Newby needs help with choosing batteries

[SunEagle]

I think I'm going to go with a 200 watt kit that comes with a 30amp charge controller with this set up instead of the 55 ah battery what size should I go battery should I go with ?

The battery size will depend on what type (PWM or MPPT) charge controller you get.

With a PWM then the charging amps will be the total of that 200 watt system can produce. Probably around 11 amps which would match up to a 100Ah battery.

If you are using a MPPT CC that could produce almost 17amps (200w / 12volt = 16.7a) which would allow you to go with a 150Ah battery.

Sunking answered your question. 20% DOD means there is 80% SOC left in the battery. SOC = State of Charge.

[Jessejames801]

I think I'm going to go with a 200 watt kit that comes with a 30amp charge controller with this set up instead of the 55 ah battery what size should I go battery should I go with ?

[Sunking]

When you say 20% do you mean you only use 20% and want stop using the battery once it drops down to 80% charged ? Or you want to stop using the battery once it drops down to 20% charged ?

Stop at 80% SOC or 20% DOD. If you plan to use 1 Kwh per day takes a 5 Kwh battery.

a 12 volt 55 AH battery has a total capacity of 660 watt hours or .66 Kwh with a daily usage 130 watt hours per day.

[Jessejames801]

When you say 20% do you mean you only use 20% and want stop using the battery once it drops down to 80% charged ? Or you want to stop using the battery once it drops down to 20% charged ?

[SunEagle]

So if I get the 100 watt panel and the 55ah battery is it possible to add another 100 watt panel and another battery later on ? What I don't get is why you see people on tv with solar set ups like 15 batteries if adding batteries doesn't raise how long the power lasts ? Also what does dod mean?

First off don't believe everything you see on YouTube. 98% is for entertainment and not truthful.

Second if you want to expand your system adding a new battery to an old one doesn't work because the new battery will drop in life to match the old. That is battery technology which like Physics you can't change. If you want a 200 watt system then get a 100Ah battery now. Don't try to "expand".

Third any battery system that has multiple strings wired in parallel increases the chances of a premature failure. That is because for each battery to charge and discharge "equally" there can't be any difference in resistance. The more connections the higher the resistance.

DOD = Depth of Discharge. Batteries have an estimated number of cycles. Most batteries have the longest life if they are only discharge 20%. Discharging more or a higher DOD % will reduce the number of cycles and shorten it's life.

[Sunking]

Suneagle bail out while you can.

[Jessejames801]

So if I get the 100 watt panel and the 55ah battery is it possible to add another 100 watt panel and another battery later on ? What I don't get is why you see people on tv with solar set ups like 15 batteries if adding batteries doesn't raise how long the power lasts ? Also what does dod mean?

[SunEagle]

His system isn't solar I'm just talking about how long his battery lasts. That kind of got us off track solareagle what do you think about those two battery options ? I also found a fan that is 12 volts and only uses 15watts

I would go with the 12v 55Ah battery. Even if you got 2 of those 6volt batteries your system would only be 12volt 20Ah which is too small and that sales person is incorrect that it would "supply power longer". Going with multiple lower voltage batteries allows you to build a larger Ah rated system with smaller components.

I have 2 x 6volt 232Ah batteries in my RV. That gives me a 12volt 232Ah system which cost about $250. The cost for a single 12volt 232Ah battery would be much more than $250 and it would weigh over 120 pounds.

As for a 15watt 12volt fan, that will help reduce your load but just the fan and pump would consume more than 120 watt hours in less than 7 hours.

Try to remember a small solar battery system (100w panel & 55Ah battery) can only provide you with a small amount of energy on a daily basis. You could use more of the battery but going from just a 20% DOD to 50% DOD will easily cut the life in half.

[Sunking]

I'm not getting ahead of myself at all ! I did not buy anything nor did I plan on buying anything yet I was just looking at prices and i don't think I need a $1400 dollar battery to run a little fan a 10 watt led light and a 3 watt water pump if that really was the case then solar power would be absolutely retarded and I don't think anyone would ever turn to solar power if they had to replace a battery that costs $1400 every couple of years plus the cost of all the other equipment in order to simply run a fan,tiny water fountain pump and a 10watt led light . Paying the electric company for the amount of energy to run these items would be less than paying $1400 for a new battery every couple of years . My friend has a 5th wheel camper and he runs more items than this overnight without recharging the battery on his camper and he said he only paid $200 for them

He is full of crap too.

