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looking for LM317 similar regulator

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Hello. So, I am setting out to build a constant current charger for hobby NiCd / NiMH packs labeled at 9.6v. However, this charger's supply will have to be coming from a 12v car battery. Does anyone know of an ajustable voltage regulator similar to the LM317 that can safely use a Vin-Vout difference less than 3v?

Thankyou in advance!
 

CafeLogic

New Member
Charging voltage for NiMH is 1.4-1.6V per cell. 12V would be 1.5V per cell for your 8 cell, 9.6v battery. You don't need to reduce the voltage.
 

Sig239

Member
A fully charged car battery can be up to 13.8V. With the engine running the voltage output of the alternator is approx. 14.4V. The voltage may sag to 12V or lower while cranking the starter though. :)
 

CafeLogic

New Member
Open circuit voltage of a fully charged lead acid 2.1V - 2.13V per cell or 12.8V. If you pull it straight off the charger it could read higher but as long as you wait a few minutes, that is it. The car need to charge the battery, so alternator output is higher, nominally 13.8V, although 14.4v being common wouldn't surprise me. So, I concede, that if it is to be charged from a running car, other things may need to be considered. If no other charge regulation is employed, current should be limited to C/10 anyway. C being the battery rating at 1 hour. Hence for a 1000mAH battery, unregulated charging should take place at 100mA.
 
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