Polarity reversal protection,how to??

[Antonio Spedicato]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

 

[mike]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

Protection from what?
Does the light care?
Batteries in wrong? Use mechanical means.
Charger backwards? Use dedicated cable.
Other??? use fuse.
It can obviously get much more sophisticated if you can
describe exactly what you're trying to protect against.
100% protection is MUCH harder than 90%.
mike

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[Tam/WB2TT]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

Not sure why a lamp would care about polarity, but assuming you want no
voltage drop, you could use a fuse, and a shunt diode to blow it if it is
wrong.

Tam

 

[Fred Bloggs]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

I think we have posted this 10,000 times in the past:

View in a fixed-width font such as Courier.



+--------------+---------+
| | |
| | |
| | +-+
--- | |L|
- BATT | |O|
| | |A|
| | |D|
| | +-+
| G |
| ----- |
| - - - |
+------------D S-------+

N-CH MOSFET

 

[Antonio Spedicato]

Protection from what?
Does the light care?
Batteries in wrong? Use mechanical means.
Charger backwards? Use dedicated cable.
Other??? use fuse.
It can obviously get much more sophisticated if you can
describe exactly what you're trying to protect against.
100% protection is MUCH harder than 90%.
mike

I forget a word......polarity reversal, this is the problem.
For me is hard to do it..can you expplain me how i can protect batteries?
Thanks

 

[mike]

I forget a word......polarity reversal, this is the problem.
For me is hard to do it..can you expplain me how i can protect batteries?
Thanks

You need to remember MORE words. Polarity reversal where?
When installing the batteries?
When connecting a charger?
Some other thing we don't know about?
Might, depending on your objectives, be helpful to know the
current drain and technology of the lamp, depending...maybe...who knows...

Making some grand unsubstantiated assumptions, I'd say put the batteries
in, put a screw in the cover so some idiot can't get them out and use
a polarized charging connector.

Now, there are a whole bunch of issues surrounding charging. But you
haven't asked that...

Then there's the issue about leaving the switch on and reverse charging
some of the cells. Low voltage cutout is likely to be more of a
necessity than putting the cells in backwards.

I'm starting to rant, but what the heck, bits are almost free...
Rechargeable batteries are unsuited to use with flashlights. And here's
why. You need to turn the light off IMMEDIATELY at the first sign of
dimming to prevent cell reversal. If you haven't charged it in a week,
this may happen almost immediately when you try to use it.
So, do you want the light to turn itself off to protect the
batteries? Or do you want it to stay on as long as possible to help
you through the emergency?
"He was hit by a car in the dark...but the good news is that the
batteries in his flashlight were protected".
mike
--
Return address is VALID.
500MHz Tek DSOscilloscope TDS540 $2200
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Joop]

I think we have posted this 10,000 times in the past:

View in a fixed-width font such as Courier.



+--------------+---------+
| | |
| | |
| | +-+
--- | |L|
- BATT | |O|
| | |A|
| | |D|
| | +-+
| G |
| ----- |
| - - - |
+------------D S-------+

N-CH MOSFET

When one wants to connect multiple devices to the same battery and
share a common and quality ground (HF equipment) it would be desirable
to 'switch' in the + line.
Do you perhaps have a simple solution for this as well? I was thinking
along the lines of moving this mosfet to the + line and use an helper
voltage generated by some inverters to lift the gate way above the
battery level.
But when things get too complex, a relay would become a simpler, but
less energy effecient solution.

Joop

 

[Fred Bloggs]

When one wants to connect multiple devices to the same battery and
share a common and quality ground (HF equipment) it would be desirable
to 'switch' in the + line.
Do you perhaps have a simple solution for this as well? I was thinking
along the lines of moving this mosfet to the + line and use an helper
voltage generated by some inverters to lift the gate way above the
battery level.
But when things get too complex, a relay would become a simpler, but
less energy effecient solution.

Joop

Just use a P-channel FET with SOURCE terminal on the LOAD, GATE to gnd,
and DRAIN to Batt(+).

 

[Brian]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

If you want to keep a battery (in a series string), from developing a
reverse polarity, put a diode across each battery. Hook the cathode of the
diode on the positive side of the battery and the anode on the negative side
of the battery. I think this is what you are looking for.
Brian

 

[James Meyer]

If you want to keep a battery (in a series string), from developing a
reverse polarity, put a diode across each battery. Hook the cathode of the
diode on the positive side of the battery and the anode on the negative side
of the battery. I think this is what you are looking for.
Brian

By the time a cell has discharged to the point that a diode will turn on
and "protect" it, it is likely to be already ruined.

Jim

 

[Brian]

By the time a cell has discharged to the point that a diode will turn on
and "protect" it, it is likely to be already ruined.

Jim

I use to work at a place, where we used these types of batteries in our
equiptment. We had battery packs, with six in series. At first, we had
problems with some reverse charging. If they weren't damaged, we would
revive them by hitting them with a heavy charge (for a short time). Most of
the time, this would work. After we put diodes across each battery in
series, we had no more problems with them reverse charging. The diode would
keep them from overheating. They would charge normally, when put on a
charger (without the short high current burst).

Another thing that works, is to match the batteries. Give them all a full
charge and then discharge them (recording how long each one lasts). Put only
those in series, that had the same discharge time.
Brian

 

[Antonio Spedicato]

If you want to keep a battery (in a series string), from developing a
reverse polarity, put a diode across each battery. Hook the cathode of the
diode on the positive side of the battery and the anode on the negative side
of the battery. I think this is what you are looking for.
Brian

Wich type of diode and wich value?
Can you send me in pvt some picture about it?
Thanks

 

[Brian]

Wich type of diode and wich value?
Can you send me in pvt some picture about it?
Thanks

You could use something like a 1N5820. Go to http://www.digi-key.com/ and
type in 1N5820 (in the search box), it will take you to where you can get
the data sheet.
Brian

 

[Brian]

of negative

You could use something like a 1N5820. Go to http://www.digi-key.com/ and
type in 1N5820 (in the search box), it will take you to where you can get
the data sheet.
Brian

While the diode protection method works, the best all around method is to
match the batteries in series. This way, they all die at about the same
time, and will give you the longest running time per charge.
Brian

 

[Fred Bloggs]

By the time a cell has discharged to the point that a diode will turn
on and "protect" it, it is likely to be already ruined.

Jim

Right- the deep discharge limit for NiMH is +1.0V and not -1.0V or
thereabouts on a bypass diode at 3Amps. This type of information is
available in the various handbooks from manufacturers like Panasonic.
It would be better to use batteries with reverse battery and
overdischarge protection built-in:
http://www.gpina.com/industrial/batteries/NiMH/NiMHspecs.htm

 

[Active8]

Hy, i would to build a polarity protection for my dive light (12 volts
nimh batteries) but i don't known ho to do it!!
Can someone help me?
There are 10 batteries 1,2 volts 3000 mah serial installed.
Thanks
Antonio-Italy

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