The killer is the fan and based on the info you provided will take exactly what I have lined out. 90 watts x 10 hours is 900 watt hours every day of the week in any school. You may not like the facts but they are what they are. No 100 watt panel or 50 AH battery is going to touch that fan.

You are right, taking anything off-grid is silly expensive. 5 to 10 times more than buying it from the POCO. It is just a simple fact. Batteries are EXPENSIVE.

[Jessejames801]

His system isn't solar I'm just talking about how long his battery lasts. That kind of got us off track solareagle what do you think about those two battery options ? I also found a fan that is 12 volts and only uses 15watts

[SunEagle]

I'm not getting ahead of myself at all ! I did not buy anything nor did I plan on buying anything yet I was just looking at prices and i don't think I need a $1400 dollar battery to run a little fan a 10 watt led light and a 3 watt water pump if that really was the case then solar power would be absolutely retarded and I don't think anyone would ever turn to solar power if they had to replace a battery that costs $1400 every couple of years plus the cost of all the other equipment in order to simply run a fan,tiny water fountain pump and a 10watt led light . Paying the electric company for the amount of energy to run these items would be less than paying $1400 for a new battery every couple of years . My friend has a 5th wheel camper and he runs more items than this overnight without recharging the battery on his camper and he said he only paid $200 for them

Your friend may have a balanced system but I doubt he only spent $200. You may also be able to spend less than $1400 for a battery system if it is matched to your loads.

I will say you have found out what a few of us having been saying all the time. That power generated from a solar/battery system is much more (5 to 10 times) costly than purchasing it from the electric company. The biggest cost is the battery system which needs to be baby sat and replaced after a few years.

Solar power is not retarded but is expensive. As of now the only way people have been able to save on their electric bill and pay for the system (which can take 8 years) is to use a "Grid Tie" solar system. Any time you add a battery into the mix is when you start to spend a lot more money and end up not saving money.

[Jessejames801]

I'm not getting ahead of myself at all ! I did not buy anything nor did I plan on buying anything yet I was just looking at prices and i don't think I need a $1400 dollar battery to run a little fan a 10 watt led light and a 3 watt water pump if that really was the case then solar power would be absolutely retarded and I don't think anyone would ever turn to solar power if they had to replace a battery that costs $1400 every couple of years plus the cost of all the other equipment in order to simply run a fan,tiny water fountain pump and a 10watt led light . Paying the electric company for the amount of energy to run these items would be less than paying $1400 for a new battery every couple of years . My friend has a 5th wheel camper and he runs more items than this overnight without recharging the battery on his camper and he said he only paid $200 for them

[Sunking]

You are getting way ahead of yourself and should not be buying anything until you determine how many watt hours you need in a day.

[Jessejames801]

I went to a store called batteries plus and there are two batteries I'm looking at getting one is a agm and is a 12 volt 55ah and the other one is a 6 volt 20ah fla battery which I would need 2 of and these are going to be placed outside the trailer so toxic fumes won't be a problem the guy working there said the two 6 volt ones will supply power longer what do you think would be better for my application?

[SunEagle]

Thank you so much suneagle you're making this project seem more attainable. im going to look for a smaller fan that runs off of 12volts and uses a lot less power cause I won't use the led lights very often but I do want to run the pump and fan at night cause I'm making a small little air conditioner (swamp cooler) to keep us cool at night and it doesn't need to be super powerful cause the inside of the trailer is only 4'x6' wide and 4' tall. If I get a battery thatis closer to the 66ah instead of 50 ah would that give me a little more run time ? Also what amp of charge controller would be best for this set up ? And are deep cycle batteries the best type of batteries to use ?

If you are only going to use a 100 watt panel then a 10 amp charge controller will work. Although you might find a 20amp charger for a little more which would allow you to add a second 100 watt panel.

Deep cycle Flooded Lead Acid (FLA) batteries would be my first choice. There are also AGM (Absorbed Glass Mat) which are sealed lead acid batteries that also work but cost more. Their benefit is that being sealed they can be used in places that do not have a lot of ventilation and will not lose their fluid if tipped over.