Watts, Amps, AC electrical systems

[Trisha]

I want to switch out TV's. Or rather, I just did. My question is this, There's a good listing in the BF manual that has converter calculations for DC items so you can see how the items you use affect the overall available DC power.

but there really isn't that much available to explain how the AC items add up, and how they affect a 30-amp system. TV 1 says it's 75 watts. (5 on standby) I'm sure each appliance has it's wattage ratings, but how do I get, from that, a calculation that shows me where I stand with my 30 amps, or even where I stand on the particular circuit I'm plugged into?

I am sure I learned a formula once, but I cannot remember it.

trsh

[Bill Ruh]

Hi Trisha,

watts = volts x amps

Use 120 volts for ac and 12 volts for dc. So your 75-watt ac tv is 0.6 amps ac.

Exceeding 30 amps ac requires several big-draw items, like the ac, toaster, hair drier, and/or microwave.

[Randy Wilson]

Trisha, the simple answer is that watts is the product of amps multiplied by volts. Example: 240 watt load on a 120 volt circuit would draw 2 amps of current (2 amps x 120 volts = 240 watts). However, to be tecnically correct, this applies to resistive loads such as a toaster, incandescent light bulb, etc. or direct current (DC) circuits such as the battery supplied 12 volt system. Motorized devices running on alternating current circuits (AC) are affected by something called "power factor" and also require a higher current flow on being started. In other words, when you start your air conditioner (especially when the compressor and fan are both starting up), the starting current is greater than the running current that will maintain it after starting. This is why the generator seems to momentarily slow down when the air conditioning compressor cycles on.

The answer you probably want is to use the formula above to calculate your required amps, but be aware that motorized devices may make some additional demands that are more difficult to determine so don't cut it too close. Our Born Free coaches use 120 volt circuits for shore power, but that is a nominal voltage. In any particular location it may vary somewhat.

[Trisha]

Cool. Thanks guys.

when I start up the Air conditioner, I usually don't have anything else running. Or rather anything much.

I don't even use a blow dryer. that's what wind is for. I have one but I am not sure what for?

But then my sewing machine can draw too. I usually take into consideration the large draw that the A/C can have when it first starts and don't have other things (other than lights or things) running.

New Question: what happens if one is running the generator while plugged into shore power?

Trish

[Dave&JanPotter]

Cool. Thanks guys.

when I start up the Air conditioner, I usually don't have anything else running. Or rather anything much.

I don't even use a blow dryer. that's what wind is for. I have one but I am not sure what for?

But then my sewing machine can draw too. I usually take into consideration the large draw that the A/C can have when it first starts and don't have other things (other than lights or things) running.

New Question: what happens if one is running the generator while plugged into shore power?
Trish

Trish,
You definitely want to operate your coach from only one power source at a time. My Born Free (2005 BFT) and I am assuming yours, has an automatic transfer switch which will prevent you from operating from more than one source at a time. When you start the genset, it senses that and after a minute or so to let the genset settle out, it automatically switches the load to the genset. As an aside, you should not start the genset with any significant loads operating in the coach as it will slam them onto the genset when it switches.
There is a long technical answer as to why you should only operate from one source at a time, but suffice to say it is not a procedure you or anyone should enter into lightly as severe damage or injury to you or others can result when you attempt to operate your small genset in parallel with the power grid. There was a lineman in one of the southern states electrocuted earlier this year when someone plugged in their home genset improperly after a storm.
My brand X motorhome didn't have an automatic trabsfer switch such as described above, but the power cable and plug were arranged such that I could only plug the coach into one source at a time. Same protection, just a manually operated procedure.

[Trisha]

Good to know! It did not sound like it made much "common sense" but I did not know anything more than that.

I figured it was 30 amps either way. so you're plugged in or your on genset but I did not know what it would or could do except maybe overload something and maybe fry something.

I so appreciate these forums! How do folks live without them?

Trish