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Old 01-20-2013, 12:25 PM   #11
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Re: How To: Bus Electrical Systems - DC

Quote:
Originally Posted by CAMO-MONSTER
I HAVE ABOUT A 32" TV AND I DON'T THINK THAY MAKE A 12v IN THAT SIZE.

BUT I WOULD LIKE TO SWICH MY COMPUTER TO 100% 12v.
DOES ANYBODY HAVE ARY HELP WITH THIS ????


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Quote:
Originally Posted by greaper007
To the computer question. . . . . . The advantage of the 12vdc power supply is that your computer uses 12vdc, and normally has to convert 120vac from a wall circuit. . . . .
Older desktop power supplies had regulated +12 volts, - 12 volts, and +5 volts coming out. Newer computers run at +3.3 volts to the processor instead of +5 volts. Most of the computing is done at +5 or +3.3 volts, I think. If you open the cover on a desktop, the AC power supply should have a sticker with the output voltages and currents, or else get the OEM model number, and search the web for specifications.

Laptops I have seen usually charge the batteries from about +18 volts DC out of the charger, and would need a DC-DC step-up converter to run them on mobile DC. Getting a small (~100 watt) Radio Shack or similar inverter to power the AC charger is usually simpler and cheaper. Just turn off/unplug the inverter when not in use.

Providing the -12 volts for a desktop is the toughest, as you would need a DC-DC converter, and cannot just regulate down the positive battery voltage. But I think the -12 volts was only used in old serial and maybe parallel ports, where the digital ones and zeros were sent as plus and minus instead of on and off. A 9-volt transistor radio battery might be enough to supply the reverse polarity if you needed that for a port. The new USB ports have 5-volt power, but I don't know the signal voltages. I would suspect a desktop would run just fine on the +5 and/or the +3.3 volts, or maybe that plus the +12.

Building step-down regulators to run a desktop off of 12 volts is somewhere way, way down my list of theoretical projects for when I get a "round tuit." But if I get to it at all, I will likely only get as far as converting an ancient IBM Thinkpad laptop with a failing display that sits in my junk box. I would use it as a CPU with external monitor, as I know from experience that 12 volts to the battery clips will run one of these units. I can get an adapter that uses a camera memory chip to replace the ancient hard drive for storage.
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Old 12-24-2014, 05:50 PM   #12
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Quote:
Originally Posted by lornaschinske View Post
I planned on powering the TV, lights and possibly computer off a small inverter. I know the POS Onan generator in the Class C wasn't smooth enough to power my desktop computer. Every time it surged slightly, the computer shut down.
You're not going to get away with a "small" inverter if you want to do all that. Be thinking 1000watts continuous or more depending on what kind of lighting you're talking about. You're better off running dc lights off your house battery bank (isolated via diode from bus batteries hopefully so you can always still start the bus) directly. Get some LED lighting, in many cases there are direct replacements for bulbs that fit the fixtures you probably already have in your bus, and you can run them damn near forever off a couple deep cycle batts.

The onan generator isn't a POS persay (maybe it is, idk) its just not designed to produce a pure sine wave that electronics usually require. When you're charging a laptop off 110v, most of that "dirty power" is hidden by the 110vac to ~14-18vdc step-down and the fact you're charging a battery not providing power directly to the cpu. If you want to power a conventional desktop cpu, you'll want a dc-to-dc power supply as they're more efficient than stepping up from 12vdc to 110vac then back to 5-12vdc. Check out mp3car.com for more info on dc to dc power supplies (as someone suggested above.) If you'd like to run whatever you want off your genset, you can run whats called a power conditioner. This will smooth out the irregularities in the power being generated. A standard computer ups will also do this to a degree.

