I've got a small auxiliary sailboat with an 8hp outboard "iron genoa". My electrical needs are meager at best (depth sounder, VHF radio, stereo.) My house battery is a a single 12v deep cycle. Is the charge coming off the outboard sufficient to charge the battery for a weekend of gunkholing on the Chesapeake? How long would the engine need to run? Presently, when the battery stops providing enough power, I systematically begin turning unnecessary things off and lug the battery home with me at the end of the day to charge in the garage. Not an easy feat as I'm on a mooring ball and must dink it to shore in my little 8 foot Walker Bay plastic cup. Would one of those 1.5 or 2 watt solar charges be of ANY value, or just money wasted. Thanks for your responses.
Battery from Honda 8 hp 4-stroke
- Thread starter bcwave
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Outboard Alternator
If your engine is electric start then your alternator should put out enough current to keep the battery charged. If it's pull start, then I would guess not.
If your engine is electric start then your alternator should put out enough current to keep the battery charged. If it's pull start, then I would guess not.
Depends on how often you
use the boat/electicity. The VW solar panels are rated about 3.5 watts which will equal about 35 watts per day this time of year. or about 3 ampere hours in your 12 volt battery. 5 dats would be 15 Amp Hours. Full charge on your battery might be 100 amp hours. so maybe 6 weeks to fully charge. How Long to discharge?
use the boat/electicity. The VW solar panels are rated about 3.5 watts which will equal about 35 watts per day this time of year. or about 3 ampere hours in your 12 volt battery. 5 dats would be 15 Amp Hours. Full charge on your battery might be 100 amp hours. so maybe 6 weeks to fully charge. How Long to discharge?
Energy Budget
You need to do an energy useage budget. Size of your battery in amp hours + charging capacity - amps of energy used per day. You'll need to know the amps each appliance uses, the hours/day you use it, your battery capacity, and the amps the OB's charger puts out. Be conservative; more capacity than you actually need is always better than less. Don't plan to draw the battery down below 50% of capacity or you'll have a short battery life. West Marine (link below) has a spreadsheet to help you do the budget. Based on what you said, I imagine you'll have trouble putting the charge you need back into your battery. A high capacity solar panel may be your best bet. And they are expensive! Good luck!
You need to do an energy useage budget. Size of your battery in amp hours + charging capacity - amps of energy used per day. You'll need to know the amps each appliance uses, the hours/day you use it, your battery capacity, and the amps the OB's charger puts out. Be conservative; more capacity than you actually need is always better than less. Don't plan to draw the battery down below 50% of capacity or you'll have a short battery life. West Marine (link below) has a spreadsheet to help you do the budget. Based on what you said, I imagine you'll have trouble putting the charge you need back into your battery. A high capacity solar panel may be your best bet. And they are expensive! Good luck!
I know I'm dense...
what does this all mean? The Honda is a pull start so there is no big alternator. Once the engine is running, there's a DC output on the side that, according to the owners manual, will but out some sort of battery charge. I just don't know what kind or how much charging I can reasonably expect. I don't understand amp hours and that sort of thing. Is there someplace where I can go to get a dumbed down lesson? DC power for idiots? Sorry for the dumb questions.
what does this all mean? The Honda is a pull start so there is no big alternator. Once the engine is running, there's a DC output on the side that, according to the owners manual, will but out some sort of battery charge. I just don't know what kind or how much charging I can reasonably expect. I don't understand amp hours and that sort of thing. Is there someplace where I can go to get a dumbed down lesson? DC power for idiots? Sorry for the dumb questions.
Try this
Don Casey's "Sailboat Electrics Simplified". Good book, lots of info, easily understood. The link below is for it at Amazon, but it's available from West Marine, as well as Borders or Barnes & Noble. There are other boat electrical books that are as good, but Casey is the modern "guru". Your battery capacity is like the amount of gasoline you need to buy and carry aboard for a trip on the boat (assuming no sailing). How many gallons you need to start with depends on how far it is between places you can re-fuel (like your battery's re-charging capacity), how much fuel you use (the electrical draw of the appliances you use) and how far you have to go. The battery problem is a little more complicated than with gasoline, as you can almost always refill the gas tank to the top at any place you have fuel available, no matter how much fuel you've used, whereas with a battery, your ability to "re-fuel" (i.e. your charging capacity) may be less than the rate at which you're using the "fuel" (i.e. burnign electricity). If that's the case, you need to be able to start with a bigger "gas tank" (bigger battery), or find more "re-fueling stations" on the way (more charging capacity).
