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Old 13-01-2025, 06:53   #1
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Electrical system review: switch to Lithium

Hi all,

Many posts like mine here, but I figured I get some advice on my specific case. Let me start by saying I'm an absolute beginner in electrical system design and may be getter very obvious things wrong.

I am doing some upgrades to the current electrical system of my Elan 40 (2001):
- Add solar
- Switch to Lithium house bank
- Add inverter

Please see attached the previous electric system schema, and the new (to be) electric schema.

My main questions:
- Are there any mistakes I am making?
- Are my proposed components the most cost effective way to achieve this?
- Am I missing elements? E.g. I'm sure I'm missing fuses
- Does my idea make sense to use the old charger only for the starter and bowthruster battery and just buy a new charger for the lithium bank?
- I have currently assumed to charge the starter battery directly with the alternator, but have a DC/DC charger going from the starter to the lithium bank. Are there better ways to do this considering efficiently charging lithium using the engine?
- I am planning to bring one of those 2200W mobile generators. Will this work with the current shore charger setup?
- Any other suggestions?

Thanks a lot!
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Old 13-01-2025, 07:17   #2
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Re: Electrical system review: switch to Lithium

Welcome to the forum!

Each battery should have its own fuse, two in parallel as shown is unusual. I will absolutely NOT comment on whether MRBF is appropriate. (OK I will, for a 12V system yes it is, one per battery.)

The engine battery negative can go straight to the negative busbar and only one negative connection from the DCDC to the busbar, the DCDC presumably being the non-isolated version. Definitely get the 50A XS version DCDC.

Bowthruster batt gets charged only via the Matervolt charger? I would get a smallish DCDC and charge it from the house battery, and get rid of the Mastervolt. The engine battery you can charge from the secondary output out of the Victron shore charger, 4A max.
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Old 13-01-2025, 07:37   #3
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Re: Electrical system review: switch to Lithium

Hi HeinSdL,

Thanks for the response!

For the engine battery negative: can the negative go to the negative busbar where also the negatives of the LPFs are connected?

Good idea for charging the bowthruster with a DC/DC. If my understanding is correct the DC/DC normally only turns on when the engine is running. Wouldn't this take away the ability to charge the bowthruster on the shorecharger? In the current proposed setup, the bowthruster gets charged anyway by the engine through the Victron battery isolator as far as I can tell.

I would love to be able to get rid of the old Mastervolt charger as it would free up space for the victorn ip43
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Old 13-01-2025, 08:46   #4
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Re: Electrical system review: switch to Lithium

You need Jedi and his assistant Captain Rivet here but I will stand in for the time being.

Engine battery negative definitely goes to the LFP negative busbar. if the DCDC charging the LFP from engine battery is at some distance from the engine use oversized cabling (all cabling between engine and LFP) to minimize losses otherwise the DCDC engine on detection will not work well. Also make sure you have good sized cables all the way to the alternator. What size alternator do you have? (I have a very similar setup to yours, I have the Hitachi 85A with a 50A XS DCDC and am currently operating at 45A, with a relatively cool alternator, can touch it by hand, no problem.) My engine on detection did not work well solely because of thin OEM cabling between alternator and engine.

I am almost sure you can discard the Mastervolt charger, using the secondary output out of the Victron shore charger to charge the engine battery (which is what I did but almost never does any 'work').

With 400Ah house battery capacity why not connect the bowthruster direct to the LFPs? If indeed you want to retain the battery upfront then a very small DCDC charger set to always on will keep that battery completely happy (always on meaning no engine detection algorithm running). I also think you don't really need the argofet but there I have no experience (I haven't been schooled yet on this unit, I don't have one myself and I don't feel I am missing something!).

Having said all this you end up with more or less the same set up as on my boat which is serving me very well (I chose a single 300Ah Litime). No bowthruster but windlass runs directly from the LFP. But others will probably recommend to charge the LFP directly with an externally regulated alternator which somewhat changes things, though not much. Main change would be on the engine side which I did not want to do on my boat.
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Old 13-01-2025, 11:36   #5
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Re: Electrical system review: switch to Lithium

Agree that the MRBF fuses should go on the battery terminals themselves, and you should put one one each battery sized appropriately to protect the wiring you plan to use to connect the battery to the positive bus bar.

I would make sure you keep your wire lengths consistent between the batteries so they discharge similarly -- it might be a good idea to have a separate bus bar located near the batteries that is just a "paralleling" bus bar. That way you can more easily control these cable lengths, and then have a single cable coming off these bus bars and going to your +DC and main negative bus.

