Off grid trailer power


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Joined
May 25, 2017
Messages
411
I plan to build my own trailer over the next couple years, and I'm looking to build a 4s 18650battery for a few electrical needs.

The trailer build is here:DIY Trailer Build
The plan for thetrip I'm designing it for is here:Epic Ural North

I plan to keep everything running on 12V so I don't need power conversion. I think my biggest power draw will be a laptop that I plan to plug in using a DC brick instead of the regular AC one. But until I actually pick out all the parts I want, I don't really know how much power I will need. So I will report back later as I make progress. :)
 
Joined
May 25, 2017
Messages
411
It's been a while since I first started this thread, but I've been learning and designing, and I've finally gotten to the point where I can start figuring out the electrics and the battery. The link in the first post to the trailer build should still work if you want details, but here are the latest design pics of the actual trailer:

image_jityvx.jpg

image_qdpgqd.jpg

image_kuxlmd.jpg

image_epcxrd.jpg


I'm toying with the idea of installing a couple of peltier coolers for hot days. Originally, I had considered a DIY evaporative cooler. But it would have been bulky, required lots of water, and I was concerned about condensation in such a small area. I think the peltiers will work much better. They're a bit power hungry, but I plan to use them at 25-75% capacity. Apparently, that will make them more energy efficient. Here's what I kind of have in mind:

image_nsnuwg.jpg


I've been shopping for the various components I'd like to use for the trailer as far as electrical stuff goes, and I've taken note of the power requirements of each device. Another thing I had to consider is what battery chemistry to use. Lead/Acid was out; too heavy. LiFePO4 was out; I can't afford them. So I'm back to good ol' 18650 Li-Ions. So 3s or 4s? The question that forever vexes people who want to make a 12V battery out of Li-Ion. I've decided to go with 4s. For me, it makes sense to have the higher voltage, because it means less Amps per Watt. Because I use old laptop cells, I like to keep the Amps of each cell at 0.5A if I can. So that is almost always the limiting factor as far as how few cells in parallel I can get away with.

Anyway, here is what I came up with:

image_kkytch.jpg


I'll have 4 USB charging ports, several 12V things, mostly lights and fans, and 1 24V outlet for my CPAP machine. After "translating" all those Amps back to 14.8V, I have an idea of how much current I'll be drawing from the battery if I ran everything at the same time. Comes out to something like 42A. Of course, I won't be running everything at the same time. That would be dumb. I played around with numbers for a while, and decided 30A is a good compromise between too much power, and not enough. Also, 30 is a nice round number, and I can get a breaker for that.

Note that in the above picture, I've got over 2000 Wh on the battery. Should be closer to 1400. I guess I fixed that after the screen capture.

Anyway, I know I won't be using everything at once, and I also know that I won't be using them all the time. I had to figure out both Amps and Watt-hours to know just how big to make the battery.

image_umzohm.jpg


I may have made this image too small. I have that problem when sharing spreadsheet stuff.
What I did was to estimate at what capacity I would use each device. For example, the interior lights and reading lamp would probably need to be dimmed to be comfortable for me. The interior fan has two settings, Lo, and Hi, and I'll probably use it on low. The peltier A/C I'll use at less than full capacity. Say 50% on average. Things like that. Also, just because the 12V outlet can deliver 15A, it's unlikely I'll use it at 15A unless I have to inflate a tire. My electric tire pump has an initial surge of 15A then drops off to about 5-10A. Other things like the door light and the vent fans would always be run at full power.

Also, I had to estimate how many hours per day I would be using these devices. For example the floodlights are so I can see what's going on outside my trailer at night without getting out of it. Like if a bear is trying to steal my gas can for his dirt bike. Most days I wouldn't even turn them on. And since this is basically a sleeping box, I might run the interior lights for a couple hours and the reading lamp for maybe an hour.

After counting up all those things, I figured the battery will do an average of 10A for about 10 hours per day. But with the possibility of drawing as much as 30A at a single instant. And I'll need around 1400 Wh for the battery to last a whole day's use. Running this through all the regular math to build a battery, I came up with 4s64p, 256 cells total. Based on past experience I'll need around 45 laptop batteries' worth of cells.

