critique my design?

jayhocking

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Oct 26, 2021
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Working on a design for a truck camper I'm building in the spring - this is my first real system, beyond just using a goal-zero, or slapping a single panel on top of my SUV with a PWM controller. I'm planning on a 24v system. I think I have all the info needed to critique it on here, but let me know if I didn't include everything needed. The plan is to be able to run an induction cooktop, as well as water kettle off the inverter, and the 12v side needs to be able to handle the 12v water heater, as well as the startup of the water pump, amongst other more normal level loads.

I have a couple of questions right off the bat -
  • For the line running from the truck battery to the DC/DC charger, I was planning on a breaker right by the truck battery, and another one back in the camper, so I can easily flip off the truck battery from there, to make sure I'm isolated before doing any work in there. Is that a problem? Not necessary?
  • Do I need a breaker between the bus bar and the 24v to 12v converter?
Happy for any suggestions, improvements, etc - this is still just in the drawing stage, so haven't purchased anything yet.

I'm planning on victron for the items labeled that way, the batteries are SOK, with low temp protection (and planning on a heating pad for them as well). The 24v inverter is a Giandel. I also tried to simplify the gauges of wiring I'd use too, just using 10awg for a lot of it, even when smaller would work. Then 6 and 2 for where I needed larger, and probably 14 for the longer runs to the small 12v lights, fans, etc.

Thanks in advance for any advice!

Screen Shot 2021-10-26 at 11.51.51 PM.jpg
 

HRTKD

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If I had the opportunity to do a from-scratch build of an RV and I planned to use a 24v system, I would be searching high and low for 24v compatible appliances. Seaflo makes 24v water pumps. Maybe there are 24v furnaces (Webasto) and water heaters. The selection is very limited, for sure. But ditching the 12v step down converters would be nice. Many LED lights will run 12v-24v.

Some day, I plan to replace my propane/120v absorption refrigerator with a 12v compressor refrigerator.
 

rmaddy

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The 70A breaker between the 24V-12V converter should be 85A or 90A. Since the converter can output 70A you might get nuisance trips with a 70A breaker.

The 40A breaker between the solar panels and the SCC is much bigger than needed. You have two panels in series so the amps won't be too high. Look at the Isc of the panels. Multiply by 1.25 and round up. Probably a 15A or 20A would be fine.

You should consider 1AWG instead of 2AWG for the battery/inverter wires. 3000W / 24V / 0.8 is about 156A. That's better with 1AWG. The 200A fuse should be good.

You probably should have a fuse/breaker between the 24V->12V converter and the bus bar. The idea is to protect the wires.

Not that it changes anything but if those are SOK batteries then they are 206Ah, not 208Ah.

What is the Voc of the solar panels and which SCC are you planning on? The 100/30? If the Voc is near 45V or more than the 100/30 may not work since Voc goes up in colder temperatures which could put you over 100V. You might need the 150/35.
 

rmaddy

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If I had the opportunity to do a from-scratch build of an RV and I planned to use a 24v system, I would be searching high and low for 24v compatible appliances. Seaflo makes 24v water pumps. Maybe there are 24v furnaces (Webasto) and water heaters. The selection is very limited, for sure. But ditching the 12v step down converters would be nice. Many LED lights will run 12v-24v.
I have a 24V system and I tried hard to have just 24VDC loads but there is always something that runs on 12V. So I have both a 24V fuse panel for 24V loads and a 12V fuse panel for the 12V loads. I originally was thinking to get as much as I could at 24V to be more efficient. But really once you have a single 12V load and you need the buck converter, there's really no gain to using any 24V loads since the system is going to lose efficiency no matter what with the converter in place.

Examples of 12V loads I couldn't get rid of: Maxxair fans, propane detector, 12V power outlets, tank (fresh and gray) sensors, oven light.
 
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jayhocking

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Oct 26, 2021
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The 70A breaker between the 24V-12V converter should be 85A or 90A. Since the converter can output 70A you might get nuisance trips with a 70A breaker.

The 40A breaker between the solar panels and the SCC is much bigger than needed. You have two panels in series so the amps won't be too high. Look at the Isc of the panels. Multiply by 1.25 and round up. Probably a 15A or 20A would be fine.

You should consider 1AWG instead of 2AWG for the battery/inverter wires. 3000W / 24V / 0.8 is about 156A. That's better with 1AWG. The 200A fuse should be good.

You probably should have a fuse/breaker between the 24V->12V converter and the bus bar. The idea is to protect the wires.

Not that it changes anything but if those are SOK batteries then they are 206Ah, not 208Ah.

