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Old 03-03-2010, 10:08 AM   #1
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'School me' on the basics - Electric 101.

ok. im more of the 'right-brained artist type' and seeing how I'm posting among nuclear physicists, rocket scientists and aerospace engineers (just read the "what we do for a living thread" ).... maybe someone can 'school me' on the basics of electricity in RV's.

there's... amps, voltage, 110v, 30A, 50a , umbilical cords, inverters, converters, trasformers, chargers, adapters, batteries, volt regulators, low power concerns, power surge concerns.....

HELP?! specifically...

i know that when we picked up the trailer my pops had to remove the plug and hard wire it to the TV power to get lights. what kind of plug should go on the cord to plug into the TV?

he also had to hardwire the 'umbilical cord' (main cord to plug into city power). what goes here?

do i need adapters to plug in at campgrounds? why do i need adapters? what adapters?

we plan to use a household-type mini fridge w/ 110v, but the water pump is 12v - so we need both to work when we are on battery power / city power. Pops recommends a 'transformer', like the one that makes the fan work on city or batt power, except for whole trailer.

batteries - need enough to last us about 1 day off the grid. how many? what kind? how to i charge them?

do i really need to be concerned over low power/ brown outs? how does one monitor that?



--------------------------------
addl info on all appliances:
--------------------------------
Fridge: Volts/Amps 115/1.5
water pump: 12v / 7amps max
wastewater pump: 12v / 2.4 amps (only turned on when shower on)
lights: unknown usage. there are 5 total light fixtures with one bulb on each side of teh fixture 12v and the other side 110 (i assume)
portable ac unit:115v / 8 amps

i also will have my laptop plugged in at all times.

no microwave, no television, no hairdryer, etc - no other electric appliances.
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Old 03-03-2010, 11:02 AM   #2
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I have to agree that so many forums gurus seem to be coming from the meta-engineer/rocket scientist realms.. ;-)

I would first off recommend a few good books:

- the Woodall's RV Repair (exact title?) Guide has a VERY good run down of Ohm Law and that whole '3 parts of the equation' thing you'll need to get your left brain around, as well as a ton of other good reading..

- ditto the above for the Trailer Life RV Repair Guide (Livingston)...

- "Managing 12 Volts" (Barre) is a great book for starting to figure out your 12 volt stuff....you'll learn why a 12 volt battery really only has ONE usuable volt ;-)

...and of course, airforums, ground-zero for most things repair related..

to fully benefit here, use the Google Search function, which is a pull down from the Search button in the blue band above...

wow, you got a '62 GT, awesome rig to be starting out in 'streaming!
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Old 03-03-2010, 12:06 PM   #3
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i know that when we picked up the trailer my pops had to remove the plug and hard wire it to the TV power to get lights. what kind of plug should go on the cord to plug into the TV?
One that fits into the matching connector on the TV, if there already is one. The 7-blade rv connector is the modern standard. I use a six-pin connector because it's what my truck came with and I don't want to have to drill another hole. Either will work.

Quote:
he also had to hardwire the 'umbilical cord' (main cord to plug into city power). what goes here?
It's no longer possible to get connectors that will fit the original setup on your trailer. You can replace it with a modern equivalent, the Marinco shore power connector, which uses this type of cord.

Quote:
do i need adapters to plug in at campgrounds? why do i need adapters? what adapters?
In general you do not however you may occasionally encounter sites that only have 20A service, or you may wish to plug into an outlet in your house or garage. You will need one of these

Once in a great while someone encounters a site where there is 50A service only but these are extremely rare and are only found at high-end sites, usually seasonal ones. Some people carry a 50A to 30A adapter just in case.

Quote:
we plan to use a household-type mini fridge w/ 110v, but the water pump is 12v - so we need both to work when we are on battery power / city power. Pops recommends a 'transformer', like the one that makes the fan work on city or batt power, except for whole trailer.
You need a converter for that and should replace the original one unless that's already been done. Head over to BestConverter - Converters, Inverters, Electrical Supplies, Electronics and look at their Xantrex converters.

Quote:
batteries - need enough to last us about 1 day off the grid. how many? what kind? how to i charge them?
You can get by with one but if you have room for two I'd start there. Get deep-cycle batteries. The converter will charge them for you when you're plugged into power in a campground or at home.

Quote:
do i really need to be concerned over low power/ brown outs? how does one monitor that?
I tend to believe that the extent of these problems and their effects are overrated but you may run into problems occasionally when you are running your air conditioning and everyone else in the campground is, too. You can get a plug-in voltmeter to see whether there's a problem or not. I have a cheap Camco meter which I don't like but many people use them.

Quote:
lights: unknown usage. there are 5 total light fixtures with one bulb on each side of teh fixture 12v and the other side 110 (i assume)
I would keep the original setup like that although some people switch to the modern system where everything is 12 volt.

