Lifepo4 house / lead starting bank interaction?

[ERTF]

For those with a lithium house bank, how are you getting the alternator charge to your house? And then conversely, how are you keeping your lead start batts charged if you are not moving around regularly? Is two "dc to dc" chargers (one for each direction) the standard solution? Or is there a better way?

I need to switch my house bank from GC2's to Lifepo4. I'm disapointed to see how much other stuff i'm going to need to add/replace in the process.

 

[J.T kearney]

For those with a lithium house bank, how are you getting the alternator charge to your house? And then conversely, how are you keeping your lead start batts charged if you are not moving around regularly? Is two "dc to dc" chargers (one for each direction) the standard solution? Or is there a better way?

I need to switch my house bank from GC2's to Lifepo4. I'm disapointed to see how much other stuff i'm going to need to add/replace in the process.

ERTF,
this subject has worked over pretty well on the TF. I switched to lifpo4 this winter and so far very happy with it. We pulled out 6 cc (6volt) and replaced them with for 100 amp lifepo4 batteries. Instead of replacing my 100 amp alt with external regulator I decided to use my current system which will charge my start battery first, then through an ACR to the house battery. What I did was remove the ACR and added a 12 volt 30 amp DC to DC charger. Once the start was fully charged it would send 30 amps to the house bank (lifepo4). If for some reason I want more charge while underway I can add another 30 amp DC to DC and double my imput to my house. This I felt was the least expensive route to start with and still use most of the components I have. Just make sure you're fusing at battery connections. Some on the forum are proponents of house battery charging first, but I would prefer to start my engine than keep the refer going.
Cheers J.T.

 

[ERTF]

ERTF,
this subject has worked over pretty well on the TF. I switched to lifpo4 this winter and so far very happy with it. We pulled out 6 cc (6volt) and replaced them with for 100 amp lifepo4 batteries. Instead of replacing my 100 amp alt with external regulator I decided to use my current system which will charge my start battery first, then through an ACR to the house battery. What I did was remove the ACR and added a 12 volt 30 amp DC to DC charger. Once the start was fully charged it would send 30 amps to the house bank (lifepo4). If for some reason I want more charge while underway I can add another 30 amp DC to DC and double my imput to my house. This I felt was the least expensive route to start with and still use most of the components I have. Just make sure you're fusing at battery connections. Some on the forum are proponents of house battery charging first, but I would prefer to start my engine than keep the refer going.
Cheers J.T.

Ok but i don't see anything about keeping the starting batteries charged. Are you running your engines frequently enough that this is of no concern? The dc to dc chargers are 1 direction, correct?

 

[Carpello]

This article is circulated a lot. I believe it’s exactly what J.T. describes.

Easy LiFePo4 Conversion - Marine How To

Easy LiFePo4 Conversion Before reading this article please read the 101 article on Drop-In's: Drop-In Batteries Be An Educated Consumer Hardly a day goes by where we don't see or hear

marinehowto.com

 

[SteveK]

@ERTF
Once the start battery is topped up it should no longer feed the house battery thru the DC2DC. Then it will stay fully charged for many weeks, probably months.
That is my system now and the start battery is waiting to start the engine. My online view says 12.64V now.
I see no need to have a charge go to it in between trips to the boat.

 

[ERTF]

@ERTF
Once the start battery is topped up it should no longer feed the house battery thru the DC2DC. Then it will stay fully charged for many weeks, probably months.
That is my system now and the start battery is waiting to start the engine. My online view says 12.64V now.
I see no need to have a charge go to it in between trips to the boat.

So you have no way to charge your starting batteries besides a running engine? Is your lithium house bank capable of turning your engines over as a back up?

 

[SteveK]

So you have no way to charge your starting batteries besides a running engine? Is your lithium house bank capable of turning your engines over as a back up?

I don't remember saying that. I tried to convey that you don't need to if the boat does not sit for months without use. A good battery will hold charge for at least a month.
Maybe I misread post 1.
Before you switch from the GC, how did you keep the start battery charged when the engine is not running.
Two way DC2DC, are you expecting perpetual charge back/forth when the engines are not running or another charge source available?

