Testing myself

[Scott3569]

Ok guys and gals, I want to see if I am comprehending correctly from the people that have tried to explain things to me..

Amps X V= W

So an agm battery that is rated for 100Ah= 1200wh

If you only use 50% of available wh your battery will last longer..

So with the battery above I would have 600wh to bring me down to 50%.. 

That sound about correct?

 

[highdesertranger]

Yes,

Do I win something.

Highdesertranger

 

[Scott3569]

Yes,

Do I win something.

Highdesertranger

yeah incredibly you have won 10 million dollars monopoly money

 

[bullfrog]

^^^what he said, is there a second place prize? Now you need to figure out how many watts you will use for how many hours. Total it all up and see if you have a large enough battery bank. Do some testing and then see if you have enough charging capability to fully charge the battery bank at least every 24 hours, whether it be generator, solar, charger, alternator or grid powered converter in any or all combinations. For most in a small van it will be a small generator with the largest solar system you can fit or carry aided by isolated vehicle alternator charging. If using lithium batteries to save weight and space a DC to DC charger seems to be the best option for aided charging from the vehicle's alternator. Remember you must replace the power you use and a little more in the battery at least every 24 hour cycle while staying above 50%, in my opinion if you want batteries to last several years size your bank to not go below 75% most of the time.

 

[highdesertranger]

Shoot, I thought you were going to say I won the Nigerian Lottery. LOL Highdesertranger

 

[PeterPiper]

Something like that

 

[ldsreliance]

Not to muddy the waters, but the battery capacity rating is measured at a specific "hour rate". I won't attempt a detailed explanation right now, but basically they take an arbitrary time in hours, commonly 20 hours, and then measure what the maximum current the battery can supply for that length of time is. Then they multiply that amount of current by the hours and get the capacity. That is most true for lead acid batteries, but applies in a lesser fashion and different physics with lithium.

For example, if a given battery is tested at the 20 hour rate and can supply a maximum of 5 Amps for that entire length of time, it will be rated at 100Ah (20 hours x 5 Amps = 100).

The reason I bring this up is that the capacity depends on the amount of current you are drawing. If you are drawing that same battery at 1 Amp you would think it should last 100 hours, logically. But it will last longer than that. How much? Tough to say without manufacturer testing data. Good brands like Trojan will rate their batteries at several different hour rates to give you a good idea.

This phenomenon is called the Peukert Effect.

/class dismissed

 

[Scott3569]

Ok so thank for the reassurance Guys..

@ldsreliance
You obviously have a lot of technical knowledge of batteries which is pretty cool..

I don't my mind does not seem to work that way, I am just trying to get the basics down.. try to be a little more laymen when you explain things. Just my opinion.

And thank you for your knowledge

 

[Scott3569]

So now that I have the very basics of the battery..

Lets talk about the Solar panel.

Example:
100W solar Panel

On a perfect day this panel may charge my battery bank at a rate of 9-12 amps Per hour.. Most likely I will never get a full 12 amps of charging out of it..

So for simplicity Lets say I am amble to get 10amps of charging from this solar panel.

That means that in 10 hours it has the capability of giving me 100 amps of power a day..

And if that is true, and we back track to the battery again (100AH battery)

if I consume 50% of the battery a day, then the 100w Solar panel should have no problems keeping up with my consumption.. Again we a talking about a perfect day here..

If I add another 100w Solar panel for a total of 200W then that will basically double the amount of amps gong back to my battery bank..

So If I am consuming 500W of power each day.. 1 Solar panel might be enough as long as I have good weather.. But 2 panels will ensure that I have plenty of power going back into my batteries..


Is that about right?

 

[MrAlvinDude]

For understanding the concept, of using solar to charge batteries, then the math is correct.  And looking simplistic at how batteries are charged, then it is also correct.


However, when a battery comes closer to a full charge, then it is no longer able to store up the energy, at the same rate.

For lead acid batteries, the last about 3-5% will happen very slowly, and the last about 10-20% will just happen slower, than at the maximum rate.
Lead acid batteries will last longer, the more frequent they have a chance to get fully charged. So fully charge once or twice a week, is a good practical goal.

So in your math example, it is a good idea to have the 200W, so the majority of the charge can be done as soon as possible. So there is also a good chance that the slower charge rates can get some time to complete.


