solar powered heater

[crazycarl]

i'll be doing some work inside the boat this winter and i'd like to stay warm so i keep a small ceramic heater in the boat that works quite well.

what i'd like to do, is run the heater off the boat's deep cycle batteries (2-205 amp/hr) while connected to solar panels.

this would allow me to keep the boat heated all winter long.

i have been looking into small heaters (including the one i have) but can't find any info on the amperage they draw, only the wattage ratings. 

i'm not even sure this would work with the solar panels i'm looking at (3X15=45 watts) but i know someone, ok, everyone on this board is smarter than me, so let's have your input.

carl

[Bob23]

CC:
  Why don't you buy one of those oil filled radiators from Home Depot and plug it in? They have thermostats and I think the lowest setting is 600 watts. Gotta be simpler than trying to run  a heater through your boats batteries. Just my humble opinion. I did this the first year I owned my 23 whilst I was refinishing all the interior teak. Worked great.
Bob23

[MacGyver]

There is a way to tell what the wattage is in Amps, I have a book with that info on my desk.

Also, I like Bob23's idea of the oil heater thing, we had one in the house one year for a bit, they work well at keeping a room/space warm and retain their heat so dont use much power overall I think.
Also, ours had switches to amp it up a bit up to 1500 I think.

They are cheap too, but I would get a better one, hell, they might only sell one type.

Mac

[Bob23]

   We are currently using 7 of these heaters on an ocean front renovation project to keep the house warm although at the present 26 degrees outside, if we can stay at 40 inside, I'll be happy. The highest setting is 1500 watts with the middle setting at 900. Made in China of course but the construction seems higher than normal, whatever normal is.
   I like these better than the forced air cheapo heaters. If the fan seizes up (mine did) the element will probably overheat and melt apart...I'd rather not have a call from the fire department that my renovation project burned down.
Bob23

[brackish]

I = P/V

Current, measured in AMPs = P (watts)/V (volts)

Are you talking about using an inverter with an AC heater?  Or are you using a 12V ceramic heater?  

So, look at the specs on your heater to see what the watts are, divide by your chosen type of power, AC or DC, and you can get the amperage and figure the draw down over time and what your solar panels will replenish.  If an inverter, not sure about the efficiencies, but the sites that sell them will offer you info. Not sure I would want to cycle my batteries for that purpose, maybe just string a long weatherproof cord to an AC source.

[brackish]

They are cheap too, but I would get a better one, hell, they might only sell one type.

Yep  I think the difference in price is based mostly on features and marketing, not quality.  And most portable space heaters no matter what the type, Oil, Ceramic, Air over coil, etc.. have a max power of 1500 watts which is what a 115v 15AMP circuit will handle at startup without tripping the breaker.  Mass produced for that purpose.  Most will have a turndown setting to 7-800 watts and often a T-stat so that it turns on and off but still when on drawing the amperage of the setting
I use a ceramic (AC) on my boat, at the dock set to come on at freezing.  Unfortunately I still have to winterize, because the marina power is not reliable.

[crazycarl]

the heater i'm using is a ceramic 120v a/c unit.

being a cheap a#$, i'm looking for a way to heat the boat 24/7 until the weather warms.

the heater is currently plugged into a 12ga. extension cord, but like i said,  if i could invest $ now, i may save $ in the long run.  maybe not.

carl

[skip1930]

So let me get this straight.
The heater is alternating current, A/C. 120 volts and ? watts.
The battery is direct currant, D/C. 12 volts.
The cell is D/C, ? volts at ? amps or ? watts.
So a D/C to A/C inverter would be necessary to make 120 volts A/C from 12 volts D/C.

I don't see how the heater is going to run on two deep cells very long. Maybe like a load test done on batteries to determine their health ... a matter of seconds.

I read the posts ... it's way beyond me.
A guy at the airport has two Tesla's. A roadster and a four door. [His son works for Tesla Motors.]
He says the roadster hits 60 mph in 4+ seconds and has a range of 220 miles using 7,000 battery cells.
Full load amps must be tremendous. Ever run around in an electric fork lift? A 1,200 lb battery lasts 8 hours.

