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Sweet inverter and stereo installs
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jwallis
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PostPosted: Tue Jun 05, 2012 12:34 pm    Post subject: Sweet inverter and stereo installs Reply with quote

I bought the van about 4 months ago in anticipation of the ?-month-long (until the money runs out) roadtrip I'm currently a month into. The first 2 months were spent working on the van daily. One of the best things I've done is install an inverter (and the stereo was necessary of course).

Here goes:
First thing I did was pull the seats and cut out the sheet metal that prevents you from using "under the seat" as easily accessible storage. It does not seem to provide much if any structural support. I put down some dynamat and glued down some red velour-ish fabric I had been given (the curtain of an old stage) which was heavy enough to dampen a little more sound.
I got a Powerbright 1100W inverter and so far I'm pretty happy with it.

I went for the 1100 over the 900 mainly because it wasn't much more $ and the 1100 had a fancy LED display. It's supposed to display Watts or Volts at the flip of a switch but the Watts seems to have stopped working. Doesn't matter because all I care about is how much juice I have in the aux batter, so I leave it on V all the time.
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Also installed an ANL fuse (using a calculation online I got a 125A fuse which I now realize is way too big)
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So here's the cool part:
The 1100W has 2 outlets on the front, one of which I put a kiddie guard on so I don't zap myself while feeling around to turn it off, and the other of which I bought an extension cord for and ran to the aux battery compartment
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Then cut a hole in the side of the aux box with a dremel and wired the ext cord to create some cabin-facing 110V AC!
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The inverter sticks out enough to reach to switch on/off while driving and check voltage easily (I drive with seat all the way back). And I believe there's plenty of clearance for heat dissipation
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The bad news is of course this is a modified sine wave inverter and it's bad to power/charge some things with modified sine.
I think using it to charge my macbook (did hear some buzzing) caused the battery to swell up and now I have to replace the battery. I've used it for lots of other projects though, used to power the dremel the other day to cut some bolt off or something like that...
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jwallis
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PostPosted: Tue Jun 05, 2012 12:51 pm    Post subject: Reply with quote

Stereo install not as sweet, but a decent solution if, like me, you couldn't find a better place to install it. My van has aftermarket AC (doesn't work) so there was no room in the console.
This is a very small head unit. It has no cd or tape player and wouldn't fit as well if it did because it's very short front to back. It's a Boss 612UA "media player" which I just plug in using USB or AUX.

So I bought a large hinge, cut it down and affixed it to the metal under the fusebox near the door (after measuring several times very carefully). I screwed a couple pieces of metal across the other end of the hinge and glued the head unit to them.
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To keep the thing up, I drilled a hole under the console, glued an angled piece of metal to the head unit and used a thumbscrew to screw through the angled piece into the hole. ghetto indeed.
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Now you can unscrew the thumbscrew and flip the unit down to check fuses. By pure luck, if the unit is all the way down, the door storage won't hit it when closed. I have tried to close the door with the head 1/2 way down and almost torn the head unit off the hinge though...
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Over all I'm really happy with this install. It's definitely the best place it could go, and just the other day I blew and replaced a lighting fuse. I also replaced the wiper relay after doing this install, so it's possible to get to that stuff as well.
It's ghetto when you know how it's rigged but if you don't it looks pretty decent...
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Summers420us
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PostPosted: Wed Jun 06, 2012 8:04 am    Post subject: Reply with quote

Ghettolicious Very Happy

I do like your 110 Install. It's a good use for the space under the seat. Well done.
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tencentlife
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PostPosted: Wed Jun 06, 2012 7:12 pm    Post subject: Reply with quote

Quote:
Also installed an ANL fuse (using a calculation online I got a 125A fuse which I now realize is way too big)


Your wire looks like 6ga.? If so, then yes, the fuse is too big, it won't protect that small a wire. But that inverter can surge-load to twice it's rated output so the fuse size to allow that would be about a 200A. Ideally you would use 00 wire on both legs, and fuse the pos. at 200A to have use of the full capacity of the inverter. But even if you never intend to use it for power tools, you still need a fuse that will protect your feeders and that 125 is too big for 6ga. or even 4ga. wire. I'd get it down to 75-80A for 6ga. and 100A for 4ga.
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jwallis
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PostPosted: Thu Jun 07, 2012 2:22 am    Post subject: Reply with quote

tencentlife wrote:
Your wire looks like 6ga.? If so, then yes, the fuse is too big, it won't protect that small a wire. But that inverter can surge-load to twice it's rated output so the fuse size to allow that would be about a 200A. Ideally you would use 00 wire on both legs, and fuse the pos. at 200A to have use of the full capacity of the inverter.


That was the wire that came with it and it is indeed 6ga.
Did you come up with 200A using the following?

