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Adding USB outlet

Posted: Sun Nov 11, 2018 7:27 am
by PatSea
I am planning to add a USB outlet to my 13 Sport. There are many variations but I like the ones with the LED digital voltage display. I plan to install this on its own circuit. My concern is if the digital voltage display is always on it will eventually run down the battery while in storage for several weeks. I could add a switch to the circuit or run it through the main engine switch, but I don't really want to do this. Any suggestions?

Re: Adding USB outlet

Posted: Sun Nov 11, 2018 8:25 am
by jimh
PatSea wrote:...if the digital voltage display is always on it will eventually run down the battery while in storage for several weeks.

Your analysis is correct. The power to operate a digital display monitoring the voltage will come from the battery powering the display. Although the current may be low, over time it will discharge the battery. The only solution is to disconnect that circuit when you put the boat in storage. There is no disadvantage to that. If the boat is in storage you won't be there to see the display not working.

Re: Adding USB outlet

Posted: Mon Nov 12, 2018 1:57 pm
by Dutchman
Does that digital display really use that much power to drain a perfectly good battery in a couple of weeks? The power useage would be minimal but why not put a switch in like Jim said.

Re: Adding USB outlet

Posted: Thu Jan 31, 2019 5:49 pm
by Simon
Maybe try something like this that has battery voltage and on/off button.

MASO 4 Hole Toggle Switch Panel with Dual USB Socket Charger 2.1A&2.1A + LED Voltmeter + 12V Power Outlet + ON-OFF Toggle Switch 4 in 1 Multi-function Panel for Marine Car Boat Trailer Motorhome(Red)
MASO.jpg (15.37 KiB) Viewed 11311 times

Re: Adding USB outlet

Posted: Fri Feb 01, 2019 10:52 am
by Dutchman
Simon--that is a great set-up for my camper.

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 7:58 am
by PatSea
Simon--that would work for me. I want a three-position switch, two USB outlets, and a Voltmeter. I don't need the cigar lighter outlet. And I don't have a lot of space.

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 9:16 am
by Ridge Runner
PAT--get a dual LED Waterproof Rocker Switch Control Panel and change out one of the switches with a rocker style USB outlet.
This would keep more of a marine appearance.

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 10:01 am
by jimh
None of the recent suggestions overcome the initial objection to having a digital Voltmeter display that is always on, thus always drawing current. The suggestion of using a switch to control the branch circuit has been rejected by the OP.

PatSea wrote: I could add a switch to the circuit or run it through the main engine switch, but I don't really want to do this.

I don't see any possible solution for having a digital voltmeter that is always connected to the battery. It will, of course, eventually drain the battery.

The ONLY remedy for this problem is to use a switch to disconnect the digital voltmeter from the battery when monitoring of the battery voltage is no longer necessary.

Also, most USB outlets supply 5-Volts DC. If they are fed from a 12-Volt DC source, as occurs on a boat when the device is connected to a 12-Volt battery, then some sort of voltage conversion has to take place. Any sort of circuity performing a voltage conversion will likely have a quiescent current drain on the source of power. In that regard, just about any USB outlet will need to be on a switched circuit, or the quiescent current drain will eventually drain the battery.

Until the OP relinquishes his insistence that there must not be a switch to control this circuit, the outcome will be a constant drain on the battery. This is just the nature of electrical circuitry. It cannot be overcome. A switch in the circuit feeding the USB outlet is a must.

The simplest solution is often the best: get a USB outlet designed for marine use. For example, a BLUE SEA SYSTEMS USB outlet. For example, a 12/24V Model 1016 Dual USB 2.1A Charger

Fig. 1. BLUE SEA SYSTEMS USB Outlet, model 1016.
BlueSeaSystems1016USBOutlet.png (62.06 KiB) Viewed 11304 times

The Model 1016 has an MSRP of about $31 and often sells for around $22 from discounting retailers.

If you want a voltmeter, SEADOG has a model 456217-1 dual USB with Voltmeter (that measures the input voltage, not the USB voltage) that sells at a discount for about $28. (See DEFENDER.COM for more information.)

As I mentioned, there is a quiescent current drain when voltage conversion is accomplished. In the specifications for their Model 1016 USB outlet, BLUE SEA SYSTEMS notes:

Parasitic Current Draw: 15mA (or 0.015-Ampere)

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 10:12 am
by jimh
Regarding having a voltmeter associated with a USB outlet:

Does the voltmeter monitor the 5.0-Volts of the USB outlet?

Or does it monitor whatever the supply voltage to the USB outlet that is to be converted to 5.0-Volts?

It seems a bit confusing to me to associate a voltmeter with a USB outlet if the voltmeter does not monitor the voltage at the USB outlet.

I would also be concerned about plugging a $900 Smartphone for charging into some $4 Made-in-China no-brand "USB" outlet. For me, using something with a real manufacturer behind it would be more reassuring that I wasn't going to smoke an expensive device by trusting some unknown seller on a web site to deliver a quality device.

Finally, on a 13-foot open skiff, I'd just keep my smartphone or tablet in a waterproof pouch.

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 12:45 pm
by jimh
If a device with a constant quiescent or parasitic current of 0.015-Amperes is connected to a storage battery, we can calculate how long the battery will hold a charge and how long it will take for the parasitic current to dissipate that stored charge.

At a rate of 0.015-Amperes, the device will consume 1-Ampere-hour of stored electrical charge in 66-hours.

If the battery has a capacity to hold 40-Ampere-hours, a figure that might be typical for a 12-Volt battery used on a small boat, then at a rate of 1-Ampere-hour per 66-hours, the battery will be discharged completely in 2,666-hour, or in about 111-days.

