Brand New Catamaran, Lithium Bank addition

[dooleedooroo]

Need advises about adding the lithium bank to the new catamaran. Since it is new boat, I would like to add lithium bank with minimum change to the existing system. Current system has 600amp AGM. Here are some basic idea. Appreciated the comments whether it make sense or any better option available. This is for liveaboard.
1. Adding 700amp Lithium bank (Assuming 1000amp usable capacity is enough for everything including watermaker/washing machine/aircon. Aircon use expecting 1-2 hours a day at night for dry up the boat.
2. 24V bank instead of 12V bank for efficiency and wire size.
3. 300W x4 big panel and 100w walk on ones here and there. Make 1500W total
4. Existing AGM will support all DC use. Lithium will support mainly AC(aircon, watermaker, washing machine)
5. AGM, mainly charged from alternators. Lithium mainly charged from solar. Expect to run engine, one hours a day average even at anchor.
6. Currently 2000W multiplus is connected to AGM. Add another 24V multiplus 3000W at the lithium.
7. Idea is if Lithium bank is low in rainy days, run the engine to charge AGM and also make AC using 2000W multiplus inverter and connect to lithium side of multiplus AC in and charge the Lithium as well. Basically alternator DC output convert to AC and convert back to 24V dc to charge lithium bank. Reverse the process if Lithium is full and still lots of sun. Have not seen anybody doing this. I wonder whether this make sense. It will loose some power but this kind of charging happens not that often.
8. In the future, planning to change one of the engine alternator to high power one which can charge 24V lithium bank.
9. Location of the lithium bank, I wonder where is the best location. Cockpit locker, inside rounge under the sofa, stern side cabin under the bed. Cockpit locker looks easy to reach both from electric panel and engine alternator. It is outdoor but shaded. Wonder this location is good enough.

[CatNewBee]

It depends on your space and weight restrictions.

I would probably go fo a simpler setup and not mix up two different systems in different voltages, otherwise you have a parallel second wiring with all gear and different potential problems. It is way more expensive, because you cannot reuse what is already there.

Chose either AGM or LFP and go for it. Dont mix it up in the house installation. It is OK for start battery vs. house battery, this are separate applications and already existing, usually AGM for start and AGM dual use or GEL for the house.

I would stay at 12V at the LFP side anyway, only short big wires ro the inverters, not too much fuss. Think about your inverter size an features for interoperability if you want them to team up on the same 220V installation, only few units can sync and do this options are power assist mode (serial configuration with transfer switch inside of the second unit) or parallel config (you need the exact same units communicating to each other) .

[dooleedooroo]

Thank you for the advise. I agree that combining dc systems, different voltage or different battery type make things complicated. My basic idea is that separate the AC system and DC system starting from the source.

Using existing DC systems as DC supply, alternator, AGM battery, DC loads.

And AC boat system will be supplied by solar, lithium, inverter, AC loads.

90% of time this two systems will operate independently.

10% of time, when either one of the system charging source is not enough, plan to charge one battery to the other using inverter and AC charger. This battery to battery charging is not through DC/DC charger. But DC, inverted to AC and goes to battery specific charger. So I think these two systems still separated.
Do you see any issues I may missed? Thanks

[CatNewBee]

Originally Posted by dooleedooroo

Thank you for the advise. I agree that combining dc systems, different voltage or different battery type make things complicated. My basic idea is that separate the AC system and DC system starting from the source.

Using existing DC systems as DC supply, alternator, AGM battery, DC loads.

And AC boat system will be supplied by solar, lithium, inverter, AC loads.

90% of time this two systems will operate independently.

10% of time, when either one of the system charging source is not enough, plan to charge one battery to the other using inverter and AC charger. This battery to battery charging is not through DC/DC charger. But DC, inverted to AC and goes to battery specific charger. So I think these two systems still separated.
Do you see any issues I may missed? Thanks

No, except of weight, space and possible unnecessary replacements of the AGM cells. Your LFP setup can do the job alone.