Quote:
i also will have my laptop plugged in at all times.
You'll be happiest if you get a 12 volt adapter for your laptop then use that.

Good luck, ask questions.
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Old 03-03-2010, 12:14 PM   #4
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Missed this the first time through

Quote:
Originally Posted by NJtoNC View Post
we plan to use a household-type mini fridge w/ 110v, but the water pump is 12v - so we need both to work when we are on battery power / city power.
That kind of fridge won't work on batteries.

Get a fridge that is set up to run on either 12 volts (battery) or 120 volts (campground), like this one. Any 12 volt fridge with a Danfoss compressor will work fine.

Or, for a cheaper option, you can get one of those coolers with an electrothermal module. They work, but not as well, and they tend to be too small and don't lend themselves to permanent mounting.
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Old 03-03-2010, 12:38 PM   #5
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ok, i apologize - fridge is actually 115v. why wont 110 or 115 work, but 120 does?
---
and for the odd day or 2 we are off grid, is there a reason i cant use an inverter like this;

http://www.homedepot.com/Outdoors-Ge...atalogId=10053

for fridge / laptop?
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Old 03-03-2010, 12:46 PM   #6
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Primer

Well, you asked for it, so here we go

Ohm's law is fine, but what you really need to know is that
Power = Watts = Volts x Amps

So let's say you want to use your 1800 watt Conair hair dryer, run the microwave, and run the a/c. How many amps do you need? Add up the power ratings:
(1800 watts for hair dryer) + (1500 watts for microwave) + (2000 watts for a/c) = a total of 5300 watts. OK, you're plugged into 120 volt service. So Amps = Watts/Volts = > Amps = 5300 watts/120 volts = 44 amps. So, there we can see, that on a 30amp circuit, you can't run all three.
That formula will be a big help to you.

A CONverter changes alternating current to direct current; so it allows you to run 12v DC stuff off the 120v AC shore power.

An INverter changes direct current to alternating current. One of those would allow you to run 120v AC stuff off your 12v DC batteries.

You don't often see inverters on RV's because they're already packing a couple of 12v batteries. But you almost always see a converter on board to recharge your 12v batteries and operate all the 12v stuff while you're hooked to shore power.

The brand of converter mentioned above is a good one. Progressive Dynamics is another good one. There are others, but these two are the ones most guys seem to like.

I have a Progressive Dynamics 50amp converter and panel I am going to wire into my coach this spring (if the crummy weather ever ends) and convert it from 30amp to 50amp. If I go to a campground that only has 30amp, I'll simply use the 30amp to 50amp adapter plug and practice energy management, as I do now. But if they have 50 amp service, I'll plug right in and let it all hang out

Umbilical cord is nothing more than a heavy extension cord with the proper plug ends on it to plug your coach into shore power. Some of them retract (like my Excella had), some just coil up into the storage panel (like the one on my Avion), and others disconnect from both ends and you carry them inside the coach (like many of the 50 amp cords).

On the "brownout" (low shore power voltage) issue, it can really damage things like air conditioning compressors. There's another thread on here where they go into great detail on devices out there to monitor this. I don't have one, but plan to get one. Well, you can simply take a multimeter check any of your 120v outlets when you're at the campground. That's how I have done it. But I believe you can buy a little device that just plugs into an outlet and you leave it there and it's got a readout that shows you what the campground voltage is. You want it up around 117-122 volts. You start getting down around 105-110, it's too low. But if you can't find one of these doohickies, any good multimeter will suffice.

On a trailer this old, honestly, I think you would be better off to tear out all of the original wiring and redo it from scratch. I think that would be easier than trying to patch up the original stuff. The books mentioned above are good ones. I have "RV Repair & Maintenance Manual" by Bob Livingston, put out by Trailer Life. It's a really good reference book. I highly recommend you buy it. It's like $18 or something, but it's money very well spent.

To summarize: You'll want two big 12v batteries; probably 1000amp deep cycle marine batteries or similar, you'll need a power converter from a reputable company, you'll need some boxes, outlets, and various lengths and gauges of wire. For 30amp, you'll want at least 10 gauge wire for the main circuit and 12 gauge wire for the lighter branches; for 50amp you'll want I believe 6 gauge wire for the main and the same 12 wire for the branches. You might need 10 wire for the a/c (10 wire is good for 30 amp, 12 wire is good for 20amp, 6 wire is I believe good for 55amp). The 12v stuff will be lighter for the lights, and probably similar for the brakes. I'm not sure off the top of my head on that one, but reference the books and you'll be good.