What I haven't figured out yet is how to charge it. I'd like to be able to camp off grid, so I plan to have a solar panel and charge controller, which I think I've got figured out, but also, I might as well charge it off the motorcycle while I'm traveling, and I've got a battery isolator picked out. My motorcycle has a small car alternator on it rather than thestator and magneto things that regular bikes have, so it can generate quite a bit of power for a bike. But I need a 12VDC charge controller to safely charge the battery. I haven't found one yet. Also, when there is an electrical hookup, I'd like to charge the battery with 120VAC. I'll either need a controller for that, or a 120VAC to 12VDC converter capable of outputting, say, 10-30A. Haven't found anything like that either. I can balance easy enough with my iMax.

So if anyone knows of a good source for a charge controller, at least 10A output,for 4s batteries (one that just starts when you plug it in), I'd love to hear about it. :)
 

Geek

Member
Joined
Aug 15, 2017
Messages
920
Interesting idea with the peltier. Perhaps experiment with water cooling it to make it more efficient.

I wonder if you could use a solar charge controller? I cannot find any info, but I wonder if it is possible to connect the PV side of a controller to a battery.
 

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,835
Nice setup. I agree with Geek on the Peltier idea. Those things are not very efficient. If you get a dehumidifier and redesign the housing and such, you could turn it into a small cooler. You would take the condenser coils and put them outside instead of having them in line with the evap coils.
Dehumidifiers are sold that run on 12VDC and are far cheaper than an A/C unit.

I would recommend going with 24VDC instead of 12VDC. You will incur a lot less losses and the wiring will be a lot more manageable. You can get some really good buck converters for decent prices and there's even some that can do 15A (about $30USD if I remember correctly)

For your camper, if you can take the siding off and clad the whole thing in heat reflective styrofoam, that will drastically reduce your temps inside the camper. This is what I mean: https://www.lowes.com/search?searchTerm=styrofoam+insulation
 
Joined
May 25, 2017
Messages
411
I've changed tactics and instead of looking for a charge controller, I've started looking for circuit board type things that will do the job. I think I found one that will work. It's a CC CV Boost unit able to take as low as 10V, and boost it well above 16.8V. It also can output up to 30A. It's a rather big fellow, and comes with a heatsink and fan.

image_blznqu.jpg


I've also decided to get one of those 12V power supplies that come encased in the shiny metal box. 120VAC in, 12VDC out. Again, 30A.

image_leiapd.jpg


I'm thinking of maybe getting two of the CC CV boosts; one for the motorcycle limited to say, 10A, and one for the power supply at say, 25A. It's good practice not to run stuff like this at full capacity for long.

I wonder if I should get one of those 30A "bms" circuit boards? I put a 20A one on a battery I made once for my lawn mower, and it cut the power quite effectively. My mower's starter was drawing 22A. So I guess they work.
 

Crimp Daddy

Member
Joined
Feb 21, 2018
Messages
970
If you are going to use that many DC-DC bucks converters, I think you would be better off with at least a 7s system.

For a trip like that, reliability is king, and you should be looking at brands like Victron and Samlex DC-DC converters. The Victron models with adjustable output voltage can also be used for battery charging.

Personally I like the Victron more because the price is better AND they have remove on/off so you can wire them to ignition or regular switches for control, eliminating the need for relays. They also come in isolated and non-isolated versions so if you needed to connect in series or needed isolated grounds, you have options.

https://www.victronenergy.com/dc-dc-converters

Victron Orion 12/24-10 fo 12 to 24 v for battery charging at 10 amps
Victron Orion 24/12-40A (40 amp DC-DC supply)

They have different sizes and amperage ranges for both, but those are the two I went with for my off-road 4x4 adventure setup. Most of my kit was all 12v lead acid, but ever since getting into lithium cells, I have been running 7s banks with similar challenges to yours to power my ARB fridge / freezer, ham radio communications equipment, lighting loads, and other accessories.
 
