i'm looking into what size small generator i might need to charge the 2x80 A/hr batt bank on my hunter 23. if i use the formula p=ie i get my capacity at 1920W. looking at small 1000W generators it looks like i could recharge my batteries in 2 hours max. BUT, when i see these 1000W generators rated at 8A-12V, that tells me i would need 20 hrs to charge my batteries. what am i missing here? any recomendations on small, quiet, economical on gas, 4 stroke generators? is this a practical alternative? i hope to use this as back-up to solar but obviously a 23' boat can't carry a lot of solar panel. tia~ william
generator size vs battery capacity question
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Generators are AC output c/w DC Auxillary
You’re Ohm’s Law calculation is correct, but missing the Battery’s Efficiency Factor - which might be assumed to be 125% - hence P = (I x E) x 1.25 = 160A x 14.4V = 2304W x 1.25 = 2880 Watts (200A @ 14.4V). Your re-charging time is limited by the battery’s Acceptance Rate - how much current it will accept, and by your Charging Source Output. Assuming a 25% Acceptance Rate (2880 x 0.25 = 720), you will require about 720 Watts (50A) of power for 4 hours (minimum). The 1000 Watt Generator is a 120VAC Source of Power (which could power a 60 Amp Battery Charger) which would accomplish the task in 4 hours. Were you to use the Generator’s internal 8 A DC source, it would take about 25 Hours to recharge. Clear as mud ??? Gord
You’re Ohm’s Law calculation is correct, but missing the Battery’s Efficiency Factor - which might be assumed to be 125% - hence P = (I x E) x 1.25 = 160A x 14.4V = 2304W x 1.25 = 2880 Watts (200A @ 14.4V). Your re-charging time is limited by the battery’s Acceptance Rate - how much current it will accept, and by your Charging Source Output. Assuming a 25% Acceptance Rate (2880 x 0.25 = 720), you will require about 720 Watts (50A) of power for 4 hours (minimum). The 1000 Watt Generator is a 120VAC Source of Power (which could power a 60 Amp Battery Charger) which would accomplish the task in 4 hours. Were you to use the Generator’s internal 8 A DC source, it would take about 25 Hours to recharge. Clear as mud ??? Gord
clear as a bell Gord
i was sorta ballparking the 12V vs 14.4V but i really didn't understand the 1.25 efficiency factor. so you're saying that the DC output on the small generators is the pits and i would be better off looking at using a generator to power a charger. i hate overcomplication. :{ william
i was sorta ballparking the 12V vs 14.4V but i really didn't understand the 1.25 efficiency factor. so you're saying that the DC output on the small generators is the pits and i would be better off looking at using a generator to power a charger. i hate overcomplication. :{ william
Sizing Information
William A Google on Honda generators comes up with the link. May be of use. Try the wattage calculation link, and other information. A Google on generator sizing should also help. Stu
William A Google on Honda generators comes up with the link. May be of use. Try the wattage calculation link, and other information. A Google on generator sizing should also help. Stu
you are also assuming
that you are charging your batteries from a totally discharged state. Hopefully that will never happen. Batteries should never be discharged more than 50%. It's better to keep them above that. As a battery rises above 75% state of charge, amperage needs to be tapered off to prevent overheating of the batteries. So you need to use a good 3 stage charger anyway. You won't get that from the DC side of a small generator. The other advantage of having the generator run an AC battery charger is that when the boat is in a slip or on a trailer you can charge the batteries from shore power.
that you are charging your batteries from a totally discharged state. Hopefully that will never happen. Batteries should never be discharged more than 50%. It's better to keep them above that. As a battery rises above 75% state of charge, amperage needs to be tapered off to prevent overheating of the batteries. So you need to use a good 3 stage charger anyway. You won't get that from the DC side of a small generator. The other advantage of having the generator run an AC battery charger is that when the boat is in a slip or on a trailer you can charge the batteries from shore power.
