Portable GFI for space heater

[lpranger467]

Is your refrigerator a gas-electric RV fridge? If so, it works by boiling a water and ammonia mixture and you may have to add some supplemental heat to the rear of the enclosure to keep it working when it gets that cold. It also draws about 300-500 watts in electric mode which can be an additional load (2.5-5 amps) on your electric supply.

I'm running it on electric to conserve my propane, the fridge is on the opposite wall from the plug I was using but as that theyre both in the living area I'm starting to suspect that its on the same circuit as that the space heater in the bedroom hasnt had any fuse issues at all, Thanks as well Lou for taking time to reply

 

[Gary RV_Wizard]

Thanks for both recent replies, when the fuse blew I know it took a lot of the lights with it.

The confusion here is that the heater is a 120vac electric device and is protected by a circuit breaker. It can't "blow a fuse" because there is no fuse in its circuit. Fuses are used to protect most 12dc circuits in the RV, e.g. the lights, control boards, etc. Please clarify whether it's a fuse or a breaker that opens the circuit.

A 1500 watt heater draws about 12.5 amps from the supply circuit, so a 15A circuit is heavily loaded. Just about anything else sharing that circuit (not necessarily the same outlet) will push the total high enough that the circuit breaker (not fuse) opens because of excessive amps. You need to put that heater on a circuit that has nothing else on it. Or run it direct to the outlet on the pedestal, which will have its own circuit breaker protection.

 

[Ex-Calif]

You can also be "tricked" when a circuit breaker blows.

There seems to be little rhyme or reason on what outlets are ganged on one circuit.

I lost several random circuits early in my liveaboard life. No circuit breaker breaker had popped. Took me a while to figure out the outlet on the vanity was a GCFI and had tripped taking out the whole string.

 

[Trivet]

Does your trailer have an inverter? If so, does it power most of the outlets or just a few select ones?

I ask because your absorption refrigerator probably doesn't run through the inverter, and if the outlet you're using for the space heater does run through the inverter, then it's obviously not on the refrigerator's circuit.

Also, a couple of years ago I bought a Duraflame ceramic space heater. I have a Kill-A-Watt and measure everything because it's fun. It goes up to 15 amps maximum, and the space heater was exceeding that so I couldn't get an accurate measurement of what it was using--the Kill-a-Watt just flashes at that point.

Some space heaters surge when they come on but then settle down to under 15 amps, but this one never did settle down. I unplugged half of the heating elements inside and it still was using 10 amps. This space heater would have been a real problem if I hadn't measured it.

I would suggest that you try plugging the space heater that's tripping the circuit breaker into the plug in the bedroom that your other heater is working well on, just to rule out a rogue space heater.

I agree with Gary that the best way to run a space heater is to plug it directly into the pedestal, but be sure the pedestal is equipped to provide 30 amps to your trailer at the same time it provides 15 amps to the "regular" outlet on the pedestal. It could be an either/or situation when it comes to the 30-amp outlet and the 15-amp outlet.

Just a general warning about space heaters--they might be drawing more electricity than they're supposed to. Also they loose oomph over time, so they also might be drawing less, which is useful information if trying to maximize the heat you can get from space heaters.

 

[lpranger467]

Does your trailer have an inverter? If so, does it power most of the outlets or just a few select ones?

I ask because your absorption refrigerator probably doesn't run through the inverter, and if the outlet you're using for the space heater does run through the inverter, then it's obviously not on the refrigerator's circuit.

Also, a couple of years ago I bought a Duraflame ceramic space heater. I have a Kill-A-Watt and measure everything because it's fun. It goes up to 15 amps maximum, and the space heater was exceeding that so I couldn't get an accurate measurement of what it was using--the Kill-a-Watt just flashes at that point.

Some space heaters surge when they come on but then settle down to under 15 amps, but this one never did settle down. I unplugged half of the heating elements inside and it still was using 10 amps. This space heater would have been a real problem if I hadn't measured it.

I would suggest that you try plugging the space heater that's tripping the circuit breaker into the plug in the bedroom that your other heater is working well on, just to rule out a rogue space heater.