Joined
May 25, 2017
Messages
411
I'm intrigued by the dehumidifier idea. I will look into that.

Also interesting is going with a 7s battery. Same number of cells, but different configuration, and half the Amps. I did the same calculations as above, but with the new Voltage. Rearranged some circuitry, and came up with this:


image_zlsuho.jpg


I'd have a 7s36p battery at minimum, though 7s40p would be better. The CPAP would need a buck/boost converter to keep the Voltage at 24, but at only 4A, I bet I can find one. For the 12V buck converters, if I put them before the fuses,I may not need so many.Maybe just 2. This may work out very well. I'm going to look for components that will work for this. :)
 

rodagaster

New member
Joined
Feb 9, 2018
Messages
16
rebelrider.mike said:
It's been a while since I first started this thread, but I've been learning and designing, and I've finally gotten to the point where I can start figuring out the electrics and the battery. The link in the first post to the trailer build should still work if you want details, but here are the latest design pics of the actual trailer:

image_jityvx.jpg

image_qdpgqd.jpg

image_kuxlmd.jpg

image_epcxrd.jpg


I'm toying with the idea of installing a couple of peltier coolers for hot days. Originally, I had considered a DIY evaporative cooler. But it would have been bulky, required lots of water, and I was concerned about condensation in such a small area. I think the peltiers will work much better. They're a bit power hungry, but I plan to use them at 25-75% capacity. Apparently, that will make them more energy efficient. Here's what I kind of have in mind:

image_nsnuwg.jpg


I've been shopping for the various components I'd like to use for the trailer as far as electrical stuff goes, and I've taken note of the power requirements of each device. Another thing I had to consider is what battery chemistry to use. Lead/Acid was out; too heavy. LiFePO4 was out; I can't afford them. So I'm back to good ol' 18650 Li-Ions. So 3s or 4s? The question that forever vexes people who want to make a 12V battery out of Li-Ion. I've decided to go with 4s. For me, it makes sense to have the higher voltage, because it means less Amps per Watt. Because I use old laptop cells, I like to keep the Amps of each cell at 0.5A if I can. So that is almost always the limiting factor as far as how few cells in parallel I can get away with.

Anyway, here is what I came up with:

image_kkytch.jpg


I'll have 4 USB charging ports, several 12V things, mostly lights and fans, and 1 24V outlet for my CPAP machine. After "translating" all those Amps back to 14.8V, I have an idea of how much current I'll be drawing from the battery if I ran everything at the same time. Comes out to something like 42A. Of course, I won't be running everything at the same time. That would be dumb. I played around with numbers for a while, and decided 30A is a good compromise between too much power, and not enough. Also, 30 is a nice round number, and I can get a breaker for that.

Note that in the above picture, I've got over 2000 Wh on the battery. Should be closer to 1400. I guess I fixed that after the screen capture.

Anyway, I know I won't be using everything at once, and I also know that I won't be using them all the time. I had to figure out both Amps and Watt-hours to know just how big to make the battery.

image_umzohm.jpg


I may have made this image too small. I have that problem when sharing spreadsheet stuff.
What I did was to estimate at what capacity I would use each device. For example, the interior lights and reading lamp would probably need to be dimmed to be comfortable for me. The interior fan has two settings, Lo, and Hi, and I'll probably use it on low. The peltier A/C I'll use at less than full capacity. Say 50% on average. Things like that. Also, just because the 12V outlet can deliver 15A, it's unlikely I'll use it at 15A unless I have to inflate a tire. My electric tire pump has an initial surge of 15A then drops off to about 5-10A. Other things like the door light and the vent fans would always be run at full power.

Also, I had to estimate how many hours per day I would be using these devices. For example the floodlights are so I can see what's going on outside my trailer at night without getting out of it. Like if a bear is trying to steal my gas can for his dirt bike. Most days I wouldn't even turn them on. And since this is basically a sleeping box, I might run the interior lights for a couple hours and the reading lamp for maybe an hour.