If you plan on joining the batteries with short lengths of cable to make them parallel, it's a little more tricky to get them so the resistance path is equal for each battery. Some people with this arrangement do it so the main positive cable is connected to one end of the parallel arrangement, and the negative is connected to the opposite end, but I'm not sure how well this works in practice.
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Old 13-01-2025, 12:03   #6
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Re: Electrical system review: switch to Lithium



Hi Ryban,

Noted on the fuses, so add 1 fuse per battery or just 1 at the positive end of all batteries of the house bank?

As for the battery arrangement and wire lenghts, I'm still struggling with that. Please see the image I added to my post on the battery arrangement. I could keep all negative cables at around 40cm by choosing the shortest route for these. However the positive cables may still end up a bit longer. This would be the non-busbar setup as you are describing. I think your busbar proposal would be hard given the arrangement of my batteries.
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Old 13-01-2025, 12:19   #7
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Re: Electrical system review: switch to Lithium

Quote:
Originally Posted by HeinSdL View Post
You need Jedi and his assistant Captain Rivet here but I will stand in for the time being.

Engine battery negative definitely goes to the LFP negative busbar. if the DCDC charging the LFP from engine battery is at some distance from the engine use oversized cabling (all cabling between engine and LFP) to minimize losses otherwise the DCDC engine on detection will not work well. Also make sure you have good sized cables all the way to the alternator. What size alternator do you have? (I have a very similar setup to yours, I have the Hitachi 85A with a 50A XS DCDC and am currently operating at 45A, with a relatively cool alternator, can touch it by hand, no problem.) My engine on detection did not work well solely because of thin OEM cabling between alternator and engine.

I am almost sure you can discard the Mastervolt charger, using the secondary output out of the Victron shore charger to charge the engine battery (which is what I did but almost never does any 'work').

With 400Ah house battery capacity why not connect the bowthruster direct to the LFPs? If indeed you want to retain the battery upfront then a very small DCDC charger set to always on will keep that battery completely happy (always on meaning no engine detection algorithm running). I also think you don't really need the argofet but there I have no experience (I haven't been schooled yet on this unit, I don't have one myself and I don't feel I am missing something!).

Having said all this you end up with more or less the same set up as on my boat which is serving me very well (I chose a single 300Ah Litime). No bowthruster but windlass runs directly from the LFP. But others will probably recommend to charge the LFP directly with an externally regulated alternator which somewhat changes things, though not much. Main change would be on the engine side which I did not want to do on my boat.
Not sure what alternator I have, would need to check next time at the boat. For DC/DC detection, noted, but distance from engine to DC/DC should not be too large.

Would love to get rid of the mastervolt but indeed need to solve the bowthruster charging issue. I'd prefer to keep the bowthruster battery as otherwise bowthruster would run with cables at significant length to the LFPs. Next to this I feel keeping that the same will reduce installation effort. I am a bit worried about the DC/DC solution always on for this: would this not drain the LFP batteries unnecessarily? I am planning long offshore passages where all energy needs to be conserved.

Is there a way of splitting the lower amperage engine charging output of the victron ip43 to both starter and bowthruster battery?
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Old 13-01-2025, 12:42   #8
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Re: Electrical system review: switch to Lithium

Quote:
Originally Posted by KaiaElan View Post
Not sure what alternator I have, would need to check next time at the boat. For DC/DC detection, noted, but distance from engine to DC/DC should not be too large.

Would love to get rid of the mastervolt but indeed need to solve the bowthruster charging issue. I'd prefer to keep the bowthruster battery as otherwise bowthruster would run with cables at significant length to the LFPs. Next to this I feel keeping that the same will reduce installation effort. I am a bit worried about the DC/DC solution always on for this: would this not drain the LFP batteries unnecessarily? I am planning long offshore passages where all energy needs to be conserved.

Is there a way of splitting the lower amperage engine charging output of the victron ip43 to both starter and bowthruster battery?
You need to check the capacity of the alternator and make sure you limit the offtake to about 50% of capacity. Anything below 85A alternator capacity would be too small for amount of LFP capacity installed.

No, the DCDC to the front battery would not drain the LFP unnecesarily, once the battery is full, it's full, but if/when you are on a long offshore passage you should have an isolator between LFP and DCDC to completely turn it off. Personally I am not keen on any weight in the bow so that would encourage me to run some thick cables back to the LFPs.

Splitting the low amp output on the IP43 which? Only the shore charger has one additional low amp offtake, the DCDC does not and about the Argofet I don't know very much at all. But that component would seem to be superfluous in this setup.

One MRBF per LFP battery, not the bank. And then (I think) each offtake of the positive busbar should be fused too.

Very valid point about the wire lengths to each battery. On the negative side each cable to the shunt must be the same length, and on the positive side each cable to the busbar same length. Why not use 2 x 200Ah batteries? I eventually chose 1 x 300Ah to not have to worry about this.
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Old 13-01-2025, 20:49   #9
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Re: Electrical system review: switch to Lithium

I would not go with 4 house batteries. If you go with two you can use a Victron Lynx with class "T" fuses. Run a DC/DC charger from your start battery to the house bank, and a second DC/DC charger for your bow battery feeding from your house battery.

https://invertersrus.com/product/vic...ss-t-power-in/

I am running 27" of Victron gear....Power in / shunt & master fuse / power distributor.

