solar

[Henry]

I just want to operate a residential fridge thru my inverter. How many 12v batteries and will a 100w panel work?

[pianotuna]

BFL13,

Cold weather use and ability to be partial charged are my interests. I have not set eyes on my RV for 10 months now. Makes me quite sad.

[BFL13]

pianotuna wrote:
jshupe,

Do you have a picture of the panels?

What controller are you using?

SiO2 can manage c/4 (25 amps per 100 amp-hours). They don't have to be fully recharged each cycle. Of course, that is no match for the charging rate on Li chemistries, but it is double that of regular flooded.

PT, you know regular RV FLAs can be recharged at 25% charging rate too, no harm. SiO2 "advantage" is only when amps taper with FLA and amps are still at Bulk Stage with the SiO2.

In my example you saw, a 50-80 would be at the same amps/same time, but if you go on to 90, the 80-90 part takes longer with the FLA due to tapering amps. So it is scenario dependent how much "faster" it would be with SiO2 and whether that amount of time saved has value wrt the price.

[n0arp]

pianotuna wrote:
jshupe,

Do you have a picture of the panels?

What controller are you using?

SiO2 can manage c/4 (25 amps per 100 amp-hours). They don't have to be fully recharged each cycle. Of course, that is no match for the charging rate on Li chemistries, but it is double that of regular flooded.

Fifth wheel:



9x 325W panels, 3x strings of 3 in series, Victron SmartSolar MPPT 150/35 controllers

Depending on how much time we spend in the fifth wheel moving forward, we may pull up all the panels and build a raised rack that holds twelve. We've been spending more time in the truck camper lately.

Truck camper:




5x 360W panels, 1x string of 5 in series, Victron SmartSolar MPPT 250/60 controller.

Truck camper has a Coleman Mach 11 AC unit and we haven't been able to test it in the summer yet. There are no easy provisions for a mini-split in the rig, though I'm still scheming.

[pianotuna]

jshupe,

Do you have a picture of the panels?

What controller are you using?

SiO2 can manage c/4 (25 amps per 100 amp-hours). They don't have to be fully recharged each cycle. Of course, that is no match for the charging rate on Li chemistries, but it is double that of regular flooded.

[n0arp]

BFL13 wrote:
... It is really about carrying more usable AH in the same small space in a RV that is weight limited, but IMO the fast charging claim is not realistic.

The charging speed becomes much more important as you scale it up. It doesn't make a lot of difference if you have a small setup with four GC2s or two BattleBorns, but if you have several thousand watts, tens of thousands of Wh of storage, and a load that can draw the bank down significantly overnight, it becomes quite important.

For our 2925W array we can usually harvest around 18kWh of energy per day in AZ in summer. We have a 22.8kWh bank in that rig. In 100F temps, we'll consume right around 22kWh per day keeping the rig at 72F. That leaves us with a deficit of around 4kWh, that we want to cram into the bank as quickly as possible, in the middle of the day so we're not having to listen to it during the evening. It's not unusual to run the genset around lunch time and when the AC compressor kicks off, push 3800W from the generator and 2500W from the solar array to the bank at the same time. 525A of charging if it were a 12V system (it's 48V).

A bank of 16 225AH GC2s has a max charge rate (C/3) of 600A@12V, a recommended charging rate (C/10) of 180A@12V, and an absorb stage that substantially tapers the charge above 85-90%. They also need to be routinely charged to full to retain that ability. We'd either trash the batteries in short order, never make it to full, or more than likely, some combination of both. By contrast, the recommended charge rate (C/2) for our LFP bank is 900A@12V, so we easily make it to full each day and never have to worry about it.

We are far from the only people with setups like this.

[BFL13]

You can do more amps with a Power Factor corrected charger (if you can find one--there are a few) with the same VA sized gen, but you still have limits on gen size in an RV set-up. With the 5er we could carry the Honda 3000 in the truck. No room for it in the Class C (with no built-in gen) so 2200 gen is our limit.

