Knowledgeable electrical folks?

I’m upgrading the sonar on my boat.
Got everything hooked up, and looking at the voltage displayed on the depthfinders I got a little perturbed. I was showing over 2 volts lower at the bow than directly off the battery post. But before I started pulling bigger wire, I decided to actually check with a meter. Borrowed a nice fluke dvm, and checking at the pins in the depthfinder plug, I’m only down .2 volt from battery to bow unit. It’s a 22 foot boat, and the way it’s laid out, I’ve got about a 30 foot wire run.
Battery at stern, up to center console, then back to stern, then up the gunnel to the front. No good path to fish wire through directly from center console to bow. But my question,
2 tenths of a volt drop is within reason, yes? And are the voltages shown on the units possibly that far off from reality? New H’bird helixes.
Thank you.


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.2 volts is fine. 2 volts is not. How many amps does the unit pull.

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Originally Posted by DockShootinJack

.2 volts is fine. 2 volts is not. How many amps does the unit pull.

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3.2 for the head unit, but I’ve got 2 other things on that same wire - one at 165 milliamps, the other 950 ma

Ive got a fuse block in the front fed from the back, so I do have individual fuses for each item


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This is where my lack of electrical knowledge shows - (I’m a machinist by trade)
I’m getting .2 drop under a no load situation. Is it possible that under load it IS pulling the voltage down?
I think this evening I’ll check it at the fuse block up front with everything powered up.


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It certainly can happen. Test it under a load of possible and see what your results are

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Originally Posted by DockShootinJack

It certainly can happen. Test it under a load of possible and see what your results are

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Well, the units ain’t lying. With everything powered up, I’m back to
-2.0v
But, I know what I’m gonna do to fix it.
Pull in some 12 gauge wire, and run directly from my main battery disconnect. From H’bird’s website, it says 12 gage is good for 24 feet. This will shorten my run by 8 foot or more as well, and eliminate several splices. Lesson learned.


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We should remember that the voltage shown on an electronics screen is not direct voltage from the battery (like a Fluke meter reads).

The voltage on the screen is after the load to power the unit ... which is why your test at the pins was only down .2v ...

In a nutshell - the electronics unit is not a voltage meter ... and the voltage shown on the screen should only be noted as a general voltage of the battery itself ...

A better way to monitor actual battery voltage would be to install a battery meter ...

Rickie

If you have Lowrance units, some models are known read the voltage low. My 9 Live at the bow does.

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Originally Posted by rnvinc

We should remember that the voltage shown on an electronics screen is not direct voltage from the battery (like a Fluke meter reads).

The voltage on the screen is after the load to power the unit ... which is why your test at the pins was only down .2v ...

In a nutshell - the electronics unit is not a voltage meter ... and the voltage shown on the screen should only be noted as a general voltage of the battery itself ...

Rickie

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I’m known to overkill stuff, was going to go 10 gage. But I rummaged around in the shop and found a roll with a 100 feet or so of 12. It’s paid for, think it’s worth a go. Heck, as much as I have, may pull in 2 runs of it and divide the load up. For the record, what I was using was in the boat from previous owner. It’s 14 at best, may be smaller.


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Within reason nothing wrong with oversizing wiring. Never hurts to have extra capacity in place if you wish to add things in the future.

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Originally Posted by J White

I’m known to overkill stuff, was going to go 10 gage. But I rummaged around in the shop and found a roll with a 100 feet or so of 12. It’s paid for, think it’s worth a go. Heck, as much as I have, may pull in 2 runs of it and divide the load up. For the record, what I was using was in the boat from previous owner. It’s 14 at best, may be smaller.


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Couple of things, I hold a USCG Unlimited Chief Engineers License so this was a big part of earlier life. First the type of wire you run should be Tinned DC wire, lots of little strands to prevent Counter EMF. Stranded AC wire or Automotive grade will have a higher resistance to electron flow. Second is the terminals used, you want Silver plated Copper only. To further reduce voltage drop after crimping solder them. Adhesive lined Shrink Tubing applied to a bare soldered terminal is a Top Shelf way to terminate. Back to front like you are running 10 gauge wire is the minimum size I ran for electronics on these 24ft Bay Boats when in my shop for a T-Top. I run a single pair then install sub-distribution equipment in the bow. Blue Sea Systems fuse bus with ground distribution is all I use they come with a clear Cover/Guard. Sum of the voltage drops equals source voltage, wire quality & size - termination quality - and in some cases Induction can lead in good direction or bad. You don't want your supply wire to run next to the trolling motor supply wire due to Induction. Anytime I have had to run supply lines next to DC Motor supply lines shielding over the wire must be used. :twocents

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Originally Posted by rojoguio