I agree with Gary that the best way to run a space heater is to plug it directly into the pedestal, but be sure the pedestal is equipped to provide 30 amps to your trailer at the same time it provides 15 amps to the "regular" outlet on the pedestal. It could be an either/or situation when it comes to the 30-amp outlet and the 15-amp outlet.

Just a general warning about space heaters--they might be drawing more electricity than they're supposed to. Also they loose oomph over time, so they also might be drawing less, which is useful information if trying to maximize the heat you can get from space heaters.

Sorry guys I was out of the loop for a few, I ended up drilling a hole in the floor under a cabinet and ran an extension cord to the post. The floor was actually insulated and while drilling through my spade bit scaped a electric wired. I made the hole larger and checked the wire, looks like it only scraped the sheathing; I taped it non the less. So far heater runs great on extension cord, I'm keeping the other heater in bedroom at 750w and have had no issues. Because its smaller the bedroom is always nice and warm, the living area not as much but as that its 9 degree out that may explain it. Thanks for all the help folks

 

[DonTom]

I'm keeping the other heater in bedroom at 750w and have had no issues.

But there should be no issues with 1500W. 1500W divided by 120VAC=12.5 amps.

The real questions here are:

Is the heater really only 1500 watts? Really only drawing 12.5 amps?

Is the voltage correct? Higher voltage will mean higher current as well, so a lot more wattage with higher voltage. Double the voltage and get double the current.

IE, 240VAC will be 25 amps or 6000 watts (volts times amps) and that would pop a 20 amp fuse for sure.

But where is this fuse located that blows with 1500W? And what is the current rating of that fuse? And the type of fuse?

Things just not adding up, so I think we have some info. missing.

-Don- Mayo, FL

 

[NY_Dutch]

But there should be no issues with 1500W. 1500W divided by 120VAC=12.5 amps.

The real questions here are:

Is the heater really only 1500 watts? Really only drawing 12.5 amps?

Is the voltage correct? Higher voltage will mean higher current as well, so a lot more wattage with higher voltage. Double the voltage and get double the current.

IE, 240VAC will be 25 amps or 6000 watts (volts times amps) and that would pop a 20 amp fuse for sure.

But where is this fuse located that blows with 1500W? And what is the current rating of that fuse? And the type of fuse?

Things just not adding up, so I think we have some info. missing.

-Don- Mayo, FL

Sorry, but with a straight resistive load, as in most electric space heaters, doubling the voltage halves the current. Some commercial heaters are designed for 240 VAC operation for just that reason, the lower current allows smaller gauge wires. A 1,500 watt heater draws 12.5 amps at 120 VAC, but the same heater operating on 240 VAC draws just 6.25 amps. Check out Ohms power law: I=P/E

 

[Lou Schneider]

Sorry, but with a straight resistive load, as in most electric space heaters, doubling the voltage halves the current. Some commercial heaters are designed for 240 VAC operation for just that reason, the lower current allows smaller gauge wires. A 1,500 watt heater draws 12.5 amps at 120 VAC, but the same heater operating on 240 VAC draws just 6.25 amps. Check out Ohms power law: I=P/E

Nope - the resistance stays constant, so if you double the voltage you get twice as much current and 4 times as much power. And all the magic smoke comes out.

 

[DonTom]

but with a straight resistive load, as in most electric space heaters, doubling the voltage halves the current.

I would like to see you prove that one with Ohm's law:

Say we have 100 volts, 5 ohms. (Voltage over resistance=amps): Current is then 20 amps. 100 volts time 20 amps=2,000 watts.

But now we increase to 200 volts. Still 5 ohms. Current then is 40 amps. 200 volts time 40 amps =8,000 watts.

To make this very simple, use the Ohm's Law Calculator here.

Or see the Ohm's law formulas here.

-Don- Mayo, FL

 

[DonTom]

A 1,500 watt heater draws 12.5 amps at 120 VAC, but the same heater operating on 240 VAC draws just 6.25 amps.