Before buying a bunch of LFPs, just be sure you can carry what's needed to charge at 200 amps or whatever. How many know how to calculate what's needed? 😞

Another thing I don't understand is where they advertise how great LFP is with solar for "fast charging". You have all day to do a recharge, so what's the hurry? With FLAs now you can be "full" by just after lunch. AND where are you going to carry the solar panels to produce the high amps to do it faster anyway? 800w of panels flat on the roof will do maybe 50 amps at noon and less the rest of the day. 50 amps is peanuts. That's why solar takes all day. Where is the LFP fast charging advantage?

It is really about carrying more usable AH in the same small space in a RV that is weight limited, but IMO the fast charging claim is not realistic.

[pianotuna]

time2roll wrote:

jshupe wrote:

pianotuna wrote:
Start with an energy audit. Decide how much reserve capacity you want. From that design the battery bank. Build a solar panel system that will recharge the battery bank.

This is the proper way to go about it.

I prefer to max out the solar and deal with the consequences.
Solar is so inexpensive today there is no reason to aim for the minimum.

Which is why I recommend the largest capacity charge controller that one can fit the budget. There are at least 2 100 amp controllers available.

[StirCrazy]

BFL13 wrote:


I don't think you have done the calculations for that.

You keep seeing this claim about faster charging with LFP, but nobody explains how to do that. EG this "4 times the rate" claim that will reduce gen time.

To me that must mean restoring four times the AH in the same time that it would take with FLAs . Or same AH in 1/4 the time.

If you now have four 6s at 460AH and a 75 amp charger powered by a 2200w gen (like my set-up), that means you can do a "50-90" (184AH) in about 3 hours.

To do that in 1/4 the time- 45 minutes-that means charging at 245 amps. (184 x 60/45) So first you need a 245 amp charger or combination of chargers, and a generator to run that.

I doubt that is what was meant! So how about some realistic numbers with a realistic RV set-up for chargers and gen sizes and the LFP bank vs the four 6s, a 75 amper, and a 2200w gen?

EDIT--ok, say I had the same set-up only with LFP so no amps tapering. It all gets done at 75 amps. 184/75 is 2 hrs , 27 min. so I would save 33 minutes (from 3 hours) of gen time. Not quite the same as "four times faster" is it?

How about I do a 50-80 with my four 6s? Now it all gets done at 75 amps where amps start to taper at 80% SOC. 150AH in two hours. Swap to LFP and--oops--still 150AH in two hours.

you can charge at a 1C rate with LFP, so if you have a 486 ah battery bank and you are setting up your system to be compatable with a generator why wouldnt you get a larger charger? aside from they get ecpensive above a point but relisticly a 150 amp charger wouldnet be out of the question if you were setting up for Li in the first place, so 150 in one hour. or if you have money to spend you could set that bank up with a 300 watt charger and 150 in 30 min. that is the big advantage of LFP, you build to pound the amps in when you have them available. so hugly oversized solar, or chargers and so on. not saying most people do this so in 80% of the cases your example may be right, the LA may have some aceptance limitations but for the most part it will be close.

Steve

[Crabbypatty]

We dry camp around 40 nights a year, have 648 watts of solar and 4 trojan t125s wet cells. That gives us 250 amps usable power, that is if you want your wt cells to last. they are designed for full draw down, but then you'll get around 3 years out of them. I sold my first TT after 10 years and they were still going strong. All you need is either a volt meter plugged into the 12 volt house system, or check them manually. I would love lithium but prices haven't come down enough for me. As stated a back up gen is a good idea. Since we solar-ed we no longer carry the 3000i, but rather the 2000i. We seem to use it maybe 2x a year as we also work while camping.

While im a solar fan, I am wondering what the cost would be for a propane rv fridge vs cost of solar & batt set up.Just a thought. We seem fine with up to 4 people for a week in terms of food storage typically without a cooler outside.

Good Luck and happy trails!

[BFL13]

Yes, that is correct. In my case, the max size gen we can carry is the 2200 and it runs max at 1700VA which is what the 75 amper wants, so 75 amps is our max amps no way around it. (In the woods, no solar to add more amps)

There is not a single advantage to get LFP in our situation. No weight issue, got enough AH , Gen time is ok. What we have works, no problem for our situation.

