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Old 05-07-2016, 11:46 AM   #1
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What size generator do I need?

I am sure this question will draw some attention.

I own this battery charger.

http://www.harborfreight.com/10250-amp-12v-manual-charger-with-engine-start-60653.html

I want to use it to keep my batteries charged when boon docking. Will run my batteries to about 50% charge then bring them back up to full charge using this charger.

My question is what size generator will I need and roughly how long will it take to bring the batteries back to full charge? Will a 1000 watt generator work alright using this?

Jim
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Old 05-07-2016, 12:31 PM   #2
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That generator would be large enough. Why not use the charger built into your camper? The charge you linked to will probably charge at a slower rate than the one in you trailer. If you want to use an external charger try to find a 3 or 4 stage unit.
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Old 05-07-2016, 01:58 PM   #3
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FYI: Before my amputation I use to fish using a deep cycle battery and electric motor on my boat. I used this charger and this inverterhttp://www.harborfreight.com/750-watt-continuous-1500-watt-peak-power-inverter-66817.html to charge the battery in the evening. I would hook the inverter up to my truck when I came back to my camp site. It worked OK but don't think it would work too well on my two trailer batteries except for an emergency case.
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Old 05-07-2016, 03:00 PM   #4
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If you don't plan on running the microwave and just want it to recharge the battery, then a 1000w will be fine.

Unless you've got and older trailer, not sure why you just don't plug the trailer's shore cord into the generator.

That's what we've been doing with our '07 Roo and Honda 2000i, for nearly 10 years and works great.
Don't have to haul around a separate charger.
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Old 05-07-2016, 03:50 PM   #5
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Originally Posted by Happy Vibe View Post
That generator would be large enough. Why not use the charger built into your camper? The charge you linked to will probably charge at a slower rate than the one in you trailer. If you want to use an external charger try to find a 3 or 4 stage unit.
You are right, it would be foolish not to just use the existing converter. I just researched it and it will charge up to 55 amps when nothing is running. If I was running a few LED lights and my LED TV that charge rate might drop down to 45 amps, maybe 40 amps? I didn't realize it had that high of a charge rate. I knew it had a 55 amp output but didn't think it would use all of it for charging. Today is not a wasted day, I learned something! Will still keep my charger, worked good for my boat. Might need it someday to start my truck but not for a while. Recently had it checked so know its in good shape.

Now, if I am thinking right (I admit I am going brain dead!) a 1000 watt generator is only going to supply about 28% of what my 30 amp converter is capable of using? So at 28% times 55 amps means the converter would supply a charge rate of around 15.4 amps. I am sure someone will argue with me on my thinking. A 30 amp converter could utilize 3600 watts and a 1000 watts is roughly 28% of that, so its output would be limited to 28% of its 55 amp charging capability? That would be 15.4 amps, right?

Now, am I overthinking this whole thing, LOL?

Jim
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Old 05-07-2016, 04:17 PM   #6
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Y
Now, if I am thinking right (I admit I am going brain dead!) a 1000 watt generator is only going to supply about 28% of what my 30 amp converter is capable of using?...
No, I think you have that wrong. Let's say you have a 55 amp converter and it is trying to charge your batteries at full current and let's say that would be at a voltage of 14 volts. 55 amps x 14 volts = 770 watts. Remember the 55 amps is at 14 volts, not 120 volts. Now there are efficiencies in the converter to consider, but a 1000 watt generator will handle that fine and have a little left over for other things.

Now for the hard part. If you really get 55 amps, for each hour you run you will put 55 AH back in your batteries. But you won't get 55 amps for that long and it will take quite a while to get back 100 AH, say conservatively about 3 hours of generator time.
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Old 05-07-2016, 04:58 PM   #7
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Thing is that it usually only costs a little more for a 2000w unit.
Personally, it's not worth buying a 1000w unit, since the 2000w units are so close in price.
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Old 05-08-2016, 10:03 AM   #8
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No, I think you have that wrong. Let's say you have a 55 amp converter and it is trying to charge your batteries at full current and let's say that would be at a voltage of 14 volts. 55 amps x 14 volts = 770 watts. Remember the 55 amps is at 14 volts, not 120 volts. Now there are efficiencies in the converter to consider, but a 1000 watt generator will handle that fine and have a little left over for other things.
You could be right but got to think about it a little. It is true the converter is capable of putting out 55 amps at 14.X DC volts, or roughly 770 watts as you state. but doesn't it require 30 amps at 120 volts AC in order to do so? Or roughly 3600 watts? So wouldn't the DC wattage output lower as the AC input lowers?

Jim
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Old 05-08-2016, 10:47 AM   #9
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You could be right but got to think about it a little. It is true the converter is capable of putting out 55 amps at 14.X DC volts, or roughly 770 watts as you state. but doesn't it require 30 amps at 120 volts AC in order to do so? Or roughly 3600 watts? So wouldn't the DC wattage output lower as the AC input lowers?

Jim
Nope, Progressive Dynamics rates their 60 amp converter as 60 amps at 13.5 volts which is 810 watts. Their spec for the unit is 1,000 watts which I am sure is conservative on their part. My experience is that the converter will almost never stay at nameplate current for very long. You may be confusing the WFCO 55 amps converter which also includes an AC power distribution panel. The panel can accommodate 5 ac circuits and is rated for 30 amps. The converter doesn't use anything like that.

1,000 watts will do fine with only the converter running.
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Old 05-08-2016, 10:47 AM   #10
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Thing is that it usually only costs a little more for a 2000w unit.
Personally, it's not worth buying a 1000w unit, since the 2000w units are so close in price.
You may be right, I haven't priced generators in a while. Last one I priced was a 3000 watt Honda, which I own, but am trying not to carry any more weight than necessary.

I do know I can get a 2200 watt generator for $530.00 that has a Sound Level at 23 feet, 50% load 64 dB. Sound level and weight are important to me. Just looked at Hondas 1000 and 2000 watt units and they are about $200.00 in difference so you are right about the prices.
Jim

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