Generally if long service life is desired from a lead-acid storage battery, the battery should not be allowed to fall below about 20-percent discharge. On that basis we de-rate the 40-Ampere-hour battery, and limit consumption of stored energy to only 20-percent of the capacity or 8-Ampere-hours. With a discharge rate of 1-Ampere-hour per 66-hours, 8-Ampere-hours will be consumed in 528-hours or 22-days.

The above calculations don't include any self-discharge in the battery. Also the Ampere-hour rating of most batteries varies with the rate of discharge, so for very low rates of discharge the Ampere-hour rating might be higher than the battery manufacturer indicates using the typical discharge rate of a certain fixed time period, usually 20-hours. That is, if a battery is rated at 40-Ampere-hours, to get that rating the battery can tolerate a 2-Ampere discharge for 20-hours. If discharged at a higher rate, the Ampere-hour rating would be lower. If the discharge rate is lower, we must know the Peukert constant of the cell in order to calculate a new Ampere-hour rating at the smaller discharge. For a reasonably readable summary of Peukert's Law see

Peukert’s Law | A Nerd’s Attempt to Explain Battery Capacity

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 1:19 pm
by PatSea
Jim, I agree with your analysis. My original concern for not wanting a switch in the circuit was because I believed that at some point I would forget to turn it off as the boat went into storage. I was hoping there was a combination usb plug and voltmeter with some type of an auto off feature.

Re: Adding USB outlet

Posted: Sat Feb 02, 2019 4:40 pm
by jimh
The most common method of providing a 12-Volt power distribution on a boat--even on a 13-foot boat--is to have a MASTER BATTERY ON-OFF switch. When the boat is not in use, the master battery switch is set to off. This disconnects all loads, with the exception of special loads that are desired to remain on 24-hours-a-day.

If the USB outlet is wired so that it is in the circuits disconnected from the battery when the master switch is set to OFF, then any parasitic load from a USB voltage convertor or a digital voltmeter will be shut off.

Re: Adding USB outlet

Posted: Mon Feb 04, 2019 10:48 am
by jimh
PatSea wrote:I was hoping there was a combination usb plug and voltmeter with some type of an auto off feature.

Re having an "auto off" feature: this would be best implemented by using a mechanical relay to completely disconnect the USB circuit from the battery. The relay coil would be controlled by a circuit that would stop current to the relay coil after a predetermined time has elapsed from the circuit being energized. This is known as a TIME-OUT circuit.

Such a circuit is not particularly hard to design, but the first decision would have to be the duration of the TIME-OUT period.

I suggest a mechanical contact for disconnecting the USB circuit and the TIME-OUT circuit because this ensures that there cannot be any current flow when the relay contact opens. The time-out circuit would be powered from the closed relay contacts. When the relay opens it also stops the time-out circuit from drawing current.

I don't believe there is any consumer-off-the-shelf (COTS) product available that could perform this function, so if PATSEA wants this function in order to have to avoid installing a switch, he might have to hire someone to design and build it for him. I would expect that such a service won't come cheaply, so a new question then becomes: how much is a TIME-OUT function to control a USB charging output worth?

Here is a possible hint for a simpler method: on most boats with outboard engines, the operator will stop the engine from running when the boat is no longer in use. Since it seems quite normal for the operator to shut off the engine, if the USB circuit is powered from a circuit controlled by the outboard engine ignition switch, then the USB circuit would become shut off at the same time the outboard engine is shut off. This might be a workable arrangement for controlling the power to a USB outlet.

Re: Adding USB outlet

Posted: Wed Jun 05, 2019 5:03 am
by B.E.Coyote
A disadvantage to having an always-on LED voltmeter on the dash is their brightness can be annoying at night. They are brighter than you might think. On my recent installation I put in a switch for the LED voltmeter.

Re: Adding USB outlet

Posted: Wed Jun 05, 2019 12:15 pm
by jimh
Adding a switch to cut off the power to an LED voltmeter is a good solution to prevent the voltmeter from running continuously and discharging the battery, but in this discussion the originator makes clear he eschews this approach and wants something different.

The originator of the discussion appears to want the LED voltmeter to be somewhat self-aware and to automatically shut itself off, but the originator does not explain the basis that the LED voltmeter will use to determine when it should shut itself off. I suggested a method in which TIME would be the basis for the self-aware LED voltmeter to shut itself off, but that suggestion did not elicit any comments from the originator of the discussion.

Suggestions that some sort of means for the operator to shut off the LED voltmeter seem to violate the fundamental requirement that shutting off the LED voltmeter NOT be accomplished by some action on the part of the operator. I believe that the LED voltmeter must be able to shut itself off if the solution is to fit the requirements posed in the initial question.

Re: Adding USB outlet

Posted: Fri Jun 07, 2019 9:57 pm
by MarkCz
I thought I would add some information regarding the concern about running the battery down if he left the voltmeter on. My daughter had a 2005 Honda Accord that had a radio that was causing the battery to run down overnight when the car was sitting. WE disconnected the radio but she hated going without music. A new radio was crazy expensive $700 plus installation. We nded up adding an after market unit called a "priority start". This automated sensing switch gets installed between the battery Pos terminal and the the house wiring. When the unit senses a load is draining the battery it will shut off power to the car when the voltage gets below a certain value. When you get in the car everything seems dead but by turning on the lights or pumping the breaks to turn the lights the switch opens back up allowing you to start the car. It worked great for her car and they even make one for marine applications. I would not use one of these if the boat was wet slipped and depended on a bilge pump but for other applications it does provide some assurnace you can start the vehicle or boat.