After counting up all those things, I figured the battery will do an average of 10A for about 10 hours per day. But with the possibility of drawing as much as 30A at a single instant. And I'll need around 1400 Wh for the battery to last a whole day's use. Running this through all the regular math to build a battery, I came up with 4s64p, 256 cells total. Based on past experience I'll need around 45 laptop batteries' worth of cells.

What I haven't figured out yet is how to charge it. I'd like to be able to camp off grid, so I plan to have a solar panel and charge controller, which I think I've got figured out, but also, I might as well charge it off the motorcycle while I'm traveling, and I've got a battery isolator picked out. My motorcycle has a small car alternator on it rather than thestator and magneto things that regular bikes have, so it can generate quite a bit of power for a bike. But I need a 12VDC charge controller to safely charge the battery. I haven't found one yet. Also, when there is an electrical hookup, I'd like to charge the battery with 120VAC. I'll either need a controller for that, or a 120VAC to 12VDC converter capable of outputting, say, 10-30A. Haven't found anything like that either. I can balance easy enough with my iMax.

So if anyone knows of a good source for a charge controller, at least 10A output,for 4s batteries (one that just starts when you plug it in), I'd love to hear about it. :)
Hi mate can i ask were you got your plans for the teardrop cheers .
 
Joined
Mar 7, 2018
Messages
1,062
Like the plan. For cooling go with a fridge/freezer and make ice with excess power. I still have 10 Peltier devices in a box to play with but they are a low priority after a few hours messing with one of them.... Ice is way better than batteries for energy storage.... and way more efficient...

Humidity control - compressor dehumidifier if 20C and above, otherwise a desiccant dehumidifier for cooler conditions as they provide space heating as a bonus and perform better in colder conditions. Humidity is usually an issue in colder conditions as the windows and general air circulation should provide enough in warmer situations.


"Like if a bear is trying to steal my gas can for his dirt bike." - LOL..

I have found that leaving a remote light on outside (few watts) makes for a good way of attracting all the flies and insects away from where you dont want them to be...


"I might as well charge it off the motorcycle while I'm traveling" - extra solar panel will work out more efficent than vie the engine...
 

Crimp Daddy

Member
Joined
Feb 21, 2018
Messages
970
completelycharged said:
Like the plan. For cooling go with a fridge/freezer and make ice with excess power. I still have 10 Peltier devices in a box to play with but they are a low priority after a few hours messing with one of them.... Ice is way better than batteries for energy storage.... and way more efficient...

Humidity control - compressor dehumidifier if 20C and above, otherwise a desiccant dehumidifier for cooler conditions as they provide space heating as a bonus and perform better in colder conditions. Humidity is usually an issue in colder conditions as the windows and general air circulation should provide enough in warmer situations.


"Like if a bear is trying to steal my gas can for his dirt bike." - LOL..

I have found that leaving a remote light on outside (few watts) makes for a good way of attracting all the flies and insects away from where you dont want them to be...


"I might as well charge it off the motorcycle while I'm traveling" - extra solar panel will work out more efficent than vie the engine...




This is a solid recommendation... a good quality DC fridge/freezer is super efficient. I have a 50 quart fridge/freezer and it uses about 50 watts when onand probably runs 50-60% dutycycle. It really sips power and the performance is amazing. I've held freezer temps with a 100 degree F differential.

Many are also 12-24v native which makes it even more efficient if you can exclude the DC-DC from the circuit.

I run mine directly off a 7s pack.


image_devpfw.jpg

image_higrwm.jpg


That from my Las Vegas trip in the summer.
 
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Mar 7, 2018
Messages
1,062
Even better when the fridge is full of beer...
 

Crimp Daddy

Member
Joined
Feb 21, 2018
Messages
970
completelycharged said:
Even better when the fridge is full of beer...

Absolutely...The 50 quart model can hold 72 cans... it's amazing how muchyou can carry when you don't need to leave room for ice.

