DC to DC charger behavior

[singlehander]

This is probably a stupid question, I tried search but struggled with search terms so here goes.

I have a sailboat currently equipped with an AGM start (120 AH) and two AGM house (2x120 AH.

My 140 amp alternator is regulated by a Balmar regulator and current limited to 7O AH to allow lengthy hi amp operation. This charges house and house charges start via Xantrex echo charger.

The house bank batteries are bad. I would like to replace them the simplest way possible with LIPO4.

What I am thinking Is buying three 100AH lipos to replace house. Move start to another location closer to engine and charge it directly from regulated alternator.

Buy DC to DC charger to charge LiPo from same circuit charging the AGM is on (that is the regulated alternator output set to AGM battery charge parameters in the regulator).

And that is the question: Can I successfully draw up to 50 amps from a DC to DC charger while that charger is simultaneously connected to a battery requiring a three stage charging process?? Can the regulator follow an appropriate three stage AGM charge program with a 50 amp load on the same circuit? is another way to say it.

 

[sunshine_eggo]

And that is the question: Can I successfully draw up to 50 amps from a DC to DC charger while that charger is simultaneously connected to a battery requiring a three stage charging process??

Can the regulator follow an appropriate three stage AGM charge program with a 50 amp load on the same circuit? is another way to say it.

Doesn't help clarify. It almost sounds like you're placing house and starter in parallel, but that doesn't make sense when discussing a DC-DC charger.

Typical DC-DC charger use is to supply charger INPUT power with the starter electrical system, i.e., starter battery and alternator. The alternator is presumably following a 3 stage charging process. Provided the supply voltage stays above minimum, the DC-DC charger should charge the house batteries according to its programming (LFP also requires 3 phase).

Looks like this. The unlabeled boxes are (+) and (-) bus bars.

 

[singlehander]

I guess it is correct to say I am putting the systems in parallel.

The start system charges directly from the alternator which provides appropriate regulated three phase charging to the start AGM battery.

There is also a 50 amp DC to DC charger added to this circuit. The input is the alternator as managed by the regulator. The output is set for the lipo charge profile and will deliver up to 50 amps charge current to the house lipos.

All DC loads are serviced by the lipo with exception of start.

At least that is what I would like to do if this will operate successfully.

 

[sunshine_eggo]

I guess it is correct to say I am putting the systems in parallel.

If the main (+) and (-) of your house batteries are connected to the main (+) and (-) of your starter battery, then they are in parallel. If the batteries are never connected to each other, they are not in parallel.

The start system charges directly from the alternator which provides appropriate regulated three phase charging to the start AGM battery.

There is also a 50 amp DC to DC charger added to this circuit. The input is the alternator as managed by the regulator. The output is set for the lipo charge profile and will deliver up to 50 amps charge current to the house lipos.

The above describes what I sketched above, which is the normal use case.

 

[marionw]

I guess it is correct to say I am putting the systems in parallel.

The start system charges directly from the alternator which provides appropriate regulated three phase charging to the start AGM battery.

There is also a 50 amp DC to DC charger added to this circuit. The input is the alternator as managed by the regulator. The output is set for the lipo charge profile and will deliver up to 50 amps charge current to the house lipos.

All DC loads are serviced by the lipo with exception of start.

At least that is what I would like to do if this will operate successfully.

Vehicle alternators produce "wild" AC that is rectified by diodes pressed into the frame of the alternator. The frame is the heat sink. The regulator, usually build into the alternator (often also controlled by the Engine Control Module or ECM) controls the voltage/current provided to the rotor to manage the alternator output voltage. The vehicle battery acts as a large capacitor/filter. The DC-DC converter is a one-way device (generally). The starter battery and alternator output are converted by the DC-DC converter to provide charge voltage and/or load power to the house battery. The house battery, due to the DC-DC converters one-way design cannot feed back to the starter battery. You could consider installing a diode (or more) rated for the charge current to the house battery in series with one leg of the DC-DC converter, on either the input or output. The issue is how well the DC-DC converter manages the Bulk and Float charge of the house battery.

 

[mikefitz]

My 140 amp alternator is regulated by a Balmar regulator and current limited to 7O AH to allow lengthy hi amp operation.

