Small inverter charger for RV

jasowiii

Any advice on an inexpensive inverter charger (or another option) for a small system? 100-200 W solar, 12 V 30-50 AH battery and 400-500 W 120 VAC output. I want to be able to top it off with a little gas powered generator as needed.

Are there other good options for 120VAC charging? 

Jim

jasowiii

I did more research and as far as I can tell most inexpensive inverters only support lead acid batteries I was planning to use 1 or 2 small LFP batteries as opposed to lead acid. I like the low self discharge, fast charge and other attributes of LFP batteries.

Is this correct or does anyone know of a better approach? An inverter charger with a transfer relay seams like the way to go for for a generator supported system but is there a better option?

This is a small trailer where the main power need is a diesel air heater that uses very little power to run (1-2 amps 12 VDC). That said I want to get through a sub zero night and have a little left for lights in the morning.
I was thinking warm LFPs inside would be better than cold lead acid outside. Maybe not... If it is the most economical solution I guess I could put the battery (s) out on the trailer tongue in a box.

As far as loads, in addition to the heater I'll run a couple lights, charge a phone/headlamp etc.

BB.

Welcome to the forum Jasowiii,

Can we back up a moment and better understand your loads? For example, a 500 Watt AC inverter (with a 500 Watt load) will quickly drain a 30-50 AH @ 12 volt battery bank:

• 500 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff = 56 Amps
• 30 AH / 56 amps = 0.5 hours to bank dead (max--full to dead)
• 50 AH / 56 Amps = 0.9 hours to bank dead

You should plan on using  only 50% to 80% battery capacity... And few Lead Acid type batteries (AGM batteries can support high drain applications)... Add cold weather, and less capacity.

A 2 amp load over 10 hours (diesel heater):

• 2 amps * 10 hours = 20 AH

You pretty much would drain a small battery bank to near dead (or real dead) overnight (maybe less, depends on the duty cycle of your heater and average Amperage load).

Anyway--What are your expectations for loads (how much, how long, etc.).

While LiFePO4 batteries are nearly the perfect battery (with some operational requirements like a Battery Monitor System, over and under charge protection)--The big drawback is that they cannot really be charged much below 40F or 32F... If you are going to be camping/traveling in sub freezing conditions, Flooded Lead Acid or AGM are going to be better--Unless you can guarantee the Li Ion batteries are kept "warm".

What you can do, and what equipment you can use, does depend on size... Larger systems have "smarter" hardware (inverter-chargers with more programmable options, and such). Until you have nailed down your loads/power/energy needs--It is difficult to even begin to pick what hardware would support those needs...

Sort of like picking motor cycle/VW Bug/station wagon/pickup/18 wheeler tractor trailer -- Without knowing what it is you are going to haul (restaurant food delivery, or 80 tons of concrete mix).

From your post, you are saying DC loads (DC heater, LED interior lights, USB chargers for cell phone & headlamp)...Of those, the DC heater is probably your largest load. Some very rough numbers:

• 2 amps * 10 hours * 12 volts = 240 Watt*Hours per day (night)
• 20 WH cell phone charging (USB)
• 10 WH headlamp charging (USB)
• 3 Watts of LED lighting * 5 hours a night = 15 WH per night

240 WH DC heater and 45 WH for "everything else"... The heater is going to be the big driver for your energy needs. The other stuff--Almost "in the grass"...

Why would you want to use an AC inverter? Or at least that large of inverter?

A small genset (Honda eu1000i or eu2200i or similar inverter genset--There are many different brands of inverter-generators out there these days) are pretty nice. Quiet and fuel efficient. Possibly use the Genset for AC inverter needs--And just use the battery+solar for small DC loads.

Obvious things like lots of insulation, some sort of heavy curtains/insulation for your windows and ceiling vents, etc. will help reduce the heater electrical loads--Picking small/efficient heater (small/efficient fan, or one that does not use a fan)...

• 285 WH load "per night" * 1/12 volt battery bank * 1/0.50 max planned discharge = 47.5 AH @ 12 volt battery minimum suggested.

If you are going to run the battery "cold", then you will need to account for loss of capacity for Lead Acid:

http://support.rollsbattery.com/support/solutions/articles/5860-temperature-vs-capacity-flooded-lead-acid-batteries

If you are going to run to 0F (-18C), then the FLA/AGM battery will be ~50% of capacity--So you would probably want closer to a 100AH @ 12 volt FLA/AGM battery.

If you can keep your LiFePO4 battery "warm" (32F/0C), they only lose 10% of capacity (roughly).

There are lots of Li Ion battery options... Batteries with integrated Battery Monitor/Protection circuit (not cheap) to build your own batteries from individial blocks and your own BMS.

Here is an example of a LiFePO4 battery that is intended to be (more or less) a drop in replacement for a Lead Acid battery:

solar-electric.com/battle-born-bbgc2-100ah-12v-lithium-battery.html

These batteries will "shutdown" if you attempt to over charge / over discharge / charge at cold temperatures, etc.

