I've seen some posts on using various amounts of AA batteries and standard 9v batteries, however I haven't found any info on using larger mAh capacity batteries. If I connected up some D batteries to the arduino uno DC input jack, would I fry the thing or would the larger mAh capacity just give me some longer operation times over the AA's?
I'm a beginner in electronics, but this makes sense to me that the D batteries are still providing 1.5 each just larger capacity? Or am I asking a stupid question and most likely will fry my arduino with too much current?
thanks, i may have asked my question prematurely. I did a bit more research and it pretty much gave me the same answer you are giving me now.
Looks like I can't have too much current on input, but if I had batteries that could potentially supply a large amount of current and then I had a short circuit somewhere on a shield or arduino pin than I would have a much larger problem since the batteries could supply a lot more current to exacerbate the short circuit?
maybe a fuse to make things safer is best when using larger capacity batteries?
maybe a fuse to make things safer is best when using larger capacity batteries?
Yep, and in general the fuse should be as close as possible to the current source. On my solar setup fuses are bolted directly to the battery terminals.
I wouldn't be too paranoid about powering an Arduino though.
If you have a high current supply then sometimes its wise to add a series-resistor to limit the current while you experiment/tinker with the circuit - that's when an accidental short can happen.
For medium/large lead-acid batteries or any sort of lithium polymer cell(*) its important to avoid shorts (even if fused) as the currents are so large as to generate destructive arcs (melting part of your circuit, flinging tiny droplets of molten metal out - use eye protection if working close up to high-current circuits for this reason). Be careful with metal objects and tools and remove metal jewelry like watches and bracelets - accidental contact can melt/weld/heat these up and cause burns.
D-cell NiMH will create small sparks but aren't that hazardous in my experience.
Some people are confused by the difference between capacity and current-handling ability - the internal resistance of a call determines how much current it can source to a large degree, and this can vary quite a bit between different designs of cell. The capacity relates to the total charge held by the battery, and this is usually measured at a low discharge rate (high discharge rates make cells less efficient in various ways). Because both capacity and internal resistance vary between makes and types of battery it is never a good idea to mix and match different types.
(*) lithium polymer batteries may overheat and catch fire if mistreated, and a lithium fire is very intense and can use water (and thus human flesh) as an oxidizing agent. Special care is needed with them as a result. Other kinds of lithium battery may have built-in protection circuitry and more robust packaging to reduce these risks, and the safest kind is probably LiFePO4.
One other thought is that a fuse is designed to blow at a higher current than it's rated or marked current. the marked value is it's current carrying capacity not the current that will 'blow' the fuse. This data is from Mersen, a fuse mfr I found in a quick Google and typical of ALL fuses: I quote from their website this interesting text as there are Many misconceptions about fuses...
UL ampere rating tests are conducted at 100%, 135%, and 200% of rated current. The fuse must carry 110% of its ampere rating and must stabilize at a temperature that does not exceed a 75C rise at 100%. The fuse must open at 135% of rated current within one hour. It also must open at 200% of rated current within 2 minutes for 0-30 ampere ratings and 4 minutes for 35-60 ampere ratings.
. I always use fuses where ever applicable BUT they are principally for fire protection from catastrophic failure and NOT for circuit protection. MarkT... sometime take a common paper clip and bend it so it can contact the pos and neg ends of a "D" Ni-Cd or Nimh cell, hold it with a pair of pliers (NOT your Fingers) and 'short' the cell with the iron wire paper clip... Note how long it takes for the shorting clip to turn a bright yellow color. Don't hold it for too long > 5 sec's you might build up gas pressure in the cell faster than it can be vented through the safety vent... even though it is a low voltage there is tremendous short circuit current available... Look at the old school Soldering Guns a 150 watt gun heats up by applying about .75V @ 200A through a 5" piece of 14 Ga solid copper wire with a formed copper 'blob' on the end.
