generator size vs battery capacity question

[Malcolm Young]

Advantages of inverter gensets

P323ms - I agree that your solution may be cheaper and would work to produce regulated DC power for charging batteries. (although it would be not regulated to properly charge deep cycle batteries).However I have several reasons to use gensets designed as such:1. A whole lot less noise. The gensets are designed to be very quiet - 47 to 57db - it would sound like someone talking normally at the next restraurant table. With one running you can easily carry on a conversation sitting next to it. What you are talking about will be as noisy as a gas lawn mower. Others anywhere nearby will not like you.2. The gensets are a lot more compact and light. The Yamaha (and Honda is similar) is about 17.7"x9.4"x14.9" and both weigh around 28lbs.3. Fuel economy - the gensets are designed to do exactly what you want - the Yamaha will run 12 hours on O.66 gallons of fuel at 1/4 load. Try that on the Techumseh.4. Auto throttle that adjusts speed to load - this saves fuel and reduces noise. In your arrangement you would have a governor however it is not geared well to generator load. 5. Abiltity to use AC devices - you can power small handtools or a computer with a small generator (or a microwave and larger handtools with a larger generator)6. The gensets are better able to seal off methods of gas fume escape (read explosion possibility)- fuel shut off to burn fuel out of carbuerator and fuel tank vent shut off (similar to small outboards (- still not perfect thus concerns re. storing)7. The gensets are designed to reduce vibration - if you have one running on your deck you will be happier. A better place at anchor would be to run a portable genset is a swim platform (if you have one) or I have heard that people put them in the dinghy and run the power to a stern AC connector. This would be safer from a CO (carbon monoxide) point of view.8. The output of engine of about 2hp operates a generator which can supply at least a 30 amp 14.4volt output charger and most likely a 40 amp charger.9, You can touch the outside case of one of the gensets I am talking about (not at the exhaust of course)A genset designed for the purpose may cost a little more, however the benefits are worth it.

 

[Fred Ficarra]

And Tom,

if it were that simple, generators as we know them would not exist.

 

[p323ms]

Good reasons

A few years ago I saw plans for making a portable generator on the internet. Of course they were talking about remote locations or emergency power. Something to sit in a garage or back of a truck.  I have never seriously considered putting a gas generator on my boat. Soon I will install two large solar panels over my bimini to power the refrigerator as my wife is tired of using ice chests. Our present power consumption is being met by the alternator when we do incidental motoring. Our power demands right now are low only the depth sounder, radio and Navigation/reading lights. I try to leave the dock with the batteries fully charged.Tom

 

[Gord May]

see: Bill, Malcom.,

Tom:Bill, Malcolm,

 

[william3045]

great information all...so ballparking again...

my first course of action is just plain conservation. on a 23' boat i carry very few aminities to begin with. VHF, SW Rx, depth sounder, running lights, cabin lights, 1500W inverter. i plan on taking my small 5W solar and making a dedicated battery charging system for NiMH/LiIon batteries for computer, GPS, cell phone, flashlights, etc, and adding possibly 80W solar w/ charge controller on the stern for my main bank. (murphy's law says the sun will always be the other direction here tho).so, as shore power has always been an option, it looks like installing a 110, 15A shore power input, running the AC output of a 1000W Honda or Yamaha into it, and running a 3 stage, 40A charger off of it, is about as "simple" as i can get to keep batteries topped off. (this will have to be switchable won't it as i can't run both solar and "non-solar" charging simutaniously?)again, i have a habit of "ballparking" so does this sound about right? and i agree with Ruedi, i would never let my batteries go totally dead. i understand the loss due to efficiencies, but i like to work to a worst case scenerio. (my degree is actually electronics with a bent toward physics but all the formula in the world don't make-up for the experience and advice of someone thats actually "been there-done that"). thanks again~william

 

[Gord May]

30 Amp

William:I’d go with a more conventional 30A 120VAC Shore Power Inlet, even if the 15A would drive your assemblage. Gord

 

[jmcclain]

Am I missing something?

Forgive for asking the obvious, but is your Hunter a trailerable boat, or is it in the water? Do you have access to shorepower? If either is the case, it would seem to me that a small 110V charger and additional batteries would be the much more economical. Sounds like the time to do a power audit. A generator, large 110V charger, etc seems to be a bit of overkill to me.Jon

 

[p323ms]

Wow a lot for 23'

What do you do on your boat???? On our old Mac 26 two deep cycle batteries kept us going for a week on the hook. No charger at all. Even with the pearson 323 we have two 200 amp hour deep cycle batteries and only the diesel's alternator to stay out a week. I suggested a television but the wife said that if we are going to sit and watch TV we might as well stay at home.Of course we believe that a boat is a place to get away from it all.Tom

 

[william3045]

yeah, seems like a bit of overkill, but...

first off i believe in overkill/redundancy/contengency planning. i have no alternator on my nissan 5 outboard. i keep the boat in the water in the summertime without shore power although i do have a trailer. limited number of slips w/ power even if i wanted to get gouged for them and no transient slips if i just wanted to spend the night to charge. i have 4 day "weekends" so 2-3 days on the hook is nothing but getting recharged after that can be iffy before next weekend. i have a 7 week sabatical from work coming up that i plan on spending at lake texoma and hopefully after that i would like to sail the ditch down on the s texas coast for a couple of weeks. being as independent as possible of shore power is my goal. hopefully the solar and generator will go with me to a larger boat someday. i suppose if i calculated 1 night/wk in a marina transient slip getting charged-up, if there were any on my lake, vs the cost of buying a system to be independent of shore power i would see which is truly more "economical" but, then there's that independence thing again. :{ williambtw, thanks Gord. i meant 120V 15A but since i'm not familiar w/ shore power standards i'll opt for 120V/30A.

