Hybrid Battery Bank?

[Alfabiker]

I presently have three sealed Exide 115Ah 12v lead acid batteries paralleled in the battery bank of my canal boat which are charged by the engine alternator (70A) and 300w of solar panels with an MPPT controller. I could do with a bit more battery capacity so I wonder if it would be possible to connect a 12v LiFePO in parallel with the others, as the charging requirements are very similar, rather than replace the whole lot which are basically working OK? I try not to allow the bank to drop below 12.2v off load which I assume be would be a safe level for the lithium as well as the SLAs.

 

[Danny]

I presently have three sealed Exide 115Ah 12v lead acid batteries paralleled in the battery bank of my canal boat which are charged by the engine alternator (70A) and 300w of solar panels with an MPPT controller. I could do with a bit more battery capacity so I wonder if it would be possible to connect a 12v LiFePO in parallel with the others, as the charging requirements are very similar, rather than replace the whole lot which are basically working OK? I try not to allow the bank to drop below 12.2v off load which I assume be would be a safe level for the lithium as well as the SLAs.

I isolate the lead acid and sla with a sterling pro batt ultra charger. I have paralleled only when I was at a high state of charge on both batteries. It is not recommended. See my video thread on this subfourm.

 

[Alfabiker]

I isolate the lead acid and sla with a sterling pro batt ultra charger. I have paralleled only when I was at a high state of charge on both batteries. It is not recommended. See my video thread on this subfourm.

Hi Danny
Thanks for that, your video is very interesting. I also found quite a bit of helpful information for a canal boat setup on the Canalworld forum, e.g. https://www.canalworld.net/forums/index.php?/topic/99667-another-lithium-battery-thread/page/9/

An affordable way to fit Lithium Batteries?

There's been loads of discussion on various threads on the use of lithium batteries on canal boats. None have however really looked at an affordable way to do ie get the benefit of lithiums but at a realistic cost. We've now had LiFePo's on our boat for 3 months and so I now understand them....so...

www.canalworld.net

and there is also another interesting article here:

Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design

Electrical design considerations for the integration of lithium battery systems on board marine installations.

nordkyndesign.com

It looks as though some people think it's actually safer to keep at least one SLA in parallel with the lithium batteries, as a safeguard for the rest of the system (especially the alternator) if the lithium batteries are automatically disconnected perhaps because of an over-voltage situation, and as in my idea, just to provide some extra capacity. I didn't quite gather why you don't like the direct parallel connection? But in any case I guess that in your system, the alternator is connected directly to the SLA bank only, with the lithiums charged by the Sterling B2B, so disconnecting the lithiums wouldn't damage anything else.
Regards
Nigel

 

[Danny]

Hi Danny
Thanks for that, your video is very interesting. I also found quite a bit of helpful information for a canal boat setup on the Canalworld forum, e.g. https://www.canalworld.net/forums/index.php?/topic/99667-another-lithium-battery-thread/page/9/

An affordable way to fit Lithium Batteries?

There's been loads of discussion on various threads on the use of lithium batteries on canal boats. None have however really looked at an affordable way to do ie get the benefit of lithiums but at a realistic cost. We've now had LiFePo's on our boat for 3 months and so I now understand them....so...

www.canalworld.net

and there is also another interesting article here:

Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design

Electrical design considerations for the integration of lithium battery systems on board marine installations.

nordkyndesign.com

It looks as though some people think it's actually safer to keep at least one SLA in parallel with the lithium batteries, as a safeguard for the rest of the system (especially the alternator) if the lithium batteries are automatically disconnected perhaps because of an over-voltage situation, and as in my idea, just to provide some extra capacity. I didn't quite gather why you don't like the direct parallel connection? But in any case I guess that in your system, the alternator is connected directly to the SLA bank only, with the lithiums charged by the Sterling B2B, so disconnecting the lithiums wouldn't damage anything else.
Regards
Nigel

