Need help picking batteries for first time 12v solar project

solarpowernovice · December 2013

Hello

I got this full system quote from NAWS and bought everything on the list except for the things I marked red in the pictures below (solar panels, batteries , pole mount, battery interconnect cables). I ordered a Samlex 1500 watt inverter but cancelled the order before they shipped it... I want to make sure the inverter I get can run a small chest freezer (without auto defrost) converted into a fridge and a 1/10th horsepower AC pump that takes 160watts while running through a Kill-A-Watt meter, I need this for only 30 minutes a day MAX. I also would like to be able to use a few LED lights and a laptop charger.

Could anyone recommend a good inverter for my application and can I get your opinions on what type of batteries I should get as a newbie to solar (in the 400 to 450 AH range @ 12v)? I will be buying the three 250 watt solar panels, pole mount and batteries around spring time. By the way I have a 6000 watt champion generator I will use with the 90 amp battery charger when needed, but I would like to keep this to a minimum.

SolInvictus · December 2013

Re: Need help picking batteries for first time 12v solar project

... 1/10th horsepower AC pump that takes 160watts

Because 1/10 hp is 75 W, something is amiss. Do you mean the chest freezer and AC pump together consume 160 watts?

What are the wattages of the LED lights and laptop charger, and how long do you plan to operate them?

waynefromnscanada · December 2013

Re: Need help picking batteries for first time 12v solar project

SolInvictus wrote: »

Because 1/10 hp is 75 W, something is amiss. Do you mean the chest freezer and AC pump together consume 160 watts?

Most likely the 1/10 hp is referring to the actual work the motor can do, minus all the heat it produces because of it's less than 100% efficiency. It's only been in the last couple of decades that manufacturers have taken to using the energy consumed by a motor to rate its hp. A form of hyper inflation they can get away with, that's awesome for misleading customers and increasing sales. This is especially rampant in the sale of air compressors and lately shop vacuum cleaners.
In the old days of truth in advertising, if you purchased an electric motor rated at 1 hp, you could be sure it could do 1 hp in mechanical work regardless of energy consumed.

solarpowernovice · December 2013

Re: Need help picking batteries for first time 12v solar project

When I hooked the AC transfer pump up to my generator and started pumping water out of my cistern it started at 170 watts and then dropped to 160 and stayed there for 38 minutes until i turned it off (when the kill-a-watt meter hit .1KWH). Keep in mind I would never use this pump that much in one day maybe 20 minutes or so just to get water into the cabin down the hill about 60 feet. The chest freezer to fridge conversion I have not bought the thermostat or the chest freezer yet so I don't know the running watts but I've heard they take .5KWH or less a day. I plan on getting a small 8 cubic ft. newer model chest freezer with no auto defrost. I also want to run my 22 watt laptop charger for 5 hours a day and 50 watts of LED lights for 5 hours a night and a 5watt cellphone charger for an hour or 2. I'd like 2 to 3 days of backup for all of this.

solarpowernovice · December 2013

Re: Need help picking batteries for first time 12v solar project

so basically as long as the chest freezer conversion is under .5kwh a day like everyone says... then 1 kilowatt hour a day should be all that I will require.

westbranch · December 2013

Re: Need help picking batteries for first time 12v solar project

So what you need to cover is the TOTAL instantaneous draw of all units turning on at the same time. The battery and Inverter need to be able to handle that total load...

solarpowernovice · December 2013

Re: Need help picking batteries for first time 12v solar project

okay i guess I will start looking for a small chest freezer on craigslist then ill have ALL of my appliances loads and can give you an accurate number

thanks ya'll

westbranch · December 2013

Re: Need help picking batteries for first time 12v solar project

Check specs carefully, a lot of small units use as much as a regular sized one.

solarpowernovice · December 2013

Re: Need help picking batteries for first time 12v solar project

what if I email tech support on some of these small deep freezer manufacturers do you think they can tell me their best freezer with lowest power consumption? If so what should I ask them for specifically startup watts? I also could just unplug the freezer whenever I start the pump (once or twice a day)so i dont have both running at the same time... I'd need to go outside to start the pump anyway im sure id remember to unplug the fridge first. I already bought 2/0 gauge cable for the 1,500 watt inverter and they're rated 1500 watts max on a 12v inverter:(

westbranch · December 2013

Re: Need help picking batteries for first time 12v solar project

to your questions
1 - Yes, find out which year the evaluation was done in, standards have changed, always going up... more efficient.
2 - Absolutely, this is most important in order to size the Inverter.
3 - that is a good low tech solution.

good luck on the hunt...

SolInvictus · December 2013

Re: Need help picking batteries for first time 12v solar project

Look for freezers with EnergyStar ratings which will indicate the kWh/year that they consume when operating normally. Converting it to a refrigerator will naturally use less than the rated power. Top loading chest freezers are usually the most efficient for this conversion.

For example, Frigidaire 8.8 Cu. Ft. Chest Freezer, Specifications:

Annual Energy (kWH): 294
Amps @ 120 Volts: 5.0
Connected Load (kW Rating) @ 120V: 0.60
Minimum Circuit Required (Amps): 15A

294 kWh/year = .81 kWh/day on average
It uses .6 kW when running which is easily within the ability of the Samlex 1,500 W inverter including your other loads.
The AC current rating is up to 15 A (1,800 W), so it is not clear whether the 1,500 W Samlex inverter could start it. Maybe?

I would try to find a freezer with better specifications than this one.

SolInvictus · December 2013

Re: Need help picking batteries for first time 12v solar project

Another option is the SunDanzer 225 liter DC refrigerator. It is expensive, but uses little power and would allow you to use a lower powered inverter and eliminates the worry about whether the inverter could start the compressor motor.

jcheil · December 2013

Re: Need help picking batteries for first time 12v solar project

Someone on here made some kind of a relay type switch that prevented (I believe) a fridge and A/C from both running at the same time. You could do something like that also.

Need help picking batteries for first time 12v solar project

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