I have a P3, on a whim I plugged my 1a Apple charger in and charged my phone. It read 0.09A. I plugged my CPAP in which should draw about 2.5A and was getting 0.28A even with heater on.
it’s on AMP setting and displays “amps” on the screen. Voltage says 123V.
Any ideas?
the iPhone charger is a 2a charger (I was wrong, using one for iPad) and looking at the mAh battery rating it should spit out two amp per hour into my phone right? The 2900mAh battery charges in about 1.5a on the 2a charger. How can it do this if it draws 0.09a from the wall?
i’m trying to calculate how quick i’ll Drain my boat battery. Am I getting confused on the voltage change with transformer and how that affects amps? I think the iPhone charger is 5v 10w which may be accounting for the 24X difference i’m Seeing in input amps vs what I expected.
the boat battery bank is 12v so instead of 0.22a input at 124v I should see about 2.2a from the 13v bank or so right?
i’m trying to calculate how quick i’ll Drain my boat battery.
This, you'll also want to use dc -> dc (Think cigarette lighter chargers) converters to charge devices like phones and tablets. A lot of things now days also run directly from 12v power. Anything that has a wall wart usually converts to 12vdc or 5vdc.Answering the first question is that electrical power (Watts) is a product of Volts and Amps (Watts = volts * amps). So, in the first question, the iPhone charger outputs 5 volts and as you say 1.5 amps giving a total power of 7.5 watts. To determine how many amps that takes at 120 volts, take the 7.5 amps and divide by 120 to get .0625 amps. In any energy transformation device, there is always losses caused by inefficiencies so your measurement of .09 amps is very reasonable. The extra power will be converted to heat in the charger and is why it gets warm.
As far as draining your boat battery, obviously it will depend on how big the battery is, but a typical car battery has about 45 Amp/hours of capacity (45000 mAh). However, this can't simply be compared to a device battery or external charger bank because again the voltages are different. The car battery at 12 volts has 540 watt hours. The external charger banks use about 4v batteries so it would take a 135 amp hour charger bank to be equivalent.
Going back to the iPad, it has a 32 watt hour battery, so you should be able to charge your ipad about 16 times (540/32) from your boat battery, assuming it is equivalent to a typical car battery. Unless it is a sail boat and the battery isn't critical on getting an engine started and back to shore, I wouldn't want to charge it more than 3 or 4 times before I got the engine started and recharge the battery!
--Rick
Reading about the cpap it’s supposed to draw about 2.5a during use.
the iPhone charger is a 2a charger (I was wrong, using one for iPad) and looking at the mAh battery rating it should spit out two amp per hour into my phone right? The 2900mAh battery charges in about 1.5a on the 2a charger. How can it do this if it draws 0.09a from the wall?
i’m trying to calculate how quick i’ll Drain my boat battery. Am I getting confused on the voltage change with transformer and how that affects amps? I think the iPhone charger is 5v 10w which may be accounting for the 24X difference i’m Seeing in input amps vs what I expected.
the boat battery bank is 12v so instead of 0.22a input at 124v I should see about 2.2a from the 13v bank or so right?
Are you running these two devices from a power inverter when on the boat?
Otherwise, why are you measuring 120 VAC current, because that not the actual intended use.
I'll wait for an answer before I continue my thoughts.
Stop thinking in amps, think in watts, and add 10-15% loss if you are using an inverter.
This, you'll also want to use dc -> dc (Think cigarette lighter chargers) converters to charge devices like phones and tablets. A lot of things now days also run directly from 12v power. Anything that has a wall wart usually converts to 12vdc or 5vdc.
Final notes, you state "battery bank" if you have multiple 12v batteries connected in parallel you get to add their collective amp hours. We have a runabout with a single starter battery and can play in the lake all day while running the radio, external audio amp, and charging phones without killing it.
OK, you've thought farther ahead than I thought you did.Eventually. I have a 12v system and will be charging phones from a 12v outlet and have a dc-dc converter for the cpap. Claims it’s 90w.
i have always been thinking of amp-hours. I’ll have two 135AH six-volt batteries in series. So I figure I have about 65AH to play with.
OK, you've thought farther ahead than I thought you did.
Ideally, DC-DC converters should be the most efficient path. Avoid 120 VAC if at all possible. But, I would advise against connecting the CPAP directly to the battery.
Depends on the CPAP. Mine runs off a 12v battery just fine with the 12v DC cable from Respironics. On 12 vdc it pulls 3A.