Converting house and starter batteries and charging them from engine.

[fursoc]

Hi! Ok, so background is I’m on a cat with 2 yanmar 30s from 2006 with their lead 12v batteries and stock alternators. I am replacing the existing 2 house lead acid battery banks with 1 lifepo4 bank of greater size and moving from a 12v to 24v system to satisfy our inverter. These are currently charged from solar and shore power only.

Here are my new requirements:
1. Charge the batteries from the engines at a high rate
2. Remove lead batts from engine/kids room

Here are some options I see:

1. Add a second 24v alternator to the engine with external regulator. Requirement 1 sorted, but not 2.

2. Do Option 1, plus add another 8 cells to house bank and convert engine starters to 24v and hook them up to house bank. Is starter conversion possible?

3. Replace starter batteries with lifepo4 and replace existing alternator with bigger 12v and external regulator. For this to make economical sense I feel like I would want to use these batteries for house as well. Is there a way to step up the 2 x 12v to the house 24v with those big alternator loads?

4. Not worry about the engines and just get a portable generator to plug into shore power. This doesn’t deal with requirement 2 though, but is easily the simplest solution for charging. Though there is the extra engine to maintain.

I like the simplicity of option 2 but I don’t know the cost and difficulty of changing starter motors. Not to mention I then have the single battery for house/starter dilemma.

I’m sure I can’t be the first person with this problem. If anyone knows a good solution please let me know. Or if you can comment on my options that would be great!

Thanks
Graham

[smac999]

how big is your inverter? 3000w is fine off 12v.

sounds like a lot of work just for the inverter. everything would likely be easier if you stayed at 12v

switch the starter batteries to AGM's. problem 2 solved


do not make a single large bank that will do house and start the engines. you lose all redundancy

[fursoc]

Yep 3000w, and it is 24v. Yes a lot of work. I’m looking for the right option to move forward with. Your comments are appreciated, but they don’t really help me

I’m looking for the solution which provides the most elegant simple end result. The easiest solution is option 1 and add agm (if that is better than lead acid). But now I’ll have 2 extra alternators and a total of 3 battery banks. Is that the best end result? I don’t know. Hopefully someone can chime in with experience in this example.

[smac999]

with 2 engines you should have 3 battery banks. 2 starts and a house.

this is how every good boat is done. with a gen you'd have a 4th gen start battery.

for 3000w I'd stay at 12v. charge the house direct from each engine alt. upgrade both of them. stay with one 12v alt on each. both run direct to house bank. feed starter banks with 2 ACR's or 2 echo chargers from house bank.

[fursoc]

Thanks smac, but I think you’re missing the point of my post. I have a 24v lithium house system now, no going back. Ok, you may think I made the wrong decision but it is what it is. How do I move forward with what I have?

[smac999]

New bigger 12v Alts. Charging agm start batteries.

12v to 24v battery chargers. From each start battery to house bank. So each engine and each alt can charge the house as well was own start battery.

Sterling power makes some. With Settings for charging lithium batteries.

[CatNewBee]

Originally Posted by fursoc

Thanks smac, but I think you’re missing the point of my post. I have a 24v lithium house system now, no going back. Ok, you may think I made the wrong decision but it is what it is. How do I move forward with what I have?

Its a pitty you are going to 24V. What about all your systems on board, that were 12V originaly - step down converter?

Anyway, there are starter for 24V, and alternator too for some trucks. Replacement could be possible. Than you need at least a 24V start battery, you can use 2 small (20...40Ah) unmanaged 12V LFP start batteries and charge them along with the house bank by using a battery combiner relay. You have to watch the mid point voltage, there are cheap balancer that can do this. Because those are not cycled.

You can then use the start battery emergency combiner switch of the vessel to connect both engines to the same start bank. As backup you can use your big house battery, by a simple big battery switch.

Other option would be to stay with 12V at the engines and give each one its own 12V 20..40Ah unmanaged LFP start battery for edundancy, the wiring can stay untouched for the starter then.

You can charge them with your onbard 220V/12V charger set to lower voltages, so they are not overcharged, use a voltage sensitive relay to just cut charge sources above 14.0V. Replace the alternators with 24V and external regulator with LFP settings to charge the house bank only. You also can use a DC/DC converter or even a MPPT controller to charge the start batteries from 24V, but I think it is an overkill.

