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Old 16-12-2019, 16:34   #1
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Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Good afternoon all,
My wife and I are a few weeks away from closing on a 1995 Contest 46. Shortly before the survey the original Mastervolt battery charger malfunctioned and stayed in bulk charge mode for two days, resulting in 8 totally fried batteries (the entire 24v system). For better or worse, I am now faced with getting to replace the charger and batteries with new units asap, before I properly understand the boat. She has a very complex (convoluted?) AC and 12/24v DC electrical system that I have only barely wrapped my head around after 2 days spent on the boat during survey and sea trial. I am trying to think through the current system and determine how to proceed and I could use advice from you all.

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

Current system:
24v system:
  • Consumers: Main engine starter, fridge, freezer, autopilot, pumps, etc
  • Charging sources:
    • Main engine alternator - Balmar with external reg
    • Battery charger - Mastervolt 220-240v-in, 24/100 out - powered by shorepower or Genset
    • 250w solar (assuming external regulator)
    • Air Breeze wind gen (internal regulator)
  • Battery system
    • House bank - 6 12v Trojan AGM in parallel/series - 300ah 24v
    • Main engine starting bank - 2 12v Trojan AGM in parallel/series - 100ah 24v
12v system
  • Consumers: Genset starter, instruments, lights, SSB
  • Charging sources:
    • Genset alternator
    • It's possible that there is an additional source, like a 12v alternator on the main engine, a DC to DC charger from the 24v system, or an additional 12v-out battery charger, but it was not listed in the survey and I didn't think to examine at the time
  • Battery system
    • House bank - 2 12v Trojan AGM in parallel - 200ah 12v
    • Genset starting bank - 1 12v Trojan AGM in parallel - 100ah 12v
Hydraulic system (mentioned because these are not demands on electrical system)
  • Consumers: Windlass, bowthruster
  • Power source: main engine driven pump
Note that this system has 11 (ELEVEN!!) 12v AGM batteries.

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. Let's not turn this into a debate about their merits and assume that they will operate as expected and that I will utilize their ability to deeply discharge down to 20%. It's entirely possible that I would also add additional batteries to one or both banks if we determine that usable capacity is not enough, but we want to cruise the boat for a season first. But really the question is about redundancy in the design, not whether the total AH is enough for our style of crusing.

Question for Cruisersforum about my potential set up:
  • 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.
    • If 24v bank is drained and I cannot start main engine, the 12v bank can be used to start the genset, which will provide AC power to the battery charger, thereby recharging the 24v bank and allowing the main engine to be started.
    • If 12v bank is drained and I cannot start the genset, I can use the 24v bank to charge the 12v bank via DC-to-DC charger. I still maintain the ability to start the main engine through this entire process. This is is a much less critical problem, anyway.
  • Does anyone have experience with one of those battery powered portable jump starters in a marine application? Would it be an adequate back-up if I kept a 12/24v unit charged up in the event that I manage to drain both the 12v and 24v battery banks?
This is a long post with a lot of details for what on the surface seems like a simple question, so I appreciate your time in reading through it and thinking through the particulars of this boat. Thanks CF!
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Old 16-12-2019, 16:49   #2
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Not to mention the obvious, but shouldn't the seller replace the batteries and charger before the sale? Didn't this problem appear on the survey? Maybe you can negotiate how much each pays?

If for some reason you have to fix this problem, and I were in your shoes, I would keep the electrical system the same. I would change things only after I would find a competent local electrician who has a handle on the situation. Until then, I would just replace what's broken. Last thing I would want is to introduce more problems.

The boat worked this long the way it is.

Just my humble opinion...
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Old 16-12-2019, 17:00   #3
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Just so you don't feel alone... there are production boats out there with "complex" electrical systems and they work very well.

Our Amel has both 24 and 12 volt systems. The 24 Volt system (Eight G31 Firefly) handles all the house loads. The 12 volt system (One FLA G31) is basically dedicated to the main engine and the genset. The Main Engine has both 12 and 24 volt alternators, and the genset has a 12 volt alternator.

Our "back up" system for starting either engine is simplicity itself. We have a pair of jumper cables. In the very unlikely event our starting battery was ever insufficiently charged to turn over the engine or genset we could jump it from any of the individual batteries in the house bank.
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Old 16-12-2019, 17:04   #4
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by boom23 View Post
Not to mention the obvious, but shouldn't the seller replace the batteries and charger before the sale? Didn't this problem appear on the survey? Maybe you can negotiate how much each pays?

If for some reason you have to fix this problem, and I were in your shoes, I would keep the electrical system the same. I would change things only after I would find a competent local electrician who has a handle on the situation. Until then, I would just replace what's broken. Last thing I would want is to introduce more problems.

The boat worked this long the way it is.

Just my humble opinion...

We negotiated a big chunk off our original offer based on the failed charger/batteries and various other defects uncovered during the survey. So yes, definitely! Very glad the charger failed right before the survey. I thought about asking the seller to rectify the problem, but opted to negotiate for cash and make my own decision about the replacement equipment.


I have a well regarded ABYC-certified electrician working with me. He examined the system after the failure was discovered. I am opting to have him replace the charger. I will replace the batteries at the same time. I have yet to talk through the idea of eliminating the starting banks with him, but I will.



