Single Battery 12V only expo trailer build recommendations

[BigSwede]

If I may jump into the fray with similar questions - I have a recently acquired very small camper and I am trying to figure out how to "boondock" as the camper folks call it. I currently have an Optima yellow top 35 rated at 48 ah (I had this battery laying around). I also have a CTEK 56-158 charger available. When I do have shore power, the camper, which is 23 years old, has a Carson CP10FK power pack that I *think* puts out 3 amps charge to the battery "only when the battery requires charging" (information on this unit is a bit sketchy). My power needs are quite modest - just some lights, the roof vent fan, and most importantly the CPAP (which draws 1.3 amps) overnight.

While this battery should last 2-3 days at least, I would like to add solar to the mix for longer trips away from civilization. How much solar do I need? Is 50W enough (I am looking at some folding panels that can be stowed in the camper underseat compartments when not in use)? Is an MPPT controller worth the extra ~$100?

What do you guys do to reduce the chances that your solar panels will walk away while you are away from the camper?

 

[luthj]

What is your CPAPs rated watts when running? What region are you using the solar panel in? What season? For a low power/budget setup, a PWM controller should work just fine. Just pick a quality one with the correct voltage setpoints.

 

[dreadlocks]

2-3 days off a 48aH? yeah right.. you do know you shouldn't use more than 60% of that capacity right? you only have about 28aH unless you want to buy new batteries every season..

need your CPAP wattage, 1.3A on 120v is ~156W.. which on 12v is 13A, plus inverter losses.. if it pulls 150W continuously for 8h while sleeping your gonna need a MUCH larger power system.

Personally I would not mess w/solar under 120W, how I keep em from walking away is mounting em onto the roof.. otherwise portable ones you just gonna have to trust your fellow outdoors men.. Most people need far more solar thank they think they do, because in the field conditions are never ideal.. since you have medical device thats not optional, I'd look at a GenSet first.. that will recharge your batteries as long as you have fuel.

 

[BigSwede]

What is your CPAPs rated watts when running? What region are you using the solar panel in? What season? For a low power/budget setup, a PWM controller should work just fine. Just pick a quality one with the correct voltage setpoints.

My CPAP can run on 12V directly and draws 1.3 amps (I don't use a humidifier, which makes a BIG difference in power draw). So 15.6 watts?

I live in Minnesota and do short trips regionally, but do go to Utah, Colorado, Wyoming etc. occasionally, and these are longer trips where I am more likely to need charging ability.

Seasons? Generally not winter

I am considering this controller https://www.amazon.com/dp/B07MY49FF...olid=2DOH8R4BJUTSZ&psc=0&ref_=lv_ov_lig_dp_it
Don't know if it is quality, but it costs twice as much as the cheapest ones, and it has settings for lithium battery which I may transition to in the future.

 

[luthj]

15.6W is doable for a couple days on a 48AH battery. Estimate at 12Ah per night plus whatever else you have connected. A 100W panel should recover 16AH a day or better in non-cloudy conditions. More if you can angle it to follow the sun.

 

[BigSwede]

2-3 days off a 48aH? yeah right.. you do know you shouldn't use more than 60% of that capacity right? you only have about 28aH unless you want to buy new batteries every season..

need your CPAP wattage, 1.3A on 120v is ~156W.. which on 12v is 13A, plus inverter losses.. if it pulls 150W continuously for 8h while sleeping your gonna need a MUCH larger power system.

Personally I would not mess w/solar under 120W, how I keep em from walking away is mounting em onto the roof.. otherwise portable ones you just gonna have to trust your fellow outdoors men.. Most people need far more solar thank they think they do, because in the field conditions are never ideal.. since you have medical device thats not optional, I'd look at a GenSet first.. that will recharge your batteries as long as you have fuel.

I was told by the manufacturer by email 1.3 amps, I believe we were taking 12 volts (which this unit will do directly, so no inverters/adapters involved). I will need to find that email to verify though, it was a while ago. The specs online for the unit say a maximum of 65 watts on AC. My pressure setting is half of maximum, so I am probably using less than that. I should probably just get a meter and find out for sure.

I have operated my CPAP off of car batteries many many times overnight with no apparent effects on starting power for the vehicle, but have not done it for multiple days. But I am pretty confident I can do two nights even with this battery.

The battery is nothing great but it was handy. Someday I will replace it, not sure with what though. Thinking lithium, my only hesitation there is I would probably need to change out the camper power converter for lithium charging when plugged into shore power. There is a Progressive Dynamics converter for lithium that would probably work well.

 

[dreadlocks]

Best thing too do right now is use what you got and put a shunt w/meter in your camper, go out this season and keep a journal of how much you consumed and the length of each trip.. come up with an average and then start designing from there.. solar is usually the last thing to go on, after you've got the batteries and house charger you need.

 

[john61ct]

Anything "designed for lithium" will have voltage set too high.

Get voltage adjustable charge sources, or a Sterling BB series to front-end all the rest.

