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DC-DC charger (B2B) options and general discussion

Hi do not really understand the difference
in the Specs: DCC50S
  • Designed to charge service batteries from two DC inputs—solar panels and alternator.
Which is B2B and Alternator , right? so looks like Dual and Triple Function?
Difference in the specs as compared to what? That is what I believe you think it is. A combination alternator charger, solar charger, and isolator, yes (also known as a dc dc charger, but having the mppt is non-standard and a ”bonus” with this unit, if you need it). whatever you get, it’s a good idea to make sure it is an isolator. Would be terrible to tap into your chassis battery system and drain them to your house batteries when the engine isn’t running.
 
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I would like to suggest adding a “max input (amps)” column to this table. My alternator has a max output rating of 250 amps at 24v. I have no intention of trying to push it to that limit, but I want to be sure that the b2b charger is capable of seeing those amps on the input and not frying... Alternately, if there are reasons this is irrelevant or there are other best practice ways to go about protecting the b2b charger, I am all ears. I have not done a lot of research into this myself, just yet. Only enough know what I want to do and to recognize some of the risks that need to be mitigated.
The alternator should supply only the current the b2b is drawing, not all the current that the alternator could possibly supply.
 
Yes, but how to see and control? Battery LED is green, which indicates battery is full but no trickle charging of starter measured?
What am I doing wrong?
Thx
The manual outlines the charger's behavior, it will only charge the starter battery if it's voltage is below a certain value.
 
The alternator should supply only the current the b2b is drawing, not all the current that the alternator could possibly supply.
Right, but what happens when the alternator current ramps up for other reasons? Or....perhaps a fault of some sort?
 
Some areas for further research/documenting:
  1. Which of these B2B's are isolated (or offer an isolated model)? I am aware Victron does, Kisae doesn't. Not sure about others. Anyone have more info to share?
  2. Power sharing, for the dual and triple input devices, how does the device manage inputs? The sub questions here are is it Solar and B2B or Solar or B2B, or a middle ground, and which source takes priority.
2. The Renogy dual input charger when the engine is running will allow for a maximum of 25A from both inputs, even if you are only getting a few amps from the solar. A switch to disconnect the solar panels is recommended so you can prioritize alternator charging when you need it on cloudy days.

The wording in the Kisae manual is a little vague, but I think it just switches between the solar input and alternator input depending on if the alternator is running.
 
Right, but what happens when the alternator current ramps up for other reasons? Or....perhaps a fault of some sort?
Alternators supply the amount of current being drawn by loads, the "extra" current would go to those loads not the charger. You can have a few LED lights connected to a large battery bank and they don't burn up even though the battery bank can supply enough current to burn them up because they are part of a circuit designed to only draw enough current to power the LEDs, the charger connected to your alternator is no different in concept.

Sure, something bad can happen, but any charger will likely have some form of built-in overcurrent protection and you should fuse the positive input wire.

If this were a problem then every electrical circuit on your vehicle would constantly be failing.
 
Alternators supply the amount of current being drawn by loads, the "extra" current would go to those loads not the charger. You can have a few LED lights connected to a large battery bank and they don't burn up even though the battery bank can supply enough current to burn them up because they are part of a circuit designed to only draw enough current to power the LEDs, the charger connected to your alternator is no different in concept.

Sure, something bad can happen, but any charger will likely have some form of built-in overcurrent protection and you should fuse the positive input wire.

If this were a problem then every electrical circuit on your vehicle would constantly be failing.
Ahh, well that seems to make sense, and thanks for that explanation. I guess part of what had me concerned is some of the first dc dc charger isolators I looked at several days ago, did specify a maximum input amperage. I will have to retrace my steps and make sure I understood what I was looking at. Thank you.
 
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2. The Renogy dual input charger when the engine is running will allow for a maximum of 25A from both inputs, even if you are only getting a few amps from the solar. A switch to disconnect the solar panels is recommended so you can prioritize alternator charging when you need it on cloudy days.
(y)
The wording in the Kisae manual is a little vague, but I think it just switches between the solar input and alternator input depending on if the alternator is running.
I confirmed with Kisae, if memory serves its Either/Or. I'll post the e-mail when I get a chance.
 
