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tara-dee avatar image
tara-dee asked

Victron Orion 24/12 25a Max Output Current + Fuse Sizing

Hi All,

I'm looking to order a Victron Orion 24/12 25a Converter to power 12v domestic boat electrics from 24v battery system. Few quick questions:

1. Do we know for how long the max 35a output current rating is recommended? There's a small chance my 12v draw may jump above 25a for approx. 5 mins when my 12v diesel heater startup glow plug is on (it draws 10a!)

2. Assuming it is advisable to work to a 35a max output current, I'll have a 40a fuse on the 12v output cable and 20a fuse on the 24v input cable (because 35a @ 12v = 17.5a @ 24v). Does this sound OK?

3. Or, if 25a is the strict maximum output I should plan for, would it be advisable to fit a 25a breaker to the 12v output to protect the Orion if draw does go above 25a? (it's pretty unlikely this will ever happen, as everything would need to be on, inc. horn, headlight, bilge pump, water pump etc)

Thanks

Orion DC-DC Converters not smartfuses
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11 Answers
kevgermany avatar image
kevgermany answered ·

The max current is for a few seconds only. Might depend on which model, but the tr smart isolated manual says 10s. You can download the manual for the charger you're considering.

Fuse input at the battery end for max current. Output close to the Orion as well if you wish.

Remember that pumps and other equipment can have a high startup current. This is the reason for allowing temporary overload.

You could try it like this. If necessary add a second Orion to cover the heater.

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tara-dee avatar image
tara-dee answered ·

Thanks for taking the time to reply, that's all really helpful.

The info in the manual for non-isolated is quite limited, assuming this is the right one https://www.victronenergy.com/upload/documents/Manual-Orion-DC-DC-converters-non-isolated-2412-25A-EN-NL-FR-DE-IT-PT-ES.pdf so, I'll go with the 10s you quote.

Even if it's longer than 10s for non-isolated, I can't believe it's going to be as high as 5 mins. So I won't go over 25a, and do as you suggest.

Just to completely clarify - and apologies if this should be obvious - but when you say "fuse input at battery end for maximum current", do you mean the input should be fused for maximum current at 24v - ie 17.5a (20a fuse)? Or simply fused for the maximum current in data sheet ie 35a (40a fuse)?

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kevgermany avatar image
kevgermany answered ·

Thinking about this I realised that I have the same one in my van. If I can think of a safe way to do it, I'll measure.

Fuses are to protect wiring. So they need to be able to handle the current in the circuit they protect but blow if it is exceeded. So on the 24V side, yes 20A is good. And double on the 12V side. There's another recent thread where someone asked about fusing the output side. Your wire should be sized to handle max continuous current. So if there's a short and you don't mind the unit draining the battery at full power you can skip it.

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tara-dee avatar image
tara-dee answered ·

Only if you can think of a safe way to do it!

And, understood. Thank you for clarifying. Have checked out the other thread on output fusing too. Is making a lot more sense to me now. Thanks for your help on this.

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tara-dee avatar image
tara-dee answered ·

Hi again... after a little more research... I have a further question... could I add a buffer battery to handle diesel heater startup load?

To be sure, the 24v Lead Carbon batteries to be connected to Orion 24/12 inputs are for electric propulsion, with 800w solar.

The plan was already to have a 100ah 12v backup battery, charged via an additional small solar setup (160w w/ 15a MPPT). And use a simple selector switch to draw from the Orion 24/12 output or 12v backup battery, as needed.

But, could I instead place the backup battery in parallel with Orion 24/12 25a outputs and the 12v loads?

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tara-dee avatar image
tara-dee answered ·

convertercircuitexample2.jpg


Just roughly added above idea to relevant part of my schematic.

My thinking is that..

When Orion is switched on, it would supply load to 12v system (with option to trickle charge 12v battery). 12v LA battery would take strain when loads higher than Orion output...?

When Orion is switched off, LA battery would power 12v system alone.

Does the above make any sense? It may not.

What I can't wrap my head around is how the Orion and solar MPPT would interact when they're both supplying power..

Sorry that I'm going a bit off my own topic here, but just trying to work out the best way to do this! Any thoughts appreciated.


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kevgermany avatar image
kevgermany answered ·

Haven't found a safe way yet. I have some power resistors, but not enough.

On the extra battery. Yes can do. Ignore solar for a minute. That Orion is a simple fixed voltage charger. So a battery connected to the output will be charged as needed all the time the Orion is switched on. Best to adjust the Orion output to the float voltage of the battery. That's your trickle charge.

