C-Pap power usage

Hah! Having a normal lifestyle fully equivalent to camping out keeps me, er, on my toes.

MEXICOWANDERER wrote:
Checking amp draw accumulations must be done with meters not by assumptions from reading an instruction book.

Inspiration cycle uses significantly more watts than expiration with a BiPap.

Use something like a Kil-A-Watt meter with the power brick connected to it. Multiply accumulated kWh fraction x 90% for a reasonable guess as to what to expect. A tubing insulation sleeve available from your medical supplier will SIGNIFICANTLY reduce humidifier accumulations because you will set the humidification to a much lower number.

(Above derived from experience not guesswork or assumptions)

Mex makes a good point on use of an insulation sleave for the tube. At least for resmed, they are inexpensive and reduce the need for tube heating and condensation. And along the way will reduce AH useage.

Vintage465 wrote:
I checked the amp draw on both of the units. The amp draw must include the Humidifier. If it didn't the two units would use 106.72 amps over an 8hr period. That would have taken my to 50% of their capacity. That has not happened. I have used the two Phillips Respironic units quite a few times. The Resmed unit uses about 1.25 amp hr. more. I am thinking with my Phillips Respironics and the Resmed unit both running w/o Humidifiers on would be just about the same(it will draw 10a more over night) as the two Phillips units w/o the Humidifiers on. Thinking it will be OK.
Finishing up from my perspective..........the one thing I am not good at is unplugging the unit from the 12v for traveling. I have logged quite a few miles with it plugged in, but I will need to get better. These things are a bit too pricey to be irresponsible with!

and with the humidifier, the current draw is NOT a constant function of time. It is high initally to heat the water, then will drop way down and the heating unit will cycle to keep the water at a constant temperature. How much cycling and how much current will depend on air flow rate, and air temperature as well as outside temperature and how much water remains in the reservoir. as water level drops energy needed to keep it at a constant temperature decreases.

But the spec's are for worst case max draw conditions, likely full reservoir, highest airflow rate, lowest outside temperature, very low humidity and line voltage that will draw max current. Then a safety factor added to that.

Having designed test equipment to meet UL spec's one NEVER NEVER EVER wants to ship a unit that draws more current than the nameplate spec. That will get you in big trouble with U.L.

Probably even worse for medical equipment.

So. I'd take the nameplate current draw as a serious absolute worst case operating condition.

I've found the easiest way to estimate the actual AH draw is to read my trimetric before going to bed and in the AM to see battery SOC and then calculate AH useage. Need to do that in the evening when everything else is off and in the AM before turning on the heat etc.

And I've run mine off a 200WH Lithium Ion battery pack and seen how many hours till it quites. Usually sometime in the third night. That works out to between 1 and 1.5A, consistent with what I get from the trimetric.

It's not peak Amps you care about it's the Amps integrated over the time it is on.

I am intending for the temperature NOT to be in the thirties in my trailer. The coldest I let it get to is 55 degrees then the heater comes on.

When temps dropped into the thirties, I hid the entire machine beneath a blanket including the tubing. With my audible temp alarm. These medical units with their redundant safety features are near goof proof. Even after twelve hours with humidifier set on 5, the unit temperature was 6F over ambient. kWh usage decreased 80%. Air circulation beneath the blankets caused me to be careful as to where to place it because a beneath the covers "breeze" can be uncomfortable at this temperature.

MEXICOWANDERER wrote:
Checking amp draw accumulations must be done with meters not by assumptions from reading an instruction book.

Inspiration cycle uses significantly more watts than expiration with a BiPap.

Use something like a Kil-A-Watt meter with the power brick connected to it. Multiply accumulated kWh fraction x 90% for a reasonable guess as to what to expect. A tubing insulation sleeve available from your medical supplier will SIGNIFICANTLY reduce humidifier accumulations because you will set the humidification to a much lower number.

(Above derived from experience not guesswork or assumptions)

I will just turn the Humidifiers off on both units..............way less amp draw. Gonna say, more than likely I will do this by trial and error.......AKA seat of the pants. I will run them both with the Humidifiers off and see if it works. If it doesn't, then I will purchase a lower amp draw unit.

Checking amp draw accumulations must be done with meters not by assumptions from reading an instruction book.

Inspiration cycle uses significantly more watts than expiration with a BiPap.

Use something like a Kil-A-Watt meter with the power brick connected to it. Multiply accumulated kWh fraction x 90% for a reasonable guess as to what to expect. A tubing insulation sleeve available from your medical supplier will SIGNIFICANTLY reduce humidifier accumulations because you will set the humidification to a much lower number.

(Above derived from experience not guesswork or assumptions)

I checked the amp draw on both of the units. The amp draw must include the Humidifier. If it didn't the two units would use 106.72 amps over an 8hr period. That would have taken my to 50% of their capacity. That has not happened. I have used the two Phillips Respironic units quite a few times. The Resmed unit uses about 1.25 amp hr. more. I am thinking with my Phillips Respironics and the Resmed unit both running w/o Humidifiers on would be just about the same(it will draw 10a more over night) as the two Phillips units w/o the Humidifiers on. Thinking it will be OK.
Finishing up from my perspective..........the one thing I am not good at is unplugging the unit from the 12v for traveling. I have logged quite a few miles with it plugged in, but I will need to get better. These things are a bit too pricey to be irresponsible with!

And furthermore (Jacques Clouseau)...

When solenoid contacts open voltage in amplitude jumps the gap between receding contacts. Look at solenoid contacts sometime. The erosion is not hypothetical. A 1Kv transient can bridge quite a distance. Mercury filled relays are not for the heck of it :)

DrewE wrote:

pnichols wrote:

MEXICOWANDERER wrote:
Again stick your finger onto the starter motor power terminal crank the engine release the key then scrape yourself off the wall.

It first - takes voltage (higher than 12 volts), then second - adequate current driven by that voltage for a person to get plastered to the wall.

I understand that the necessary current is available, but where is high voltage coming from during the engine starting procedure? The alternator of course is a source of relatively high AC voltage when it's spinning, but it's hardly doing that during engine start.

Induction in the starter motor or solenoid coils when the circuit is broken. Recall that an inductor is the complement of a capacitor; it tends to prevent changes to current (rather than voltage) by supplying or sinking voltage (rather than current). Open the circuit, and the current immediately goes from many amps to zero, and the response of the inductance of the coils causes the voltage there to spike. For this reason, coils on relays etc. often have snubber diodes or resistors to provide a path for these transients to discharge.

That particular voltage spike oughtn't make it back into the 12V system since it's on the disconnected side of the circuit, but there are other sources of probably lesser voltage fluctuations when the vehicle is started. Car and truck electrical systems are not particularly clean or stable supplies.

yup. Put a scope on many of the power lines in a car and you may be suprised what kind of spikes are there as relays switch etc. and the starter motor being a DC motor with brushes and comutator is particularly bad for putting big spikes on the 12V lines.

I've found several aftermarket accy for a car that would die pretty quick and prematurely. In all the cases, I found they had no snubber diodes on the supplies to prevent voltage spikes from getting into the circuit. And when your looking at logic rated at 20 or 30V destruct limits, it isn't very hard at all to kill stuff in short order with the voltage spikes running around in the car.

voltage across a capacitor can't change instantaniously, current through an inductor can't change instantaneously. So when you interupt these circuits you get big voltage or current spikes.

A good example is the arc you likely have seen when disconnecting somthing like a hair dryer while running from an outlet. that voltage spike is related to the inductance and interupting the supply quickly. The result is a big voltage spike.

Note that disconnecting a resistive load doesn't give any noticeable arc.