Help me understand amps/volts/watts in terms of charging

rh71

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I have a portable tire inflator that can be charged in 2 ways (see the "In" ports). I have typically used the micro-USB method but it's super slow and takes hours. I'm looking around the house for a power adapter that would fit the other IN port and finally found one, but I'm not sure what I'm reading here and whether it's safe to use (for the good of the portable inflator). Power plug shows OUTPUT: 12V == 2000mA. IN port shows 12V / 5A. Does that mean it will still charge it but it will be at less than half the speed it should? Is the micro-USB method connected to a wall outlet plug faster?
 

lxskllr

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Micro usb is slightly faster if the port delivers the full rate of charge. FWIW, I like charging batteries as slowly as possible. If you don't need it right away, it doesn't matter how long it takes as long as it's ready when you need it.
 

BoomerD

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Micro usb is slightly faster if the port delivers the full rate of charge. FWIW, I like charging batteries as slowly as possible. If you don't need it right away, it doesn't matter how long it takes as long as it's ready when you need it.

It really depends on the charger that the micro-USB cable is connected to. A GOOD one would charge much faster than some old "1 amp" cell phone charger. (the micro-USB cables and connectors are only rated for "up to" 2 amps.
 

pete6032

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Micro usb is slightly faster if the port delivers the full rate of charge. FWIW, I like charging batteries as slowly as possible. If you don't need it right away, it doesn't matter how long it takes as long as it's ready when you need it.
What? DC port is faster for charging. Micro USB in is 5v 2.1A = 11w. The DC in is 12v 5A = 60w.
 

bbhaag

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I think the OP is asking about the power supply and whether or not it would be safe to use on the tire inflator.

The power supply outputs 24 watts and the tire inflator can receive a maximum of 60 watts. So the answer is yes it will be safe to use the power supply you found in your house to charge your tire inflator.
 
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Ken g6

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I think the OP is asking about the power supply and whether or not it would be safe to use on the tire inflator.

The power supply outputs 24 watts and the tire inflator can receive a maximum of 60 watts. So the answer is yes it will be safe to use the power supply you found in your house to charge your tire inflator.
This seems backwards. The power supply can only safely provide two amps, but the inflator will try to draw five. This does not look safe to me!
 
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rh71

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It looks like I've stumped some tech gurus on a Friday night. :D

So if I can find a 12V/5A power supply, it will charge at more than twice the speed vs. the micro-USB? Is that bad for electronics? Is it bad to super-fast-charge your cell phone for instance even if it's advertised as a feature?
 
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rh71

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It really depends on the charger that the micro-USB cable is connected to. A GOOD one would charge much faster than some old "1 amp" cell phone charger. (the micro-USB cables and connectors are only rated for "up to" 2 amps.
The micro-USB cable is plugged into an Anker 40W 5-port charger, that specifies Output 5V == 8A, and it's the only thing plugged into the ports right now. So it's going at 2A (or is it 2.1A).
 

lxskllr

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Is it bad to super-fast-charge your cell phone for instance even if it's advertised as a feature?
The way I see it, almost everything in the world does best at a steady state. Second best is changing states slowly. When a state changes fast, the item gets stressed and weakened.

My current cell phone will be 2 this February. I've short stroked the battery since I've had it, and I've charged it very slowly from a usb port on my computer all but a couple times. Battery degradation has been negligible so far. My old phone was treated the same way, and at almost 4 years, the battery had degraded slightly, but was still fully usable, even with less than a full starting charge. I'm not an EE, and don't follow battery tech closely, but I'm happy with the way I deal with batteries, and have no interest in changing. I don't know for a fact that what I'm doing is best, but the odds say it is.
 

bbhaag

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This seems backwards. The power supply can only safely provide two amps, but the inflator will try to draw five. This does not look safe to me!
Crap I didn't even think of the amp draw I just focused on the watts.
 

deadlyapp

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DC port supply will charge faster but probably overheat and fail due to the battery wanting more. Battery could absolutely have circuitry that would limit the Amp draw however and keep it fine.
 

bbhaag

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Really no way to separate the two since watts=volts x amps. The power supply can only output 24 watts but the tire inflator requires 60 watts.
Well thats what I thought but then Ken made me second guess myself so now I'm not sure.
 

Red Squirrel

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The charger is only going to draw what it's made to draw, so as long as the power supply feeding it is HIGHER than the rating, you'll be ok. It's not going to push more current in. Of course the voltage needs to be the same as what the charger expects. That said, some chargers may be smart enough to see the input voltage drop and they will reduce the charge rate if the input source can't provide that much current and the input source supports voltage dropping (vs: just popping a fuse) if you draw too much from it. I think this is how phone and USB in general works which allows you to use a low input power source and still charge, just slower.

Long story short to play it safe you just want to find a power source that has the same voltage and an equal or higher amp rating than what you're trying to power.
 

Ken g6

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The charger is only going to draw what it's made to draw, so as long as the power supply feeding it is HIGHER than the rating, you'll be ok. It's not going to push more current in. Of course the voltage needs to be the same as what the charger expects. That said, some chargers may be smart enough to see the input voltage drop and they will reduce the charge rate if the input source can't provide that much current and the input source supports voltage dropping (vs: just popping a fuse) if you draw too much from it. I think this is how phone and USB in general works which allows you to use a low input power source and still charge, just slower.
I don't think that's how it works. You have to consider the load like a simple resistor. The power supply is attempting to maintain a 12V differential between source and sink. At 12V the load will allow 50A through. So either the charger will overheat dangerously, or the voltage will sag to about 20/50*12V = 4.8V (from Ohm's law), or a fuse or circuit breaker will blow. On a cheap charger I'd guess the fuse option is the best case scenario.

