DC to AC 110V inverter problem.

[thebutcher1942]

Happy Thanksgving everyone. I am new here sorry if this is the wrong place to post. I am a novice in electronics (as in fixing circuit boards, building electronic stuff). But I know a little bit, like how to build a computer, soldering, I know when a Capacitor is blown ect...

Anyway, I am working on a project, I have a small closet space pop up green house that I need to warm for my tomato plant and others, I am in the Philadelphia. This is how my system works for heating it up. I have 1 12v deepcycle 32ah and 3 12v 12ah batteries in parallel. I will be hooking these up to a DC to AC converter. The heat is coming from two 55w ceramic chicken coop heat lamps or 100w bulbss if I can get pass my inverter problem.

I went through about 7-8 Inverters (returned them, price range $15-$70 150w-750w) that all sound an alarm then shut off after the voltage drops to 11.5 and some 10.5. This is meant so people can start there cars, but I am using stand alone batteries and just want to drain them the most to a safe level to get extra time. I need them to run for about 12 hours over night and them will switch and charge during the day since it gets warm with the sun as needed.

The inverter arrives tomorrow the other sometime next week and is a 180 watt dc to ac the other 150 watt. Is there a way of disabling these shut offs or alarms if I take some photos when i get them and let me know where the solution could be? Has anyone here had experience with working with DC to AC inverters?

Thanks All

 

[Pommie]

A simpler solution would be to just use the 12V direct. Use 3Ω 50 watt resistors (See here) and 12V computer fans. Three resistor/fan combinations can be spread around for more consistent heating. Note this will take 150/12 = 12.5A and will flatten your batteries in about 5 - 6 hours. Letting lead acid batteries go flat severly shortens their usable life.

Edit, I see you only need 100W of heating so your batteries will last around 7-8 hours.

Mike.

 

[thebutcher1942]

Thanks, Mike I'll look into that

 

[Reloadron]

The ability to disable inverter low battery function will vary from inverter to inverter. My suggestion would have been before buying an inverter to contact a known reputable company like APC (American Power Conversions) and speak with (or email) one of their applications engineers. These are the guys who are happy to suggest an entire system (inverter and batteries) to meet and exceed your needs. The deep cycle batteries are the way to go as they are designed with deep discharge in mind. The problem with disabling the shutoff feature is different units use different sensing and some allow the user to disable the feature or set the shutdown voltage. So it really comes down to who made the inverter. Beyond just running down a battery so a vehicle won't start there is more to it. A typical 12 volt SLA (Sealed Lead Acid) battery when fully charged will be about 12.6 volts. The numbers actually look a little like this:

Voltage State of Charge:
12.6+ 100%
12.5 90%
12.42 80%
12.32 70%
12.20 60%
12.06 50%
11.9 40% This is a cardinal point.
11.75 30%
11.58 20%
11.31 10%
10.5 0%

Running a 12 volt SLA below that 11.9 volt level starts to become detrimental to the battery. Battery Stuff has a few good reads on the subject and Battery University is another very good source for information.

Wish I could help further.

Ron

 

[thebutcher1942]

Thanks Ron, I should of done a little more homework before I purchased. Ohwell, I will get this and learn alot along the way especialy here now. My 100 watt chicken coop heat lamp lasted 3 hours on the deep cycle until the alarm shut down at 11.5. So then I had the idea of running 2 50 watt bulbs one after the other. I am hoping to get 6 hours off the deep cycle and same with the 3 parallel.

And today I had the idea of getting a light timer where you can make it go off and on (the one I gotdoes it up to 10 times per day). So if I time it right giving the battery a break like 30 min intervals it may do justice. I even bought a two remote control power on and off switches so i can turn off and on from the house (prior to learning about the the timer) and have a remote control thermonitor that tells me the temp in the small green house. It is 6ft high, 5 ft wide and 3ft side and kind of insulated.

Thanks both of you and I am open to all suggestions, I think I spent $250 all for a tomato plant and some other small veggies. This is what the greenhouse is.

Thanks again,
Brian

 

[Reloadron]

Those green houses are pretty cool. So you can have fresh home grown off the vine tomatoes in January while living in Philadelphia, PA. I am guessing there is no easy way you can just run house power out to the little greenhouse?
Here are some of the problems you will face. A pretty good deep discharge 100 AH (Amp Hour) battery runs about anywhere between $140 to $170 USD. Now one would think a 100 AH battery would deliver 100 Amps for 1 hour or 50 Amps for 2 hours, 25 Amps for 4 hours and you get the picture. However in real life the actual discharge curves don't quite look like that. So we have that going against us. More on that later. Let's say you have a 120 VAC 200 Watt load, so at 120 VAC that 200 Watts is about 1.7 Amps. That same 200 watts on the 12 volt side of things is about 200 / 12 = 16.66 or say 17 Amps and we have not began to figure in the inverter inefficiency so we could likely say about 20 Amps. In theory at a 20 amp load our 100 AH battery should last about 5 hours starting with a full charge. Unfortunately looking at discharge curves I doubt anyone will get that lucky, The ideal situation would be to run GFIC protected house current out to the green house. You can easily end up with several hundred dollars in batteries, inverters and solar panels to charge the batteries. On average I thing the greater Philadelphia area pays about $0.10 (ten cents) per KWH so running two 100 watt lamps (200 watts) for 5 hours cost about ten cents or 10 hours about 20 cents.

Ron

 

[dr pepper]

I know this doesnt answer your question and may not be the direction you want to go, however have you thought about a 12v bulb direct off the battery, such as a car headlight bulb, with something like this you could still have low battery shutdown protection:
**broken link removed**

 

[michael8]

You said "during the day since it gets warm with the sun as needed". I'd recommend saving heat from when the sun is up and using that during the night. This could be much cheaper than storing the energy in batteries. How do you get the batteries recharged anyway?

 

[Pommie]

To add to what Michael8 said, your battery bank stores 12*56*60*60 = 2.5 million Joules (MJ). To store this amount of energy as heat in water by heating it during the day would require about 30 liters (6 gallon) of water to be heated by 20C. Just six 1 gallon black containers hung in your green house will match your battery system. Worth considering I think.

Mike.