Solar Questions from a Solar Noob

[tomkatb]

400 watts of panels will often not be enough.

If you live in the Midwest the sun does not always shine. The best campsites for ac operation have lots of shade trees that disturb the sun.

The further north you are the less the panels will produce.

The deal killer is the refrigerator. The hotter the weather the more they use. The gas furnace is also a big user.

With that fridge I would guess that operating the generator less than daily might be an issue.

First you need batteries. Likely a fancy new Li type of converter. That will get you thru the night. You need close to 200 amps available to get two nights. Two battlebornes and a converter is likely $2500.

The more panels the better. Most folks in the Midwest do not get 100 amps a day from 4 100 watt panels mounted horizontally. Out west maybe.

[Flybob]

I would not get discouraged by the above comments. If you boil down all the suggestions above, the message is; before you purchase anything, try to get a good estimate of your actual demands then tailor your system to meet that demand. Also if you are going solar, I always recommend getting a controller that is about 30-40% larger than you think you need to allow room for the addition of additional panels if needed.

[aircommuter]

Originally Posted by Flybob

I think you are referring to amps and not watts. Four 100W 12V panels connected in parallel will produce about 20A of current in the lines between the panels and the charge controller. The same four panels connected in series will produce approx 48V at approx 5A of current in the lines. The total power is the same in both cases you simply have lower line loss in the series setup.

Since watts is just amps times volts it comes out the same, with solar panels the voltage varies with sun angle and load. The charge controller and the batteries stabilizes the voltage. Just explained it that way to try to minimize confusion because it seemed necessary.

[bikendan]

Originally Posted by IchLiebeBier

Geesh...clearly I don't get this at all. I'd probably flip a switch and my trailer would take the park out like Bikini Atoll.

I'd probably need to be safe and take it to an installer and cough up the money.

I am clueless when it comes to electricity. Clearly.

That's one reason why we have a Honda 2000i inverter generator. Couple hours each day to recharge batteries.

[IchLiebeBier]

Originally Posted by bikendan

That's one reason why we have a Honda 2000i inverter generator. Couple hours each day to recharge batteries.

that's where I'm leaning. I'd just need to upgrade the batteries to get through the night with the fridge and furnace fan if necessary.

You say it recharges in a couple of hours. what is your battery setup?

[bikendan]

Originally Posted by IchLiebeBier

that's where I'm leaning. I'd just need to upgrade the batteries to get through the night with the fridge and furnace fan if necessary.

You say it recharges in a couple of hours. what is your battery setup?

I've had dual 12v dual purpose marine batteries setup and single 12v group 27 setup.
Will be going to dual 6v golf cart batteries in January/February.
Changed all lights to led before summer and don't have to run furnace much, living on West Coast.

[James Ww]

Originally Posted by bikendan

I've had dual 12v dual purpose marine batteries setup and single 12v group 27 setup.
Will be going to dual 6v golf cart batteries in January/February.
Changed all lights to led before summer and don't have to run furnace much, living on West Coast.

What would be the advantage of (2) 6v golf batteries vs (2) 12v batteries - wouldn't that be less capacity (sorry if I'm hijacking the thread for a quick question, but I figured the OP opened it up lol

[Larry-NC]

Originally Posted by James Ww

What would be the advantage of (2) 6v golf batteries vs (2) 12v batteries - wouldn't that be less capacity (sorry if I'm hijacking the thread for a quick question, but I figured the OP opened it up lol

James, the golf cart batteries are different construction than typical 12v batteries (car batteries or marine batteries).

They have more capacity. They have the same footprint but they are taller and probably have more plates. They can deliver more amp-hours than a pair of 12v car or marine batteries. This is possibly because they have more lead plates than a car or marine battery.

They also can withstand deeper discharge without damage than car or marine batteries by design. This could be a result of thicker plates (less likely to develop holes when lead plates are converted to lead sulfate in solution--the holes don't fill in when the battery is charged.). A battery expert may have a better answer.

There is apparently only one manufacturer who makes a 12v battery to golf cart battery design parameters. They seem to be expensive. That's why folks tend to use two 6v batteries in series.

