Originally Posted by majdrew
Could someone please tell me, I am buying
a small 25' boat. I will need to run a pc for nav. purposes, and some other small electronic gear
, maybe a small tv/radio etc..
Would a solar panel, wind generator
and 2 batteries suffice? How do I find out know how much battery power I would need?
Any advice most gratefully received,
Calculating power needs is a bit of math. You can create an excel spreadsheet for this. The basic formula is that Watts = volts X amps. This is consumption
per hour. 40w light takes 3.3 amps. A 12V DVD
player with LCD screen
might take 3.0 amps.
List all the 12 V things you have on the boat and then put in a "hours per day" factor - i.e.
nav lights = 3 lights X 4 hours X (40W/12) = 40 amp hours
= 2 amps X 8 hours = 16 amps
For AC stuff it gets a little trickier - watts is a measure of "work" if you have more volts you need less amps. So my Dell laptop has a 65 watt power supply.
65 / 110V = 0.6 amps
65 / 12V = 5.4 amps
What this means is that running my 110V laptop power supply through a 12V inverter
will draw 5.4 amps. A 400W inverter running at max load is drawing more than 33 amps off your batteries not counting the inneficiencies of converting the power from DC to AC - yikes...
So Inverter for laptop = 5.4 amp X 6 hours = 21.6 amps
When you add it all up you will know your daily usage. Then you have to have enough storage
so that you don't run out of amp hours before you can recharge. Then you have to figure out how to put the amp hours back in. Most commonly we know about alternators. however Solar and Wind
I am assuming you don't have inboard engine
We have a small boat and have added lot's of gizmo's - fridge, twin DVD
players, 400W inverter, fans etc. I added a third battery and have them split between starting and house.
We don't run the fridge much as I have been trying to figure out how to recharge the batteries (after a weekend) while we are away from the boat.
With our size boat (yours and mine), lot's of solar starts to become problematic. I have figured out that I want two ~50-65 watt panels
that will mount on the bimini
frame - which I may need to reinforce. The reason for the smaller panels is that I can't fit one 85 watt or bigger panel anywhere that makes sense. Two smaller panels will fit on the bimini
frame on each side of the backstay which runs through the bimini.
For reference (probably optimum numbers)
50 watt solar = ~120ah week
80 watt solar = ~200ah week
110 watt solar = ~280ah per week
If we run our 4 amp 12V fridge for 48 hours we need 192 AH to fill up the batteries that coming week. I'd love to get about 110 watts of solar on our boat.
I reckon with that we can stick the fridge on Friday afternoon, turn it off Sunday and be all charged up next Friday. Especially if we count on some motoring time with the alternator
Now I just need to come up with the ~$1,000+ boat bucks - LOL.