I forgot
to say you can get a 1000w yamaha 4 stroke generator on ebay new for about $675.00. It weighs under 30lbs and uses an inverter coupled to a DC generator to produce 120V AC. the result is a very clean AC waveform that always produces 60 Hz. Other generators will vary the frequency slightly with varying loads. Also the engine rpm will vary with the load. When you have a light load the engine slows down considerably. I have used these, they work very well and are very quiet.
to say you can get a 1000w yamaha 4 stroke generator on ebay new for about $675.00. It weighs under 30lbs and uses an inverter coupled to a DC generator to produce 120V AC. the result is a very clean AC waveform that always produces 60 Hz. Other generators will vary the frequency slightly with varying loads. Also the engine rpm will vary with the load. When you have a light load the engine slows down considerably. I have used these, they work very well and are very quiet.
How to pipe the AC current in..
I was just looking at the Yahama generators on eBay. If I have shore power do I plug the generator output into the shore power and run the 3 stage charger that way or do a direct extension cord to the charger. Thanks, Dan B Sotto voce 1973 Catalina 27 Dinette
I was just looking at the Yahama generators on eBay. If I have shore power do I plug the generator output into the shore power and run the 3 stage charger that way or do a direct extension cord to the charger. Thanks, Dan B Sotto voce 1973 Catalina 27 Dinette
Plug into shore power
If you have shore power and your charger is wired in, then plug into your shore power. Depending on your exisitng shore power system you may need to make up an adaptor to go from the standard 15 amp U ground receptical on the generator to your 20 or 30 amp connection on the boat.
If you have shore power and your charger is wired in, then plug into your shore power. Depending on your exisitng shore power system you may need to make up an adaptor to go from the standard 15 amp U ground receptical on the generator to your 20 or 30 amp connection on the boat.
..... and a question
How do those of you who have gasoline gensets store them on board. I go out of my way to make sure the gasoline for the tender's outboard is stored lashed to the rail so no fumes get below. The generator containing gasoline is essentially the same hazard, however I am sure the generator would disappear if I lashed it to the rail (and if I was in salt water it would corrode). I realize that a propane type locker vented overboard would be best, however has anyone come up with a better idea?
How do those of you who have gasoline gensets store them on board. I go out of my way to make sure the gasoline for the tender's outboard is stored lashed to the rail so no fumes get below. The generator containing gasoline is essentially the same hazard, however I am sure the generator would disappear if I lashed it to the rail (and if I was in salt water it would corrode). I realize that a propane type locker vented overboard would be best, however has anyone come up with a better idea?
Honda 2kw
Makai carries a 2kw Honda gas generator. We store it in a locker that is ventilated overboard. We have been using it for almost a year and it has worked and held up well. When in use we keep it on the dive platform or on the bow with a lock and cable. We have 600 Amp battery bank with a 2.5KW Heart invertor. at about 60% it takes about 2 hours to recharge to float. The only time we use it is when we run the watermaker all day and the it is cloudy. Otherwise soalr maintains our house bank. As mentioned earlier we just plug the generator into the shore pwoer outlet via a 110 to 30amp cord adapter Genset size. Gas generators are more efficent on fuel at lower loads (unlike diesel). A 1KW generator is the peak load recommended, but the operating load is generally lower. I would recommend a little large genset as we only paid $900 for the 2kw Honda last year. The generators are much quiter when they are not loaded up and the fuel efficency is better. The weigh difference and the overall nosie are not significantly different. We have met cruisers who have had the 1KW and the genset were not able to run power tools.
Makai carries a 2kw Honda gas generator. We store it in a locker that is ventilated overboard. We have been using it for almost a year and it has worked and held up well. When in use we keep it on the dive platform or on the bow with a lock and cable. We have 600 Amp battery bank with a 2.5KW Heart invertor. at about 60% it takes about 2 hours to recharge to float. The only time we use it is when we run the watermaker all day and the it is cloudy. Otherwise soalr maintains our house bank. As mentioned earlier we just plug the generator into the shore pwoer outlet via a 110 to 30amp cord adapter Genset size. Gas generators are more efficent on fuel at lower loads (unlike diesel). A 1KW generator is the peak load recommended, but the operating load is generally lower. I would recommend a little large genset as we only paid $900 for the 2kw Honda last year. The generators are much quiter when they are not loaded up and the fuel efficency is better. The weigh difference and the overall nosie are not significantly different. We have met cruisers who have had the 1KW and the genset were not able to run power tools.