[mikedefieslife]

Originally Posted by CatNewBee

Its a pitty you are going to 24V. What about all your systems on board, that were 12V originaly - step down converter?

Most modern electronics accept 9-36 or even up to 48v.

It seems motors like those on winches and windlasses, electrics toilets and the like are things like a specific voltage.

[fursoc]

I didn’t really want this to be a 12v Vs 24v thread. But to answer a few questions. I have a power hungry kitchen and plenty of solar and the Victron easysolar 24v 3000w inverter charger was going cheap so I bought one.

So I have 24v house bank, with a 12v step down converter for small 12v items, then all the big things like multiple fridges, windlass, and potential electric winch in near future all run on 24v just fine. So as far as house is concerned 24v makes more sense for me.

The issue is charging from engines. An honest question for the liveaboards out there, is having redundancy in your batteries a major concern? We’re not there yet but I can’t imagine a time when I’m not monitoring battery use when I’m living onboard. If I have one battery bank to rule all battery banks as a live aboard, is that really a major concern?

I do like CatNewBee’s idea of having the 24v system charge the starter batteries if that is how it goes. That would simplify things for sure. I could replace the current alternator with 24v high output and run it straight to house bank. Then through converter and possible a dc charger, charge starter battery. That would probably be easier than replacing starter motor.

Good food for thought there

[roland stockham]

One of the best electrical setups I have seen on a cat had a rear porch made from 5 large solar panels. I saw it generating 1KW!! The entire boat was electric and had a family of 5 living aboard. I would be inclined to look at keeping the existing 12v System for start and all the Nav and boat stuff. 2 start batt + smallish house bank. Then your big lithium hooked up to the inverter and charged via solar running the majority of domestic stuff on 110v just like living on the bank. This fits in well with a family and high demands. If you absolutely cant have the electrics down ever get a backup genny but maybe a small one with a 12/24v charger. 24v geny tend to be large, heavy and expensive.

[guyrj33]

You may find that your 12v starter works fine at 24v, just spins a little faster.

[CatNewBee]

Yes, I guess this will work. Start batteries are only discharged when crancking the engine, they are immediately re-charged when the engine runs, so it is a few Ah DOD at all. You can easily recharge the energy by a small solar charger in few minutes using either the solar panels or the house bank.

Regarding using a 12V starter on a 24V installation - I would not do that in the long run. 12V starter have thicker wire for more amps, if you double the voltage by using a LFP, that has a very low resistance, your starter will consume 2 times the power, heat up and burn the coil or the brushes / collector if cranking a little longer, there is almost no voltage drop with lithium batteries, especially large banks.

It would be too risky to end up with broken starters in a gale when you need the engines.

[Rapanui]

Surely what you need are 2 12v to 24v echo charge units one between each start battery and the house bank. Use the house bank BMS to trip a relay which breaks both echo charger links on LIPO overvoltage. Keep lead 12v engine start batteries. That way your alternators are protected from open circuiting and over loading, either engine charges house bank and house bank is protected from over charging.

[CatNewBee]

Originally Posted by Rapanui

Surely what you need are 2 12v to 24v echo charge units one between each start battery and the house bank. Use the house bank BMS to trip a relay which breaks both echo charger links on LIPO overvoltage. Keep lead 12v engine start batteries. That way your alternators are protected from open circuiting and over loading, either engine charges house bank and house bank is protected from over charging.

Well, this is the opposite approach to keep 12V alternators and step-up to 24 Volt. It is expensive, but doable too. It involves 2 powerfull B2B 12-24V charger mathing the alternator output, also some losses due to heat by the conversion.

It is a budget question, weather the 24V power alternator and 2 low current MPPT controller / step down charger - or the B2B 12-24V high amp charger and a 12V power alternator with external regulator are economically better.

With 24V the currents are half, means smaller cabling too, so I guess it is favorable to do as much as possible in higher voltages...

[fursoc]

Thanks everyone, I'll give it a good think over the weekend and see what else I can come up with. I'll also pull out the books and see if they have any insights. Probably should've done that first.

Cheers!