DC-DC Converter instead of DC-DC Charger

svfalkor

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Apr 20, 2020
Messages
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Hi solar lovers!

I have the following system:

alternator -> starter battery (lead acid) -> [missing component] -> house battery (lithium) <- mppt charge controller <- solar

My starter battery is charged by the alternator, my house battery is charged by mppt controllers

To add redundancy I would also like to charge the lithium battery with a B2B charger, like Orion-Tr Smart DC-DC Charger Non-Isolated. However they are relatively expensive. I am wondering if I couldn't use a simpler DC-DC converter, like Orion-Tr DC-DC Converter and set the output to the lithium "float" voltage. I know it won't charge to 100% that way, but that's ok, its for filling up in the bulk stage.

I am pretty sure that setup wold work if either the mppt or the Dc Dc converter would be on. But what happens when they are both on and we are in absorption stage?
In this case
the mppt applies up to 14.4 Volt (Absorption)
the DCDC charger tries to apply 13.5 Volt (Float)

=> what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed?

Looking forward to your answers!
Thanks
Patrick
 

Dzl

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To add redundancy I would also like to charge the lithium battery with a B2B charger, like Orion-Tr Smart DC-DC Charger Non-Isolated. However they are relatively expensive. I am wondering if I couldn't use a simpler DC-DC converter, like Orion-Tr DC-DC Converter and set the output to the lithium "float" voltage. I know it won't charge to 100% that way, but that's ok, its for filling up in the bulk stage.
I'm pretty sure Victron discusses this as a possibility in one of their technical videos. Its something I watched a long time ago so my recollection is at best very hazy. There were some tradeoffs/downsides to using something not purpose built for the application, but I believe they considered it a valid solution with caveats.

I'll see if I can unearth that video.

I am pretty sure that setup wold work if either the mppt or the Dc Dc converter would be on. But what happens when they are both on and we are in absorption stage?
In this case
the mppt applies up to 14.4 Volt (Absorption)
the DCDC charger tries to apply 13.5 Volt (Float)

=> what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed?
good questions
 

pierre

Somewhere down South
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Dec 21, 2019
Messages
841
I am pretty sure that setup wold work if either the mppt or the Dc Dc converter would be on. But what happens when they are both on and we are in absorption stage?
In this case
the mppt applies up to 14.4 Volt (Absorption). THIS ONE WILL WIN.
the DCDC charger tries to apply 13.5 Volt (Float)

=> what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed? WILL STOP CHARGING - CURRENT CANNOT FLOW BACK INTO DC/DC.
 

Dzl

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Possibly this is the video I was talking about. I didnt have a chance to rewatch so I'm not sure, but you may want to check it out.
 

MakeMePower

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Oct 11, 2021
Messages
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for lithium its simple, set what ever voltage you want to charge too and be done. you don't need stages. it will start CC to CV. its an extremely simple charge setup

unless you want bluetooth, the other unit has no connectivity just a pot to adjust voltage.
 

Ampster

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for lithium its simple, set what ever voltage you want to charge too and be done. you don't need stages. it will start CC to CV. its an extremely simple charge setup
The only thing I would add is that is is helpful if the charging source can be programmable. There are really only two phases of any battery charging, Constant Current and Constant Voltage. All the Pb terms like Bulk, Absorb, Boost Float, Equalize and others are just CV or CC with different voltage and current settings. Depending on your use case you may want the charger to turn off completely at the end of the CV phase.
 

MakeMePower

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The only thing I would add is that is is helpful if the charging source can be programmable. There are really only two phases of any battery charging, Constant Current and Constant Voltage. All the Pb terms like Bulk, Absorb, Boost Float, Equalize and others are just CV or CC with different voltage and current settings. Depending on your use case you may want the charger to turn off completely at the end of the CV phase.

In a vehicle setting though, when is there every 0 load. i read this alot and when i did my rc stuff it made sense since there was only a battery, but my RV is never at 0 load, literally impossible unless i disconnect it, and if i am running the engine, I have other systems running.
 

svfalkor

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Joined
Apr 20, 2020
Messages
38
I am pretty sure that setup wold work if either the mppt or the Dc Dc converter would be on. But what happens when they are both on and we are in absorption stage?
In this case
the mppt applies up to 14.4 Volt (Absorption). THIS ONE WILL WIN.
the DCDC charger tries to apply 13.5 Volt (Float)

=> what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed? WILL STOP CHARGING - CURRENT CANNOT FLOW BACK INTO DC/DC.
Thank you! Thats the answer I was looking for.
 

svfalkor

Solar Enthusiast
Joined
Apr 20, 2020
Messages
38
for lithium its simple, set what ever voltage you want to charge too and be done. you don't need stages. it will start CC to CV. its an extremely simple charge setup

unless you want bluetooth, the other unit has no connectivity just a pot to adjust voltage.
Well I have a Battleborn battery bank and they recommend to use a "absorbtion" phase.
This is essentially just a higher voltage for a little while so that the BMS can balance. Since I have that programmed into my mppt controller there will be a situation where battery will have a higher voltage (14.4) than the setting for the DCDC converter (13.5). Thus my question if a DCDC converter can handle that.
 

