This post was aroused by another I saw talking about a Peltier unit, which reminded me of my own questions :P.
I don't claim to be an expert in electronics (obviously :P), and I fail to understand what's going on here.
I have a Peltier unit rated at 14.5 VMax and 8.5AMax (Datasheet), which I have used via a USB cable (stripped at ends). That means it's (supposedly) running on 5VDC and about 500mA (if my USB ports are functioning correctly). I have checked the output with a DMM, and the output it right at 5.05 V, but I can't seem to determine the Amperage for some reason (perhaps I just don't understand how to check it).
The unit seems to function normally under those conditions (the "hot" side gets very hot, and the "cold" side gets very cold), and I have it on a heat sink intended for use with a Computer processor.
However, when I attempt to use it with a battery (I've tried every type I have, including 9V, 12V, multiple 1.5V), it produces no noticeable change in temperature whatsoever. I am clearly surpassing the Voltage provided by my Computer, so the only conclusion I have come to is that the batteries do not supply enough Amps.
Can someone inform me if this is correct or not? Does the change in temperature in Peltier units depend on the Amperage going in? If so, how can I practically run it without using my computer?
I know this doesn't really seem Arduino related, but I plan on eventually using it with my Arduino (not directly of course, probably through Transistors or Relays once I figure it out).
That doesn't even complete the circuit (I assume, because the Peltier isn't working under that configuration). I've tried the same with a motor, and it just sits there. FYI, I tried driving this motor directly and it worked, but this doesn't seem to..
Your DMM leads have to be set correctly for a current measurement. Typically many DMM use a different plug position for the positive lead when measuring current and use the same negative position as used for voltage readings. Also most DMMs have an internal protection fuse in the current lead and should be checked for being blown open if you can't seem to get a current reading on a simple powered circuit.
On closer inspection, the fuse Appears to be intact, but below it it says "315mA/250V". If I'm not mistaken, USB ports put out 500mA, so I can see why it would be non functioning, but I appear to be measuring Voltage just fine (which I assume flows through the same Fuse). This is very confusing..
EDIT: I discovered that if you remove the fuse, and then try to check voltage, it still works! I don't see how the fuse can be doing any good if the Electricity doesn't even run through it..... :o
I discovered that if you remove the fuse, and then try to check voltage, it still works! I don't see how the fuse can be doing any good if the Electricity doesn't even run through it.....
The fuse is only used when measuring current, not voltage. You can use your ohm meter function to measure the fuse to see if it's open or not. If it is indeed a 315ma fuse then you can't use to measure current value above that without blowing the fuse. Some DMM have two current positions for current measurements, one for low currents and the other for high currents.
You really should read and study the manual for your DMM to under stand it's various functions, features and limits. Also it is easy to create a short circuit condition if the meter is used incorrectly.
I just tested the Fuse using the DMM, and I'm getting a .0L reading (which is what it does if you're on too low of a setting (meaning that the OHMs are infinite because there's no connection)). That kind of sucks, but I guess I can run to RadioShack tomorrow and pick up another fuse... (Does RS even sell fuses?)
Question: Could I get a higher AMP rated fuse, or would that defeat the entire purpose of the fuse in the first place? ;D
Yes, RS sells fuses, however not in all physical sizes, bring yours so you can compare fit. If you try and measure a current greater the 315ma you will just blow the fuse again. So study your meter manual. Find out what current ranges it can measure. See if there is a second higher current mode and if it has a fuse also. My Fluke meter use two current fuses one for the 100ma position and one for the 10 amp position.
hmm ... the owners manual says limited to 200ma, that's kinda surprising
well, you could try a bigger fuse and chance your meters life
if your in the states, dont forget about the holiday and the after holiday store madness. I dont even want to goto the gas station on the corner on black Friday!
the 29$ radio shack one is one I am eyeballing (and it handles up to 10ADC)
This dumb RadioShack meter only goes up to 200mA -.-....Seems kind of pointless
Yes it does, but then RS is not where I would shop for a DMM, they sell lots of junk items along with a few useful items. A decent DMM is a very important item to own if you are going to be serious about building stuff around an Arduino.
SparkFun has a couple at good prices with useful features:
That first one looks pretty good for the price! I did laugh at:
Decent quality probes (not great, but they'll hold up for years)
But at least they're honest!
In the comments a person was speaking about it being a pain to replace fuses, so I guess if you're not sure what amperage a circuit is drawing, you start from the highest setting and work your way down?
Ooo that looks very similar (if it's not the same) to the one I posted :P. Good find though. Auto range finding would be useful, but I assume those are substantially more than these?
