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Old 05-25-2007, 12:55 AM   #1
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Power Invertor Size

I just bought a mini toaster oven at Target {1300 W} and I plan to run a microwave {? W} but not at the same time, so a 2000W should be fine. My soon to be SMB has no inverter or microwave yet so I'll be putting it in myself. I might have a tv and av equipment, but everything but the toaster will be used very rarely, and there will be no issue with not toasting and watching TV at the same time or whatever.

My question is if I go way overkill and buy a 5000W inverter will it kill my batteries quicker than running a 2000W inverter?

By the same token, when installing the 2000W inverter should I also install my 300W to run the laptop or other small things? (meaning will running the 2000W invertor to power the 180W laptop run my battery down faster than running the 300W)?

Also, how important is the pure sine for my laptop, a tv, etc? Does it really matter?
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Old 05-25-2007, 06:54 AM   #2
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Jage, a 2000 watt inverter should run what you're talking about just fine. I run a whole house on a 4000 watt inverter. Everything running at the same time, three fridges, washer, dryer, etc. Just be sure you're not using more then 2000 watts at one time. Most inverters will also be able to handle more then their rated watts as a surge so you will be covered for motor startups, etc.

As far as also getting a second 300 watt model to save your batteries, check the 2000 inverter specs and see what the power consumption is just to have the thing on. The better the inverter (I.E. cost) usually the less it will use while "idleing". Some of the cheaper cig. lighter plug in types might use more juice then a good 2000 watt one. Off the top of my head, I would think you'd be fine with just one good inverter.

Pure sine wave is nice to have when running electronics. Matter of fact, it's almost a necessity. The modified sine wave can cause an annoying hum in many things with motors and a very noticable flicker in TVs and computers. Some electronics will not run at all on a modified sine wave. If it were me, I would only consider a pure sine wave unit. I've used the little 300 watt plug-ins for charging lap tops and other devices, but some of the plug-in transformers get pretty warm on a modified sine wave. I feel it's false economy with the modified wave inverters.

You don't mention the batteries you'll be running all of this on. Toasters and microwaves use a LOT of power. You can calculate what you can run if you know the watts you'll be using and for how long. Also need to know the capacity (amp hour rating) of your house batteries. You planning on solar panels or a generator or running your engine to keep the batteries charged?? Maybe other folks can chip in on how long they can run stuff in their rigs and what they do to keep charged up. My inverter/power/charging experience is not in my SMB (12v fridge only), but in setting up systems for cabins and houses. Same idea, just different amounts of use. Good luck. When you gonna get your rig??
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Old 05-25-2007, 10:34 AM   #3
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Go DC-DC whenever possible

For things like your laptop and ANYTHING else for which you can get a DC-DC converter, do so. An inverter is a last resort; you can't get much less efficient for powering electronics from a DC source.

As Scatter pointed out, just plugging in an inverter and turning it on wastes energy. Futhermore, the efficiency of those things is usually pretty horrible, as in 80-85%. Fantastic ones get 90%, but I've never seen any give 90% in practice. The problem is that your laptop runs on DC, not AC. So by using an inverter, you are taking DC from the van and converting to AC (~85% efficient) and then your laptop power supply is taking that AC and converting it back to DC (depends on the computer, but can go from 75-85% efficiency usually.

Instead, many of the computer companies sell DC-DC power supplies for their laptops. I have an IBM (Lenovo), and I use this:

http://www.shoplaptop.net/oribmleacauc.html

although I found it elsewhere for less $. Now, when I need to run in the van, I plug in the DC plug and it upconverts the 13VDC to my required 20VDC, which is probably 85-90% efficient for the total energy transfer, thus giving off less heat and using much less power. Many other laptop manufacturers have similar items.

Same thing goes for cell phone chargers (use the cig chargers, not the inverter with the AC wall wart).

Now, when it comes to your toaster/oven... I've seen a 12V pizza oven at www.roadtrucker.com. Haven't used it, but if it works, then it's probably a way more sensible way to go. See:

http://roadtrucker.com/12-volt-cooking/ ... ooking.htm

Now, you really can't do anything about your microwave. For that you'll need an inverter. But almost everything else you should be able to get away with going straight DC-DC. Highly recommended.
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Old 05-25-2007, 11:18 AM   #4
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Well the van I'm getting (June 2nd ) has the 4cf fridge and the large 40-AGM. No solar.