There are posts elsewhere on this forum that give comparative amp-hours for two 12v batteries in parallel and two 6v batteries in series.

Larry

[bikendan]

Originally Posted by James Ww

What would be the advantage of (2) 6v golf batteries vs (2) 12v batteries - wouldn't that be less capacity (sorry if I'm hijacking the thread for a quick question, but I figured the OP opened it up lol

For one thing, nearly all 12v batteries, on RVs, are not true deep cycle batteries. They are dual-purpose marine batteries. 6v golf cart batteries are true deep cycle batteries. True 12v deep cycle batteries, lime those from Trojan, are not common and cost more than 6v golf cart batteries.

[tomkatb]

GC2 batteries (interstate) 6 volt batteries have a smallish foot print. However, are typically taller than 12 volt batteries. Got to measure!

Output sort of has to do with weight. Heavier batteries have more amps(lead acid).

6 volt GC2 batterie sets have fewer cells than a set of 12’s. Bigger parts.

Generally they have more recharge cycles. I.E. more durable, less damaged by abuse.

So if you can tolerate the weight and size, two sixes should be better in an rv.

Interstates are typically $100 each at Costco. The Trojan equivalent are more expensive. Better? Likely, do not know.

[TitanMike]

Originally Posted by tomkatb

GC2 batteries (interstate) 6 volt batteries have a smallish foot print. However, are typically taller than 12 volt batteries. Got to measure!

Output sort of has to do with weight. Heavier batteries have more amps(lead acid).

6 volt GC2 batterie sets have fewer cells than a set of 12’s. Bigger parts.

Generally they have more recharge cycles. I.E. more durable, less damaged by abuse.

So if you can tolerate the weight and size, two sixes should be better in an rv.

Interstates are typically $100 each at Costco. The Trojan equivalent are more expensive. Better? Likely, do not know.

If one can't tolerate the weight and size, and wants extra USABLE capacity, more charge discharge cycles, faster charging, all at 1/4 the weight of two GC-2's, ONE LiFePo 100 ah battery will fit that need.

Yes, GC-2's will work but a LiFePo will deliver all 100 amp hours which is what most GC-2 users will get from their battery bank if they follow the 50% "rule". Even better, the LiFePo battery can be recharged in a fraction of the time a Lead Acid Battery will take to replace the same number of amp hours.

Yes, they do cost more. But they provide the benefit of smaller footprint, lower weight, and will be the last battery the average "camper" will ever buy with a lifetime of 2,000 to 5,000 cycles.

No more battery watering, corrosion, or depth of discharge anxiety.

Buy once, cry once.

BTW, one does not HAVE to replace their converter just because they change to LiFePo batteries. Especially if they use them in conjunction with Solar.

Yes, the old converter will not charge to 100% state of charge, only about 95%. The solar controller however can most likely be set to the higher voltage for LiFePo/s that will top off the batteries at 100% in short order.

[larry2c]

Originally Posted by IchLiebeBier

I'd probably need to be safe and take it to an installer and cough up the money.

If you decide that is the route you want to go, make sure you do your homework and get references/recommendations on the folks designing and installing your system. Otherwise you may pay more than it's worth and get less than you expected.

[IchLiebeBier]

Originally Posted by larry2c

If you decide that is the route you want to go, make sure you do your homework and get references/recommendations on the folks designing and installing your system. Otherwise you may pay more than it's worth and get less than you expected.

I'm leaning towards two or three LiFePO4 and a small generator twice a day to top it off. Living and doing all our current camping in the Virginia area, I doubt the solar option would be worth the expense. When we camp, there are a usually lot trees blocking the sun, and 400 watts of portable panels to deal with that would be too much hassle IMO. Plus, if we go to the boondocking sites we want to go to (in the mountains), I'd probably only get 3 to 4 hours of halfway usable sun anyway.

The other reason I was considering solar was in the event we had a long-term power outage or something due to storms. But I'd probably need to run the generator around here anyway, especially in the summer.

I might add them on if we start travelling out west. I wouldn't mind moving away from here anyway

[IchLiebeBier]

All,
I'm trying to wrap my head around the mathematical calculations so I can understand this fully. I built an Excel spreadsheet with formulas so I can visualize it.