Quote:
Originally Posted by Redbear View Post
Laptops I have seen usually charge the batteries from about +18 volts DC out of the charger, and would need a DC-DC step-up converter to run them on mobile DC. Getting a small (~100 watt) Radio Shack or similar inverter to power the AC charger is usually simpler and cheaper. Just turn off/unplug the inverter when not in use.
You may have different experience, but I've yet to see a single laptop which would run off a 100 watt inverter. You'd typically need something in the 250-400 watt range. Make sure you test it out first or keep your receipt. You could do the math but these things are plagued by inefficiency and false claims, so ymmv.

Quote:
Originally Posted by Redbear View Post
Providing the -12 volts for a desktop is the toughest, as you would need a DC-DC converter, and cannot just regulate down the positive battery voltage. But I think the -12 volts was only used in old serial and maybe parallel ports, where the digital ones and zeros were sent as plus and minus instead of on and off. A 9-volt transistor radio battery might be enough to supply the reverse polarity if you needed that for a port. The new USB ports have 5-volt power, but I don't know the signal voltages. I would suspect a desktop would run just fine on the +5 and/or the +3.3 volts, or maybe that plus the +12.
Wait what? -12? Negative voltage doesn't exist, its just shorthand for saying the polarity is reversed. In a DC system you have positive direct current and ground. That's it. Ones and zeros have always been ones and zeros. They're either on or off, electrically speaking. Polarity only relates to how the wires are hooked up, and most modern electronics feature biased polarity, meaning they'll figure it out for themselves and either not work at all until you correct it or work just fine.

Quote:
Originally Posted by Redbear View Post
Building step-down regulators to run a desktop off of 12 volts is somewhere way, way down my list of theoretical projects for when I get a "round tuit." But if I get to it at all, I will likely only get as far as converting an ancient IBM Thinkpad laptop with a failing display that sits in my junk box. I would use it as a CPU with external monitor, as I know from experience that 12 volts to the battery clips will run one of these units. I can get an adapter that uses a camera memory chip to replace the ancient hard drive for storage.
dc-to-dc power supplies already exist, and are designed specifically for the problems that vehicle computers face, namely remote switching by a key/aux switch, surviving low current states during cranking the starter and dealing with highly volatile power fluxuations. No sense reinventing the wheel when its been done elegantly already.

This howto is definitely in need of some construction :P Maybe I'll work on something later when I'm a little more solid on my pv knowledge.
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Old 10-26-2015, 11:37 AM   #13
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So, back to the how-to for DC, I'm looking at 2 separate systems, unless otherwise suggested:

- chassis/body from the factory
- "house"

All of the chassis/body grounds to the body. Should I also ground my house system to the body? Why or why not? If no, then where will it get its ground? Is there a risk of feedback between the two 12v systems?
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Old 10-26-2015, 12:00 PM   #14
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IMHO the house dc system should have its ground side connected to the body rather than being kept floating. Even if you tried to keep it floating, inevitably there'll be some appliance built with its chassis connected to the negative wire and that's the end of the floating setup. Better to have the main connection in a known place with suitably-sized wire.