What is the Voc of the solar panels and which SCC are you planning on? The 100/30? If the Voc is near 45V or more than the 100/30 may not work since Voc goes up in colder temperatures which could put you over 100V. You might need the 150/35.
Super helpful!! Thanks so much. I updated the drawing, taking all of that into account. My panels I had picked were out of stock now, so I swapped them for some slightly larger ones. Not sure which ones I'll actually end up with, probably won't order for another few months, but in any case, they'll be near that VOC, so I upgraded to the 150/35 SCC. Again, thanks so much for taking the time to look over this, it was really, really helpful. I added a 90a breaker between the 24v->12v converter and the bus bar - this should just be good for the 70a converter, and the 6awg wire, correct?

Screen Shot 2021-10-28 at 12.15.09 AM.jpg
 

rmaddy

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I added a 90a breaker between the 24v->12v converter and the bus bar - this should just be good for the 70a converter, and the 6awg wire, correct?
The 24V->12V converter outputs 70A on the 12V side. So the 90A breaker on the 12V side is good. On the 24V side it will be half (a bit more due to inefficiencies). So assume 40A on the 24V side. So you really only need a 50A breaker between the converter and bus bar. A 90A breaker is safe for 6AWG wire but a 50A breaker would be sufficient for the load.
 

jayhocking

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If I had the opportunity to do a from-scratch build of an RV and I planned to use a 24v system, I would be searching high and low for 24v compatible appliances. Seaflo makes 24v water pumps. Maybe there are 24v furnaces (Webasto) and water heaters. The selection is very limited, for sure. But ditching the 12v step down converters would be nice. Many LED lights will run 12v-24v.

Some day, I plan to replace my propane/120v absorption refrigerator with a 12v compressor refrigerator.
I totally wanted to...but ran into a couple of roadblocks (like water heater - I've only found a single 12v water heater, and no 24v ones, or the Maxxair fan), and decided I wanted to have 12v available, at which point it became somewhat pointless to have another bank of 24v appliances. Planning on a diesel heater, so that's not an issue...but I also want to be able to plug in other 12v appliances later, so planning on a 12v plug anyway...at which point I might as well just have a 12v panel, and go that simpler route.
 

Dzl

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I have a 24V system and I tried hard to have just 24VDC loads but there is always something that runs on 12V. So I have both a 24V fuse panel for 24V loads and a 12V fuse panel for the 12V loads. I originally was thinking to get as much as I could at 24V to be more efficient. But really once you have a single 12V load and you need the buck converter, there's really no gain to using any 24V loads since the system is going to lose efficiency no matter what with the converter in place.
Are you sure this is a correct understanding?
My understanding (which is quite limited) of buck converters, is that the inefficiency is the result of the conversion, not the result of the converter being 'on' (in use). If we were talking about an inverter, then yeah, you lose efficiency in conversion and from the no-load power draw. But my impression is that DC-DC converters (buck and/or boost) have very low self-consumption. So for example if 80% of your loads were 24v and 20% had to pass through the buck converter, only 20% would be subject to the efficiency penalty of conversation. If my understanding is correct, there is some value to running as much as possible at 24v and avoiding conversion (from an efficiency perspective, but the 'juice may not be worth the squeeze' for a few % gain at best).
 

BIGFOOT

Here comes the sun....
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FL SWAMPS
Working on a design for a truck camper I'm building in the spring - this is my first real system, beyond just using a goal-zero, or slapping a single panel on top of my SUV with a PWM controller. I'm planning on a 24v system. I think I have all the info needed to critique it on here, but let me know if I didn't include everything needed. The plan is to be able to run an induction cooktop, as well as water kettle off the inverter, and the 12v side needs to be able to handle the 12v water heater, as well as the startup of the water pump, amongst other more normal level loads.

I have a couple of questions right off the bat -
  • For the line running from the truck battery to the DC/DC charger, I was planning on a breaker right by the truck battery, and another one back in the camper, so I can easily flip off the truck battery from there, to make sure I'm isolated before doing any work in there. Is that a problem? Not necessary?
  • Do I need a breaker between the bus bar and the 24v to 12v converter?
Happy for any suggestions, improvements, etc - this is still just in the drawing stage, so haven't purchased anything yet.

I'm planning on victron for the items labeled that way, the batteries are SOK, with low temp protection (and planning on a heating pad for them as well). The 24v inverter is a Giandel. I also tried to simplify the gauges of wiring I'd use too, just using 10awg for a lot of it, even when smaller would work. Then 6 and 2 for where I needed larger, and probably 14 for the longer runs to the small 12v lights, fans, etc.