If a 110 A/C fridge runs at 6.5 amps, that means 6.5 amps per hour at 110v. For 50% cycle time, that equates to roughly 6.5 amps x 12 hours = 78 amps/day (more with inverter efficiency calculated in).

All the online solar use calculators seem to agree with this. But what I don't understand is why I don't need to convert the amp draw to DC. Some websites imply you do.

Since the battery amp hour rating is based on 12v, why would I not use the DC amps conversion for the calculation (65 amps/hour for fridge)? It's pulling from 12v after all.

Thanks.

[Flybob]

You do need to figure in the voltage as the power consumed is in watts not amps. So the 78 AHr at 110VAC is approximately 780Ahr at 12VDC. Another way of looking at it, Your 6.5A AC is approximately 65A at 12VDC.

[SlowrideHD]

First, change your volt value to 120 in your spreadsheet, nothing actually runs on 110v any more. So the Amp draw from your 12v battery bank is ten times that of what your 120v appliances are consuming. Actually, your battery bank is closer to 12.7v but using the (10X) factor helps take into account the loss in efficiency from inverters.

What might help you is to just use "watts" as your comparative. P=V*C or watts=volts x amps.
For example, lets use a 12 volt battery bank with two 6v golf cart batteries in series. Each GC battery rated at 6v, 225 Amp. In series you have 12v and 225 amps. Using the "50%" rule, useable power of 12 volts and about 110 amps, or 1,320 watts of power. Assuming your fridge will use about 350 watts while running (3 amps at 120v) your battery bank will run it continuously for less than 4 hours. This is why so many people are surprised that their new rig with the big residential fridge runs their batteries down every night.
A nice device to have is a "Kill-o-watt" meter. (search amazon). You plug this in a receptacle and then plug your 120v appliance into that. It will tell you volts, amps, watts, etc and keep a running total of use as long as it remains plugged in. A very valuable tool for estimating just how many watts you will use over a 24 or 48 hour period. Pretty inexpensive as well.

[tomkatb]

1. What will my refrigerator amp rating be? I’ve seen several numbers such as 6.5 amps and 3 amps, and several discussions about compressor kick on, defrosting, etc. I found one post that said count on anywhere from 100-150 amp hours per day.

Find out the wattage of the fridge, usually the easiest to work with. P=IV In general ac to dc amps is 10 to 1.

2. If 150 is correct, and with other electrical requirements, I assume I should shoot for at least 400 amp hours for batteries to keep the charge above 50%. So we’ll assume 4 x 100ah batteries for the sake of discussion. Correct?

Depends on the fridge. However you will use more juice. Parasitic loads, stereo, lights, etc. 4 Costco six volt batteries would be best.

3. How long would it take a 3500 watt generator to charge the 4 batteries wired in parallel from 50% to full?

Depends on the converter but a 80-90% charge of 100 amps in 2-3 hours. Lead acid batteries then require slow charge to get higher. Solar does this well. Lithium is better.


4. If I get 6 hours of full sun and can use solar, how much solar wattage would I need to keep the batteries full throughout the day (following generator charging), if only the fridge is running?

6 hours x per 12 volt panel at 100 watts equals 25 amps. You will use near 3-4 amps per hour. So one panel might stay even on the best day for a few hours. 4 or more. More to be sure. 12hours

4a. What amount of solar would I need to NOT use the generator, given good sun to get from 50% to full?

200 amps? 8-10 panels 25 per panel on a good day. I suspect more batteries might be necessary.


5. Is my Furrion solar ready wiring of a sufficient gauge to handle the required wattage from #4 above, or should I attach directly to the batteries?

No Wire size.

6. And finally, if I plug the solar into the Furrion plug, or even directly to the batteries, should I remove them before turning on the generator, or can they remain connected?

Does not matter. I think. You need a fancy controller for the panels which would take care of everything.

Residential fridges are not really intended for boondocking. Most folks plug in every night.

4 panels on the roof and 4 costco six volt batteries or two lithum batteries and a gas electric fridge would be wonderful out west

[IchLiebeBier]

All,
Thanks for the replies. Before I address my confusion again, I'll let you all know the specifics of my system right now. That might clear up the reason I'm asking the question.

