DC-DC Charger

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
Jeff F said:
That's not correct. The BMS in this context is just an on/off switch. It's the regulation on the charge device that limits current when the battery is fully charged. The BMS is standing by during this.
Click to expand...

I am not sure what context your taking about in this.

Let me correct myself, the setting within the charger will turn the charger on or off. What the batteries will accept is up to the BMS. Or at lest thats what was explained to me by tech support. Not all BMSs are created equally.

Charger settings: Li do not like a constant charge voltage. So my charger/inverter and solar are set to turn on 12.5 volts and turn off at 14.1. Once they hit 14.1 they slowly drop to 13.5volts. So there is this period of on-off charging. Rather than a constant charge as little as it may when using a lead type battery.
 
Last edited:
Iggy said:
Let me correct myself, the setting within the charger will turn the charger on or off. What the batteries will accept is up to the BMS. Or at lest thats what was explained to me by tech support. Not all BMSs are created equally.
Click to expand...

The BMS will shut the battery off if the charging source goes crazy and grossly overcharges the battery. But that's an exceptional case. In practice it should be invisible.

If the BMS ever steps in to limit charge something is seriously wrong.
 
PennBruce said:
Okay,

Getting back to subject of DC/DC chargers. These chargers are designed to charge the house bank from the start batteries. They detect that the alternator is working and trigger the DC/DC charger.

I (and others) want to use it by having the alternator charge the house bank and then the DC/DC charger charges the start batteries. No problem, the charger detects that the alternator is working and triggers the DC/DC charger.

However, when the house bank is being charged by an A/C charger or solar how is the DC/DC charger triggered?

Or do I need to add a second A/C charger to handle the start batteries?

Bruce
Click to expand...
Bruce, the charger is not designed to charge from a starting battery. It is designed to charge from one bank to another. It doesn't care which is the master.
 
Correct me if I'm wrong, but I thought the big ABYC issue with drop-in LFP batteries was the requirement for a BMS to signal that it's going to disconnect the battery bank before it actually does it. This to allow time to do something before your house bank and potentially your MFD, autopilot, etc. goes offline.

This seems to require an external BMS to manage the LFP batteries as it'd be hard to know what to do if a single battery in your bank sends the signal.
 
heysteve said:
Correct me if I'm wrong, but I thought the big ABYC issue with drop-in LFP batteries was the requirement for a BMS to signal that it's going to disconnect the battery bank before it actually does it. This to allow time to do something before your house bank and potentially your MFD, autopilot, etc. goes offline.

This seems to require an external BMS to manage the LFP batteries as it'd be hard to know what to do if a single battery in your bank sends the signal.
Click to expand...


I was told that the standard has changed. The warning signal is no longer needed. But for me, that's why I like the idea that I can bluetooth into the batteries.
 
Jeff F said:
It's missing the alternator shut down signal from the BMS.
Click to expand...


OK, that's not required. The requirement, and it's only a note so really just a suggestion, is a reminder that the BMS can disconnect at any time and needs to be taken into consideration in the system design. There 'might' be a statement about not damaging other equipment, but I'd have to check.


As this and other discussions have covered, there are multiple ways to protect an alternator from sudden unloading. A BMS shutdown signal is one way, as is a clamping diode like the Sterling or Balmar products. Throwing in a lead battery also solves that problem, but it creates a different one by mixing battery types in the same bank, so it's not recommended.
 
It certainly would be helpful if the ABYC clarified their thinking on alternators and lithium batteries.

It’s really not an electrical safety issue if you blow your alternator diodes — so I don’t know why the ABYC is getting involved. Cruisers have been blowing the diodes for decades with lead acid batteries by turning off their battery switch while the engine was running.

In all those years the ABYC never felt the need to protect against this by requiring some sort of interlock in the battery switch. Worse, I believe they continue to allow the alternator positive cable and starter cable to be un-fused. A clear safety hazard.
 
twistedtree said:
OK, that's not required. The requirement, and it's only a note so really just a suggestion, is a reminder that the BMS can disconnect at any time and needs to be taken into consideration in the system design. There 'might' be a statement about not damaging other equipment, but I'd have to check.
Click to expand...