Good luck with your project!
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Old 03-03-2010, 01:12 PM   #7
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ok, i apologize - fridge is actually 115v. why wont 110 or 115 work, but 120 does?
---
and for the odd day or 2 we are off grid, is there a reason i cant use an inverter like this;

Sima Dual-Outlet DC-AC Power Inverter With Soft Start - 300-Watts Continuous, 800-Watts Peak - STP-325 at The Home Depot

for fridge / laptop?
110, 115, 117, 120, 125 all mean the same thing in practice with most equipment so rated working acceptably well on anything between around 105-130 volts.

In general the cheap inverters don't perform well, but you could try it. The problems involve reliability, heat, efficiency, electrical noise, and ability to deliver the rated power. If you got that inverter and a compact fridge, and ran it for a couple of years, and came back to this forum and told us it worked great, I would be surprised.

For laptops it might work OK but you can get a 12 volt power supply for under $100 with much greater efficiency and reliability and fewer cords to fiddle with.
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Old 03-03-2010, 01:15 PM   #8
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To summarize: You'll want two big 12v batteries; probably 1000amp deep cycle marine batteries or similar
Jim I think he's going to need an axle tire and frame upgrade if he takes your advice.
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Old 03-03-2010, 01:19 PM   #9
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this is the only electrical panel in the trailer. seems PO's removed any batteries and water storage and only camped w/ hookups. so there is no existing converter / charger. and i didnt really see a spot for it...
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Old 03-03-2010, 01:20 PM   #10
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Jim I think he's going to need an axle tire and frame upgrade if he takes your advice.


..."She"....

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Old 03-03-2010, 01:31 PM   #11
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this is the only electrical panel in the trailer. seems PO's removed any batteries and water storage and only camped w/ hookups. so there is no existing converter / charger. and i didnt really see a spot for it...
ouch! they turned into a "park" model... but if you like using campground hookups its not a problem..

feel like running some 8 gauge wire? 12v is big plus in AS..

re: refrigerator if you're shopping, consider one that also runs on PROPANE, pricier, but wow, what a convenience and saves the batteries like crazy..
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Old 03-03-2010, 01:41 PM   #12
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this is the only electrical panel in the trailer. seems PO's removed any batteries and water storage and only camped w/ hookups. so there is no existing converter / charger. and i didnt really see a spot for it...
Then it's going to take some work and you probably ought to involve someone who has experience with electricity to avoid basic mistakes that could compromise safety or cause reliability problems later.

In brief the steps are to evaluate the condition, usability, and location of the existing wiring (it may be fine and there are parts of it that you might want to reuse to avoid having to tear up the trailer to run new wire), decide on location, size, and type of batteries, select and install a new fuse or breaker panel for the 12 volt system, and then decide what to do about the 120v and the converter.
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Old 03-03-2010, 01:55 PM   #13
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re: refrigerator if you're shopping, consider one that also runs on PROPANE, pricier, but wow, what a convenience and saves the batteries like crazy..
The thing to watch is the installation and venting requirements. I looked at your photos on the other thread and can't tell whether your original fridge was propane.

If not, the Danfoss-equipped fridges are the way to go. They use much less power than a gas fridge would on 12 volts, and are much easier to install and maintain.
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Old 03-03-2010, 02:06 PM   #14
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feel like running some 8 gauge wire? 12v is big plus in AS..
the 12V is still in place. not too much work to bring it back...

Quote:
The thing to watch is the installation and venting requirements. I looked at your photos on the other thread and can't tell whether your original fridge was propane.
old fridge was propane. was weighing pro's and cons... too little storage ruled it out. 70% - 80% of our camping will have hookups. when not camping on the road, the trailer will be on our 9 acres of land in NC (w/ hookups) and used while we build our house. Our TV will be run on veggie fuel, so the only thing we have propane for is cooking gas (a decent flame for cooking trumps being eco-friendly).

but our month-long road trip in Sept will have about 7 days, non consecutive, of dry camping - only 1 or 2 days between sites w/ hookups.

Quote:
you probably ought to involve someone who has experience with electricity to avoid basic mistakes that could compromise safety or cause reliability problems later
my father has been in construction for over 30 yrs. He's well versed in the construction / assembly aspect, but not necessarily "as it applies to trailers".

ie., he's not used to thinking about electric / plumbing being compact in size, needing to hook up converters / inverters or flexible for dry camping.

in fact, its funny to watch him - he normally works quickly and professionally with a sort of 'grace' ... he makes it look so easy. but working on the plumbing in the back of a curved tiny space really drove him nuts. and i admit, i got a little smug =)

see:
http://www.airforums.com/forums/f134...tml#post816703
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Old 03-03-2010, 02:25 PM   #15
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You'll probably end up wanting two GC-2 golf cart batteries. They should be in an enclosure and vented to outside. You can google dimensions and weights.

You have the converter link.