Thanks in advance for any advice!

View attachment 70293
What software did you use ?
 

chrisski

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I totally wanted to...but ran into a couple of roadblocks (like water heater - I've only found a single 12v water heater, and no 24v ones, or the Maxxair fan), and decided I wanted to have 12v available, at which point it became somewhat pointless to have another bank of 24v appliances. Planning on a diesel heater, so that's not an issue...but I also want to be able to plug in other 12v appliances later, so planning on a 12v plug anyway...at which point I might as well just have a 12v panel, and go that simpler route.
Not sure how much heating will get done with a 12 volt, 17 amp water heater. Is this for drinking water, which I could see, or shower, which to me seems way undersized.

I think the 1 AWG wire should be a little thicker. 1 AWG may work fine when the battery is charging and full at 27.6 volts, but if the cells are nearly drained and the battery drops to 2.5 volts per cell (almost completely empty), or 20 volts total, and that is the inverter low voltage cutoff, than you could see 172 amps through the battery to inverter, counting inverter losses. 2/0 wire would be better suited for this load.

20 volts may be lower than your system is capable of, but your wiring needs to handle the output of the BMS and inverter. The inverter will still produce 3000 watts AC, but to do that with the lower voltage, amperage will skyrocket.
 

rmaddy

Full-time Solar-powered Trailer Life
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Are you sure this is a correct understanding?
My understanding (which is quite limited) of buck converters, is that the inefficiency is the result of the conversion, not the result of the converter being 'on' (in use). If we were talking about an inverter, then yeah, you lose efficiency in conversion and from the no-load power draw. But my impression is that DC-DC converters (buck and/or boost) have very low self-consumption. So for example if 80% of your loads were 24v and 20% had to pass through the buck converter, only 20% would be subject to the efficiency penalty of conversation. If my understanding is correct, there is some value to running as much as possible at 24v and avoiding conversion (from an efficiency perspective, but the 'juice may not be worth the squeeze' for a few % gain at best).
Good points. I certainly didn't mean to imply the buck converter had a no-load power draw. But I have a few 12V loads on 100% of the time. A little computer fan for the compositing toilet and a propane detector are on 24/7. Of course between the two it's less than an amp. But I run the Maxxair fans quite often. I'm recharging my phone and laptop regularly with a 12V outlet.

But you are probably right. Having some 24V loads in my setup is slightly more efficient which was my original thinking. But I suspect it's pretty minimal. I have plenty of battery and solar so in my case the trivial difference makes no difference in the end.
 
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chrisski

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I am adding the Orion 70 amp 24 to 12 volt converter. The handout has around 10% losses, bit it has a sleep mode where the idle draw kicks back to almost nothing.
have plenty of battery and solar so in my case the trivial difference makes no difference in the end.
I think with plenty of batteries, that loss won’t be a problem either.
 

jayhocking

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Not sure how much heating will get done with a 12 volt, 17 amp water heater. Is this for drinking water, which I could see, or shower, which to me seems way undersized.

I think the 1 AWG wire should be a little thicker. 1 AWG may work fine when the battery is charging and full at 27.6 volts, but if the cells are nearly drained and the battery drops to 2.5 volts per cell (almost completely empty), or 20 volts total, and that is the inverter low voltage cutoff, than you could see 172 amps through the battery to inverter, counting inverter losses. 2/0 wire would be better suited for this load.

20 volts may be lower than your system is capable of, but your wiring needs to handle the output of the BMS and inverter. The inverter will still produce 3000 watts AC, but to do that with the lower voltage, amperage will skyrocket.
thanks for that insight. I'd rather build it to handle any eventual situation, so I'll bump up the wiring gauge. Are my 200amp fuse and breaker okay? I'm assuming my 1 AWG for the negative distribution block would still be okay? As the negative to the inverter is separate, and I'll bump that up to 2/0 as well.
 

jayhocking

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Not sure how much heating will get done with a 12 volt, 17 amp water heater. Is this for drinking water, which I could see, or shower, which to me seems way undersized.

I think the 1 AWG wire should be a little thicker. 1 AWG may work fine when the battery is charging and full at 27.6 volts, but if the cells are nearly drained and the battery drops to 2.5 volts per cell (almost completely empty), or 20 volts total, and that is the inverter low voltage cutoff, than you could see 172 amps through the battery to inverter, counting inverter losses. 2/0 wire would be better suited for this load.