Don Casey's "Sailboat Electrics Simplified". Good book, lots of info, easily understood. The link below is for it at Amazon, but it's available from West Marine, as well as Borders or Barnes & Noble. There are other boat electrical books that are as good, but Casey is the modern "guru". Your battery capacity is like the amount of gasoline you need to buy and carry aboard for a trip on the boat (assuming no sailing). How many gallons you need to start with depends on how far it is between places you can re-fuel (like your battery's re-charging capacity), how much fuel you use (the electrical draw of the appliances you use) and how far you have to go. The battery problem is a little more complicated than with gasoline, as you can almost always refill the gas tank to the top at any place you have fuel available, no matter how much fuel you've used, whereas with a battery, your ability to "re-fuel" (i.e. your charging capacity) may be less than the rate at which you're using the "fuel" (i.e. burnign electricity). If that's the case, you need to be able to start with a bigger "gas tank" (bigger battery), or find more "re-fueling stations" on the way (more charging capacity).
10 Years Ago It worked
I had a 8 hp Honda charging a group 27 battery. Never used anything else to charge battery ever. Never had a dead battery. I would sail away for 3 or 4 days at a time but no night sailing.
I had a 8 hp Honda charging a group 27 battery. Never used anything else to charge battery ever. Never had a dead battery. I would sail away for 3 or 4 days at a time but no night sailing.
Peter's advice is well put
You could buy the book, but Peter's link is the place to go first. WWW.westmarine.com has advisors that will tell you what the power requirements are for each of your loads. Stu
You could buy the book, but Peter's link is the place to go first. WWW.westmarine.com has advisors that will tell you what the power requirements are for each of your loads. Stu
Honda a minimal charger
My 1996 Honda 8 had a rated 5 amp charging output at full rpm. At typical cruising rpm the output was 2-3 amps. My electrical load was pretty much just the three running lights. Bow light, forward powering light, and the stern light. At one amp each, the Honda barely kept up, with no real charging accomplished. Running without any lights or other load it would take something like 25 hours or more to charge a half depleted 70-amp battery! I regarded the Honda as not much more than a trickle charger. I always recharged at the dock. If your loads are truly minimal, it may work for you.
My 1996 Honda 8 had a rated 5 amp charging output at full rpm. At typical cruising rpm the output was 2-3 amps. My electrical load was pretty much just the three running lights. Bow light, forward powering light, and the stern light. At one amp each, the Honda barely kept up, with no real charging accomplished. Running without any lights or other load it would take something like 25 hours or more to charge a half depleted 70-amp battery! I regarded the Honda as not much more than a trickle charger. I always recharged at the dock. If your loads are truly minimal, it may work for you.
Let me help
bcwave, sometimes you just have to step in and help. Given that you have a VHF, Depth sounder and stereo and assuming you use them in the following fashion: VHF on all the time and it uses 1 Amp Stereo on most of the time and it uses 1 amp depth sounder on while sailing and it uses 0.5 amps Your motor puts out 5 amps while it is running. Your battery (you didn't say how big)is (most likly) a 75 AH (amp-hour) one. You don't want to use more than half of those AH in your battery for lots of technical and lifetime reason so you really have a 75/2= 37.5 AH battery for the purposes of this discussion. So you start out with a fully charged battery or 37.5 AH, You start the motor and motor out to the bay. You have the VHF (1 amp), stereo (1 amp) and depth (0.5) going so you are consuming 1+1+0.5= 2.5 amps but you are producing 5 amps with your motor. You would normaly be charging your battery but your battery is already fully charged so you still only have 37.5 AH when you get to the Bay. You shut off the motor and begin to sail. You are still drawing 2.5 amps like before but now you are drawing them from the battery. 2.5 amps X 1 hour = 2.5 amp hours drawn from your battery each hour you sail. If you sail for 10 hours you will be using 25 AH from your battery. If you sail for 3 hours you will be using 7.5 AH from your battery. Lets say you sail for 5 hours to get to your gunkholing location. That means you have 37.5 - (2.5 X 5) = 37.5 - 10 = 27.5 AH in your battery as you start your motor. If you run your motor for 1 hour (getting complicated here) you will be charging at (5 amps charge - 2.5 amps consumed)X 1 hour = 2.5 AH charge added to your battery each hour you run the motor. So you add 2.5 AH to you AH balance or 27.5 + 2.5 = 30 AH in you battery after one hour of cahrging. You drop anchor and turn off the depth sounder so now you are using just 2 amps each hour or 2 AH. Since your AH balance in you battery is 30 AH, after 8 hours on the hook you will have drained 8 hours