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Building a Battery Generator Part 2

 
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Hello everyone,

A little less than a year ago I built a little 12 volt battery box based on an 12 volt, 15 amp hour SLA battery contained in a .50 cal. ammo can.  The unit has worked out pretty well, and with a small solar panel attached, it charges in a surprisingly short amount of time.

This was always a 2-fold project.  First, I wanted to get a working device, which I now successfully have.  Secondly, I wanted practice building so I could build a full sized 120v AC inverter battery generator based on a 100 amp hour battery.  The inverter will be a 1200 watt pure sine wave inverter that works at 90% efficiency.

So I am starting to plan for the larger build now.  I am pricing out parts and finding that if I shop around a bit I can get them quite affordably.  I do have a couple of questions though and I was wondering if anyone here could help me.

1)  What is the difference between a PWM and a MPPT charge controller?  Is there an advantage to having one over the other in this particular situation.

2)  What type of amperage should I be looking for in a charge controller?  Is 20 amps fine?  Does this just mean that it will take longer to charge the battery?  

3)  Are there any other specs I should be looking for in a charge controller?  Are there any that are considered quality but still affordable?  Are there any that I should stay away from?

4)  For outputs I plan on the following
    A)  USB
    B)  Cigarette 12 volt
    C)  Banana jack 12 volt
    D)  120 volt ac
    E) Anything else?

5)  For inputs I plan on
    A)  Solar charge MC4 style input
    B)  Anything else?

6)  Anything else obvious that I missed?

Thanks in advance,

Eric
 
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1. PWM vs. MPPT: https://zhcsolar.com/mppt-vs-pwm/
I think a PWM charge controller should be fine if you don't need the highest efficiency under all conditions.

2. That depends on the solar panel you use to charge the battery. The charge controller should be rated for the [sum of the] short-circuit current[s] of the solar panel[s] (or higher).

4. I would add a wire clamp (those used on speakers).
(I hate cigarette connectors… )

5. Maybe a 120V AC charger?
 
Eric Hanson
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Sebastian,

Regarding the speaker type connections:  I am adding in banana jacks which give me a sort of generic universally accepted connection that I can wire in easily so I think I have that base covered.  Still, that is a good idea and I may add it in.

On the AC charger side, that is a really good idea.  At the moment I have tried converting a couple of old, orphaned power supplies (I think to old printers).  Unfortunately they charge extremely slowly, as in they will take multiple days to charge to a full charge due to having a very low amperage output.  I have thought about buying a better one or possibly making a better one.  I would imagine that whatever I would need for a 100 ah battery had better be a serious charger, as in a car charger with a speed charger setting.  

One idea I had for another output was a buck converter which lets me dial in a specific voltage within a range.  Say I want to run a computer directly without its own power supply, I could dial up 19.5 volts, a common voltage for computer motherboards.

Thanks for the input,

Eric
 
Sebastian Köln
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Regarding the charger, I have a used 60W 12V power supply which can be adjusted to 13.5V. It is a pretty decent car battery charger. But I suppose something like 300W - 600W would be more useful for you.
(Something like this. Note the trim potentiometer on the right side of the connectors.)

The boost converter is a good idea! Just get a powerful enough one … I had to put on in silicone oil to keep it from overheating when powering my laptop.
If you get one with adjustable voltage and current, it doubles as LED driver for high power LEDs.
 
Eric Hanson
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Sebastian,

Nice idea with the transformer!  That might be just what I need to charge up the battery.  At present I have been using a charger running 16 volts (not too bad), but less than half an amp (terrible!).  Actually the amperage is so low that the charge controller doesn’t always even recognize the charger is attached.  It took a full night to charge from 12.2 to 12.3 volts.

The little 28 watt solar panel on the other hand, is amazing as long as it gets full, direct sunlight.  Today we have had some thin clouds and in about an hour the panel charged the unit from 12.3 to 12.7 volts—quite a bit better than the pathetic little AC to DC charger.

Eric
 
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