Bit You Are Missing
William, The bit you are missing is the dratted small generators all have a 12/15 Volt DC output at about 8 amps which is only about 180 watts - but their line voltage output (120 or 220 V) is 600 watts or more. The trick is to use the line voltage output and feed it into a battery charger rated to take the full output from the generator. Beware, the clever multi stage chargers sometimes do not like the AC waveform of these small generators but all the simple non-regulated ones couldn't care less and are much cheaper.
William, The bit you are missing is the dratted small generators all have a 12/15 Volt DC output at about 8 amps which is only about 180 watts - but their line voltage output (120 or 220 V) is 600 watts or more. The trick is to use the line voltage output and feed it into a battery charger rated to take the full output from the generator. Beware, the clever multi stage chargers sometimes do not like the AC waveform of these small generators but all the simple non-regulated ones couldn't care less and are much cheaper.
Generator Sizing
Just looking over the thread. One thing you should be clear on is that the specs for both the Honda and Yamaha 1000 type generators indicate that the capacity is really only about 900 watts continuous. (You should check the specs - that is from memory) In addition while it would be nice to think that they would run a 50 amp DC output charger I have been told by someone who tried that the Honda wouldn't run his 50 amp charger. If the 50 amp charger was 100% efficient in theory it would draw a bit over 700 watts at 14.4 volts output. (if it were 100% efficient) However the chargers are something less - perhaps 70 or 80% which means you are likely over the rating for the generator. I have bought a Yamaha EF1000iS which should handle my 30 amp charger. However don't expect it to handle a microwave (not of concern to us). Both the Honda and Yamaha inverter generators output pure 60 cycle sine wave power as has been said earlier (as Donalex has indicated some generators do not output pure sine wave power and some chargers do not like this, howeve both the Yamaha and Honda inverted output generators can be used even with computers). The DC output of both the Honda and Yamaha although relatively low in amps is unregulated as has been already said you don't want to plug it into your battery and leave it as it does not taper down to a trickle charge. You could plug it in for short periods depending on your battery and its state of charge. As already said - it is better to use the generator to power a proper 3 stage AC charger - it will be faster and properly regulated.
Just looking over the thread. One thing you should be clear on is that the specs for both the Honda and Yamaha 1000 type generators indicate that the capacity is really only about 900 watts continuous. (You should check the specs - that is from memory) In addition while it would be nice to think that they would run a 50 amp DC output charger I have been told by someone who tried that the Honda wouldn't run his 50 amp charger. If the 50 amp charger was 100% efficient in theory it would draw a bit over 700 watts at 14.4 volts output. (if it were 100% efficient) However the chargers are something less - perhaps 70 or 80% which means you are likely over the rating for the generator. I have bought a Yamaha EF1000iS which should handle my 30 amp charger. However don't expect it to handle a microwave (not of concern to us). Both the Honda and Yamaha inverter generators output pure 60 cycle sine wave power as has been said earlier (as Donalex has indicated some generators do not output pure sine wave power and some chargers do not like this, howeve both the Yamaha and Honda inverted output generators can be used even with computers). The DC output of both the Honda and Yamaha although relatively low in amps is unregulated as has been already said you don't want to plug it into your battery and leave it as it does not taper down to a trickle charge. You could plug it in for short periods depending on your battery and its state of charge. As already said - it is better to use the generator to power a proper 3 stage AC charger - it will be faster and properly regulated.