You'll want a distribution panel: Distribution Panels

Here are some prices on 12 volt fridges: 115 Volt AC /12 Volt DC Refrigerators

This place will have some of the pieces and parts you'll need: http://www.wiringproducts.com/
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Old 03-03-2010, 03:05 PM   #16
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ok, thanks for all the tips.
im trying to calculate how much energy ill use at once. so the formula is

Quote:
So let's say you want to use your 1800 watt Conair hair dryer, run the microwave, and run the a/c. How many amps do you need?

Add up the power ratings:

(1800 watts for hair dryer) + (1500 watts for microwave) + (2000 watts for a/c) = a total of 5300 watts.

OK, you're plugged into 120 volt service. So Amps = Watts/Volts = > Amps = 5300 watts/120 volts = 44 amps. So, there we can see, that on a 30amp circuit, you can't run all three.
That formula will be a big help to you.
teh fridge specs i have only say 292kwh/yr.

kwh= kilowatt hours, and 1000 watts = 1 kilowatt...

but how to i get a watt rating from kwh (kilowatt HOURS?)
----------
UPDATE
----------
i think i got the hang of this. any math teachers in the house?

fridge: 115amp x 1.5 volts =172.5w
a/c = 900w
shower waste pump = 2.4 amps x 12 v = 28.8w
water pump - 12v x 7 amps max = 84 w
lights 30w x 5 lights = 150w
laptop 18.5 v x 3.5amps = 65w
----------
1400 w

1400watts / 120amp = 11.6V

which is way below the 30V service provided.

am i right?
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Old 03-03-2010, 03:53 PM   #17
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i think i got the hang of this. any math teachers in the house?

fridge: 115volt x 1.5 amp =172.5w
a/c = 900w
shower waste pump = 2.4 amps x 12 v = 28.8w
water pump - 12v x 7 amps max = 84 w
lights 30w x 5 lights = 150w
laptop 18.5 v x 3.5amps = 65w
----------
1400 w

1400watts / 120volt = 11.6A

which is way below the 30Aservice provided.

am i right?
Yes. I fixed the amps and volts for you but still. You would also have to add the converter in, which is around 5 amps depending on size. Still well below 30a.

That was easy.

Batteries are harder to size because you have to figure run time.

I take it you'll have no heat in the trailer?
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Old 03-03-2010, 03:57 PM   #18
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You'll probably end up wanting two GC-2 golf cart batteries.
oy. more math. y'all are killing me!!!

so based on my research - correct me if I'm wrong.
If we want use approx 12amps for 24 hours. with a max DoD of 50% (seems to be whats recommended)...

ah = most amps we can get over 20 hrs

so if
10 Amps X 20 hours = 200Ah

and we use

12amps for 24 hours, it would be the same as using 14.4 x 20 hours, either way, 288ah.

so it sounds like we need twice that to achieve desired dod of about 50%, or 576ah.

2 6v batteries w/ 225 ah = 450ah
or
3 6v batts @ 225ah =675 ah -> probably better for 2 days battery time off grid w/ a/c

is my math right here? note that my calculations are based on running both pumps and a/c 24/7 which won't happen.
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Old 03-03-2010, 04:01 PM   #19
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Yes. I fixed the amps and volts for you but still. You would also have to add the converter in, which is around 5 amps depending on size. Still well below 30a.

That was easy.
Batteries are harder to size because you have to figure run time.
I take it you'll have no heat in the trailer?
Lol. whoops! amps, volts... still working that out in my head...thanks
a/c has heat pump, same energy usage. we don't plan to camp below 40* and if we do ill bring a plug-in electric room heater.
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Old 03-03-2010, 05:23 PM   #20
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A Honda EU3000i or a pair of EU2000i's will help you out a lot too

Maybe I missed it in an earlier post, but I did read through them...what air conditioner is out there that will run off 12v? I've only ever seen 120v ac models for RV's.

I've personally not tried the golf cart batteries...but I know many on here swear by them. I've been considering it. I'd need to build a larger battery box. I may have them mixed up here, but I believe my battery box was originally sized for group 27 batteries. But, the group 27's were made bigger at some point in history than their 1987 dimensions, and so now I can only fit a pair of group 24's. (I may have 24 and 27 flipped....I had to go to the next smaller size battery to get them to fit in the box) At any rate, I have a pair of 750 amp batteries, but I prefer 1000amp or bigger. You can never have too much. Actually, I thought the golf cart batteries were bigger and heavier than the car batteries? Cool if they're not.

1962 you are definitely going to need a new axle. If it were a 1959 I'd say you'd be OK because it should still be leaf sprung, but in '62 they had already gone to torsion type axles and there will be nothing left of the rubber in one that old.

It wouldn't hurt to inspect the frame either. She wasn't built yesterday.

Sounds like a cool project though. Have fun!
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