Still, one of my favorite things is being able to run afreezer. Being the only guy at a camp site with an ice cream cone in your hand never really gets old either. "Uhh, where did you get that"
 
Joined
May 25, 2017
Messages
411
Well, all the 12V dehumidifiers I've seen that I might turn into an A/C use peltiers. I'll keep looking, but I'm not sure that idea will pan out. I'm a bit suspicious of those 12V refrigerators as well. I bet they use thermoelectric too; which means peltiers.I'll look into those, but I'm not sure how I'd use them or ice to cool the trailer. Remember, this is basically a 6' by 3' sleeping box. I don't have much room for bulky stuff, which is why I nixed the DIY evaporative cooler idea.

I do plan to use some rigid foam insulation in the walls. They're going to be quite thin though, to save space and weight. I don't plan to mount the solar panels on the trailer. I'd like to park in the shade if possible, and set the panels out in the sun. That would probably do more for keeping cool than using an A/C anyway.

Charging will primarily come from the motorcycle. It has a 40A alternator, and the bike only uses around 10-15A, so there's plenty to spare. The manufacturer designed it that way on purpose. I'm thinking maybe 5-10A. That would be 2-4A into the 25V battery I think.

The solar panels would provide a little power so the battery might drain more slowly while I'm camped for the afternoon. Or if I stay the whole day, I'll leave the panels hooked up all day. Since I haven't picked out all the charging hardware yet, I don't know how much power in I can expect yet.

Speaking of hardware, I'm wondering how I'll get power from the bike to the battery. I guess I'll need a booster that goes from 12-14V to around 30V, and then get a charge controller that can do 30V in and charge 7s Li-Ion. I wonder if it would be better to put the boost converter closer to the motorcycle and run the higher voltage back to the controller? Fewer Amps and more Volts means less loss, right? If anyone can suggest a good charge controller, that would be awesome!

Also, DC circuit breakers. I'd like to find some of those wall mounted ones I see folks using instead of the cheap inline ones I'm finding.

I appreciate the suggestions folks! I may not use them all, but I am considering them seriously. :)
 

Crimp Daddy

Member
Joined
Feb 21, 2018
Messages
970
You should absolutely be weary of cheaper 12V fridges because there are those that are thermoelectric and the best you can get is 40 degrees below ambient. You need to spend some coin on a fridge that has a compressor and is very efficient and high performance. Being able to hold 100F below ambient and only use 50 watts isn't bad at all and it cost as much as a real home appliance.

Somehow I missed the entire fact that ur pulling this with a motorcycle. For some reason I thought this was more of a standard camper trailer than you pull with a truck or SUV. This obviously changes everything so I apologize for missing that detail.

Vents and fans are going to do a lot for you... along with the insulation, but I agree with your ideas on keeping cool. If you were worried about staying warm there are actually plenty of DC 12v heated blankets to choose from too. I have a couple and we love them for winter trips.

You could easily buy/diy your own charger using a current limiting DC-DC converter. Just use it for maintenance / bulk charging at a lower than full voltage at whatever current level work for you. If you wanted a proper charger, you could look into something like a CTEK which is pretty poplar in the off-road crowd but I would keep a close eye on voltages since it is a Pb charger.

https://smartercharger.com/products/batterychargers/ctek-d250s-dual-2/

But again, Victron pretty much has something for everything you mentioned.
 
Joined
Mar 7, 2018
Messages
1,062
Breakers - for DC at 24V use DIN rail mounded breakers and I use these type :
https://www.aliexpress.com/item/1P-10A-DC-125V-Circuit-breaker-MCB-C-curve/32788935201.html
They are cheap and work ok. They are type C so delay tripping a while.

Boost, use the 1500W boost version of the unit in the earlier post, has a fan and will work upto 30A depending on voltage range (check the actual spec as the 30A is only for a certain voltage range). I had a few experiments with them on this post https://secondlifestorage.com/t-How-to-get-a-cheap-charger-with-over-100A-at-12V
The boost would only provide a CC CV charge so sill balancing to sort out...

Critical : set the input limit on the boost to the float level of your bike battery, otherwise the boost unit can end up discharging your bike battery and then have no juice to start the bike... !!!!

