Help with 12v build as I can afford trailer solar

Moving off grid into a camper trailer end of December.  Need a power set up that I can use for basic electric without running a generator all the time. Unfortunately the trailer has neither batteries nor a propane fridge. I'm looking at getting a pair of deka gc-15 6 volt deep cycle golf cart batteries for power - about $500 in my area. I can get 300 watt mono solar panels for $315 each locally as well:
Maximum Power Voltage (Vmp): 32.15 DC V
Maximum Power Current (Imp): 9.33 A
Open Circuit Voltage (Voc): 39.61 DC V
Short-Circuit Current (Isc): 9.78 A
Module Efficiency: 17.21 %
These are the most watts for the least $$ I can find locally, but I believe they are designed for a 36 volt system? Everything I can find locally for 12 volt systems is closer to $2 a watt. Can they be used for a 12 volt system, and what is the down side?

I know I need a charge controller, but need advice as to what I'm looking for.
I know I also need an inverter, but my experience with them is limited to cheap ones that plug into your car.
The trailer is equipped with a PD-9040 converter/charger, is that an inverter?

Ideally I would like to get a basic system going so I'm not running a generator all the time to charge the batteries. I know batteries will only charge so quickly no matter how much power you give them, so I don't want to burn all that fuel just to run a charger. I also want a system that I can upgrade as I get more money. What would you excellent people at permies recommend? (I'm an automotive technician, so the wiring parts come easily for me, I'm just used to systems that are already designed and diagrammed. )

I believe you will be looking for a MPPT charge controller.

AS far as i am aware. they accept various voltages and convert them to different voltages so they can get the best charging possible with the given amount of solar coming in.

So i believe the panels being 36v is normal. I know when our charge controller is working on a cloudy day it can show 110v coming in with a low amount of current.

So yea they will work with 12 volt. Personally i would go with a reputable brand.
Check out this site. they seem to carry good brands
https://www.cdnsolar.ca/shop-wholesale-solar-products/victron-energy-smartsolar-100-50-mppt-solar-charge-controller/

AS far as inverter. It will depend on what kind of power you are wanting to use? Do you want to be able to use your chop saw? or do you only want to grind your coffee and charge a laptop? I would suggest a pure sine wave inverter. Try the industrial pure sine wave samlex inverters. Here is the 1000 w one https://prairiesunsolar.com/product/samlex-1000/

You can add a bigger/better inverter later. Can be nice to have a low wattage one for most things, and a big one for tools and large loads.

You can add more charge controllers and solar panels later, and run multiple charge controllers going to one bank.
Ideally with lead you want one controller with enough power/panels to do an equalize cycle in a timely fashion, but maybe that isn't your first controller.

Don't cheap out on wiring or fusing.. I had a jumbo automotive style fuseholder melt into smoking horror. Mighta burned me out if I hadn't been home to smell it.

Adding batteries is less great, once your first ones age a bit you end up with mismatched cells when adding new batteries, and things just are not as lovely.



In your shoes, I would get a good charger to power with a generator, and save long enough to get a good battery bank from the start. A quality true sine inverter, like a samlex, and away you go; running the gen to charge is still wayless badness than running it for all power needs..


An undersized battery bank and undersized solar system will still leave you running the gen, and with a larger bank from the start you are setting yourself up for success once you add solar.


A good cooler, with maybe some extra insulation added, can do a lot, esp. in winter when you can sometimes just leave bottles of water outside to get more ice..

Black River Cottage wrote:Moving off grid into a camper trailer end of December.  Need a power set up that I can use for basic electric without running a generator all the time. Unfortunately the trailer has neither batteries nor a propane fridge. I'm looking at getting a pair of deka gc-15 6 volt deep cycle golf cart batteries for power - about $500 in my area. I can get 300 watt mono solar panels for $315 each locally as well:
Maximum Power Voltage (Vmp): 32.15 DC V
Maximum Power Current (Imp): 9.33 A
Open Circuit Voltage (Voc): 39.61 DC V
Short-Circuit Current (Isc): 9.78 A
Module Efficiency: 17.21 %
These are the most watts for the least $$ I can find locally, but I believe they are designed for a 36 volt system? Everything I can find locally for 12 volt systems is closer to $2 a watt. Can they be used for a 12 volt system, and what is the down side?

I know I need a charge controller, but need advice as to what I'm looking for.
I know I also need an inverter, but my experience with them is limited to cheap ones that plug into your car.
The trailer is equipped with a PD-9040 converter/charger, is that an inverter?