X 2 amps = 16 AH from you battery AH balance and you will have 30 - 16 = 14 AH left Where are we; you started a 12:00 motored to the bay and sailed for 5 hours then motored for an hour then where on the hook for 8 hours or 12:00 + 14 hours = 2:00 AM the next day. You turn off the stereo so you are drawing only 1 AH from your battery each hour while you sleep. You wake up at 7:00 AM (6 hours later) and your battery will have 14 - (6 X 1) = 8 AH left in it. You (now) know you are low on battery AH balance and decide to motor with the depth and stereo off (gunkholing right) so your motor will be charging your battereis at 5 - 1 = 4 amps or be putting 4 AH into the battery each hour. If you motor for 1 hour your battery AH balance becomes 8 + 4 = 12 AH. You sail back with only the VHF on arriving 5 hours later and your battery AH balance is 12 - (5 X 1) = 7 AH. It takes you a half hour to motor back to the slip and dock so add 4 X 0.5 = 2 more AH to the battery for a grand AH balance of 7 + 2 = 9 AH surplus for the overnighter. You are still going to have to dink in the battery for charging at home. If you connect to a solar charger for a week you will get something like 15 AH added to the battery which will not bring it up to full charge. If you connect to a wind generator and the wind blows enough to put out 1 amp on average each hour you get 24 AH the first day and 24 AH the second and 24 the third and at that point you are just dumping amps into your battery cause it is charged up. Wind generators are cheaper too. The risk is that the wind will not blow for a 5 days.
bcwave, sometimes you just have to step in and help. Given that you have a VHF, Depth sounder and stereo and assuming you use them in the following fashion: VHF on all the time and it uses 1 Amp Stereo on most of the time and it uses 1 amp depth sounder on while sailing and it uses 0.5 amps Your motor puts out 5 amps while it is running. Your battery (you didn't say how big)is (most likly) a 75 AH (amp-hour) one. You don't want to use more than half of those AH in your battery for lots of technical and lifetime reason so you really have a 75/2= 37.5 AH battery for the purposes of this discussion. So you start out with a fully charged battery or 37.5 AH, You start the motor and motor out to the bay. You have the VHF (1 amp), stereo (1 amp) and depth (0.5) going so you are consuming 1+1+0.5= 2.5 amps but you are producing 5 amps with your motor. You would normaly be charging your battery but your battery is already fully charged so you still only have 37.5 AH when you get to the Bay. You shut off the motor and begin to sail. You are still drawing 2.5 amps like before but now you are drawing them from the battery. 2.5 amps X 1 hour = 2.5 amp hours drawn from your battery each hour you sail. If you sail for 10 hours you will be using 25 AH from your battery. If you sail for 3 hours you will be using 7.5 AH from your battery. Lets say you sail for 5 hours to get to your gunkholing location. That means you have 37.5 - (2.5 X 5) = 37.5 - 10 = 27.5 AH in your battery as you start your motor. If you run your motor for 1 hour (getting complicated here) you will be charging at (5 amps charge - 2.5 amps consumed)X 1 hour = 2.5 AH charge added to your battery each hour you run the motor. So you add 2.5 AH to you AH balance or 27.5 + 2.5 = 30 AH in you battery after one hour of cahrging. You drop anchor and turn off the depth sounder so now you are using just 2 amps each hour or 2 AH. Since your AH balance in you battery is 30 AH, after 8 hours on the hook you will have drained 8 hours X 2 amps = 16 AH from you battery AH balance and you will have 30 - 16 = 14 AH left Where are we; you started a 12:00 motored to the bay and sailed for 5 hours then motored for an hour then where on the hook for 8 hours or 12:00 + 14 hours = 2:00 AM the next day. You turn off the stereo so you are drawing only 1 AH from your battery each hour while you sleep. You wake up at 7:00 AM (6 hours later) and your battery will have 14 - (6 X 1) = 8 AH left in it. You (now) know you are low on battery AH balance and decide to motor with the depth and stereo off (gunkholing right) so your motor will be charging your battereis at 5 - 1 = 4 amps or be putting 4 AH into the battery each hour. If you motor for 1 hour your battery AH balance becomes 8 + 4 = 12 AH. You sail back with only the VHF on arriving 5 hours later and your battery AH balance is 12 - (5 X 1) = 7 AH. It takes you a half hour to motor back to the slip and dock so add 4 X 0.5 = 2 more AH to the battery for a grand AH balance of 7 + 2 = 9 AH surplus for the overnighter. You are still going to have to dink in the battery for charging at home. If you connect to a solar charger for a week you will get something like 15 AH added to the battery which will not bring it up to full charge. If you connect to a wind generator and the wind blows enough to put out 1 amp on average each hour you get 24 AH the first day and 24 AH the second and 24 the third and at that point you are just dumping amps into your battery cause it is charged up. Wind generators are cheaper too. The risk is that the wind will not blow for a 5 days.
