File: D:/web/homefly/reference/NiMH_charging.htm
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<p><strong>NiMH charging instructions</strong></p>
<p align="left"><strong><font size="+1"><b>Never charge batteries unattended.
Otherwise, severe damage or injury can result.</b></font></strong><br>
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<p align="left">NiCd peak chargers will not work with NiMH cells because the <a href="/reference/NiMH_c70-6_charge.gif">voltage
behavior</a> is different. Specially-designed NiMH peak chargers will work or
you can cut off rapid charge manually as follows:</p>
<p align="left">For rapid charging, use 1C charge current to about 90% capacity
and interrupt charging when the voltage levels off. Monitor battery temperature
during the charging process. Allow battery to cool prior to commencing rapid
charge. Do not rapid charge a new battery -- break it in with C/10 charge first.
Use of an automatic NiMH peak charger is strongly recommended for rapid charging.</p>
<p align="left">Ideal charge current is C/10 for about 15 hours. A standard NiCd
overnight charger can be used for a small NiMH pack. Insert a 1.0k pot in series
with the battery. Adjust the pot to give a current of C/10. The 9.6V side of
the charger usually works best.</p>
<p align="left"><img src="/reference/nimh_charger.gif" width="417" height="186"></p>
<p align="left">The value of the dropping resistor = 10<sup>4</sup>(<i>V<sub>in</sub>-V<sub>batt</sub></i>)/<i>Q</i>,
where <i>Q</i> is battery capacity in mAh. The series resistance should be at
least 50<font face="GreekC">W</font>. If not, increase <i>V<sub>in</sub></i>
.</p>
<p align="left">Self-discharge rate is approximately C/20. Do not trickle charge
NiMH for more than 12 hours. Do not allow cell voltage to drop below 1.0V, i.e.
stop flying as soon as thrust falls off.</p>
<p align="left">NiMH cell capacity will increase after a few cycles.</p>
<p><a href="/reference/power_supply.htm">DC supplies for externally-powered battery chargers</a></p>
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