Home-made battery charger - batteries getting hot

Hi again,


Yes that looks right accurate to about one quarter of one degree C.
For circuits like this a quick test is in order also. You can do this easily by turning on the circuit and heating the thermistor up with a soldering iron held close (not too close) to the thermistor. You can measure temperature if you like too and note what temperature it turns off at.

I assume that the reference voltage is 2.000 volts or thereabouts, but the nice thing is both resistor circuits connect to it so it doesnt have to be exact.

Do you really need a cap as big as 1uf for that noise damping? Perhaps 0.1uf will be enough, but yes the more the better usually.

Hi Al, thanks for the response. I chose that 1uF cap because for some reason that's what they used the in the MAX712 datasheet:
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However, i also found this schematic on the web & he uses all .022uF caps.
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I will change the 1uF cap to .022uF. Thanks again Al!

I've redesigned my perfboard layout to accommodate the thermistor. Earlier this week I emailed Maxim's customer support and a representative got back to me with some useful thoughts. He said this about my layout:

"The electrical connection looks good. Only exception is the C1 cap should be at the V+ pin versus going through D3 to get there. But it sounds like the batteries are charging so I don't see this as the issue."

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He was looking at the old layout without the thermistor, but i'm not sure what he means about D3. Looking at the LED schematic from the MAX712 datasheet, it looks to me like i have it correct... but i'm obviously very new to this stuff. Should D3's cathode be going to ground or BAT- instead?

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Thanks a lot for all your time & help! -Scott

Hi,


OH yes, another point is sometimes you want it to track ambient, if you think that will change a lot while charging.

I think this is the correct way to do the LED's now... does this look better?

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Hi,


The LEDs should be easy to figure out, right?