12v circuit refit - ideas/refinements?

[GHA]

Slowly digging out spare bits & getting (hopefully small) shopping list for a rewire of the 12v circuits onboard - what have I missed??

So overview, boat normally lives away from mains power, honda genny can run the 20a pro charge ultra mains charger if need be. 300W solar is enough to get trojans back to 100% more days than not (no float in regulator, batts take less than 2A @ 14.8v) . 12v battery doesn't exist yet.

So thinking is -

• BIG fat cables to +ve/-ve bus bar close to batteries & BIG fat cables to engine.
• Solar can charge either/both battery and bus bar can come form either/both batteries. So that batts can be either get a definite 100% charge with no loads coming off it, equalized or given some sort of capacity test without having to shut down the boat.
• 2nd 12v battery can be trickle charged with dc buck/boost converter, hopefully this one will almost never be used anyway, lived without it for a good few years already.
• Extensive monitoring already in place so alarms for any high/low voltage easy to implement.

1st stab at it, very much an overview but I think the main bases are covered. Bilge pumps might as well come of the bus bars. Would be great to get a Firefly battery for 12V so if it's cloudy for weeks it won't get so trashed by not getting back to 100% every time, but can't find a dealer in Europe & they are pricy..

Thinking of getting some stainless flat & drill / tapping M8's to make bus bars.

Please don't start banging on about how awful 1/2/both are, there are 2 on the boat looking a job so might as well get used....

 

[Daverw]

Would not use stainless for bus bar, higher resistance than brass or copper, if you want to keep the 1/2 switches you could use them as isolators and still fit VSR

 

[GHA]

Would not use stainless for bus bar, higher resistance than brass or copper, if you want to keep the 1/2 switches you could use them as isolators and still fit VSR

Can't see the need of a VSR tbh, I can do all that and the engine rarely gets used for charging anyway.
Edit - thinking a bit further over some sandpaper just now - wiring in a FET transistor to the existing monitoring board would make it easy to automate the DC buck/boost to the 12v battery, just have it turn on for an hour or so if the voltage gets below 12.7v or whatever.

Is the resistance on a short lump of, say, 300 x 50 x 8 stainless flat bar really an issue?

 

[lw395]

As drawn, your two battery banks will be connected together nearly all the time by the 1both2 switch on the solar?
I would prefer to see the engine battery isolated from the house battery whenever the engine is not running.
I would probably run the windlass direct to the house battery via a single breaker or megafuse. Probably bypassing the shunt.
Stainless is rubbish for bus bars. In any case I would try to take the starter cable direct from your isolator/1b2 switch not via an unnecessary 2 busbar connections. Same on the -ve. Take the starter -ve straight to the battery.

 

[GHA]

As drawn, your two battery banks will be connected together nearly all the time by the 1both2 switch on the solar?

No. nearly all the time the main bank will be connected to both solar & bus bar, 2nd bank not connected to anything, just receiving a little boost charge now and again. Trojans have been running the boat on their own fine for a few years now, solar getting them back to full charge most days.
It's not really an engine battery, it's there for emergencies & to allow for 2 separate sources so each bank/battery can get a really good charge/equalized/load tested. And if it is a cloudy month then the trojans can still get to full charge now and again even if the second battery doesn't, a firefly would be great for that, they're getting rave reviews from people who really know in the US, no sign in Europe yet though & pricey.

I would prefer to see the engine battery isolated from the house battery whenever the engine is not running.

Agan, not really an engine battery. almost always it won't be connected to anything.

I would probably run the windlass direct to the house battery via a single breaker or megafuse. Probably bypassing the shunt.
Stainless is rubbish for bus bars. In any case I would try to take the starter cable direct from your isolator/1b2 switch not via an unnecessary 2 busbar connections. Same on the -ve. Take the starter -ve straight to the battery.

That's 3 big fat cables on 1 terminal, getting a bit busy but agree, keep the path as simple as poss. Both engine & windlass need to able to be connected to 2nd battery.

 

[lw395]

The main claimed advantage of a firefly battery is longer life in terms of cycles. So it might be a good choice for a house battery. But they are expensive AIUI, although low cost per cycle is claimed.

If you want to start the engine off the house battery or run the pick winch off the engine battery, setting either 1b2 switch to both will enable that.

You seem to be starting from a wish list of switching things around for the sake of it.

Personally my wish list would be:
starter battery is reserved for engine start only
high load currents such as starting or abusing the windlass don't drop out the GPS or other nav, PC if applicable
charging all banks should be automatic, at least from the main sources, ie engine and solar.
The engine battery should float at a proper float voltage, when the house battery requires bulk charging
it should be possible to isolate all batteries
separate connection for low current 'permanent' live, e.g for radio memory, enough light to find the breakers etc.
High load currents go through minimum components and connections.