P = IV
2200watts = Xamps * 12volts
200 = Xamps

I sometimes am able to convince myself I understand when I don't but I feel pretty sure this is where you're coming from. Thanks for the input, I'll try to get a smaller fuse when I can find one...
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jwallis
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PostPosted: Thu Jun 07, 2012 2:34 am    Post subject: Reply with quote

jwallis wrote:
I sometimes am able to convince myself I understand when I don't


and there you go, I just did it. That equation doesn't make sense because it's not producing 2200W at 12V. It will surge to 2200W but that's at 120V AC. I just read the .pdf specsheet and it says it will produce 9.2A. That makes sense, because
P=IV
1100W = 9.2A * 120V

so I guess we can assume that if it's providing 1100W, it's consuming at least 1100W, and hopefully not much more. So I guess that all jives...
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PostPosted: Thu Jun 07, 2012 8:11 am    Post subject: Reply with quote

You're on the right track, but watts is watts, it's the same amount of power whether DC or ac. DC amps going in are traded for commensurate ac amps going out, the change being the change in voltage as the divisor in P=IE. So if you're using 2200w ac the battery has to produce 2200w DC, and more because the inverter isn't perfectly efficient.

So your first estimation was basically what I did quickly in my head: 2200w / 12V = 183A (my head spit out "<200", and I rounded up to the next larger common fuse size, since the target in that figure was to find the fuse size that would not limit inverter output).

If you want to be more precise, you would include inverter efficiency in that equation. Mod-square (called "modified-sine" by the marketing dept.) inverters will typically run 94% efficient at full output, but as low as 65-70% at very low outputs (which is a reason not to install one larger than you really need, especially if battery capacity is small, which yours looks like).

Since we want to know the DC input fuse size that won't limit inverter output at a full-load starting surge, first find out the total DC wattage it will demand including power lost to inefficiency (powering the inverter's circuits and heat) at a full-bore surge load. That is 2200w / 0.94 = 2340w.

Since all of that wattage is supplied by the battery, the DC amperage is 2340 / 12 = 195A. So now we're even closer to that 200A.

Then you need to find the DC input wire size that will carry more than the fuse size, so that the fuse is the weak link and will blow to protect the wires. Remember, current is the same at every point in a simple circuit, so both your DC input wires must be this size or larger.

By the book, you would find that by looking in ampacity tables for the type of wire you are using and the environment in which it is used. In your case the environment would be called "single wire in open air" since you aren't enclosing your DC wires in conduit.

The tables also derate an wire's ampacity depending on the expected temperature in the environment (and the wire insulation must be rated for that temp or higher). In this case the highest expected temp is pretty much the expected ambient temp inside the van, which could easily be higher than the 30C (86F) threshold where you begin derating ampacity for heat. Assuming conservatively that your wire is the lowest rated building wire insulation type of TW (which has 60C (140F) insulation), and going for a 40C (104F) max temp, you would derate the wire to 82%, so the ampacity you want to meet in the table is 195A / 0.82 = 237A

and that size in a TW wire is the next size larger than what I guessed in my earlier comment, 000 (triple-aught). Pretty big wire.

But, if you had a higher-rated insulation the wire size could be smaller because it requires less temp-derating. A 90C insulation would only require derating to 91%, so 195 / 0.91 = 214A. That can be handled safely with just a 1ga. in a USE-2, THHW or several other available 90C insulation types.

OK, confused yet? You should be, but it all makes sense when you understand the demands put on the wire and its insulation. All of this stuff about wire types and derating for temp are going by the book, assuming that the circuit will be used full-bore all the time and in the worst conditions. That's how you make a system like this as safe as possible.

But the inverter can only produce full surge capacity for several seconds, and is able to produce more than the rated wattage for typically a minute at most, so the wire wouldn't be subjected to those high currents for long in the worst case and a wire can actually handle current quite a bit above it's rated ampacity for some time, as long as it isn't sustained. The wire ratings are calculated for the constant current that would not degrade the wire's insulation, not the constant current above which the copper would begin to melt.

I am also assuming that the inverter can handle surge loads to twice its rated wattage, because that is typical for a mod-square inverter, but the manual may say that the max surge load is less, or even more, than a factor of 2, if so you would start with the surge wattage that the manufacturer specifies as the maximum the unit will handle.

OK, having all that stuff out of the way, let's wander off the NEC reservation for a bit and talk about what you would really want to do. By far the best wire type to use for inverter inputs is not any code-approved building wire, the best thing to use is welding cable, it's just not approved by the NEC. It typically has insulation rated at 105C, higher then the best common building wire at 90C. So practically speaking, little-to-no temp derating is required to use welding cable in open air. It is very flexible making it easier to use in cramped spaces, and the coverings are extremely tough because they are designed to stand up to the abuse of welding.

So using welding wire, and knowing that the max current it needs to handle is only brief surges, you could skip temp derating and go with the first ampacity requirement we figured of 195A. At that current a 1ga. welding wire would be more than up to the task. And you could protect that with just the 200A fuse.

