Electricity 101

[Legacy Posts]

:o OK I need help...

If a lamp has 45 milliamps, how much is that in real amps? Is it .045 amps?

I'm going to show how confused I am with all this stuff - Duh. Can someone help me?

Using water as an analogy
volts = pressure
watts = ?
ohms = ?
amps = volume

I found this website and would like to know how to use it.

http://www.currentsolutions.com/knowledge/..._calculator.htm

[Legacy Posts]

Michael,

I went to the site you had linked...Neat stuff. I bookmarked it for future reference. Now to edit my original post.

Watts is energy or work done. (748 watts per horsepower) It is analogous to a measurement of how far the water pushed something when you blasted it with the hose.

Amps would be like the capacity available (gallons)

Ohms would be like a restriction or orifice.

I know you didn't ask but...
Switches are opposite (than valves) from what many think when using the water analogy. An "open" switch is "off" (no electric flow) while a "closed" switch is "on" (allows electric flow). An "open" valve flows water and a "closed" valve does not (unless its leaky)

[Legacy Posts]

Orginally posted by Michael Sanders

:o OK I need help...

If a lamp has 45 milliamps, how much is that in real amps? Is it .045 amps?

I'm going to show how confused I am with all this stuff - Duh. Can someone help me?

Using water as an analogy
volts = pressure
watts = ?
ohms = ?
amps = volume

I found this website and would like to know how to use it.

http://www.currentsolutions.com/knowledge/..._calculator.htm

So...

Using water as an analogy
volts = pressure
watts = gallons
ohms = restriction
amps = flow volume

I like your explanation of the switch vs valves, very good.

Now, when I want to start adding up my electrical use how do I do that? I have a 12 volt respirator I use at night (all night, every night). How much battery do I need? How much extra do I need.

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Michael,

You need to know how many amps the respirator draws at 12 volts (dc). Lets assume it draws 1 amp.
Now assume you have a battery that has a capacity, at 12 volts dc of 50 amp hours.
The respirator would run (theoretically) for 50 hours.

The missing pieces of the puzzle are the amp draw from the respirator and the amp hour capacity of the battery. The calculation is the division of the capacity by the draw.

amp hours/amps=hours

[Legacy Posts]

Does this make sense to you? The respirator says...

100-120 V~/230-240~V50/60 Hz 12 V ---
AC 1.0 A max. / DC 3.0 A max

Class II Type BF

115 VAC - T800 mA. 250 V 5x20 mm
230 VAC - T315 mA. 250 V 5x20 mm

I’m not sure what the amps of standard 17’ Casita battery is.

My guess is on 12 V it uses 3.0 amps per hour, right?

[Legacy Posts]

The subject is analogous systems. Consult an engineering reference handbook for mind-boggling math and details...

I believe Amps is equivalent to flow (gallons per hour). Amps over time is capacity (gallons per hour divided by hours), as in "the battery can deliver x amps for y hours because it is an x*y AmpHour battery. The tank can deliver x gallons for y hours because it is an x gallon tank.

Indeed, voltage is pressure, resistance can be either orifice or laminar pipe loss (orifice merely being a point pipe loss), transformers are hydraulics, and switches and valves have conventions.

It's been a more than just a few decades since I took a course in this stuf...

Pete and Rats

[Legacy Posts]

Michael,
I guess it can be set to operate on 12 Volts DC from what you have related. Also it looks like the maximum amp draw is 3.0 Amps. So...
a group 24 deep cycle battery should have a capacity of about 85 amp hours. 85/3=28 hours of operation for that one component. If anything else is added such as lights, tv, furnace the battery life would be less. If you could have a dedicated battery to service the respirator it should at least go a whole day/night before needing a recharge.
Hope this helps.

[Legacy Posts]

:cblob Thanks Steve.

I use the respirator about 8-9 hours a night.

I've been thinking of moving the Casita battery to the Boat. So if I replace the battery, what battery would you recommend? I heard that two 6 V batteries are better then One 12 V.

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If you have the room, I also have heard that 2 6v golf cart batteries will have more capacity. I have not checked it out though. I am currently running a group 24 Interstate marine deep cycle on my Minicruiser. It has about 85 ah cap but I have not had the oportunity to put it to the test.

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Michael:

You know (from somewhere) that the type (size) 24 battery in the Casita can be replaced by a 27, 29, or 31?! Slides right in, just have to move the angle bracket and drill a new hole to hold it down. Switching from a 24 to 29 is supposed to increase the amp/hrs capacity from something like 85 to 135.

And/Or......carry a spare battery in your tow vehicle, in a plastic box, wired to a its own 'pigtail' 7 prong trailer plug, and plug the trailer in to it when you park. No 'installation' required. Kinda like using a 'jump-it' but would provide 5 times the power capacity.

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6-volt batteries have no inherent advantage over 12-volt, except that the larger amp-hour sizes are easier to move and handle in 6-volt packages.

A pair of golf cart batteries wired in series for 6 volts has a capacity of 220 amp-hours, and can be purchased for under $150. They are popular because they have the highest capacity and longest life for the money. Obviously, they will not fit in a Group 24 case.

BTW, don't assume that 220 Ah means that you can use that much every night. Allow a safety cushion of 20% of capacity, that is, don't take more than 176 Ah out of a fully-charged 220 Ah battery.

Michael, assume that your respirator will be in use for 12 hours (large margin of safety). This is 36 Ah. 36x1.25=45 Ah. That's your 20% reserve charge. Then another margin of safety, let's say at least a 50 Ah battery, and that assumes that you will only be dry-camping for one night. I would recommend a dedicated battery for this load, assuming there's room for one. It's a good thing it will run on DC, so you don't need an inverter.

Does this help?

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The primary advantage of a matched pair of six-volt golf cart batts over the equivalent pair of 12V batts is that the sixes will stand many more charge-discharge cycles over their lives than will the 12s. I believe they also cost a little less, but most definitely they will produce the least cost per total amp-hours (at 12VDC) according to the folks in the BulgeMobiles who have extensive power requirements, esp when equipped with four-stage chargers and maintained properly.

Best source seems to be Sam's Club; be sure to read up on this first before trying it out, and get two batts from the same manf's lot to be sure they are as matched as possible.

Pete and Rats