Nazo
2[H]4U
- Joined
- Apr 2, 2002
- Messages
- 3,672
Ok, so I've recently started getting the hang of using lithium ion batteries for everything and have a bunch of fairly good quality 18650s by Panasonic and Samsung (which are two of the best, so I'm not using cheap UltraFires or whatever.) These batteries are capable of quite a lot of performance, so should be quite sufficient to most tasks, including this one. I've been connecting them to DC-DC converters set to output 5V and they seem to work great for most things. Unfortunately, with things like my Samsung Galaxy S3 smartphone and my Google/Asus Nexus 7 tablet, they worry me. On chargers I've bought in stores (which also used 18650s, but usually cheap unbranded ones) they get so hot that insulation on the wires melt or that sort of thing. So I took one of these DC-DC converters and set it up in a metal tin with a heatsink on each side and some thermal epoxy not just holding the heatsinks on, but connecting them to the tin such that the whole tin becomes one giant heatsink to some extent. When I connected my phone though, it started making a horrible buzzing that worried me and also got extremely hot, so I didn't leave it connected for long. As I recall I had similar issues with a different one in the past.
As far as I can tell, this should be WAY within specs. The power supplies that come with these devices aren't rated for any higher than that converter is made to handle without any extra cooling (though in retrospect the ultra-tiny converters they use on those devices they sell in the stores probably can't handle more than 500mA or so though they claim 1A usually.) In fact, I think they aren't supposed to actually be pulling more than 1A, right? Or do they just pull whatever the device will allow or something crazy like that? One thing I've been wondering is if I'm going to have to do some sort of current limiting. If it's just pulling as much as it possibly can without the device actually limiting it itself, maybe it's going up to ridiculous amounts when the device doesn't actually limit it to 500mA or whatever (though it seems like with cooling it should be able to handle 3+ amps and surely it's not drawing more than that?) Or is it something else? It's hard to believe it could possibly be pulling anywhere near to as much as 2A even, much less anything more than that even if it's trying to do an ultra-fast charge. Could the problem be something else? The fact that it made even official chargers struggle so badly too makes me wonder though.
EDIT: I forgot to ask, but I do want to also ask about those DC-DC converters with a "constant current" control. Does this actually try to force even a minimum current? I know they tend to be used for things like LED driving and battery charging (so most are down stepping anyway) so I'm wondering if they literally try to make it constant to the point that they might try to force a minimum? If so, I have no idea what would happen, but I would be afraid to do that to any USB device. If they only limit the maximum obviously that would work fine, so I'm kind of hoping that's all it is.
As far as I can tell, this should be WAY within specs. The power supplies that come with these devices aren't rated for any higher than that converter is made to handle without any extra cooling (though in retrospect the ultra-tiny converters they use on those devices they sell in the stores probably can't handle more than 500mA or so though they claim 1A usually.) In fact, I think they aren't supposed to actually be pulling more than 1A, right? Or do they just pull whatever the device will allow or something crazy like that? One thing I've been wondering is if I'm going to have to do some sort of current limiting. If it's just pulling as much as it possibly can without the device actually limiting it itself, maybe it's going up to ridiculous amounts when the device doesn't actually limit it to 500mA or whatever (though it seems like with cooling it should be able to handle 3+ amps and surely it's not drawing more than that?) Or is it something else? It's hard to believe it could possibly be pulling anywhere near to as much as 2A even, much less anything more than that even if it's trying to do an ultra-fast charge. Could the problem be something else? The fact that it made even official chargers struggle so badly too makes me wonder though.
EDIT: I forgot to ask, but I do want to also ask about those DC-DC converters with a "constant current" control. Does this actually try to force even a minimum current? I know they tend to be used for things like LED driving and battery charging (so most are down stepping anyway) so I'm wondering if they literally try to make it constant to the point that they might try to force a minimum? If so, I have no idea what would happen, but I would be afraid to do that to any USB device. If they only limit the maximum obviously that would work fine, so I'm kind of hoping that's all it is.
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