Always configure the alternator charge process with a lead acid or AGM is connectecd to the alternator regulated output. Under certain conditions the lithium battery bank BMS could shutdown the charge path, thus with lithium only as the alternator load, there is a possibility of alternator damage.
You have two options to charge the lithium bank.
A) have the alternator charging the starter battery and install a 50 amp DC to DC charger with lithium charge profile, between starter battery and house bank. Alternator set with an AGM charge profile. The Victron Orion XS is a recomended DC to DC charger.
B) again with the alternator charging the starter battery, using either a manual switch or idealy an ArgoFET splitter , effectively connect the house bank in parallel with the starter battery. Set the alternator with a lithium charge profile. Since the starter battery will take very little current after a short time of engine runnung, most of the 70 amps will be directed to the house battery.

For emergency arrangements fit suitable switching so the house battery or starter battery could power critical loads, example nav lights, radio, navigation systems, pumps. Lead batteries are ultra reliable, lithium batteries can sometimes behave badly.
If you have high power loads, example windlass, check that the lithium pack can deliver enough power.

 

[mikefitz]

start system charges directly from the alternator which provides appropriate regulated three phase charging to the start AGM battery.

A correction here to avoid confusion, I guess you mean the regulater has a three stage charging profile, bulk, absorbtion and float.
Three phase charging could Imply something completely different.

 

[singlehander]

A correction here to avoid confusion, I guess you mean the regulater has a three stage charging profile, bulk, absorbtion and float.
Three phase charging could Imply something completely different.

Mike

Thanks for the response. This is what I was looking for. Yes, I am speaking of alternator regulator having the three stage charge profile for the AGM start battery.

And yes. I share concerns about bms taking the lithium down and will be implementing AGM backup switching. Your plan I really want to get some mileage on the lithium before I go further. When I say further I mean transition to electric cooking and windlass with inverter, alternator and shore power upgraded with lithium profiles and then using DC to DC to charge the AGM start. All in due time.

I understand batteries and charging fairly well and an well aware of alternator protection vs lithium, that is the whole point of the DC to DC charger.

What I am struggling with is the DC to DC charger living on the same circuit as my AGM start battery trying to experience a decent three stage charge from the regulator while the DC to DC charger is exerting a large load on the same circuit.

You are telling me this is not an issue, correct?

 

[mikefitz]

You are telling me this is not an issue, correct?

Correct, having the additional current taken by the DC to DC should not effect the the starter battery charge. The DC to DC charger takes power from the alternator and does not care about the alternator/starter battery voltage . The Balmar regulator you have could be a ARS5 or a MC618. After engine startup the alternator regulator will be in bulk stage and putting out maximum current in an attempt to bring the battery volts up to bulk volts target, say 14.4 volts, once reached, the absorbtion voltage is held constant for the absorbtion period, after this the charge control regulator drops to float volts, example 13.8 volts.
The Balmar has variable absorbtion period that may run for an extended time due to the current being taken by the DC.to DC. You may need to make adjustments to the Belmar if this time period in over long, say more than 3 hours, if you are running the engine for long periods.
The DC to DC charger, the recomended Victron OrionXS, automatically detects starter battery volts and is enabled and disabled at set voltage levels. Although these are user adjustable the default settings should be OK. It's easy to set up, monitor charge status, control charge current, via the Bluetooth app.

 

[singlehander]

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Correct, having the additional current taken by the DC to DC should not effect the the starter battery charge. The DC to DC charger takes power from the alternator and does not care about the alternator/starter battery voltage . The Balmar regulator you have could be a ARS5 or a MC618. After engine startup the alternator regulator will be in bulk stage and putting out maximum current in an attempt to bring the battery volts up to bulk volts target, say 14.4 volts, once reached, the absorbtion voltage is held constant for the absorbtion period, after this the charge control regulator drops to float volts, example 13.8 volts.
The Balmar has variable absorbtion period that may run for an extended time due to the current being taken by the DC.to DC. You may need to make adjustments to the Belmar if this time period in over long, say more than 3 hours, if you are running the engine for long periods.
The DC to DC charger, the recomended Victron OrionXS, automatically detects starter battery volts and is enabled and disabled at set voltage levels. Although these are user adjustable the default settings should be OK. It's easy to set up, monitor charge status, control charge current, via the Bluetooth app.