I hear what you're saying about keeping the boat the same, but in my opinion and the electrician's, the boat has way more batteries than is optimal. Particularly since I want to go with Firefly batteries, this seems like the best time to make some decisions about the system. Otherwise I'm shelling out $3k just to replace Trojan AGMs in a system that I probably won't want to retain or even more money to buy way more Fireflies than I need.



Not knowing the boat really does make this a difficult choice, though. Thanks for your reply.
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Old 16-12-2019, 17:09   #5
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Much more to do, but starter to your genny might be swapped for 24vdc starter thereby consolidating your hi amp DC loads. Gen alternator is likely small - 15a or so. You could keep it to charge 12v Batts or swap out for 24v.
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Old 16-12-2019, 17:09   #6
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by billknny View Post
Just so you don't feel alone... there are production boats out there with "complex" electrical systems and they work very well.

Our Amel has both 24 and 12 volt systems. The 24 Volt system (Eight G31 Firefly) handles all the house loads. The 12 volt system (One FLA G31) is basically dedicated to the main engine and the genset. The Main Engine has both 12 and 24 volt alternators, and the genset has a 12 volt alternator.

Our "back up" system for starting either engine is simplicity itself. We have a pair of jumper cables. In the very unlikely event our starting battery was ever insufficiently charged to turn over the engine or genset we could jump it from any of the individual batteries in the house bank.

Amels are the most obvious example of a similar production system. I have been reading owner reports extensively over the last few days. The one primary difference, however, is that Amel uses 12v to start the main engine whereas this Contest 46 uses 24v.


How do you like your fireflies? What depth of discharge do you usually take them? What's your average daily AH consumption? We've historically been pretty light on power usage (no AC, kitchen appliances, etc) so I'm thinking that 8 fireflies would be unnecessary for us unless we decide we want reaaaally long periods between running the genset.
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Old 16-12-2019, 17:11   #7
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by mvweebles View Post
Much more to do, but starter to your genny might be swapped for 24vdc starter thereby consolidating your hi amp DC loads. Gen alternator is likely small - 15a or so. You could keep it to charge 12v Batts or swap out for 24v.

That's a thought that crossed my mind, but we'd still need to keep the 12v bank for the instruments so we wouldn't be reducing complexity much. I don't know for certain, but I wouldn't have thought that a battery like a Firefly or the existing Trojan AGM would mind the brief high loads necessary for cranking the starter on the genset. I could very easily be misinformed, however.
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Old 16-12-2019, 17:12   #8
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

battery powered portable jump starters

The real big amp pricey ones are needed for big diesels.

Don't use for other tasks. Test and top up every few months.
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Old 16-12-2019, 17:16   #9
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

I would use for "belt & suspenders" backup purpose only.

You don't need a separate dedicated Starter batt for every engine.

I'd put in a largish Reserve bank to power Essential circuits in the event House fails.

Sould be used for purpose if tested regularly, but otherwise kept offline. Charged via DCDC if needed, otherwise a VSR/ACR from House.

Cranking would be switchable between that and House.
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Old 16-12-2019, 17:20   #10
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Consider converting everything possible to native 24V.

Small DCDC converters can power most of the remainder.

If absolutely required, a 12V circuit with its own small bank can be retained charged via DCDC.

So all significant charge sources go direct to the main big House.
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Old 16-12-2019, 17:30   #11
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by john61ct View Post
Consider converting everything possible to native 24V.

Small DCDC converters can power most of the remainder.

If absolutely required, a 12V circuit with its own small bank can be retained charged via DCDC.

So all significant charge sources go direct to the main big House.

As I replace instruments, lights, etc I will be doing as you suggest and opting for 24v. These upgrades are all planned in the nearish future. The one big ticket exception is the SSB, but I'm not sure if I will ever use it in this era of Iridiums so maybe it will get nixed.
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Old 16-12-2019, 17:33   #12
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Running a local 12V circuit for low-current loads off a converter is really NBD
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Old 16-12-2019, 17:41   #13
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by john61ct View Post
Running a local 12V circuit for low-current loads off a converter is really NBD

Are you suggesting that I install something like this (https://www.invertersupply.com/index...4aApj4EALw_wcB) on each individual circuit for things like wind and depth, chartplotter, etc?


If so, I hadn't even considered that but maybe that would do the trick until i eventually replace those units with 24v devices.
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Old 16-12-2019, 17:52   #14
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

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.
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Old 16-12-2019, 19:36   #15
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Re: Engine and house 24v, Genset and instruments 12v - dedicated starting batteries?

Quote:
Originally Posted by billknny View Post
Just so you don't feel alone... there are production boats out there with "complex" electrical systems and they work very well.

Our Amel has both 24 and 12 volt systems. The 24 Volt system (Eight G31 Firefly) handles all the house loads. The 12 volt system (One FLA G31) is basically dedicated to the main engine and the genset. The Main Engine has both 12 and 24 volt alternators, and the genset has a 12 volt alternator.

Our "back up" system for starting either engine is simplicity itself. We have a pair of jumper cables. In the very unlikely event our starting battery was ever insufficiently charged to turn over the engine or genset we could jump it from any of the individual batteries in the house bank.
Hello fellow Amelian! (if that's a word...)

From what I remember, my boat has one (single) 12v starting battery for the main engine and generator. As Amel provides backups, I'll need to figure out what I need to do in case this one battery goes bad. Jumper cables are easy!

Thank you!
On my To Do list...
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