[dooleedooroo]

I agree that full LFT setup is way to go. But in my case existing AGM setup is brand new, comes with the boat as standard. I need to keep it for the cost and also warranty etc.
After a few years, I plan to go Full Lithium.

[warrior 90]

Don´t know about Your available space but You could substantially improve on the solar panels

Sunpower SPR-x22-360
360 W - 59,1 V - Efficiency 22,2%
61,3 inch x 41,2 inch

Sunpower SPR-x21-470
470 W - 76,2 V - Efficiencey 21,7%
81,4 inch x 41,2 inch

[dooleedooroo]

Like these panels. I can use three of these and also go for 48V lithium. Since Lithium is mainly for AC supply, I may not care about DC volatage as long as I have right voltage inverter. I heard 48V installation will be easier due to wire size and more efficient. But just do not have first hand experience of advantage or disadvantage.

[CatNewBee]

Not only the wiring, you can use a smaller MPPT controller. Instead of a 150/100 a 150/35 may be sufficient. You need one with 48V output, the smaller Victron have only 12/24V AFAIK.

[hzcruiser]

Originally Posted by dooleedooroo

[...]

Using existing DC systems as DC supply, alternator, AGM battery, DC loads.

And AC boat system will be supplied by solar, lithium, inverter, AC loads.

90% of time this two systems will operate independently.
[...]
Do you see any issues I may missed? Thanks

This concept will work, however, you're now splitting your storage capacity which will likely lead to a situation where you might need more juice on the DC side at some point or more on the AC side. Getting the balance between the two just right will be impossible as the demand likely changes as well.

Transferring energy via the inverter path will cause losses that are higher than some quoted inverter efficiencies might suggest.


My recommendation is a decentralised system where the batts are close to the big consumers and every batt can be disconnected from the bus via a voltage and current monitoring module with a latching relay. All controlled from a central point. Then you can have different chemistries and/or gradually replace the AGMs with LFP over time, once they AGMs are getting too weak.

[dooleedooroo]

I think I am folding the idea of going 48V. Looks like Victron makes MPPT 100/20-48V now so that is ok. But considering the other basic parts like relay, switch etc.. Known brands(like bluesea sys) do not make 48V version yet. Maybe 48V is too early for the boat community.

[warrior 90]

Yes, those panels with 59,1 and 76,2 output are great for 48 V and I am sure they make a good tandem with the Victron mentioned by CatNewBee. The better if You only charge them by solar. Alternators and Lithium batteries are a much more complicated issue.
However there are a few real cons very well pointed out by hzcruiser. If it would be for me I would use a DC to DC unit from the 48V Lithium to the 12V AGM to supplement if requiered and keep the AGMs in good shape. I like this route
Let´s asume You need some additional charge to the 48V Lithium from the AGMs where You have capacity from the 2 alternators maybe a DC to DC is also the simplest solution even so that it is not the most efficient. However the size of this unit and the wires will not be enough to support the AC unless this DC to DC unit has a very large capacity which otherwise makes not much sense.
I find this kind of imposible to answer without knowing the AC in real life conditions.
Maybe once it´s time to replace the AGMs and You have more real life experience with the use of Your system then it´s time to take the next step. You will know much better then anybody what You really need for Your lifestyle because You live on the boat. For the moment with the solar panels and charge controller You are good and the DC to DC units are simple and cheap compared to other solutions. With the Dc to Dc units it´s more or less plug and play while a total system integration would result in a mayor surgery in the whole electrical installation+the hassle with the 48V components that You already mentioned.

Just my opinion. For me the salty marine environment is a real thread. I always try to keep it simple, nothing fancy and just functional. The heart is the Lithium battery that gives me the capacity. The rest are are my charging sources and consumers and simple reliable instruments for info.... NO entertainment instruments.

BTW, I heard sometimes those panels are a little hard to come by.
The other day I also read about available tax credits for installations on boats under certain conditions but I can´t remember where I found it. Should be interesting to explore the interpretation for an installation on a boat

[hzcruiser]

Originally Posted by dooleedooroo

[...] Maybe 48V is too early for the boat community.

