Hello,

I am trying to build a charger circuit for a NiMh battery pack that will hopefully be using with a custom Arduino board.

I just have one or two questions.

I am confused as to whether or not USB outputs 100mA or 500mA. I am not sure if it would have an effect on the charger but I was trying to determine that.

I am trying to charge a 6 pack of Eneloops in series that will be 2000mAH @ 7.2V. After using a step up IC, will I still have enough juice to effectively charge these batteries? I was thinking a fast charger would be good, but trickle is still acceptable.

So I am trying to find an IC that will step up voltage nicely. I like Mouser.com for ordering stuff, but it doesn't matter.

I'd like something like this but I can't find anywhere to buy an LTC3458:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1060,P9230

Anything else like it?

Also looking for a decent charger circuit for NiMH if anyone has a recommendation there.

Thank you very much.

Have a nice day.

-Tim

 

USB provides 500mA tops.
U cannot use this port to charge rates above this without blowing the mobo regulators

 

USB provides 500mA tops.
U cannot use this port to charge rates above this without blowing the mobo regulators

Regardless if I use a step up regulator?

 

Regardless if I use a step up regulator?

If your software "tells" the motherboard that USB port can source 500 mA that means it can provide 500 mA at 5V = 2.5W

With a 100% efficient inverter taking 5V to 7.5V would limit the current to 333 mA as 2.5W is 2.5W

 

If your software "tells" the motherboard that USB port can source 500 mA that means it can provide 500 mA at 5V = 2.5W

With a 100% efficient inverter taking 5V to 7.5V would limit the current to 333 mA as 2.5W is 2.5W

Ah....well, I don't want to get that involved. Well, I guess I'll just be hooking up the Arduino via a crappy 300mAH rechargeable. I wonder how long that will last.

Or just a DC plug in.

By the way, is there way either by IC or circuit that can enable two power inputs? I was thinking I could have it running off wall DC under most circumstances, but then have it be able to easily switch over to a 9V battery when needed. (Kind of like a laptop?)

Can anyone give me a pointer to how to achieve that?

Thanks.

 

If losing 0.7V is no big deal just put diodes in series with both supply inputs, that way one can't feed back into the other but either will work as a supply input.

 

If it is easy then tap off the 5V from PC supply.
Then u can charge any value of li-on's u want

 

If losing 0.7V is no big deal just put diodes in series with both supply inputs, that way one can't feed back into the other but either will work as a supply input.

0.7V shouldn't be a problem. Arduino needs 5V and I highly doubt I'd be loose >3V in the power regulation process. As for power from the wall, well yeah, that's cool too. Well, they won't be working at the same time will they?

 

With the diodes in there it won't matter anyway, the regulator will just pull current from the source that's presenting the highest voltage.