Sizing a 24 to 12 volt converter for 5.0

[GregWCIL]

Hello all,


I am planning an electric upgrade on a 5.0 to a 24 volt system. What size converter do I need to reduce the 24 volts to 12 for the existing fuse panel?

Some details:

Am going with the Norcold compressor fridge but plan to run it on the native 24 volts of the new system.
Looks like there are typically 7 other 15 amp 12 volt circuits. That would be 100 amps.

Largest Victron offers is an Orion 24-12 v. converter with 70 amps. I see some folks using much smaller such as 40 amp converters.



We recently signed off on our build sheet for a 5.0 for June completion so I don't have the camper yet to check and a search here didn't turn up this answer.


Thanks,
Greg


edit to add: Will the existing fuse panel accept 6 guage wire on the input?

[alanmalk]

Just one question. Have you considered going in the "opposite" direction? That is, staying with the original 12 Volt system and boosting one circuit (the refrigerator circuit) with a voltage booster?

[GregWCIL]

I've been studying this for over a year and I've gone back and forth. 12 volt is easier, but I have a 1600 watt solar array planned and 24 volt batteries and SCC's take best advantage of that.

I'm planning on switching the fridge to 24 volt (anyone know how that is done on the compressor fridge?) for two reasons: Less voltage loss with a given wire size and keeping a constant load off of the 24-12 converter.

[Centex]

Just FYI attached find the 'As-Built / As-Delivered' electrical schematic and DC fuse/distribution for my 2021 5.0. Note not everything powered by 12VDC is routed through the WFCO DC fuse panel (stabilizer jacks).

Note also this trailer does not have:

• Power awning
• MaxxFan vent
• any solar or lithium related options
• any other 12VDC options

Finally, note that my OE WFCO 8955lis Power Center Converter (~12VDC) section is rated to deliver a maximum of 750 watts continuous power with a rated DC current of 55A to the internal fuse panel. You can get these values for whatever power center ETI installs in your trailer from the Manual download on the WFCO website.

As always, anything could be different on your trailer as it is delivered (hint - don't get too invested in details before you actually have your trailer in hand and have thoroughly examined what you actually get in the way of electrical equipment, wiring, etc .

I hope perhaps this data is useful for your project planning?

Have Fun!

[GregWCIL]

Hey Alan, good to hear from you. I'll shoot you an email this evening. Maybe we can visit by phone if you are available. I have lots to catch up with you about.


I understand about needing to see the trailer first but I plan on taking some of the basics along when we pick up the camper and install before our long trip home. Thus I'm trying to plan ahead as best I can.

[hugh]

I have the same question, as I'm considering a 24V upgrade for my 21C when it arrives in July.


It seems the Victron 70A would definitely work, but might be overkill if the surge currents aren't too large.

[GregWCIL]

Originally Posted by hugh

I have the same question, as I'm considering a 24V upgrade for my 21C when it arrives in July.


It seems the Victron 70A would definitely work, but might be overkill if the surge currents aren't too large.

Of course it depends on the size of your system. In my plan it happens to give me the flexibility of 4 parallel panels or 2 series, two parallel. I like keeping options open.

[alanmalk]

Originally Posted by GregWCIL

...
but I have a 1600 watt solar array planned
...

Clearly you are planning to generate, and use, 10 times more power than I do while camping, so my questions may be biased by my smaller outlook.

Another question: Have you considered 2 buck converters with a rating of 50 Amps each to achieve your goal of 100 Amps (at 12 V)? It is my understanding that they can be paralleled easily.

[GregWCIL]

Originally Posted by alanmalk

Clearly you are planning to generate, and use, 10 times more power than I do while camping, so my questions may be biased by my smaller outlook.

Another question: Have you considered 2 buck converters with a rating of 50 Amps each to achieve your goal of 100 Amps (at 12 V)? It is my understanding that they can be paralleled easily.

No, I wasn’t aware of that option.

[BobG]

Greg, I have 21NE that I ordered without batteries or solar. I went with 24 volts lithium (2x 12v (170Ah) batteries, 1040 watts of solar and 5.5cf Norcold compressor fridge. Solar is 2 strings of panels wired in series (4x 160 watt and 2x 210 watt).

I went with the Victron 24-12 70 amp converter and struggled with the same question you have. I suspect that the 70 amp converter is not very efficient at the lower loads it operates at. I am wishing I had gone with a smaller converter because I don't experience anywhere near 70 amp load on the DC side. I suggest you add up the actual DC loads you will be running at one time and add a margin of capacity.

As mentioned by others, you will need to operate any power jacks and of course the emergency brakes at 12 volts. I used a $15 converter straight off the 24 volt battery bus for the brakes. People have suggested that this be protected with a thermal breaker. I agree. I think you can figure the amp capacity from looking at the manual that discusses your axle. I don't have a power jack so I didn't have to include it.

I disconnected the 12 volt line from the tow vehicle so I do not have charging when towing. Solar takes care of charging. I have not plugged into shore power since leaving home January 14 and have been hanging out in different areas of the Mohave desert in Arizona. Currently in Yuma area for a few days getting dental work done in Los Algodones. Five crowns $1850. I forgot to turn the air conditioner off before heading to Mexico for dental yesterday so it was on for about 24 hours.

If you want non solar charging ability you will need to add a 24 volt charger. I went with an inverter/charger that charges at up to 70 amps (adjustable) at 24 volts and removed the Escape furnished converter. The inverter runs the air conditioner, microwave, induction water heater for coffee, etc.

