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Old 11-08-2022, 06:06 PM   #1
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Building 24v system, best way for 12v side?

I am looking for my next trailer and am thinking out the power system in my head. It will be a 50A trailer used full time primarily boondocking with power needs for remote working.

What I am considering:

Start with one Multiplus ii 24|2x120 inverter charger but leave space and a junction boxes for adding a second one in the future, 2,400W for the entire trailer at first but then 4,800W output with second unit. Once set to parallel mode I can simply join, B->B, R->R, G->G, W->W and be all good

4 Gamechanger batteries wired as two 24v 270Ah battery banks each connected parallel via a Lynx Power In (so 24v @ 540Ah), or some other similar capacity setup.

1.2-1.6kW (or more in future if space allows) of solar using 24v panels and appropriate SCC. I know I don't have to use 24v panels but smaller wiring is good. Maybe go to higher voltage, still need to decide but 24v min.

Lynx Shunt and one Lynx Distribution box, Cerbo GX and all the cool and yet annoying bits in the middle

Where I am looking for feedback:

Given the above 24v stuff being currently isolated from the 12v house system, I was thinking I could just leave a basic AGM battery in the factory location and let the converter charge it and power the rest of the 12v needs from the inverted power. Like being on shore power in an OEM config. Since the 24v system is isolated, there is no loop issue

I know there are stacked losses along the way, but with this big of a system, it shouldn't even be noticeable right? I mean the inverter(s) will basically be on all the time thus the converter is powering the 12v side as-is.

I could put a small 24|12-20 DC-DC converter in the mix and directly charge the "house" battery from my 24v battery bank and this would allow my big solar system to charge the house battery via that DC-DC if/when in storage but would rarely get used since most of the time the inverter(s) will be on and thus the converter running for lights, fridge, etc.

Or put a larger Orion unit, like the 24|12-70A version and pull direct from my main battery bank to run the entire trailer 12v side, getting rid of the house battery and factory converter since the Orion is 70A capable. Breakaway brakes and other hardwired safety stuff would still work.

Any opinions on those options?
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Old 11-14-2022, 10:26 AM   #2
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Only thing I would question about your well laid out plan is why the need for a 70a 12v converter? 20 should be plenty I would think. Even with a 12v freezer and all lights on I've not seen more than 15-17 amps on the 12v system, tho I don't have a propane fridge or furnaces.
Also, I could be wrong, but since you are getting the 24v MultiPlus, it will not touch or charge your 12v battery system, hence the need for the separate converter.
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Old 11-14-2022, 01:54 PM   #3
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Originally Posted by un4givn85 View Post
Only thing I would question about your well laid out plan is why the need for a 70a 12v converter? 20 should be plenty I would think. Even with a 12v freezer and all lights on I've not seen more than 15-17 amps on the 12v system, tho I don't have a propane fridge or furnaces.
Also, I could be wrong, but since you are getting the 24v MultiPlus, it will not touch or charge your 12v battery system, hence the need for the separate converter.
I don't know the amps for the slides or tongue jack or auto level system and was assuming they could be fairly high. If a 20 or 30 amp unit works then great, save me some money.

Correct the 24v multiplus won't directly charge the 12v side, but since it will always be inverting given the solar and battery capacities I plan, the OEM converter will have 120v power and that will will supply the charge to the 12v system and well as support the 12v loads.

But that is why I asked my question since it is less efficient to go 24v DC -> 120v AC -> 12v DC when I could just go 24v DC -> 12v DC via a separate converter and bypass the factory AC->DC converter all together.

Maybe I have been focusing the 45-65A output of the converter for charging purposes and not just on house loads. I'm still wrapping my head around paralleling split phase 120v 50A circuits so it could be possible I focused on the wrong requirements....
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Old 11-14-2022, 02:25 PM   #4
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Quote:
Originally Posted by TravelSolo View Post
I don't know the amps for the slides or tongue jack or auto level system and was assuming they could be fairly high. If a 20 or 30 amp unit works then great, save me some money.

Correct the 24v multiplus won't directly charge the 12v side, but since it will always be inverting given the solar and battery capacities I plan, the OEM converter will have 120v power and that will will supply the charge to the 12v system and well as support the 12v loads.

But that is why I asked my question since it is less efficient to go 24v DC -> 120v AC -> 12v DC when I could just go 24v DC -> 12v DC via a separate converter and bypass the factory AC->DC converter all together.

Maybe I have been focusing the 45-65A output of the converter for charging purposes and not just on house loads. I'm still wrapping my head around paralleling split phase 120v 50A circuits so it could be possible I focused on the wrong requirements....
I did miss that you were working on a travel trailer....
It's different when you have to consider those items on the 12v system.
In your situation, I think I would go 24v-12v DC-DC converter and eliminate the factory converter.
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Old 11-14-2022, 02:31 PM   #5
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Originally Posted by un4givn85 View Post
I did miss that you were working on a travel trailer....
It's different when you have to consider those items on the 12v system.
In your situation, I think I would go 24v-12v DC-DC converter and eliminate the factory converter.
I have not decided on TT or 5er but I think I'll go the DC-DC option
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Old 11-17-2022, 08:42 AM   #6
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I've had a similar Victron system in place for 2 1/2 years now. I have dual 24/3000 Multiplus inverters with Cerbo, Lynx, and Orion DC-DC (2) and we went with dual Orion 24-12/70 converters as the leveling system in our DP calls for a maximum of 125A on the 12V side.....even though real-world has been much lower.

I would recommend the 24-12/70 as it's really not that expensive at around $135-150 based on where you buy it in the whole scheme of things. One of the nice things about those converters is that they can be daisy-chained if more capacity is needed (based on whether you go 5er or TT).

You will have a great system there........ one thing to remember is not only will you get more wattage with a second inverter/charger but also an additional 70A (@24V) of charging and I'll tell you that when you're putting 140A into your batteries (the equivalent of 280A@12V) your batteries will get topped off pretty darn quick
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Old 11-17-2022, 06:16 PM   #7
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I have a similar setup in my class A and thinking of swapping from 12 to 24v because of solar. I went with a Quattro 5000w as it's plenty for my needs. Also the Quattro has 2 inputs so you can run shore/generator and it'll automatically transfer with no loss of power. I'm thinking the 24/12-70 since its pretty cheap and you can easily add more.

Another thing to note the MP and Quattro have a trickle charger port inside.. at least the 12v does. Not sure about how the 24v works and if it trickle charges to 12v but with mine I use for my starter batteries to trickle charge them.

Remember you need a 24/12v converter that's adjustable to 13.4v or whatever your charge rate is on the "house" battery if you go that way. Orion are adjustable but the cheap Amazon ones aren't. He'll you could even just use a battery tender type for the "house". I was just looking at a sailboat that even uses separate solar panels to trickle charge the engine starter battery for each engine separately.
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