140Amp DC/DC Charging System

[CarpeDiem 431]

Now surplus to requirements due to modifications to my LFP setup. 

CTEK 120S and CTEK 250SE

Selling as a pair:  $850

Includes:

  * Solar MPPT (20A)

  * Alternator to Battery 140A

  * Three CC/CV Profiles (20A) suitable for LiFePO4, AGM, PbC (Lead Carbon) or flooded LA

  * Suitable for 40Ah to 800Ah, but you realistically need 80Ah minimum to see a benefit from the 120S

  * Automatic low voltage disconnect for non essential services

Happy to assist with install if you're Westhaven (or nearby) based for a couple of bottles of Rum. Can loan hydraulic crimping tools, installation design and experience. 

 

[B00B00 310]

Could work for me. I currently have a 100A balmar alternator and MC614 Smart regulator charging 400AH lifepo4 but the whole setup is under performing. The charge is split 3 ways to the bow battery bank, house and start. I was considering changing to a DC-DC charger setup.

[Island Time 1,239]

21 hours ago, B00B00 said:

Could work for me. I currently have a 100A balmar alternator and MC614 Smart regulator charging 400AH lifepo4 but the whole setup is under performing. The charge is split 3 ways to the bow battery bank, house and start. I was considering changing to a DC-DC charger setup.

Why is it under performing? Should be a pretty good setup. What continuous amps does the alt output, and at what alt temp? 

If it's not over 90 amps, then it's not set up right. 

[B00B00 310]

I can only get around 50A into the house batteries.  Charging goes into a 3 way battery isolator to the house,  start and thruster battery banks. Biggest issue right now is that the new balmar smart regulator is set on the Lifepo4 profile and cuts out all charging when the house bank is full until they get down to around 90% again.  Anchor winch feeds off the start battery which isn't ideal when the regulator has shut the alternator down. Fine to just drop the anchor but if you have to reset a few times the start battery gets very low. I can put the solar into the start battery if needed. 

I was thinking about putting all the charge into the house and using a DC to dc charger to the start and 2 big AGM bow thruster batteries. I could also very easily feed the anchor winch from the bow thruster bank. 

I have 620w of solar, a 400w wind generator and a 600w watt & sea hydrogenerator so don't usually have a shortage of juice. But the 100a per day drain from the starlink made it much harder to keep up this summer cruise. 

 

[Black Panther 1,591]

You are allowed to turn starlink off

[aardvarkash10 968]

100a/hrs a day?  Bloody hell, I'm even more put off starlink...

[CarpeDiem 431]

The issue with the Balmar regulator with LFP is that it can't do a measured charge termination. You'll either undercharge or overcharge your LFP it will never be right. The only way to fully charge LFP is with a measured charge termination current.

Like you say, you need two separate dc/dc chargers to top off your Independant LA banks.  You'll never achieve that with a LFP charge profile. 

What do you use the bow battery bank for? How many Watts do you typically pull out of it before a recharge?

[B00B00 310]

Bow bank is currently just for the Bow thruster. I have no real way of measuring the discharge on these other than the voltage but it's only used in short bursts. 

[Island Time 1,239]

Bow batteries are cranking batts, (or should be!) So voltage is what matters.

Ideally the balmar should be controlled by the battery BMS, so it does have current measurement etc. If it's not, it should be. The bms can switch the balmar  ignition wire safely. 

So, when the house is a bit down, turn off the start and thruster batts, and make sure the alt is putting out full output. If not, adjust the balmar till it is.

Combiners for charge are not great - the banks being charged are different types and chemistry, and have different charge profiles. Ideally alt to house only, and DC-DC for the other two.

There is no need for huge dc-dc, as neither the start nor the thruster batts should run for long periods. I often use around 20a for this.

Move the winch to the house bank.

 

[Bad Kitty 252]

17 hours ago, Black Panther said:

You are allowed to turn starlink off

It's BooBoo we're talking about, I imagine the stereo power draw is roughly 27,000 times the starlink draw?  

[B00B00 310]

7 hours ago, Bad Kitty said:

It's BooBoo we're talking about, I imagine the stereo power draw is roughly 27,000 times the starlink draw?  

Haha only 3 amplifiers and a couple of cooling fans. It's the smoke machine and laser lights that really do the damage! 

[B00B00 310]

11 hours ago, Island Time said:

Bow batteries are cranking batts, (or should be!) So voltage is what matters.

Ideally the balmar should be controlled by the battery BMS, so it does have current measurement etc. If it's not, it should be. The bms can switch the balmar  ignition wire safely. 