I would like to suggest adding a “max input (amps)” column to this table.
So my limited understanding is that one of the primary purposes/functions of these B2B chargers (what makes it safe to charge lithium from your vehicles charging system) is that they are "current limiting." LiFePO4 batteries are thirsty and can overtax an alternator if connected directly, The DC-DC charger acts as a middleman between the charging system and the lifepo4 battery and will limit the current to some maximum value (which I believe should be output current + inefficiency).

Someone can hopefully correct me if I got anything wrong, or incomplete.
 
Hi

ok, but Australia is having a lot of sun.....how man Watts do you have roofed?
Just 400w , and the redarc back then was a 40a output , batteries were 2x 140ah ex ups ( 47kg each )
Sold the redarc and batteries late last year , also the vehicle 20a redarc and 120ah agm , box etc ,
 
Thanks for creating this thread and collecting the data Dzi. First some extra data for your table and then I've got some general discussion.

You might want to include the Orion-Tr DC-DC Isolated Converters (non smart) in your table as they have 48v step down models.

I spotted this because that's the model I've been looking at getting for my build. I'd love some feedback on what I'm considering. I'm planning on running 48v LiFePo4 house batteries but floating my 12v Lead acid starter battery from it. Why? This way I can run all my 12v loads off of that battery including vehicle accessories. I don't like having to treat my headlights left on different to any other lights. It also gives me 1400 CCA of surge capacity if I ever needed more than the converter can produce in the short run.

I know the other direction is more common and I wouldn't mind being able to charge my 48v house bank off the alternator but it's just a nice to have feature that I don't think I'll need, I'd rather save fuel. If I ever add it later I would probably wire it up to a switch so I can enable it on downhill drives for regenerative engine braking, but that's mostly for my own satisfaction.

So questions for the hive mind:
1) does floating 12v loads on the starter battery sound sensible? (I know i risk not being able to start the bus if the converter dies in the night but I can deal with that)
2) is the Orion-Tr 48/12 the best solution for this? I suspect it's overkill when all I need is a cheap buck transformer but that's getting back to 1)
3) any clever ways to get my optional alternator charging as well?

Edit: I just noticed this thread "...concerns charging a LFP house bank from a vehicles starting system..." so feel free to tell me to go create my own for this question.
 
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Thanks for creating this thread and collecting the data Dzi. First some extra data for your table and then I've got some general discussion.

You might want to include the Orion-Tr DC-DC Isolated Converters (non smart) in your table as they have 48v step down models.
I'm not convinced the DC-DC converters should be included in this table, but that's something I have been meaning to look into more. I believe they are not designed for this purpose (B2B charging from vehicles starting system), though maybe they will work for this purpose (in a more basic capacity)? Is this something you have looked into?

I spotted this because that's the model I've been looking at getting for my build. I'd love some feedback on what I'm considering. I'm planning on running 48v LiFePo4 house batteries but floating my 12v Lead acid starter battery from it. Why? This way I can run all my 12v loads off of that battery including vehicle accessories. I don't like having to treat my headlights left on different to any other lights. It also gives me 1400 CCA of surge capacity if I ever needed more than the converter can produce in the short run.
interesting approach (y) I'm intrigued

Edit: I just noticed this thread "...concerns charging a LFP house bank from a vehicles starting system..." so feel free to tell me to go create my own for this question.
You could create your own thread for better visibility if you want, but I don't mind it being discussed here, since it is relevant to B2B charging broadly.
 
I'm not convinced the DC-DC converters should be included in this table, but that's something I have been meaning to look into more. I believe they are not designed for this purpose (B2B charging from vehicles starting system), though maybe they will work for this purpose (in a more basic capacity)? Is this something you have looked into?


interesting approach (y) I'm intrigued


You could create your own thread for better visibility if you want, but I don't mind it being discussed here, since it is relevant to B2B charging broadly.
I'm still in the early stages of scoping this out, perhaps I should ask Victron. Their data sheet says:
Adjustable output voltage: can also be used as a battery charger For example to charge a 12 Volt starter or accessory battery in an otherwise 24V system.
So I assume setting it to some nice lead acid float voltage like 12.8v will keep the battery happy and well tended to through its life without taxing it. But there's a lot of hoping going on there.

