Many years ago I made it from Hawaii to Bellingham WA on a 30 footer with a 20 30 watt solar panel.
There was a 4 cylinder gasoline engine, but that had to be mostly saved for landfall other than a 10 minute run every few days to make sure it would still start and maybe use the SSB/HAM radio at the same time.
Boy, that was along time ago, and our (and mine) expectations of electrical power on a sailboat have changed!
My power budget was replacing enough in the house bank to keep the navigation lights on at night, and that didn't completely work after getting closer to the Pacific Northwest and all those darn clouds.
Anyway - as somebody earlier mentioned, those little devices like phones or tablets much less a laptop use far more power than you might think. So be sure to factor that in.
As others have mentioned, you do not want to trickle charge a LifePO4. The biggest issue there is when it does fill up, you are keeping it at maximum (or higher) voltage and will severely damage it. If you do something like this, you will need to put in an MPPT charger that can 'do the right thing' in regards to shutting off charging when appropriate.
For your power budget - you need to factor in a safety margin as well. As the boat and resources get smaller, this margin is a larger proportion of your overall capacity. Think about a bad situation where the bilge pump needs to run continuously and you need to use (or recharge) the VHF.
Some may disagree with this, but I think I would split my power bank into two portions.
1. The permanent boat system, with as much solar as possible that can fit in a permanent kind of way, appropriate MPPT charger and a 50AH or 100AH (probably 100) LifePO4. When on the mooring, the only power consumption is the bilge pump, which hopefully runs very little or not at all? On this, you need to be sure the solar power puts out enough voltage in moderate sun to be able to drive the MPPT charger and actually do some charging. Easily overlooked with very small panels - some can do it. You also have a nicely setup boat at minimal cost for some day sailing or quick overnighting whenever, and if you ever sell, the new owner will appreciate it.
2. My 'go kit' which would include one of the newer LifePO4 power stations that are targeted towards the glamping crowd. And one of those folding solar panels. I would use this for all my day-to-day activities, including recharging the VHF, generally keeping the 'boat system' as my emergency reserve. The more modern power stations can be charged off land power, the folding solar, 12-volt or USB. So from time to time, with weather (i.e. sunshine) permitting I would feel comfortable draining the boat battery down to say 70-80% recharging the power station. And charging the power station whenever possible while the sun is shining and the boat battery is already full. This entire kit, you can take with you off to a cabin or wherever else as well. Some of the newer power stations are pretty small/lightweight. Easy enough if you go ashore to cafe to politely ask if you can top it up while grabbing a bite to eat. The Pecron E500LFP (not the 600 you will find at Walmart) for example has a very good capacity to weight ratio.
Having the two power sources split this way reduces the fixed cost you put into the boat and more importantly - clearly separates your power consumption against the potentially very tempting situation of draining the main battery way down, then finding bad weather and troubles. You can also use the power station to top up the house bank in a pinch.
Anyway - mostly just ideas and food for thought.
I know some will be against or hesitant about a camping LifePO4 station on a boat, but as long as it is stored/used well away from wet environments and treated with respect for what it is, for me it would be 'safe enough'. Being LifePO4, a cel phone or a laptop is more of a fire hazard.
EDIT: This probably drives your budget through the roof and is more than the initial request. Having some kind of spare electricity source besides a 20 watt panel is going to be useful though if/when the boat battery gets lower than anticipated.
There was a 4 cylinder gasoline engine, but that had to be mostly saved for landfall other than a 10 minute run every few days to make sure it would still start and maybe use the SSB/HAM radio at the same time.
Boy, that was along time ago, and our (and mine) expectations of electrical power on a sailboat have changed!
My power budget was replacing enough in the house bank to keep the navigation lights on at night, and that didn't completely work after getting closer to the Pacific Northwest and all those darn clouds.
Anyway - as somebody earlier mentioned, those little devices like phones or tablets much less a laptop use far more power than you might think. So be sure to factor that in.
As others have mentioned, you do not want to trickle charge a LifePO4. The biggest issue there is when it does fill up, you are keeping it at maximum (or higher) voltage and will severely damage it. If you do something like this, you will need to put in an MPPT charger that can 'do the right thing' in regards to shutting off charging when appropriate.
For your power budget - you need to factor in a safety margin as well. As the boat and resources get smaller, this margin is a larger proportion of your overall capacity. Think about a bad situation where the bilge pump needs to run continuously and you need to use (or recharge) the VHF.
Some may disagree with this, but I think I would split my power bank into two portions.
1. The permanent boat system, with as much solar as possible that can fit in a permanent kind of way, appropriate MPPT charger and a 50AH or 100AH (probably 100) LifePO4. When on the mooring, the only power consumption is the bilge pump, which hopefully runs very little or not at all? On this, you need to be sure the solar power puts out enough voltage in moderate sun to be able to drive the MPPT charger and actually do some charging. Easily overlooked with very small panels - some can do it. You also have a nicely setup boat at minimal cost for some day sailing or quick overnighting whenever, and if you ever sell, the new owner will appreciate it.
2. My 'go kit' which would include one of the newer LifePO4 power stations that are targeted towards the glamping crowd. And one of those folding solar panels. I would use this for all my day-to-day activities, including recharging the VHF, generally keeping the 'boat system' as my emergency reserve. The more modern power stations can be charged off land power, the folding solar, 12-volt or USB. So from time to time, with weather (i.e. sunshine) permitting I would feel comfortable draining the boat battery down to say 70-80% recharging the power station. And charging the power station whenever possible while the sun is shining and the boat battery is already full. This entire kit, you can take with you off to a cabin or wherever else as well. Some of the newer power stations are pretty small/lightweight. Easy enough if you go ashore to cafe to politely ask if you can top it up while grabbing a bite to eat. The Pecron E500LFP (not the 600 you will find at Walmart) for example has a very good capacity to weight ratio.
Having the two power sources split this way reduces the fixed cost you put into the boat and more importantly - clearly separates your power consumption against the potentially very tempting situation of draining the main battery way down, then finding bad weather and troubles. You can also use the power station to top up the house bank in a pinch.
Anyway - mostly just ideas and food for thought.
I know some will be against or hesitant about a camping LifePO4 station on a boat, but as long as it is stored/used well away from wet environments and treated with respect for what it is, for me it would be 'safe enough'. Being LifePO4, a cel phone or a laptop is more of a fire hazard.
EDIT: This probably drives your budget through the roof and is more than the initial request. Having some kind of spare electricity source besides a 20 watt panel is going to be useful though if/when the boat battery gets lower than anticipated.
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