There can be situations where an RVer can take advantage of LFP for weight, space, usable AH, etc, but "faster charging" is too easy to be misleading. An RVer must use some actual numbers for his comparison with what "speed" of charging he would get anyway using ordinary batteries, so he is not fooled by the advertising.

He may find that like us, he is gen size limited to a charger size that means no "faster charging" by enough time that makes his life better.

[n0arp]

BFL13 wrote:
...

EDIT--ok, say I had the same set-up only with LFP so no amps tapering. It all gets done at 75 amps. 184/75 is 2 hrs , 27 min. so I would save 33 minutes (from 3 hours) of gen time. Not quite the same as "four times faster" is it?

How about I do a 50-80 with my four 6s? Now it all gets done at 75 amps where amps start to taper at 80% SOC. 150AH in two hours. Swap to LFP and--oops--still 150AH in two hours.

The "4x faster" component comes from the C rates the batteries are rated for. Most GC2 batteries are rated for C/3 charging while LiFePO4 1C or above. That's three times the speed - not accounting for the "aboves". They also don't have a slow absorption stage at the end (as you alluded to in your edit). If you have the chargers/generators to support the charge rates, they do charge that much faster. If you want the most life out of your lead acid batteries, most manufacturers say not to charge at more than C/10. That means for optimal life, you should be charging your bank of four GC15s at only 46A.

In practical application, you can buy larger chargers (or parallel them), larger generators, and charge off your solar array at the same time - so you can get closer to those theoretical limits. I've seen as much 6.3kW going into the LiFePO4 bank in my fifth wheel from multiple sources - that's a charge rate of over 500A in 12V terms. If I had a bigger genset, I could add more chargers or swap out my current ones to charge faster. A lot of people who upgrade to Lithium also upgrade their chargers at the same time, to take at least partial advantage of this.

[BFL13]

wintersun wrote:
An electric only fridge is a poor choice for dry camping. It will take 300AH of battery capacity and 300W of solar panel production at a minimum. With lead acid batteries the 300AH will provide only 150AH for the fridge and everything else in the RV as going below 50% SOC will greatly decrease their useful life and increase the time it takes to recharge them.

For an electric only fridge the best solution is to invest in lithium phosphate batteries that can take a 80% discharge without damage and that can be recharged at 4 times the rate of lead acid batteries so the generator run time will be greatly reduced and solar charging will be more effective during the limited hours of daylight.

I don't think you have done the calculations for that.

You keep seeing this claim about faster charging with LFP, but nobody explains how to do that. EG this "4 times the rate" claim that will reduce gen time.

To me that must mean restoring four times the AH in the same time that it would take with FLAs . Or same AH in 1/4 the time.

If you now have four 6s at 460AH and a 75 amp charger powered by a 2200w gen (like my set-up), that means you can do a "50-90" (184AH) in about 3 hours.

To do that in 1/4 the time- 45 minutes-that means charging at 245 amps. (184 x 60/45) So first you need a 245 amp charger or combination of chargers, and a generator to run that.

I doubt that is what was meant! So how about some realistic numbers with a realistic RV set-up for chargers and gen sizes and the LFP bank vs the four 6s, a 75 amper, and a 2200w gen?

EDIT--ok, say I had the same set-up only with LFP so no amps tapering. It all gets done at 75 amps. 184/75 is 2 hrs , 27 min. so I would save 33 minutes (from 3 hours) of gen time. Not quite the same as "four times faster" is it?

How about I do a 50-80 with my four 6s? Now it all gets done at 75 amps where amps start to taper at 80% SOC. 150AH in two hours. Swap to LFP and--oops--still 150AH in two hours.

[Dusty_R]

You also need to consider where you spend most of your time with your RV. For example, Michigan is 47th of the 48 continental states.

[n0arp]

time2roll wrote:

jshupe wrote:

pianotuna wrote:
Start with an energy audit. Decide how much reserve capacity you want. From that design the battery bank. Build a solar panel system that will recharge the battery bank.

This is the proper way to go about it.

I prefer to max out the solar and deal with the consequences.
Solar is so inexpensive today there is no reason to aim for the minimum.

See my sig - I will counter though, that batteries are heavy, expensive, or both when in large quantities.