question

crazseas avatar image
crazseas asked

What's the best way to pull power from a main LiFePO4 24V bank to charge a smaller LiFePO4 12V bank?

I have:

2 LiFePo4 banks (24V main & 12V smaller),

one 12V lead acid starter battery,

one 24V alternator and

one 12V alternator.

I can use 1 "Orion-Tr Smart 12/12-30 Isolated DC/DC Charger", connecting the 12V starter battery, 12V alternator, starter motor (12V?) to the 12V LiFePO4 bank for alternator charging.

Can "Orion-Tr 24/12-30 Converter Isolated" be used to pull power from the 24V main LiFePO4 bank to charge the 12V smaller LiFePO4 bank (DC/DC charging), even though Victron states that "Not intended for battery charging"? Is there a better way?

Since there's only one 12V lead acid starter battery, can an "Orion-Tr Smart 24/12-30 Isolated DC/DC Charger(s)" be used to connect the 12V starter battery, 24V alternator, starter motor(12V?) to the main 24V LiFePO4 bank for alternator charging?

Thank you.

battery chargingOrion DC-DC Converters not smartorion dc-dc
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3 Answers
mvas avatar image
mvas answered ·

Use a DC-to-DC Charger

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crazseas avatar image crazseas commented ·

From Victron's diagram, DC to DC Charger needs to be connected to the alternator, starter battery and then the bank. How do you connect just between 2 banks with different voltage? Thanks.

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mvas avatar image mvas crazseas commented ·

Yes, it can be connected to the starter battery / alternator. But, nowhere does it say, it must be.

It can be connected between any two batteries, of the correct voltage like 24v & 12v.

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crazseas avatar image crazseas mvas commented ·
Thank you for your answers.
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bathnm avatar image
bathnm answered ·

@Crazseas Use an Orion TR Smart 24/12. This will take from the 24v bank and provide a 3 stage charge to the 12c lithium bank, configured with a lithium charge profile. The Orion TR (non smart) is basically a power supply, which will provide a single voltage.

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crazseas avatar image crazseas commented ·
From Victron's diagram, DC to DC Charger needs to be connected to the alternator, starter battery and then the bank. How do you connect just between 2 banks with different voltage? Thanks.
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kevgermany answered ·

I read three questions.

First, yes

Second, sort of, but better with a charger model

Third yes.

You're going to have to configure carefully. In automatic/engine detect mode, they need to see a charge level voltage to turn on. An alternative is manual switching with LH terminals.

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crazseas avatar image crazseas commented ·

Thank you. You mentioned that bank to bank charging is ok with converter, but better with charger. I thought the charger is only used for alternator to bank charging, no? How do you connect bank to bank charging with charger? The Victron's diagram doesn't show that info. The 3rd answer, you're saying it's ok to have the 12V charger AND the 24V charger be connected to the same 12V starter battery, while they're connected to their respective alternator and bank?

Assuming the one on the right is 24V, so both charger (24V and 12V) are connected to the same 12V starter battery and get power from their 12V or 24V alternator to charge their 12V and 24V banks?

screenshot-20230715-144233-832.png

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kevgermany avatar image kevgermany ♦♦ crazseas commented ·
Converter supplies a fixed output voltage, and hasn't got the ability to recognise when to be on or off. It also has no charge profiles. So you'd set its output voltage at battery float.

With non isolated devices in your system you need a common earth/ground.

All Orions are unidirectional. So the input positive goes to the source positive, output positive goes to battery to be charged positive. The chargers will normally use input voltage as the on/off trigger. So in a sequence like alternator/battery A/Orion/battery B, battery B will charge when the voltage on battery A is high enough to switch the Orion into charge mode. With lithium the voltage shift between resting and charging is very small, which makes setup tricky, here the LH terminals are your friend.


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