svfalkor

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Messages
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The only thing I would add is that is is helpful if the charging source can be programmable. There are really only two phases of any battery charging, Constant Current and Constant Voltage. All the Pb terms like Bulk, Absorb, Boost Float, Equalize and others are just CV or CC with different voltage and current settings. Depending on your use case you may want the charger to turn off completely at the end of the CV phase.
I do want to turn the DCDC converter off at the "float" voltage setting. But the MPPT controller will bring the voltage higher up (for a short while so the battery can balance). Thus my question if it will harm the DCDC converter.
Additionally I will also add a manual switch, I will only use the DCDC converter if needed (the main power source is solar, assisted by wind)...
 

eXodus

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what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed? WILL STOP CHARGING - CURRENT CANNOT FLOW BACK INTO DC/DC.
correct, and towards the battery and the DC/Dc getting close in voltage level - charging will get incredible slow.

Voltage is like water - you got a lot of height difference between two things - water will flow fast - as soon as both things equal out - it crawls to a stop.
 
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svfalkor

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Messages
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correct, and towards the battery and the DC/Dc getting close in voltage level - charging will get incredible slow.

Voltage is like water - you got a lot of height difference between two things - water will flow fast - as soon as both things equal out - it crawls to a stop.
@eXodus, thats a good way to visualize it!

Although I think we have a different situation here.
Phase 1: DCDC converter Voltage > Battery Voltage: charging
Phase 2: DCDC converter Voltage = Battery Voltage: nothing happens
Phase 3: DCDC converter Voltage < Battery Voltage: What happens now?

Or to stay with your analogy:
Phase 1: DCDC bucket stands higher than battery bucket: Water flows DCDC => battery
Phase 2: The DCDC bucket is at the same height as the battery: nothing can flow in either direction
Phase 3: The DCDC bucket is lower than the battery: what happens now? Does now the battery pour into the DCDC bucket? This is the question I'm looking for.
Or maybe to rephrase it: Does the DCDC usually have a valve that lets the water run into only one direction (out instead of in)?

As for why the battery bucket is higher than the DCDC bucket: Since the battery is charged by a proper mppt charger that will temporarily raise the voltage above the DCDC voltage.
 

Dzl

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Voltage is like water - you got a lot of height difference between two things - water will flow fast - as soon as both things equal out - it crawls to a stop.
I (have no formal electrical education (neither theory nor practice)), struggled with an intuitive understanding of the basic units at first (knew how to use them but didnt *understand* them). The water analogy, and especially conceptualizing voltage as something akin to "electrical pressure" or a pushing force was what helped it all click for me, and finally turned I = V/R (or V = IR) from a formula that I knew how to use, into something that I actually intuitively understood (at least a little).
 

eXodus

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Messages
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Phase 3: The DCDC bucket is lower than the battery: what happens now? Does now the battery pour into the DCDC bucket? This is the question I'm looking for.
Or maybe to rephrase it: Does the DCDC usually have a valve that lets the water run into only one direction (out instead of in)?
very likely a converter will have diode at the output which in the water analogy, acts as check-valve - or backflow preventer.


Voltage is water pressure in bar or psi.
Amps is diameter of the pipe

Resistance/Resistor is restrictive piece in the pipe

A capacitor is a Pressure tank (bladder pressure tank)

Watt is total flow of the water


The water analogy, and especially conceptualizing voltage as something akin to "electrical pressure" or a pushing force was what helped it all click for me, and finally turned I = V/R (or V = IR) from a formula that I knew how to use, into something that I actually intuitively understood (at least a little).

Good that I taught high school engineering once upon a time :)
The water analogy is not perfect, but good enough for many purposes.
 

-sgt-

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Oct 26, 2021
Messages
5
currently I'm on progress to build a kind of "Power Box" for my car...
and to fill the "missing component" on your system, I used a equipment which maybe suit with your situation...
The box consist of Atempower and DC-AC inverter...
The battery was installed out of the box...
Still ongoing project, not yet finished, since it was my week end DIY activity...
Need make a good ventilation to make sure inside box temperature kept cool...
Awaiting my 6 cm fan (2 pcs) to replace the original fan from inverter...


Hi solar lovers!

I have the following system:

alternator -> starter battery (lead acid) -> [missing component] -> house battery (lithium) <- mppt charge controller <- solar

My starter battery is charged by the alternator, my house battery is charged by mppt controllers

To add redundancy I would also like to charge the lithium battery with a B2B charger, like Orion-Tr Smart DC-DC Charger Non-Isolated. However they are relatively expensive. I am wondering if I couldn't use a simpler DC-DC converter, like Orion-Tr DC-DC Converter and set the output to the lithium "float" voltage. I know it won't charge to 100% that way, but that's ok, its for filling up in the bulk stage.

I am pretty sure that setup wold work if either the mppt or the Dc Dc converter would be on. But what happens when they are both on and we are in absorption stage?
In this case
the mppt applies up to 14.4 Volt (Absorption)
the DCDC charger tries to apply 13.5 Volt (Float)

=> what happens to the DCDC charger when it's output voltage is lower than the battery voltage? Will it just stop charging? Or will it be destroyed?

Looking forward to your answers!
Thanks
Patrick
 

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