OK, great. I thought this was how it worked but wanted to get a sanity check from someone. Looking forward to doing the install.

 

[singlehander]

Just a quick update. I have completed the installation of the ecoworthy 280 AH battery.

The Ecoworthy app is telling me the battery cells are well balanced. I assume this data is reliable.

I have done testing on shore power charging at 20 amps via the Victron 50 DC-DC charger and this has performed well.

I connected my Kid Solar controller directly to the LIPO because the Kid has an appropriate charging profile for LIPO4 batteries (as tweaked a bit for Ecoworthy specific voltage levels). This is also working well.

I have not yet tested alternator charging. Plan to do that in a day or two. I currently have the DC-DC current limited to 20 amps. I am going to open that up the the full 50 amps and see how my alternator behaves with that load over a 60 minute period. I am most concerned about excess heat, I'll be running at the dock at about 1400 engine RPMs (around 3.5 K alternator RPMs) so that should stress the alternator (rated for 125 amps) about as badly as it is going to be stressed. I will start reducing current limits if I see things getting too hot, rinse and repeat until I have determined an alternator safe current limit for long runs.

 

[yabert]

The Ecoworthy app is telling me the battery cells are well balanced. I assume this data is reliable.

Just take care, that always the case when cells are in the range of 3.2-3.3V.
A 100% SOC battery with most cells over 3.45V will tell you if the cells are well balanced.

 

[singlehander]

Just take care, that always the case when cells are in the range of 3.2-3.3V.
A 100% SOC battery with most cells over 3.45V will tell you if the cells are well balanced.

Very good to know. The last time I checked cell balance was very near full charge (or what the Ecoworthy app is telling me is 99% SOC). It was showing well balanced cells at approx 3.37V. The app is telling me I am at 99% SOC at this point. Does this sound correct?

 

[tpenfield]

@singlehander . . . I have my DC-DC charger connected on the input side to a SLA battery, same as what you have diagrammed. If you use the Victron Orion series of chargers, you can have it sense if the alternator (engine) is running and only power the LFP's when the alternator is providing power. Other DC-DC chargers may have similar sensing capabilities.

 

[yabert]

well balanced cells at approx 3.37V. The app is telling me I am at 99% SOC at this point. Does this sound correct?

Can, or can not. What was the current when you see those at 3.37V?
BMS SOC of LFP cells are highly recognized to be off regularly.
So, the only way to know if cells are balanced is to charge up to 3.45V/cell or higher.
Still all cell at 3.37V is good and if the battery isn't balanced, it's probably not far and you probably only lost few % of capacity.

 

[singlehander]

Can, or can not. What was the current when you see those at 3.37V?
BMS SOC of LFP cells are highly recognized to be off regularly.
So, the only way to know if cells are balanced is to charge up to 3.45V/cell or higher.
Still all cell at 3.37V is good and if the battery isn't balanced, it's probably not far and you probably only lost few % of capacity.

I was on my small solar system only as I approached full (per the app) charge. I was drawing about 8 amps. But the solar will only provide about 14 amps best case.

Will I see a significant drop in current as I approach full charge? I am laboring under the impression LFP is like a bucket, if I keep filling it is going to keep accepting - until something breaks.

Having said this, I think I may drive the battery a bit more and see what happens when I get to 100% per the app, and, yes, understand the app may not be accurate which is why I am trying to zero in on a good cell voltage I should shoot for or, at least, be aware of.

 

[singlehander]

@singlehander . . . I have my DC-DC charger connected on the input side to a SLA battery, same as what you have diagrammed. If you use the Victron Orion series of chargers, you can have it sense if the alternator (engine) is running and only power the LFP's when the alternator is providing power. Other DC-DC chargers may have similar sensing capabilities.