So, when the house is a bit down, turn off the start and thruster batts, and make sure the alt is putting out full output. If not, adjust the balmar till it is.

Combiners for charge are not great - the banks being charged are different types and chemistry, and have different charge profiles. Ideally alt to house only, and DC-DC for the other two.

There is no need for huge dc-dc, as neither the start nor the thruster batts should run for long periods. I often use around 20a for this.

Move the winch to the house bank.

 

Pretty sure the BMS is not connected to the Balmar 614 but it could be. It's all a bit above my skill set. 

I have a victron 30a DC-DC charger which I was going to use to the start battery and then look at getting another one for the thruster batteries. You are right that if I connect the Anchor winch to the house bank then the start and thruster batteries will not need a huge charging setup. They don't do much work really. 

What do I need between the alternator and lifepo4 bank to protect the alternator if the BMS shuts the batteries off? 

[CarpeDiem 431]

1 minute ago, B00B00 said:

Pretty sure the BMS is not connected to the Balmar 614 but it could be. It's all a bit above my skill set. 

I have a victron 30a DC-DC charger which I was going to use to the start battery and then look at getting another one for the thruster batteries. You are right that if I connect the Anchor winch to the house bank then the start and thruster batteries will not need a huge charging setup. They don't do much work really. 

What do I need between the alternator and lifepo4 bank to protect the alternator if the BMS shuts the batteries off? 

What BMS do you have?

The BMS would shut down the alternator before it shuts off the charge circuit.  Then the alternator won't get damaged.

A solution which shuts off the alternator when charged is not great, but it is better than nothing.  Ideally the alternator should be switched into a holding voltage of 13.35v once the LFP is fully charged.  If the engine is still spinning you might as well use the alternator to power everything, including those DC/DC chargers rather than start depleting the LFP.   But you can't do that with the 614.

Likewise the solar should also be going into holding mode, so your BMS should be controlling the solar too.

The 250SE would meet your needs, but with the 120S, it would be overkill.

Without knowing what kind of BMS you have, you might be better to put your anchor winch to the bow thruster batteries.  I have seen several BMS's that have gone up in smoke due to the flyback voltage spike that comes off the winch motors.

[B00B00 310]

The BMS is built into the lifepo4 batteries. 

 

[B00B00 310]

 Were you expecting there to be an additional BMS somewhere in the system? 

 

This was all installed in 2017 and done alot of miles. Nothing wrong with it I just think I can get more out of it. The only change I made was an upgrade from the Balmar 612 to a 612 party due to a terminal breaking off the 612 (fixed a while ago but not perfect) and I thought the Lifepo4 charge profile might extract a bit more juice out of the alternator.  Obviously I have played with the belt manager and other settings to make sure the field current is not being limited.  

[CarpeDiem 431]

Oh yep.  As you say these have BMS's built in.  You can't get any signal out of them so no option to control the regulator.  They are also MOSFET type BMS's so I do not recommend connecting a winch to them - although with 4 BMS's you'd probably be OK - but I would still not recommend it cause if the BMS's blow up you'd be pretty annoyed 

The key issue you face is that you cannot control the charge termination from the 614.  It has no ability to detect the tail current and therefore you cannot safely fully charge from the alternator.

My recommendation would be to:

1. set the 614 to charge to 14.4v and then switch to float at 13.4 as soon as 14.4 is reached

2. 2x small DC/DC chargers set to the appropriate profile for each of your lead banks

3. Continue with your 3-way splitter so that if all 4x BMS do switch off any load dump will be absorbed by the LA's

4. Let the solar top up the LFP

Troubleshooting:

1. Bring your LFP bank down to ~75% and disconnect your bow batteries from the splitter

2. Start the engine and check the voltage at the back of the alternator and the voltage at the LFP - how much voltage drop is there?

3. How much current is going into the LFP?  (I can loan you an amp clamp)

4. How much is going into the Start battery (it should be negligable)

I went through this exact troubleshooting exercise myself.  Turned out that the voltage drop was 0.9v, this resulted in the LFP being charged at 13.8v so the current dropped right down giving me ~40Amps at the LFP's.  By winding the alternator up to 15.6v I was able to get 90A into the LFP.  The permanent answer was 70mm2 cables AND re-routing the cables to make the run shorter.

[mcp 32]

Does the balmar voltage sense run on a separate wire all the way to the battery. If not run one. Then custom set your absorption voltage to 13.9v, float 13.35v. Your alternator needs to have a temperature sensor attached to the alternator.You won't over charge with this profile and you will get 99% charged.  You don't need a current sensor to fully charge a battery on a alternator as the field current is reduced as the alternator finds it easier hold target voltage. This is called charge acceptance.

