Lead Acid battery using a boost converter is possible?

[Sink0]

Lead Acid battery charger using a boost converter is possible?

Hi would like to know if i will have any problem to charge a 12V lead acid battery using a boost converter (LT1618 as example) from USB 5V?

Thank you!

 

[eanema]

Are you are referring to a 12v car battery? Because it would take about a month to charge a 100Ah battery by drawing 500mA from your USB port.

Also, if its nominal voltage is 12v then you will probably require a higher voltage to charge it with. You might want to find out what type of current/voltage characteristics your battery requires to charge. Google gave me this link as a start How to charge sealed lead acid batteries. Custom battery chargers for OEMs in a hurry from PowerStream

 

[Sink0]

No... not a big one. Just a small 12V one. But it will be a secondary power supply to the system if the USB get disconnected so, at normal operation it will just deliver few miliampers. But about the charging. I am afraid the switching circuit can damge the USB or do not charge the battery correctly. And yes.. probably i ill tune the boost to 14V. But will that work?

Thank you!!

 

[rajudp]

in some new computers there is a current limiter inbuilt with usb, but some don't. so better not connect high current applications to USB or you have to include a current limit circuit in your application, the maxim usb current is around 1A so i dont think it is ok for led acid battery( around 250-300ma at charging volt)

 

[eanema]

Actually the maximum USB current with out enumeration is 100mA - this is the largest current that can be drawn from a USB hub (according to the standard). BUT a USB hub also *must* be able to provide a minimum of 500mA regardless of the circumstances. So this means that you can draw up to 500mA from a port with out enumeration provided you are not sharing the hub with any other devices. In the case of a USB port on a computer's motherboard, each port *is* a root hub, so there are no worries with driving a 500mA load.

The LT1618 has an option for total current limiting - this is the ISP and ISN lines on either side of the sense resistor (0.1 ohm).

As far as the concern of damaging the computer I wouldn't be too concerned, but if you are, you could put an RF choke in the power/ground lines to prevent hi frequency noise leaking back.

Also If this is just a charging circuit (as opposed to a power supply *and* a charging circuit) you might consider configuring the circuit as a constant current source. I talked about doing this in a post I made a few days using a similar device. Check it out: https://www.edaboard.com/threads/195645/#post820013

---------- Post added at 16:55 ---------- Previous post was at 16:54 ----------

Also, just to ensure that your not drawing too much current, you should just take a look at it on the 'scope.