A less windy way of doing it
VHF = 1 amp Stereo = 1 amp depth = 0.5 amp you use the VHF 24 hours --> 1 amp X 24 hours = 24 AH you use the stereo 16 hours --> 1 amp x 16 hours = 16 AH you use the depth for 6 hours --> 0.5 amp x 6 hours = 3 AH Total consumption in 1 day --> 24 + 16 + 3 = 43 AH Your motor produces 5 amps and you use it for 2.5 hours --> 5 amps x 2.5 hours = 12.5 AH Total production in 1 day --> 12.5 AH You started with 37.5 AH in the battery so your balance after one day is 37.5 + 12.5 - 43 = 7 AH You need to come up with 37.5 - 7 = 30.5 AH production over the week (5 days) to recharge the battery. That means on average you will need 30.5/5 = 6.1 AH per day production. A solar cell produces for about 8 hours per day in the summer so you will need a cell that produces 6.1/8 = 0.76 amps. Factor in clouds/rain/shading and you can double that or 1.5 amps. That is a 12 volt X 1.5 amps = 18 watt solar cell. $159.95 at WM A wind generator produces all the time the wind blow so we look at an average wind for 24 hours. This means you need the same 6.1 AH production each day but now spread it out over 24 hours or 6.1/24=0.25 amps. Most wind generators will produce 1 amp in a 5-7 knot wind so you can get away with the smallest model. $1024 at WM I'd go with the solar panel unless you anticipate increasing your electrical usage. The next size up in solar panels is a 65 watt one for $700 so solar is still the way to go.
VHF = 1 amp Stereo = 1 amp depth = 0.5 amp you use the VHF 24 hours --> 1 amp X 24 hours = 24 AH you use the stereo 16 hours --> 1 amp x 16 hours = 16 AH you use the depth for 6 hours --> 0.5 amp x 6 hours = 3 AH Total consumption in 1 day --> 24 + 16 + 3 = 43 AH Your motor produces 5 amps and you use it for 2.5 hours --> 5 amps x 2.5 hours = 12.5 AH Total production in 1 day --> 12.5 AH You started with 37.5 AH in the battery so your balance after one day is 37.5 + 12.5 - 43 = 7 AH You need to come up with 37.5 - 7 = 30.5 AH production over the week (5 days) to recharge the battery. That means on average you will need 30.5/5 = 6.1 AH per day production. A solar cell produces for about 8 hours per day in the summer so you will need a cell that produces 6.1/8 = 0.76 amps. Factor in clouds/rain/shading and you can double that or 1.5 amps. That is a 12 volt X 1.5 amps = 18 watt solar cell. $159.95 at WM A wind generator produces all the time the wind blow so we look at an average wind for 24 hours. This means you need the same 6.1 AH production each day but now spread it out over 24 hours or 6.1/24=0.25 amps. Most wind generators will produce 1 amp in a 5-7 knot wind so you can get away with the smallest model. $1024 at WM I'd go with the solar panel unless you anticipate increasing your electrical usage. The next size up in solar panels is a 65 watt one for $700 so solar is still the way to go.
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