Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

[mvweebles]

Originally Posted by john61ct

Well that is a tiny one, but yes.

Not separate for each device, but a cluster of them within a physical area serviced by a common circuit.

Too far on thin gauge wire, the voltage drops too much.

Too many amps at once, the converter gets real expensive.

There are all kinds of good makers out there, Samlex, Mean Well, Mastervolt

DCDC chargers sometimes have a "power supply mode"

If so inclined, can get crazy cheap deals on eBay, ex-industry units
Artesyn, Bel Power, TDK (Lambda), Cosel, Vicor

Also DIY UPS modules, keep a local battery charged and switch over quickly if the main feed goes down.

I agree. The Victron Orion line run in power supply mode and provide very clean power. I believe Newmar also makes a step-down converter (I know they make a step-up converter). Either would be high quality and intended for years of continuous service. You could use a single one to a bus bar and feed each 12v consumer with a separate fuse (or breaker from your panel if so equipped). I would look to convert the Gen starter to 24v to get out of need for 12v battery altogether. If your Gen has an 12v alternator, it is probably low output so simply abandon it.

Sounds like you have a good electrician. Please follow up - interesting thread.

[ranger58sb]

Originally Posted by MondayNever

In short, I am considering eliminating the 3 dedicated engine and genset starting batteries in interest of saving weight and complexity.


Porposed near-future system:
24v System

• Charger replaced with Victron Skylla-I 220-240v in, 24/100 out
• Battery system
  • Single house + main engine start bank - 4 12v Firefly parallel/series - 220ah at 24v

12v System

• Charging - add 24v-to-12v DC to DC charger
• Battery system
  • Singe, combined House + genset start bank - 1 12v Firefly - 110ah at 12v

Hydraulic System - no changes

Note that this results in a total of 5 12v batteries, a savings of 6 batteries/~200 kilos. I've already bought 5 Group 31 110ah 12v Fireflies.
[*]Do I need dedicated starting battery banks for both the main engine and genset (3 more batteries beyond the proposed 5)? Conventional wisdom on conventional single voltage boats is yes, of course, because otherwise you have no way to restart your power source (engine and/or genset) if you drain your one and only battery bank. However, I am wondering if there is sufficient redundancy on this boat because the main engine is started by 24v and the genset is started by 12v.

I suspect the boat won't notice any weight savings.

Neither proposed Firefly bank gives you huge capacity; 220 Ah and 110 Ah isn't much, in the grand scheme of things.

What runs your fridge(s)?

Were it me, I think I'd replace main engine and genset start batteries as is, perhaps not with Firefly*, then use the boat. When those three batteries reach end of life, I'd decide then about potential changes, using what I learn in those several years as guidance.

*Firefly doesn't supply huge cranking amps, so compare what you'd have versus what each engine needs... plus reserve, etc. But then if you use something different, also study how you'd handle potential charge voltage differences.

-Chris

[witzgall]

We have a similarly powered boat. 24v house and engine. 12v sub-panel for some electronics and VHF. 12v starter for Genset. The biggest difference is we have a beefy Newmar 24-12v dc-dc converter for all of the 12v gear. The genset engine start battery is not wired into or part of that system. I have thought of incorporating them together, but have not done so. I have not come up with a truly compelling reason to do so.

I have yet to wire up our ham radio - if and when that ever happens it will go to the genset battery, and a dc-dc batt charger will be installed. Actually that missing charger is the one issue I have. The genset bat gets charged only by the genset, and a silly plug in trickle charge I use manually.

Chris

[Dockhead]

There are different approaches to the architecture of such a system, and you can't say definitely that any of them is "right" or "wrong". There is a certain amount of engineering taste involved.


Contest are fine boats with fine electrical systems. The original architecture of your is much like what I have on my Moody (other than split service/house banks on my boat, which is bad and which I eliminated).



I would not personally mess with the way that is set up. Having completely separate systems for engine and generator start is a very good thing, adding to robustness of the whole system. No fault whatsoever in the house system can compromise any element of either engine or genset start system -- that is a VERY good thing. Engine and generator back each other up, too (carry jumper cables). A couple of start batteries is not a big deal to carry, especially since your boat already has a place to keep them and already has all the wiring. You already have the separate alternators. What's not to like about this? Would you really rejig the whole system just to get rid of two start batts?


That's just my view reflecting my own engineering taste, but maybe gives you something to think about.

[Dockhead]

Originally Posted by witzgall

We have a similarly powered boat. 24v house and engine. 12v sub-panel for some electronics and VHF. 12v starter for Genset. The biggest difference is we have a beefy Newmar 24-12v dc-dc converter for all of the 12v gear. The genset engine start battery is not wired into or part of that system. I have thought of incorporating them together, but have not done so. I have not come up with a truly compelling reason to do so.

I have yet to wire up our ham radio - if and when that ever happens it will go to the genset battery, and a dc-dc batt charger will be installed. Actually that missing charger is the one issue I have. The genset bat gets charged only by the genset, and a silly plug in trickle charge I use manually.

Chris

My boat was built with several droppers for several items of 12v gear which can't be bought in 24v. It works fine.


