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Old 05-04-2006, 06:07 PM   #11
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See here's the thing, Jason....I'm on a college budget and the 12 horse is free and works great. I have a 2300 watt 1960 something Briggs generator that runs GREAT, but if I use that for charging it doesn't leave much else left and it's not exactly quiet.

The reason I want to isolation is both for when I'm parked and when I'm driving. I'm not opposed to using the alternator on the bus for charging the batteries when I'm stopped if the need arises. My homemade alternator-generator thing is low priority right now. Most of all I just want to get the bus ready to go for this summer.

I probably should just breakdown and buy a diode type isolator. I just don't like the idea of paying a decent chunk of change for something with so many compromises.
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Old 05-04-2006, 07:29 PM   #12
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Small engine 12VDC generators are not new (I have built one). Google the net and you will find sites like:
http://theepicenter.com/tow082099.html
http://www.green-trust.org/equipment.htm

If one wants to dig into batteries and charging I would start at
http://bart.ccis.com/home/mnemeth/12volt/12volt.htm
Just remember that this can be a very large subject that has many answers depending on your own situation. Given the price of batteries though, it is worth getting familure with. You will also discover that there are many many view points about this subject.

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Old 05-04-2006, 09:57 PM   #13
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The biggest compromise that comes with the isolator is the cost to do something I KNOW there has to be a simpler way around.
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Old 05-04-2006, 11:03 PM   #14
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My isolator is a switch between the starting battery pos. and the house battery pos. (that are in parrallel) I can reach it from the driver's seat. Turn it on, all batteries are charged by alternator. Turn it off, only draw from house batteries so as not to drain starting batt. Cheap, effective.
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Old 05-04-2006, 11:12 PM   #15
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You have no problems getting the house batteries to charge in parallel like that? I still can't see any reason why it wouldn't work, but electricity hardly ever follows the laws of physics like it should.....there's a reason why I chose mechanical engineering instead of that electrical crap.
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Old 05-05-2006, 09:48 AM   #16
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I felt the same way

I felt the same way about those darn flowing electrons untill I realized all the formulas were basically simplified flow thru tubes. once I converted all the variables into fluid dynamics I was able to understand most of what was going on then convert it all back again to get the right answer on the test
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Old 05-05-2006, 12:51 PM   #17
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I try the same thing and it works great on paper. Where I run into problem is in the real world

In theory the batteries in parallel would be just like two pipes in parallel. Overall mass flow rate would be the total number of amps supplied by the alternator and the individual mass flow rates would be determined by the draw from each battery bank Either way...the total mass flow rate would have to be equal so the volumetric flow rate would be lower on each one taking more time to charge due to the lower velocity of the "fluid"....blah blah blah....

The problem with this is that some people have expressed that they have trouble getting their house batteries in parallel to charge. On paper it doesn't make sense, but calculations on paper only take you so far
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Old 05-05-2006, 07:32 PM   #18
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So far, my batteries charge completely via alternator. However.... I have limited time on the setup and all batteries are new. Performance may decrease over time, I'll have to wait and see, But for now, all is well.
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Old 05-06-2006, 03:22 PM   #19
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I've seen it before in small lithium batteries

I work for NASA on mini UAV's and we have seen this on our aircraft. the rechargeable lithium ion batteries can be hooked up in parallel and work fin in the system but you can't charge them that way we had to remove them and charge them indipendently. the sparkies couldn't sufficiently explain that one to me though.
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Old 05-18-2006, 06:16 AM   #20
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battery charging problems


I'll postulate a theory here.
when you have voltage in parallel, current varies. ( ohms law )
now at the beginning of your charging process you have one battery charged or nearly charged, and the other nearly drained.
What will happen is the sensing circuitry in the regulator will determine that not much output is needed because of the higher charged battery and will slow the charge rate considerably. You see this when you jump start a car and only get a "surface" charge.
Now IF you provide to the regulator a voltage sense based on the current status of the lowest charged battery ( which is essentially what an isolater does ) then the isolater will channel the current to the battery that needs it the most and feed some bias back to the more charged battery to test it to see if it now needs charging.

Hope that helps some
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