Amperage v watts

[boisesmith]

Need a tutorial on Amperage v watts. Basic question are: (1) how many watt generator do I need to run a 50 amp trailer (including air conditioners)? and (2), if only 30 amp service is available and I use a dog bone to plug in my 50 amp trailer, what are the possible ramifications?

[BB_TX]

50 amps at 120 vac is 12,000 watts. That’s a large generator.

You can run 2 A/Cs on a lot less if you are careful about everything else you use. An A/C will pull 13-15 amps, with a surge on startup. That surge can be reduced with a soft start A/C or by adding a soft start kit to a standard A/C. Then a matter of adding up amps for all the “essential” other items.

And, yes, you can use a dogbone adapter to connect your 50 amp trailer to 30 amp service. Have done it many times. And a few times to 20 amp service. 30 amp is only 3,600 watts so you really have to be aware of how much power you are pulling or you trip a breaker. No harm. Just turn something off and try again.

[boisesmith]

Thanks for the reply. Any thoughts on the second question?

[BB_TX]

Originally Posted by boisesmith

Thanks for the reply. Any thoughts on the second question?

I was editing my first answer when you asked about the second question.

[kowbra]

Originally Posted by boisesmith

Need a tutorial on Amperage v watts. Basic question are: (1) how many watt generator do I need to run a 50 amp trailer (including air conditioners)? and (2), if only 30 amp service is available and I use a dog bone to plug in my 50 amp trailer, what are the possible ramifications?

Basic (really basic) tutorial...
Volts x Amps (amperage) = Watts

So 1200 watts could be 100 amps @12 volts, but only 10 amps if on 120 volts.
While basic, it is really key to understand how watts is different if you are on a 12 volt system vs a 120 volt system.

50 amp RV circuits are actually 50 amps @ 240 volts, split into dual 50 amp x 120 volt legs. So, the total amps at 120 volts is 100 amps (not 50). That is why it is correct to say that a 50 amp circuit delivers a total of 12,000 watts (100a x 120v).

But a 30 amp circuit is a single leg so a total of 3600 watts (30a x 120v).

Consider that a typical "large" installed generator for an RV is an Onan 5500 watt (or about 45 amps). And portable generators are typically 2000 to 3500 watts (or about 15 to 30 amps).

So, now think of a single AC drawing 15 amps @120 volts = 1800 watts. Which is about maxing out a 2000 watt generator. And, running both AC units is about 3600 watts, more than most portable generators, and using all of a 30 amp circuit. Both AC's plus a light bulb likely trips the 30 amp breaker.

Ok, the above is a bit simplistic, but hopefully that is the level of information you were looking for.


Brad

[Daryles]

It's all about power management

[MT167]

You also need to take into consideration the length of cords and and less than ideal connections, i.e. slightly corroded plugs. Both will use up available amps and while they may not trip a breaker, they will cause heat build up and possible damage.

[mlh]

There is something else you need to consider. The listed wattage on most if not all generators isn’t what you need to consider. Starting watts is what is listed you need to know the running watts. Running watts is usually about 20% lower. My little 2000 watt inverter is 1600 running and my 3000 watt Honda is 2600 running watts I think.
Lynwood

[DQDick]

In a 30amp site we can only run on AC and have to have the frig and the water heater on propane. Using electric cooking appliances and hair dryers etc will use up the rest.

[DutchmenSport]

Watch this video.

https://www.youtube.com/watch?v=GoOR2AJGjOI

[TAKPAK]

[QUOTE=kowbra;1226896]Basic (really basic) tutorial...
Volts x Amps (amperage) = Watts



50 amp RV circuits are actually 50 amps @ 240 volts, split into dual 50 amp x 120 volt legs. So, the total amps at 120 volts is 100 amps (not 50). That is why it is correct to say that a 50 amp circuit delivers a total of 12,000 watts (100a x 120v).


Ok, the above is a bit simplistic, but hopefully that is the level of information you were looking for.

