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From: Kevin McMurtrie
Subject: Re: LM317 with current limited can charge Ni-MH ?
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Thu, 19 Dec 2002 21:15:40 GMT
NNTP-Posting-Date: Thu, 19 Dec 2002 13:15:40 PST
In article <3E01D08F.36BD8936@fanwap.com>, New Kid
>I like these circuit.
>but I am newbie. I read the datasheet LM317.
>They recommended to add a "diode" and a "capacitor 10uF"
>to protect output short circuit. They also recommended to add "Rs".
>1. How to add them into these circuit ?
>2. To add them, there are any side effects to the BC547 and the
>concept of these circuit ?
>3. Is these current limited method can charge Ni-MH ?
>The brand new batt can recharge at C/10 to 2C.
>I plan to charge batt 1500mAH at rate 1A and set the voltage to
>1.45v/cell. When the voltage reach 1.45v, the current will reduce
>to zero or a few mA, right ? If these correct as I understand,
>I think it can work with Ni-MH too. Just ask your suggestion.
>Thank for advance
NiMH batteries are charged very differently from Lead-Acid. You apply a
regulated current and monitor the voltage closely. When the voltage
plateaus or drops, it's done. Cut the current down to a trickle charge.
The voltage plateau can be hard to detect so a thermal sensor checks for
a sharp rise in battery temperature too.
Lead-Acid batteries are much simpler. A constant voltage with some
current limiting is all that's needed. A full charge is easily detected
by a sharp drop in current consumption. Sometimes there's positive
feedback of current to voltage so that the charge rate better matches
the state of the battery.
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