Thanks. I just went back and reread your post on this. https://www.trawlerforum.com/forums/showthread.php?t=66233


It's very well written, and doesn't talk about the need for comms. Sorry, I get much of my perspective from following along on this forum. I haven't read the ABYC standards.

I'd hate to be perpetuating a myth.
 
CarlF said:
It certainly would be helpful if the ABYC clarified their thinking on alternators and lithium batteries.

It’s really not an electrical safety issue if you blow your alternator diodes — so I don’t know why the ABYC is getting involved. Cruisers have been blowing the diodes for decades with lead acid batteries by turning off their battery switch while the engine was running.

In all those years the ABYC never felt the need to protect against this by requiring some sort of interlock in the battery switch. Worse, I believe they continue to allow the alternator positive cable and starter cable to be un-fused. A clear safety hazard.
Click to expand...


I'm not sure what's unclear if you read the spec. I agree that blowing an alternator isn't necessarily a safety issue, though it could lead to one. But that's one reason why some things are Notes and not requirements.
 
catalinajack said:
Bruce, the charger is not designed to charge from a starting battery. It is designed to charge from one bank to another. It doesn't care which is the master.
Click to expand...

I agree, as mentioned I am charging my Li bank with two DC to DC chargers and a charger/inverter. So now the charger/inverter has nothing to do with the starting bank. I added a 17A charger that I use when in my slip.

I added and VSR and switch to that charger to keep the genset battery fully charged too. That switch is only turned on during the winter months since the boat is on the hard.
 
CarlF said:
It’s really not an electrical safety issue if you blow your alternator diodes — so I don’t know why the ABYC is getting involved. Cruisers have been blowing the diodes for decades with lead acid batteries by turning off their battery switch while the engine was running.
Click to expand...

As an armchair observer, I'd note a couple of key differences. First is that people are going to max sized alternators along with LFP. So max continuous charge rate is probably triple OEM. 150a is more dangerous than 50.

The other difference with BMS vs disconnect switch is the scale of damage. Both may take out an alternator, but a BMS shut off exposes the house system to a sudden voltage spike, which can take out electronics etc in the worst case.

It's a greater threat to vessel safety, and probably a much bigger insurance claim.

I agree that your system is well thought out, properly configured and perfectly safe, as is mine, almost. But it's far from idiot-proof.
 
Last edited:
I have a large solar bank and 50 amp ac charger for my LiFePO4 200ah house bank battery on my motor yacht. I have a dc to dc charger for my AGM start bank for solar charge and my engine alternators charge only the AGM start bank. This was preserved as a means to continue to use the existing alternators, AGM batts and regulators. Battey switch is never set to both! Only disappountment is the BMS output limit is 100amp sustained. It will not run my 2000 watt inverter.
 
MVDarlin said:
I have a large solar bank and 50 amp ac charger for my LiFePO4 200ah house bank battery on my motor yacht. I have a dc to dc charger for my AGM start bank for solar charge and my engine alternators charge only the AGM start bank. This was preserved as a means to continue to use the existing alternators, AGM batts and regulators. Battey switch is never set to both! Only disappountment is the BMS output limit is 100amp sustained. It will not run my 2000 watt inverter.
Click to expand...
You lost me.
what is a large solar bank? watts?
why do you have a DC2DC charger for AGM start, do you have input from solar bank that way?
Your 200Ah house bank does not run a 2000 watt inverter then what does?
Besides shore AC, where does AC come from to charge the LiFeP04?
 
He lost me a little too.

A 200Ah bank is small for the house. It sounds like he has two ALTs. So why the DC to DC charger than?
 
You must log in or register to reply here.

Similar threads

X
Batteries
Replies
12
Views
1K
Barking Sands
Barking Sands
Mischief Managed
Interesting "trick" to improve dual alternator charging performance
Replies
3
Views
1K
Mischief Managed
Mischief Managed
dhays
Question on Victron Orion DC/DC charger settings
Replies
5
Views
432
dhays
dhays
CharlieO.
Another Alternator Question
Replies
14
Views
1K
CharlieO.
CharlieO.
X
New Lithium Bank
Replies
1
Views
403
READY
R

Latest posts

Back
Top Bottom