 

[BigSwede]

BB Series? I see a lot of stuff on their website, nothing by that particular name.

 

[dreadlocks]

If this is your first setup I would suggest a dual 6v golf cart battery setup, its the most capacity for the least money and robust enough to handle abuse from someone figuring out what they need and how far they can push things.. however if you see Lithium in your future (which is wise, prices have been falling dramatically), as you add a nice multi-stage house charger, solar setup, low voltage disconnects, and etc make sure you can reprogram them to whatever voltages and charge profiles you want.. then you can in the future swap out battery chemistries without needing to change out all that equipment.

If you go Lithium right now your going to be jumping off a huge expensive learning curve cliff, without much personal experience and data to help you along the way.. in all likelihood you dont need to spare the expense unless your on a severe weight diet and your looking at a lead bank of 150-300lbs+

 

[BigSwede]

Good advice. As sexy as lithium sounds, this may not be the time for me to jump in. My needs are actually pretty simple; I may be overthinking this.

Either way, in the long run I am trying to decide if I want to get a new power converter (with built in charger) for the camper or just do it all with separates. Obviously, separates are more flexible in the long run, but would require some rejiggering of wiring in the camper and probably the connection system for shore power etc.


And the immediate question remains, how to have power for an extended stay sans shore power. While I do have a quiet 2200 watt generator, I'm not crazy about making room for it and fuel amongst all my kit. And talk about getting legs, a generator is like a magnet for thieves. Which brings me back to solar.

There is one additional option though - I have a small lithium "generator power station" (lol) I bought after my last power outage https://www.amazon.com/Generator-St...X2T6ZWYJM60&psc=1&refRID=ZY9WMFZV1X2T6ZWYJM60
I have successfully powered my CPAP overnight with it, I need to try two nights on one charge. But I can charge it from my vehicle during the day.

 

[dreadlocks]

The problem with trailers is vehicle charging is its slow, your trailer wiring can only provide a few amps at best so unless you intend on driving >8h+ when your batteries go flat you wont ever get back to full and then at your next site you've got even less capacity, and so on and so forth.. If your just a weekender its not much of an issue, but when your on the road for 2 weeks or more you may find the only way to get the batteries back full is a generator or solar..

You already have a generator you can use for charging so use that for now for any extended outings, Solar is a beast of its own, field conditions are rarely ideal.. they output practically nothing while shaded so you can easily find your solar panels you setup in the morning quickly became shaded and you didn't get anything that day, or its overcast, or partly cloudy etc.. You may not ever get back to full charge while on solar but it can help extend your battery time by a few days, its better to have too much solar than too little so most people bring along as much as they can because output can be so variable when your portable/mobile.. its nothing like fixed solar in fixed locations.

You probably have a 120v breaker for the old/dumb house converter, if you take the wire going to that breaker out it will disable it and you can hardwire in your own separate multi-stage smart charger that will safely float the batteries and keep em maintained while in storage.. should be pretty straight forward.

 

[john61ct]

BB Series? I see a lot of stuff on their website, nothing by that particular name.

https://www.sterling-power-usa.com/batterytobatterychargers.aspx

The ones without a BB designation do not accommodate user-custom setpoints.

They can be stacked for greater ampacity.

 

[john61ct]

You can charge at whatever rate your alternator puts out if you get the wiring upgraded to a thick enough gauge and Anderson connectors.

Can get pricey, but a once-off cost - for that vehicle anyway.

The Sterling will help even if you don't go LFP, will accommodate any bank chemistry or alternator, and can be used on the next rig too.

Or with portable banks, just swap them between TV and trailer.

 

[dreadlocks]

You can charge at whatever rate your alternator puts out if you get the wiring upgraded to a thick enough gauge and Anderson connectors

You can charge at whatever rate your batteries will take a charge at, not what the alternator puts out.. most people have >100A alternators, yet a single 12v battery typically wont take more than 15-20A and only for a short time, majority of the charge will be <10A.. you can go through all that expense and hassle of running heaver gauge wiring but your still looking at 6h+ of driving/engine running required to recharge a lead battery from a low charge state.. This would become more worthwhile as the battery bank gets bigger, if you got 300AH+ of battery to recharge then getting 30-50A charge out of your engine would be a great idea.. its still going to take 6h+ to refill but its better than 18h or more you'd need out of your OEM trailer plug.

For me personally I would spend a few hard days on the road getting to the general area, and then spend a few weeks hopping around from location to location.. but those hops were typically only a few hours of driving tops.. If your style is to spend a day or two at one location then drive 500m+ to the next it might be completely suitable, but thats not how my trips ended up turning out.

This is where solar can help, if by the time you get to your destination your battery bank is in absorb stage and only taking 5-6A of input tops then thats pretty easy to finish off the last 3-4h or so of charging w/the sun.. A fixed panel on the trailer can also help augment your alternator source while on the road, if you get 5A off your tow vehicle and its a clear day you can get 5-10A off the roof mounted solar and have no need for more amps from alternator more than likely.