Battery charging with an outboard

[dgr]

Pedcab,
Thanks for posting this. It looks like it could be used for any charging system that needs to have the load dumped; solar, wind, etc.

For those of us that don't have a regulated powersupply to provide 14V for the calibration procedure, do you have an alternative suggestion?

Have you measured the parasitic amperage draw on this when it isn't doing anything? It looks like all that would be pulling current is the LM741 and the series of resistors that includes the variable resistor. If I am reading the spec sheet correctly on the LM741, it only looks like it draws 2 milliamps and the series of resistors would draw another 2 milliamps.

Why did you pick 2.3V for the cutout voltage?

Sorry for all the questions


thank you

[timangiel]

Originally Posted by dgr

Pedcab,

For those of us that don't have a regulated powersupply to provide 14V for the calibration procedure, do you have an alternative suggestion

You may be able to put two 9 volt radio batteries in series to get 18 volts, and then use a variable resistor to knock the voltage down to where you need it. To do this you will need to remove the lamp that acts as the dump load because that will be too much of a load for those small batteries, but they will power the 741 opamp just fine.

Originally Posted by dgr

Pedcab,
Have you measured the parasitic amperage draw on this when it isn't doing anything? It looks like all that would be pulling current is the LM741 and the series of resistors that includes the variable resistor. If I am reading the spec sheet correctly on the LM741, it only looks like it draws 2 milliamps and the series of resistors would draw another 2 milliamps

It looks to me like the combination of R5/D2(led 2) will draw some current. It looks like that LED is used as a power-on indicator.

The voltage divider network of R1, R3 & R2 will draw some current.

The combination of R4, D1 will draw some current.

And of course the LM741 istelf will draw some current.

I don't really know what the total draw would be (maybe 6 or 8 milliamps??), although not very much really, you wouldn't want to leave it connected to your batteries when not in use for extended periods of time.

Originally Posted by dgr

Pedcab,
Why did you pick 2.3V for the cutout voltage?

I really don't see where you are getting that number from? sorry. I hope I helped.

[pedcab]

Answering your questions:

About the regulated supply, I suggest everyone with any sort of DYI project in hando to build one. IC´s like the LM317 make an easy task to build a cheap and very acceptable regulated supply.

About the residual current draw: That´s what it is, residual. As such I don´t bother much about it since I don´t usally have the device connected when the engine is not running.

About the cutout voltage, I really don´t know what you mean...

Cheers

[dgr]

Thanks for the replies. My question regarding residual current draw is simply wondering if I'm going to kill my battery If I forget to turn this off.

As far as cutout voltage, it's possible I'm not understanding what you are doing here. I thought that you were reading voltage and when it hit a certain level, the battery was assumed to be fully charged and the current was dumped to the lightbulb. I assumed you picked 2.3V per cell as that voltage as you are calibrating with 14V and 14V/6 cells is 2.33 volts.

[pedcab]

Originally Posted by dgr

Thanks for the replies. My question regarding residual current draw is simply wondering if I'm going to kill my battery If I forget to turn this off.

As far as cutout voltage, it's possible I'm not understanding what you are doing here. I thought that you were reading voltage and when it hit a certain level, the battery was assumed to be fully charged and the current was dumped to the lightbulb. I assumed you picked 2.3V per cell as that voltage as you are calibrating with 14V and 14V/6 cells is 2.33 volts.

Ah! Now I get it

About the residual current draw: Yes, this device will probably wil kill you battery but only if you leave it connected for an absurde amount of time. Maybee your battery self discharge rate is higher than the residual consumption of this device.

Nevertheless it´s always a good policy to disconect any electrical equipment when unnatended or not in use...

About the 14 volt, I´ve chosen that voltage because it´s a pretty standard value to charge lead-acid 12V batteries with. For instance, you automotive alternator, most certanly, produces something arround that value. Anyway, you can tune to whatever voltage you want within reasonable values...

Hope I was helpfull...

Cheers