wiring plan for new LFP batteries

[REO]

Here is a drawing of how I am planning to re-wire for LFP batteries. Some of the cables already exist. To keep things simple for discussion, no emergency cutoff switch, fuses, inverter/charger or second battery charger wiring are included. Comments and suggestions are welcome.



The boat is an Albin 27 trawler with a Beta Marine 50 hp diesel. It has a 120 amp alternator and will have an external regulator. I am planning to use two 60 amp DC to DC chargers wired in parallel to maximize charge from the alternator. The boat also has a 6.5 kw generator and will have a 2000 watt inverter/charger with 80 amp charger wired to the house bank. It currently has a 20 amp 3 way charger that charges the current house, starter and generator batteries.

I have gathered as much information as I could find, and think that this is a workable plan, but sure would appreciate some expert input. I have a few questions:
If I parallel two 60 amp DC to DC chargers will this significantly decrease the time to fully charge the LFP bank?
How many amps (max) will the LFP batteries actually get from the DC to DC chargers?
Will the ACR connected between the generator battery and engine start battery cause a problem?
Does the capacity of the generator battery matter for Dc-DC charging through it?
The proposed parallel wiring for the house batteries is supposed to be good for balancing the load between batteries on discharge, but it uses different lengths of jumper cables between batteries. Doesn't this cause a problem with different resistances when charging?

 

[DavidM]

So..... you will have an external regulator on your alternator trying to maintain some sort of charging profile- FLA or Li? And you will have two 60A DC2DC chargers pulling current from that alternator. The DC2DC chargers will present as low an impedance as necessary to cause the charging source to provide 120A OUTPUT at whatever voltage its charging profile requires.

This means that the input to the DC2DC charger which is the output of the alternator might be at a rather low voltage to get the full 120A DC2DC output that is required. I am sure that it will be too low to trigger the ACR to provide any charging to the other batteries. Only when the Li bank is full will it charge anything else.

Why not get a Balmar 618 regulator with a Li profile or the new Wakespeed regulator and let it do all of the work and don't use a DC2DC charger.

Your existing wiring diagram and components present so many unanswered questions that it is hard to comment any further.

But one important last comment- what kind of alternator is that? Is it rated to continuously put out 120 amps? I doubt it. I hope its external regulator is one like a Balmar that has an alternator temp probe which will cut output in half if it gets too hot. Which BTW compromises everything you are trying to do with the DC2DC chargers. Another good reason to not go with the DC2DC chargers.

David

 

[Jc180]

As you have configured, will over charge the gen start battery because the DC -DC charger will want more voltage for a longer time to charge the house bank. Consider alternator with regulator with LI profile as David M suggests straight to house bank with DC-DC Charger from house bank back to AGMs. Likewise for the same reason, would wire your AC powered charger directly to the house bank.

Never been a fan of powering thruster and windlass from engine start batteries. Need to save engine start batteries for the unlikely event must start engine for emergency propulsion.

No problem paralleling two 60A charging sources to get 120A. Although if configure as we suggest, won’t need that capacity.

 

[Jc180]

Forgot to address the ACR. Not a fan of the ACR in this application because the two engine start batteries in parallel have more capacity than the single gen start battery (and likely different sizes as well). The ACR acts like a switch simply resulting in a direct connection. Again result in over charge gen start battery. Balmar makes a product called Duo Charge that has a smart voltage profile that won’t over charge the small battery. Configure DC-DC charger to the engine batteries and then the Duo Charge fron the engine start to gen start battery.

 

[SteveK]

I am not yet up to speed on DC-DC chargers. As drawn it shows then working in both direction. I thought they were one way.

Another thought, why have a separate Gen start battery. Option add it to the engine 1 & 2. Chances are either the engine is running or the genny and both have alternators to recharge the start bat.

 

[Iggy]

I set up my boat last year with lithium. So far so good!

If it was my setup....

1. I would wire the Li as you did the starting bank. Meaning on the Neg OR Pos side, one cable from each battery to a common post. Each cable the same size and gauge.

2. ARCs work on voltage not amperage. Once the ARC sees charging voltage it will close.

3. I would set up your ALT to charge the starting bank first! But install a switch so the ARC can be disabled. Why you might ask. Most gensets have there own Alt. You don't want it's Alt charging all 3 banks when your on a mooring. Your on board charger may be doing just that as the genset is running? Keep in mind, genset Alts are much smaller and it may over heat seeing all 3 banks.