Ideally I would like to get a basic system going so I'm not running a generator all the time to charge the batteries. I know batteries will only charge so quickly no matter how much power you give them, so I don't want to burn all that fuel just to run a charger. I also want a system that I can upgrade as I get more money. What would you excellent people at permies recommend? (I'm an automotive technician, so the wiring parts come easily for me, I'm just used to systems that are already designed and diagrammed. )

Do you know if the trailer has a plug in? When you run a generator do the 12 volt lights work? If the do you have a 12 volt converter/charger somewhere on board. They usually hide them under a flase shelf in a closet or something similar. If you have one it will charge your batteries when the genny is running which will help you out a lot. As mentioned above for a cheap set up with a generator use a small puresine inverter for most things and the generator for larger loads. When you have theoney then invest in a larger puresine inverter. If you are only ever going to do 300 watts of solar a smaller mpppt charger is ok minimum of 25 amps preferably 30 amps. Watch out what you buy some cheap chargers call themselves mppt but are made to work with 12 volt panels only. You want one with a minimum panel voltage of 50 volts. I've used this one in a trailer before. Not cheap but it's been reliable.
https://volts.ca/products/smartsolar-mppt-100-30?variant=36527666462882¤cy=CAD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gclid=Cj0KCQiAkZKNBhDiARIsAPsk0WhDgPz9jAyhvq3kADbf_HJXldcocbhhCrVohBI8Ixbu6qoYzVLFhlMaApoFEALw_wcB

Since you already have components in mind, it's time to start matching equipment up to make sure you have a balanced system.  I agree with the comments above about the MPPT controller, and the Samlex inverter, but now you can start to identify which one.  Basically, you want to match the equipment so you create a stable system.

Looking at the battery you mention, it appears to be the 448Ah model, is that correct?  Here's where the numbers become important.  For good charging, you want at bare minimum charging at 1/20th of C, 1/10th C is good, and 1/8th C is best.  So, for a 448Ah battery, 1/8th would be 448Ah/8 = 56A.  1/10th would be 45A, and 1/20th would be 22A.

Assume also that the panel never puts out it rated output, because it's rated in a test chamber with artificial sunlight.  Assume you only get 85% of rated output at noon on a clear, sunny day.  So, you include a fudgefactor to compensate for lower output.  The reciprical of 0.85 is 1.175, so use 1.175 as your FF.  

The second assumption is that a 12V battery does not charge at 12V, but rather 12.5-13V while in the bulk phase.  So, for the various charging rates, here is the math to determine what you want.
1:8     56A X 13V X 1.175FF = 855W of panels
1:10   45A X 13V X 1.175FF = 687W of panels
1:20   22A X 13V X 1.175FF = 336W of panels

Now, panels laying flat on the roof are never going to be optimally directed towards the sun, so you want to use a larger fudgefactor, so 75% instead of 85%.  So, the same situation, but laying flat on the roof of your trailer would be...
1:8     56A X 13V X 1.33FF = 968W of panels
1:10   45A X 13V X 1.33FF = 778W of panels
1:20   22A X 13V X 1.33FF = 380W of panels

So, it looks like you'll need either two or three of those 300W panels, depending on your useage, but also how much space you have up on the roof.

Let's use two as the example.  If you have two 300W panels wired in series, they would have a maximal power voltage of 64V, but an open circuit voltage of 79.  Have three in series and the two numbers are 96Vmp and 119Voc respectively.  With two 300W panels, you'd get about {(300W X 2 panels)/13V charging} X 0.75FF =34.6A of charging current.  An inexpensive 40A MPPT controller like the Epever Tracer 4210AN could handle that load because it has a max Voc of 100V and a max Amperage of 40A.

Bump that up to three panels and the math changes to 119Voc and 52A [{(300W X 3 panels)/13V charging} X 0.75FF =51.9A of charging current], so the cheaper controller will be overwelmed.  Get a higher capacity controller like the Epever 6415AN, which can handle a max voltage of 150Voc and a max amperage of 60A

Mate that together with your Samlex sine-wave inverter, and you'll have a nicely performing system.

I think the PD-9040 converter/charger is a charging unit where you run out an extension cord with 120V AC from your house to the trailer, and it converts the AC into battery charging current, so it is actually the opposite of an inverter.

BTW, this statement above has caveats...
I know batteries will only charge so quickly no matter how much power you give them
There are limits, that I referenced above.

How much charge you apply is directly proportional to the 20hour Amphour size of the battery, identified as C.  For example, the battery I referenced above has a 20hour amphour rating of 448Ah.  Here are some guidelines and what you can expect.