Lithium batteries will also slow down, when they are close to being fully charged. But they will maintain the high charge rate closer to the last 5-10%, and might only noticeably slow down, at the last few % .

Unlike lead acid batteries, Lithium batteries do not need to be fully charged at regular intervals. They will do just fine with only being charged to whatever state the solar of the day, is able to do.

 

[Spaceman Spiff]

Lets talk about the Solar panel.

Example:
100W solar Panel

On a perfect day this panel may charge my battery bank at a rate of 9-12 amps Per hour.. Most likely I will never get a full 12 amps of charging out of it..

A 100W panel will give about 6A at about 17V under ideal conditions.  An MPPT controller will modify this to give your batteries about 7A at 14.3 volts.

So for simplicity Lets say I am amble to get 7 10amps of charging from this solar panel.

That means that in 10 hours it has the capability of giving me 100 amps of power a day..

General rule of thumb:  A 100W panel will give 500W of power in a day if fixed horizontal (in the summer).  You can get another 100W if they are fixed, angled toward the sun or ~200W more if you track the sun (again under ideal conditions).

And if that is true, and we back track to the battery again (100AH battery)

if I consume 50% of the battery a day (50A X 12V = 600W), then the 100w Solar panel should have no problems keeping up with my consumption.. Again we a talking about a perfect day here..

If I add another 100w Solar panel for a total of 200W then that will basically double the amount of amps gong back to my battery bank..

So If I am consuming 500W of power each day.. 1 Solar panel might be barely enough as long as I have good weather.. But 2 panels will ensure that I have plenty of power going back into my batteries..


Is that about right?

 

[highdesertranger]

Also you are only getting full solar if you are tracking the sun. For a flat panel on the roof you are only going to get at most 5 hours of max output and max output will never be 100 watts. I would go with 200 watts minimum for that battery. But we are not doing this in the right order.

1. Add up daily power usage.
2. Size battery to #1
3. size solar to #2

Highdesertranger

 

[bullfrog]

There is a lot of lack of consideration and over expectation when it comes to charging with a solar panel, Lots of little things can determine how well it works. The general rule is to over estimate your needs and realize a lot of times you use power during the day and using that power prevents the battery from getting a full charge that it needs. Even lithium batteries need full charge every so often so their Battery Management System can balance them is my understanding and lead acid batteries depend on it even more. It has been said here before you can never have enough solar and that is generally true unless you are daily bulk charging from another source such as the grid or a generator. I use a generator daily at my home base and a 100 watt panel that is angled and moved several times a day to track the sun to keep my 200 Amp battery bank charged it is necessary with heavy overnight loads ( batteries are usually at 50% come morning). I plan to increase my solar charging to 400 watts and my battery bank to 300 amps so I may not have to run the generator more than when we cook using the microwave. At present during the winter in Arizona we have to run it a few hours longer to keep the batteries charged. On my DIY toyhauler I currently have a 210 Amp battery bank with a 305 watt panel and under light loads (batteries never go below 75%) does fine in summer and sunny skies and barely good enough in winter. What I may do is connect the two battery banks when at home base in the winter. Nice thing about solar is you have several options when more is needed and I like the fact I can have a backup system.

 

[XERTYX]

Probably one of the saddest sights I have ever seen is my 200 watt array topping off my battery in that last little bit before full. 200 watts potential, and only about 50w being used to charge the battery. And that's on a bright sunny day.

Physics ham strings you on this one. Think of it like this. If you were trying to fill a drum with water to the very tip tip top without spilling a drop you could fill it very quickly when it was empty. As it gets closer to the top you have to be more careful. And that last couple % you're just dripping water in.

It's a good analogy I think for lead acid charging. So just cuz you have a 200 watt charger doesn't mean it will replace 600wh in 3 hours.

When I was sizing my system I was a bit more pessimistic. Most people assume 5 hours of sun on a good day. I assume 4 hours of sun. 4 hours X 200w I expect about 800 watt hours potential on that good day.

As I normally use no more than about 400 watt hours this suits my needs just fine. My panels are mounted flat on my roof. No tilt mount YET. Usually as soon as its light out I'm seeing charging to my battery. Most days in fact after about 9am my fridge is no longer pulling down my battery. It's running on solar while the battery is charging.