4. As someone else mentioned, using the starting battery for the thruster may be a problem in starting. My thruster pulls 300A and my Li back can discharge 450A. Which also gives my more run time if needed.

 

[REO]

WOW----A lot of good information to digest. Thank you to everyone.

David- Your first paragraph is an accurate description of my proposed configuration. If the ACR will not close when it sees voltage the system will not work for me. I need to digest the suggestions in your post as well as those following. I'll do some more homework and get back with a revised proposal tomorrow. The other issue that your post suggests is to charge the Li battery bank first. I believe this will give me. faster charging of the house bank.

Here is more information about my system that I didn't include in the first post:

My alternator is a small case 120 amp. It came with the new engine and has less than 20 hours on it. I am planning on installing an external regulator with, temperature probe on the battery and alternator to compensate for its inability to do continuous duty. Suggestions welcome.

The engine and windlass/thruster switch makes it possible to dedicate battery one to the engine and battery two to the windlass and thruster. The both setting would be used only if the engine start battery were kaput. This system has worked well for 5 years. I do have to be careful to rotate which battery will receive a charge.

All of my current batteries are 100 amp AGM. I plan to keep that setup for non- house batteries in the new configuration.

The proposal to direct alternator output through a smart regulator to the Li house bank and then use a DC2DC charger to charge the rest of the AGM batteries sounds good. I will look at equipment suggestions.

Another question: Does the amp hour rating of the battery that is used as the passthrough for the DC2DC charger matter? I thought that this battery will just pass the current through to the DC2DC charger when it is fully charged. Charging a large battery bank through a smaller battery this way will not damage the passthrough battery. Or will it???

 

[REO]

I am re-drawing the system proposal, but a few questions stopped me. If I do not use a DC@DC charger, and I configure the Balmar 618 external regulator for Li batteries, how do I charge the AGM batteries for the engine, etc.? Don't I need the DC2Dc charger to deliver the correct voltage?
When using a DC2DC charger, does the passthrough battery need to be fully charged before the DC@DC charger kicks in. If this is the case my AMG's could wait a long time before the house Li batteries are fully charged.

 

[Jc180]

Another question: Does the amp hour rating of the battery that is used as the passthrough for the DC2DC charger matter? I thought that this battery will just pass the current through to the DC2DC charger when it is fully charged. Charging a large battery bank through a smaller battery this way will not damage the passthrough battery. Or will it???[/QUOTE]

Complicated question. Agree DC-DC Charger voltage input can vary and that Charger is designed to provide an isolated output voltage profile on a program based on battery chemistry. The current output will be based on the demand of the battery bank being charged and driven by the voltage difference between Charger output and battery voltage. So yes this current is passed through, but the voltage is driving the current. In your application, the Charger input is the alternator whose output is voltage regulated, not current regulated (although may be current limited to rating of alternator). The alternator will keep voltage high (around 14 volts) to drive current into the load it is charging, in this case the DC-DC Charger/House bank, as long as required. But your gen set starting battery is connected to the alternator output also, so it will see high alternator output voltage as long as the house bank is asking for it. Too long for the smaller gen set battery, thereby overcharging.

 

[Jc180]

I am re-drawing the system proposal, but a few questions stopped me. If I do not use a DC@DC charger, and I configure the Balmar 618 external regulator for Li batteries, how do I charge the AGM batteries for the engine, etc.? Don't I need the DC2Dc charger to deliver the correct voltage?
When using a DC2DC charger, does the passthrough battery need to be fully charged before the DC@DC charger kicks in. If this is the case my AMG's could wait a long time before the house Li batteries are fully charged.

Yes you will need the DC-DC charger to deliver the correct charging profile for the AGMs. You need to find a DC-DC charger that “turns on” when the input voltage increases as the house bank is being charged by either the alternator or the AC inverter/Charger. You do not need house bank to be fully charged only that the house bank be in the process of being charged.

Take a second look at previous post about ACR.

 

[Jc180]

Another comment. Don’t think in terms of a pass through battery. They are not passive. They will react to the voltage they see. The system you are designing will work best if the input to the DC-DC Charger is always the larger AH size.