My SSB radio is wired to the 24v system using a large Victron dropper. A big advantage of this approach is that the Victron will maintain exactly 13.6v output over a wide range of input from the 24v side -- so no voltage sag. HF radios hate voltage sag and perform much better with stabilized 13.6v.


Another and probably better albeit more costly approach would be to use the M801E radio, which can take 24v directly and which has its own voltage stabilizer built in, unlike the M802 which needs nominal 12v power and has no stabilizer, one reason why the M801E is more expensive.

[MondayNever]

Originally Posted by ranger42c

I suspect the boat won't notice any weight savings.

Neither proposed Firefly bank gives you huge capacity; 220 Ah and 110 Ah isn't much, in the grand scheme of things.

What runs your fridge(s)?

The air-cooled self-contained ~5 cu ft fridge (forgetting the model) runs off the 24v system. The separate water cooled evaporator frigoboat freezer is currently inoperable. We're not historically ravenous meat eaters while cruising, so we will likely leave it decommissioned for the first season before deciding whether we want the added expense and power demands of fixing/replacing the freezer system. The fridge's power usage is definitely the big question mark for how much power storage we need on the house bank.



You probably already considered this, but keep in mind that it is 220ah at 24v, so it's not as tiny as it sounds on the surface. Fireflies are also designed for 80% depth of discharge, so that gives a usable 176ah/24v and 88ah/12v.



The current system using (a lot more) Trojan AGMs only offers a usable 200ah/24v and 100ah/12v assuming 50% DOD.


So while I agree that it's not huge capacity, it's not a massive departure from where the boat currently stands. On my electrician's advice, I was planning to err on the small side while I learn the boat over the first season and consider what I want to do with the complete system. Running the genset twice a day instead of once for a few months isn't a show stopper.

Originally Posted by ranger42c

Were it me, I think I'd replace main engine and genset start batteries as is, perhaps not with Firefly*, then use the boat. When those three batteries reach end of life, I'd decide then about potential changes, using what I learn in those several years as guidance.

*Firefly doesn't supply huge cranking amps, so compare what you'd have versus what each engine needs... plus reserve, etc. But then if you use something different, also study how you'd handle potential charge voltage differences.

-Chris

I believe that the 3 Trojan AGMs that make up the current 12v house and starter system are still in reasonable condition, so I could potentially retain one as the 12v genset starter and repurpose the other two as a 24v main engine starter. That would avoid spending any extra money upfront and no immediate changes to the overall system architecture.

[MondayNever]

Originally Posted by Dockhead

There are different approaches to the architecture of such a system, and you can't say definitely that any of them is "right" or "wrong". There is a certain amount of engineering taste involved.

Contest are fine boats with fine electrical systems. The original architecture of your is much like what I have on my Moody (other than split service/house banks on my boat, which is bad and which I eliminated).

I would not personally mess with the way that is set up. Having completely separate systems for engine and generator start is a very good thing, adding to robustness of the whole system. No fault whatsoever in the house system can compromise any element of either engine or genset start system -- that is a VERY good thing. Engine and generator back each other up, too (carry jumper cables). A couple of start batteries is not a big deal to carry, especially since your boat already has a place to keep them and already has all the wiring. You already have the separate alternators. What's not to like about this? Would you really rejig the whole system just to get rid of two start batts?

That's just my view reflecting my own engineering taste, but maybe gives you something to think about.

I appreciate your perspective. Thanks to the advice given here, I am starting to learn towards not messing with the current architecture until I know the boat well. Particularly if the 3 batts on the 12v side aren't damaged and can be repurposed for all my starting needs.


Even so, I am still curious to hear thoughts in direct response to the original philosophical question: if the main engine starts from a 24v bank, and the genset starts from an isolated 12v bank, does this provide sufficient redundancy across the complete system?


Or thinking of it in a slightly different way: does the architecture described above have greater or less redundancy than a simple 12v boat with a single main engine and a separate house bank and starting bank (which we widely accept as being sufficient)?

[MondayNever]

Originally Posted by Dockhead

My boat was built with several droppers for several items of 12v gear which can't be bought in 24v. It works fine.


My SSB radio is wired to the 24v system using a large Victron dropper. A big advantage of this approach is that the Victron will maintain exactly 13.6v output over a wide range of input from the 24v side -- so no voltage sag. HF radios hate voltage sag and perform much better with stabilized 13.6v.


Another and probably better albeit more costly approach would be to use the M801E radio, which can take 24v directly and which has its own voltage stabilizer built in, unlike the M802 which needs nominal 12v power and has no stabilizer, one reason why the M801E is more expensive.

Do you get any interference in the SSB from the dc-dc converter? I have exactly zero experience with SSBs, but I am led to believe that they are sensitive to RF noise and DC-DC converters often put out a lot.


But it may be a moot point for me if I never use or decommission the SSB in favor of the Iridium that will be going in immediately. That comment may open up another can of worms best left for another thread!

[Mikado]

I would wire both house and engine starting battery banks 24v, alternator and charger also 24 volts as well as starter. Run everything that requires 12v off
24v-12v dc/dc converter.