Would it be possible?
for those of you contributing to this interesting thread to state the size of your vessel or craft? It makes a BIG difference to the understanding of those of us who read them, and to how, for instance, we can make use of the storage ideas you propose. Thanks. From what I understand, the "best" recommendation is to use a 1,000 to 2,000 watt AC generator to plug into existing shorepower outlets. Wow, what could be simpler? Stu
for those of you contributing to this interesting thread to state the size of your vessel or craft? It makes a BIG difference to the understanding of those of us who read them, and to how, for instance, we can make use of the storage ideas you propose. Thanks. From what I understand, the "best" recommendation is to use a 1,000 to 2,000 watt AC generator to plug into existing shorepower outlets. Wow, what could be simpler? Stu
efficiency etc...
Good thread ... Malclom Young Was correct about charger efficiencies (missing from my original post): ie - Xantrex Spec’s: True-Charge Efficiency @ 85% -&- Pro-Sine (Inverter/Charger) 81% on Charger. Reudi Ross also correctly points out that you should never be re-charging your batteries from more than 50% DOD. “Southbound” (a C&C 29) carried a 600 Watt Yamaha Portable Gas Generator, stored (empty of fuel) in a plastic box lashed in front of the helm (was our cockpit table). In use aboard (also used it ashore), it was located downwind of the companionway. Fuel was stored in Jerry Can on Rail (marked “no oil”). Connection was via either 15A 120VAC “Generator/Charger Inlet” or via “15-30A Adaptor & Shore Power Inlet” (had both - Gen. Inlet wired to DPDT Selector Switch on Charger, Shore Power wired to AC Panel). The 600 W Genny operated the 60A “Ferro-Resonant” Charger (3-20A Battery Outputs tied together), or the 20A “True-Charge” (3-Stage) Charger. Only used the DC Output once or twice (playing around). Don’t bother with it (see Donalex’ post). I’m not certain what the Genny waveform output (true sine or square sign) was - but the Xantrex “True-Charge” claims to accept any waveform input, 90 - 135VAC, & 50-60 Hz. frequencies. The whole idea of using a portable gas generator is kind of “Micky Mouse” - and not what I’d normally recommend - but what are you going to do on a small boat (28.5' LOA, in our case) with aspirations towards “long legs” (6 months at anchor, in our case)? FWIW, Gord
Good thread ... Malclom Young Was correct about charger efficiencies (missing from my original post): ie - Xantrex Spec’s: True-Charge Efficiency @ 85% -&- Pro-Sine (Inverter/Charger) 81% on Charger. Reudi Ross also correctly points out that you should never be re-charging your batteries from more than 50% DOD. “Southbound” (a C&C 29) carried a 600 Watt Yamaha Portable Gas Generator, stored (empty of fuel) in a plastic box lashed in front of the helm (was our cockpit table). In use aboard (also used it ashore), it was located downwind of the companionway. Fuel was stored in Jerry Can on Rail (marked “no oil”). Connection was via either 15A 120VAC “Generator/Charger Inlet” or via “15-30A Adaptor & Shore Power Inlet” (had both - Gen. Inlet wired to DPDT Selector Switch on Charger, Shore Power wired to AC Panel). The 600 W Genny operated the 60A “Ferro-Resonant” Charger (3-20A Battery Outputs tied together), or the 20A “True-Charge” (3-Stage) Charger. Only used the DC Output once or twice (playing around). Don’t bother with it (see Donalex’ post). I’m not certain what the Genny waveform output (true sine or square sign) was - but the Xantrex “True-Charge” claims to accept any waveform input, 90 - 135VAC, & 50-60 Hz. frequencies. The whole idea of using a portable gas generator is kind of “Micky Mouse” - and not what I’d normally recommend - but what are you going to do on a small boat (28.5' LOA, in our case) with aspirations towards “long legs” (6 months at anchor, in our case)? FWIW, Gord
Cruiser
Makai is a 38 foot Voyage Yacht. We have been living a board in the Cribe. Makai is priamrily powered by solar and shortly a wind gen will be added. We chose the the portable genset as a low cost alternative to an $8,000 permanent genset. It is meant to be a limited use item and does not run daily. At anchor it is rarely used. As Gord said it is somewhat Mickey Mouse, but I believe it is an effective low cost alternative. We see a of lot of cruisers with samll to large boats using a portable. I don't belive it should be used as a permanent soultion.