I have a little 120 volt 'box' with coils over a ceramic plate and a small fan. It comes with a thermostat and is overloaded protected. When I'm down inside the boat and working on things, the interior becomes too warm and I switch off.

NateD ... Hummm~Geeeee my head is spinning so fast, I'll need ball bearings on my electric meter!

skip.

[Shawn]

" i'm looking for a way to heat the boat 24/7 until the weather warms.

the heater is currently plugged into a 12ga. extension cord, but like i said,  if i could invest $ now, i may save $ in the long run.  maybe not."

If you want to heat it 24/7 you would need a diesel heater. Your batteries would run a 120v 1500w heater for about 2-3 hours on full power. 45w of solar power won't do a thing to help you.

Shawn

[brackish]

the heater i'm using is a ceramic 120v a/c unit.

being a cheap a#$, i'm looking for a way to heat the boat 24/7 until the weather warms.

the heater is currently plugged into a 12ga. extension cord, but like i said,  if i could invest $ now, i may save $ in the long run.  maybe not.

carl

Naw, your investment in an inverter would be more than many years of metered power with a heater set to maintenance level, and you would shorten your house battery life by the number of cycles they would see.  Don't think you can make that work.

[NateD]

Ok, let's say 1,000 watts at 120 volts.

1,000 watts/120 volts = 8.33 amps

If you go with a cheap modified sine wave inverter, you're looking at about 87% efficiency, so 8.33/.87=9.57 amps draw.

If your solar panels put out 45 watts at 14 volts for 10 hours/day, that is (45/14)*10=32 amps. But that doesn't include efficiency losses, and it's unlikely you'll get full output for 10 hours, so cutting the rated output in half is a decent rule of thumb (if I remember right). On sunny days I think you can expect the panels to give you about 16 usable amps.

In rough numbers, every sunny day would give you 1.7 hours of heater run time. Since you have 2-205 amp hour batteries (and I assume you don't want to run them down past 50%), that gives you 205 amp hours to run on, which should last 205/9.57=21.4 hours of heater use, so it looks like you've got enough battery capacity to run the thing for a day while working on it. But if you ran the heater for 6 hours on a Saturday, it would eat 57.4 amps, which would take (57.4/16=) 3.6 sunny days to replenish. I have no idea how many sunny days to expect during the winter in your neck of the woods.

Before I ran the numbers I didn't think you'd have enough capacity from the panels, but as long as you're just doing some work for a day or two on the weekends, it looks like you should be able to use the panels and an inverter. But if you can run an extension cord, I would save the wear and tear on the batteries and just plug the thing in.

Disclaimer: I'm not an electrician or engineer and I don't have extensive experience with solar panels or inverters, so if someone says my math and assessment is BS, they are probably right.

[Shawn]

Nate,

Good try... but your consumption numbers are *way* off. The important thing to remember is that what drives a heater (or any electronic device) is watts. They are the correct measure of power.

You can not compare amps at 120v vs amps at 12v. They are  apples and oranges. What you compare is watts.

A plug in heater on full power draws around 1600 watts.

Forget all about DC/AC conversion efficiency (important in real world but not needed to be considered here for reasons that will be clear in a moment...)
Watts = Power
Just look at that 1600watts of power the heater requires. Power/Volts = Current 
1600/120v = 13.3 amps

Now.... run the same situation at 12v
1600/12v = 125 amps.

In other words to drive that heater for 1 hour requires 125amps from the house battery. As you said he has 405 amp/hours total capacity. He shouldn't discharge more that 50%... so basically 200 amp/hours of discharge. Running that heater at full bore will consume 200 amp/hours from the battery in about 90 minutes. 45w of solar will do next to nothing to help. 1600/45 = 35 hours of full charging to replenish. If you get 5 full hours a day it takes a week to recover that hour run time.

Shawn

[NateD]

Shawn,

     Thanks for the correction. Intuitively I didn't think there would be enough power to run the heater, so I was surprised when my math said there was.

Nate