120 VAC times 12.5 amps:1,500 W
240 VAC times 6.25 amps:1500 W

That part was true, the rest wasn't. It draws half the current at 240 VAC because current was halved at the same resistance/impedance for the SAME WATTAGE. Don't reduce the resistance for the higher voltage by having double the windings or whatever and see what happens. It will then be destroyed from overheating.

I assume that heater has a switch for 120 VAC or 240 VAC operation. That makes it simple to double the windings for 240 VAC or add resistance or whatever the switch does.

But these days, more is possible with various types of tricks, especially in switch-mode power supplies.

For an example, I have an electric motorcycle that charges at 1.4 KW if 120 or 240 VAC is used.

I have another where if I charge with 120VAC it will charge at 1.4KW, but with 240 VAC it will charge at 2.8KW.

The first example has a switch mode power supply type of charger with some very tricky circuity to reduce the current as the voltage increases to keep the wattage the same. The 2nd example has no such special circuity, but still uses a switch-mode power supply. So then the power is allowed to increase.

The reason the first example will not allow the wattage to increase is because the small power supply would have to waste that power in heat and would then blow itself out. The 2nd example has a much larger power supply and can allow more than double the wattage with 240 VAC.

So, there are times when some items these days can SEEM to be going against Ohms law, but in reality, they are not. They are just being tricky.

In fact, if I use the OBC (On Board Charger) with the electric motorcycle I have with me now, there is NO difference in charge time or wattage with any AC voltage from 90 VAC to 250 VAC. But the heat and current draw will then be MUCH less at the high end of the voltage range.

But I also have two 2.5 KW external power supplies with me for the same bike. They will be at 1.4 KW with 120 VAC but 2.5 KW if I use 240 VAC.

Do I have you confused yet? .

-Don- Mayo, FL

 

[NY_Dutch]

Not confused at all... Based on Ohm's power law, doubling the voltage halves the current for the same WATTAGE output. I never said the RESISTANCE is the same in both cases, just the output.

 

[NY_Dutch]

Nope - the resistance stays constant, so if you double the voltage you get twice as much current and 4 times as much power. And all the magic smoke comes out.

OK, I see the confusion. And it's my fault for not clarifying that the 1,500 watt heater I was envisioning was wired for the dual voltage using two resistance coil sets, so no "magic smoke" would be released. The two coils are connected in parallel for 120 VAC use and in series for 240 VAC use, with the same 1,500 watt output in both cases.

 

[Gary RV_Wizard]

But there should be no issues with 1500W. 1500W divided by 120VAC=12.5 amps.

You cannot assume that the heater is the only load on that circuit. If fact, in an RV, it is highly unlikely that it is. Even another small load, maybe the charger, is enough to push it over the top. Or a load that is thermostat controlled, e.g. the fridge, will intermittently oush it over the top. Furthermore, a 15A circuit is only rated deliver 80% of that (12 amps) as a sustained load, i.e. more than 30 minutes of run time. Some breakers will trip after operating some time at 12.5A

 

[DonTom]

You cannot assume that the heater is the only load on that circuit.

I didn't and wouldn't. Notice how I said it, "But there should be no issues with 1500W".

If there is other stuff on the same line, total will be more than that 1500W and that can explain why the fuse blows.

-Don- Mayo, FL

 

[Kirk]

Furthermore, a 15A circuit is only rated deliver 80% of that (12 amps) as a sustained load, i.e. more than 30 minutes of run time. Some breakers will trip after operating some time at 12.5A

What most of us never realize is that any circuit breaker is designed to have at least 3 different trip levels and the rating you read on the box is the mean amperage and not an exact one. At the design level the circuit breaker has a "long time" trip point which is typically around 80% of the label stated amperage, a "short time" trip point that will be on the order of 120% of the labeled amperage and an "instantaneous" trip point that is probably at least twice the labeled amperage.

 

[Gary RV_Wizard]

Thanks for that excellent explanation, Kirk. I avoided getting into it as too complicated for this discussion, but you said it all quite simply! Hope I can remember it for the next time.