Fuses going into this and fuses for power out. I might be a bit over fused but I used to fight fires for work.

And if your lucky CR will not get in this to confuse you.
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Old 14-01-2025, 08:23   #10
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Re: Electrical system review: switch to Lithium

I'm an electronic engineer, but I don't have experience with this, except that I've been watching most of Clark's youtube video's on the subject and is in the process of doing something simmilar myself. .......... Looking at your drawings I don't spot any obvious mistakes, looks like you've done your re-search and that your thinking is good. ....... LiFePo4 batteries generally has a built in BMS who will also work as a fuse, so I don't necessarily see a need for individual fuses as long as the BMS's are correctly configured with regard to your cables. .... I do like your old style additional fuses though. .... If there's a better way of doing it ?,.......... Well Clark think there is, just search him up on youtube. ...... But you know well enough yourself I think. ...... Much depends on your existing installation and how much work you want to make out of it, and your drawing do sugests that you have done your re-search and understood most issues. Good Luck :-) ............ Edit : You have two solars in series,... then you have to mount them such that they get the same sunlight both of them (not shadow on one of them as then the one with shadow will limit the one without (paralell solves that, but requires thicker cables).
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Old 14-01-2025, 19:45   #11
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Re: Electrical system review: switch to Lithium

Quote:
Originally Posted by finnstru View Post
{snip} LiFePo4 batteries generally has a built in BMS who will also work as a fuse, so I don't necessarily see a need for individual fuses as long as the BMS's are correctly configured with regard to your cables. {snip}

I have to disagree here
A BMS is not in anyway a replacement for a fuse. The BMS is a necessary device who's job it is to protect the battery. The fuse protects the boat (and you) from the worst case catastrophe - a fire at sea.
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Old 14-01-2025, 20:26   #12
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Re: Electrical system review: switch to Lithium

Have you read this?
https://marinehowto.com/drop-in-life...ated-consumer/
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Old 15-01-2025, 07:23   #13
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Re: Electrical system review: switch to Lithium

Quote:
Originally Posted by NorthCoastJoe View Post
I would not go with 4 house batteries. If you go with two you can use a Victron Lynx with class "T" fuses. Run a DC/DC charger from your start battery to the house bank, and a second DC/DC charger for your bow battery feeding from your house battery.

https://invertersrus.com/product/vic...ss-t-power-in/

I am running 27" of Victron gear....Power in / shunt & master fuse / power distributor.

Fuses going into this and fuses for power out. I might be a bit over fused but I used to fight fires for work.

And if your lucky CR will not get in this to confuse you.
Already bought the batteries. Reason this is the only option is the available space: only 19cm hight.

For charging bowthruster, seems like DC/DC from house bank is a good option.
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Old 15-01-2025, 08:14   #14
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Re: Electrical system review: switch to Lithium

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Originally Posted by HeinSdL View Post
You need to check the capacity of the alternator and make sure you limit the offtake to about 50% of capacity. Anything below 85A alternator capacity would be too small for amount of LFP capacity installed.

No, the DCDC to the front battery would not drain the LFP unnecesarily, once the battery is full, it's full, but if/when you are on a long offshore passage you should have an isolator between LFP and DCDC to completely turn it off. Personally I am not keen on any weight in the bow so that would encourage me to run some thick cables back to the LFPs.

Splitting the low amp output on the IP43 which? Only the shore charger has one additional low amp offtake, the DCDC does not and about the Argofet I don't know very much at all. But that component would seem to be superfluous in this setup.

One MRBF per LFP battery, not the bank. And then (I think) each offtake of the positive busbar should be fused too.

Very valid point about the wire lengths to each battery. On the negative side each cable to the shunt must be the same length, and on the positive side each cable to the busbar same length. Why not use 2 x 200Ah batteries? I eventually chose 1 x 300Ah to not have to worry about this.
Quote from Victron: Argofet isolators allow simultaneous charging of two or more batteries from one alternator (or a single output battery charger), without connecting the batteries together.

I guess in the new setup we lose the need for charging the house bank using the Argofet as we use DC/DC. Then we may not need it anymore for the bowthruster as that one can also be charged by installing a DC/DC from the house bank to the bowthruster. That DC/DC from house bank to bowthruster then covers both cases of charging on shore power and from the alternator.
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Old 15-01-2025, 08:18   #15
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Re: Electrical system review: switch to Lithium



Based on all the feedback above, I came up with the above adapted schema. Let me know what you think!
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