[Vermilye]

Originally Posted by GregWCIL

Hello all,


I am planning an electric upgrade on a 5.0 to a 24 volt system. What size converter do I need to reduce the 24 volts to 12 for the existing fuse panel?

Some details:

Am going with the Norcold compressor fridge but plan to run it on the native 24 volts of the new system.
Looks like there are typically 7 other 15 amp 12 volt circuits. That would be 100 amps.

Largest Victron offers is an Orion 24-12 v. converter with 70 amps. I see some folks using much smaller such as 40 amp converters.



We recently signed off on our build sheet for a 5.0 for June completion so I don't have the camper yet to check and a search here didn't turn up this answer.


Thanks,
Greg


edit to add: Will the existing fuse panel accept 6 guage wire on the input?

You do not need to provide a 24V to 12V converter that provides the total capacity of all the 15 amp circuits. Like your home circuit breaker panel, and the circuit breakers in your trailer that deal with your 120V circuits, the main breaker is not sized to equal the sum of the branch circuit breakers. You can consider the 24V to 12V DC converter as a "Main".

The original converter was only 55 amps and that is designed to include powering the absorption refrigerator on DC, a 25 amp load as well as charging the batteries. Since you won't have that, your largest peak load will be the jacks, and the largest long term load the furnace. I don't know what the jacks draw, but if all the current branch fuses are 15 amps, I suspect it is under that. A 45 amp converter will likely work; the 70 amp would definitely provide more than you will need.

[GregWCIL]

Thanks Bob. Sounds like my dream is your reality. As you note I may not need the 70 amp converter. The tradeoff is possible inefficiency vs. making sure I have enough power for everything. Its about impossible to predict which loads may occur at the same time. IE: will the furnace be running, TV on and maxxfan when I happen to retract the power awning?

The 70 amp model is listed at 92% efficient. Their next smallest model is a 40 amp which is 95% efficient.

Originally Posted by BobG

Greg, I have 21NE that I ordered without batteries or solar. I went with 24 volts lithium (2x 12v (170Ah) batteries, 1040 watts of solar and 5.5cf Norcold compressor fridge. Solar is 2 strings of panels wired in series (4x 160 watt and 2x 210 watt).

I went with the Victron 24-12 70 amp converter and struggled with the same question you have. I suspect that the 70 amp converter is not very efficient at the lower loads it operates at. I am wishing I had gone with a smaller converter because I don't experience anywhere near 70 amp load on the DC side. I suggest you add up the actual DC loads you will be running at one time and add a margin of capacity.

As mentioned by others, you will need to operate any power jacks and of course the emergency brakes at 12 volts. I used a $15 converter straight off the 24 volt battery bus for the brakes. People have suggested that this be protected with a thermal breaker. I agree. I think you can figure the amp capacity from looking at the manual that discusses your axle. I don't have a power jack so I didn't have to include it.

I disconnected the 12 volt line from the tow vehicle so I do not have charging when towing. Solar takes care of charging. I have not plugged into shore power since leaving home January 14 and have been hanging out in different areas of the Mohave desert in Arizona. Currently in Yuma area for a few days getting dental work done in Los Algodones. Five crowns $1850. I forgot to turn the air conditioner off before heading to Mexico for dental yesterday so it was on for about 24 hours.

If you want non solar charging ability you will need to add a 24 volt charger. I went with an inverter/charger that charges at up to 70 amps (adjustable) at 24 volts and removed the Escape furnished converter. The inverter runs the air conditioner, microwave, induction water heater for coffee, etc.

[GregWCIL]

Thanks, Jon.

Note my reply to Bob above - the quandary of predicting loads. I may even divorce the power landing gear and emergency brakes from the system and put in a small battery up front charged from the pickup 7 pin.

The 40 amp converter says it can handle 55 amps peak but doesn't say for how long. Not sure what happens if you exceed it? The 70 amp converter isn't many more dollars, I'm more paranoid about parasitic power losses from a larger than needed converter. Funny how we seldom think of such things when we have the luxury of the power grid at home. When you are generating your own suddenly it is a concern, lol.

Originally Posted by Vermilye

You do not need to provide a 24V to 12V converter that provides the total capacity of all the 15 amp circuits. Like your home circuit breaker panel, and the circuit breakers in your trailer that deal with your 120V circuits, the main breaker is not sized to equal the sum of the branch circuit breakers. You can consider the 24V to 12V DC converter as a "Main".

The original converter was only 55 amps and that is designed to include powering the absorption refrigerator on DC, a 25 amp load as well as charging the batteries. Since you won't have that, your largest peak load will be the jacks, and the largest long term load the furnace. I don't know what the jacks draw, but if all the current branch fuses are 15 amps, I suspect it is under that. A 45 amp converter will likely work; the 70 amp would definitely provide more than you will need.

[BobG]

Greg, Two thing


The emergency brakes have to be powered by the trailer in case the trailer disconnects from the tow vehicle. A small cheap 24 to 12v converter with a thermal breaker can take care of this or a battery mounted in the trailer but then you have to keep the battery charged.


I doubt you will have more than 40 amps and I am suspicious the 70 amp converter is not very efficient at the typical loads it is carrying. Some day I will measure it but not while I am traveling.


I'm off to get new crowns in "Molar City", Mexico.