  charge bank 1 or bank 2 but not both via the alternator but I critically did not want the 2nd bank (older wet lead batteries) to be charged via the victron multiplus as this is now set to charge the sealed Numax batteries. 

Eventually when the older second batteries wear out then I will make a compatible bank up and then I can easily  rewire to a more conventional 1 2 both setup. Charging parameters are set up for the sealed batteries my hope is that the solar panels will take up the shortfall when charging the 2nd Bank and will look after their equalisation. If it doesn't then not a lot lost as 2nd bank is just a reserve, priority is to look after the new sealed batteries anything else will be a bonus and as I said earlier it will be easy to convert to a more conventional setup at a later date. 

Eta forgot to mention that 1st Bank also has 350w solar power dedicated to it so each bank has independent solar power (which is the basic inefficiency in the system but one a I can live with for the benefits gained) 

Edited by reg
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15 minutes ago, Nickhlx said:

If you are using the switch for charging, is there not a risk of momentarily opening-circuiting the alternator, unless you are only going to operate the switch when the engine is off ?

Nick

That's taken care switch is below running board and is only really accessible when engine off also has make before break design(if that's the correct term) I will also have to make some clear labels as the services master switch is stand alone from the 1 2 both switch. 

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27 minutes ago, reg said:

Was hoping not to get into this:)

Started out with a simple idea the grew into a less simple idea. 

Old 5 year old lead acid Bank of batteries just prematurely replaced with 4 x Numax calcium 105s. However once the old batteries were taken out I decided that they still had maybe 2 or 3 years light use in them so I wired them up as a seperate bank and dedicated 2 solar panels (240w total) to charging them up. They seem to of took and held the charge well so I thought why not retain them as a separate bank and have a separate  reserve circuit powered by solar only. ok so far but then having done that I thought I may as well have a 1 2 both bank switch so that I have the ability to either  charge bank 1 or bank 2 but not both via the alternator but I critically did not want the 2nd bank (older wet lead batteries) to be charged via the victron multiplus as this is now set to charge the sealed Numax batteries. 

Eventually when the older second batteries wear out then I will make a compatible bank up and then I can easily  rewire to a more conventional 1 2 both setup. Charging parameters are set up for the sealed batteries my hope is that the solar panels will take up the shortfall when charging the 2nd Bank and will look after their equalisation. If it doesn't then not a lot lost as 2nd bank is just a reserve, priority is to look after the new sealed batteries anything else will be a bonus and as I said earlier it will be easy to convert to a more conventional setup at a later date. 

Eta forgot to mention that 1st Bank also has 350w solar power dedicated to it so each bank has independent solar power (which is the basic inefficiency in the system but one a I can live with for the benefits gained) 

Reg, I guessed you would have solar charging the reserve bank :) and that answers the question totally. Fully understand what you are doing. Do you think we can put the lid back on the can of worms that I have opened?

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19 minutes ago, Dr Bob said:

Reg, I guessed you would have solar charging the reserve bank :) and that answers the question totally. Fully understand what you are doing. Do you think we can put the lid back on the can of worms that I have opened?

Not really a can if worms I'm actually quite happy with the way it has turned out. If I had sat down to design it I wouldn't of come up with this arrangement but what I will have is a totally separate 2nd circuit running 3 extra leds down starboard side, power to small car type 12v TV and power to rear led spotlight. In summer I can run either circuit and in winter I can rest the main bank for a few days and primarily  use the 2nd bank. Sort of design by accident. 

2nd bank will in reality only have light loads but gives me a backup system for winter time

Edited by reg
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2 hours ago, reg said:

Not really a can if worms I'm actually quite happy with the way it has turned out. If I had sat down to design it I wouldn't of come up with this arrangement but what I will have is a totally separate 2nd circuit running 3 extra leds down starboard side, power to small car type 12v TV and power to rear led spotlight. In summer I can run either circuit and in winter I can rest the main bank for a few days and primarily  use the 2nd bank. Sort of design by accident. 

2nd bank will in reality only have light loads but gives me a backup system for winter time

:)

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