If your sla 400ah bank is at 50% soc and your 200ah Lifepo4 is 100%, your C rate could be dangerously high between lifepo4 and sla banks? You could manage this?Also charging sla and lifepo4 have different charge profiles in terms of voltage. This is minor I guess, I charge to 13.8 on Lifepo4. Slas like 14.4v but you would kill off your sla bank a bit early. Maybe not a big deal if slas charging at 13.8? My alt is connected to sla so no issue with bms lifepo4 disconnection. I built my lifepo4 bank for house loads less than 50amps to keep my cost down on lifepo4 connecting hardware. I my starter is group 27 fla. I’m happy charging lifepo4 at 30a. I don’t want to make risky large changes in my systems for now. $400 b2b charger was a cheap insurance in my case because I use low current house loads. I think I will always have a fla starting battery dedicated.

 

[Danny]

Hi Danny
Thanks for that, your video is very interesting. I also found quite a bit of helpful information for a canal boat setup on the Canalworld forum, e.g. https://www.canalworld.net/forums/index.php?/topic/99667-another-lithium-battery-thread/page/9/

An affordable way to fit Lithium Batteries?

There's been loads of discussion on various threads on the use of lithium batteries on canal boats. None have however really looked at an affordable way to do ie get the benefit of lithiums but at a realistic cost. We've now had LiFePo's on our boat for 3 months and so I now understand them....so...

www.canalworld.net

and there is also another interesting article here:

Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design

Electrical design considerations for the integration of lithium battery systems on board marine installations.

nordkyndesign.com

It looks as though some people think it's actually safer to keep at least one SLA in parallel with the lithium batteries, as a safeguard for the rest of the system (especially the alternator) if the lithium batteries are automatically disconnected perhaps because of an over-voltage situation, and as in my idea, just to provide some extra capacity. I didn't quite gather why you don't like the direct parallel connection? But in any case I guess that in your system, the alternator is connected directly to the SLA bank only, with the lithiums charged by the Sterling B2B, so disconnecting the lithiums wouldn't damage anything else.
Regards
Nigel

Good links. The nord link does not like b2b chargers but I found Rod at https://marinehowto.com/lifepo4-batteries-on-boats/ like b2b. How are you going to limit your alternator charge to 50% of its capacity so you don’t burn it up with the high C rate lifepo4 bank?

 

[Getyourbone]

Burning up alternator… There was just a video on YouTube post in the last couple days…

 

[Getyourbone]

 

[Alfabiker]

Good links. The nord link does not like b2b chargers but I found Rod at https://marinehowto.com/lifepo4-batteries-on-boats/ like b2b. How are you going to limit your alternator charge to 50% of its capacity so you don’t burn it up with the high C rate lifepo4 bank?

That's a very good point, it could put people off using lithium batteries completely if they knew they also had to have a new alternator or an extra $400 (at least) charge controller! But some companies do seem to sell LiFePO batteries as "drop in replacements" for lead acid on boats, don't they, so how does that work?

 

[Danny]

That's a very good point, it could put people off using lithium batteries completely if they knew they also had to have a new alternator or an extra $400 (at least) charge controller! But some companies do seem to sell LiFePO batteries as "drop in replacements" for lead acid on boats, don't they, so how does that work?

If you use a b2b charger you can limit the charge on your lifepo4 bank. I don't think drop-ins are configurable to regulate a variable c rate. They must somehow have a "kind?" way to cut back on C rate but I think their C cutoff is way higher than you want your alternator to charge at. A B2B system is more reliable for limiting charge your lifepo4 bank will accept. Drop-ins are fine but you need to limit your alternator charge to the lifepo4. Drop ins also have a pretty high upper limit on charge shutoff, and are a "black box" with very little transparency. I'm pretty sure you don't have a smart voltage regulator on your alternator so maybe it is best to do a B2B or consider a smart voltage regulator on your alternator like a balmar 614. Here is a video where I am testing my Sterling B2B charger. I have an additional module where I shut off my Lifepo4 charger and don't let it even float because I have seen issues with the charger where it will continue charge when it floats. Maybe I just have not found the magic setting but I'm afraid of letting my lifepo4 B2B charger run. This is a very complex topic you stumbled into.. Drop-ins seem great but I don't think they are usually a good fit because they have an integrated bms that you can't control and they are expensive so maybe you should just bite the bullet and build your own cheap lifepo4 4s bank.

