DC-voltage losses over sliprings????

Question

DC-voltage losses over sliprings????

Parcifal (Marine/Ocean)

(OP)

26 Feb 02 13:19

Hello,
I am currently working on a project which includes a long electrical/optical cable (1100m) which is wound onto a large winch.  This cable will be used on a ship to tow a data-acquisition box (geotechnical research).
Now the electrical wires are connected to a slipring-box and hence we can connect our power and signal wires without risking to have spaghetti-situations. :)
Now following problem is bugging me :
I connect 12VDC over 2 terminals of the cable and measure the output : 12 VDC.  This looks ok. (resistance of 1 wire of the cable is 40 Ohm).
Now next thing I do : I connect a load (acquisition tool) with an internal resistance of 65 KOhm, rated to operate on 12VDC.  I apply the power and measure 4.3 VDC on the output-terminals of the cable!!!!!.
I am puzzled but not defeated : I vary the input voltage in small steps from 5 to 16 VDC. Result : The measured voltage remains 4.3 VDC (+- 0.1 VDC).
Does anybody have any clue which might be causing this phenomenon?  Only thing I can imagine is there is a voltage drop over the slip-rings of the winch which is current-related.  Any (argumented) guess is welcome.
Regards,
Puzzled Parcifal. :(

busbar (Electrical) · Answer 1 · 2002-02-26 13:36:19

PP-- have you measured voltage drop directly across the brush/slipring assembly? Does the circuit use two slipring/brush assembiles or {one brush and} the winch frame for one of the 12V connections?

teco (Electrical) · Answer 2 · 2002-02-26 18:48:20

parcifal:- try looking at the brush grade on the sliprings. had a simular problem and changed drush grade to a silver graphite type and this fixed the problem.
kind regds.

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DC-voltage losses over sliprings????