Diodes for 12v battery charging

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I put in a 12v solar panel to charge up 2 ATV's and a mini tractor.  Ran
some speaker wire and battery clips to charge all of them in parallel.  The
tractor battery seems to not hold a charge very well.  I'd like to add 3
diodes to protect the other 2 batteries in case at night with no input
current, the low battery would siphon off power.

The setup is in a very remote location with no power lines and I've
misplaced to specs for the panel and the 7amp  regulator, but they both came
from Harbor Freight.  The bigger battery is 14 amp-hr, the 2 smaller ones
are 10 amp-hrs.

Can someone please suggest an appropriate diode to purchase at Radio Shack
or Fry's that will handle up to 7amp and not waste too much charging
ability?



Re: Diodes for 12v battery charging


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Assuming no broken batteries, just put them in parallel,
the batteries will distribute present charge.
One good quality diode in series with the panel is however
important, because the panel itself is a bad quality diode,
and will discharge the batteries in dark weather and at night.

Re: Diodes for 12v battery charging


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we do that at work how ever, we have breakers on each battery with a
large DIODE across each breaker leads.



Re: Diodes for 12v battery charging



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I assume by the application that they are lead acid batteries. I am never
comfortable charging LA batteries in parallel because of the different
states of discharge when you put them on charge.
Your batteries are close to the same capacity so I suppose that you can get
away with it. You need to know the maximum charging current you will be
using and select a diode with about a 50% safety margin.
BTW: What is "speaker wire" What I really am saying is gauge your wire
appropriately.
Tom



Re: Diodes for 12v battery charging


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They are all lead acid batteries and physically about the same size.  I was
planning on putting a diode on each individual battery so that it could not
be drained if another one took too much current.  It's embarrassing that I
don't remember, but I believe that the panel is 25 watts.  The system is
simply supposed to maintain charge on reasonably new batteries.  The
"speaker wire" is probably 14 or 16 gauge.  I am unable to go check because
of distance.  Want to get parts before the next 3 day weekend.  Can't run to
the store very easily .:. any minor modification takes ~ 3 months to plan
and try out.



Re: Diodes for 12v battery charging



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The answer to your question; "what type of diode", the best choice would be
a shottky-barrier type as it has a lower forward volt drop than standard
silicon.

If you are using a regulator to give the correct charging voltage for the
battery, you will have to take into account the diode volt drop.

You quote a figure of 7A and say you are using "speaker wire", If I were you
I'd check it isn't getting too hot when there's plenty of sun on the solar
panels! Thicker wire would drop less voltage at full current and reduce
power lost heating the wire.



Re: Diodes for 12v battery charging



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http://www.frys.com/product/1003123?site=sr:SEARCH:MAIN_RSLT_PG

from Fry's
  NTE6083

   Make sure you mount these to a heat sink.

  Also, not sure about your charging unit, it may be regulating voltage
to a close degree. You'll get a slight drop in voltage to the batteries
if the charge regulator does not ramp up to maintain current.
   Drop will be around .7 volts.


Re: Diodes for 12v battery charging




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I don't even know how that 45volt rectifier could be used as a diode.  This
is a link to the regulator I have.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber96%728

Harbor Freight doesn't seem to carry the solar panel any more.  I guess I'll
just gamble with a 2 legged diode.

http://www.frys.com/product/1001633?site=sr:SEARCH:MAIN_RSLT_PG

http://www.radioshack.com/product/index.jsp?productId20%62591#



Re: Diodes for 12v battery charging



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If you put diodes in series with the output of the regulator, the volt drop
of the diodes might result in under-charging.

The ideal solution would be to give each battery its own regulator.

If you only want to use one battery at a time then you can connect the +
terminal with an alligator clip, if you want the full capacity from all 3
batteries at once, you'll need output isolating diodes to feed the +
terminals to your load - these diodes will need to be rated considerably
more than 7A !!!



Re: Diodes for 12v battery charging


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I'm getting confused.  The 3 batteries are in 3 separate vehicles.  It might
be convenient to have no diodes so that the other 2 batteries could act as
"jumpers" when starting one, but then I would risk having one battery fail
and drain the other 2 during a possible 2 month period with no attention.
It seems safer to isolate the batteries from each other, yet allow a single
solar panel to charge all 3 simultaneously.

I assume that a 25 watt panel would supply ~2 amps at 12 volts .:. the Radio
Shack diode http://www.radioshack.com/product/index.jsp?productId20%62591#
would be OK for charging and for reducing risk from an unexpected discharge.
I was looking for some confirmation because I am a trial and error sort of
fellow and an error can mean a bad trip and added expense.

Thanks for considering my problem.



Re: Diodes for 12v battery charging



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The 1N5822 40V 3A shottky-barrier diode would probably handle as much
current as your speaker wire.

Personally, I'd go for a bit bigger safety margin like the devices here;

http://uk.farnell.com/jsp/search/browse.jsp?N50%0006+1004178+5056622&Ntk=gensearch_001&Ntt=shottky+barrier+diode&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues50%0006+1004178&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D500006%2B1004178%26Ntk%3Dgensearch_001%26Ntt%3Dshottky%2Bbarrier%2Bdiode%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D500006%2B1004178

If you want to charge 3 batteries in parallel, it would be better to feed
each battery with its own regulator. If you want to split the current with a
diode to each battery (from a single regulator) you will need a regulator
that allows you to adjust the output upwards to compensate for the diode
volt drops.