The above are just some suggestions and observations... Electrical/Energy usage is a highly personal set of choices. Conservation (reducing your loads as much as possible) is usually your best first step with off grid solar/battery systems.

-Bill

jasowiii

Wow Bill that's a bunch of info. Thanks. 

I think I am going to look into a Duracell PowerSource 660 that I saw at Costco for $450. Add a panel and wah lah!

https://www.duracellpower.com/products/1440-watt-power-station

BB.

Jason,

I would suggest you read the manual (I think this is the correct one):

https://www.manualslib.com/manual/1713063/Duracell-Powersource-660.html

It is a 660 WH battery, 12 volts, 55 AH, probably LiFePO4 type (guess).

Max 1,440 Watt AC inverter (1,880 Watts surge)

MSW (modified square wave inverter)--This can be a big flag. Some electonics/power supplies/battery chargers do not like MSW wave form... Normally if you want "quality", you want PSW/TSW inverter (Pure/True sine wave inerter).

You can only charge with a 100 Watt solar panel... Which gives you, at best, (full sun, middle of summer, something like 75 Watts of charging power). 660 WH / 75 Watts = 8.8 hours to charge... Most places with "good sun" are around 3-6 hours of sun per day (in deep winter, can be 1-3 hours of sun per day).

You can connect an external battery bank with a 200 Amp fuse/breaker... It would seem that you could improve the charging capacity by that route--But that is just a suggestion for research--I do not know if that is possible or not.

Temperature range is 32F to 104F operationational. and -4F to 104F or 122F (manual typo? 50C = 122F) for storage.

If you did not need much power (about 10 Watts to run the inverter + AC loads)... 660 WH / 200 Watt load (TV+Lights) = 3.3 hours (estimate).

I don't think it is a good fit for your needs... But this is your NEEDS, not mine or my guesses.

If you want something quick and simple--And don't need much power (and do not need PSW AC power)--It could work OK for you. I would expect you would "outgrow" it after a year (again, my guess, not your needs).

-Bill

Photowhit

jasowiii said:

Wow Bill that's a bunch of info. Thanks. 

I think I am going to look into a Duracell PowerSource 660 that I saw at Costco for $450. Add a panel and wah lah!

https://www.duracellpower.com/products/1440-watt-power-station

Gosh, not a fan of all in one units, usually they are a compromise for any one use.

Most inverter chargers are quite expensive. Samlex Makes an EVO line that is reasonably priced for a camper/RV. 
It's 1200 watt output, has in integrated 30 amp transfer switch, it supports Lithium battery banks. If yu choose to do a small Lithium battery bank, it will also limit the charging current. I've never owned one, but it appears to fit your needs pretty well. 

Samlex EVO-1212F 1200W, 12V Pure Sine Inverter/Charger | DonRowe.com

They also make a hardwire version, which would be my preference, same cost.

Northern Arizona Wind and Sun, is a Samlex dealer, might give them a chance to price match! They support this forum, but don't list it in their inventory.

jasowiii

Thanks Photowit for the Samlex suggestion. That was my original question with regards to an inverter/charger recommendation. I should add that I am trying to go low budget on this project. I would like to stay well under a $1000 total. $600 for the inverter might put me over budget. This application is just a camp trailer for 1 person occasional use.
 
I think I might give up on The LiFePO4 battery idea and just put a big cheep Lead Acid battery on the tongue of the trailer. If I have to buy a new $125 battery every 3-4 years so be it. I might even do 2 6V batteries if I have room.

I wonder if something like this for $279 might be a better choice considering my budget. 
https://www.donrowe.com/Samlex-SAM-1500C-12-Inverter-Charger-p/sam-1500c-12.htm
It only has two stage charging (bulk and float).
A solar charge controller for $35. 20A so I could add a panel if I decide.
https://www.donrowe.com/KISAE-SC1220LD-20A-12V-Charge-Controller-p/sc1220ld.htm

I decided against the Duracell. It has a SLA battery just to answer Bill's suggestion that it might be LFP. Agreed that it has limited storage (but probably enough) it is also only has a 6 amp charger and could take to long to top off with a generator. 

Jim

Photowhit

Well that might work, I didn't read up on it, but a 2 stage is 'how' I would use a inverter/charger with a Flooded lead acid battery. The last 15-20% of charging the battery accepts less current, so it's not very cost effective to use a generator.

jasowiii said:

 I want to be able to top it off with a little gas powered generator as needed.

So this is sort of the wrong way of thinking, rather do the bulk of charging in the morning and let the solar "top it off".

The other issue/problem is that that is a modified sine wave inverter, so it's likely to shorten the life of your compressor and use a bit more energy while powering it. Might research modified sine vs pure sine inverters. It might also damage sensitive electronics.