<1:20C  Not good.  Most likely the battery will almost never be fully charged and you risk an early death from sulfination.
1:20C charging rate.  Low.  The battery most likely will only reach full charge on optimal days.  Won't reach full charge on marginal days like partially cloudy weather. You will struggle to keep the battery charged
1:10C Good rate.  Will keep the battery charged most of the time, except in rainy/cloudy weather
1:8C Most manufacturer recommended rates.  Will keep the battery charged almost all days, except really dark rainy days.
1:5C Really high.  Some batteries will not tolerate routine charging this high.  Approach this rate with caution.  If the batteries start feeling hot to the touch, the rate is too high.  At this rate though you can keep your battery charged even in the rain.

OP,

Just for starters, what is the amp-hour rating of those batteries and what applications do you see yourself needing?

I built a little 15 amp hour DC only battery box last year that is great for charging phones, tablets and the like.  I can charge it up with a little 28 watt solar panel.

I am planning on building a much larger, AC capable device and I am designing it as well.  

I think that my larger device would work well for your application, but it would be helpful to know your expected needs.  Also, it would be nice to compare notes.

Eric

Looking at the Deka GC-15, I see a 230ah battery ... so a pair will cost about $500. Even in golf cart format, you may not want to pull more than half the amp hours out of it (the 50% penalty of FLA batteries when used in solar) in a house battery bank scenario. You might get upwards of 1000 cycles, but there will be size, weight, maintenance, and so on with these, and odds are you'll kill the first pair much sooner (most folks do).

For less than $500 these days (or thereabouts), just get a single 12v 100ah LiFePO4 battery (SOK, AmpereTime, etc.), and pull upwards of 80 to 90ah's a cycle off of it, for 1000's of cycles. It's much lighter in weight, requires no maintenance, you can keep it in  the house with you, and so on.

With the battery out of the way, just get a $500 pure sine wave inverter, a $100 or so 12v charger, and a small form-factor propane inverter/generator (or your fuel of choice) at about $750. Figure about 1 minute of run-time per amp-hour (or thereabouts), that's how long the genny will run to drive the charger to top your battery off each day or period of time that you use 80 - 90ah of power. In the same charging period, you'll be able to run other things while the genny is running ...

Done ...

If you look carefully at inverters, you'll see some that have both 120v plugs *and* a wiring block; this gives you alternatives in drawing power from the inverter.

Depending on the specs of your RV's built-in converter/charger, you might be able to do something with it when the genny is feeding the RV directly, thru the shore-power inlet. Might save you the cost of the battery charger ...

Later on, add in some solar, an mppt, and try to reduce the genny use even further. Or, add another 12v 100ah battery. But, if off-grid, you'll almost always need/want the genny. If not, it's still a great parallel power system for (inevitable) on-grid outages.

Howdy

I have a Outback inverter with a built-in charger. I have a RV gen set from old rv that I use when my micro hydro is down and the sun won't fully charge my batteries. The built in charger will let me run all the house loads and charge my batteries at the same time. I haven't had to run the gen set very much, and only run it during the day when I am home, and never all night(4-9 hrs a day, 4 days). BUT I have micro hydro and the longest its been down is 4 days.

Also   Alternative Power and Machine is only 40 miles away (Grants Pass, Oregon) AND Jerry makes house calls. So, I would also suggest trying to put together a system from a local solar electric supplier, for when you need help or want to add different products, you can see actual products in use. I haven't had very much help over the internet.

My whole system was built up over 40+ years.  

Ok,so I had my budget severely cut and I won't be able to afford panels right away. I need a generator, batteries, and an inverter for now. Looking at 235 ah 6 volt batteries from crown. They seem to be the cheapest decent quality batteries available locally. $259 each. I could get 2 or 4, depending on the cost of the other items. Inverter - modified sine wave or pure sine wave?. I don't know if I should get a 12v one though, because once I have money for panels I will probably want to move to a 24 volt system. If I get a 24 volt one then I have to buy 4 6v batteries. I have seen ones that accept multiple input voltages, but they seem to cost a lot more. I would rather spend more on an inverter now and not have to upgrade it when I get panels. I eventually want to run 3-4 300 watt panels. Generator - ideally it would be big enough I could use my small welder with it. I use hat at home on a 220volt 30amp circuit with no issues. I don't mind running the genny for welding, power tools, etc, but I want to be able to run freezers on my solar setup eventually. Thoughts?

Oh and the trailer's charger/converter is an intelli power 9000. PD 9040 13.6 volt 40 amp

LiFePO 12v 100ah batteries are about $800 each here. Canada sucks for batteries.

I could be mistaken, but it seems that if you want a 24v system you may as well get the 4 6v batteries now and go with a 24v charge controller.