If more complication was considered worthwhile, I might consider an emergency battery to keep the GPS and VHF powered (and perhaps a light over the chart table) when everything else is submerged or has popped the breakers.

Basically design driven by the functionality required.


When it comes to the physical layout of buss bars and so forth, that would be inevitably a compromise around the physical location of things.

 

[PaulRainbow]

Slowly digging out spare bits & getting (hopefully small) shopping list for a rewire of the 12v circuits onboard - what have I missed??

I'd like to tell you to bin the 1-2-both switches, but i know you won't

There is no need for a breaker between the solar controller and the panels. This should be next to the main bank, protecting the controller and the wiring going to it.

Remove the 1-2-both switch in the solar circuit, along with the buck/boost and all of the associated wiring. So the solar panels go straight to the controller, then to the main battery via a fuse.

Connect the 2nd battery to the engine, using the now redundant 1-2-both switch. Connect the engine to the common terminal, the 2nd battery to (1) and connect a cable from terminal (2) to the load terminal of the other 1-2-both switch. With both switches set to (1) they are isolated circuits. If the engine battery is flat, turn the switch to (2) to start from the main bank, or turn to Both to start from both. If the domestic bank failed you can turn its isolator Off and turn the engine switch to Both for emergency domestic use. Re-label it.

Connect the Sterling charger to both banks.

Move the windlass to the main bank battery, via its breaker.

Move the breaker from between the +ve busbar and the domestics next to the battery, thereby protecting the wiring, the switch and the busbar.

The 1-2-both switch near the main bank now becomes an on/off switch. Re-label it.

Split charging, add a VSR or zero loss splitter to allow the alternator to charge both banks. Make it a dual sensing VSR and the solar panels will also keep the 2nd battery charged.

Think that covers it Knock a sketch up and see what you think.

Edit. Busbars, no need for M8. The one you show in your diagram only needs to be a negative stud, this can simply be an M8 bolt. Where you have the +ve busbar i would include a -ve one too, but not M8. There are plenty of ready made ones available with screw connections, ring terminal connections or spade terminal connections. If light enough loads are involve a group of Wagos could be used.

 

[GHA]

I'd like to tell you to bin the 1-2-both switches, but i know you won't

Well, thanks for spending some time to reply . Doesn't work though..

There is no need for a breaker between the solar controller and the panels. This should be next to the main bank, protecting the controller and the wiring going to it.

Yup.

Remove the 1-2-both switch in the solar circuit, along with the buck/boost and all of the associated wiring. So the solar panels go straight to the controller, then to the main battery via a fuse.

So now how do you give bank B the sole attention of solar to get a full charge or equalize?

Connect the 2nd battery to the engine, using the now redundant 1-2-both switch. Connect the engine to the common terminal, the 2nd battery to (1) and connect a cable from terminal (2) to the load terminal of the other 1-2-both switch. With both switches set to (1) they are isolated circuits. If the engine battery is flat, turn the switch to (2) to start from the main bank, or turn to Both to start from both. If the domestic bank failed you can turn its isolator Off and turn the engine switch to Both for emergency domestic use. Re-label it.

That would work if you could route to solar to either/both banks, which you can with the original circuit. Almost identical to the original except engine goes to common of left 1/2/b switch , solar to the right 1/2/b and both "1's" commoned as well.

Connect the Sterling charger to both banks.

Yup, each line switched so you can do an equalize cycle on either bank in isolation..

Move the windlass to the main bank battery, via its breaker.

In the middle of a long load test or equalize of bank A and something happens which means getting the hook up - can't do it on bank B so you wreck your load test. Or main bank finally dies, now you can't lift the hook for months til you find a country that sells good batteries. Or something happens like that.

Move the breaker from between the +ve busbar and the domestics next to the battery, thereby protecting the wiring, the switch and the busbar.

:encouragement:

Split charging, add a VSR or zero loss splitter to allow the alternator to charge both banks. Make it a dual sensing VSR and the solar panels will also keep the 2nd battery charged.

Really can't see the point of a VSR for a few amp hours a year. The engine never gets used just for charging , might not get started for weeks at a time. So maybe a handful of long motor passages a year, seems a lot of money and more complexity for near zero return. The trojans get charged at 14.9v, not all batteries are able to cope with that every day. Plan is to treat 2nd battery with utmost politeness to try and get as many years as poss out of them Well, both banks really - sort of the point of all this is to allow isolation from everything to do any maintenance on either bank.

