Boat Battery system ovehaul - thoughts please

I wouldn't start engines from the house bank routinely (as one poster suggested). If you have one bank for both house and starting and accidentally flatten it ... you are screwed.

You need at least one battery bank that does nothing but start the main engine(s).

Then the house bank is emergency back up for the starter bank(s).

 

Im with you on that Iron Price

I am in the process of doing the work (its taking ages as I'm only getting the odd hour here and there and its a nightmare not having a vertical bulkhead - everything is mounted on the underside of the deck!) 70mm2 cable is a pig to crimp! and i'm using a combo of 70mm2 for engine, 35mm2 for house / windlass (was already there) and 25mm2 for charging. I have pulled meters of cable out!

I am keeping the cranks as cranks and the house is now 6 batteries configured as 2 parallel banks of 3 - connected via a 1-2- both switch. The intention is to keep it on both, but I can isolate if one bank has an issue.

I'm now just trying to work out the 24hr circuits - I either take them from either crank or take them from the switched side of the house switch - but then the 24hr circuits can be switched off if needs be. I dont want to run them off one bank of 3 as then I could deplete the one side and cause a mismatch as the wire lengths wont be exact like they currently are to the switch (so as to balance current / voltage under load) although the 24h circuits wont draw much I guess (4 bilge pumps should draw nothing - and a stereo feed with will be a couple of hundred mA I guess so probably wont cause an issue.

I'm also still mulling over the 1 or 2 vsr's and how to stop them from joining the charging outputs (3 output charger) when on the mains. I have the issue that if i start the engines when on shore power - the battery charger will end up with all 3 outputs being linked - which i'm guessing may make it go boom. - the other option is just use the first output at 60amps connected to the house and let the crank batteries charge that way - main issue is with that is that the cranks may get depleted into the house if the VSR opens while charging. (blue sea have some nice diagrams as do others - however no-one ever includes a shore charger with the diagrams.. I now know why! ll the searching I have done has not come up with a specific answer...

Steve

 

After some more research - yes the VSR's do screw with the chargers which is why they are never shown..

blue sea show some options here Solving ACR/Multi-Program Multi-Output Charger Interference - Blue Sea Systems https://www.bluesea.com/resources/504 - I prefer Automatic as I forget to much stuff - so i'm planning on a DPDT cradle relay and a 12v plug pack to switch both negatives on the VSR's using the NC terminals on the relay this way when there is mains... there is no VSR and vice versa - the only issue will come if the plugpack fails.

I was pondering over a switch mode PSU (15w) in a small plastic box and splitting an IEC lead in and out so i could have the box inline with the chargers cable - but again still an issue if the smps fails (not to mention its a non certified device - kinda) - something to ponder over though!

Steve

 

OK after some debate with myself - I have now built a small jiffy box with a 15w PSU (240>12v) and a cradle mount Relay DPDT. This has been added to the charger power lead (IEC type) so the 240v runs though - and the PSU provides switching voltage. The reason for the PSU rather than a 240V relay (apart from quick local availability) is that I am using 3 LED's -
Green for PSU Ok / Mains on - connected to the PSU DC out directly
Red for Relay Failed - this will be connected to one of the normally closed poles - if there is mains power - this should never light - if there is mains power and the relay doesnt switch - it will light indicating an issue.
Green for ACR's off - - Connected to the NO pole on the same side as the red one - So when relay operates - this lights to show the ACRs / VSRs are disabled.

The other Pole will have the VSR negative running through the NC so mains will open the -ve circuit and disable the VSRs.

I'll post some pics when I get chance

Steve

 

And to keep things up to date.. the as built layout - it may help someone in the future

 

HI Guys

Weird one here.. and probably something I wouldnt have noticed if I had not redone my wiring / battery charging etc. circuits.

As part of the install I have two ACR/VSR’s one from each crank to the house bank, I also have had to make a mains sensing relay box that turns off the ACR/VSR’s when shore charging so the 3 banks of the charger dont get paralleled up and go bank. This box uses a relay to break the ACR/VSR negative and prevents it from operating. Works great too.. except…. and this is where is gets weird.

The ACR/VSR have digital displays and show status / voltage. When the crank battery switches are off and the house bank is on – the starboard crank to house ACR/VSR’s display comes on even when the negative is removed. Having done some investigation it appears that there is some continuity from the engine main +ve cable to negative – enough to allow the ACR/VSR to power itself up when a positive feed is fed from the house – the engine cable provides the negative – albeit faintly.. but enough to shove about 7v through the system.

If I switch the engine battery switch to on – all behaves normally – ACR/VSR goes off when the negative is removed – switch the battery off and the ACR/VSR comes back on.

So has anyone got any ideas where the feed to -ve could be coming from or do I have to start stripping wires off here and there until I find it – to make it worse the STB engine starter is almost impossible to get to so removing cables is done by feel and cursing!

Any ideas where to look would be greatly appreciated – or other testing I could do?

Steve

 

As your boat is 40ft I'm going to assume it's in the water 24/7. Therefore it should be wired so that it's impossible to turn off your 4 bilge pumps. I would connect two of them to each house bank to balance the load. A convenient point would be the non-switched terminals on your 1-2-both switch as you identify - connect two pumps to each terminal. The pumps will run no matter what you select on the switch. Use fuses and if you ever need to stop a pump you can pull the fuse.

The stereo memory current is inconsequential from a load balancing perspective, just wire that circuit (again fused) to one of the same non-switched terminals.