USB has electronic protocols for communicating between the device being charged and the charger. USB devices are allowed to draw up to 1.5A based on the configuration of the other pins. For power delivery beyond that, active negotiation is required.
 

BoomerD

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I don't think that's how it works. You have to consider the load like a simple resistor. The power supply is attempting to maintain a 12V differential between source and sink. At 12V the load will allow 50A through. So either the charger will overheat dangerously, or the voltage will sag to about 20/50*12V = 4.8V (from Ohm's law), or a fuse or circuit breaker will blow. On a cheap charger I'd guess the fuse option is the best case scenario.

USB has electronic protocols for communicating between the device being charged and the charger. USB devices are allowed to draw up to 1.5A based on the configuration of the other pins. For power delivery beyond that, active negotiation is required.

The device (appears to be a TackLife X1 tire inflator) requires 12v 5 amps...not 50 amps. Looking at new versions on Amazon and Newegg:

AWR7S210713dc7v7.jpg



It comes with a basic USB cable and a cigarette lighter/12v automotive power plug. Presuming the plug fits, this should do the job:
 
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PowerEngineer

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The charger is only going to draw what it's made to draw, so as long as the power supply feeding it is HIGHER than the rating, you'll be ok. It's not going to push more current in. Of course the voltage needs to be the same as what the charger expects. That said, some chargers may be smart enough to see the input voltage drop and they will reduce the charge rate if the input source can't provide that much current and the input source supports voltage dropping (vs: just popping a fuse) if you draw too much from it. I think this is how phone and USB in general works which allows you to use a low input power source and still charge, just slower.

Long story short to play it safe you just want to find a power source that has the same voltage and an equal or higher amp rating than what you're trying to power.

Actually this is the way it works. In essence the voltage of the charger has to be high enough to push current into the battery against the battery's own voltage - hence the 12 volt requirement for the charger. Five amps rating is the maximum current that this battery can be expected to draw when effectively discharged - hence the 5 amp rating. And the 60 watt rating. Any charger with a 12 volt rating and at least a 5 amp rating should do the job.
 

Torn Mind

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The power adapter will probably work in the short term.

Long term, it might be overwhelmed because of too much heat. The higher amp draw will do that. It looks like a dumb charger. (Like, just a transformer type, no fancy circuits to limit current).

Amp draw might vary based on how much charge the battery has. So, the wall wart may not pull excessive amps when the battery is like 50-70% full. But the if battery is almost empty...I would expect the full 5 amps to be pulled.
 

sdifox

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It's a 2Ah battery, just charge with USB charger.
 
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Paperdoc

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General items first. Voltage is the force or "pressure" of the power supply to push current through the load. Amperage is the rate of current flow through the circuit. The rate of actual energy flow into the battery of your inflater is the WATTS, which is the product of Voltage times Current. P = VxA. So the higher the Watts provided by the charger unit is, the faster the battery can be changed up fully. (Since Voltage from any charger is fixed, the Watts rating will be limited to the Amps rating, which is a max rating, not a fixed value.) The inflater's battery charging system will draw from the charger whatever it can according to the charger's max rating, until the battery is charged up.

In your case, the inflater has two possible power input sockets. One will accept power at 5 VDC, and up to 2.1A current flow. That is a max power flow of 10.5W. The other accepts power at 12 VDC and a max current of 5A, so 60W. That's almost six times as fast a charging rate if you have a charger that can provide that. However, what you do have right now is a charger rated at 12 VDC but limited to 2000 mA, which is 2.0A. That's 24 Watts charging rate, still 2.3 x faster than a 5 VDC 2.1 A charger would be. So YES, use that charger you have for now. IF you get a charger able to provide 12 VDC at up to 5A, that would be even faster. IF you get a charger at 12 VDC able to provide more than 5A max current, the inflater's charging circuits will not use more than 5 A anyway.

As an aside, often today's USB charger units can provide 2A max current, or even more, if it is a CHARGER. But the standard older USB2 computer ports (the larger Type A ports like the one in the upper right of your inflater) can provide only 0.5 A max current. The newer USB 3.2 ports like the smaller Type C one can provide up to 0.9 A. So using either of those types of power source would be much slower as a charger unit.

Here's another factor to consider. The inflater has a battery and charging system inside, so you can charge it up at whatever rate you can over a period of time. When you go to USE it, though, the air pump inside uses power from that charged battery at a pretty fast rate. IF you have your charger unit plugged in at the same time, SOME of the power used by the pump can come from the charger to help out the battery, so it lasts a bit longer. The max power the unit will consume from the charger source, however, will be limited by the max rating of the charger. In my experience with the tire inflater I have (has no battery, plugs into the car's cigarette lighter socket) it uses 12 VDC at 5A max current from a large battery. So my suspicion is that YOUR inflater pump would use about that much power. Its designers appear to have anticipated that and provided internal charging circuits able to FULLY power the pump from the external charger only IF that charger is rated for the full 12 VDC at 5 A. In other words, IF you had a new heavier charger unit with those ratings, you might be able to use that inflater with the charger connected even if the battery were not already charged.
 
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