Think that covers it Knock a sketch up and see what you think.
Edit. Busbars, no need for M8. The one you show in your diagram only needs to be a negative stud, this can simply be an M8 bolt. Where you have the +ve busbar i would include a -ve one too, but not M8. There are plenty of ready made ones available with screw connections, ring terminal connections or spade terminal connections. If light enough loads are involve a group of Wagos could be used.

Yeah, but not shown, there's a few other bits piggy backed onto the shunt stud at the moment that could really do to be tidied up.

 

[<152587>]

There is no need for a breaker between the solar controller and the panels. This should be next to the main bank, protecting the controller and the wiring going to it.







.

DANGER
Beware open circuit voltage generated by panels which can be circa 130v. Current instructions for fitting MPPT control specify breakers between PV panel and control.

 

[lw395]

DANGER
Beware open circuit voltage generated by panels which can be circa 130v. Current instructions for fitting MPPT control specify breakers between PV panel and control.

That rather depends on the panel configuration.
If it was 130V, an over current breaker is not going to help if you touch it.
Most boat systems have panel configs which won't go above 50V open circuit in the brightest sunshine.

 

[GHA]

DANGER
Beware open circuit voltage generated by panels which can be circa 130v. Current instructions for fitting MPPT control specify breakers between PV panel and control.

40v.
Might put on in anyway, handy sometimes to reset to bulk if the reg has gone into float earlier than you'd like.

 

[GHA]

You seem to be starting from a wish list of switching things around for the sake of it.

Not at all, as per first post - constantly on the hook doing any kind of battery maintenance can be a nightmare, turn everything off, watch the fridge defrost while you do a load test or try to get 100% fully charged. Having the ability to run the boat from 2 descrite sources and route solar/charger to either bank will be a great leap forward.

 

[lw395]

If you want a system to experiment with, as distinct from a good system to actually use, I'd suggest basically:
1) separate engine battery that is sacrosanct.
2) make the house bank 2 small banks normally paralleled with your 1b2 switches. You could use one for loads and the other for charging?

 

[PaulRainbow]

Also, if the solar controller has auto battery voltage selection, make sure that you can never break the circuit between the controller and the batteries, or the controller can sense the panel voltage, think it's a 24v system and boil the batteries (depending upon various factors of course).

 

[PaulRainbow]

DANGER
Beware open circuit voltage generated by panels which can be circa 130v. Current instructions for fitting MPPT control specify breakers between PV panel and control.

Could i have a link to those instructions please ?

 

[GHA]

If you want a system to experiment with, as distinct from a good system to actually use, I'd suggest basically:
1) separate engine battery that is sacrosanct.
2) make the house bank 2 small banks normally paralleled with your 1b2 switches. You could use one for loads and the other for charging?

Ta, I want good system to actually be of use on a off the grid cruising boat, not a weekend boat. Very different things.

What you suggest is actually done by the original circuit. Except as stated the 2nd battery will almost never be touched, but can be used to isolate the main bank so maintenance can be done on it if necessary.

Bearing in mind voltages are constantly logged into a database once a minute and will be for the soon to be added 2nd battery, very useful for spotting trends, main bank hardly ever goes under 12.5v under load.

 

[GHA]

Getting there now, no doubt more tweaks.
So easy to operate, left switch controls where the boat gets its power from, 1-main bank, 2-emergency bank or both. Right switch controls where the solar goes, same.

Both charger feeds switched as well so at anchor the boat can be run from one bank with solar while the charger/genny does an equalizing cycle on the other. Might have missed something basic though,,,,, where you lot come in
(Edit, just spotted one, feed to windlass is after the domestic breaker, which would be better above the bus bar anyway probably..)

Which leaves trickle charging the emergency battery now and again, need to test a buck/boost voltage/current limited device, can't see why it wouldn't be fine though.

And commoning the big fat leads vaguely tidy, piled up on the same stud just always looks a mess.

 

[lpdsn]

You appear to have three breakers between the battery and the windlass. Not to mention that the domestic breaker is going to have to be sized to take the windlass load, so is unlikely to be sized correctly for your domestic circuits.

I've got a completely different circuit and isolator switch for the windlass but then I wouldn't use a 1-2-Both switch so we've diverged already.

 

[GHA]

You appear to have three breakers between the battery and the windlass. Not to mention that the domestic breaker is going to have to be sized to take the windlass load, so is unlikely to be sized correctly for your domestic circuits..

Already spotted, edit above.

 

[lw395]

Running the windlass through 3 circuit breakers and a 1b2 switch is not elegant.
Are you intending to size those battery breakers for the starter motor?