VOLTAGE ACROSS FUSE BUS, BASS TRACKER 190 TX

[Mr. Swabby(aka westtennessee1)]

Help! I'm getting ready to install a Hummingbird 998Csi, in teh place of the stock Lowrance X51. I disconnected leads from the fuse bus for the Lowrance and wanted to verify 12V dc with a voltmeter before connecting the Humminbird. I get a "creeping" voltage which starts at about 5mV and works up to about 9mV. Never get straight 12V dc. I tried turning the motor over a couple time to see if I get the 12V and had the same "creeping" voltage result... Any advice? :-/

[Fishing Rhino]

What voltage do you get when you test the main positive and negative leads?

[Wayne P.]

Connect the unit directly to the battery by extending the power cable with at least 16 guage wire.

You won't get any voltage across the fuse block, you have to check between the fuse and the ground. It still may not support the unit due to the wimpy wire harness causing too much resistance.

You may have enough unloaded voltage, but the capacity may not be there.

Been there, done that with my Tracker.

Do it right the first time and you won't have to re-do it later.

[Mr. Swabby(aka westtennessee1)]

Rhino- I have 12V off of the main but the fuse block does not have a voltage, well it's a small voltage that starts low and increases over time. (5mV to about 9 mV or so). The old Lowrance ran off of the fuse bus with no problems. I measured the voltage at the terminals that the old unit was connected to. Can't figure out why I don't get 12V. The boat is only a year old, should not have a short or anything like that... :-[

[TimJ]

I am not knowledgeable about Trackers specifically but if the system uses the hull as a ground, one bad connection to ground at either end will cause your low (or no) voltage reading. tighten ground screws AND, first, clean the metal under the screws, for better connections.

there was a good suggestion to run a new set of wires directly to the 998...remember to put an inline fuse on the +12v side just before the 998.

(basically 5mv to 9mv are zero)

TJ

[triglet]

well without looking at it i'm really not much help.  but talk about "hull" ground reminds me when i was trying to check voltage on mine and realized i was checking off the wrong ground.  just a thought!

[Fishing Rhino]

I'm not sure how you got your first reading.  Did you have the Lowrance unit powered on, then test across the fuse?

If so, that could account for your "creeping voltage" since the current would pass through both the fuse and your meter, each carrying a part of the total current.

To test the voltage available at the sounder end of the fuse, the meter should be contacted to the ground block, and the sounder end of the fuse.  No need to power up the unit. 

That will show you the voltage output across the fuse.

[Mr. Swabby(aka westtennessee1)]

thanks to all of you for contributing to this post-

I tested the voltage across the exact positions that the old Lowrance was attached to. The unit was disconnected at the time I tested. I tested the positive side of the fuse terminal and ground bar on the fust block. I also tried positive terminal and hull of the boat to see if there was any difference and there was not. I'll post pictures tonight or tomorrow to help describe how I am measuring the voltage...

[Way2slow]

You have a bad connection somewhere. When you check it with nothing connected and get 12 volts (open circuit voltage), that's because there is no load on the circuit. When you connect your unit, that places a load on it and it becomes a resistive circuit and depending on the amount of resistance, determines the voltage the unit will actually see. In your case, it's almost pure resistive, to the point it's close to being an open.

Leave the unit connect or connect a small 12V bulb across the two wires you're using. Then just start following the voltage (or lack of) back to the point you find where you're loosing it. My first place would be the circuit breakers if it has them. Check both terminals an see if one has 12 volts on one side and you millivolts on the other. Then I would check the switches on the console. First make sure it's not controlled by a switch you haven't turned on, then check the input and output of the switch.

Always, have any circuit you're checking under a load. Open circuits will almost always lie to you. Then you just follow the voltage drop until you find the point of the drop, there will be your cause/problem.

DO NOT check to the hull. There should never be any connections made to the hull. I know with aluminum boats it's convenient to use the hull as a negative but that's it very bad and very wrong. You will create all kinds of hull corrosion problems doing that. ALWAYS run two wires, one battery positive and one battery negative.

Thin needles, like hat pins or T-Pins work greate for tracing the voltage. Just stick it in the wire. Check each side of every connection point, fuses, switches, plugs etc.

Also, work from a known good point to an unknown, and don't forget it takes two wires to make a circuit.  Too many times people go crazy trying to figure out what's wrong with the positive wire, when it's the negative that's causing the problem. 

[Mr. Swabby(aka westtennessee1)]

All,

Well after all of your great advice, I have traced the problem to a blown in line 20A fuse stashed between the gas tank and the live well. Everything is "up & up" now and I plan to complete the Humminbird install this weekend. I appreicate everyone's advice!

Good Fishin!

Jeff

[triglet]

woohoo glad you found it.  enjoy that new finder!

[nubasser]

Do you know what caused the inline 20A fuse to blow.You may have done this when testing your connection but if not you should try to locate that issue.