Eric

Howdy,
I agree with Eric. Also higher volt inverters allow higher wattage draws. I remember back a # of years, 12 volt IS the RV market. With the right inverts you can"stack" them, tie in more than one for VERY HIGH wattage draws(36v,48v,etc). I do run a small 110v welder, but for multiple power tool usage,(planer and table saw/ welder and air compressor) I have my gen set on and it will also charge the house batteries thru the Outback built in charger. My system is 24 volts.

wow, awesome advice all the way through.
I am 22 years on solar, and will never look back. I do NOT consider myself an expert. I know what I have been through and what has worked for me. I am a retired specialty electrician and have some knowledge on this. I have what I live on, and a couple I have "inherited" that others put in and walked away, and I was asked to help.

I just want to add my 2 cents, but don't let it detract from this great info. more batteries and using the genset to charge will likely help you get into the "zone" and be used to the limits of your battery bank, and not have to wait until daylight to fix the issue.(charge)
might help you decide on what wattage PV  you actually need for your system.
free power from the sun is just way cool. I wouldn't plug in for any reason now.
in my limited experience - a couple months difference in batteries does not make any noticeable difference -(any experts feel free to enlighten)  if you stay with the same brand and type/size - and can only afford 1/2 now and can't wait - get them and get the others as soon as you can.
 at a year difference I have seen problems as  the originals start going away - and then you really don't want to start piecing in new against way older - might as well get all of the life you can out of all of them, which means usually "same age". But  I know what I went though getting started on it. seems like a lot of money for a "will it work"
not all battery chargers will work on all generators - I had heard that, and had to test it. I have to agree.
I can tell you (some from) from experience:
unless you specifically only need 12 volt: (RV and radio sites come to mind)
go with the higher voltage - charging and battery bank. and use appropriate sized fuses where recommended.
if you don't understand the difference between series and parallel circuits - do some research, talk to someone in the trade - the potential for damage/injury is very high if you don't have that solid foundation. those six volt batteries have a lot of energy in them! color code wires! best if following NEC type codes - then others can help you easier if ever needed.

Run bigger wire than you think - you will always lose a percentage of your power - relative to wire length/gauge/current draw -(ohms law is a real thing!) if you lose only 1/2 a volt - you might think no big deal - but especially at 12 - it is way more wasted percentage-wise. and you can hit the unusable level way to quick at the lower voltages.

don't plug sensitive things in to non-pure sinewave inverters.  if you have a mix of pure and modified, I would bet at some point you will forget. laptops can be very susceptible.
I got rid of the one modified I had. yes, I learned that the hard way.
the small inverter for when you only need that, and larger  for when you need more has worked well for me.

depending on wire length  length you can lose more - think of it as friction - and wasting power as heat along the wire. there are charts available for wire gauge versus voltage and loss per (usually) 100 foot. using watts or amperage as your deciding factor, most of the charge controllers have a wire sizing guide in the manual. or you could check it on NEC guides - it is all in the code for a reason. build it for the maximum output on charge and use- some days you might be there!
shorter wire lengths help a lot (keeping them A: within reason, B: protected form animals!! rats/mice/porcupines etc LOVE to chew up wires!) it is worth the wire length to keep the wire in a safe zone, where it can't be damaged. fish it in a wall, pipe it, protect it - you will be protecting yourself.
I spent last Sunday at 6,000 feet on a mountain top that had a solar array out of commission - was wired from the PV panels to the charge controller with with mostly 18 gauge wire, and about 40' of it. I initially thought the panels were too old and tired until I looked closer. 1/2 the array (4 panels) were on phone wire!
and no fuses anywhere.
low voltage does not mean less fire risk.
I replaced it all with 10 Gauge - put it in conduit and it seems to be flying now, all the equipment that it was there for has been online for a week now.

Don't know anything about canadian purchasing, but just a tad bit of research yielded a lifepo4 12v-100ah battery for around $600 canadian. Alberta Lithium is the company ...

Prices are falling here in the states, and I can't imagine why they wouldn't be there as well. Might be many other choices in canada by now ...

It is harder to kick the tires on lifepo4 batteries, unlike FLA, as they aren't in every gas station or other local place of purchase, but don't let that stop you from switching away from the old, problematic technology of FLA, if at all possible. The lifepo4's will last way longer than the fla batteries, so they won't cost you more in the long run. We're talking multiple thousands of cycles ...

This is one area of solar where lifepo4 batteries really shine ...

The first time you have to lift a 6v fla battery, vs a 12v lifepo4, you'll remember this conversation ... the 100th time you are bent over an fla battery doing maintenance, vs just staring lovingly at the lifepo4's that don't need anything but admiration, you'll really remember it!

