DC-DC Charger

[PennBruce]

I am in the planning stage for upgrading my alternator, batteries and charger.

My thinking is to use a DC-DC charger to maintain my engine batteries from my house bank. The house bank would be charged directly from the alternator.

What I am finding on the web is just the opposite. Alternator charges the engine batteries and the DC-DC charger maintains the house bank. My thinking is that the house bank needs the bulk of the alternator output, The engine batteries have little need of being charged up until the next time they are needed to start the engine.

The alternator will be upgraded to higher output with an external regulator.

Input on this will be appreciated.

Bruce

[Jeff F]

Are you using or contemplating using lithium batteries? That's the big decider in my mind. See my recent thread.

[PennBruce]

The batteries will be Lifepro4. I have room for either one 400ah, two 200ah or five 100ah. I'm am thinking Renogy.

I want to relocate the batteries under the berth in the rear cabin.

Bruce

Originally Posted by Jeff F

Are you using or contemplating using lithium batteries? That's the big decider in my mind. See my recent thread.

[O C Diver]

On my boat, one of the banks is charged off of another through the inverter and a battery charger. In configuring the setup, I rationalized that the largest bank should be charged off the alternator. It seems to me that the efficiency loss on most KW having to be bumped into one bank to be pushed into another is counter productive. I guess part of the question deals with how large a DC to DC charger you can get relative to your bank size.

Ted

[DavidM]

Within the last month this same topic was discussed on another thread. Look it up.

The conclusion was to charge your Li house bank with a high output alternator with a Balmar Li capable regulator. Then charge the start bank with an ACR or combiner or with a DC2DC charger.

Make sure you have the alternator temp probe with the regulator to protect your alternator from cooking.

David

[Iggy]

Originally Posted by PennBruce

The batteries will be Lifepro4. I have room for either one 400ah, two 200ah or five 100ah. I'm am thinking Renogy.

I want to relocate the batteries under the berth in the rear cabin.

Bruce

Just an FYI: Look at the highest discharge current that you have or thats going to be pulled from the house bank. In my case it was the bow thruster. But this may not matter to you. My house bank and thruster are only 8ft apart so the builder or past owner went that route.

Renogy with one 400ah batteries, highest discharge is 350Amps. But two 200ah would be a total 400amps. Also five 100ah would be a total of 500amps.

Personally, I would go with two 200ah battery. It would be easier to carry 2 lighter batteries than one heaver battery. Plus if the BMS shuts down on one battery you have the other batter to fall back on. Redundancy. With five batteries you have a lot of wiring to do to balance that bank.

I tend to agree with David, but I felt better going the other way. My ALT is charging my starting bank and a 60A DC to DC charger does the house. If my Li house bank BMSs shuts down I can hit two switches disconnecting the house bank and use the starting bank to power the house. The other problem, if your charging the house bank and the BMS disconnects what happens to the ALT?

Here is a good link with TT's input on this. https://www.trawlerforum.com/forums/...nce-66233.html

There was something about this in the ABYC standards 18 months ago when I was planning. But I have heard that the ABYC standards on Li have been changing from time to time on this. Not sure what they are now.

[Jeff F]

Originally Posted by Iggy

Renogy with one 400ah batteries, highest discharge is 350Amps. But two 200ah would be a total 400amps. Also five 100ah would be a total of 500amps.

I'm not sure that's a good way to look at this. If in parallel there is no guarantee that load is evenly distributed across batteries, and if one BMS shuts down there's a danger of cascading shutdowns under high load.

[Iggy]

Originally Posted by Jeff F

I'm not sure that's a good way to look at this. If in parallel there is no guarantee that load is evenly distributed across batteries, and if one BMS shuts down there's a danger of cascading shutdowns under high load.

If the bank is balanced properly, than the load should be even across the each battery in that bank. There is account on how each battery would react in the real world, but balancing the bank would help to prevent this. This is one reason why balancing is done.

[sunchaser]

PB
"Marine how to", Rod Collin's website, has many good tips and articles on this multi layered subject. Nigel Calder is on top of this area as well. He has a great ongoing blog worth pulling up on UTube.

BTW, not all are fans of Renogy LFPs so double check pros and cons of others with Rod's website as a guide.

[mvweebles]

For LFP batteries suggest fewer the better. Use a power post to parallel them vs daisy chain (certainly true if you go with 5x100AH). Keep the cables exactky the same length.

I personally would avoid Renogy at all costs. They seem to have a relatively high DOA rate and RMA with them is impossible. If you do buy, do so via Amazon and plan to install ASAP within the return period.

Will Prowse, a solar geek, has an interesting YouTube channel where he tears down batteries and analyzes. Might be worth an hour perusing. I seem to recall he liked SOK batteries in the budget category.

I too was confused by guidance to charge to engine first. I decided it was dated advice from days before oversized LFP bank and DC-DC chargers.

Peter

[Ken E.]

I have a DC-DC charger in my RV and it works well in that application. But as mentioned above by David M, a better way for you would probably be charging the house bank with your alternator(s) and then using ACR's to maintain the start batteries, which is how my boat is set up and it works well

[Iggy]

Originally Posted by O C Diver

On my boat, one of the banks is charged off of another through the inverter and a battery charger. In configuring the setup, I rationalized that the largest bank should be charged off the alternator. It seems to me that the efficiency loss on most KW having to be bumped into one bank to be pushed into another is counter productive. I guess part of the question deals with how large a DC to DC charger you can get relative to your bank size.