Since I started this thread, I have upgraded to 2 x Battle Born LiFePO4 100ah batteries and the PD4655LIV converter to charge them fully. The batteries are wired in parallel. I may or may not add solar. I do not have it at this time.

I also installed a Victron monitor.

My inverter is a 1200 watt Xantrex Freedom and only powers my 10.7 cu ft residential fridge (6.5 amps).

My new camping generator is 2000w/1600w Champion generator. I would not bring my 4000w/3500w generator due to noise.

Now, back to the question...

When I do the GoPower solar calculator, and manipulate the number to get 80 amps (their calc is based on 10 amp fridge), it counts the fridge at approx 80 amps for the entire daily run time and tells me I have 120 amp hours to spare (not counting anything DC at this time). So in my case, that should be around 12 hours or so run time with 50% duty cycle. That leaves the same 120 amp hour reserve.

So what confuses me is if it's 10x that for DC amps, why is the calculation not 65 amps per hour, bleeding off 200 amp hours of batteries in 3 hours (give or take), since the batteries are DC?

The watts calculation makes sense. And I set up my spreadsheet for that at first. But I was just trying to figure out why the online calculators use AC amps vice DC amps for the fridge in the daily calculation. Is it because the inverter is pulling WATTS from the battery, and the fridge is now using power already converted to AC?

I hope that's a bit more clear on my part.

[Larry-NC]

Originally Posted by IchLiebeBier

All,
Thanks for the replies. Before I address my confusion again, I'll let you all know the specifics of my system right now. That might clear up the reason I'm asking the question.

Since I started this thread, I have upgraded to 2 x Battle Born LiFePO4 100ah batteries and the PD4655LIV converter to charge them fully. The batteries are wired in parallel. I may or may not add solar. I do not have it at this time.

I also installed a Victron monitor.

My inverter is a 1200 watt Xantrex Freedom and only powers my 10.7 cu ft residential fridge (6.5 amps).

My new camping generator is 2000w/1600w Champion generator. I would not bring my 4000w/3500w generator due to noise.

Now, back to the question...

When I do the GoPower solar calculator, and manipulate the number to get 80 amps (their calc is based on 10 amp fridge), it counts the fridge at approx 80 amps for the entire daily run time and tells me I have 120 amp hours to spare (not counting anything DC at this time). So in my case, that should be around 12 hours or so run time with 50% duty cycle. That leaves the same 120 amp hour reserve.

So what confuses me is if it's 10x that for DC amps, why is the calculation not 65 amps per hour, bleeding off 200 amp hours of batteries in 3 hours (give or take), since the batteries are DC?

The watts calculation makes sense. And I set up my spreadsheet for that at first. But I was just trying to figure out why the online calculators use AC amps vice DC amps for the fridge in the daily calculation. Is it because the inverter is pulling WATTS from the battery, and the fridge is now using power already converted to AC?

I hope that's a bit more clear on my part.

There is no difference between AC and DC amps.

Watts = amps times volts, or as EEs say, P=V*I.

So your residential refrigerator consumes P=120v * 6.5 amps= 780 watts.

Assuming your inverter is perfect, that's 780 watts in and 780 watts out. So the current (amps) in at 12 v is calculated as: I=P/V or I=780/12=65 amps.

I've avoided using the AC/DC nomenclature. It's a short cut for 120v/12v but it's confusing you. It really has nothing to do with whether the current is alternating or direct.

Note that the algebra shows at factor of 10 change in the current. This is a consequence of holding the power constant and changing the voltage by a factor of 10. The current has to change inversely by the same factor.

Algebra is good!

[Flybob]

I think what is confusing things is you are using amps at several different voltages. 80A (this is actually 80AHr) in an entire day is 3.3A or roughly 6.5A for an item that only runs 50% of the time ( as you stated earlier). This current X the number of hours it is drawn is the number of amp hours. The problem is this is 80AHr at 120VAC. The 12VDC current needed to supply that is ten times that number or 800AHr at 12VDC. As suggested, I would get a Kill-a-watt and actually measure the fridge power consumption.