Whether the body is actually used as the ground return or not is a separate question -- one could run a ground/negative return line along with each supply. That could make sense when installing something in an area where the nearest structure is fiberglass, wood, or covered in foam insulation. It's probably easier to ensure clean reliable rust-free connections when they're wire-to-wire rather than wire-to-steel-frame. If the body/frame is used as the return, then be sure the connection back to the battery is big enough. A good way to check that is, with the loads operating, measure the voltage between the battery post and the frame (ie, include the cable-to-lug and lug-to-post (or frame) connections in the measurement). I don't know of any standard for this but to me less than 1% (0.1v in a 12v system) would be good.
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Old 10-29-2015, 04:22 PM   #15
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I have an electrical/ac question. Has anyone done or think it would work to use a ductless split a/c unit? Mount the outside part on the back of the bus and one or two inside units- one above the back door and maybe one towards the front. Would this use too much power? Would a battery bank and solar panels be able to support running these day and night in hot climates along with the usual appliances? Most of ones I have seen are 220v, I have seen 12v to 220v inverters, would your batteries need to be setup as more than 12v to support the power draw- 36 or 48v?
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Old 10-29-2015, 05:57 PM   #16
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Quote:
Originally Posted by buslife2015 View Post
I have an electrical/ac question. Has anyone done or think it would work to use a ductless split a/c unit? Mount the outside part on the back of the bus and one or two inside units- one above the back door and maybe one towards the front. Would this use too much power? Would a battery bank and solar panels be able to support running these day and night in hot climates along with the usual appliances? Most of ones I have seen are 220v, I have seen 12v to 220v inverters, would your batteries need to be setup as more than 12v to support the power draw- 36 or 48v?
somewhereinusa has two separate units on his
http://www.skoolie.net/forums/f11/so...a-6318-25.html
Maybe a good place to start at least.
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Old 10-29-2015, 06:50 PM   #17
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Quote:
Originally Posted by buslife2015 View Post
Would this use too much power? Would a battery bank and solar panels be able to support running these day and night in hot climates along with the usual appliances? Most of ones I have seen are 220v, I have seen 12v to 220v inverters, would your batteries need to be setup as more than 12v to support the power draw- 36 or 48v?
Mostly it depends on how much heat you want to pump from one place to another, which in turn depends on the target temperature, how many windows you get rid of, how much insulation you add, how many people are inside, and how much heat is produced inside by operating the usual appliances.

Most often, people work through the numbers to figure out how much power it'll need, how much solar panel and battery that'll require, how much that'll cost... and they choose a different way. Don't get me wrong: if you lose most of the windows, insulate heavily, keep internal heating low, keep the temperature setpoint on the warm side, and have a modest to generous solar budget it could be doable. But a quiet generator or campground with hookups are probably the most common answers to powering air conditioning.

If the hot climates are dry enough then evaporative cooling could be worth a look.
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Old 10-29-2015, 11:04 PM   #18
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AC ground should only be bonded to the chassis / body in one location.

AC and DC grounds should both be bonded to the Chassis / body of the bus.

Number of DC ground bond locations is not relevant.

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Old 01-31-2016, 10:52 AM   #19
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I'm ready to run wires to connect the rear lights and running lights, with conduit in place and lights installed...but I'm having a hard time figuring out what gauge wire to use.

I've replaced the stop/turn/running and backup lights with LED fixtures, so they'll use less amperage than the original fixtures. That said, during the interior demolition we noticed signs of MANY fires in the original wiring, which the school district fleet maintenance crew had replaced with new wires while leaving the burnt-out wires in place. My interpretation of these observations was backed up when I read the maintenance records for the bus, which include several electrical fires in the lighting circuits. So I know that the original wiring was not of sufficient gauge for the draw of the original fixtures: generally 14# wire was used, although wire as heavy as 10# was used in the beginning of some of the circuits with many parallel fixtures and higher power draw (red and amber flashers).

As I research what I should use to wire the new systems, however, I'm coming up with results that seem excessive by comparison. Most charts showing power drops in 12V systems and respective wire gauge requirements don't show distances longer than 50', although Amps and Wire Gauge - 12V Circuit goes up to 90', which is about right for getting a circuit "there and back again" on a 40' bus. This chart states that for a 5A Circuit, which is more than enough for any of the lighting circuits involved (the heaviest draw is for the turn/stop lights, at 0.21A each), an 8# wire is required for an 80-90' circuit.

I know from the physical evidence and the maintenance records that I don't want to directly replace any 14#, but sizing up all the way to 8# seems like overkill. Does anyone have any recommendations? I'll err on the side of caution and safety, but even using 10# would save a significant amount of money over the 8# and provide a much safer system than the original 14#.
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Old 01-31-2016, 11:53 AM   #20
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Most buses ground their circuits to the steel body so your max run would be closer to 45' which would let you use the #14 wire with plenty of safety margin for your .21 amp load. You want low voltage automotive wire, not the heavier 120v house wire.

The factory wiring is usually more than enough to handle a given load. Burned wiring suggests some other problem, maybe shorted lights or someone tapping into a circuit overloading it.
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