If each battery is used individually, that's all you need to do, if you
wanted to use all 3 batteries in parallel, you'd need 3 more (much higher
current) diodes to combine the three batteries into the load - it would sort
of defeat the object of the first 3 diodes to then strap the 3 batteries
together in parallel.



Re: Diodes for 12v battery charging



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Don waste your money on that part at Fry's, its not what you need. that
is a protection diode and has nothing to do with what you need.

  The one at Radio shack that you have pointed out would most likely
work , even though its under rated by 1 amp and also, likely will have a
  higher forward voltage than what I pointed out.

    I picked the one at Fry's because of your 7 Amp unit you have and
keep the voltage loss down.

   The diode from the shack will most likely get a little warm, the
Fry's one, you can mount it to some AU to extract the heat and it's
simple to hook up with an iron.

   It's up to you.




Re: Diodes for 12v battery charging



Stumpy wrote:
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Here is the data sheet:

http://www.nteinc.com/specs/6000to6099/pdf/nte6083.pdf


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   A recitifer is a diode.  Look at the data sheet.  The terminal marked
'K' is the cathode.  This is the same as the banded end of a typical
diode. The other lead is the anode.


 
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   That website is for their retail stores.
http://www.harborfreightusa.com/ is the main site, and there is another
site for their "Inside Track Club" members. The site you referenced only
lists the most popular items. They have a printed catalog with more
items, as well.


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   This is only rated for six amps.


--
Greed is the root of all eBay.

Re: Diodes for 12v battery charging


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Thanks,  I see it only has 2 leads.  Now it makes sense to me.
Paul pointed it out before but I needed to see the picture.

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---snip----

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I'm pretty sure that the panel can only supply ~2 amps.

I'd be happy to get 3 of the NTE 6083s for $4.80 at Fry's
but Radio Shack is about 5 miles closer with a $2.50 4-pack of the
274-3631s.
Don't need heat sinks either.



Re: Diodes for 12v battery charging



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The picture of the rectifier shows a three-lead TO-220, but description
says two-lead.

Drop will decrease to about 0.3V at low current when regulator goes into
float voltage mode.

You might be able to cannibalize a Schottky rectifier from a computer power
supply. Maybe a three-lead diode which can be used in parallel for even
less voltage drop.

Here is the manual for a 7A Harbor Freight charging unit:
http://www.harborfreight.com/cpi/ctaf/manuals.taf?f=form&ItemID96%728

Paul



Re: Diodes for 12v battery charging


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Many sights use generic images for their parts. They look at the TO-220
and think they're all the same.

  AS far the manual, it really does not give much info to break  down the
circuit how ever, it does state (+.5) above 14V, so I think it should
still charge the batteries, just maybe a little slower, which could be a
good thing if it's left to keep the units at float.



Re: Diodes for 12v battery charging



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The higher the current rating of the Schottky diode, the lower will be the
voltage drop at a certain current. Here is a diagram of a typical 200W
computer supply:
http://www.pavouk.org/hw/en_atxps.html

The output rectifier is a D83-004 which is rated at 30A. At 6A, or 3A
through each in parallel, the voltage drop is just about 0.35V.
http://pdf1.alldatasheet.com/datasheet-pdf/view/61331/FUJI/ESAD83-004.html

So it might be worthwhile to take apart some junk computer PSUs to get
these diodes. However, you can get an MBR4060 from Mouser for $2.60 each.
Dual 40A 60V.

Another idea to try is a set of three relays which take turns connecting
the regulator to each of the three batteries. And you can add a small diode
and resistor across each contact so that bateries not directly connected
will still get a trickle charge. At least in this way the
charger/controller will be able to interact with the battery in the way it
was designed.

Paul



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I second that, any passive scheme can be defeated by a shorted
cell in one battery. (or an open cell if you charge in series)


OTOH if you can get theee independant 14+V outputs from the solar
panel you could set up each with an independant charge circuit.
that would be another way to go, or just get three solar panels...


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Those relays sound like a fun project, but too sophisticated for me.  Where
do you guys post diagrams of your circuits?  If  Sci. E. B. is text only is
there a companion group for binaries?



Re: Diodes for 12v battery charging


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I'll bet the relay project is something you could tackle,
with a little help.

Regarding schematics, there are a number of possibilities:
http://tinypic.com/
Spice lists
a.b.s.e  (alt.binaries.schematics.electronic)
ASCII art

For example here's ascii art showing the diode isolation you
mentioned:

   ------------
  | Solar     +|------+--->|---[Battery1]---+
  | Controller |      |                     |
  |            |      +--->|---[Battery2]---+
  | Harbor     |      |                     |
  | Freight    |      +--->|---[Battery3]---+
  | Model (?)  |                            |
  |           -|----------------------------+
   ------------

Each approach has its pluses and minuses. For example
the ACSII art above must be viewed in fixed font such as
Courier.

Ed

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