If your battery monitor is a victon, I would use the inbuilt relay to turn the alternator off at 14.2 volts to protect the batteries from high cell voltage and disconnecting from the alternator.  

Yes my voltages are conservative, but you will get 99% charged with the alternator. Your renewables should be able to handle the rest.

[B00B00 310]

9 hours ago, CarpeDiem said:

Oh yep.  As you say these have BMS's built in.  You can't get any signal out of them so no option to control the regulator.  They are also MOSFET type BMS's so I do not recommend connecting a winch to them - although with 4 BMS's you'd probably be OK - but I would still not recommend it cause if the BMS's blow up you'd be pretty annoyed 

The key issue you face is that you cannot control the charge termination from the 614.  It has no ability to detect the tail current and therefore you cannot safely fully charge from the alternator.

My recommendation would be to:

1. set the 614 to charge to 14.4v and then switch to float at 13.4 as soon as 14.4 is reached

2. 2x small DC/DC chargers set to the appropriate profile for each of your lead banks

3. Continue with your 3-way splitter so that if all 4x BMS do switch off any load dump will be absorbed by the LA's

4. Let the solar top up the LFP

Troubleshooting:

1. Bring your LFP bank down to ~75% and disconnect your bow batteries from the splitter

2. Start the engine and check the voltage at the back of the alternator and the voltage at the LFP - how much voltage drop is there?

3. How much current is going into the LFP?  (I can loan you an amp clamp)

4. How much is going into the Start battery (it should be negligable)

I went through this exact troubleshooting exercise myself.  Turned out that the voltage drop was 0.9v, this resulted in the LFP being charged at 13.8v so the current dropped right down giving me ~40Amps at the LFP's.  By winding the alternator up to 15.6v I was able to get 90A into the LFP.  The permanent answer was 70mm2 cables AND re-routing the cables to make the run shorter.

All makes good sense thanks Rowan. Might have to employ you for a few days to have a look at it.

What is the advantage of keeping the 3 way splitter and adding the DC-DC chargers as well? 

Would you ever drop the thruster/anchor winch out of that circuit and then just use a bigger DC-DC charger onto them? 

[B00B00 310]

26 minutes ago, mcp said:

Does the balmar voltage sense run on a separate wire all the way to the battery. If not run one. Then custom set your absorption voltage to 13.9v, float 13.35v. Your alternator needs to have a temperature sensor attached to the alternator.You won't over charge with this profile and you will get 99% charged.  You don't need a current sensor to fully charge a battery on a alternator as the field current is reduced as the alternator finds it easier hold target voltage. This is called charge acceptance.

If your battery monitor is a victon, I would use the inbuilt relay to turn the alternator off at 14.2 volts to protect the batteries from high cell voltage and disconnecting from the alternator.  

Yes my voltages are conservative, but you will get 99% charged with the alternator. Your renewables should be able to handle the rest.

 

Yup my battery monitor is a Victron BMV 702 as well as my 3 Solar regulators. All Bluetooth on my phone. see attached screenshot of all victron units.

Note that screenshot was taken in at night and the top one is on the start battery hense the different voltage readings. 

Yes there is alternator and battery temperature sensors on the regulator. 

Also a picture of the alternator type and boat for reference. 

[CarpeDiem 431]

Just now, B00B00 said:

What is the advantage of keeping the 3 way splitter and adding the DC-DC chargers as well? 

Would you ever drop the thruster/anchor winch out of that circuit and then just use a bigger DC-DC charger onto them? 

The 3way ensures that in the very unlikely event that all 4 bms's close the charge circuit that your alternator is still connected to a battery.

The LFP profile will never fully charge the bow or start.  So the dc/dc takes care of this. 

Eg, let's assume a quality group 31 ca/ca start battery. The charge requirement is 14.9v till the current reaches 2A.  Then float at 13.2v indefinitely.

While your LFP profile might be charge till the voltage reaches 14.4v (the balmar can't do a current termination) then hold (aka float) at 13.4v.

So the charge profiles are incompatible with one another. Hence the dc/dc makes up the difference. 

You could definitely do it with just a two way splitter. But as you have a 3 way you lose nothing by leaving it in.

I would also recommend a manual self resetting 'enable charging' switch on the 614.  LFP is a different mind set - everytime you start the engine you should decide 'Do I need to charge the batteries?' eg if you have just been running the engine for 5hrs you stop it and 10 minutes later you need to move the boat again cause you put the anchor in the wrong place you shouldn't really start a new lfp charge cycle... Over charging lfp is very easy.