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Old 18-08-2008, 10:23   #1
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correct 12 voltage for autopilot?

I just installed my second pair of Grp 24 Gels in my sloop; the first pair went in in 1992...[16 years, though the last two were questionable as far as capacity, but it still seems the gels are worth the $$.]

I checked the standing voltage on both before installing: 12.62 & 12.59 volts with a mulitmeter.

Installed the pair and connected my onboard 3 stage charger and the leads to the dc panel. Checked the no-load voltage again and all the same :12.62 & 12.59v.

So, I decided to check my cockpit power port for connection of an autopilot [planning to go with a Simrad TP20 tiller mount]. The voltage read at the powerport = 12.15v.

Does this seem to be an inordinate amount of voltage drop running from the dc panel to the port?
Here are the wiring specs:
From the battery well to the dc panel = 15' lineal feet wiring +/_
from the dc panel to the cockpit powerport = 15' lineal feet wiring +/-
both are 12-14 ga. conductor.

Thanks for looking; any comments appreciated.
Patrick
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Old 18-08-2008, 10:31   #2
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Is something else drawing current from that same circuit?

There should be no voltage drop if there is no load for such a short circuit. The greater the current in amps, the greater that the voltage drop will be. Sometimes a 10% drop is acceptable and for some things you want no more than a 3% voltage drop. I like wiring for no more than a three percent drop because it gives me a little leeway if some corrosion occurs or a fastener comes loose.

If your voltage drop is too great then check all the terminals for corrosion, bad crimps or looseness. If the voltage drop is still too great then you need to check the tables for wire gauge vs run and current to make sure your wire is not under gauged.

Apply your wire specs to these tables: DC Wire Table

Distance or "Run" is measured from the source to the load and back. Measuring just one way is a common mistake.
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Old 18-08-2008, 10:32   #3
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Yes it does
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Old 18-08-2008, 11:22   #4
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OK. Than the source beng the battery well and the load being the appliance, to and from would equal nearly 60 lin feet. I think that, combined with the original [1980] non-tinned wire, is definitlely not helping.
As a test, i'm going to run, but not immediately install, all new wire thru the circuit and measure again at the powerport.
That may explain why my old Tillermaster seemed to die for no logical reason- never did noticed the low voltage until now.

The operational requirement for the Simrad TP20 is 0.5 amp.

I've seen a wiring guide for sizing relative to req'd current/distance to load, etc.
I'll look around here to see if anyone has it posted; in the meantime I'll update you on whether or not my temporary test lead changes the voltage at the powerport.

Thanks,
Patrick
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Old 18-08-2008, 11:56   #5
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Quote:
Originally Posted by jps10 View Post
... I've seen a wiring guide for sizing relative to req'd current/distance to load, etc.
I'll look around here to see if anyone has it posted ...
See the Wire Size (Amp-Foot) Chart, and explanation at:

http://www.cruisersforum.com/gallery/showimage.php?i=1321&c=500&userid=79
and
http://www.cruisersforum.com/gallery/showimage.php?i=1322&c=500&userid=79
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Old 18-08-2008, 19:56   #6
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It would be interesting to get the reading at the port while loaded. The meter draws effectively nothing.

I am surprised the TP only draws .5A. Is that just "idling"? Is the load higher when the tiller is actually being moved? I don't know the specs I am just "speculating" <groan>
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Old 18-08-2008, 20:57   #7
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Here's the link for the Simrad TP20 user manual;

Manuals

it states on pg 7:
Power Consumption Standby = 0.06 amp
Auto mode = 0.5 amp
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Old 18-08-2008, 21:02   #8
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I cant imagine any autopilot being able to move a rudder with just 0.5 amps. 0.5 amps times 12 volts is 6 watts. The motor certainly draws more power than that.

I think what you may need to do is put an ammeter across the autopilot and measure the current being drawn when it is moving the rudder while underway. This would give you an actual figure that would allow you get the correct sized wire.
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Old 18-08-2008, 22:26   #9
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I bet you have some corrosion at the ends of the wires (check both ends)
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Old 19-08-2008, 22:50   #10
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Maybe the 0.5 amp spec is based on the smallest fine and momentary correction in "auto" mode.
On the other hand, maybe its a typo which should have read 5.0 amp. That seems like way to much current to exert less than 100 lbs of thrust force for only about 10 seconds or less.

Reading further in the manual, they specify to use a 10 amp fuse in the power distribution panel and that circuits of less than 13 ft require 16 ga and up to 27 ft requires 14 ga conductor.
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