12 VDC Relays

please dumb-it-down for me.

relay?

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Usually 75% of the rated coil voltage at 25C, but the best bet would
be to get the data sheet for the relay because it\'ll vary with
temperature.  And manufacturer.

John,

Thanks for the feed-back.

Sure I'm interested. Please go ahead and post your schematic.

Thanks again for all of your help,

Conan Kelly

please dumb-it-down for me.

relay?

Volts?

push-button switch (and maybe diodes) so that each

there is probably some similar way of wiring 2

drill. I gutted an old Makita battery charger and

drill battery. I read somewhere that the ideal

guessing that there are 8 cells in a Makita 12V

discharge) Right now, it is wired directly to the

lighter charger is left on it too long. I was hoping

shut off when it reaches the target voltage.

please dumb-it-down for me.

VDC relay?

Volts?

John, remember this old thread

A very similar question, and you even posted a spice simulation.

please dumb-it-down for me.

VDC relay?

Volts?

--
I\'d completely forgotten that one!

A few value changes and it\'ll be perfect for what the OP wants. 

Thanks, that\'ll save me a bunch of work. :-)

--
OK, I\'ll post it sometime this afternoon or early tomorrow.

BTW, please bottom post. :-)

--- You're welcome, but just to clear up a couple of things, a NiCd battery, when fully charged, starts off at about 1.4V. Then, when a load is placed across it slowly falls to 1.2V, then very quickly falls to 1.0V, which is considered its 'cutoff' voltage.

So, your 12V battery pack is probably made up of 10 cells, with an expected cutoff voltage of 10V, which is when you'd want to disconnect the load.

This should do it for you:

View in Courier

IRF4905L VBAT>--+----------+-----------+-------S D--->LOAD | | | G | [150k] | | | | +---|---[1M]--+ [412k] | | | | | +-[1k]--+--|+\\U1A | | | | >-------+ +----------|----------|-/LT1017 | | | | K|2.5V | +--|+\\ [137k] [LM385] | | | >

| | | +--|-/U1B | | | | GND>---+----------+-----------+---+----------->GND

-- JF

please dumb-it-down for me.

relay? How can I wire 2 relays with resistors so

Volts?

push-button switch (and maybe diodes) so that each push

there is probably some similar way of wiring 2 relays

drill. I gutted an old Makita battery charger and

drill battery. I read somewhere that the ideal

guessing that there are 8 cells in a Makita 12V

discharge) Right now, it is wired directly to the

lighter charger is left on it too long. I was hoping to

shut off when it reaches the target voltage.

Some general information not discussed in other replies: Nominal voltage for a NiCd is ~1.2V per cell. When fully charged, and immediately after being removed from the charger, voltage from the cell is ~1.43V. NiCd packs should not be discharged below ~.9V per cell. The "standard" 14 hour charge rate is ~C/10 where C is the Ampere-hour rating of the cell.

When you have the specific recommendations from the manufacturer, they should be followed. Otherwise you can use the general information above.

Ed

John Fields,

Thanks for the feedback.

You where right, my drill's battery pack has 10 cells.

Remember that I do not have a background in electronics, so I do have a couple of questions about your scematic.

I'm not going to post them here because I have pix to go with them. Go to

to see the pix/questions.

Please confirm or correct my assumptions.

Are these components that can be purchased at Radio Shack? ...Fry's Electronics?

Thanks again for all of your help,

Conan Kelly

of questions about your scematic.

Electronics?

Conan, I don't want to steal John's fire, but I'd like to jump in here and answer your questions. Yes, the numbered components with no other information are resistors. K means 1000, M means 1,000,000. Yes, the + means connected and the other pictorial that looks like under-over means no connection. The positions of the components on the actual circuit boards might (probably will) be different in the actual execution than in that schematic, and the "wires" will actually be copper traces, if you fab an actual pc board for the circuit. Or you could do point-to-point wiring where you use wires soldered to the component leads. This you can accomplish in different ways, for example

1 wire wrap (I don't know how many people do it any more) 2 "dead bug" construction (google it) 3 or you can insert the components in perf board and run wires from lead to lead.

The component you asked about, the LM385, is a voltage reference, similar to a zener diode. You can look up datasheets on websites like digikey.com and mouser.com, which are also good places to buy from.

The U1A and U1B are both contained in a single chip, the LT1017 dual comparator. You only need one comparator, so you were right that U1B does not function in the circuit.

As for how to change the voltage setpoint, look at the two resistors on the comparator's negative input, 412k and 137k. They take the battery voltage and divide it by a certain ratio for the comparator to look at. They form a voltage divider. You could make the circuit adjustable by replacing them with a potentiometer.

of questions about your scematic.

Electronics?

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I don\'t know, but they\'re surely available from Digi-Key and
probably also Mouser; check their web sites.