Makai is a 38 foot Voyage Yacht. We have been living a board in the Cribe. Makai is priamrily powered by solar and shortly a wind gen will be added. We chose the the portable genset as a low cost alternative to an $8,000 permanent genset. It is meant to be a limited use item and does not run daily. At anchor it is rarely used. As Gord said it is somewhat Mickey Mouse, but I believe it is an effective low cost alternative. We see a of lot of cruisers with samll to large boats using a portable. I don't belive it should be used as a permanent soultion.
Alternator??
What if I bought a 3hp Tecumseh motor with a horizontal shaft for under $300.00 and then attached it to a self regulating self exciting alternator say 45 amp GM for about $50.00 via an appropriately sized pulley??? It would seem like a simple solution and cheap.Mount the engine and alternator on a simple platform the alternator would have to be grounded to the battery and the positive single wire lead to the positive pole. No complications involving inverters etc. A 3hp motor should easily drive a 45amp alternator. Tom
What if I bought a 3hp Tecumseh motor with a horizontal shaft for under $300.00 and then attached it to a self regulating self exciting alternator say 45 amp GM for about $50.00 via an appropriately sized pulley??? It would seem like a simple solution and cheap.Mount the engine and alternator on a simple platform the alternator would have to be grounded to the battery and the positive single wire lead to the positive pole. No complications involving inverters etc. A 3hp motor should easily drive a 45amp alternator. Tom
poor solution
Tom: The general rule of thumb is: Diesel Engine ~ 1 HP for each 30A (12V) of Alternator Output Gas Engine ~ 1 HP for each 15A (12V) of Alternator Output So your 3HP Engine SHOULD power your 45A Alternator. BUT - It’s a poor solution!
Tom: The general rule of thumb is: Diesel Engine ~ 1 HP for each 30A (12V) of Alternator Output Gas Engine ~ 1 HP for each 15A (12V) of Alternator Output So your 3HP Engine SHOULD power your 45A Alternator. BUT - It’s a poor solution!
Why??Gord give your reasoning please
Hi Gord: Please give me us reasoning. My reasoning is expense and simplicity. I like self regulating alternators in that they put out 14.4 volts which is ideal for wet cell batteries. If you are running a motor to charge I assume you don't worry about the final 10% of charging that requires a long time of motor running. With the alternator you don't lose efficency by having to convert AC to DC. I know that an alternator converts AC to DC but it is more efficent than a simple DC generator. I assume that the Honda generator is actually an alternator. Your reasoning is probably very sound but just saying that it is a poor choice isn't very enlightening. Thanks Tom BTW I think that a gasoline powered generator on a boat is generally a bad ideal.
Hi Gord: Please give me us reasoning. My reasoning is expense and simplicity. I like self regulating alternators in that they put out 14.4 volts which is ideal for wet cell batteries. If you are running a motor to charge I assume you don't worry about the final 10% of charging that requires a long time of motor running. With the alternator you don't lose efficency by having to convert AC to DC. I know that an alternator converts AC to DC but it is more efficent than a simple DC generator. I assume that the Honda generator is actually an alternator. Your reasoning is probably very sound but just saying that it is a poor choice isn't very enlightening. Thanks Tom BTW I think that a gasoline powered generator on a boat is generally a bad ideal.
Tecumseh/Alternator
Tom, You'll sound like a lawnmower running in the anchorage. Won't be near as quite as the Honda. It will sound like the 4-5 kw units that ran for days after our last hurricanes. Bill
Tom, You'll sound like a lawnmower running in the anchorage. Won't be near as quite as the Honda. It will sound like the 4-5 kw units that ran for days after our last hurricanes. Bill
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