DEC RK05 Emergency Retract Batteries

Paul Koning paulkoning at
Mon Mar 14 12:01:18 CDT 2016

> On Mar 14, 2016, at 12:55 PM, Christian Corti <cc at> wrote:
> On Mon, 14 Mar 2016, Doug Ingraham wrote:
>> The only difference in NiMH and NiCd charging schemes occurs when rapid
>> charging them.  When rapid charging both types would use a DV/DT technique
>> coupled with a temperature sensor.  The DV/DT is much smaller for NiMH than
>> NiCd.  So if they went to the effort to recharge fast after an event (why
>> since you could probably do several retracts on a charge) you would not
>> want to use NiMH replacement batteries.  It is unlikely that anything other
>> than a trickle charge was used with these batteries since it is cheap,
>> simple and reliable.  The trickle current would have been 30 to 50 ma.  I
> Hello... we're talking about an RK05... no fast or trickle charging at all. The battery charge circuit consists of a 750 ohms resitor in series with a D672 diode and the battery, attached between ground and -15V.

That fits with Doug's comment: 20 mA charge current (ignoring the internal resistance of the battery).

Interesting that they used a battery; I thought the usual mechanism was a large capacitor, I hadn't seen batteries used for this.


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