Re: Diodes for 12v battery charging

[Jamie]

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?

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.

 

[Paul E. Schoen]

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.

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&ItemID=96728

Paul

 

[Jamie]

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&ItemID=96728

Paul

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.

 

[Jamie]

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?Itemnumber=96728

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?productId=2062591#

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.

 

[Paul E. Schoen]

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.

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

 

[Jasen Betts]

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.

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...

--- news://freenews.netfront.net/ - complaints: [email protected] ---

 

[ehsjr]

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?

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