This is my system and it works perfectly. My dc breaker panel has a section of 12v and section of 24v.

[TheoWjr]

Originally Posted by MondayNever

I appreciate your perspective. Thanks to the advice given here, I am starting to learn towards not messing with the current architecture until I know the boat well. Particularly if the 3 batts on the 12v side aren't damaged and can be repurposed for all my starting needs.


Even so, I am still curious to hear thoughts in direct response to the original philosophical question: if the main engine starts from a 24v bank, and the genset starts from an isolated 12v bank, does this provide sufficient redundancy across the complete system?


Or thinking of it in a slightly different way: does the architecture described above have greater or less redundancy than a simple 12v boat with a single main engine and a separate house bank and starting bank (which we widely accept as being sufficient)?

It seems like it's really the level of redundancy that you are personally comfortable with. For me that sounds like an okay plan. Although I am doing the opposite in my electrical system refit with 2 12v banks, house & start, and a 24v LifePO house. My engine and gen are 12v so I'll have the ability to start from the 12v house bank if needed. Part of my decision was that I had the batteries for the 12v banks already.

But note that you will not have exactly the same redundancy as with the simple boat you describe above. With the simple system you could start the engine immediately from the house bank if needed. In your proposed setup you might need to wait some time for the start battery to get enough charge before it could start the main engine. Maybe that's fine for you... maybe not?

BTW I'm also using a step 24/12 70amp step down convertor from Victron for some of the 12v electronics. Nice unit and affordable at less than 150 usd.

[sailone3032]

I have a Contest 50 and am very happy with the way the electricals are set up. The Contest are great boats You will be happy with it. Im my mind you can never have too many batteries on board a boat unless you intend to costal cruise and minimize and passages.

[MondayNever]

Originally Posted by sailone3032

I have a Contest 50 and am very happy with the way the electricals are set up. The Contest are great boats You will be happy with it. Im my mind you can never have too many batteries on board a boat unless you intend to costal cruise and minimize and passages.

Is your Contest 50 wired the same as my current system? Given that there is so little information about Contests available in English, I have no idea whether this boat was designed this way or is the product of a couple of decades of owner modifications.


Also, does your boat have a Lewmar Mamba steering system and a Mamba autopilot drive unit? If so, have you ever calculated your average draw while on offshore passages?

[Dockhead]

I agree.

But keep in mind that keeping the systems separate is not only an advantage in redundancy. It's also a big advantage in SIMPLICITY. You can't beat the sheer simplicity of a start batt running a starter motor and maybe engine instruments, and charged by an alternator which does nothing whatsoever except to up the start batt. There is like an order of magnitude less things to go wrong with such a system, than one which is interconnected with a bunch of other gear.

This is a very desirable quality.

Originally Posted by TheoWjr

It seems like it's really the level of redundancy that you are personally comfortable with. For me that sounds like an okay plan. Although I am doing the opposite in my electrical system refit with 2 12v banks, house & start, and a 24v LifePO house. My engine and gen are 12v so I'll have the ability to start from the 12v house bank if needed. Part of my decision was that I had the batteries for the 12v banks already.

But note that you will not have exactly the same redundancy as with the simple boat you describe above. With the simple system you could start the engine immediately from the house bank if needed. In your proposed setup you might need to wait some time for the start battery to get enough charge before it could start the main engine. Maybe that's fine for you... maybe not?

BTW I'm also using a step 24/12 70amp step down convertor from Victron for some of the 12v electronics. Nice unit and affordable at less than 150 usd.

[ranger58sb]

Originally Posted by MondayNever

Even so, I am still curious to hear thoughts in direct response to the original philosophical question: if the main engine starts from a 24v bank, and the genset starts from an isolated 12v bank, does this provide sufficient redundancy across the complete system?

Or thinking of it in a slightly different way: does the architecture described above have greater or less redundancy than a simple 12v boat with a single main engine and a separate house bank and starting bank (which we widely accept as being sufficient)?

I think voltage doesn't really matter; if the main engine starts from it's own dedicated bank and the genset starts from its own dedicated bank... decent redundancy. A parallel switch, as from a bow thruster, windlass, or house bank might add yet another layer...

But a pair of jumper cables can maybe do that latter too... at least in a diesel boat and if some other banks are at same voltage.

Originally Posted by MondayNever

You probably already considered this, but keep in mind that it is 220ah at 24v, so it's not as tiny as it sounds on the surface. Fireflies are also designed for 80% depth of discharge, so that gives a usable 176ah/24v and 88ah/12v.

The current system using (a lot more) Trojan AGMs only offers a usable 200ah/24v and 100ah/12v assuming 50% DOD.

Yep, I was taking that into account. Just thinking that maybe another pair of Fireflys might not hurt, if you have the space... and if your wallet can stand the gaffe... especially if you have fridge issues. Adding another pair later (if you decide to) maybe wouldn't necessarily be as good as adding them up front.

-Chris

[FAST FRED]

I would check to see if the charger is actually bad.

It is very common for one batt in a bank to go bad and cause the charger to stay on , overcharging all the rest in the bank to destruction.