 

[ERTF]

I don't remember saying that. I tried to convey that you don't need to if the boat does not sit for months without use. A good battery will hold charge for at least a month.
Maybe I misread post 1.
Before you switch from the GC, how did you keep the start battery charged when the engine is not running.
Two way DC2DC, are you expecting perpetual charge back/forth when the engines are not running or another charge source available?

I'm not telling you how to run your ship, just asking a question. With a lead house, you always have that as a back up option for starting. My understanding is that shouldnt be done with lithium because of how the bms react to extremely high cranking current.

Personally, i just have 1 big bank, a massive solar array, and a little auxillary gas generator with an internal battery + pull start. So i'm not a stickler for traditional standards myself. But now that setup has to be changed for lithium.

As for the dc to dc charger, my stated assumption was 2 seperate chargers, so I could choose to charge in whichever direction it's needed. It seems like not the most elegant solution, but maybe there's no better way?

 

[ERTF]

As i think more about this, I could probably just utilize a cheap trickle charger on a periodic timer to keep the start batteries topped.

 

[SteveK]

I have a crossover switch, which could allow house to top up the start, then disconnect before cranking.
House to start via DC2DC means the house bank has capacity to share.
I have a separate charger for start battery from shore/GEN.
I have inverter/charger for house from shore/GEN in addition to ALT when running.

But you have a solar array that on a bad day will trickle charge the start.

 

[J.T kearney]

I have a crossover switch, which could allow house to top up the start, then disconnect before cranking.
House to start via DC2DC means the house bank has capacity to share.
I have a separate charger for start battery from shore/GEN.
I have inverter/charger for house from shore/GEN in addition to ALT when running.

But you have a solar array that on a bad day will trickle charge the start.

SteveK, Thats the way mine is set up with a switch to combine both banks to transfer power from house to start, but have not needed too yet. I'm curious how long it takes to transfer power to charge up the start? I was told not to use both at the same time do to inrush with lifepo4. The only difference is I choose my start to get the initial charge. 6/12 half dozen or the other
Cheers J.T.

 

[cafesport]

Our lithiums only see a charge from a dedicated charger or solar. We use a dc to dc charger to float charge the house agms which are in use while at anchor.

Two alternators on each engine, one to charge the start batt with internal regulation and external regulation for the house bank when underway. Otherwise we use a generator and an assortment of chargers.

 

[twistedtree]

As i think more about this, I could probably just utilize a cheap trickle charger on a periodic timer to keep the start batteries topped.

How do you keep your start batteries topped up today?

 

[twistedtree]

For those with a lithium house bank, how are you getting the alternator charge to your house? And then conversely, how are you keeping your lead start batts charged if you are not moving around regularly? Is two "dc to dc" chargers (one for each direction) the standard solution? Or is there a better way?

I need to switch my house bank from GC2's to Lifepo4. I'm disapointed to see how much other stuff i'm going to need to add/replace in the process.

As others have already stated, there are lots of way to do this with varying levels of work/cost and various levels of performance.

What is your current setup? Single or twin engine? Single alternator on each engine, or dual? What charging sources exist for start batteries and for house bank? How do things charge underway, and how do things charge while on shore or gen power?

Once we know what your starting point is, we can offer some alternatives for how to proceed.

 

[CharlieO.]

Is your concern about running down your start battery with the Dc 2 Dc charger while the boat is not running?
Pretty sure you can run the dc2dc charger to only charge when the boat is running so your start battery stays isolated.

 

[Iggy]

ERTF,
this subject has worked over pretty well on the TF. I switched to lifpo4 this winter and so far very happy with it. We pulled out 6 cc (6volt) and replaced them with for 100 amp lifepo4 batteries. Instead of replacing my 100 amp alt with external regulator I decided to use my current system which will charge my start battery first, then through an ACR to the house battery. What I did was remove the ACR and added a 12 volt 30 amp DC to DC charger. Once the start was fully charged it would send 30 amps to the house bank (lifepo4). If for some reason I want more charge while underway I can add another 30 amp DC to DC and double my imput to my house. This I felt was the least expensive route to start with and still use most of the components I have. Just make sure you're fusing at battery connections. Some on the forum are proponents of house battery charging first, but I would prefer to start my engine than keep the refer going.
Cheers J.T.