Well, I will probably PO a few people, but you do NOT have a total of 100 amps, only 50 amps, available on each leg. Look at the breaker, it is not a 100 amp breaker, it's two 50's. Won't get into the aspects of alternating current at this point. The thing about RV's is they do NOT (as a rule, there are always exceptions) have anything in them that runs on 240 volts, unlike your stick house. The main panel is split into two segments of 120 volt feeds, of 50 amps for each feed. If you were to install something that required 240 volts, you would still only have 50 amps available for it. The manufacturers try to balance the panel out on loads. Don't want 40 amps on one lead and only 10 amps on the other! If you have two AC's they should each be on a separate leg. You would be surprised at how fast the loads add up today. Microwave, AC's, fireplace(s), and don't forget the wife's hair dryer (mine DW is 1800 watts) hot plates, toasters, coffee makers, the converter (which can pull up to 15 amps) and on and on. Regarding a generator, you would need a minimum of 6000 watts, and that is bare minimum. Especially for AC's, it's the "surge" (starting) watts that get a generator down. If you are careful, you CAN manipulate the loads so that you can get by with the smaller unit, but it will never be like your house, at least not while on a generator. And yes, I was a licensed electrician prior to retirement.

[kowbra]

[QUOTE=TAKPAK;1227405]

Originally Posted by kowbra

Basic (really basic) tutorial...
Volts x Amps (amperage) = Watts



50 amp RV circuits are actually 50 amps @ 240 volts, split into dual 50 amp x 120 volt legs. So, the total amps at 120 volts is 100 amps (not 50). That is why it is correct to say that a 50 amp circuit delivers a total of 12,000 watts (100a x 120v).


Ok, the above is a bit simplistic, but hopefully that is the level of information you were looking for.

Well, I will probably PO a few people, but you do NOT have a total of 100 amps, only 50 amps, available on each leg. Look at the breaker, it is not a 100 amp breaker, it's two 50's. Won't get into the aspects of alternating current at this point. The thing about RV's is they do NOT (as a rule, there are always exceptions) have anything in them that runs on 240 volts, unlike your stick house. The main panel is split into two segments of 120 volt feeds, of 50 amps for each feed. If you were to install something that required 240 volts, you would still only have 50 amps available for it. The manufacturers try to balance the panel out on loads. Don't want 40 amps on one lead and only 10 amps on the other! If you have two AC's they should each be on a separate leg. You would be surprised at how fast the loads add up today. Microwave, AC's, fireplace(s), and don't forget the wife's hair dryer (mine DW is 1800 watts) hot plates, toasters, coffee makers, the converter (which can pull up to 15 amps) and on and on. Regarding a generator, you would need a minimum of 6000 watts, and that is bare minimum. Especially for AC's, it's the "surge" (starting) watts that get a generator down. If you are careful, you CAN manipulate the loads so that you can get by with the smaller unit, but it will never be like your house, at least not while on a generator. And yes, I was a licensed electrician prior to retirement.

Well, you found an interesting way to disagree... I was never saying that it was 100 amps all on a single leg with a single 100 amp breaker. I said there was dual 50 amp legs, which equals a total of 100 amps...



And, to go back to the OP question about running 2 AC units... is this not commonly done by wiring each AC unit to a separate 50amp leg? And is that not why it's been a problem to run dual AC units on 30 amps? And is it not accurate to say that the total wattage on a 50 amp circuit is 12,000 watts, not 6,000?



I don't get your math, maybe you can clarify.



Brad

[BB_TX]

Originally Posted by TAKPAK

………………
Well, I will probably PO a few people, but you do NOT have a total of 100 amps, only 50 amps, available on each leg. Look at the breaker, it is not a 100 amp breaker, it's two 50's. …………..
………………

First I will say I am not PO’d.

But I will say you do in fact have the POTENTIAL of 100 amps. It is possible to draw up to 50 amps on hot leg 1. And simultaneously draw up to 50 amps on hot leg 2. And not trip the breaker. So with a perfectly balanced loading where half your devices are drawing from hot leg 1 and the other half are drawing from hot leg 2, you can in fact draw a COMBINED total of up to 100 amps, 12,000 watts power, at 120 vac.

And interestingly enough, at a perfectly balanced load on the two hot legs there would be no current flow thru the neutral wire.

[firestation12]

This topic was discussed on a previous thread and quickly degenerated to a point a moderator had to close it. The link to Mark Polk's RV 101 video titled "30 amp VS 50 amp" posted by DutchmenSport (post #10 above) adequately explains the topic and near it's end, Mark Polk correctly identifies the 50 amps as a split phase source, each phase providing 50 amps at 120 volts times 2 equaling 12,000 watts. Let's all watch the video and eliminate the need to split hairs. 120v X 100a is equal to 50a X 2 X 120v in terms of wattage (12,000).

[bcrvman]

Originally Posted by boisesmith

Need a tutorial on Amperage v watts. Basic question are: (1) how many watt generator do I need to run a 50 amp trailer (including air conditioners)? and (2), if only 30 amp service is available and I use a dog bone to plug in my 50 amp trailer, what are the possible ramifications?