 

[Alfabiker]

I certainly agree about avoiding the drop in batteries, I would much rather follow Will's advice about building your own and bring able to control the BMS setup. As for the rest of it, I shall certainly need to think some more!

 

[Danny]

In general, I think the paralleling idea is pretty cool. It makes sense but adds a bit of manual management possibly? I may do some experiments. If you keep your lifepo4 bank small enough relative to your SLA bank ... I don't think you can get in to too much trouble with blowing up your alternator and shore charger. Maybe get an amp meter for your alt ? It is sort of a steroid shot for the lead acid batteries when charging over 90% SOC.

 

[Alfabiker]

In general, I think the paralleling idea is pretty cool. It makes sense but adds a bit of manual management possibly? I may do some experiments. If you keep your lifepo4 bank small enough relative to your SLA bank ... I don't think you can get in to too much trouble with blowing up your alternator and shore charger. Maybe get an amp meter for your alt ? It is sort of a steroid shot for the lead acid batteries when charging over 90% SOC.

Well the SLA bank is total 345Ah and I'm thinking of maybe a 120Ah lifepo4 so that may be ok as you say, but anyway, I think the next step when I go back to the boat in a couple of weeks' time, is to check out the exact specification of the alternator and if necessary, enquire with the manufacturers. It is certainly a modern one because the original one failed a couple of years ago (the boat is about 15 years old). I do have a clamp meter for measuring currents but I haven't tried it on the alternator cables with the engine running so I'll do that as well. I can also see one definite requirement is to have a separate manual isolator for the lifepo4 so that it doesn't get a float charge from the solar panels when we're away from the boat (which is what we do for the SLA's, rather than using a shore charger).

 

[Danny]

I have Victron 75/15 MPP solar charging my SLA bank set to FLA when I'm off the boat even when I'm connected to shore power because the shore power cord gets disconnected from time to time. etc. I have a manual on/off switch for the Li Batt like you are thinking about. I like to store lifepo4 OFF at 40% SOC and I charge to 90% SOC before trips. The Victron MPPTs float my lithium perfectly without overcharging at 13.8 on custom setting. You could float your parallel Li/FLA at 13.8 maybe while on solar. Most alternators output about 14.4v ( 3.6 vpc) and my Lifepo4 cells start to get out of balance ( > 30mv pc) at around 13.8v (3.45vpc). I'm not sure how you plan do deal with this. My comfort zone is 13.8v. I'd get a volt meter you really trust to do the voltage measurements. I'm using a cheap an8008 voltmeter and it is accurate. I also trust a cheap drok voltmeter to be used at the lifepo4 battery I did a video on on my youtube channel. Depending on your alternator wiring setup, your voltage at the Li battery may be lower than the voltage at the alternator and this could be a good thing for you. You can just kill the Li/FLA parallel connection when your lifepo4 battery voltage gets to say ~13.8v pack. There are also 200a switches that you can configure to automatically do the cutoff. I have a few modules on my youtube channel you could do the voltage sensing to activate the switch turning on and off your Li/SLA parallel well before your BMS kicks in. The BMS kicking in is a last resort thing for me so I have layers of protection before the BMS kicks.

 

[Danny]

One more thing.. Maybe get your schematic reviewed by some of the people on the Lithium Batteries on Boats Facebook group. You need to join to post. The FB group people are really smart but they tend to be very high end Cats etc. However, they do seem to have quite a bit of paralleling of starter batteries.