How accurate are online solar calculators?

Van Living Forum

Help Support Van Living Forum:

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
I have about 364 watt hours total. I don't know how accurate that is becuase im guessing on hours used and wattage of leds but 364 ah is what i inputed.

Alt e gave me 300 watts panel, 310 ah battery, 25 amp charge controller.

Renogy gave me 196 watt solar and 60 ah battery

Doing my own calculation (following instructions on renogy website) I got 252 watts solar and 61 ah battery.
364/2=182/.8=227.5/90%=252 watts
364×2=728/12=61ah
60 amp hours sounds really low and i think i should be able to get by on 200 watts.

My loads are:

Maxxair fan 60 watts (probably high but i used 12v ×5amps) 3 hrs
Dometic cf18 37 watts 4hrs
Cell phone 24 watts 1hr
Laptop 50 watts 2hr
3 LEDs ?watts i think i used 1w in the calculation but i used the same for both.

What do you think? Which calculation sounds right? Or am i way off and missing something?
 

Wabbit

Well-known member
Joined
Jan 26, 2015
Messages
2,030
Reaction score
13
I would go the 300w 300ah route.

Your fridge at 4 hours, why not 24 hours?

Not sure what led lights you have, but 1w seems low, maybe?

Depending on where you plan to stay, hot weather the fan might be on longer than 3 hours.

Best of luck! And I'm not a hundo on anything I say lol.
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
The fridge will only cycle that infrequently in the mildest conditions.

Plan for worst case not optimal scenario.

300w for sure, of course more would be better when you're on hot cloudy weather.

A pair of Duracell FLA GC2s from Sam's or B+ is a bit over 200AH, good cheap $/AH starting point, anything less won't be true deep cycle.
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
> Your fridge at 4 hours, why not 24 hours?

Average is usually 20-40% duty cycle as a fridge, only gets above 70% as a freezer and/or crazy hot conditons.
 

Wabbit

Well-known member
Joined
Jan 26, 2015
Messages
2,030
Reaction score
13
Yeah, but the fridge is rated at 35w, doesn't that 35w per hour already take that cycling into effect? I don't know, but I would think it does.

X2 on the battery choice John 31st posted up above.
 

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
Wabbit said:
I would go the 300w 300ah route.

Your fridge at 4 hours, why not 24 hours?

Not sure what led lights you have, but 1w seems low, maybe?

Depending on where you plan to stay, hot weather the fan might be on longer than 3 hours.

Best of luck! And I'm not a hundo on anything I say lol.

Im doing alot of guessing becuase I have no idea how these refrigerator work. LEDs guessing again. Not the best idea but i couldnt find anything online. I thought i would get a rough idea then bump everything up a little.
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
> doesn't that 35w per hour already take that cycling into account?

Maybe, or that may be the consumption only while it's running. Side nitpick, no such thing as "35w per hour", either "35 watts as averaged over time" or "35 wH per hour", both are equivalent.

In reality doesn't matter, the % cycling time will vary enormously depending on a dozen different varying factors.

You can't go by mfg estimates, as you buy the gear, get an AH meter on it to get real numbers.

And again, plan your system capacity for suboptimal conditions:

Cloudy weather or panels gets some shading.

High ambient temps, low food-safe internal temps.

Adding new contents regularly without pre-chilling.

Regularly opening the unit to remove contents.

Keeping it half-empty, or low-mass contents.

Only using included insulation, allowing heat build up around condenser/electronics.
 

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
John61CT said:
The fridge will only cycle that infrequently in the mildest conditions.

Plan for worst case not optimal scenario.

300w for sure, of course more would be better when you're on hot cloudy weather.

A pair of Duracell FLA GC2s from Sam's or B+ is a bit over 200AH, good cheap $/AH starting point, anything less won't be true deep cycle.
What about the Vmaxxtanks? Maybe 2 of the 125ah and 300 watts? It's way more expensive but i want sealed batteries so i dont have to worry about maintence and off gassing.
Thats the biggest confusion for me is watts to Ah ratio. To little ah and you drain the battery too far down and too much ah im not really sure. Maybe theres not enough solar to maintain it
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
Really these rules of thumb all yield to two hard facts:

1 don't deplete below 50% often, and

2 don't use as much as you actually put back each cycle

Your situation will be unique and will change, you need the knowledge and tools to properly care for the bank.

IMO nothing beats those FLA GCs for value long term. Topping up with water and fume issues are a tiny price to pay IMO.

Sealed are harder to care for and, even coddled, won't last nearly as long as FLA, even Odyssey, Lifeline or Northstar, and those are expensive.

I'm very skeptical of any other AGM, maybe cheaper up front but will cost even more $ per AH per year of service.

On the other hand, making that big an investment with your first "learning bank" is risky.
 

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
Ok thanks. I guess if i put them in a battery box that would help.i dont mind checking the water, i just don't want it to be dangerous and i don't want to cut holes to vent.
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
Putting them into a sealed box concentrates the hydrogen, that's when you need to vent.

Let it dissipate is safer, unless you find you're sensitive.

If dwelling you need to generally ventilate somehow anyway.
 

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
John61CT said:
Putting them into a sealed box concentrates the hydrogen, that's when you need to vent.

Let it dissipate is safer, unless you find you're sensitive.

If dwelling you need to generally ventilate somehow anyway.

So if I'm inside and the van is all closed up do you think cracking the windows and running the maxxair fan would be enough? I plan to put the batteries behind the seats.What exactly is the problem with offgassing? I mean is it really as dangerous as its made out to be? It sounds like maybe no more dangerous than running a heater inside if you have proper ventilation. Is there a smell or any other symptoms that i should look for when its happening or about to happen?or is it a natural reaction to the charging process?
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
Yes MaxxAir is very high air exchange.

Besides the active side, say drawing into the space, you need a passive exit port.

Locate that near the batt, ideally also fridge heat and cooking smells, all go out together.

Or reverse, really the same deal at high CFM.
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
Gas is produced by bubbling when charging at high amp rates, toward the end of the process, very healthy for the batts.

Only dangerous if allowed to build up in the batt box, spark+concentrated hydrogen = "sudden fast expansion event" :cool:

Some find it smelly or irritating, not dangerous with a little ventilation.
 

Wabbit

Well-known member
Joined
Jan 26, 2015
Messages
2,030
Reaction score
13
Yeah there's a bit of a smell with my 200w and 215ah battery bank at times, and I wouldn't sleep over the batteries. I think off gassing is more of an issue for people that have bigger setups than mine or smaller living area than me. So, it is something to be aware of, it might apply to you or not.
 

Scout

Well-known member
Joined
Oct 3, 2017
Messages
161
Reaction score
0
Thanks everyone for all the help. I have one more question. I plan to put the batteries behind the seat.I was going to ratchet strap them down but if it has caps maybe i cant do that. How do you mount your batteries?
 

John61CT

Well-known member
Joined
Nov 22, 2016
Messages
8,057
Reaction score
8
Any strong strapping system is fine, just remove when necessary for maintenance checks if you can't find a path clear of the caps.

Kayak or canoe straps take up less room than ratchet style.

Or for many standard sizes, you can buy steel frames.

A plastic tray to catch any spills is a good idea, or special paint to protect steel.
 
Top