AUTOTRANSFORMERS Manufactured by Hughes, Frank’s and Power Master.
- At 105 volts we get 30 amps of power, or 3150 watts of energy.
- At 130 volts we get 30 amps of power, or 3900 watts of energy.
- We get 8% increase in usable energy. Or 750 watts of power.
- 750 watts can run some coffee pots, a blender, vacuum cleaner, and some toasters
- Most space heaters draw 15 amps.
- The circuit breakers in most rigs are 20amps. But not hair dryers, microwave ovens, or larger appliance.
- Most campgrounds have 6-8 sites on a 200-amp breaker.
- 200 divided by 6 is 33 amps, but line losses can subtract another 5 amps.
- HEAT is a major loss on energy from any electrical device.
- We lose less heat (energy) the lower the amperage we can obtain.
- The higher the voltage (up to 130volts) the less power we use while operating any electrical device.
- A 600-watt electrical appliance will use 5.45 amps at 110 volts.
- This 600-watt device will draw 4.6 amps at 130 volts.
- We save almost one amp using the higher voltage.
- Your converter/battery charger will use 3-4 amps off the top.
- These autotransformers act as a superior Surge-spike protector.
- The autotransformer will draw ½ to one amp of power on it’s own.
Do we steal power-when we use an autotransformer?
The following scenario is offered by Dave & Helen Dmouth, www.damouth.com:
You and one neighbor in a remote part of the RV Park share a long power
feed from the park’s distant feed. I’ll assume that the main feed is always at
120vac, but that the long power wires shared by these remote sites have a
resistance of 0.25 ohms (not unlikely – that’s only 200 feet of #8 cable).
You and one neighbor in a remote part of the RV Park share a long power
feed from the park’s distant feed. I’ll assume that the main feed is always at
120vac, but that the long power wires shared by these two remote sites have a
resistance of 0.25 ohms (not unlikely – that’s only 200 feet of #8 cable).
Further assume that both of you are using exactly the same appliances which
would add up to each of you drawing 25 amps, if the voltage remained at 120
volts.
But the voltage won’t remain at 120 volts (because of the resistance in the
long power feed). Under these conditions, the voltage at each site will b
e108.68 volts and each site will be drawing 22.64 amps.
Now suppose you, but not your neighbor installs an autotransformer. The
(older) Autoformer increases the voltage by a fixed 10% in a low-voltage
situation, so inside you Rv, you now have 118.88vac. This raises your current
draw inside the RV up to 24.66 amps. (This additional load causes more
voltage drop in the shared line, dropping the voltage coming into each RV to
1-7.62 volts, so your inside voltage increased a bit less than the expected
10%).
Your use of the Autoformer has reduced your neighbor’s voltage from 108.68
to 107.62 volts. Reduced his current from 22.64 to 22.42 amps, and reduced
his power usage from 2.46 kilowatt to 2.41 kilowatts. You voltage inside the
RV increased from 108.88 to 118.88, your inside current increased from
22.64 amps to 24.66, and you power from 2.46 to 2.92 kw. Your neighbor has
a 2% power reduction while you see a 19% increase in you own power usage.
This analysis assumes that the loads in your RV are resistive. (Fred’s
comment = no motors)
This seems like a pretty good tradeoff, unless your neighbor has a power
management system that shuts off her power when the voltage drops below a
certain level. In some situations your ability to use additional power by using
the Autoformer could result in enough additional incoming voltage reduction
so that your neighbor loses power completely. If you want to be a nice guy,
you can turn off a bit more of your own power usage, returning her voltage
and power to where it was before you used your Autoformer while still
retaining the advantage of having normal voltage in your own rig.
Note that even though you may have a 30-amp power pedestal, you cannot
increase your internal current all the way up to 30 amps in a low-voltage
situation. This is because when the Autoformer increases the inside voltage
by 10%, (which is 20% increase in power), it also must increase the current
drawn from the power pedestal by a bit over 20%. So if you turned on 30
amps of load inside the RV, you would be drawing considerably more than
the 30 amps from the pedestal, tripping the 30 amp circuit breaker.
Happy Camping,
Fred b. 101BYFRED.COM