 

[Malcolm Young]

I must apologize

WilliamI was writing my reponses generally based on other responses in the thread and my own experience with my current boat. In my previous boat with battery capabilities similar to yours (before I had refrigeration) I could last almost a week anchoring without charging the batteries, however we were quite frugal with power.The big question in your power needs is what do you need the 1500 watt inverter for? Otherwise I would go along with what Tom and Jon had to say as you apparently don't have refrigeration. I certainly understand your desire for indpendence. Getting away totally on your own is great.

 

[william3045]

1500W inverter

Malcolm, thanks... truthfully, so far i have NEVER needed it. it isn't even hooked-up yet! (i have a 400W hooked-up). but, once again its one of those contengency things. it doesn't cost me any more pwr to let a 1500W inverter sit idle than it does to let a 400W sit idle. (and a 1500W could handle allot more than just charge a cell phone if necessary). most importantly tho, it was given to me new in the box!

 

[John Nantz]

Start Up Power Requirements for Generator

William - it's good that you're asking these questions. This morning I read a number of answers in response to your post and many have provided good information.What I'd say is that finding a generator doesn't necessarily lend itself to the standard calculations that you would normally think. For instance, as was pointed out, a 1000W generator doesn't produce a 1000 watts continuously. At least the Honda doesn't. It's continuous rated output is 900W. This is just one example of why just running the numbers through formulas won't give you the right answer unless the right numbers are used. Also pointed out is the inefficiency of the inverter, the acceptance rate for the batteries, etc. All important considerations.One very important thing that hasn't been stated is that some inverters will require a rush of current when they first start up and this will trip the breaker on a generator. For example, the Heart 1000 a.k.a. Freedom 10 that I have, it's an excellent inverter/charger with a three-step charger, one that has been around for years and was one of the best. However; it will kill a EU1000i generator! By kill I mean it will overpower it as the inverter kicks in and trip the generator circuit breaker. I know because I have one.There is an optional LED control panel available for the Heart which allows one to reduce the charge rate in increments down into the 30/20/and I think 10A range. The toggle switches are on the backside of the panel and it takes a very small tool or pen to set them. It's a total pain. Even so, my experimentation with this inverter showed that even at the reduced settings there is still a large current thats required at startup - enough to trip the breaker on a 1000W generator.Recommendation: Use the 1000W generator because of it's light weight compared to the 2000W but go with a smaller inverter/charger. If it's a Xantrex inverter/charger you want (these are the people who bought out Heart) call their tech desk (toll free) and talk to them about your plans. Taking what you've read here, and knowing what you know about electrical forumulas, they should be able to tell you what Xantrex inverter/charger would be a good unit to marry up with a 1000W generator like the Honda or Yamaha.Plan to use the AC output on the generator - not the DC output - because there is more power available. If your boat has a shorepower connection just run the connectiong cord to it from the generator. If not, with the new inverter/charger it would be good if you would add one.If you use the boat on salt water (you're in Colorado so this might not happen) avoid exposing the generator to salt air because it isn't marinized. Keep it covered whenever possible and out or away from the salt air and not below deck in an improper space.Otherwise, it sounds like a real fun project.

 

[Stu Jackson]

Inverter Question for John

JohnI understand the inverter kicking in to drop the generator, but why would you use the inverter at all when the generator is running and producing AC?If the Freedom 10 is wired (the same as my Freedom 15), then when shorepower (or the generator - if it is plugged into the shroepower inlet) is connected, the inverter is off. Shouldn't be able to run both AC sources at same time.Please help me understand. I think perhaps you are referring to the charger side of the combo inverter / charger Freedom unit that is popping the generator breaker.Thanks,Stu

 

[John Nantz]