First of all it is good to know someone else is running a similar configuration, In my case it is basically baby steps into the LFP era. Better late than never I guess. I had a failing AGM house bank so I just decided to go LFP rather than replace the AGMs. Plus, I had no frikking intention of carrying two 77 pound replacement AGMs down to the dock when I could get twice the power out of half the weight using LFP!

Eventually I need to do a complete boat rewire, at least at the panel and the battery box(s) which are a rats nest level after 25 years. When I do that (and have the budget) I will redesign the whole thing with LFP and comprehensive monitoring in mind.

Yes, I was aware of this engine off function and contemplating its use. I was concerned about shore power with engine off. But won't a stopped engine lock the Victron and prevent shore power from reaching my LFP when at the dock?

BTW, my solar is configured for LFP charging and is connected directly to the LFP and is not connected to the AGM start circuit. I figured there was no need to worry about solar charging the lightly used start battery since it gets Alternator and shore. If you have solar, how did you manage it?

 

[yabert]

Will I see a significant drop in current as I approach full charge?

If your Solar Charge Controller is correctly set, yes.

 

[singlehander]

If your Solar Charge Controller is correctly set, yes.

Yes. I have confirmed my Solar Charge Controller is correctly configured for Lithium with charge voltages per battery mfg. data sheet.

So it sounds like I am good to go on that front.

 

[yabert]

Yes. I have confirmed my Solar Charge Controller is correctly configured for Lithium with charge voltages per battery mfg. data sheet.

So it sounds like I am good to go on that front.

Do you mean 3.65V/cell, so 14.6V?
Lower voltage is generally better as it allow some time to the BMS to balance cells

 

[singlehander]

Do you mean 3.65V/cell, so 14.6V?
Lower voltage is generally better as it allow some time to the BMS to balance cells

I meant 14.6 V? This is consistent with BMS cutoff voltage, which implies it is too high or right at too high, But I don't know what other voltage to use. What would your recommendation be? I would like to push the battery to, or very close to 100% SOC based upon Will Prowse's video re cell balancing these inexpensive batteries.

 

[143107]

Vehicle alternators produce "wild" AC that is rectified by diodes pressed into the frame of the alternator. The frame is the heat sink. The regulator, usually build into the alternator (often also controlled by the Engine Control Module or ECM) controls the voltage/current provided to the rotor to manage the alternator output voltage. The vehicle battery acts as a large capacitor/filter. The DC-DC converter is a one-way device (generally). The starter battery and alternator output are converted by the DC-DC converter to provide charge voltage and/or load power to the house battery. The house battery, due to the DC-DC converters one-way design cannot feed back to the starter battery. You could consider installing a diode (or more) rated for the charge current to the house battery in series with one leg of the DC-DC converter, on either the input or output. The issue is how well the DC-DC converter manages the Bulk and Float charge of the house battery.

 

[yabert]

I meant 14.6 V? This is consistent with BMS cutoff voltage, which implies it is too high or right at too high, But I don't know what other voltage to use.

If you can charge up to 14.6V that perfect.
The thing is if there is a small imbalance between cells, the battery will never reach 14.6 because a single cell reach 3.65V before the others, who can be at 3.4V by example. That way the BMS will kill the charge (disconnect).
If you set the SCC at lower voltage (13.8V - 14.0V) that can allow the BMS to balance the higher voltage cell before reaching high voltage disconnect.
Any cell at 3.45 to 3.65V can be consider 100% charge anyway (when staying at that voltage long enough).

 

[singlehander]

OK. Thanks. I installed the overkill app and it provides much more insight into the BMS set up. Excellent recommendation!

Interestingly the internal BMS settings indicate BMS sees 100% SOC at 3.35V. that seems a bit low vs some other numbers I have seen. Not sure what to make of that. The good news is both the overkill and the ecoworthy app indicate cells are well balanced.

I am not sure there is much difference in terms of practical power capacity between, say 3.35 and 3.45 V so I may be obsessing over nothing?

 

[yabert]

I am not sure there is much difference in terms of practical power capacity between, say 3.35 and 3.45 V so I may be obsessing over nothing?

Depending of C rated charging current, that can be an important % of the capacity.
But in your case, at low current charge, that probably not a lot.
Still, nothing wrong to charge at higher voltage to have a bit more capacity.