BASIC electrical system info.

[Evan_Gatehouse]

> A typical laptop uses 60-110 watts for a day of use.

A watt is a unit of instantaneous power consumption. If you multiply it by time you get watt.hours (or more commonly kW.hrs which you see on your electric bill)


In boat's electrical systems we often use amps for loads and amp.hrs for batteries.

A typical cheaper low end laptop running thru an DC power supply (for example only) might be 5A. If you use it for 5 hrs you consume 25 A.hrs

So you add up all the loads you have for a typical day like this
Load Amps hrs A.hrs
Laptop 5 5 25
LED running lights 1.5 3 4.5
LED cabin light 0.3 3 0.9
Total 30.4 A.hrs

That's 1 day consumption. If your battery is being charged every day, you should (at a bare minimum) use a battery 2x the daily load. Because a typical lead-acid battery lifespan will be greatly reduced if used lower than 50% of it's rated capacity. So in this example you need something 2 x 30.4 A.hr = 60.8 A.hr -> pick something like a Group 24 (true deep cycle) battery that has a rated capacity of around 75 A.hr

IF you charge less frequently, or want to avoid charging for an extra day for example, the battery capacity must be multiplied by the number of days you expect to operate before recharging. So in our example if you wish to go 2 days without running the engine you need 2 x 30.4 A.hr x 2 days = 121 A.hr. minimum. Then you might need 2 batteries etc.

CHARGING OPTIONS
- you can only charge a lead-acid battery at about 1/4 it's amp.hour capacity. And that rate tapers down as the battery gets more charged. So in our 1 day battery a 75 A.hr battery can charge at about 1/4 x 75 A.hr = 19 amps. But only for the first hour or so. Then a good charger will slowly reduce the charge rate. So it might take 8 hrs for 'smart' charger to charge the battery.

- generator: costly but lots of power, reliable. Need a 12V smart charger to charge fastest
- solar: quiet, but more $/output. Will charge your battery on sunnier days, and rather slowly on cloudy days unless you have a lot of solar. Hard to have enough room on a small boat. But a 100W panel will charge at around 8 amps which is not bad. You also need an external regulator to avoid overcharging the batteries. Rule of thumb - on a sunny day divide panel wattage by 3 to get approximate daily amp. hours. So a 100W panel gives you about 33 A.hr/day on a sunny day in summer.
- outboard motor built in rectifier circuit: very low power (a Yamaha 9.9 is about 4-6 amps at cruising speed so it will take hours of motoring to charge a bigger battery)

TYPICAL WIRING DIAGRAM
really good step by step explanation here:
https://newwiremarine.com/how-to/wiring-a-boat/

[OrangeQuest]

I'll be the a$$ hat on this.

You already have fuel on board. For the price of a proper solar charger to maybe keep up with your day time demand on perfect days, you can buy a very very quiet (and small) Honda generator to run a charger/conditioner and/or inverter. The simple path is the right path in this case.

That said, spend about $2k in panels, charge controller and LiPO batts and you can do it with solar/wind but you will have to go a couple days with no use to get batts topped off. Inverters are WAY less efficient than folks think they are.

For the record, I'm doing the "full solar" thing for an off-grid project chicken coop/food plot. Dumbest idea I've ever had. pretty sure it would be smarter to just pay for power on the lot.

Think deer feeder with solar charger to keep the feeder battery charged up.

[Jaysen]

OQ, it’s less the feed and more the water (irrigation and animal), pest control and monitoring. It’s almost to the point that I’m just going to drop a trailer on the lot and stay there a few nights a week. It’s only a mile up the road from the house but… that dang water pump is a real problem.

[jbo_c]

Wow, Evan. Thanks!! That’s exactly the kind of answer/detail I need. I appreciate your time.

Jbo

[narfi]

To add to the confusion. Have you considered a "solar generator"?

If your main use is charging your laptop, a properly sized one with a folding "briefcase" panel or two should be plenty?

You may not even need the panels, depending on how much long you go out at a time.

The term is weird because "solar generators" aren't really generators. They are portable batteries with built in inverters.

Another advantage to the solar generator is it can be beneficial to "prepping" your house for emergencies. The battery could run essentials for a short time during power outages. (My house heats with very efficient diesel heaters, so it wouldn't take much electricity storage to keep my house warm for a while)

I've kind of gone the opposite direction and going more complex. Just got my shipment of 4x 400ah self heating Bluetooth lithium batteries and 4x 550w bifacial solar panels for my boat. I've toyed with the idea of getting a solar generator for my house and in emergency could haul in the boat batteries for an extra 20kw of energy which would last me a long time under emergency conditions.

[fallguy1000]

Fallguy, you are speaking out your posterior on that one. You can buy official power supplies for DC. You can regulate DC much easier than square wave or pwm AC. These things aren’t new tech. They just aren’t profitable so no one wants to sell them.

And before you start trying to argue with me look at every last car, truck, boat, plane or other thing out there that isn’t on mains. They all run on DC and all have the same sensitivity to power regulation. It’s not rocket science, just boring science.

I don't want to argue.

I looked for and had a hard time finding DC power supplies for our two laptops and then considered everytime needing to buy one for any new laptop. My inverter on the Skoota is a 2000w inverter. I used it so far for laptop and a vaccum cleaning job away from the dock. It was like $1500 and weighs 50 pounds and lotsa wiring work, so I'm not even a large fan of inverters.

I want to thank Evan for the correction. I started down a long path and tried to shorten it and made a hideous error in verbage.

My laptop uses 2.3A at just under, call it 20v, or 45w.

For DC 12v battery, this would be 45/12 or call it 4 amps. Inverter loss takes that to just under 5 as Evan suggested. I'm not sure how a DC 12v battery provides power to a 20v charging system, and this was why I recommended inverting. Maybe you can explain it to me. One of the more difficult challenges for me was boat electrical, but I got it done and the surveyor was pleased.

[jbo_c]

I looked at a few of the solar “generators”, but for the money and space thought I might go back to a very small generator.

Jbo

[Jaysen]

I'm not sure how a DC 12v battery provides power to a 20v charging system, and this was why I recommended inverting. Maybe you can explain it to me.

Most DC-DC systems use boost converters for upward conversion and buck converters for downward voltage change. Both are swapping voltage and amperage. Both feed into formal regulators as well as significant capacitive and inductive smoothing. In the end, both boost and buck converters are simple diode switch and capacitor circuits. check out this Wikipedia article that give you a lot more info.

Dirty little secret... your inverter is a big ol' boost converter operating on a dual cycle of "damn fast" over 60hz. "Damn fast" gives you a constant 60v±. Then a 60hz comes along and ramps a variable wave across ground to make that look like AC. There are other methods, but that's how most of the budget units have been doing it.

Second dirty secret... A laptop running on the wall may pull 20a. The same laptop charging will typically pull < 10a. Macs have less disparity than others. The best plan for computers on the boat... run with things unplugged, turn them off, then plug them in to charge. Much more efficient.

[fallguy1000]

Okay Jaysen.

How does a submarine communicate with a surface vessel?

cuz I wanna know

[Jaysen]

Not in my area of previous experience. Unlike my hobby of building various electronics projects, I’ve not bothered with underwater communications.

That’s not completely true… at one point infrasonic sound waves were used as carriers for encrypted communication signals. But these were easily intercepted, required “in water” listening, and messed with marine life.

One of us may just have been a bit more of a nerd than the other. It is probably me.