The idea to do this was inspired by @cinergi's build, but I cheaped out and didn't use a 12v LiFePo4 battery as my buffer.

If all else fails I suppose I can always run a Battery Tender Charger off my 120v inverter for proper(?) Lead Acid management logic. Hopefully there's a better option than that though.
 
I'm still in the early stages of scoping this out, perhaps I should ask Victron. Their data sheet says:

So I assume setting it to some nice lead acid float voltage like 12.8v will keep the battery happy and well tended to through its life without taxing it. But there's a lot of hoping going on there.
Yes I think this is a valid use case, but I would still confirm with Victron.

Similarly, you could possibly use it in the same manner with LFP set to an appropriately low voltage.

However one thing I believe its lacking that the Charger version has (apart from 3 stage charging), is awareness of the state of the vehicle charging system (not an issue for your usage probably, but as a starter --> house B2B is very important). It would not have the logic to know when to charge and when not to charge. There may be workarounds (a simple on-off switch is one but that would be susceptible to human error/forgetfulness)

The idea to do this was inspired by @cinergi's build, but I cheaped out and didn't use a 12v LiFePo4 battery as my buffer.
lead acid as the buffer might be better in some regards as well. Certainly simpler and cheaper
 
However one thing I believe its lacking that the Charger version has (apart from 3 stage charging), is awareness of the state of the vehicle charging system (not an issue for your usage probably, but as a starter --> house B2B is very important). It would not have the logic to know when to charge and when not to charge. There may be workarounds (a simple on-off switch is one but that would be susceptible to human error/forgetfulness)
Yes agreed. Anyone interested in using it this way would probably be best to wire a relay from their ignition switch (inline with an on-off switch). But at a certain point you're just building what you could have just paid Victron to build in.
 
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Some areas for further research/documenting:
  1. Which of these B2B's are isolated (or offer an isolated model)? I am aware Victron does, Kisae doesn't. Not sure about others. Anyone have more info to share?
  2. Power sharing, for the dual and triple input devices, how does the device manage inputs? The sub questions here are is it Solar and B2B or Solar or B2B, or a middle ground, and which source takes priority.
The renogy is also an isolator (one model is ignition, they also have one that auto senses voltage). Also, it looks like the red arc DPS is a dc power supply, not a b2b isolator/charger. Red arc does seem to have b2b charger/isolators but none appear to be 24v.
 
The renogy is also an isolator (one model is ignition, they also have one that auto senses voltage).
In this context I am using Isolated different than Isolator. The isolated DC-DC chargers will keep the two sides of your system separate even when connected. I'm probably explaining that horribly in technical terms, but that is the gist of it. This is different than a battery isolator. If you are a visual person like I am see the pictures I have attached. This shows an isolated DC-DC charger (first attachment) and non-isolated DC-DC charger. The main difference (maybe only difference is with the isolated the input and output circuits have their own dedicated negative, and the non-isolated have a common negative. In many cases this doesn't matter, in some cases it does. I believe the Renogy is non-isolated.
Also, it looks like the red arc DPS is a dc power supply, not a b2b isolator/charger. Red arc does seem to have b2b charger/isolators but none appear to be 24v.
Good catch, I think you are right, i'll update tomorrow.
 

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Here I am using Isolated different than Isolator. The isolated DC-DC chargers will keep the two sides of your system separate even when connected. I'm probably explaining that horribly in technical terms, but that is the gist of it. This is different than a battery isolator. If you are a visual person like I am see the pictures I have attached. This shows an isolated DC-DC charger (first attachment) and non-isolated DC-DC charger. The main difference (maybe only difference is with the isolated the input and output circuits have their own dedicated negative, and the non-isolated have a common negative. In many cases this doesn't matter, in some cases it does. I believe the Renogy is non-isolated.

Good catch, I think you are right, i'll update tomorrow.
ok, not trying to confuse the two or make a reference to isolated vs non, but in a b2b alternator charging system, ensuring that the chassis batteries are isolated when no power is supplied by the alternator seems like an important feature to note (unless all b2b chargers have this feature, which i would not take for granted). That is specifically what I am referring to.
 
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