Solar can be 3kWh per kWh of capacity, depending on location, sun rise/set, etc.

I would opt for more solar to try and avoid charging from the bike at all as this should in the long run cost less in fuel.. still prepare for options to have the bike as a backup charger.. weight may become an issue though as larger 300W panels can be 20kg each.

With alternators if they are brushed connections to the rotor using them at higher amps will burn out the brushes earlier. I had a car alternator, which they put on test after a "repair" and the brushes burnt out in seconds at full load (130A), burning the copper connection surface from the rotor.... toast. suppose the other option is to provide the ability to run the bike from the battery pack in the case of an alternator failure, use a small buck to charge the 12V bike battery..
 

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,835
Yeah, didn't think about that all the 12V version stuff would be peltiers. Don't recall if you would be using an inverter, but seems like that'd be the only way to get the "freon" version of the dehumidifiers.
Hrmm...

Did some searching, and I'm either getting peltier styles, or evaporative coolers (which u don't want as it raises the humidity in the camper)
I suppose this is something you're gonna have to think about. If you go the DC route, you might as well get a full blown RV style cooler, the type that goes ontop of the camper. If you want a smaller unit, or go with modifying something, then you'll need an inverter to run it.
 
Joined
May 25, 2017
Messages
411
I've been looking into the power input side of things. It's not as good as I'd hoped. For times when a power outlet is available, I'll have no problems, but I also want to be able to just pull off the road and camp. No power, water, anything. For those time, I'm going to have to really conserve my battery.

The folks on the Ural forum tell me that I can easily draw 10A from my alternator all day with no problems. So I can get 14V x 10A = 140W, and if I ride for, say, 4 hours, that's 560Wh minus losses.

I've decided to put 2 12V panels together instead of my original plan to have just one. Each would be 100W, so I figure if I'm lucky I can get 160W out of both in parallel. If I can set those out and get good sun for maybe 3 hours a day while camping, I could get 480Wh.

This would be 1040Wh total, which is quite a bit less than what I was planning on using. Which was around 1500Wh per day. Also, I completely forgot about my little netbook which has this cool OBDII access in case I have trouble with the bike. And also, it's just nicer to have a larger screen and a real keyboard if I want to do any computer stuff along the way.

So I plan to work on this from both ends.

On the consumption end, I think I will completely eliminate the A/C, and just live with the fans for ventilation. Also, I'm going to do away with the 12V outlet. I've been trying to think of what it would be good for, and I just can't come up with anything. Other than an electric tire pump. But that would be better suited for the starter battery, as it uses high Amps, but for a short time. I've already got a 12V outlet on the bike anyway. I can also disable the heater and humidifier functions on my CPAP. I don't use the humidifier anyway. This should greatly reduce the Amps that the machine will need. I'll have to put it on a power meter and see what the real difference is. With all that, It looks like I can get the power down to 1200Wh per day.

On the production side, I'm thinking of doing something like mounting the panels to the trailer while I ride, and then be able to detach them while camping so I can have the trailer in the shade and the panels in the sun. Still have to think on that, but then I could get 4 hours of solar while I ride, in addition to the 3 while I'm camping. That would put me at 1680Whr if conditions are good.

Even so, the sun is not always going to be out, and I may not want to ride 4 hours every day. In fact, if the weather is crappy, I'm less likely to want to ride anyway, and I might generate no power at all for a day. I'm going to have to figure out a minimum power usage plan! Or find a campsite with power.

The 7s battery has allowed me to clean up the wiring diagram quite a bit.

image_reclur.jpg
 
Joined
May 25, 2017
Messages
411
I don't know about the towing services either.
But definitely pick the trailer that will suit your needs first, then modify it for off-grid, or whatever you want to do. :)
 

Overmind

Member
Joined
Jan 16, 2019
Messages
455
Why the unnecessary complex shape of the trailer ?

All you get from that is a lot more work, lower structural integrity, less usable space and the probability of it ending up looking like undesired objects.

I'd do that as simple as possible, like a cube.
 
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