Hds power question

[shadillac]

Running an hds 7&12 on an isolated grp27 ac delco wired through my switch panel. The voltage supply readings are 10.9 on the 7 and 10.4 on the 12. I had a reading of 13.5 on the battery before turning the units on. Out of curiosity I left them on to see how long they would last and that was just about an hour. The 12 cut off and the 7 stayed on. Any idea what's going on? I initially had the problem when I was wired through the cranking battery which is alternator charged. So I tried the isolated battery. Are those units draining my batteries that fast ?

[mwardncsu]

What you are seeing is the voltage drop across the wire, as a result of the load of the units.

What gauge wire are you using from the battery to the switch panel and then to the units? And how long is the run? I'd recommend beefing up the gauge of the wire...... both the positive supply wire and ALSO the return ground wire.

[shadillac]

What gauge wire would you recommend? I'm guessing it's probably 12-14 gauge going from battery to switch panel.

[Deleted]

I have an hds12 and an hds8. I am running two dedicated 12 Guage wires (- and +) from the battery (24 series) to the 12 and a splice to the 8 upfront....also 12 Guage. I see a drop of 0.2volts with this setup.

[mwardncsu]

For your electronics you ideally want to be at 3% or less voltage drop - so nor more than a drop of ~0.4V with a 12V source

To determine the drop, you need to know the current load. You can find this in the HDS user manual in the back in the technical specs section - they should under 1A each if I recall.

This site has a good voltage drop calculator..... you plug in all the variables and it tells you what the drop will be. So change the option for wire size till you come up with the drop you are happy with. You will need to also know the one-way length of the circuit run - that is how long is the wire from the battery to the switch to the unit.

www.genuinedealz.com/voltage-drop-calculator

In your case, you may have a heavier wire feeding the switch panel, and then smaller wires off the panel to the units. It could be other loads fed off the switch panel (pumps, nav lights, etc) are resulting in enough current to cause a voltage drop at the panel - which is lowering your voltage to your units - even if the units are fed with sufficiently large wire.

12-14 ga wire from the batter to the switch panel sounds likely too low - depending on what is being powered off the panel. It sounds low to me if for no other reason than the potential to drive loads that would, in total, exceed the rated amperage load (i.e. 35A for a 14ga and 45A for a 12ga wire) But also, with additional loads on a 14 or 12 ga wire, you're going to create a larger voltage drop to the panel itself. Without knowing your panel and setup it is hard to say - but I'd say 8 ga is the minimum you'd want to run from a battery to a distribution panel.

Typically 14 ga is going to be fine for the modern fish-finders if on a dedicated run. You don't want to use anything less than 16 ga for power on a boat anyway for risk of the wire breaking. It is possible that you also are getting voltage drop due to poor terminations / crimps - the resistance from poor terminations will result in voltage drop as well.

[shadillac]

Picked up some 8 gauge wire today. Where can I get a inline fuse holder of similar size? Im on a little bit of a time crunch so ordering isn't really an option. Also what size fuse should I use? It powers my dash lights , nav lights , bilge pump, and two fishfinders. Thanks for the help guys I really appreciate it!

[mwardncsu]

Hummmm - not sure where you'd find an inline fuse holder for 8 ga wire. Likely need one that has screw terminals on each end wher you'd attach a crimped on ring terminal.

Might check with Ben at Smith Mountain Electronics or perhaps one of the auto parts stores. Maybe a car stereo shop - though they may or may not be tinned copper which is recommended for marine use.

Below is generally recommended practice. Your specifics may vary and you should run the numbers to ensure what you use is safe for your boat - aka - I'm covering my butt with this disclaimer

You want to put the fuse within 7" of the battery. You are protecting the wire - an 8 ga wire can carry around 80a ?? Check the table in the link above. You want your fuse lower than that of course so it blows before the wire becomes the fuse by catching on fire. Sum your total loads and maybe add a bit and as load it's below the max rating of the wire, use that size fuse.

Downstream of your switch panel you'd want fuses for each circuit - again, ideally fused within 7" of the switch - because that becomes the source - and size thise closer to the max draw of the load. Usually like 3A for the fish finders, 5-7a for pumps, 3-5 for nav lights, etc.

[shadillac]

Thanks buddy I'll check with Ben. I need to go see him anyways to pick up a backup shear pin for the trolling motor. I really appreciate all your help!

[Brian]

If you can't find a fuse holder with larger wire, just use the one you have for now. It's not ideal, but you'll still be better off with the 8ga wire running from a 12ga (or whatever it is) fuse holder.

What you're trying to do is lower the total resistance and voltage drop of the whole circuit. You'll have high resistance at the fuse holder, but that's only for a short distance.

[mwardncsu]

True. As long as the total amp draw is low enough for a 12 ga wire - which it likely is - think 12ga can carry about 45a

[formula180]

I would look for a 12 volt circuit breaker for the main line off the battery.  They come with automatic reset or with a fuse holder.

Little Fuse

I would check at Napa or some automotive stores to see what they carry.

[formula180]

SeaChoice makes a circuit breaker with manual reset...20, 30, 40, and 50 amps available from WalMart online for $6.28.

SeaChoice

[mwardncsu]

That would be an acceptable choice for the 8 ga wire feeding the panel from the battery.... Breakers vs fuses have different properties in terms of how they trip - but for a panel supply a fuse like that is often used.

[formula180]

May 8, 2015 13:50:24 GMT -5 mwardncsu said:

That would be an acceptable choice for the 8 ga wire feeding the panel from the battery.... Breakers vs fuses have different properties in terms of how they trip - but for a panel supply a fuse like that is often used.

Yep...breakers are slow to open and prevent roasting your wiring.   Nice to mount them at your battery terminal on batteries with the extra stud terminal.

You still need a fuse panel for your different lights, electronics, etc equipped with a fast blow fuse.  Using a breaker only for your electronics may result in sending smoke signs which will give away your secret fishing spot.

[shadillac]

Thane for all the help. I ended up going with a waterproof fuse holder for an amplifier. Cleaned all connections ran 8 gauge and they're both operating as they should! Again thanks guys!