Battery for a small Renogy system?

[MikeS63301]

I just purchased one of the Renogy 100 watt starter kits. It's the standard 100 watt panel with 30 amp charge controller. It's going in Ruby my 1997 Astro. I'll be charging the typical phone, ipad, maybe laptop, and *possibly* a very small/low draw slow cooker. What size, type, and Ah, battery would be my best bang for the buck?

 

[lenny flank]

The very very rough rule of thumb is to have a minimum of 1:1 ratio--100ah of battery for each 100w of panel. That is for a sunny summer day with no clouds. In winter, when the days are shorter and the sunlight less intense, you will get significantly less power. So many people go instead with a 2:1 ratio--200w of panel for each 100ah of battery.

I have 100w of panel and 100ah of battery, used for a laptop, camera batteries, phone, and push-on hockey puck lights. ikt works fine through the summer. In winter, it BARELY does the job as long as there aren't many cloudy days. I try to save the battery by charging the laptop in a library or something whenever possible.

PS--You need to do the math to see EXACTLY how much power you will be using for all the stuff you want to have, and then size the battery and panel to what you need.

 

[GotSmart]

Slow cooker. You had better read up on power draw.

 

[frater secessus]

My take.  Full refund of the purchase price if you don't like it.  

Door #1:  100w panel + 100Ah battery

Unless you are augmenting solar charging with alternator charging or shore power, , 100Ah of battery would be all the panel would be able to keep charged and healthy (minimum 1:1 watt:Ah).  Maybe a wally world marine battery with removable caps so you could push it hard and keep adding water?  This will work but you will have to be careful with power consumption.

Slow cooker defiinitely out.  Heating/cooling anything with electricity is extremely expensive, power wise.  

Door #2:  100w panel + (another 100w panel OR alternator charging OR shore power charging) + deep cycle bank

With augmented charging (or a matching panel, now on sale for $90 at Home Depot) you could do the traditional 2 x 6v golf cart batteries in series (200Ah+) and have a strong little setup.  You might get away with the slow cooker here but I will encourage you not to.   Step awayyyyyyyyyy from the cooker.  


Door #3:  2 x 100w panel + (alternator charging OR shore power charging) + deep cycle bank

Run a compressor fridge, leave your rotating disco ball running all night, have a party.  You sold that cooker in the garage sale, right?   Well played.

Door #4:  100w panel + upgraded starter battery

Ok, this one sounds crazier than a sack full of cats but some folks have made it work.  Basically they put a marine/rv or AGM starting battery in place of the starter battery and lightly cycle it down to 80% SoC or so.  Low Voltage Disconnect is mandatory or you could strand yourself.  That Would Be Bad.

 

[akrvbob]

I'd recommend a group 27 Marine battery from Walmart or Sams Club. If you're like most people, you're probably going to kill it so get a cheap one with a good warranty.

That'll be a flooded battery so you'll have to keep the water in it full.

 

[Trebor English]

[font=Verdana, Arial, sans-serif]Door #4:  100w panel + upgraded starter battery[/font]

I have a 75 amp hour "deep cycle" battery for a starter battery.  If it were a golf cart deep cycle the 50% suggestion would apply.  I figure it is better than a starter battery since it actually uses 20 to 30 ml of water per cell per month.  I'm good with taking 10%, 7.5 amp hours, without a second thought.  If I take 20% it still starts fine but I avoid that deep a cycling.  

Since there is one battery there is no solenoid.  On days that I drive the alternator charges.  So does the 100 watt panel.  With this setup I can stay parked as long as I want.  The fridge runs out of food first.  

This is a cheap way to have electricity.  I recommend it only if you are motivated to be cheap.  No sack, no cats.

 

[GypsySpirit]

I just purchased one of the Renogy 100 watt starter kits. It's the standard 100 watt panel with 30 amp charge controller. It's going in Ruby my 1997 Astro. I'll be charging the typical phone, ipad, maybe laptop, and *possibly* a very small/low draw slow cooker. What size, type, and Ah, battery would be my best bang for the buck?

I'm doing the exact same thing.  Still making my mind up on which battery and weeping profusely over the loss of my slow cooker.

 

[John61CT]

No slow-cooking off solar electric until you get a **lot** more panels I'm afraid sorry, get a genny or mains campsite for that.

The best battery value by far is door #2

2x6V Duracell (actually Deka/East Penn) deep cycle golf cart batteries, less than $180 per 200+AH pair from BatteriesPlus or Sam's Club.

Have yet to come across anything trustworthy cheaper at lower capacities.
And no harm in being bank-heavy for now, I'll bet your solar catches up until the roof is full anywat, and in a good bank you don't want to add more batts later, shoul all be the same age.

12V so-called "deep cycle" from big box are all a fraud, all things being equal won't last even a quarter as long as the GCs. And not even cheaper per AH anyway.

