battery question from another noob

coastalar

I have built a semi portable solar generator for use when/if the grid power in SW Florida is not available. I currently have 2 100 watt pv panels (will probably increase to 3) and will start out with a 200 ah bank (would like 400ah but dont think I can charge them with 3 or 400 watts of PVs). Ive built this on a rolling cart, the bottom shelf for the batteries, middle for electronics, and top shelf to use as a desk. The electronics are sitting on a board so there is not an open direct vent from the batteries at the lower level.

My big question is, could I get away with a wet battery or do I need to go with agm because of venting. I know agm will be better because of no maintenance but will the gases from the wet batteries under the electronics be a no go even though there is a solid separation?

Cariboocoot

Re: battery question from another noob

Welcome to the forum.

The gassing issue would depend on how much ventilation there is in the area. The solid barrier between the two levels should prevent any problems with acid spray (providing you're careful). The released hydrogen & oxygen only becomes an issue if it is trapped in a closed space and thus can build up to explosive levels. The really do not off-gas as much as some people think.

BTW, your two 100 Watt panels will only provide about 10 Amps peak current on a 12 Volt system. That's pretty marginal for 200 Amp hours as it is. The third panel would be a welcome addition.

coastalar

Re: battery question from another noob

Thanks for the reply and for the welcome!

The bottom battery area will be open so there will be no chance of any gasses collecting. I was concerned that the electronics were directly above the batteries but was hoping that with the batteries being open and a solid barrier would be sufficient. Maintenance would still be a pain.

I was already thinking I needed a third panel, your imput just moved it up on the priority list. I would like 400ah storage but even 4 panels would be difficult in my current semi "portable" configuration.

Thanks again for your help.

westbranch

Re: battery question from another noob

devils advocate: why do you want it to be semi-portable? If you don't have those batteries on a float charger all the time (or a regulated charger) they are going to die, sooner or later, but TWD... So that leads me to think the install should be more permanent. What are the limitations for a permanent PV array?
What Charge controller are you using?
Is there an inverter involved? What size?
Do you have a transfer switch installed? You weren't going to use a suicide cord were you?

lots more questions later...

hth

coastalar

Re: battery question from another noob

westbranch wrote: »

devils advocate: why do you want it to be semi-portable? If you don't have those batteries on a float charger all the time (or a regulated charger) they are going to die, sooner or later, but TWD... So that leads me to think the install should be more permanent. What are the limitations for a permanent PV array?
What Charge controller are you using?
Is there an inverter involved? What size?
Do you have a transfer switch installed? You weren't going to use a suicide cord were you?

lots more questions later...

hth

I welcome devel advocates, it helps me from making mistakes.
Im keeping this as portable because I live in an HOA that would not take kindly to such an eyesore (until they needed it to charge their cell phones). Im using a 40 amp charge mppt controller and a 2000 watt pure sine wave inverter for the electronics.

I will keep the batteries charged from the grid, use it periodically, but is meant mainly as a backup incase the grid power is not available. I plan to use is for a couple of led lights, ham radio, small 5" TV, cell phone, tablet recharge and if available, internet router. At this point I am not tapping into the house wiring so no transfer switch. This is meant for a temporary basic system.

Cariboocoot

Re: battery question from another noob

Um, when the power goes out there's thing thing you might really want to keep running: it's called a refrigerator. Saves having to throw out all that $$$ in food.

westbranch

Re: battery question from another noob

you might want to look into some of these products to use while your fridge is running

http://store.nokero.com/Product-s/1832.htm

ps your 1 battery should run your fridge for a little longer than 24 hrs, depending on its draw...

lots of options

coastalar

Re: battery question from another noob

A fridge would be a welcome item in SW Florida for sure. The full size one I have will draw 11.6 amps but I do have a little under counter one that I was hoping to use if I could that only pulls .9 amps. I dont keep a lot of refrigerated/frozen food so im not too concerned about losing a big investment. I keep emergency food that does not require refrigeration.

Since I will only be using 2 or 3 led light bulbs, radio etc sparingly for only a portion of the day, a cold beer now and then would sure help the moral.

BB.

Re: battery question from another noob

Be careful when working with Amps and how much power you use...

0.9 amps * 120 Volts = 108 Watts
11.6 amps * 120 Volts = 1,392 Watts

A typical modern refrigerator/freezer will draw around 1 amps @ 120 VAC... Although they can easily draw 5 Amps or more when defrosting/starting the refrigeration compressor.

5 amps * 120 VAC = 600 Watts

Also, remember if you are running a 12 volt battery bank and an AC inverter--The DC current on your battery bank is going to be 10x the 120 VAC current:

50 amps * 12 VDC = 600 Watts

-Bill

Cariboocoot

Re: battery question from another noob

It's actually worse than that because inverters aren't 100% efficient and they consume some power themselves.

So you get: AC Watts / inverter efficiency = DC Watts + inverter draw = DC Watts from battery.
Thus a refrigerator running at 120 Watts on a 90% efficient inverter becomes 133 Watts DC + 20 Watts for the inverter = 153 Watts from the battery bank. That's 27.5% more power than the 'frige alone uses.

icarus

Re: battery question from another noob

A 2 kw inverter form such a small battery is a non starter. In addition to built in inverter loses, (the inverter will in most cases run very inefficiently with small loads) the potential current draw is huge. 2000 watts draws in excess of 150 amps from a 12 volt battery. With that kind of load, the inverter is going to go to low voltage shutdown very quickly.

Running even a small compressor fridge off such a small battery is going to be a problem, and indeed won't power it very long.

Good luck and keep in touch,

Tony

coastalar

Re: battery question from another noob

icarus wrote: »

A 2 kw inverter form such a small battery is a non starter. In addition to built in inverter loses, (the inverter will in most cases run very inefficiently with small loads) the potential current draw is huge. 2000 watts draws in excess of 150 amps from a 12 volt battery. With that kind of load, the inverter is going to go to low voltage shutdown very quickly.

Running even a small compressor fridge off such a small battery is going to be a problem, and indeed won't power it very long.

Good luck and keep in touch,

Tony

I had my concerns about that as well. I was told that if the inverter was too small it would be inefficient as well. So I have a 1000 watt inverter as well and see which one works best for me. Worst case I’ll either grow into the larger inverter or sell to someone who can put it to good use.

Running the fridge would be great but knowing my system is small, was not a priority. If I can get the little one to work for me with the storage I have that is quite a plus. I have the room for about 400ah but my limitation right now is a convenient package for the panels.