Couple of things, I hold a USCG Unlimited Chief Engineers License so this was a big part of earlier life. First the type of wire you run should be Tinned DC wire, lots of little strands to prevent Counter EMF. Stranded AC wire or Automotive grade will have a higher resistance to electron flow. Second is the terminals used, you want Silver plated Copper only. To further reduce voltage drop after crimping solder them. Adhesive lined Shrink Tubing applied to a bare soldered terminal is a Top Shelf way to terminate. Back to front like you are running 10 gauge wire is the minimum size I ran for electronics on these 24ft Bay Boats when in my shop for a T-Top. I run a single pair then install sub-distribution equipment in the bow. Blue Sea Systems fuse bus with ground distribution is all I use they come with a clear Cover/Guard. Sum of the voltage drops equals source voltage, wire quality & size - termination quality - and in some cases Induction can lead in good direction or bad. You don't want your supply wire to run next to the trolling motor supply wire due to Induction. Anytime I have had to run supply lines next to DC Motor supply lines shielding over the wire must be used. :twocents

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Dang now I’m second guessing using what I have
It’s definitely stranded ac wire.
I should be good on trolling motor though, it’s on the complete other side by itself


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Quote:

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Originally Posted by rojoguio

Couple of things, I hold a USCG Unlimited Chief Engineers License so this was a big part of earlier life. First the type of wire you run should be Tinned DC wire, lots of little strands to prevent Counter EMF. Stranded AC wire or Automotive grade will have a higher resistance to electron flow. Second is the terminals used, you want Silver plated Copper only. To further reduce voltage drop after crimping solder them. Adhesive lined Shrink Tubing applied to a bare soldered terminal is a Top Shelf way to terminate. Back to front like you are running 10 gauge wire is the minimum size I ran for electronics on these 24ft Bay Boats when in my shop for a T-Top. I run a single pair then install sub-distribution equipment in the bow. Blue Sea Systems fuse bus with ground distribution is all I use they come with a clear Cover/Guard. Sum of the voltage drops equals source voltage, wire quality & size - termination quality - and in some cases Induction can lead in good direction or bad. You don't want your supply wire to run next to the trolling motor supply wire due to Induction. Anytime I have had to run supply lines next to DC Motor supply lines shielding over the wire must be used. :twocents

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Hence the reason I only use Ancor marine wire and Ancor marine heat shrinkable connectors on EVERYTHING in my boat. I also have 2 Blue Seas fuse boxes. I also have 3 amperage/voltage monitors, one on my livescope lithium, one on my trolling motor lithiums in series, and one for later use. Along with battery meters on my two AGM Optima Blue tops (one for cranking, and the other is for lights, pumps, stereo system), and on my two lithiums for my ghost trolling motor. I can see at a glance if there is an issue with any of the batteries. Plus everything is switched. I went way overkill, but I did it right the first time and won't have to do it again.

I am a more is better person when it comes to wiring. Within reason of course. In my case my trolling motor is within reach of my battery. At one time I used a small stern mount motor so I ran #8 wire from battery towards the bow to the stern. it ran my trolling motor and my depth finder. My boat is a 14 footer so the wire is only about 12 feet in length or so. Having a little tinny and a 9.9 outboard I take any weight into consideration, plus I already had the wire so no extra cost was involved. lol
I am including a link here that may help you.
Voltage Drop Calculator - Inch Calculator
knowing your full load amps is very important.
:fish

Voltage with no load does not equal voltage under load on the wire. For the distance, I think that 10ga marine wire run to the battery on circuit separate from the main fuse panel should still be fine for a couple of fishfinders and have only a 3% voltage drop. Wires have a built-on resistivity that causes footage reduction at distance, which is why you need such thick wire to overcome. The wire at the fuse panel and many lights and accessories are rated for 10% drop instead of 3%, which is why you see the drop that you are seeing.

Getting your water sled ready for Crankfest Jeff?

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Originally Posted by BuckeyeCrappie

Getting your water sled ready for Crankfest Jeff?

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Yes Sir, hope to get some practice in before then :)
Besides all this wiring, I’ve got to replace bunk boards on trailer.
Gosh I work on this thing more than I fish in it!


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Think I’m good to go now, thank you for all the folks that gave advice.
Powered everything up for test run, have less than 2% drop everywhere.
More like 1 1/2%. I took a whole bunch of length out of my circuits, heavier wire, eliminated a handful of splices, and bypassed my factory dash switches and fuse block. I think that was a major part of my problem, boat is 23 years old, and even new I don’t think they imagined the kind of load I have now. But everything is cut off with my main battery disconnect, and fused within a few inches of the battery connection.


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Sounds like you have it all fixed up