Solar will co-exist happily. MPPT will just apply a higher voltage than the Orion output, effectively shutting off the Orion. I guess the idea here is to prevent the backup charging and other dc loads from discharging the main house bank.

But this is quite expensive. Might be better adding a second Orion in parallel and do away with the extra battery. That gives you 50A output. And route the solar to the 24V system. Check your panels have enough voltage, you'll need about 33V minimum. Wire them in series if needed.

If you use these orions as chargers, don't set the voltage too high. Keep it at float. Charge rate will be lower, but you won't shorten battery service life by keeping them at too high a voltage/current.

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Extra thought. This is getting a little complicated. Might be possible to simplify.
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tara-dee avatar image
tara-dee answered ·

Hi again,

Cheers - that makes a lot of sense. I can see how parallel Orion Converter (or the larger output Orion models) would probably be best option in many cases.

There's a few reasons I'm thinking it be best go the way of backup/buffer battery in my case.. as long as I've now got my head around things correctly.

To explain my thinking best I can...

The constant 24v draw from my electric drive motor is roughly 40a - although more like 25a with 800w solar offset on a sunny day. I want to keep the rate of discharge on 24v batteries as low as possible, to maximise capacity. So I want the option to draw 12v domestics purely from a backup battery (ie turn off the Orion converter) when using the electric motor.

So, the purpose of backup/buffer battery would be:

A) Provide an excess 12v 'buffer' load during diesel heater startup as mentioned in my last post

B) Provide power to 12v domestics temporarily when electric motor is drawing from main bank and I have turned off the Orion.

*It helps expense-wise that I already have a spare 100ah 12v battery lying around!*

Reckon I'd generally keep the Orion output at 13.2v and have the 160w backup solar MPPT keep the 12v backup battery charged. Turning up the Orion output voltage to 13.5v trickle charge would simply be a useful option to have.

Be great if you could let me know any flaws in my logic here.

Really appreciate you putting things in layman's terms for me. Hope it's also helping others who finds themselves a bit confused on this subject.

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tara-dee answered ·

I do also have a small further query re your last post:

The Orion would effectively be shut off when a 12v backup battery wired in parallel is being charged via solar MPPT. Gotcha! But, what would happen if the draw from the 12v domestic electrics surpassed the charge current from the MPPT? Would the Orion kick back in and provide power? Or would the backup battery simply get discharged with the Orion remaining shut off?

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kevgermany avatar image
kevgermany answered ·

Makes sense.

You have the Orion as a power supply. It's outputting constant voltage when turned on. If the voltage in the output side is higher than this setting, current won't flow out of the Orion (e.g. when MPPT charges). If voltage drops due to load, current will flow from the Orion.

So the MPPT will not turn the Orion off, it simply blocks the output.

Maybe think again about the Orion output voltage. Apart from shortening battery service life by keeping it at too high a voltage, think about what the interaction is with the MPPT. Usual AGM settings will be absorption 14.4, float around 12.7V. Without the Orion the MPPT will switch to absorption for a while, then drop to float voltage because the battery is full. This is lower than your Orion setting and so the Orion will push from the main bank continuously, mppt continues to see 13.5V on the output side, so stats in float mode and delivers nothing. Meanwhile you think the solar side is servicing the load, aided by the aux battery.

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tara-dee answered ·

Great thanks. Hmm OK. So to be sure I understand:

Working alone, an MPPT connected to 12v batteries would normally see a low battery voltage ie 12.0v and do a Bulk->Absorbtion->Float charge.

But if the Orion is there holding the 12v system at 13.5v, the MPPT would instead see the 12v battery as charged and go into float mode?

Have I got that right?

Would it be the case even if the Orion output is set at default 13.2v? Or even lower?

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Yes, correct.


Orion output must be set to suit the battery. AGM will be something like absorption 14.4V, float 12.8V. If you don't do this it will overcharge the battery and shorten its life. Might even cause overheating or worse.

Might be an idea to think about how 3 stage charging works. First stage, bulk is to push as many amps in as the battery will take. Voltage will rise as the battery charges. At the absorption voltage the battery is round about 80% charged. Voltage is fixed at this level and the charge current drops as the remaining capacity is filled. Charger monitors the current and when it drops to a low level, switches to the float voltage. This is the normal fully charged voltage of the battery. A small current continues to flow through the battery, maintaining charge, but not enough to damage the battery or wear it out prematurely. If the voltage is kept above float, a higher current flows, which will accelerate wear and shorten battery life.

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