Watts is power which is the product of volts and amps. A device that can operate on either 12 V (battery) or 120 V wall plug will as an example use 240 Watts regardless. The amperage will be 20A at 12V and 2A at 120V.

Your lifestyle and equipment will dictate what generator you use. Many folks get by with a built in Onan of 5,500 W but then you are buying propane every few days if it runs a lot. Step 1 is to install soft starts for your Air conditioners, that saves a lot of start up power. I get by with a pair of Honda EU2000 (now 2200) because I have a Victron inverter that allows me to use 30A from the generators and 20A from my battery bank of 7.2kWh. We were planning on boondocking maybe 5 out of 7 days so that is why the big battery and solar. Some younger stronger folks go for a 3,500 W generator but too heavy for me so I went with the pair of smaller. When not running Air Conditioners I see on average 150 - 300 watts of power. It's that high because we got the better residential fridge which is about half the power we use. I rewired my main power panel so that of the 6 circuits on one leg, I have 1 spare, MBR AC, W, D, Fireplace, HW elec. My lifestyle allows that as we don't plan on going anywhere hot when we are off grid so don't need AC. We also don't need the Fireplace or furnace as we don't go anyplace cold. HW runs on propane, W and D wait until day 6,7. A little planning and a killl-a-watt meter will go a long way.

[TAKPAK]

Originally Posted by BB_TX

First I will say I am not PO’d.

But I will say you do in fact have the POTENTIAL of 100 amps. It is possible to draw up to 50 amps on hot leg 1. And simultaneously draw up to 50 amps on hot leg 2. And not trip the breaker. So with a perfectly balanced loading where half your devices are drawing from hot leg 1 and the other half are drawing from hot leg 2, you can in fact draw a COMBINED total of up to 100 amps, 12,000 watts power, at 120 vac.

And interestingly enough, at a perfectly balanced load on the two hot legs there would be no current flow thru the neutral wire.

On the last statement, absolutely affirmative. That's why 240 volt motors, stoves, etc. don't have a neutral per se, just a ground (bonding) wire. But I still have to disagree on the first part, you can not get a combined total of 100 amps or the 12,000 watts, as in order to do that, you would have to be able to "combine" the two 50 amp circuits into one, which would result in a "dead short" situation. In reality, the maximum you can pull on the circuit is 50 amps or 6000 watts per leg (circuit). Ohms law is volts times amps equals watts. To properly do a 50 amp RV service with a generator, you would need a gen-set that is capable of putting out the 240 volts (120 each leg) to run it. It is sometimes tough to get the facts across in a forum, I'll agree.

[TAKPAK]

Well, OK. In watching the video, I took note that he did NOT say that the combination of the two 50 amp circuits equaled 100 amps, which they do not. But, his analogy of the wattage is somewhat correct. I was basing my interpretation on a 240 volt, 50 amp load device. He is correct (sort of) in that if you have two devices, each drawing 120 volts and approximately 6000 watts on each of the two 50 amp legs, then yes, I guess you could say you are using 12,000 total watts of power. Strangely enough though, the power meter feeding the service (assuming a two leg, 240 volt meter) will only record it as 6000 watts of power usage, because of the oddity of alternating current. But, that is a whole 'nother discussion!! Sorry to be so technical....too much schooling I guess.

[firestation12]

One question I have is: did you watch the YouTube post from post #10? I’m thinking everyone here is stating that a 50 amp split phase service can provide 12,000 watts of energy. I’m not sure why you are using the term “combined” for the sake of disagreement. No one is stating that the 2 split phases are being combined within the circuits to create 240 volts. But as Mark Polk states in the video, the split phase does indeed produce voltage at the electrical pedestal that produces both 120 volt legs (2) measured to ground and 240 volts measured between phases. Again within the camper, the phases are not combined. Polk makes that distinction in comparing the 30 amp power as 3600 watts compared to 12,000 watts for the 50 amp. The OP started this thread looking for a simple explanation of watts in 30 and 50 amp. I think he’s gotten a drink from a fire hydrant instead.

[Calbrewguy]

All that was about as clear as the Electrical Code.

[rames14]

I have a question. It seems everyone is agreeing that a 50 amp service provides the ability to use 12,000 watts. But then, there are people saying there are not 100 amps available between the two legs. Isn’t watts = volts x amps? If you have 12,000 watts available at 120v, how many amps? A train leaves Pittsburg traveling 72 mph and a bus leaves Miamiat the same time - my head hurts.