 

[hausmutti]

[font=Verdana, Arial, sans-serif]Door #4:  100w panel + upgraded starter battery[/font]

I have a 75 amp hour "deep cycle" battery for a starter battery.  If it were a golf cart deep cycle the 50% suggestion would apply.  I figure it is better than a starter battery since it actually uses 20 to 30 ml of water per cell per month.  I'm good with taking 10%, 7.5 amp hours, without a second thought.  If I take 20% it still starts fine but I avoid that deep a cycling.  

Since there is one battery there is no solenoid.  On days that I drive the alternator charges.  So does the 100 watt panel.  With this setup I can stay parked as long as I want.  The fridge runs out of food first.  

This is a cheap way to have electricity.  I recommend it only if you are motivated to be cheap.  No sack, no cats.

So, you don't worry about getting stranded?

 

[John61CT]

So, you don't worry about getting stranded?

I wouldn't do that (door #4) myself without a good battery monitor (SmartGauge) and an adjustable LVD on the House Loads circuit.

Which would be almost as expensive than a 400+AH bank of 4 GCs.

I have however nominated one 12V block out of a bigger bank to act as Reserve / Starter behind an LVD.

Could do that without the BM.

But OT here.

 

[John61CT]

So, you don't worry about getting stranded?

A good Lithium jumpstarter powerpack kept charged in the glovebox can be a reserve starter too.

 

[akrvbob]

A 100 watt system probably isn't going to keep a pair of golf carts charged. They'll probably die faster than the group 27 and be twice as costly a mistake. In an Astro he doesn't have a lot of spare room for batteries and their weight.

 

[MikeS63301]

A 100 watt system probably isn't going to keep a pair of golf carts charged. They'll probably die faster than the group 27 and be twice as costly a mistake. In an Astro he doesn't have a lot of spare room for batteries and their weight.

I guess I should have mentioned this is my first build and my first trip with this is to the RTR. I'm still learning obviously. I looked at group 27 and 31 batteries. I've kept everything cheap and easy. The solar was just a bonus because of a great Amazon deal. Looks like I'll probably just go with a Duracell 31 from Batteries Plus up the street. 
I'll try not to kill it. 

:angel:

 

[John61CT]

Not saying you're wrong for your sitch, but just want to remind everyone, rules of thumb are not hard science:

As long as you **know** you're only taking out 80% of what your charge source(s) can replace every day, you can have 1000AH bank and treat it right.

If that's only 20AH a day in good weather that panel's plenty.

And a proper deep cycle bank will last for 2000+ cycles if it's rated say 800 at 50% DoD.

Yes it takes a more sophisticated user, not relying on volts to guess SoC, but a cheap DMM and $30 ammeter with AH counting's all you need for gear, if you don't want to shell out for a proper BM.

Obviously silly example (too heavy! ) just to make the point: income greater than outgo's really the only hard rule.

Especially if you're likely to add a genny or solar later, can do that anytime.

Or in a poor climate or far from the equator.

Or getting to mains power on the weekends.

And the fact the $180 spent on 200+AH is getting true deep cycle longevity, if you're going to murder the batts anyway might as well still get double-triple the lifetime at hardly any more money.

Sure, you can buy from good warranty place and file a claim before the year is up, that may work in practice, but not my choice.

'Nuff said. . .

 

[RVTravel]

This one?
https://www.batteriesplus.com/battery/rv/deep-cycle/12/sli31mdp

 

[John61CT]

This one?
https://www.batteriesplus.com/battery/rv/deep-cycle/12/sli31mdp

Rated for **way less than half** the cycle lifetime of the GCs, really just a slightly beefed up starter, would bet real money doesn't deliver rated AH even after being properly broken in.

The best of the 12V FLA G31's (and other automotive sizes) are Trojan SCS series, US Battery DCXC and maybe Crowns.

but they are also half the lifetime and **lots** more money.

Really the only economic argument against the GCs is weight.

Being unwilling to measure your AH in and out are going to murder whatever bank anyway if you don't have enough incoming.

 

[RVTravel]

John61, I was not asking you. I am asking Mike. We know you only accept golf cart batteries...lol.

 

[frater secessus]

So, you don't worry about getting stranded?

Trebor and Sternwake were the two I had in mind who were doing it, and both are clever, careful people.   

I'll point out that a solenoid and low voltage disconnect serve different purposes.  The LVD in the one-battery setup keeps you from running your battery down below a given voltage setpoint.   Luckily there is a LVD function built right into the LOAD output of many (most?) controllers.  

The solenoid is for connecting the house battery to the starter batttery's charging source.  Since there isn't a house battery in the 4th option one the solenoid has nowhere to go.

 

[frater secessus]

A 100 watt system probably isn't going to keep a pair of golf carts charged.

That's why they didn't appear until additional charging was proposed in the 2nd option.

 

[frater secessus]

John61, I was not asking you. I am asking Mike. We know you only accept golf cart batteries...lol.

John was explaining (correctly) why flooded GC batteries are typically the best overall value when charging from solar.    The choices people make will not affect him;  there is no commission paid on advice.