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Topic: Using a car battery to run Arduino for about six thousand years, need to design (Read 3 times) previous topic - next topic

draythomp

I tried it with as high as 20V and plenty of current availability.  I think you're right about the current to ground being a possible problem; I'll have to check that....as soon as I replace the 7805.  I lost it by having the output voltage higher than the input voltage and no diode to protect it.  Knew better, still made the stupid mistake.  But, that's what experimenting is all about.

Right???
Trying to keep my house under control http://www.desert-home.com/

BillO

I've done exactly this.  I have 5 LM317s set to 13.4V  (I'm pretty sure 13.9V is too high) and power them off an old 10 amp charger with a 4,700 uF cap across it.  Well, it's just a transformer with a full wave bridge.  In reality, more like a battery killer.

The set-up works like a charm and has for the past 7 years.  I can float charge 5 batteries all winter.  They range from a 4AH dirt bike battery to a 40AH garden tractor battery.  The present batteries range between 5 and 8 years old, so it seems to be working well.

I just give each battery a good, full charge with a good automatic unit, which brings them to 14.5V, keeps them there for about 3 hours then switches to a 13.4v float.  Once they reach that, I move them over to one of the LM317s.  The LM317s will limit current to about an amp and will actually charge the batteries quite effectively (if slowly for the bigger ones), but once the batteries settle in at 13.4, all five together only draw about 220ma.
Facts just don't care if you ignore them.

draythomp

That's the kind of information I've been searching all over the web for.  Information overload keeps getting in the way.  I was going to start at 13.9 and work down because I've lost many more batteries to undercharging than over charging.  The idea was to make sure the water didn't go away too fast.  13.4 sounds like a good number to start with since it should be a full charge; if I haven't misunderstood something along the way.  I only had one 317 to test with and it seemed to have the same problem with open circuit vs load regulation the 7805 had.  I only tested this a little though.

I'm trying to keep this as cheap as possible and the 317 has a different pinout than the 7805...right?  That would mean some creative mounting inside the case.

So, if I read your note correctly, you have one big DC supply and you charge all the batteries from it by putting a 317 in the middle for each battery.  Right?
Trying to keep my house under control http://www.desert-home.com/

BillO

..... I only had one 317 to test with and it seemed to have the same problem with open circuit vs load regulation the 7805 had.  I only tested this a little though.


I've not seen this problem with the LM317.  Using the ground pin for adjusting the voltage on an LM78XX the way you have done it would make it more vulnerable to load regulation problems as that ground input is quite low impedance.  You would normally employ a op-amp as a buffer, but neither method is ideal.

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I'm trying to keep this as cheap as possible and the 317 has a different pinout than the 7805...right?  That would mean some creative mounting inside the case.


Yes, it's about as different as you can get.

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So, if I read your note correctly, you have one big DC supply and you charge all the batteries from it by putting a 317 in the middle for each battery.  Right?


Right.
Facts just don't care if you ignore them.

Fletcher Chr

Hi there

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so I've been looking into a float charger that doesn't let the battery discharge or boil the water out over time.


If this is important you should reconsider the price issue.

I have good experience with chargers from ctec. I know they are expencive but they will keep your battery in good condition.

-Fletcher

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