 

[REO]

With new information here is my revised plan. It is simplified to show the most important details.
1 The Li house bank gets charge directly from the Balmar external regulator. Temp. probes are not shown. Charge rate is set for Li.
2 The AGM batteries get charged by the Balmar duo charge. Unit can be programed to begin charging at a set voltage of the house battery. Charge rate can be set for AGM batteries.
3. The generator battery will be charged by its own alternator or one leg of a 20 amp 120 volt three leg charger.
4 The house bank is wired with equal length connector cables.
5. The ACR is no longer needed.

 

[mvweebles]

Better. One comment - the four house Batts are best to a bus bar with equal length leads connecting them. One positive. One negative. Will also give a place for solar if you add

Peter

 

[Iggy]

Better. One comment - the four house Batts are best to a bus bar with equal length leads connecting them. One positive. One negative. Will also give a place for solar if you add

Peter

I did state that all ready.

 

[Iggy]

Yes you will need the DC-DC charger to deliver the correct charging profile for the AGMs. You need to find a DC-DC charger that “turns on” when the input voltage increases as the house bank is being charged by either the alternator or the AC inverter/Charger. You do not need house bank to be fully charged only that the house bank be in the process of being charged.

Take a second look at previous post about ACR.

Victron DC to DC chargers turn on automaticly when they see charging voltage.

The DC to DC charger is for the Li bank, nor the AGM bank

 

[Jeff F]

With new information here is my revised plan. It is simplified to show the most important details.

That looks like my configuration, except that I use one dc-dc charger for each of the AGM banks rather than combining them through a selector switch. So starter and thruster banks are charged independently and remain isolated from each other.

 

[Jeff F]

Another question: Does the amp hour rating of the battery that is used as the passthrough for the DC2DC charger matter? I thought that this battery will just pass the current through to the DC2DC charger when it is fully charged. Charging a large battery bank through a smaller battery this way will not damage the passthrough battery. Or will it???

The dc-dc charger doesn't care about the capacity of the source battery, and if configured properly will not harm the source bank or draw it down below a healthy charge. If the source battery's voltage falls below a preset limit the charger shuts off.

 

[DavidM]

The new configuration looks much better.

David

 

[Jc180]

With new information here is my revised plan. It is simplified to show the most important details.
1 The Li house bank gets charge directly from the Balmar external regulator. Temp. probes are not shown. Charge rate is set for Li.
2 The AGM batteries get charged by the Balmar duo charge. Unit can be programed to begin charging at a set voltage of the house battery. Charge rate can be set for AGM batteries.
3. The generator battery will be charged by its own alternator or one leg of a 20 amp 120 volt three leg charger.
4 The house bank is wired with equal length connector cables.
5. The ACR is no longer needed.


View attachment 135072

Yes. Looks good. Interestingly, that is my setup as well except have 6V golf car batteries instead of the LI bank. Gen starting battery charges from gen set alternator. Just like your car. Works fine.

 

[Jc180]

I’m intrigued by your Beta 50. Obviously a repower. Did you downsize in horsepower?

 

[Iggy]

Here is a PDF on battery balancing. Post 12 will not give you the best performance, but thats me. https://www.iotaengineering.com/resources/technical-library

It goes into the pros and cons of each set. Good reading.

Personaly, I took each pos and neg from each battery and went to a buss bar. Than attached my load wires. Keeping all cables the same size. Just an easier way vs Method 2 in the PDF. OR in my case I only have three Li batteries.

In my setup I did it the other way around. the Alt is charging the starting bank and the DC to DC charger is doing the Li bank. This saved me from replacing the ALTs regulator.

Plus, and this was very important to me. If the BMS for any reason shuts down. I can disconnect the Li bank and switch the house load to the starting bank. In order to get me home. In theory, I can run for hours/days since the ALT is charging the starting bank.

Some boaters have install a 2nd Alt. So one for the starting bank and one for the house.

 

[REO]

I installed the Beta last winter. It is a marinized Kubota tractor engine. My original engine was a 50 hp Pugeau. It ran great, but was loud, and parts were fast becoming extinct.

One last question and comment
Do I need to add a Balmar alternator protection module -APM-12? I understand that BMS shutdown or voltage spike could damage my alternator, and this unit protects against that. I will also add the suggested bus bar.

This has been a great experience. The suggestions and good advice gives me confidence that I will be able to build a safe reliable system. Thank you everyone who participated. I look at Trawler Forum several times a week and it is always interesting and valuable.

Another source for this topic for me was: marinehowto.com/drop-in-lifepo4-be-an-educated-consumer. I think that the author, Rod Collins is beginning to recover from his serious stroke.