That is how I handle Lifop4. I do have a 2nd DCtoDc charger for the house. Total 60A. Basically, no other DCtoDC charger is needed. Just make sure the seance wire from the ALT in connected to the stating bank.

If need in a emergency I can use the the house to start the engine. On shore power, I have a small charger set for AGM and the Inverter/charger for the house is set for lifop4. After 2 yrs, all good.

 

[tpbrady]

I have looked at the Sterling Power DC-DC chargers and one nice feature is reverse charging. Placed between the start and house banks it will charge the start bank when the charge source is on the house bank and the start voltage is less than 13v. They are pricey but capable.

 

[Mac2]

This article is circulated a lot. I believe it’s exactly what J.T. describes.

Easy LiFePo4 Conversion - Marine How To

Easy LiFePo4 Conversion Before reading this article please read the 101 article on Drop-In's: Drop-In Batteries Be An Educated Consumer Hardly a day goes by where we don't see or hear

marinehowto.com

I'm not sure how the dc2dc charger works. Will it protect the alternator from overheating and frying? Standard alternators are only designed to charge the starting battery. In this setup a large house bank will continue to demand power from the start battery (and alternator).

 

[J.T kearney]

Also should mention that when I'm anchored or on a mooring ball the start battery is always switched off, so no draw on battery. On shore power I have a 4 amp charger on to keep the battery topped off
Cheers J.T.

 

[Iggy]

I'm not sure how the dc2dc charger works. Will it protect the alternator from overheating and frying? Standard alternators are only designed to charge the starting battery. In this setup a large house bank will continue to demand power from the start battery (and alternator).

A normal charger that uses shore is a A.C. to D.C. charger. A DC to DC charger is just that. In my case charging from the starting bank AGM to the house Lifop4. The DCtoDC charger takes the charge current from the ALT that is set up for AGM and and uses that current and to power the DCtoDC charger with Lifop4 settings. In other words, the charging setup for Lifop4 and AGM is different.

It could protect the ALT by limiting the current. But I would install a heat sensor on the ALT for that.

 

[twistedtree]

I'm not sure how the dc2dc charger works. Will it protect the alternator from overheating and frying? Standard alternators are only designed to charge the starting battery. In this setup a large house bank will continue to demand power from the start battery (and alternator).

It protects the alternator because the load it places on the alternator is limited to the rating of the DC/DC charger. So by selecting the capacity of the DC/DC charger, you can adjust and limit the load that the LFP batteries will place on the alternator. It's still a bit of a guessing game because you seldom really know how much an alternator is capable of deliver continuously. But limiting to 70% of the rated output seems pretty common.

When LFP batteries are connected directly to an alternator with an internal regulator, the alternator will run at full output right up until the batteries are full, and very few alternators can sustained full output for any length of time without damage from overheating. In this case, a smarter regulator is used that monitors the alternator's temperature, and dynamically limits output to keep the temperature below a safe threshold. In most cases this is an external regulator like a Balmar, Wakespeed, etc., but I understand there are a few internally regulated alternators that also include temp sensing and output limiting to maintain safe temps.

 

[rslifkin]

I haven't gone LFP yet for the house, but in the current setup I haven't provided a way for the house bank to charge the start batteries. The start batteries get charged when the engines are running and also via a 120v charger if the generator is running or the boat is on shore power. Realistically, we never go more than a few days without one of those things happening for at least a short period of time, so I've never had any issue keeping the start batteries topped off and haven't felt any reason to supply power from the solar panels (via the house bank) to the start batteries. Nothing draws from them when the engine keys are off, so the only thing draining them is self discharge.

 

[Mac2]

It protects the alternator because the load it places on the alternator is limited to the rating of the DC/DC charger. So by selecting the capacity of the DC/DC charger, you can adjust and limit the load that the LFP batteries will place on the alternator. It's still a bit of a guessing game because you seldom really know how much an alternator is capable of deliver continuously. But limiting to 70% of the rated output seems pretty common.

