Comments on my 12v wiring upgrade?

[SpaceRnglr]

Hello hive mind. After lots of research I am about to pull the trigger on a complete overhaul of my high current 12v system. The existing system is a mess so needs to go.

It is intended to be a simple system based on 3x 180 AH AGM batteries, but they are on their last leg so will be replaced in the not too distant future. The design allows for future use of LiFePO4 batteries by replacing the ACR with a Sterling B2B charger and adding isolation relays on the charge / load buses (to be controlled by BMS). Hopefully I get to the battery upgrade in the next 6-9 months. Most, if not all, of the existing wiring will be replaced.

The boat is being prepped for cruising focusing on simple systems run almost all on 12v. I will install an inverter, but haven't decided the size yet. I won't have microwaves, induction cookers, aircon, or any other large AC power loads. She lives on a swing mooring and hence no AC battery charger, although there is space to add one in future.

I have attached diagrams for the AGM and LiFePO4 systems with the only difference being the battery, AC, and relays. Let me know if I overlooked anything or there are improvements to be made.

[smac999]

you will likly find it hard to connect 2/0 to you DC panel, and then find a breaker big enough to feed the windlass from the panel. more likly it should come off the load bus bar with own fuse. not the dc panel

[zboss]

The internally regulated alternator will burn up pretty quickly driving lithium batts and it may not match the charge voltages needed by the lithiums.

Add a much higher output alt, get an external regulator, and attenuate the field.

[Discovery 15797]

Great schematics. Well laid out. I recently rewired my whole vessel to remove all the old and corroded copper wire and replace with Ancor tinned wire throughout.

Did you calculate/estimate your max load(s)? Depending on your overall run, 2/0 AWG may be oversize for your vessel. For example, when I changed from incandescent to all LED my overall light load changed dramatically.

The biggest current draw is the windlass, but I only run the windlass when the engine is running so I am not really concerned with voltage drop.

Agree with SMAC999 in that 2/0 AWG to your main DC distribution is too big, and windlass should feed from load bus. Also 10AWG is likely too small for your secondary DC distribution.

I ran a 1/0 AWG backbone from the house bank to a terminal block in the fwd cabin (total run of about 60 ft. round trip). From the fwd TB is a short run to the windlass, and another to the watermaker. The 1/0 AWG is rated for >10% voltage drop for windlass at max draw and larger than recommended wire size in the Lofrans manual, and 3% voltage drop for watermaker. (Both would never run at same time.)

About 10ft away from the house bank is another TB that branches in the nav station to the 2 DC distribution panels. Both are fed by 4 AWG from the main TB. My main DC panel is electronics and safety (CO detector, LP detector, Fireboy, etc.) and secondary panel is all lights (all led), fans, other accessories. These wire sizes satisfy 3% voltage drop for all systems off the DC panels with everything on.

Matching your wire sizes to your projected loads could save you a few hundred dollars especially if you are going to completely rewire your boat.

Of course, the danger is to under-estimate and undersize the wires and risk overheating and possibly an electrical fire.

[SpaceRnglr]

Originally Posted by zboss

The internally regulated alternator will burn up pretty quickly driving lithium batts...

That’s why I’m keeping the alternator on the start battery and using a 60 amp battery to batter charger to charge the LiFePO4s. That will limit the current to within acceptable (I think) limits for my 120amp alternator.

I just had another post on this topic as it is the area I found the hardest to get feedback on in the LFP conversation. I think I will go the way shown on the diagram as it is easier. I know the alternate is to externally regulate the alternator and run it to the main charge bus. I may change my mind but either way I don’t have to decide until I actually install LFP...

[Stu Jackson]

Originally Posted by SpaceRnglr

That’s why I’m keeping the alternator on the start battery and using a 60 amp battery to batter charger to charge the LiFePO4s. That will limit the current to within acceptable (I think) limits for my 120amp alternator.

I just had another post on this topic as it is the area I found the hardest to get feedback on in the LFP conversation. I think I will go the way shown on the diagram as it is easier. I know the alternate is to externally regulate the alternator and run it to the main charge bus. I may change my mind but either way I don’t have to decide until I actually install LFP...

Well, dontcha think ya kinda do have to?


How does running "...the alternator on the start battery and using a 60 amp battery to batter charger to charge the LiFePO4s..." change the load on the alternator and eliminate the need for an external regulator?

[SpaceRnglr]

Originally Posted by Discovery 15797

Did you calculate/estimate your max load(s)? Depending on your overall run, 2/0 AWG may be oversize for your vessel.

Agree with SMAC999 in that 2/0 AWG to your main DC distribution is too big, and windlass should feed from load bus. Also 10AWG is likely too small for your secondary DC distribution.

I ran a 1/0 AWG backbone from the house bank to a terminal block in the fwd cabin (total run of about 60 ft. round trip). From the fwd TB is a short run to the windlass, and another to the watermaker. The 1/0 AWG is rated for >10% voltage drop for windlass at max draw and larger than recommended wire size in the Lofrans manual, and 3% voltage drop for watermaker. (Both would never run at the same time.