I've got a small 12v 4a battery I use for larger current projects, and I usually have pieces of 16gauge copper wire coming off the terminals
one time when I disconnected my circuit and placed th3 battery on the side, the two wires touched, and by the time I reacted to the spark(pretty darn quick too) the wires insulation had entirely melted off and I burned my finger hitting it apart
idk how much current that used but I measured a single AA battery and it'll hold 8 amps short circuit current for a few seconds before starting to slowly go down
Docedison:
One other thought is that a fuse is designed to blow at a higher current than it's rated or marked current. the marked value is it's current carrying capacity not the current that will 'blow' the fuse. This data is from Mersen, a fuse mfr I found in a quick Google and typical of ALL fuses: I quote from their website this interesting text as there are Many misconceptions about fuses...
UL ampere rating tests are conducted at 100%, 135%, and 200% of rated current. The fuse must carry 110% of its ampere rating and must stabilize at a temperature that does not exceed a 75C rise at 100%. The fuse must open at 135% of rated current within one hour. It also must open at 200% of rated current within 2 minutes for 0-30 ampere ratings and 4 minutes for 35-60 ampere ratings.
. I always use fuses where ever applicable BUT they are principally for fire protection from catastrophic failure and NOT for circuit protection. MarkT... sometime take a common paper clip and bend it so it can contact the pos and neg ends of a "D" Ni-Cd or Nimh cell, hold it with a pair of pliers (NOT your Fingers) and 'short' the cell with the iron wire paper clip... Note how long it takes for the shorting clip to turn a bright yellow color. Don't hold it for too long > 5 sec's you might build up gas pressure in the cell faster than it can be vented through the safety vent... even though it is a low voltage there is tremendous short circuit current available... Look at the old school Soldering Guns a 150 watt gun heats up by applying about .75V @ 200A through a 5" piece of 14 Ga solid copper wire with a formed copper 'blob' on the end.
Doc
Doc,
thanks for the info, I didn't know that about fuses. Does that hold true for fast acting fuses as well?
I bought a few 1amp fast acting fuses in hopes to protect a circuit.....
on a separate but related topic, if I decide to use one of my fuses, the only fuse holder i could find for this size, at the local radio shack, is hooked up to a 20AWG wire. If I soldered that to a standard jumper wire, am I in for any kind of trouble?
No problem at all but remember, fuses in feeder cables are designed to protect the cable, not the circuit the cable is feeding.
Generally speaking, a fuse cannot operate fast enough to protect a semiconductor from a circuit error. Yes they are fitted into semiconductor systems but by the time the fuse responds to a failed component, all the fuse is protecting is the circuit wiring.
I think someone said it before, fuses are more for safety of the surrounding than the device
it wont prevent an ic from internally burning up but it will prevent shorted ics, wires, caps etc from drawing large amou ts of current large enough to cause a fire, in which case the circuit is the least of your worries
Juympers for power are FREQUENTLY an issue, cut one in half and strip 10 mm of insulation and you will note that the wire is 26 -28 Ga... great fuses for high current loads but poor as power carrying conductors. If you are breadboarding I personally would use a small piece of PCB material and mount my Fet or transistor (high current control) on that PCB and connect my high power stuff to it both power and ground... continue only the ground and the control wires to the breadboard. TThis way the breadboard isn't in the high current supply path directly simply so that the motor/servo currents aren't in the control path. It might help to think of the ground rail as a long low value resistor (it is really) and so if you place a high current load on the end or middle then there will be a voltage developed across that resistor, if at the same time you are attempting an analog measurement... your reference(ground isn't ground any more and that slight voltage difference added to the measurement being done, this can happen with some PWM as it can go on in the background while you are doing other things.. like measuring an accelerometer for example, some are linear... So now what do you have. As to the fast acting fuses... Mersen I think was the name I found for fusess and that's all they do they have good information on ALL fuses from OLD 3AG 30A monsters for fire protection to poly fuses which are self resetting fuses used on the input of a regulator because they have a relatively high series resistance necessary to generate enough heat to cause to cause the silicon material to change state to non conducting. I saw your fast acting info there but didn't grab it because it wasn't relevant to the discussion. I Do hope this helps get you out of some of the darkness.