question

24V Multiplus 3000 auxiliary DC max Amps?

If I read correctly, the 24V 3000 has a 12V dc aux output. What is amps continuous and max amp burst on this?

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Not sure, but i think it is 24vdc output not 12vdc on the Multiplus 24/3000

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Yes, that may be right. It seems that way, but the purpose does not make sense. Why 24v output, when all you need to do is tie to battery.

What is purpose to have 24v pass through? I was hoping its error in documentation and its actually 12v.

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Yes, that may be right. It seems that way, but the purpose does not make sense. Why 24v output, when all you need to do is tie to battery.

What is purpose to have 24v pass through?

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Jay Kote ·

To (trickle) charge a 24V starter battery.

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Daniël Boekel (Victron Energy Staff) ♦♦ ·

Limited value it would seem to me as I cannot think of any vehicle that uses 24 volt battery to start a starter. But okay. Better would be 12v (as far more common). Best would be a 12v/24v switch. This is something I've seen on another companies. (But if you do -- DO NOT let your engineer cheat and just put a resistor for voltage divider!!!! Make him do it right and use the resistor to 1/2 the frequency so the output is 12v not 24v).

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Yep 24v out on a 24v multi and 12v on a 12v multi.

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Install a small 24 to 12 VDC down converter if you want to use this function. For me i do not use this port on my Multiplus 24/3000. If i am plugged into shore power and need to charge my RV 12 volt system i would just plug in a trickle charger that has some smart function charging.

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Hi Tom,

I installed a MultiPlus 24/3000/70-50 120V in line with my travel trailer's shore power infeed. That is, I wired the shore power infeed through a 30A breaker then connected to the 120V AC input terminals of the inverter/charger with the AC output terminals connected to the trailer’s 30A/120V AC panel.

This method seemed the simplest and least invasive integration with the trailer’s existing AC/DC system. Everything onboard operates the same whether connected to shore power or operating on solar/battery power.

Virtually all RVs have an onboard 12V DC converter/charger installed by the manufacturer to power the 12V systems and to charge the coach batteries when plugged into shore power. In my Jayco, the existing IOTA DLS45 DC Converter (with the optional IQ4 Smart Charge Controller) remains in place (in the space under the fridge) providing 12VDC for onboard systems and smart charging for the 12V battery bank mounted on the reach.

Therefore, no need for a 24V to 12V step-down converter or an additional trickle charger.

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glenn-matthiesen ·

The only down side is power loss. At best the victron is 90% efficient. Your converter, if typical of RV converters is about 80%. So the 70% power going to battery.

30% good bit of loss when you figure you are using solar when not connected to shore.

In fairness, even with a buck converter, youll get 90%. So, you'll be 80% going to battery. So is 10% worth it.

Its good to reuse. But some would want that 10%.

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Jay Kote ·

Hi rvsolartech, while I get what you're trying to say, I'm not sure I agree with the math/logic. With any system configuration, there are going to be power losses.

The Multiplus 24/3000 is rated at 94% and the IOTA DLS45 is rated at >80%. By any comparison, this is quality equipment. The point is, many RV enthusiasts choose a 12V DC inverter or inverter/charger over a 24V DC unit because their RV has a 12V DC system. The efficiency/safety factors of a 24V system do not enter their equation.

When a 24V system is selected, most, if not all of the installations I've seen (on YouTube) ignore the existing onboard AC/DC converter and install a 24V to 12V step-down converter and/or an additional 12V battery charger. At the end of the day, where's the sense in that?

As I've stated, wiring an inverter/charger inline with the existing electrical system is the simplest and least invasive integration with the RV’s existing AC/DC system. Everything onboard operates the same whether connected to shore power or operating on solar/battery power.

Moreover, if a system is so marginally sized to worry about an occasional 11 amp 120AC load, you've got bigger problems to worry about.

Cheers,

Glenn

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glenn-matthiesen ·

Yes, as I said there is something be said doing it you way and I won't disagree with you. But 94% is peak eff for the inverter, it will float between 85% - 94% and so use 90% for figuring.

The 80% convert is compared to a buck converter that is more like 95 - 98%. So let's ignore the inverter for a moment. You will loose 15% - 18%. That's not a lot. If you assume 5 hrs of sun light a day, you are only loosing about 1 hr. (But this assume you got a good buck converter o/w you're back to same thing 80%).

Many people will not mind a 1 out of 5 hr loss of sunlight. Some will. I guess it's up to each person.

This also true for people who try to save money on wiring. They will accept 3% loss as this is "industry standard". But assume 1000W solar. You use it for 24 hrs (because their wires are being used 24hr a day). You have lost 30*24 = 720Wh. What is 720Wh? That's enough to keep your 40W laptop & energy efficient monitor running basically one work day.

p.s.

Truth advertising. I charge people to install buck converters and even replace their cheap wiring jobs -- they use 10AWG and 12AWG in places they really need 2AWG or better as they should be shooting for 0% loss. So you could argue I'm biased on this. But I feel like I'm being honest with the customer.

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Hi

Thought I would jump in and ask, I am using the aux output to change the starter bank had a 5amp blade fuse in it, but it blows that, is a start interupt relay needed or a larger fuse acceptable?

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Hi @Jwfrary

A 10A fuse should not be a problem.

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Are you going from 24v to a 12v "starter" battery? If that is the case, you probably don't want to do that. You'll need a charger that is capable of running on 24v and charging the right chemistry 12v.

Curious is the "starter" part of the vehicle starter battery system?

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