Thanks for the detailed post. I did estimate the max loads and have oversized all wires... the Aux DC panel only powers LED engine lights, a small fuel pump, engine blower and the diesel tank gauges. 10awg is plenty and it’s located almost directly above the battery...

it’s good advice on the main panel. The existing wire is 10-11mm diameter (with insulation) that runs from the battery to a terminal block behind the electrical panel. I don’t know off hand how the windlass attaches, but I think it will be to that same terminal block not the panel itself. None of that detail is shown in my diagram but it should be-I will investigate and update. The actual wire from the terminal block to the DC panel is smaller, but I don’t know the size. I had sized all the wire in the diagram for the windlass (Tigress rated at 160a) and starter. Due to the Long run to the windlass (10m or so) I made it one size bigger and it should be way overkill for the DC panel. The wire up to the windlass would be a bear to replace so it will stay, but will get new terminations...

All the other wires are short so I might as well use 2/0. I suppose the terminal block behind the panel should include a fuse for the line running to the panel—I will calculate.... Thanks for the tips!

[SpaceRnglr]

Originally Posted by Stu Jackson

Well, dontcha think ya kinda do have to?


How does running "...the alternator on the start battery and using a 60 amp battery to batter charger to charge the LiFePO4s..." change the load on the alternator and eliminate the need for an external regulator?

Correct me if I am wrong, but doesn’t the Sterling BB1260 limit amps to 60? Ok maybe it draws a bit more from the supply side, but it only puts out max 60 amps... the instruction manual shows it wired exactly as I am proposing and the charge profiles are fully customisable so it should work for LFP.

I thought I was right on this, but frankly I am posting to get corrected on things I think I am right on. Much better to find out now than after I spend the money. Anyway feedback is appreciated.

[Q Xopa]

Originally Posted by SpaceRnglr

Correct me if I am wrong, but doesn’t the Sterling BB1260 limit amps to 60? Ok maybe it draws a bit more from the supply side, but it only puts out max 60 amps... the instruction manual shows it wired exactly as I am proposing and the charge profiles are fully customisable so it should work for LFP.

I thought I was right on this, but frankly I am posting to get corrected on things I think I am right on. Much better to find out now than after I spend the money. Anyway feedback is appreciated.

A few comments.

Bigger wires than 'required'. They wont hurt, in fact if money is not an issue to buy the big wire why wouldnt you. Of course physical space contraints aside. I say go for it.

Alternator connected to your Star batt. This is the safe way to NOT fry your Alternator rectifier diodes on a HVC disconnect event ie overcharging. So thats all good.

Most people do this the other way around.

But (isnt there always a 'but') what will happen is that your Start batt will be topped off quite quickly. Then your 400AH LFP bank will at 60A rate, which is 0.15C. So it would take 6.6 hours of engine to fully recharge (assuming no other draws).

Yes this will limit your Alternator output, so again will allow your 120A Alternator to live longer.

Most people aim for 0.3-0.5C.

Ok more realistically at 80% DOD 5.3 Hrs. This is kinda one of the main reasons most people go to LFPs.

Im sure someone will suggest stacking B2Bs. Doable but adds to your $ outflow.

This is a flashback of another recent B2B/ Alternator thread.

Sure what you propose sounds mostly fine.

However you have some expensive high performance bits, like a 400AH LFP bank but bottlenecked by a few lower perfomance components like an internally reg Alternator and a B2B 60A feeding those LFPs.
Like putting skinny little tyres on your Ferrari.

Its all fine if you know these limitations. Like most of us we are all limited by our finances. Maybe you intend on expanding the system as you can afford to.

I certainly do this, while I save my pennies. Or just put up with the limitations if I cant see the value in spending on the upgrades.

After all there is no limit if you want.

[john61ct]

Originally Posted by Stu Jackson

How does running "...the alternator on the start battery and using a 60 amp battery to batter charger to charge the LiFePO4s..." change the load on the alternator and eliminate the need for an external regulator?

Wut? Thats a central reason to use DCDC chargers.

The B2B limits the load drawn by the LFP, by definition with that unit, cannot be more that 60A.

The Sterlings let you derate that further if desired.

[john61ct]

Originally Posted by SpaceRnglr

Correct me if I am wrong, but doesn’t the Sterling BB1260 limit amps to 60?

Yes, exactly.

If you needed more, they can be stacked.

Some members feel the need to push for "get all the amps out of your alt as fast as possible", or even "upgrade the alt, moar amps!"

But it all depends on your usage patterns and energy budget, Ah per day in / out balance as to which approach is more cost effective for **your** use case.

[john61ct]

How long are your periods away from mains?

Is the alternator going to be a major source of your daily input?

Or is there solar, genset, other sources in the picture?

How many hours per day do you run the propulsion engine, normally, not for charging purposes?

Do you plan on running that engine for charging purposes while anchored?

[Q Xopa]

Originally Posted by john61ct

Wut? Thats a central reason to use DCDC chargers.

The B2B limits the load drawn by the LFP, by definition with that unit, cannot be more that 60A.

The Sterlings let you derate that further if desired.

Hmmm interesting,

I dont know if limit max current is the intended 'central reason'. I would say it is the design and manufactures limitation.

That is like saying a 75HP engines purpose is to limit the HP output to 75HP.

Im pretty sure its 'central reason' is to efficiently charge a battery from another battery, or DC supply.

[bcboomer]

I expect the 650 watts of solar is all that is needed for most of the time.

[Stu Jackson]

It would be an option to run the AO to the house bank and maximize the AO with an external regulator, ather than limit amps to the house bank with the B2B.


Oversizing wire is a waste of space, time and $$ and costs more for fuses. Why?