Using Charger side of Inverter

Stu - your thinking is correct, I was using the charger side of the inverter and this is what causes the generator circuit breaker to trip. We basically use 12V power on board, for lights, refrigeration (the biggest load), charging the cell phone, and probably a few other things, hence my primary use for the generator is to charge the batteries. We've used other things, though, that take 110VAC like used a vaccuum, hot plate, microwave, and maybe something else but charging batteries is the main purpose for the generator. We never have a need for an airconditioner hence the smaller generator.Charging:To expand on this further, for batteries I've got four golf golf carts plus a group 27 start. The inverter (inverter/charger but I'll call it the inverter from now on) will put out up to 50A DC when charging which is a fairly hefty current. When the batteries are fairly discharged the inverter/charger, according to the control panel, will cycle up to 50A, stay there momentarily, then trip the breaker on the generator.However, it can work. If the batteries are not very discharged the inverter will cycle up to, or maybe just close to, 50A, pause a bit, then start decreasing fairly quickly. As the panel shows the current ramping up the generator starts to indicate it's working harder until it's at or near full power output. If conditions are right the inverter DC current will start droping while the generator is still working hard. With any luck the generator will stay on without having it's breaker tripped and continue to charge the batteries. Hence, there is a point where if the batteries are not discharged too much that the inverter will stay on. What I've found is by breaking the batteries down into smaller banks I can charge one bank of batteries at a time and then when each one has been charged somewhat they can be combined and I can top them off.For my system, because of the inverter, if I had it all to do over again, I'd go with the 2000W generator. For someone who hasn't invested in an inverter/charger yet they should find one with either better contols over the inverter or just go with a smaller one.The main problem with my setup are the dip switches on the back of the control panel - you can't get at them without opening up the main panel and then they're hard to switch. There is no sense in reducing the charge rate much below the generator output because then you're loosing the generation capacity you've paid for.Our cruising style is similar to William's where we like to sit on the hook for a while and I hate to run the engine for battery charging. It's an abusive use of the diesel engine because it carbons it up and wears it out.Maybe this will help everybody to understand my concerns with the smaller generator and a large inverter/charger, or maybe just one of this type. The Xantrex tech people understand the problem and can recommend a good solution (I hope).

 

[p323ms]

Do the numbers on an outboard

You might get enough amp hours with a combination or a charger on your outboard and a solar panel!!! Maybe a flexible solar panel. I don't know your style of sailing but a lot of sailors will motor an hour or two a day. So even with a little 5 amp charger on your outboard that would be 5-10 amp hours/day. Throw in a few more amp hours from solar.I don't know if anyone mentioned it but the cheapest way to add power is to buy a couple of extra batteries. One 200 amp hour battery might be enough to supply your needs for a long weekend. Sure batteries take up space but so do generators and fuel. It is also possible to charge off of your tow vehicle!!! When you do the math unless you want to stay out a long time adding a battery is the way to go.Tom

 

[Stu Jackson]

John, Thanks

I got it and agree. I have a Link 2000 which I bought in '98 when I put the I/C in. I haven't installed the Link yet, but am sure from the instruction manual that it can be used to modify the output of the charger, since you say you can output 50 amps from the charger, what happens when you're just on a 30 amp service? I guess it's too much of a hassle to do the dip switches, and panel you have, the Link 1000 and my 2000 all let you control the output of the charger to a lower level to stop bumping the generator. Of course, the trade-off is that it'll take longer to charge the batteries, but if it's dropping down to 30 after 50 at startup, what's the difference? If I read your thread, even at 30 output it blips the smaller generator you have. Think I finally got it.Thanks again.Lotsa fun here.Stu

 

[Daniel Jonas]

Am I Missing Something?

Seems we keep mixing 120 volt amps and 12 volt amps. My shore power is 120 volts and a 30 amp service. My 12 volt charger puts out up to 100 amps charging the batteries (although we rarely see over 80). The charger should only be pulling about 8 amps or so off the 120 volt 30 amp service to produce that 80 amps at 12 volts (I'm rounding here and allowing a little for inefficiency).I'm pretty sure that I have this right, but if not, someone please explain why my 100 amp charger works off the 30 amp service. It seems that the amps are being used interchangably without conversion in some instances here.A 2000 watt generator should run a 100 amp charger easy. 2000 watts/120 = 16.66 Amps at 120 volts or 166.6 amps at 12 volts.Even at 900 watts/120 = 7.5 amps at 120 volts or 75 amps at 12 volts it seems it should run a 50 amp charger, although if much else is running and with lost efficiencies, that would be close. So John must just be on the edge with the 1000 watt generator.Sorry, just felt this thread needed some clarification on the math. So I really hope I have it right.Dan Jonas (S.V Feije II)

 

[Gord May]

Right

Daniel’s absolutely correct !Watts (Power) = (Volt x Amps) / EfficiencyHence Amps vary inversely with volts (ignoring efficiency) - in the case of 12VDC vs 120VAC by a factor of about 10 (near enough).Thanks Daniel ...Gord

 

[John Nantz]

Ans: for Stu

To answer some questions:Stu - "since you say you can output 50 amps from the charger, what happens when you're just on a 30 amp service?" Ans: The 30amp service is 110 vice the 50amp charging output of the inverter which is amps @12V. My mistake for not saying this was the amps at 12V.It's when the large inverter charge mode kicks in that it pops the Honda circuit breaker. I make sure the hot water heater is turned off and there are no other significant AC loads.Good questions Stu - hope this helps.

 

[Gord May]

I said 10x but factor of 8 closer

So a 50A 12VDC output requires > 5A* 120VAC input [probably closer to 6.25A] ~ hence a factor 8 would be a more practical rule of thumb (120v to 12V)*> due to inefficiencies.