20 volts may be lower than your system is capable of, but your wiring needs to handle the output of the BMS and inverter. The inverter will still produce 3000 watts AC, but to do that with the lower voltage, amperage will skyrocket.
oh, and this is the water heater I was going to try. It's just 1.5 gallons - but if we set it to 150 degree f, that means mixing with water that is at about 60 degrees, we should be able to end up with about 3.5 gallons of nice temp water, around 100f. This is mostly for washing dishes, although we will have a basic spray-off type shower (both external and internal taps) that will just use a kitchen sprayer style hose. I'm guessing we'll have about 2 min of water out of it. Should be enough for one person to shower off, as you can't actually leave the tap on running anyway, you have to hold the button down.
 

jayhocking

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Good points. I certainly didn't mean to imply the buck converter had a no-load power draw. But I have a few 12V loads on 100% of the time. A little computer fan for the compositing toilet and a propane detector are on 24/7. Of course between the two it's less than an amp. But I run the Maxxair fans quite often. I'm recharging my phone and laptop regularly with a 12V outlet.

But you are probably right. Having some 24V loads in my setup is slightly more efficient which was my original thinking. But I suspect it's pretty minimal. I have plenty of battery and solar so in my case the trivial difference makes no difference in the end.
I'm wondering if it's even worth setting this up as a 24v system though - do the advantages get wiped out by the losses on the 24/12v converter? Or is it worth it to keep it 24v, and just see what items I can actually run off 24v directly, and minimize what I'm going to have to use 12v for.
 

Kartox

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What software/design tools are you using to create that awesome diagram? I'm designing a build and just have a big list of parts. Creating a visual model of all the hookups would really help.

NM - I see Adobe Illustrator above, my bad
 

rmaddy

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I'm wondering if it's even worth setting this up as a 24v system though - do the advantages get wiped out by the losses on the 24/12v converter? Or is it worth it to keep it 24v, and just see what items I can actually run off 24v directly, and minimize what I'm going to have to use 12v for.
24V lets you use much smaller wire and fuses versus a 12V system, especially with such a large (3000W) inverter. I have 24V. Most of my high usage stuff is 24V (fridge, water pump, mobile router, LED lights). I also imagine the inverter is more efficient at 24V than 12V.

But you have reasons to go 12V with those jacks. And 12V items might be easier to get in a pinch if something fails. The only downside to going 12V in your case is the need for a few larger wires and fuses.
 
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chrisski

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oh, and this is the water heater I was going to try. It's just 1.5 gallons - but if we set it to 150 degree f, that means mixing with water that is at about 60 degrees, we should be able to end up with about 3.5 gallons of nice temp water, around 100f. This is mostly for washing dishes, although we will have a basic spray-off type shower (both external and internal taps) that will just use a kitchen sprayer style hose. I'm guessing we'll have about 2 min of water out of it. Should be enough for one person to shower off, as you can't actually leave the tap on running anyway, you have to hold the button down.
I’m a bit skeptical on that water heater. Wish it had reviews, but you may be the first on the block to try it. For me its too pricey to be the first.

I’m no engineer, but 200 watts does not seem like a lot of power to get 1.5 gallons of water warmed up in an hour. When I’ve looked at boiling water, and my poor research comes up to 800 watt hours to boil a gallon of water from room temperature. With heat losses, I’m skeptical. I’m sure its possible, especially in a lab.

If I’m wrong, I would certainly consider something like this for my RV.
 

jayhocking

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I’m a bit skeptical on that water heater. Wish it had reviews, but you may be the first on the block to try it. For me its too pricey to be the first.

I’m no engineer, but 200 watts does not seem like a lot of power to get 1.5 gallons of water warmed up in an hour. When I’ve looked at boiling water, and my poor research comes up to 800 watt hours to boil a gallon of water from room temperature. With heat losses, I’m skeptical. I’m sure its possible, especially in a lab.

If I’m wrong, I would certainly consider something like this for my RV.
my alternative I'm considering, which might make more sense, is to purchase a 2.5 gallon Rheem water heater, and swap in a 24v 600w heating element. I'd like to figure out how to have it automatically heat only when the batteries are full (with an override for when I need hot water, even when the batteries aren't full). Seems like this way, I'd make max use out of my available energy, and the tank would probably hold water reasonably hot for 5-6hrs (assuming I can insulate it well. That option will cost me around $275 I'm guessing, by the time I buy all the bits and bobs to make i work. Not as compact, but I could probably figure out how to fit it in, and would provide me with a bit more hot water, plus be 24v, and a lot more power going into it to heat it faster.
 
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