Maybe too early or it may never come. Even bigger sail and power boats have max. 24V bus.

At 48V you get into the realm of DC becoming deadly, even more so than getting zapped by 220V AC (which I tried twice in my life, not fun).

As you noticed, there are (virtually) no consumers for 48V DC. The only advantage really is the cable size.

Going above 24V mainly makes sense to drive electric motors in the kW range, but then you want to go to 96V DC or higher.


IOW, 48V DC is neither here nor there...

[warrior 90]

Originally Posted by hzcruiser

Maybe too early or it may never come. Even bigger sail and power boats have max. 24V bus.

As you noticed, there are (virtually) no consumers for 48V DC. The only advantage really is the cable size.

Going above 24V mainly makes sense to drive electric motors in the kW range, but then you want to go to 96V DC or higher.

IOW, 48V DC is neither here nor there...

Well, there is the inverter for all the AC loads that will drive high demand consumers. For continuous longer run times like the aircon I would feel more comfortable with a 48 V inverter as they have higher limits. Now imagine the AC is running and You are in the kitchen with some additional consumers that will produce spikes at start up and running at peak loads. Have a look and observe the patterns here.....

https://www.victronenergy.com./uploa...-5000VA-EN.pdf
&
https://www.victronenergy.com./uploa...VA-120V-EN.pdf

As temperature is rising continuous output power ratings are less watts
As a result also efficiency is decreasing
What are the causes of temp rising inside an inverter ?

On the flip side You don´t want to over size Your inverter as zero load power will increase. As You can see already with the smaller Model 3000 W inverter You have a zero load power of 20 W. That´s 240 W per day of Your total charging capacity in stand by mode. That is not much with 6 hours of 1kw solar panels per day but when You have a cloudy day or two and charge close to nothing things start looking different.

Of course my impression comfortable is nothing of mayor concern as those Victron inverters are of high quality standards. Otherwise I would say critical. However as things are adding up the details when matching the components are, and as future up grades on consumer demands are most likely on the horizon once living on board sufficient margins should be considered.

Yes, with E propulsion higher voltage is more critical but the inverter is also important as it allows many items for creature comfort that are not available in DC

[CatNewBee]

Originally Posted by warrior 90

Well, there is the inverter for all the AC loads that will drive high demand consumers. For continuous longer run times like the aircon I would feel more comfortable with a 48 V inverter as they have higher limits. Now imagine the AC is running and You are in the kitchen with some additional consumers that will produce spikes at start up and running at peak loads. Have a look and observe the patterns here.....

https://www.victronenergy.com./uploa...-5000VA-EN.pdf
&
https://www.victronenergy.com./uploa...VA-120V-EN.pdf

As temperature is rising continuous output power ratings are less watts
As a result also efficiency is decreasing
What are the causes of temp rising inside an inverter ?

On the flip side You don´t want to over size Your inverter as zero load power will increase. As You can see already with the smaller Model 3000 W inverter You have a zero load power of 20 W. That´s 240 W per day of Your total charging capacity in stand by mode. That is not much with 6 hours of 1kw solar panels per day but when You have a cloudy day or two and charge close to nothing things start looking different.

Of course my impression comfortable is nothing of mayor concern as those Victron inverters are of high quality standards. Otherwise I would say critical. However as things are adding up the details when matching the components are, and as future up grades on consumer demands are most likely on the horizon once living on board sufficient margins should be considered.

Yes, with E propulsion higher voltage is more critical but the inverter is also important as it allows many items for creature comfort that are not available in DC

20W x 24h equals 480Wh, not 240W per day.

[warrior 90]

Originally Posted by CatNewBee

20W x 24h equals 480Wh, not 240W per day.

Hahaha Yeah SORRY, I forgot.....
I should drink a beer before doing some serious math

Much worse ...480 watts is more then a panel exclusive for 1 hour just to keep the blue box running and close to a 1 KW in 2 days with cloudy sky.

Would not want to experience the consequences of my math in certain real life conditions. I hate warm beer.

Thanks