Apart from the fridge here is the potential power consumption:
Must Have:
Toaster Oven {1300 W} 5-20 mins twice a day (10-40 mins total)

Probably Use:
Microwave {??} 10 mins daily
Laptop {180W} 1 hour daily
Hair Dryer {1875 W !} 1/2 hour daily

Rare Use (probably will only even bring on rare occasions):
George Foreman Type Grill {1000W} 15-30 mins daily
Blender {350W} 10 mins daily

Someday I may have a TV, xbox, and DVD player (currently DVDs are laptop or a 12v portable and I have yet to acutally sit and watch something)
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Old 05-25-2007, 11:19 AM   #5
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When looking for appliances I have come across small 12v microwaves. I've also come across comments that it would be too big a draw and could trash your battery, that it's better to run with an inverter.

As a bit of a sidebar, look into dutch oven cooking. It's a whole other sub-culture. But it works really well. A dutch oven and a dozen charcoal briquettes and you can slow cook some amazing meals.
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Old 05-25-2007, 12:25 PM   #6
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Yes, I have some friends who are huge dutch oven fans. Frankly we don't do much of that type of cooking even at home (casseroles, stews, cakes, etc) so it would be a waste of weight and trouble.

This particular toaster oven is a matter of convenience and size more than power consumption. As you can see it's quite small. The slot on the top opens for a "traditional" toaster, and the toaster oven part is large enough for our uses. I'd rather have this than a 12V toaster and a 12V toaster oven which was larger, but made more power consumption sense.



I'm not sure it's "better" to run with an invertor, it might be the battery type. I read something (http://www.donrowe.com/inverters/inv...l#battery_type) while looking at invertors and 12v appliances that they'll kill a normal car battery in about a dozen charge cycles, whereas an RV or Marine battery is made to take the repeated discharging and recycling. I'm wondering if, since it's on an invertor page anyway, maybe the "could trash your battery" is more about car vs. RV batteries than it's safer to run an invertor and the sentiment just got "colloquialized".
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Old 05-25-2007, 12:45 PM   #7
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How about a little bit of math?

My guess is that the van has a 4D battery, not a 40 battery. Rough capacity of the ones manufactured by Concord (Lifeline, Concord, few other badges) is about 212Amp Hours. For reasonable battery life you don't want to drain even a deep cycle battery more than about 60% of its capacity. (less drain per cycle = more cycles before the battery is alive, its all up to you of course, but after about 80% down the voltage really starts to drop and things won't work well)


So 212*.6 = 127 amp hours usable

Toaster Oven: 1300W / 13V = 100 Amps
100 Amps * 1/2hr per day = 50Amp Hours

Microwave : Assuming roughly the same as the toaster oven for 12 min for easy math
100 Amps * 1/5hr per day = 20Amp Hours

Laptop : 180 / 13v = about 1.5 Amps
1.5 Amps * 1 hr per day = 1.5Amp Hours

Hair Dryer !!??!! (this is gonna hurt) : 1875W / 13v = 144 Amps
144 Amps * 1/2 hr per day = 88 Amps Hours


Lets add that up:
Toaster Oven: 50
Microwave: 20
Laptop: 1.5
Hair Dryer: 88
-----------------------------
159.5 amp hours

Now consider that you might want to turn on the fridge... We have the smaller fridge, but the numbers will give you an idea of the lower bound:

Fridge: 2.5Amps, 60% duty cycle @ 70 deg interior van temp * 24hrs
= 36 amp hours

Perhaps a few lights in the evening?
Lights 2Amps, 3 hours/day
= 6 amp hours

Now we have:
159.5 amp hours
Fridge: 36 amp hours
Lights 6 amp hours
----------------------------------
202 amp hours


This doesn't account for the fact that the inverter is probably only about 90% efficient. The Fridge is probably going to consume more than the small fridge. Batteries are less efficient (i.e. have less usable capacity) the faster you pull current out of them. You may have other electric devices you wish to use, etc.