So you limit the rating, but that doesn't account for running the alternator until the house bank is full (time). I burned up two alternators to figure this one out.

 

[GMS]

First off, I don't think it is a recommended configuration to have a simple combiner switch between LiFePO and lead-acid battery banks, if the lead-acid bank develops an issue (e.g., short circuit or other damage) when combined the LiFePO batteries would be able to dump a tremendous amount of current into the damaged cells (with possible bad results). Accordingly, if a combiner is to be used think through protection mechanisms.

We are in the planning process for a new LiFePO house bank on a boat we are in the process of purchasing. The current house bank is a large number of L16s that also function as port engine start bank and house bank. The port engine already has a large (275amp) externally regulated alternator. The current plan is to reduce the current bank to 2 or 4 L16s and use it solely as a start bank for the port engine. Charging will occur via a DC-DC charger from the new house bank. The DC-DC charger can be configured to only charge when the house bank is above a certain voltage (which will translate to the house bank being charged and limit any load sharing).

Benefits:
- Fairly simple setup
- Allows for high amp alternator output to be directed to house bank
- Port engine start bank could be setup as a back up house bank

This configuration does depend on external regulation of the alternator (which will be done by a Wakespeed regulator controlled by the BMS).

 

[Iggy]

Now TT knows a lot more than I. But when I say it could protect the Alt. Well yes it will limit current as TT stated. But in my case and maybe others. I have a 125 amp Alt and my house bank uses two 30 amp DCtoDC chargers. Total 60 amps. Than I have a 24V bow thruster bank that uses a 20 amps and the house loads say 20 more amps. Now I am hitting 100 amp and not counting the starting bank charging.

Now will everything need the the maximin amount? Most likely not, but it could and over taxi the Alt. So the Alts heat sensor comes into play and can back off the ALT if needed.

 

[Iggy]

So you limit the rating, but that doesn't account for running the alternator until the house bank is full (time). I burned up two alternators to figure this one out.

The Alt needs a heat sensor to prevent this.

 

[twistedtree]

So you limit the rating, but that doesn't account for running the alternator until the house bank is full (time). I burned up two alternators to figure this one out.

This is probably an example of how it's guess work. Say you have a 100A alternator, and you "guess" that it can do 70A continuous with out damage. Some of that output will go to charging your start bank and running the engine if it has an electric draw. The rest is available for DC/DC to an LFP bank. Say you allocate 20A to recharge your start bank and to run the engine. That leaved 50A that you could allocated for a DC/DC charger.

But the real problem is that you don't really know what that 100A alternator can do continuously Maybe is's 70A, or maybe it's 80A. Or maybe it's only 50A. The only way to really know if to monitor it's temp to see how much load it can handle before it gets too hot, and who's realistically going to do that? So I think people lean on the safe side and keep the loads low.

 

[Mac2]

Thanks TT! Very helpful. Wasn't getting the fact that an alternator has a continuous rating. Wonder if the continuous rating is listed on alternator's, or if the distributor will tell you what it is? Also wasn't sure if the dc charger had heat sensing for the alternator (does not).

 

[tiltrider1]

As previously mentioned there are several ways to do this. Currently, and subject to change in the future, I have a separate AC to DC charger for each bank, start, generator, crane and house bank. I then run my alternators to my start bank and DC to DC to the house. I do have manual combining switches that allow me to combine start and house, I hope to never need these. I keep a spare battery on board should I ever need to jump the dingy or generator.

Is this over kill? Probably but this system works well for me. This system might not work for everyone. Some one who is depending On high out put alternators for charging might not want to run through a DC to DC charger. That’s fine, there are other ways to get there.

 

[SteveK]

SteveK, Thats the way mine is set up with a switch to combine both banks to transfer power from house to start, but have not needed too yet. I'm curious how long it takes to transfer power to charge up the start? I was told not to use both at the same time do to inrush with lifepo4. The only difference is I choose my start to get the initial charge. 6/12 half dozen or the other
Cheers J.T.

I also charge the start from ALT, then DC2DC to house