 

[Iggy]

One last question and comment
Do I need to add a Balmar alternator protection module -APM-12? I understand that BMS shutdown or voltage spike could damage my alternator, and this unit protects against that. I will also add the suggested bus bar.

Yes, thats another reason why I connected the Alt to the starting bank. If the BMS disconnects it will blow your Alt. But If you read the APM-12 PDF it is not fool proof. Also, it may need to be replaced if hit with a surge. So you may want to carry a spare.

 

[REO]

The reason I originally routed the regulator to an agm battery was to establish that buffer, but tests described in the "marine how to" article indicated that a DC@DC charger charges slower than going directly from the regulator. That's a problem for me. So, I lean toward going to the house bank first and protecting with temperature probes and an APM. Maybe an acceptable risk? Sounds like a good idea to carry a spare APM, but how do I know when it is blown?

 

[Jc180]

I installed the Beta last winter. It is a marinized Kubota tractor engine. My original engine was a 50 hp Pugeau. It ran great, but was loud, and parts were fast becoming extinct.

One last question and comment
Do I need to add a Balmar alternator protection module -APM-12? I understand that BMS shutdown or voltage spike could damage my alternator, and this unit protects against that. I will also add the suggested bus bar.

This has been a great experience. The suggestions and good advice gives me confidence that I will be able to build a safe reliable system. Thank you everyone who participated. I look at Trawler Forum several times a week and it is always interesting and valuable.

Another source for this topic for me was: marinehowto.com/drop-in-lifepo4-be-an-educated-consumer. I think that the author, Rod Collins is beginning to recover from his serious stroke.

Don’t know about the APM-12. Suggest you give Balmar tech support a call. They’re in Huntsville, Al

Thanks for the feedback on the Beta. I’m also a big fan of marine how to.

 

[Iggy]

All things being equal. DC to DC chargers do not charge slower. It's in the amperage. But maybe I am missing something? Anyway, Li banks charge up faster than lead acid/AGMs. So that in it self my work for you.

To each their own???

If you read the specs on the surge protector is mentions led light and it beeps.

 

[SteveK]

Here is a PDF on battery balancing. Post 12 will not give you the best performance, but thats me. https://www.iotaengineering.com/resources/technical-library

It goes into the pros and cons of each set. Good reading.

Personaly, I took each pos and neg from each battery and went to a buss bar. Than attached my load wires. Keeping all cables the same size. Just an easier way vs Method 2 in the PDF. OR in my case I only have three Li batteries.

In my setup I did it the other way around. the Alt is charging the starting bank and the DC to DC charger is doing the Li bank. This saved me from replacing the ALTs regulator.

Plus, and this was very important to me. If the BMS for any reason shuts down. I can disconnect the Li bank and switch the house load to the starting bank. In order to get me home. In theory, I can run for hours/days since the ALT is charging the starting bank.

Some boaters have install a 2nd Alt. So one for the starting bank and one for the house.

Iggy, I know the setup you refer to but do not see it in the link provided. Wire size and length are the same to give optimum balance.

 

[Iggy]

Iggy, I know the setup you refer to but do not see it in the link provided. Wire size and length are the same to give optimum balance.

You are right! Its not in there. I was try to express the need to balance the batteries.

In the 2nd diagram from the OP the load cables are coming from opposite sides of the 4 batteries in that one bank. But doing it the way I described it does not matter how many batteries you have. A good thing! Lets say you had 4 batteries and did it the way the PDF shows. Than add a 5th battery. Than its back to rewiring.

 

[REO]

I don't understand. Can you do a sketch of the wiring.

 

[twistedtree]

I agree with DavidM’s early suggestion, and his praise for the new design. Two further suggestions…

You haven’t said what LFP batteries you plan to use, but they should have some sort of warning signal before they disconnect. That signal should be used to turn off the Balmar alternator regulator prior to the disconnect. Interjecting AGM batteries, adding alternator surge protectors, etc are all workarounds for lame batteries. Spend your money on good batteries, not hack workarounds

The other suggestion to to use a DC-DC charger, not a duo. The duo is just an ACR. Get a Victron or Mastervolt charger that supports an AGM charging profile. It doesn’t need to be large capacity since it doesn’t take much to recharge a start battery. I have used as low as 15A in the past, but would recommend a bit more, say 20-30A, especially to recharge after a lot of thruster or windless operation.