Ted

I was rereading your post and I mean this in the best way. "one of the banks is charged off of another through the inverter and a battery charger" Maybe I am not understanding? But your taking 12V dc converting it to 120V AC and than back to 12V dc. Seam like too much of a loss.

On "efficiency loss on most KW having to be bumped into one bank to be pushed into another is counter productive." We do this all the time though using ACRs, isolators or combiners. There is almost no losses in doing it this way. WELL, some old isolators have a .6v drop.

[Iggy]

Originally Posted by Ken E.

I have a DC-DC charger in my RV and it works well in that application. But as mentioned above by David M, a better way for you would probably be charging the house bank with your alternator(s) and then using ACR's to maintain the start batteries, which is how my boat is set up and it works well

If done this way, than the ALT needs to be set up for Lithium charging. So when the ARC closes I am not sure how the starting bank and I would think they are a lead type battery would handle that charging profile? Would it be better or worse in time for the starting battery?

In How to Marine.


Under "When to Use a VSR/ACR/Combiner"
----------------------------------------------------
With that in mind;

If both banks can be charged within 0.1V to 0.2V of each other, an ACR is a fine choice

Same Chemistry & Same Charging Voltages = √

Same Chemistry & Very Similar Charge Voltages = √

*Mixed Chemistry & Same Charging Voltages = √

*Mixed Chemistry & Very Similar Charge Voltages = √

*Excludes mixing lead acid and Li-Ion batteries
----------------------------------------------------------------

He is not stating why. But i would think it the charging profile?

[O C Diver]

Originally Posted by Iggy

I was rereading your post and I mean this in the best way. "one of the banks is charged off of another through the inverter and a battery charger" Maybe I am not understanding. But your taking 12V dc converting it to 120V AC and than back to 12V dc. Seam like too much of a loss.

On "efficiency loss on most KW having to be bumped into one bank to be pushed into another is counter productive." We do this all the time though using ACRs, isolators or combiners. There is almost no losses in doing it this way.

I suppose I should have explained that better. My bow thruster bank is 24 VDC and the house bank is 12 VDC. The thruster draws 200 amps. For the normal 10 to 20 seconds of docking, it consumes under 30 watts. Using a 120 VAC to 24 VDC 6 amp battery charger allows it to be charged through the inverter while underway and maintained at the dock through shore power.

For my boat, I can consume 150 amps for hours while underway. This would include the clothes dryer through the inverter, buss heater blowers, and navigation equipment. Why add more complexity, failure points, and inefficiency instead of putting your KW directly into the house bank and distribution load center?

Ted

[Iggy]

Originally Posted by sunchaser

PB
"Marine how to", Rod Collin's website, has many good tips and articles on this multi layered subject. Nigel Calder is on top of this area as well. He has a great ongoing blog worth pulling up on UTube.

BTW, not all are fans of Renogy LFPs so double check pros and cons of others with Rod's website as a guide.

Not a fan of Renogy too. Panbo has two good write ups on KiloVault.

https://panbo.com/kilovault-hlx-batt...ity-and-value/

[Jeff F]

Originally Posted by mvweebles

I too was confused by guidance to charge to engine first. I decided it was dated advice from days before oversized LFP bank and DC-DC chargers.

I'd suggest that this became common practice in response to a few concerns specific to LFP, and has been aided by dc-dc chargers.

Pluses:
1) it's possible to keep the OEM alternator and regulator
2) by disconnecting the alternator from the LFP (i.e. through a dc-dc charger) the need for alternator protection against disconnect disappears
3) implementation cost can be significantly reduced

[Iggy]

Originally Posted by O C Diver

I suppose I should have explained that better. My bow thruster bank is 24 VDC and the house bank is 12 VDC. The thruster draws 200 amps. For the normal 10 to 20 seconds of docking, it consumes under 30 watts. Using a 120 VAC to 24 VDC 6 amp battery charger allows it to be charged through the inverter while underway and maintained at the dock through shore power.

For my boat, I can consume 150 amps for hours while underway. This would include the clothes dryer through the inverter, buss heater blowers, and navigation equipment. Why add more complexity, failure points, and inefficiency instead of putting your KW directly into the house bank and distribution load center?

Ted

OHHHH, that makes a lot more sense now!

If I went with a bigger thruster as mentioned in other thread. I was thinking of doing the same thing. Than I could keep the existing wiring by going to 24V.

[PennBruce]

myweebles:

I've spent hours watching Will's videos. They are very helpful.

SOK's are also a choice. Their shape would be easier to fit into the available space under the berth.

Thanks,

Bruce

Originally Posted by mvweebles

Will Prowse, a solar geek, has an interesting YouTube channel where he tears down batteries and analyzes. Might be worth an hour perusing. I seem to recall he liked SOK batteries in the budget category. Peter

[PennBruce]

Jeff F:

The internal regulated alternator will be replaced.

This raises another question. I will be installing a 100 amp (Balmar) alternator. Batteries have different max charging rates. Many are less then the nominal output of a 100 amp alternator. How is this handled?

How common is it for the battery management system (BMS) to disconnect the LFP battery?

Finally, how are costs reduced?

Thanks,

Bruce

Originally Posted by Jeff F

I'd suggest that this became common practice in response to a few concerns specific to LFP, and has been aided by dc-dc chargers.

Pluses:
1) it's possible to keep the OEM alternator and regulator
2) by disconnecting the alternator from the LFP (i.e. through a dc-dc charger) the need for alternator protection against disconnect disappears
3) implementation cost can be significantly reduced

[Jeff F]

Originally Posted by PennBruce

Jeff F:



The internal regulated alternator will be replaced.

Why?