So, roughly, you will be trying to use all of the capacity of your house battery every single day. It will not last very long, and you will have to drive for many hours each day, or plug in each day for a few hours, to re-charge it.

Obviously the worst offenders are the toaster-oven and the hair-dryer. Toss those and you are probably ok.

I would seriously consider how to reduce usage, how to put in a second 4D battery in parallel, and how you intend to put all that power back in the next day.

Not trying to rain on anyone's parade, but the numbers you are putting out are not, in my mind, sustainable or reasonable for even one day in a van. Electric heating devices are very very expensive in terms of energy.

-e

p.s. love the smiley van
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Old 05-25-2007, 12:46 PM   #8
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Quote:
Originally Posted by jage
I'm not sure it's "better" to run with an invertor, it might be the battery type. I read something (http://www.donrowe.com/inverters/inv...l#battery_type) while looking at invertors and 12v appliances that they'll kill a normal car battery in about a dozen charge cycles, whereas an RV or Marine battery is made to take the repeated discharging and recycling.
Well, it really comes down to how much power is being drawn (total, as in Wh) and how fast it's being drawn (A) for your particular application. Going back to the laptop example, running from a DC-DC converter to your laptop vs DC-AC-DC simply uses less power to do the same task, period. It's about conversion efficiencies. Can't speak for the other equipment, since an AC toaster probably uses the AC directly (as does the DC toaster...) so there may not be any extra efficiency _in the toaster_, but extra loss from the inverter is a given.

If you're really curious about what things use, and are willing to invest a bit (perhaps $150 total and some soldering time), then do what I do and create a set of powerpole-based cig socket adapters (male and female) into which you can insert a Whattmeter (tm). See www.powerwerx.com for powerpoles and a whattmeter. With this toolset, you basically extend your cig socket with a meter insert that will give you pretty darn accurate readings of you voltage, current, and total watt hours. I have a special Whattmeter from www.medusaproducts.com so that I can also datalog direct to a computer as well as pull temperature data at the same time. Pretty cool. Allows you to check EXACTLY how much power your inverter is pulling in "standby," and EXACTLY the efficiency difference in using an inverter to your laptop vs. a DC-DC system for your laptop.
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Old 05-25-2007, 01:26 PM   #9
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Quote:
Originally Posted by etbadger
p.s. love the smiley van
Pure Badger fandom, that!

The hairdryer is easy to lose. Luckily my wife doesn't require such luxury, it just came up in the "things we might plug in". I actually wrote out the whole post then ran around checking Watts... I read it and was like "ouch".

So... 127 amp hours, putting the toaster oven on restricted duty:
Toaster Oven: 1300W/13V*0.1 (6 minutes) = 10 amp h
Microwave == 20 amp h
Laptop == 1.5 amp h
Fridge(4 cf) ~= 40 amp h
Lights/Misc ~= 6 amp h
-------------------
77.5 amp h / day
means... 1.6 days

A normal toaster (850W) brings it to 6 amp h for toast, which really makes little significant impact.

On the other hand a second 4D battery would give me 127 x2 amp hours usable so:
254 amp h/day
------------------- = 3.27 days
77.5 amp h

Which is pretty decent. May have to restrict toasting to driving days until then. I'm also experimenting with pretoasting my Gluten Free bread (the reason for the toaster in the first place)

So, 1) how long do I have to run the van to recharge the 4D? (are we talking an hour for a 127 amp h drain?)

2) I would need to invest in some solution that gave me about 90 amp h of charge per day from solar in order to cover my total daily use (keeping the sunshine amount out of it for simplicty)...

130 W / 13 V = 10 amps (but they're 7A max..) so 90 amp h / 7 amp = 13 hours charging ... is that correct?

Hmm, I'm beginning to think the 12V toaster might be an option after all although I'm not finding any power draw info on them (actually I've only seen one and it's 1 slice which means 2x the time).
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Old 05-25-2007, 01:29 PM   #10
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Quote:
Originally Posted by kzemach
If you're really curious about what things use, and are willing to invest a bit (perhaps $150 total and some soldering time), then do what I do...
Or I could just ask someone who's already done it.... hmmm... who could I ask...
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