Battery charger - Please help

Dr.No

Hello everyone.

I'm building a battery (attempting) charger with BS2.
How can I read volts using the stamp?

The idea is to turn on a relay (charge) switch if the volts fall
below x volts snd turn off if above y volts.

The battery is 6 - 12volt motorbike battery.

Any ideas?

Thanks

Mike Green

There's a discussion on reading voltages using the RCTIME statement here: www.emesystems.com.
Select the link "app-notes" near the bottom. On the linked page, look under the RCTIME command section.

Other options include using an analog to digital converter like the ADC0831. There are lots of articles and sample
code for this in the Nuts and Volts Columns and in the "Basic Analog and Digital" tutorial. Both are accessible from
the main Parallax webpage. Click on the Resources tab. The tutorials are under "Downloads", then "Stamps in Class
Downloads".

Post Edited (Mike Green) : 7/14/2008 2:54:31 AM GMT

Dr.No

Thank you very much.

erco

A noble effort, but dedicated chargers can be bought for less than the price of a BS2 that will do a much better job:

·$21·· http://cgi.ebay.com/12-Volt-SLA-Battery-Charger-1000mA-Maintainer-Condition_W0QQitemZ220184015103QQihZ012QQcategoryZ36323QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247

http://www.batterymart.com/p-battery-tender-jr-12v-0_75a-battery-charger.html

http://www.batterymart.com/p-cliplight-6-12v-1_5a-battery-charger.html

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·"If you build it, they will come."

Post Edited (erco) : 7/14/2008 10:14:39 AM GMT

Dr.No

Actually, the BS will be doing a lot more than that.
But your post has given me the idea to use the BS to read
the charger's results.

Thanks

erco

The LM339 quad comparator is one of my favorite analog chips, I use it as a poor man's A/D converter. Easy to use to establish a voltage threshhold and get a digital higher/lower signal that can be input directly into the BS2 for monitoring. Great for voltage threshold switching in battery chargers.

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·"If you build it, they will come."

Gusie

Hi

Built·this today. It measures the voltage. Look half way down the page.. Works great. There is a calibration procedure there aswell.

http://www.emesystems.com/BS2rct.htm

Gus

·

Dr.No

I'd be very interested in this... do you have any pics?

I was very concerned with the variable results that is dependent upon battery types.

Dr.No

Erco,

Do you have a diagram layout of the LM339 and all the components?
As you can figure out, I'm NEW to all this so a step by step breakdown would be greatly appreciated.
I found a website but it lists variants such as the LM339N, which one did you use? Any links?

I'd preffer that the BS do as little work as possible because of it's low power limit but I do need it
to be able to read voltage. Currently, it is powering two 5V reed relays - so I rather not use it
to power a circuit.

Thanks for your help.

I like the BS but it's terrible when it comes to power compared to other chips. It's been around
long enough for them to juice it up by now - but they haven't.

Post Edited (Dr.No) : 7/16/2008 10:56:59 PM GMT

Mike Green

The suffix generally designates the package type, temperature range, etc. The LM339N is the DIP package. Here's one link from a quick websearch: www.national.com/mpf/LM/LM339.html.

The Stamp is not very different from other microprocessor and logic chips in terms of power. The BS2 is based on a PIC processor from Microchip while the other Stamps are based on the SX processor. I/O pins can handle about 25mA individually while groups of 8 pins are limited to 50mA total and there's a limit for the entire chip. The SX has a higher total chip limit, but the other values are similar.

Post Edited (Mike Green) : 7/16/2008 1:30:06 PM GMT

Dr.No

Thanks Mike!

Dr.No

Hi Mike!

Is there such a thing as an off the shelf switching controller? What I wanted to do
was when the primary battery runs low, automatically switch to the backup battery.

This is what I think I need now.

Thanks again.

Mike Green

The simplest way to do this is just to use a Schottky diode in series in one lead from each battery. When the primary battery voltage drops below the backup battery's voltage, the backup battery will automatically supply the load. You could use a conventional power diode for this, but a Schottky diode has a lower voltage drop, so wastes less current.

Dr.No

Thanks Mike.
I solved the problem finally.