Yes, I sleep with my lifepo4's now ... I might have stared at them once or twice with more than admiration, and got caught by my better half ...

Black River Cottage wrote:Ok,so I had my budget severely cut and I won't be able to afford panels right away. I need a generator, batteries, and an inverter for now. Looking at 235 ah 6 volt batteries from crown. They seem to be the cheapest decent quality batteries available locally. $259 each. I could get 2 or 4, depending on the cost of the other items. Inverter - modified sine wave or pure sine wave?. I don't know if I should get a 12v one though, because once I have money for panels I will probably want to move to a 24 volt system. If I get a 24 volt one then I have to buy 4 6v batteries. I have seen ones that accept multiple input voltages, but they seem to cost a lot more. I would rather spend more on an inverter now and not have to upgrade it when I get panels. I eventually want to run 3-4 300 watt panels. Generator - ideally it would be big enough I could use my small welder with it. I use hat at home on a 220volt 30amp circuit with no issues. I don't mind running the genny for welding, power tools, etc, but I want to be able to run freezers on my solar setup eventually. Thoughts?

Oh and the trailer's charger/converter is an intelli power 9000. PD 9040 13.6 volt 40 amp

LiFePO 12v 100ah batteries are about $800 each here. Canada sucks for batteries.

Surretttes/Rolls are made in Nova Scotia and should be more affordable then crowns...
To me it sounds like you are trying to do too much with a starter system. My advice would be put together a bare bones system to run the trailer and save money and rebuild better later.

The problem with 24 volt systems and a trailer is all the lights and the water pump and the blower on the furnace will be 12 volts and wires to the existing battery. My advice would be to spend more on batteries so you have the capacity down the road to go to 24 volts but for now go with a 12 volt inverter. Puresine if you are running a fridge as a lot of them don't like modified sine wave. Most good charge controllers when you get there can do 12 or 24 volts most good inverters cannot switch...
Cheers and good luck,
David

Here's a way to get all the benefits of a 24V system, but still be able to run 12V stuff.  They make inexpensive 24VDC to 12VDC converters that you can just wire in series with whatever you want to power, and the voltage is transformed for you.  You can also get  12V to 24VDC converters so you can charge the batteries off the vehicle alternator.  You can make it work!

OP has an existing camper trailer ... find and review the schematic/wiring diagram for it, to both show how the converter/charger plays in it, and how the wiring is divvy'd up (if any) between 12v and 120v wiring. Should also show the devices attached to the wiring, along with the owner's manual providing more details.

A genny plugs into the camper's "shore power" plug ... match your plugs/amps, and the built-in converter/charger does the rest, converting/distributing the power to the plugs/devices in the camper.

Solar stuff also needs to be integrated in, either by being aware of the schematic/wiring diagram (but run as a parallel wiring system) or by possibly tying into it.

1.) shore power sends power to all existing plugs in the camper, with no connectivity to the inverter, and 2.) inverter sends power to a separate set of 120v plugs (or 12v, if also converting down w/ a separate device, to 12v wiring); this is a parallel system, parallel to the existing wiring in the camper. Either use the built-in plugs at the inverter, or distribute further with extension cords, power strips, etc.

3.) If there is a chance that the inverter can be wired into the existing camping wiring, you can prep for that by finding an inverter that has a 120v wiring block on it, in addition to some 120v receptacles. Otherwise, run extension cords and such from the inverter ... not hard to do in a small camper, but not necessarily up to code. Depending on amps at the plug of the inverter (the type and power ratings of inverter you buy), it may not power a whole lot in the camper before blowing circuit breakers of existing wiring.

Some careful pondering req'd, or lots of multimeter testing ...

Michael Qulek wrote:Here's a way to get all the benefits of a 24V system, but still be able to run 12V stuff.  They make inexpensive 24VDC to 12VDC converters that you can just wire in series with whatever you want to power, and the voltage is transformed for you.  You can also get  12V to 24VDC converters so you can charge the batteries off the vehicle alternator.  You can make it work!

those step down transformers are a great way to run 12 volt loads on a 24 volt system when the original poster gets to it.  If you want to go that far you could also get a stand alone transfer switch that will switch the AC plugs in the trailer automatically when the generator comes on. You would  have to wire the battery charger on a seperate circuit but that is easy enough. This is the most common way to run an inverter in a trailer. Something like this one: https://www.amazon.ca/Surge-Guard-41300-Automatic-Transfer/dp/B073PD854Q/ref=sr_1_3?crid=155WBSB8X1TXI&keywords=automatic+transfer+switch+30+amp&qid=1638840575&sprefix=automatic+transfer+switch%2Caps%2C338&sr=8-3