That oughta give you something to gnaw on awhile.
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PostPosted: Thu Jun 07, 2012 10:30 am    Post subject: watts Reply with quote

OK here's a question that has bothered me for a long time. Are the "watts" referred to in audio "watts" the same thing as the watts that are the product of Current X Voltage ? I know that a watt should be a watt should be a watt - but - I can never seem to get my head around how either the voltage or the current could be supplied to produce the wattage stated for some audio equipment.
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PostPosted: Thu Jun 07, 2012 12:38 pm    Post subject: Re: watts Reply with quote

J Charlton wrote:
OK here's a question that has bothered me for a long time. Are the "watts" referred to in audio "watts" the same thing as the watts that are the product of Current X Voltage ? I know that a watt should be a watt should be a watt - but - I can never seem to get my head around how either the voltage or the current could be supplied to produce the wattage stated for some audio equipment.


The key is time.

Watts are watts are watts, but that doesn't change the fact that most audio manufacturers lie about their specs. They'll often use watts peak, when watts RMS would be more appropriate.

With a speaker, watts usually refer to watts RMS, which is the average power the speaker is consuming. With DC voltage, the wattage is simply V * A. But when the voltage and current are changing, as in AC and a speaker, there are numerous ways to measure watts. You can measure the peak watts, which is to measure the worst case V * A at one point in time. But that doesn't tell the whole story - another way to measure watts is RMS, which means root mean squared. This approach basically takes a bunch of samples of the peak watts and calculates the average.

There are different ways to interpret RMS and peak too, depending on how often you look at the signal. Oftentimes something called "Watts peak" is really "Watts RMS peak" over some sampling time. For example, a speaker could say it can handle 300W continuous and 500W peak. That 500W peak really means it can handle a 500W RMS signal for a brief period of time.

Furthermore some meters don't actually measure RMS, they calculate it based on some assumptions. That's why you'll see meters with "True RMS" rating, which will average the signal to get you an accurate reading.

And then there is the phase of the voltage and the current, which can change due to reactance. You can read up on that if you have some time to kill.
http://en.wikipedia.org/wiki/Electrical_reactance

Clear as mud, eh? Very Happy
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PostPosted: Thu Jun 07, 2012 1:05 pm    Post subject: Re: watts Reply with quote

J Charlton wrote:
OK here's a question that has bothered me for a long time. Are the "watts" referred to in audio "watts" the same thing as the watts that are the product of Current X Voltage ? I know that a watt should be a watt should be a watt - but - I can never seem to get my head around how either the voltage or the current could be supplied to produce the wattage stated for some audio equipment.


It sure should be. Decent speakers may be rated for 100W or something, which isn't all that much, but (similarly to guitar amps) a lot of times they're WAY overrated. Like when you buy tiny $10 computer speakers that claim they can handle 300W. It doesn't make any sense, and the tiny amps inside them sure can't produce that much wattage.

Subwoofers are sometimes rated several hundred watts, but that may be peak. And the way they achieve those wattages in high-end car audio is by using capacitors which charge up relatively slowly and then produce a very large current for a short duration. They may also have multiple batteries and big alternators as well. I think the overrating happens in car audio as well since a lot of it is for show.
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PostPosted: Thu Jun 07, 2012 1:20 pm    Post subject: Reply with quote

tencentlife wrote:
watts is watts, it's the same amount of power whether DC or ac



Thank you for the very thorough treatment. That's (W) what I realized was the common factor in input and output, making me realize that we were on the same page.

The Powerbright 1100 does indeed claim to surge to 2200W, but I've had it konk out before that. Still, overall I'm pretty happy with it. I've used small power tools with it but nothing serious. I think I spun up a skill saw with it but didn't cut anything (as a test right after I bought it).
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PostPosted: Thu Jun 07, 2012 2:31 pm    Post subject: Reply with quote

Just because the inverter can surge to 2200w doesn't mean the battery can. If you were using it connected to the small battery in your pics, I rather doubt that it could start a 1.5-2 hp motor without the battery V dropping below the ~10.5 cutoff that most of these type inverters have. Or it might be able to start it only once or twice but can't recover enough to do it more.
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PostPosted: Thu Jun 07, 2012 8:40 pm    Post subject: Reply with quote

tencentlife wrote:
Just because the inverter can surge to 2200w doesn't mean the battery can.


I had that exact thought in a different vein. That was the only one I could find that would fit, and I don't think it has a cranking amps rating because it's intended to be a deep-cycle battery, but the point is I'm not sure it can produce enough amperage to blow the 125A fuse. It's about 1/2 the size of an average car battery and has those thick deep-cycle battery plates, so it's max output is < even a conventional "car starting" battery of its size.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Starting,%20Marine,%20and%20Deep-Cycle%20Batteries
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PostPosted: Thu Jun 07, 2012 9:08 pm    Post subject: Reply with quote

Oh it can definitely put some serious amps into a dead short, that's the main reason you put a fuse there.
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